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Time-of-flight measurements using a picosecond pulsed laser are made for a p-AlGaAs/GaAs/AlGaAs double heterostructure to successfully obtain the velocity-electric field relationship for photoexcited electrons at room temperature. In the high electric field region, velocity enhancements are observed, which have never been reported until now. Possible mechanisms, which attribute to the velocity enhancement, are also discussed. [ABSTRACT FROM AUTHOR]

GaN-based surface acoustic wave (SAW) filters with Ni/n+-GaN-based interdigital transducers (IDTs) were investigated. Their RF characteristics revealed a main peak and neighbouring sidelobes, which indicates that SAWs are successfully excited in the filters. The results mean that conductive GaN layers can be used for IDTs, substituting for metal layers [ABSTRACT FROM AUTHOR]

The effects of annealing process on the electrical properties of n+-Si/n-SiC and p+-Si/n-SiC junctions fabricated by using surface-activated bonding are investigated. It is found by measuring the current-voltage (I-V) characteristics of n+-Si/n-SiC junctions that the reverse-bias current and the ideality factor decreased to 2.0×10-5mA/cm² and 1.10, respectively, after the junctions annealing at 700 °C. The flat band voltages of n+-Si/n-SiC and p+-Si/n-SiC junctions obtained from capacitance-voltage (C-V) measurements decreased with increasing annealing temperature. Furthermore, their flat band voltages are very close to each other irrespective of the annealing temperature change, which suggests that the Fermi level is still pinned at the bonding interface even for the junctions annealing at high temperature and the interface state density causing Fermi level pinning varies with the junctions annealing. The reverse characteristics of n+ -Si/n-SiC junctions are in good agreement with the calculations based on thermionic field emission. In addition, the calculated donor concentration of 4H-SiC epi-layers and flat band voltage is consistent with the values obtained from C-V measurements. [ABSTRACT FROM AUTHOR]

Electrical properties of n-Si/n-Si, p-Si/n-Si, and p--Si/n+-Si junctions fabricated by using surface-activated-bonding are investigated. The transmission electron microscopy/energy dispersive X-ray spectroscopy of the n-Si/n-Si interfaces reveals no evidence of oxide layers at the interfaces. From the current-voltage (I-V) and the capacitance-voltage (C-V) characteristics of the p-Si/n-Si and p--Si/n+-Si junctions, it is found that the interface states, likely to have formed due to the surface activation process using Ar plasma, have a more marked impact on the electrical properties of the p-Si/n-Si junctions. An analysis of the temperature dependence of the I-V characteristics indicates that the properties of carrier transport across the bonding interfaces for reverse-bias voltages in the p-Si/n-Si and p--Si/n+-Si junctions can be explained using the trap-assisted-tunneling and Frenkel-Poole models, respectively. [ABSTRACT FROM AUTHOR]

The valence band offsets, ΔEV, of In0.17Al0.83N/GaN, In0.25Al0.75N/GaN, and In0.30Al0.70N/GaN heterostructures grown by metal-organic vapor phase epitaxy were evaluated by using x-ray photoelectron spectroscopy (XPS). The dependence of the energy position and the full width at half maximum of the Al 2p spectrum on the exit angle indicated that there was sharp band bending caused by the polarization-induced electric field combined with surface Fermi-level pinning in each ultrathin InAlN layer. The ΔEV values evaluated without taking into account band bending indicated large discrepancies from the theoretical estimates for all samples. Erroneous results due to band bending were corrected by applying numerical calculations, which led to acceptable results. The evaluated ΔEV values were 0.2±0.2 eV for In0.17Al0.83N/GaN, 0.1±0.2 eV for In0.25Al0.75N/GaN, and 0.0±0.2 eV for In0.30Al0.70N/GaN. Despite the large decrease of around 1.0 eV in the band gap of InAlN layers according to the increase in the In molar fraction, the decrease in ΔEV was as small as 0.2 eV. Therefore, the change in band-gap discontinuity was mainly distributed to that in conduction band offset. [ABSTRACT FROM AUTHOR]

We have investigated the structural features of a strain-compensated InGaP/InGaP multiple-quantum-well (MQW) structure on GaAs (100) substrate with a band-gap energy of around 1.7 eV for solar cell applications. In transmission electron microscopy images, noticeable thickness modulation was observed in the barrier layers for a sample grown at the substrate temperature of 530 °C. Meanwhile, the X-ray diffraction patterns indicated that strain relaxation predominantly occurred in the well layers. Decreasing the substrate temperature from 530 to 510 °C was effective in suppressing both the thickness modulation and strain relaxation. Additionally, increasing the growth rate of the well layer further suppressed the thickness modulation. In room-temperature photoluminescence (PL) emission spectra, the sample grown at 510 °C showed approximately 50 times higher PL peak intensity than the one grown at 530 °C. [ABSTRACT FROM AUTHOR]

This paper reports phase separation in thick (~1 μm) MOVPE In x Ga 1− x N ( x =0.2–0.4) films grown by MOVPE at 570–750 °C on AlN/Si(111), α-Al 2 O 3 (0001) and GaN/α-Al 2 O 3 (0001) substrates. Phase separation occurs when InGaN thickness exceeds a critical value. Critical thickness for phase separation is markedly increased with decreasing growth temperature. It is around 0.2 μm for a film grown at 750 °C, while it is more than 1 μm for that grown at 570 °C. No substrate dependencies are found in critical thickness. The cross-sectional SEM views of phase-separated films grown at 650 °C show that phase separation is initiated at parts far more than 0.2 μm from the substrate and extended to the area near the substrate. SIMS analysis shows a possibility that phase separation is initiated at a part with relatively large In/Ga ratio fluctuations in InGaN films. [ABSTRACT FROM AUTHOR]

