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Sökning: L773:0268 1242 OR L773:1361 6641

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1.
  • Wallenberg, Reine, et al. (författare)
  • In situ metal-organic chemical vapour deposition growth of III–V semiconductor nanowires in the Lund environmental transmission electron microscope
  • 2020
  • Ingår i: Semiconductor Science and Technology. - : IOP Publishing. - 0268-1242 .- 1361-6641. ; 35:3
  • Tidskriftsartikel (refereegranskat)abstract
    • A new environmental transmission electron microscope has been installed in Lund in order to investigate the growth of III-V semiconductor nanowires by metal-organic chemical vapour deposition. We report here on the concepts behind the design of the facility and on details of the operation, and we refer to early results to highlight the new information that can be accessed from in situ studies. The installation includes a gas handling system that delivers the precursors to III-V semiconductor growth under controlled conditions. The core microscope is a Hitachi HF-3300S 300 kV TEM with additional pumping that can handle up to 6 Pa of gas injected into the specimen area, or up to 400 Pa if an apertured lid is fitted to the holder. Various custom specimen holders incorporate precursor gas lines, a heating chip or a double tilt mechanism. The polepiece gap has been expanded to accommodate the holders, while the combination of an imaging aberration corrector and a cold field emission gun delivers a point resolution of 86 pm. Single images with atomic level detail are collected by one camera while another camera provides real-time video recording. A scanning unit offers high angle annular dark field and secondary electron images, and compositional microanalysis is performed with energy dispersive spectroscopy. In summary, III-V nanowires have been grown successfully in situ across a range of controlled conditions such as substrate temperature and precursor partial pressures. Atomic resolution images and movies, and spectroscopy data taken during this growth allow detailed measurements of structures, compositions and growth rates – data that are otherwise hard or impossible to obtain from ex situ studies – and further our understanding of the mechanisms of crystal growth.
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2.
  • Chen, Ding-Yuan, 1991, et al. (författare)
  • Structural investigation of ultra-low resistance deeply recessed sidewall ohmic contacts for AlGaN/GaN HEMTs based on Ti/Al/Ti-metallization
  • 2023
  • Ingår i: Semiconductor Science and Technology. - : IOP Publishing Ltd. - 1361-6641 .- 0268-1242. ; 38:10
  • Tidskriftsartikel (refereegranskat)abstract
    • This study presents a novel approach to forming low-resistance ohmic contacts for AlGaN/GaN HEMTs. The optimized contacts exhibit an outstanding contact resistance of approximately 0.15 & omega;& BULL;mm. This is achieved by firstly recessing the barrier of the heterostructure to a depth beyond the channel. In this way, the channel region is exposed on the sidewall of the recess. The coverage of the Ti/Al/Ti ohmic metalization on the sidewall is ensured through tilting of the sample during evaporation. The annealing process is performed at a low temperature of 550 & DEG;C. The approach does not require precise control of the recess etching. Furthermore, the method is directly applicable to most barrier designs in terms of thickness and Al-concentration. The impact of recessed sidewall angle, thickness and ratio of Ti and Al layers, and the annealing procedure are investigated. Structural and chemical analyses of the interface between the ohmic contacts and epi-structure indicate the formation of ohmic contacts by the extraction of nitrogen from the epi-structure. The approach is demonstrated on HEMT-structures with two different barrier designs in terms of Al-concentration and barrier thickness. The study demonstrate large process window in regard to recess depth and duration of the annealing as well as high uniformity of the contact resistance across the samples, rendering the approach highly suitable for industrial production processes.
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3.
  • Ding Yuan, Chen, 1991, et al. (författare)
  • Impact of in situ NH3 pre-treatment of LPCVD SiN passivation on GaN HEMT performance
  • 2022
  • Ingår i: Semiconductor Science and Technology. - : IOP Publishing. - 1361-6641 .- 0268-1242. ; 37:3
  • Tidskriftsartikel (refereegranskat)abstract
    • The impact on the performance of GaN high electron mobility transistors (HEMTs) of in situ ammonia (NH3) pre-treatment prior to the deposition of silicon nitride (SiN) passivation with low-pressure chemical vapor deposition (LPCVD ) is investigated. Three different NH3 pre-treatment durations (0, 3, and 10 min) were compared in terms of interface properties and device performance. A reduction of oxygen (O) at the interface between SiN and epi-structure is detected by scanning transmission electron microscopy (STEM )-electron energy loss spectroscopy (EELS) measurements in the sample subjected to 10 min of pre-treatment. The samples subjected to NH3 pre-treatment show a reduced surface-related current dispersion of 9% (compared to 16% for the untreated sample), which is attributed to the reduction of O at the SiN/epi interface. Furthermore, NH3 pre-treatment for 10 min significantly improves the current dispersion uniformity from 14.5% to 1.9%. The reduced trapping effects result in a high output power of 3.4 W mm(-1) at 3 GHz (compared to 2.6 W mm(-1) for the untreated sample). These results demonstrate that the in situ NH3 pre-treatment before LPCVD of SiN passivation is critical and can effectively improves the large-signal microwave performance of GaN HEMTs.
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4.
  • Gooth, Johannes, et al. (författare)
  • Transition to the quantum hall regime in InAs nanowire cross-junctions
  • 2019
  • Ingår i: Semiconductor Science and Technology. - : IOP Publishing. - 0268-1242 .- 1361-6641. ; 34
  • Tidskriftsartikel (refereegranskat)abstract
    • We present a low-temperature electrical transport study on four-terminal ballistic InAs nanowire cross-junctions in magnetic fields aligned perpendicular to the cross-plane. Two-terminal longitudinal conductance measurements between opposing contact terminals reveal typical 1D conductance quantization at zero magnetic field. As the magnetic field is applied, the 1D bands evolve into hybrid magneto-electric sub-levels that eventually transform into Landau levels for the widest nanowire devices investigated (width = 100 nm). Hall measurements in a four-terminal configuration on these devices show plateaus in the transverse Hall resistance at high magnetic fields that scale with (ve 2/h)−1. e is the elementary charge, h denotes Planck's constant and v is an integer that coincides with the Landau level index determined from the longitudinal conductance measurements. While the 1D conductance quantization in zero magnetic field is fragile against disorder at the NW surface, the plateaus in the Hall resistance at high fields remain robust as expected for a topologically protected Quantum Hall phase.
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5.
  • Lindelöw, Fredrik, et al. (författare)
  • III-V nanowire MOSFETs with novel self-limiting Λ-ridge spacers for RF applications
  • 2020
  • Ingår i: Semiconductor Science and Technology. - : IOP Publishing. - 0268-1242 .- 1361-6641. ; 35:6
  • Tidskriftsartikel (refereegranskat)abstract
    • We present a semi self-aligned processing scheme for III-V nanowire transistors with novel semiconductor spacers in the shape of Λ-ridges, utilising the effect of slow growth rate on {111}B facets. The addition of spacers relaxes the constraint on the perfect alignment of gate to contact areas to enable low overlap capacitances. The spacers give a field-plate effect that also helps reduce off-state and output conductance while increasing breakdown voltage. Microwave compatible devices with L g = 32 nm showing f T = 75 GHz and f max = 100 GHz are realized with the process, demonstrating matched performance to spacer-less devices but with relaxed scaling requirements.
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6.
