| 1. |
- Wallenberg, Reine, et al.
(författare)
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In situ metal-organic chemical vapour deposition growth of III–V semiconductor nanowires in the Lund environmental transmission electron microscope
- 2020
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Ingår i: Semiconductor Science and Technology. - : IOP Publishing. - 0268-1242 .- 1361-6641. ; 35:3
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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)
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Structural investigation of ultra-low resistance deeply recessed sidewall ohmic contacts for AlGaN/GaN HEMTs based on Ti/Al/Ti-metallization
- 2023
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Ingår i: Semiconductor Science and Technology. - : IOP Publishing Ltd. - 1361-6641 .- 0268-1242. ; 38:10
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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)
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Impact of in situ NH3 pre-treatment of LPCVD SiN passivation on GaN HEMT performance
- 2022
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Ingår i: Semiconductor Science and Technology. - : IOP Publishing. - 1361-6641 .- 0268-1242. ; 37:3
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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)
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Transition to the quantum hall regime in InAs nanowire cross-junctions
- 2019
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Ingår i: Semiconductor Science and Technology. - : IOP Publishing. - 0268-1242 .- 1361-6641. ; 34
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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)
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III-V nanowire MOSFETs with novel self-limiting Λ-ridge spacers for RF applications
- 2020
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Ingår i: Semiconductor Science and Technology. - : IOP Publishing. - 0268-1242 .- 1361-6641. ; 35:6
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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)
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Low temperature atomic hydrogen annealing of InGaAs MOSFETs
- 2023
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Ingår i: Semiconductor Science and Technology. - : IOP Publishing. - 0268-1242 .- 1361-6641. ; 38:5
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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)
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Design optimization of InGaAsP-InGaAlAs 1.55 mu m strain-compensated MQW lasers for direct modulation applications
- 2004
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Ingår i: Semiconductor Science and Technology. - : IOP Publishing. - 0268-1242 .- 1361-6641. ; 19:5, s. 615-625
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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)
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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
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Ingår i: Semiconductor Science and Technology. - : IOP Publishing. - 0268-1242 .- 1361-6641. ; 23:7, s. 1-10
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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)
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Phonon transmission in III-V semiconductor superlattices and alloys
- 2005
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Ingår i: Semiconductor Science and Technology. - : IOP Publishing. - 0268-1242 .- 1361-6641. ; 20:5, s. 347-352
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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)
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Contactless Electroreflectance, Photoluminescence and Time-Resolved Photoluminescence of GaInNAs Quantum Wells Obtained by the MBE Method with N-irradiation
- 2011
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Ingår i: Semiconductor Science and Technology. - : IOP Publishing. - 1361-6641 .- 0268-1242. ; 26:4, s. 045012-
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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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