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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.
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.
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.
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.
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.
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.
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.
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.
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.
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).
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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
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.

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