  • Olausson, Patrik, et al. (författare)
  • Low temperature atomic hydrogen annealing of InGaAs MOSFETs
  • 2023
  • Ingår i: Semiconductor Science and Technology. - : IOP Publishing. - 0268-1242 .- 1361-6641. ; 38:5
  • Tidskriftsartikel (refereegranskat)abstract
    • Recent work showing a strong quality improvement of the Si/SiO2 material system by low temperature atomic hydrogen annealing (AHA), and the fact that III-V semiconductors outperform Si in many applications makes the investigation of AHA on III-V/high-k interfaces to a very interesting topic. In this work, the potential of AHA as a low temperature annealing treatment of InGaAs metal-oxide-semiconductor field-effect transistors is presented and compared to conventional annealing in a rapid thermal process (RTP) system using forming gas. It is found that post metal annealing in atomic hydrogen greatly enhances the quality of the metal-oxide-semiconductor structure in terms of effective mobility, minimum subthreshold swing, and reliability. The device performance is comparable to RTP annealing but can be performed at a lower temperature, which opens up for integration of more temperature-sensitive materials in the device stack.
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7.
  • Akram, Nadeem, et al. (författare)
  • Design optimization of InGaAsP-InGaAlAs 1.55 mu m strain-compensated MQW lasers for direct modulation applications
  • 2004
  • Ingår i: Semiconductor Science and Technology. - : IOP Publishing. - 0268-1242 .- 1361-6641. ; 19:5, s. 615-625
  • Tidskriftsartikel (refereegranskat)abstract
    • In this paper, a simulation study of InGaAsP(well)/InGaAlAs(barrier) 1.55 mum strain-compensated multi-quantum well (MQW) lasers is presented. Due to a large conduction band discontinuity in this material system, a higher material gain and differential gain can be obtained from such a quantum well (QW) as compared to a traditional InGaAsP/InGaAsP quantum well. The deeper electron well should also improve elevated temperature operating characteristics and reduce the electron spillover from QWs. For MQWs, a uniform vertical distribution of holes is achieved due to a reduced effective hole confinement energy by optimizing the bandgap and the strain in the barriers. A large number of quantum wells can be uniformly pumped, reducing the carrier density in each individual well. A uniform and low carrier density in all the wells help reduce the total Auger recombination current. High p-doping in the active region is shown to enhance the carrier and gain non-uniformity in the MQWs. A simulated high modulation bandwidth has been demonstrated, promising directly modulated lasers as a low-cost source for short to medium distance (1-10 km) high speed optical links.
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8.
  • Andersson, Henrik, 1975-, et al. (författare)
  • Analysis and improvement of the position nonlinearity caused by a residual stress in MOS-type position-sensitive detectors with indium tin oxide gate contact
  • 2008
  • Ingår i: Semiconductor Science and Technology. - : IOP Publishing. - 0268-1242 .- 1361-6641. ; 23:7, s. 1-10
  • Tidskriftsartikel (refereegranskat)abstract
    • In this paper, lateral effect position-sensitive detectors based on the MOS principle have been fabricated in lengths of 15 mm, 45 mm and 60 mm. The gate contact covering the active area consists of indium tin oxide which is a degenerate semiconductor transparent in the visible spectral range. Characterization and analysis have both been performed especially withparticular focus on the nonlinearity believed to be caused by stray stress induced in the inversion channel originating in the indium tin oxide gate contact. Stress in the channel will change the resistance in a non-uniform manner because of the piezoresistance effect, thus causing a nonlinearity in the position determination. It has been shown that the heat treatmentgreatly influences the linearity of the position-sensitive detectors. A heat treatment performed correctly results in 60 mm and 15 mm detectors with nonlinearity within ±0.1% and 45 mm detectors with nonlinearity within ±0.15% over 60% of the active length. This is an improvement over the previous results with this type of MOS position-sensitive detector. By performing a correctly timed heat treatment this PSD type has the potential to be used incommon position-sensing applications.
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9.
  • Antonyuk, Vadim, et al. (författare)
  • Phonon transmission in III-V semiconductor superlattices and alloys
  • 2005
  • Ingår i: Semiconductor Science and Technology. - : IOP Publishing. - 0268-1242 .- 1361-6641. ; 20:5, s. 347-352
  • Tidskriftsartikel (refereegranskat)abstract
    • We have used the transfer matrix approach to investigate the LA phonon transmission along the [0 0 1] growth direction in GaAs/GaAlAs superlattices and in Ga1-xAlxAs alloys. Our calculated minigap in the phonon dispersion induced by the zone folding matches reasonably to the phonon filtering experiment. However, in the regime of phonon ballistic transport, we found insignificant effect of zone folding on phonon thermal conductance. On the other hand, the alloy scatterings largely suppress the phonon transmission probability and so lower the phonon thermal conductance of alloys.
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10.
  • Baranowski, M, et al. (författare)
  • Contactless Electroreflectance, Photoluminescence and Time-Resolved Photoluminescence of GaInNAs Quantum Wells Obtained by the MBE Method with N-irradiation
  • 2011
  • Ingår i: Semiconductor Science and Technology. - : IOP Publishing. - 1361-6641 .- 0268-1242. ; 26:4, s. 045012-
  • Tidskriftsartikel (refereegranskat)abstract
    • The optical properties of GaInNAs quantum wells (QW) grown by molecular beam epitaxywith and without N-irradiation (i.e. grown by the classical method) were investigated by thecontactless electroreflectance (CER), temperature-dependent photoluminescence (PL) andtime-resolved PL (TRPL). From CER measurements it was concluded that one type ofnitrogen nearest-neighbor environment (In-rich environment) is dominant for GaInNAs QWsgrown with N-irradiation whereas various nitrogen environments are present for the referenceGaInNAs QW (i.e. the sample obtained by the classical method). PL and TRPL measurementsclearly show that the optical properties of GaInNAs QWs are affected mainly by the amount ofthe incorporated nitride atoms. It was observed that the PL decay time decreased from ∼200to ∼40 ps when the nitrogen concentration is increased from 0.8 to 2.2%. In addition, thepresence of As flux during N-irradiation reduces the amount of the incorporated nitrogen andsimultaneously improves the optical quality of GaInNAs QWs (i.e. it weakens the carrierlocalization at low temperatures and improves the quantum efficiency of PL).
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11.
  • Bergsten, Johan, 1988, et al. (författare)
  • Low resistive Au-free, Ta-based, recessed ohmic contacts to InAlN/AlN/GaN heterostructures
  • 2015
  • Ingår i: Semiconductor Science and Technology. - : IOP Publishing. - 1361-6641 .- 0268-1242. ; 30:10, s. 105034-
  • Tidskriftsartikel (refereegranskat)abstract
    • The formation of recess etched Au-free ohmic contacts to an InAlN/AlN/GaN heterostructure is investigated. A Ta/Al/Ta metal stack is used to produce contacts with contact resistance (R-c) as low as 0.14 Omega mm. It is found that R-c decreases with increasing recess depth until the InAlN barrier is completely removed. For even deeper recesses R-c remains low but requires annealing at higher temperatures for contact formation. The lowest R-c is found for contacts where the recess etch has stopped just above the 2D electron gas channel. At this depth the contacts are also found to be less sensitive to other process parameters, such as anneal duration and temperature. An optimum bottom Ta layer thickness of 5-10 nm is found. Two reliability experiments preliminary confirm the stability of the recessed contacts.
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12.
  • Desrat, W., et al. (författare)
  • Antisymmetric magnetoresistance anomalies and magnetic domain structure in GaMnAs/InGaAs layers
  • 2009
  • Ingår i: Semiconductor Science and Technology. - : IOP Publishing. - 0268-1242 .- 1361-6641. ; 24:6
  • Tidskriftsartikel (refereegranskat)abstract
    • Antisymmetric magneto-resistance anomalies generated by a reversal of the magnetization are studied in a number of GaMnAs/InGaAs layers with out-of-plane (easy axis) magnetization. The anomalies occur independent of the magnetic field orientation. This shows, that once a magnetic domain with reversed magnetization is nucleated, simply the presence of the domain wall between the longitudinal contacts is sufficient to give rise to the anomaly. Very different shapes for magneto-resistance anomaly can be observed experimentally depending upon the sample. They reflect the various magnetic domain structures present inside the layers during the magnetization reversal process.
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13.
  • Dick Thelander, Kimberly, et al. (författare)
  • Control of III-V nanowire crystal structure by growth parameter tuning
  • 2010
  • Ingår i: Semiconductor Science and Technology. - : IOP Publishing. - 0268-1242 .- 1361-6641. ; 25:2
  • Tidskriftsartikel (refereegranskat)abstract
    • In this work we investigate the variation of the crystal structure of gold-seeded III-V nanowires with growth parameters, in order to gain a cohesive understanding of these effects. We investigate six III-V materials: GaAs, InAs, GaP, InP, GaSb and InSb, over a variation of growth conditions. All six of these materials exhibit a cubic zinc blende structure in bulk, but twin planes and stacking faults, as well as a hexagonal wurtzite structure, are commonly observed in nanowires. Parameters which may affect the crystal structure include growth temperature and pressure, precursor molar fraction and V/III ratio, nanowire diameter and surface density, and impurity atoms. We will focus on temperature, precursor molar fraction and V/III ratio. Our observations are compared to previous reports in the literature of the III-V nanowire crystal structure, and interpreted in terms of existing models. We propose that changes in the crystal structure with growth parameters are directly related to changes in the stable side facets.
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14.
  • Fagerlind, Martin, 1980, et al. (författare)
  • A room temperature HEMT process for AlGaN/GaN heterostructure characterization
  • 2009
  • Ingår i: Semiconductor Science and Technology. - : IOP Publishing. - 1361-6641 .- 0268-1242. ; 24:4, s. 045014-
  • Tidskriftsartikel (refereegranskat)abstract
    • A simple, room temperature, AlGaN/GaN high electron mobility transistor (HEMT) process is presented. The process consists of only two steps which can be performed by hand. The first step is to deposit gallium (Ga) metal for ohmic contacts, which without thermal processing have a specific contact resistivity ρ_c=0.10 Ohm cm2. Silver (Ag)-based conductive paint is then deposited to form a Schottky contact. The simplicity of the process facilitates fast fabrication and characterization of HEMTs, without unwanted effects on the material. The process is useful for initial material characterization and screening. The process is also found to be a useful tool for process monitoring of the conventional HEMT micro-fabrication process by detecting material/process quality problems. In this work the process is used for initial material characterization and screening, where a leaky buffer can easily be detected. The process is also used to identify the ohmic contact annealing as a potentially damaging step in a conventional micro-fabrication process. A decrease in the electron sheet carrier concentration and an increase of leakage currents are measured after annealing.
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15.
  • Fedorych, OM, et al. (författare)
  • Magnetic order in semiconducting, ferromagnetic Ga1-xMnxAs
  • 2004
  • Ingår i: Semiconductor Science and Technology. - : IOP Publishing. - 0268-1242 .- 1361-6641. ; 19:4, s. 492-493
  • Tidskriftsartikel (refereegranskat)abstract
    • Magnetic resonance studies allow us to distinguish paramagnetic, ferromagnetic and ferrimagnetic phases in Ga1-xMnxAs. The transition from ferromagnet to ferrimagnet is correlated with a metal to insulator transition. The analysis of spin wave resonance spectra, which occur in the ferrimagnetic phase, allows us to estimate the magnitude and the distance dependence of exchange coupling. The experimentally evaluated long range of exchange causes an effective averaging of the fluctuation of exchange interactions. As a consequence, in the semimetallic phase both spin subsystems coherently precess forming the ferrimagnetic structure. In the insulating phase, fluctuations of the local exchange field lead to a fast decoherence of the carrier spins and only the localized Mn spins form the ferromagnetic moment.
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16.
  • Gooth, Johannes, et al. (författare)
  • Thermoelectric performance of classical topological insulator nanowires
  • 2015
  • Ingår i: Semiconductor Science and Technology. - : IOP Publishing. - 0268-1242 .- 1361-6641. ; 30:1
  • Tidskriftsartikel (refereegranskat)abstract
    • There is currently substantial effort being invested into creating efficient thermoelectric (TE) nanowires based on topological insulator (TI) chalcogenide-type materials. A key premise of these efforts is the assumption that the generally good TE properties that these materials exhibit in bulk form will translate into similarly good or even better TE performance of the same materials in nanowire form. Here, we calculate TE performance of TI nanowires based on Bi2Te3, Sb2Te3 and Bi2Se3 as a function of diameter and Fermi level. We show that the TE performance of TI nanowires does not derive from the properties of the bulk material in a straightforward way. For all investigated systems the competition between surface states and bulk channel causes a significant modification of the TE transport coefficients if the diameter is reduced into the sub 10 mu m range. Key aspects are that the surface and bulk states are optimized at different Fermi levels or have different polarity as well as the high surface to volume ratio of the nanowires. This limits the maximum TE performance of TI nanowires and thus their application in efficient TE devices.
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17.
  • Jansen, R., et al. (författare)
  • Silicon spintronics with ferromagnetic tunnel devices
  • 2012
  • Ingår i: Semiconductor Science and Technology. - : IOP Publishing. - 1361-6641 .- 0268-1242. ; 27:8
  • Forskningsöversikt (refereegranskat)abstract
    • In silicon spintronics, the unique qualities of ferromagnetic materials are combined with those of silicon, aiming at creating an alternative, energy-efficient information technology in which digital data are represented by the orientation of the electron spin. Here we review the cornerstones of silicon spintronics, namely the creation, detection and manipulation of spin polarization in silicon. Ferromagnetic tunnel contacts are the key elements and provide a robust and viable approach to induce and probe spins in silicon, at room temperature. We describe the basic physics of spin tunneling into silicon, the spin-transport devices, the materials aspects and engineering of the magnetic tunnel contacts, and discuss important quantities such as the magnitude of the spin accumulation and the spin lifetime in the silicon. We highlight key experimental achievements and recent progress in the development of a spin-based information technology.
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18.
  • Koskelo, O., et al. (författare)
  • The effect of a material growth technique on ion-implanted Mn diffusion in GaAs
  • 2009
  • Ingår i: Semiconductor Science and Technology. - : IOP Publishing. - 0268-1242 .- 1361-6641. ; 24:4
  • Tidskriftsartikel (refereegranskat)abstract
    • Diffusion of ion-implanted Mn in semi-insulating (SI) and liquid encapsulated Czochralski (LEC)-grown GaAs has been determined employing the modified radiotracer technique. The effect of the growth technique and conditions on Mn diffusion in low temperature molecular beam epitaxy (LT-MBE)-grown GaAs has also been studied. Two distinct diffusion components appear in ion-implanted Mn diffusion in GaAs: slow and fast. As the diffusivity for the SI material is slightly higher than that for the LT-grown material, it is observed that the diffusivity of the fast component retards with increasing initial concentrations of Ga sublattice defects. At the same time the Mn concentration in the tail part of the diffusion profile is higher in the LT-grown material. Ga vacancy-assisted clustering of Mn is proposed as a likely reason for the observed effects.
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19.
  • Lefebvre, Eric, 1975, et al. (författare)
  • Comparison of shallow-mesa InAs/AlSb HEMTs with and without early-protection for long-term stability against Al(Ga)Sb oxidation
  • 2014
  • Ingår i: Semiconductor Science and Technology. - : IOP Publishing. - 1361-6641 .- 0268-1242. ; 29:3
  • Tidskriftsartikel (refereegranskat)abstract
    • The fabrication process of InAs/AlSb high electron mobility transistors (HEMTs) has been improved by depositing, after the shallow-mesa isolation of the active area, a thin SiNx-film on the exposed AlGaSb mesa floor. Devices with and without this early-protection against Al(Ga)Sb oxidation have been fabricated simultaneously on the same chip for fair comparison. Optical observations and electrical measurements over four and half years demonstrated the physical stability provided by this extra-coverage. The electrical measurements also revealed that the induced deposition of the probing pads and of the extrinsic part of the gates on SiNx slightly reduced the maximum drain current I-D (-9%) and the transconductance g(m) (-12%) to, respectively, 700 mA mm (1) and 1220 mS mm (1) for 2 x 20 mu m(2) InAs/AlSb HEMTs with a 140 nm recessed gate. On the other hand, the gate-leakage current I-G was lowered by more than one order of magnitude, leading to a better pinch-off behavior and increased values of cut-off frequency f(T) (+4%) and maximum frequency of oscillation f(max) (+36%) to, respectively, 230 GHz and 190 GHz at a drain voltage V-DS of 0.5 V.
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20.
  • Lind, Erik (författare)
  • High frequency III-V nanowire MOSFETs
  • 2016
  • Ingår i: Semiconductor Science and Technology. - : IOP Publishing. - 0268-1242 .- 1361-6641. ; 31:9
  • Forskningsöversikt (refereegranskat)abstract
    • III-V nanowire transistors are promising candidates for very high frequency electronics applications. The improved electrostatics originating from the gate-all-around geometry allow for more aggressive scaling as compared with planar field-effect transistors, and this can lead to device operation at very high frequencies. The very high mobility possible with In-rich devices can allow very high device performance at low operating voltages. GaN nanowires can take advantage of the large band gap for high voltage operation. In this paper, we review the basic physics and device performance of nanowire field- effect transistors relevant for high frequency performance. First, the geometry of lateral and vertical nanowire field-effect transistors is introduced, with special emphasis on the parasitic capacitances important for nanowire geometries. The basic important high frequency transistor metrics are introduced. Secondly, the scaling properties of gate-all-around nanowire transistors are introduced, based on geometric length scales, demonstrating the scaling possibilities of nanowire transistors. Thirdly, to model nanowire transistor performance, a two-band non-parabolic ballistic transistor model is used to efficiently calculate the current and transconductance as a function of band gap and nanowire size. The intrinsic RF metrics are also estimated. Finally, experimental state-of-the-art nanowire field-effect transistors are reviewed and benchmarked, lateral and vertical transistor geometries are explored, and different fabrication routes are highlighted. Lateral devices have demonstrated operation up to 350 GHz, and vertical devices up to 155 GHz.
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21.
  • Lu, W, et al. (författare)
  • Independent determination of In and N concentrations in GaInNAs alloys
  • 2009
  • Ingår i: Semiconductor Science and Technology. - : IOP Publishing. - 1361-6641 .- 0268-1242. ; 24:10, s. 105016-
  • Tidskriftsartikel (refereegranskat)abstract
    • High-resolution x-ray diffraction (HRXRD) and photoreflectance ( PR) spectroscopy were used to independently determine the In and N concentrations in GaInNAs alloys grown by solid-source molecular beam epitaxy (SSMBE). The lattice constant and bandgap energy can be expressed as two independent equations in terms of the In and N concentrations, respectively. The HRXRD measurement provided the lattice constant and the PR measurement extracted the bandgap energy. By simultaneously solving these two equations, we have determined the In and N concentrations with the error as small as 0.001.
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22.
  • Malmros, Anna, 1977, et al. (författare)
  • Electrical properties, microstructure, and thermal stability of Ta-based ohmic contacts annealed at low temperature for GaN HEMTs
  • 2011
  • Ingår i: Semiconductor Science and Technology. - : IOP Publishing. - 1361-6641 .- 0268-1242. ; 26:7
  • Tidskriftsartikel (refereegranskat)abstract
    • Ta-based ohmic contacts to gallium nitride high electron mobility transistor (GaN HEMT) epitaxial structures were investigated. Two metallization schemes were considered: Ta/Al/Ni(Ta)/Au and Ta/Al/Ta. The latter was superior in terms of lower contact resistance (R-c) and wider process window. The metallizations were applied to two different heterostructures (GaN/Al0.14Ga0.86N/GaN and Al0.25Ga0.75N/GaN). The lowest measured R-c was 0.06 and 0.28 Omega mm, respectively. The main advantage of the Ta-based ohmic contacts over conventional Ti-based contacts was the low anneal temperature. The optimum temperature of annealing was found to be 550-575 degrees C. From optical and scanning electron microscopy, it was clear that excellent surface morphology and edge acuity were obtained at these low temperatures. This facilitates lateral scaling of the GaN HEMT. TEM images were taken of the contact cross sections onto which EDX measurements were performed. The aim was to investigate the microstructure and the contact mechanism. Storage tests at 300 degrees C for more than 400 h in air ambient showed no deterioration of R-c.
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23.
  • Ndebeka-Bandou, C., et al. (författare)
  • Free carrier absorption and inter-subband transitions in imperfect heterostructures
  • 2014
  • Ingår i: Semiconductor Science and Technology. - : IOP Publishing. - 0268-1242 .- 1361-6641. ; 29:2
  • Forskningsöversikt (refereegranskat)abstract
    • We present the results of a quantum mechanical modelling of the free carrier absorption (FCA) in semiconductor heterolayers. Elastic and inelastic scatterers are considered with emphasis on the interface defects (optical phonons) contributions to the induced photon absorption for elastic (inelastic) scatterers. Various approaches to FCA are also presented (perturbation, Green's function technique). The connection between inter-subband absorption and FCA is thoroughly discussed. The absorption lineshape and its modification by suitable doping is presented.
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24.
  • Pan, Wenwu, et al. (författare)
  • Photoluminescence of InGaAs/GaAsBi/InGaAs type-II quantum wells grown by gas source molecular beam epitaxy
  • 2017
  • Ingår i: Semiconductor Science and Technology. - : IOP Publishing. - 1361-6641 .- 0268-1242. ; 32:1
  • Tidskriftsartikel (refereegranskat)abstract
    • InxGa1-xAs/GaAs1-yBiy/InxGa1-xAs (0.20 ≤x ≤0.22, 0.035 ≤y ≤0.045) quantum wells (QWs) were grown on GaAs substrates by gas source molecular beam epitaxy for realizing the type-II band edge line-up. Both type-I and type-II transitions were observed in the Bi containing W QWs and the photoluminescence intensity was enhanced in the sample with a high Bi content, which is mainly due to the improvement of carrier confinement. The 8 band k • p model was used to analyze the electronic properties in the QWs and the calculated transition energies fit well with the experiment results. Our study shows that the proposed type-II QW is a promising candidate for realizing GaAs-based near infrared light emitting devices near 1.3 μm
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25.
  • Pan, W. W., et al. (författare)
  • Raman scattering studies of dilute InP1-xBix alloys reveal unusually strong oscillator strength for Bi-induced modes
  • 2015
  • Ingår i: Semiconductor Science and Technology. - : IOP Publishing. - 1361-6641 .- 0268-1242. ; 30:9
  • Tidskriftsartikel (refereegranskat)abstract
    • Room-temperature Raman scattering studies of new InP1-xBix alloys grown by molecular beam epitaxy are reported. Two new Bi-induced vibrations observed at 149 and 171 cm-1 are assigned to InBi-like TO and LO phonon modes, respectively, and exhibit an unusually strong intensity for the dilute regime. Two additional modes at 311 and 337 cm-1 are resolved as well with unknown origins. The Raman intensities of the InBi-like TO and LO bands, as well as the new mode at 337 cm-1, exhibit strong and linear dependence on the Bi concentration for the composition range studied, 0.003 ≤ x ≤ 0.023. This correlation may serve as a fast and convenient means of characterizing bismuth composition not only in the ternary alloy InP1-xBix but also in the quaternaries such as In1-yGayP1-xBix and In1-yAlyP1-xBix.
  •  
26.
  • Roddaro, Stefano, et al. (författare)
  • Charge pumping in InAs nanowires by surface acoustic waves
  • 2010
  • Ingår i: Semiconductor Science and Technology. - : IOP Publishing. - 0268-1242 .- 1361-6641. ; 25:2
  • Tidskriftsartikel (refereegranskat)abstract
    • We investigate the interaction between surface acoustic waves on a piezoelectric LiNbO3 substrate and charge carriers in InAs nanowire transistors. Interdigital transducers are used to excite electromechanical waves on the chip surface and their influence on the transport in the nanowire devices is studied at room temperature. Charge pumping is studied in different biasing conditions and in pulsed operation in order to assess interference effects due to reflected waves on the sample chip. Present results constitute a key building block for the realization of acoustoelectric nanodevices based on the InAs/InP nanowire technology.
  •  
27.
  • Rodilla, H., et al. (författare)
  • Dynamic Monte Carlo study of isolated-gate InAs/AlSb HEMTs
  • 2011
  • Ingår i: Semiconductor Science and Technology. - : IOP Publishing. - 1361-6641 .- 0268-1242. ; 26:2
  • Tidskriftsartikel (refereegranskat)abstract
    • In this work, by means of Monte Carlo simulations, the static and dynamic behavior of isolated-gate InAs/AlSb high electron mobility transistors (Sb-HEMTs) has been studied and compared with experimental results. The influence of the existence of a native oxide under the gate, the value of the surface charges in the gate recess and the possible variation of electron sheet carrier density, n(s), have been studied. A decrease in the gate-source capacitance, transconductance and intrinsic cutoff frequency is observed because of the presence of the native oxide, while changes in the value of the surface charges in the recess only introduce a threshold voltage shift. The increase of n(s) shifts the maximum of the transconductance and intrinsic cutoff frequency to higher values of drain current and improves the agreement with the experimental results.
  •  
28.
  • Rodilla, Helena, 1982, et al. (författare)
  • Monte Carlo study of the noise performance of isolated-gate InAs/AlSb HEMTs
  • 2012
  • Ingår i: Semiconductor Science and Technology. - : IOP Publishing. - 1361-6641 .- 0268-1242. ; 27:1, s. 015008-
  • Tidskriftsartikel (refereegranskat)abstract
    • In this work, the extrinsic dynamic behavior and noise performance of a 225 nm isolated-gateInAs/AlSb high electron mobility transistor (HEMT) have been studied by means of MonteCarlo simulations. A very good agreement with experimental results has been achieved for fT .Discrepancies between experimental and simulated f max have been observed and attributed tothe experimental frequency dispersion of gd and Cds. The simulations of the intrinsic andextrinsic noise parameters indicate an excellent performance for this device (Fmin = 0.3 dB at10 GHz) even if we confirm that the presence of the native oxide under the gate induces asignificant decrease in fT and f max of around 20%, together with an increase of noise figureand noise resistance.
  •  
29.
  • Vasallo, Beatriz G., et al. (författare)
  • Kink effect and noise performance in isolated-gate InAs/AlSb high electron mobility transistors
  • 2012
  • Ingår i: Semiconductor Science and Technology. - : IOP Publishing. - 1361-6641 .- 0268-1242. ; 27:6, s. Article Number: 065018-
  • Tidskriftsartikel (refereegranskat)abstract
    • The kink effect can spoil the otherwise excellent low noise performance of InAs/AlSb high electron mobility transistors. It has its origin in the pile-up of holes (generated by impact ionization) taking place mainly at the drain side of the buffer, which leads to a reduction of the gate-induced channel depletion and results in a drain current enhancement. Our results indicate that the generation of holes by impact ionization and their further recombination lead to fluctuations in the charge of the hole pile-up, which provoke an important increase in the drain current noise, even when the kink effect is hardly perceptible in the output characteristics.
  •  
30.
  • Wang, K., et al. (författare)
  • Growth of semiconductor alloy InGaPBi on InP by molecular beam epitaxy
  • 2015
  • Ingår i: Semiconductor Science and Technology. - : IOP Publishing. - 1361-6641 .- 0268-1242. ; 30:9
  • Tidskriftsartikel (refereegranskat)abstract
    • We report the first successful growth of InGaPBi single crystals on InP substrate with Bi concentration far beyond the doping level by gas source molecular beam epitaxy. The InGaPBi thin films reveal excellent surface and structural qualities, making it a promising new III-V compound family member for heterostructures. The strain can be tuned between tensile and compressive by adjusting Ga and Bi compositions. The maximum achieved Bi concentration is 2.2 ± 0.4% confirmed by Rutherford backscattering spectroscopy. Room temperature photoluminescence shows strong and broad light emission at energy levels much smaller than the InP bandgap.
  •  
31.
  • Wu, X. Y., et al. (författare)
  • Effect of rapid thermal annealing on InP1-xBix grown by molecular beam epitaxy
  • 2015
  • Ingår i: Semiconductor Science and Technology. - : IOP Publishing. - 1361-6641 .- 0268-1242. ; 30:9
  • Tidskriftsartikel (refereegranskat)abstract
    • The effect of post-growth rapid thermal annealing on structural and optical properties of InP1-xBix thin films was investigated. InPBi shows good thermal stability up to 500 °C and a modest improvement in photoluminescence (PL) intensity with an unchanged PL spectral feature. Bismuth outdiffusion from InPBi and strain relaxation are observed at about 600 °C. The InPBi sample annealed at 800 °C shows an unexpected PL spectrum with different energy transitions.
  •  
32.
  • Zakharova, A., et al. (författare)
  • Optical absorption of polarized light in InAs/GaSb quantum wells
  • 2008
  • Ingår i: Semiconductor Science and Technology. - : IOP Publishing. - 0268-1242 .- 1361-6641. ; 23:12
  • Tidskriftsartikel (refereegranskat)abstract
    • Using an eight-band k p model Hamiltonian with the Burt-Foreman envelope function theory, we have investigated the optical absorption of both linearly and circularly polarized light, as well as related phenomena in InAs/GaSb broken-gap quantum wells grown along the [0 0 1] direction, with emphasis on the effects of electron-hole hybridization and the various symmetry-breaking mechanisms such as structural inversion asymmetry, bulk inversion asymmetry and interface Hamiltonian. The optical matrix elements exhibit unusual angular dependence in close connection with the spin-flip transitions which are originally forbidden. The spin split of the 2e subband results in two profound absorption peaks for the 1hh-2e transition for both linearly polarized and circularly polarized light. A large lateral optical anisotropy appears in the absorption coefficient of linearly polarized light, which can reach almost 100% with a reducing thickness of the quantum well. For the absorption of circularly polarized light, we found a large enhancement of electron spin polarization in the upper 2e subband, which was generally considered as forbidden if the polarization is along the direction perpendicular to the plane-of-light incidence. © 2008 IOP Publishing Ltd.
  •  
33.
  • Zhou, S. X., et al. (författare)
  • Effects of buffer layer preparation and Bi concentration on InGaAsBi epilayers grown by gas source molecular beam epitaxy
  • 2015
  • Ingår i: Semiconductor Science and Technology. - : IOP Publishing. - 1361-6641 .- 0268-1242. ; 30:12, s. Art. no. 125001-
  • Tidskriftsartikel (refereegranskat)abstract
    • The effect of using an In0.53Ga0.47As buffer layer on the crystalline quality of InGaAsBi epilayer with Bi concentration up to 3.1% grown by gas source molecular beam epitaxy was investigated. It is found that use of the buffer layer has a dramatic effect on the improvement of surface morphology, structural, electrical and optical properties of InGaAsBi epilayers. Bi incorporation in InGaAs up to a concentration of 3.1% causes no degradation of the electron mobility and induces p-type carriers that compensate the background n-type carriers resulting in mobility enhancement with increasing Bi concentration. With the buffer layer preparation, a maximum electron mobility of 5550 cm(2) V-1 s(-1) at room temperature is demonstrated in InGaAsBi with x(Bi) = 3.1%, which is the highest value reported in InGaAsBi with x(Bi) > 2.5%.
  •  
34.
  • Buyanova, Irina, 1960-, et al. (författare)
  • Magneto-optical and light-emission properties of III-As-N semiconductors
  • 2002
  • Ingår i: Semiconductor Science and Technology. - : IOP Publishing. - 0268-1242 .- 1361-6641. ; 17:8, s. 815-822
  • Tidskriftsartikel (refereegranskat)abstract
    • A brief review on our present knowledge of optical and magneto-optical properties of III-V-N alloys, in particular, Ga(In)NAs alloys with low nitrogen compositions is given. The main attention is focused on fundamental electronic parameters of the Ga(In)NAs alloys as well as key material-related issues which are relevant to device applications, such as identification of dominant recombination processes in the alloys, compositional dependence of electron effective mass and band alignment in Ga(In)NAs-based heterostructures.
  •  
35.
  • David, Denis, et al. (författare)
  • Optical properties from photoelectron energy-loss spectroscopy of low-temperature aqueous chemically synthesized ZnO nanorods grown on Si
  • 2019
  • Ingår i: Semiconductor Science and Technology. - : Institute of Physics (IOP). - 0268-1242 .- 1361-6641. ; 34:4
  • Tidskriftsartikel (refereegranskat)abstract
    • The optical properties of zinc oxide (ZnO) nanorods (NRs) synthesized by the low-temperature aqueous chemical method on top of silicon (Si) substrate have been investigated by means of photoelectron energy loss spectroscopy (PEELS). The ZnO NRs were obtained by the low temperature aqueous chemical synthesis on top of Si substrate. The measured valence band, the dynamical dielectric functions and optical absorption of the material show a reasonable agreement when the trending and shape of the theoretical calculations are considered. A first-principle calculation based on density functional theory (DFT) was performed using the partially self-consistent GW approximation (scGW(0)) and compared to the experimental results. The application of these two techniques brings a new analysis of the electronic properties of this material. The experimental results regarding the density of states (DOS) obtained for the valence band using x-ray photoelectron spectroscopy (XPS) was found to be consistent with the theoretical calculated value. Due to this consistency, the same wavefunctions was then employed to calculate the dielectric function of the ZnO NRs. The experimentally extracted dielectric function was also consistent with the calculated values.
  •  
36.
  • Davydova, Alexandra, et al. (författare)
  • Fabrication of thin ZnO films with wide-range tuned optical properties by reactive magnetron sputtering
  • 2018
  • Ingår i: Semiconductor Science and Technology. - : Institute of Physics Publishing (IOPP). - 0268-1242 .- 1361-6641. ; 33:2
  • Tidskriftsartikel (refereegranskat)abstract
    • We report the manufacturing of thin zinc oxide films by reactive magnetron sputtering at room temperature, and examine their structural and optical properties. We show that the partial oxygen pressure in DC mode can have dramatic effect on absorption and refractive index (RI) of the films in a broad spectral range. In particular, the change of the oxygen pressure from 7% to 5% can lead to either conventional crystalline ZnO films having low absorption and characteristic descending dependence of RI from 2.4-2.7 RIU in the visible to 1.8-2 RIU in the near-infrared (1600 nm) range, or to untypical films, composed of ZnO nano-crystals embedded into amorphous matrix, exhibiting unexpectedly high absorption in the visible-infrared region and ascending dependence of RI with values varying from 1.5 RIU in the visible to 4 RIU in the IR (1600 nm), respectively. Untypical optical characteristics in the second case are explained by defects in ZnO structure arising due to under-oxidation of ZnO crystals. We also show that the observed defect-related film structure remains stable even after annealing of films under relatively high temperatures (30 min under 450 degrees C). We assume that both types of films can be of importance for photovoltaic (as contact or active layers, respectively), as well as for chemical or biological sensing, optoelectronics etc.
  •  
37.
  • Fang, Mei, et al. (författare)
  • Inkjet printing Ag-TiO2 thin films with suppressed photoluminescence
  • 2019
  • Ingår i: Semiconductor Science and Technology. - : IOP PUBLISHING LTD. - 0268-1242 .- 1361-6641. ; 34:10
  • Tidskriftsartikel (refereegranskat)abstract
    • With ultraviolet sensitive photochemistry and photoelectric properties, TiO2 is attractive for applications like photocatalysis, photovoltaic devices, and sunscreen products, among others. By coating Ag on TiO2 surface, the sensitivity can be extended to visible light, endowing enhanced properties with potential new applications. In this work we inkjet print Ag-TiO2 films from particle suspensions, and investigate the structure, morphology, Ag distribution and the photoluminescence of the films It is found that Ag nanoparticles form bridges among TiO2 particles during the post-annealing. These metallic bridges can transport the excited electrons and suppress the recombination of electrons and holes with the photoluminescence of the film reduced by more than half. The work provides an industrial applicable, low-cost, environment friendly route of preparing Ag-TiO2 films for attractive photochemistry and photoelectric device applications.
  •  
38.
  • Fang, Mei, et al. (författare)
  • Tuning room temperature ferromagnetism of 'in-situ' inkjet printed Fe-doped ZnO films
  • 2019
  • Ingår i: Semiconductor Science and Technology. - : IOP PUBLISHING LTD. - 0268-1242 .- 1361-6641. ; 34:5
  • Tidskriftsartikel (refereegranskat)abstract
    • ZnO is a wide-band gap semiconductor widely used in optical and electric devices, associating with ferromagnetism at low dimension endowing its possibility for functional applications with magneto-optical and magneto-electric properties. We prepared ZnO and Fe-doped ZnO thin films 'in-situ' on substrate by inkjet printing, and tuned the room temperature ferromagnetism (RTFM) of the film by Fe-doping concentration, film thickness and post annealing temperature. It was found that by Fe doping the saturation magnetization (M-s) of the film can be enhanced by more than 4 folds comparing with the un-doped film, i.e. from 0.9 emu g(-1) for the ZnO film to 3.8 emu g(-1) for the Fe-doped ZnO film with comparable thickness. The enhancement was attributed to the introduction of un-paired 3d electrons which formed long range ferromagnetic ordering, as well as the consequent structure changes with smaller grains which increased the interface induced magnetism. By changing the annealing temperature and the film thickness, the defect-induced ferromagnetism was investigated. The RTFM shows thickness dependence with peak saturation magnetization value of 4.44 emu g(-1) for the 45 nm thick film. The work provides an effective way of tuning magnetism in ZnO based films for functional device applications.
  •  
39.
  • Han, Y., et al. (författare)
  • A comparative study of selective dry and wet etching of germanium-tin (Ge1-xSnx) on germanium
  • 2018
  • Ingår i: Semiconductor Science and Technology. - : IOP Publishing. - 1361-6641 .- 0268-1242. ; 33:8
  • Tidskriftsartikel (refereegranskat)abstract
    • A comparative study of selective dry and wet etching methods for germanium-tin (Ge1-xSnx) alloys (3.5% < x < 7.7%) and germanium (Ge) is carried out. Both etching methods are optimized from the perspectives of selectivity and morphology, and then compared. A special behavior of the selective dry etching process is discovered and explained, whereby the selectivity has a dramatic increase to as high as 336 when the Sn concentration is above 6%. Different morphologies of suspended microstructures fabricated by different etching methods are investigated. Comparative study shows that the selective dry etching is a better choice for high Sn concentration GeSn (above 7%) against Ge to have better morphology, selectivity and verticality. While for low Sn concentration GeSn (below 6%), wet etching is a better way to fabricate a suspended GeSn microstructure on Ge. This work provides a comparative understanding of both methods of selective etching for GeSn. This comparative understanding is expected to be applied in the processing of next generation electronic and photonic devices.
  •  
40.
  • Healy, Noel, et al. (författare)
  • A review of materials engineering in silicon-based optical fibres
  • 2018
  • Ingår i: Semiconductor Science and Technology. - : Institute of Physics (IOP). - 0268-1242 .- 1361-6641. ; 33:2
  • Tidskriftsartikel (refereegranskat)abstract
    • Semiconductor optical fibre technologies have grown rapidly in the last decade and there are now a range of production and post-processing techniques that allow for a vast degree of control over the core material's optoelectronic properties. These methodologies and the unique optical fibre geometry provide an exciting platform for materials engineering and fibres can now be produced with single crystal cores, low optical losses, tunable strain, and inscribable phase composition. This review discusses the state-of-the-art regarding the production of silicon optical fibres in amorphous and crystalline form and then looks at the post-processing techniques and the improved material quality and new functionality that they afford.
  •  
41.
  • Huang, Dan, et al. (författare)
  • Group-IV (Si, Ge, and Sn)-doped AgAlTe2 for intermediate band solar cell from first-principles study
  • 2017
  • Ingår i: Semiconductor Science and Technology. - : Institute of Physics (IOP). - 0268-1242 .- 1361-6641. ; 32:6, s. 065007-065014
  • Tidskriftsartikel (refereegranskat)abstract
    • Earlier studies of chalcopyrites as the absorber for intermediate band solar cells (IBSCs) mainly focused on Cu-based compounds, whose intermediate band is usually empty due to its intrinsic p-type conductivity. This is not beneficial to the two sub-bandgap absorptions. In this paper, we demonstrate that the intermediate bands in group IV (Si, Ge, and Sn) doped AgAlTe2 are delocalized and mainly contributed by the anti-bonding state of group-IV elements s state and Te-p state. Overall, we suggest that Sn-doped AgAlTe2 should be a promising absorber candidate for IBSCs based on the theoretical efficiency and defect stability.
  •  
42.
  • Lin, Yen-Ku, et al. (författare)
  • A versatile low-resistance ohmic contact process with ohmic recess and low-temperature annealing for GaN HEMTs
  • 2018
  • Ingår i: Semiconductor Science and Technology. - : IOP Publishing. - 1361-6641 .- 0268-1242. ; 33:9
  • Tidskriftsartikel (refereegranskat)abstract
    • Deeply recessed ohmic contacts for GaN-based high electron mobility transistors (HEMTs) are demonstrated. It is shown that low-resistance ohmic contacts can be achieved with recessing beyond the AlGaN Schottky barrier where the ohmic contacts are formed on the sidewall of the recess. This makes the process versatile and relatively insensitive to the exact recess depth. The ohmic contact is based on a gold-free metallization scheme consisting of a Ta/Al/Ta metal stack requiring a low-temperature annealing. Important parameters for this type of ohmic contact process include the metal coverage, slope of the etched sidewall, bottom Ta-layer thickness, as well as annealing temperature and duration. The optimized contact resistance is as low as 0.24 Omega mm after annealing at 575 degrees C. Moreover, this sidewall contact approach was successfully implemented on different epitaxial heterostructures with different AlGaN barrier thickness as well as with and without AlN exclusion layer. All the samples exhibited excellent contact resistances in a wide range of recess depths. The Ta-based, sidewall ohmic contact process is a promising method for forming an ohmic contact on a wide range of GaN HEMT epitaxial designs.
  •  
43.
  • Linnarsson, Margareta, et al. (författare)
  • Intentional and unintentional channeling during implantation of 51V ions into 4H-SiC
  • 2019
  • Ingår i: Semiconductor Science and Technology. - : IOP Publishing. - 0268-1242 .- 1361-6641. ; 34, s. 1-10
  • Tidskriftsartikel (refereegranskat)abstract
    • Ion implantation is a commonly used process step in 4H-SiC device manufacturing to implement precise concentrations of dopant atoms in selected areas and depths. This paper reports on vanadium (V) implantation into 4H-SiC(0001) and how the crystal lattice, with preferential directions, channels, for the ions, will influence the final dopant distribution. Concentration versus depth profiles of V-ions, intentionally and unintentionally channelled, has been recorded by secondary ion mass spectrometry. Ion implantations have been performed between 50 and 300 keV at various impact angles and fluence at room temperature as well as at elevated temperatures. Before ion implantation, the samples were aligned utilizing the blocking pattern of 100 keV backscattered protons. In addition to the aligned implantations, our standard beam line for ion implantation has been used for implantations in a 'random' direction using the wafer miscut angle of 4 degrees. The electronic stopping has been determined from these 'random' cases and the values have been used in 3D simulations to predict preferential crystallographic directions using SIIMPL, a Monte Carlo simulation code based on the binary collision approximation. The results show that, independent of the used impact angle there is always a probability that the vanadium ions will be steered into the [000-1] and the family of < 11-2-3 > crystal directions and therefore penetrate deep into the sample, resulting in unwanted 'spikes'. If the implantation is performed at elevated temperatures, a larger degree of dechanneling is present due to increased thermal vibrations and the penetration depth of vanadium is slightly reduced.
  •  
44.
  • Milanova, M., et al. (författare)
  • Experimental study of the effect of local atomic ordering on the energy band gap of melt grown InGaAsN alloys
  • 2017
  • Ingår i: Semiconductor Science and Technology. - : IOP PUBLISHING LTD. - 0268-1242 .- 1361-6641. ; 32:8
  • Tidskriftsartikel (refereegranskat)abstract
    • We present a study of melt grown dilute nitride InGaAsN layers by x-ray photoelectron spectroscopy (XPS), Raman and photoluminescence (PL) spectroscopy. The purpose of the study is to determine the degree of atomic ordering in the quaternary alloy during the epitaxial growth at near thermodynamic equilibrium conditions and its influence on band gap formation. Despite the low In concentration (similar to 3%) the XPS data show a strong preference toward In-N bonding configuration in the InGaAsN samples. Raman spectra reveal that most of the N atoms are bonded to In instead of Ga atoms and the formation of N-centred In3Ga1 clusters. PL measurements reveal smaller optical band gap bowing as compared to the theoretical predictions for random alloy and localised tail states near the conduction band minimum.
  •  
45.
  • Nour, Eiman, et al. (författare)
  • Zinc oxide piezoelectric nano-generators for low frequency applications
  • 2017
  • Ingår i: Semiconductor Science and Technology. - : IOP PUBLISHING LTD. - 0268-1242 .- 1361-6641. ; 32:6
  • Tidskriftsartikel (refereegranskat)abstract
    • Piezoelectric Zinc Oxide (ZnO) nanogenerators (NGs) have been fabricated for low frequency (amp;lt;100 Hz) energy harvesting applications. Different types of NGs based on ZnO nanostructures have been carefully developed, and studied for testing under different kinds of low frequency mechanical deformations. Well aligned ZnO nanowires (NWs) possessing high piezoelectric coefficient were synthesized on flexible substrates using the low temperature hydrothermal route. These ZnO NWs were then used in different configurations to demonstrate different low frequency energy harvesting devices. Using piezoelectric ZnO NWs, we started with the fabrication of a sandwiched NG for a handwriting enabled energy harvesting device based on a thin silver layer coated paper substrate. Such device configurations can be used for the development of electronic programmable smart paper. Further, we developed this NG to work as a triggered sensor for a wireless system using footstep pressure. These studies demonstrate the feasibility of using a ZnO NWs piezoelectric NG as a low-frequency self-powered sensor, with potential applications in wireless sensor networks. After that, we investigated and fabricated a sensor on a PEDOT: PSS plastic substrate using a one-sided growth and double-sided growth technique. For the first growth technique, the fabricated NG has been used as a sensor for an acceleration system; while the fabricated NG by the second technique works as an anisotropic direction sensor. This fabricated configuration showed stability for sensing and can be used in surveillance, security, and auto-Mobil applications. In addition to that, we investigated the fabrication of a sandwiched NG on plastic substrates. Finally, we demonstrated that doping ZnO NWs with extrinsic elements (such as Ag) will lead to the reduction of the piezoelectric effect due to the loss of crystal symmetry. A brief summary into future opportunities and challenges is also presented.
  •  
46.
  • Wang, Chang, et al. (författare)
  • Molecular beam epitaxy growth of AlAs 1-x Bi x
  • 2019
  • Ingår i: Semiconductor Science and Technology. - : IOP Publishing. - 1361-6641 .- 0268-1242. ; 34:3
  • Tidskriftsartikel (refereegranskat)abstract
    • High quality AlAs 1-x Bi x layers with Bi composition of 3%-10.5% have been successfully grown by molecular beam epitaxy. The Bi incorporation is confirmed by Rutherford backscattering spectroscopy. For a 400 nm thick AlAsBi layer, the strain relaxation occurs when the Bi composition is larger than 6.5%. Flux ratio is calculated from Knudsen-cell model and Maxwell equation, according to the geometrical relationship of our equipment. The Bi incorporation increases with increasing the As-Al flux ratio as well as the Bi flux. The extrapolation lattice constant of hypothetic zincblende AlBi alloy is about 6.23 Å.
  •  
47.
  • Werheit, H., et al. (författare)
  • Influence of dopants, particularly carbon, on beta-rhombohedral boron
  • 2017
  • Ingår i: Semiconductor Science and Technology. - : IOP Publishing. - 0268-1242 .- 1361-6641. ; 32:9
  • Tidskriftsartikel (refereegranskat)abstract
    • Due to the high affinity of carbon to boron, the preparation of carbon-free boron is problematic. Even high-purity (6N) beta-rhombohedral boron contains 30-60 ppm of C. Hence, carbon affects the boron physical properties published so far more or less significantly. We studied well-defined carbon-doped boron samples based on pure starting material carefully annealed with up to about 1% C, thus assuring homogeneity. We present and discuss their electrical conductivity, optical absorption, luminescence and phonon spectra. Earlier attempts of other authors to determine the conductivity of C-doped boron are revised. Our results allow estimating the effects of oxygen and iron doping on the electrical conductivity using results taken from literature. Discontinuities at low T impair the electronic properties.
  •  
48.
  • Yu, Yong, et al. (författare)
  • Organic bulk heterojunction photodetectors based on polymer blends with unbalanced mobilities
  • 2020
  • Ingår i: Semiconductor Science and Technology. - : IOP PUBLISHING LTD. - 0268-1242 .- 1361-6641. ; 35:10
  • Tidskriftsartikel (refereegranskat)abstract
    • We investigate bulk heterojunction organic photodetectors with unbalanced charge carrier mobilities in the active layer. We present an experimental example of an organic photodiode with very unbalanced mobilities but achieving state-of-the-art parameters in terms of external quantum efficiency exceeding 75% (at illumination 638 nm), and of bandwidth exceeding 1 MHz. The active layer of the photodiode is a 50 nm thick bulk heterojunction made of a blend of PCBM and copolymer of 5,6-difluoro2,1,3-benzothiadiazole, with mobility of slower charge carriers of order of 5 x 10(-7)cm(2) (Vs)(-1)<i, estimated using space-charge-limited photocurrent technique. To understand why such a low mobility does not have deteriorating effects on the photodetecting performance of the photodiode, we performed drift-diffusion simulations of bulk heterojunction photodiodes with Langevin recombination. According to the simulation, the bandwidth of the photodiode is approximately independent of the mobility of slower charge carriers in the blend, and the negative effect of low mobility on the responsivity can be compensated by increasing the reverse bias. Our study shows that well-performing organic photodetectors can be fabricated using organic semiconductors having too low mobility for photovoltaic applications.
  •  
49.
  • Zetterling, Carl-Mikael, et al. (författare)
  • Bipolar integrated circuits in SiC for extreme environment operation
  • 2017
  • Ingår i: Semiconductor Science and Technology. - : Institute of Physics Publishing (IOPP). - 0268-1242 .- 1361-6641. ; 32:3
  • Tidskriftsartikel (refereegranskat)abstract
    • Silicon carbide (SiC) integrated circuits have been suggested for extreme environment operation. The challenge of a new technology is to develop process flow, circuit models and circuit designs for a wide temperature range. A bipolar technology was chosen to avoid the gate dielectric weakness and low mobility drawback of SiC MOSFETs. Higher operation temperatures and better radiation hardness have been demonstrated for bipolar integrated circuits. Both digital and analog circuits have been demonstrated in the range from room temperature to 500 °C. Future steps are to demonstrate some mixed signal circuits of greater complexity. There are remaining challenges in contacting, metallization, packaging and reliability.
  •  
50.
  • Zhang, Renyun, et al. (författare)
  • Nanogenerator made of ZnO nanosheet networks
  • 2017
  • Ingår i: Semiconductor Science and Technology. - : IOP Publishing. - 0268-1242 .- 1361-6641. ; 32:5
  • Tidskriftsartikel (refereegranskat)abstract
    • The piezoelectricity of nanomaterials attracts a great deal of attention due to its broad application, including the harvesting of ambient mechanical energy to power small electronics devices. We report here a simple method to fabricate piezoelectric nanogenerators consisting of networks of ZnO nanosheets grown on aluminum (Al) foils, where the Al acts as both a substrate for growth and as an electrode contacting the ZnO network. A second, top electrode was tapped, rolled, or rubbed against the ZnO to generate piezoelectricity. This second electrode was either a copper foil or fluorine doped tin oxide (FTO) glass. A piezo voltage of up to 0.924 V was detected during rolling and 6 μA was the highest current observed when rubbing the ZnO film with a FTO glass. Due to its simplicity, this nanogenerator fabrication method has the potential to be scaled up for the industrial production of piezoelectric energy harvesting devices.
  •  
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