This paper reports the post-growth annealing effects of low-temperature grown Mg-doped InGaN. By using MOVPE, 1 μm-thick Mg-doped In xGa1- xN ( x ~ 0.36) films are grown at 570 °C. In order to activate the Mg acceptors, grown samples are treated by the conventional furnace annealing (FA) or the rapid thermal annealing (RTA). In the case of the FA at 650 °C for 20 min, the InGaN film is phase-separated. On the other hand, the RTA at a temperature higher than 700 °C enables us to get p-type samples. By using the RTA at 850 for 20 s, p-type samples with a hole concentration 1018-1019 cm−3 are successfully obtained without phase separation. [ABSTRACT FROM AUTHOR]

Electrical properties of p--Si/n--SiC, p-Si/n--SiC, p+Si/n--SiC, and n+-Si/n--SiC heterojunctions fabricated by using surface-activated bonding are investigated. Their flat-band voltages obtained from capacitance-voltage (C-V) measurements are found to be ~0.92eV, which suggests that the Fermi level should be pinned at the bonding interface. An analysis by using the charge neutral level model reveals that the C-V characteristics are sensitive to the density of interface states. The measured C-V characteristics of p+Si/n--SiC and n+-Si/n--SiC junctions are in quantitative agreement with modeled ones obtained for the interface states density and the conduction-band discontinuity of 2.3×1013cm-2eV-1 and 0.3eV, respectively. [ABSTRACT FROM AUTHOR]

The effects of thermal annealing process on the interface in p+-Si/n-SiC heterojunctions fabricated by using surface-activated bonding are investigated. It is found by measuring their current-voltage (I-V) characteristics that the reverse-bias current and the ideality factor decreased to 2.98×10-6 mA/cm² and 1.03, respectively, by annealing the junctions at 1000°C. Observation by using transmission electron microscopy indicates that an amorphous layer with a thickness of ~6 nm is formed at the unannealed interface, which vanishes after annealing at 1000 C. No structural defects at the interface are observed even after annealing at such a high temperature. [ABSTRACT FROM AUTHOR]

This paper reports the MOVPE growth of In xGa1- xN ( x ∼0.5) on Si(111) with a pn junction on the surface. By optimizing growth temperature and TMI/(TMI+TEG) molar ratio, InGaN films with In content up to 0.5 are successfully grown without phase separation and metallic In incorporation. No significant differences in tilt fluctuation in grown InGaN are found among three different substrates; GaN/α-Al2O3(0001) template, p-Si(111) and n-Si(111) with a p-type layer on the surface. The tilt fluctuation increases with increasing In content in InGaN and shows the maximum at around In composition 0.5. The n-InGaN/p-Si structures show good ohmic characteristics and the resistance obtained from the slope of I-V curves is markedly reduced with increasing In content in InGaN. The Si pn junction beneath the In0.42Ga0.58N layer behaves well as a solar cell with an InGaN filter. For both n-InGaN/p-Si and n-InGaN/pn-Si structures, the presence of an AlN interlayer between the epilayer and the substrate does not have a significant contribution to the series resistance. (© 2013 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [ABSTRACT FROM AUTHOR]

The electrical properties of pn junctions, with various semiconductor materials with different doping concentrations fabricated by using surface‐activated‐bonding (SAB), were investigated by measuring their current‐voltage (I‐V) characteristics. The I‐V characteristics of p+‐GaAs/n++‐Si, p+‐GaAs/n+‐Si, p+‐Si/n+‐Si, p++‐Si/n+‐InGaP, and p+‐Si/n+‐InGaP junctions showed ohmic‐like properties. The interface resistance and the resultant electrical loss decreased with increasing impurity concentration at the interface. These results demonstrate the significance of SAB for fabricating tandem solar cells. [ABSTRACT FROM AUTHOR]

The barrier structure in lattice-matched InAlN/GaN heterostructures with AlGaN-based spacer layers grown by metal organic vapor phase epitaxy was studied by the capacitance-voltage (C-V) method. To investigate the characteristics under positive bias, an Al2O3 overlayer was added. The C-V characteristic of a sample with an Al0.38Ga0.62N (5 nm)/AlN (0.75 nm) double spacer layer exhibited an anomalous saturation at a value far below the insulator capacitance under positive bias, which indicated electron accumulation at the InAlN/AlGaN interface. The C-V characteristic of an alternative sample with a single Al0.44Ga0.56N (1.5 nm) spacer layer did not exhibit the anomalous saturation. [ABSTRACT FROM AUTHOR]

A maximised induced current photodiode with a novel composite field structure that suppresses the space charge effect achieved a 2 V bias operation for an average photocurrent of 4 mA with a 3 dB bandwidth of over 35 GHz. [ABSTRACT FROM AUTHOR]

The valence-band offset of a lattice-matched In0.17Al0.83N/GaN heterostructure grown by metal-organic vapor phase epitaxy (MOVPE) was investigated by x-ray photoelectron spectroscopy (XPS). Atomic force microscopy and angle-resolved XPS indicated that a thin In0.17Al0.83N (2.5 nm) layer was successfully grown by MOVPE on GaN. The XPS result showed that the valence band offset was 0.2±0.3 eV. This result indicates that the conduction-band offset at the In0.17Al0.83N/GaN interface is large, i.e., 0.9 to 1.0 eV, and occupies a large part of the entire band discontinuity. [ABSTRACT FROM AUTHOR]

The first demonstration of dual-gate AlGaN/GaN high-electronmobility transistors (HEMTs) for high-power mixers is presented. The 0.7×300 mm gate device achieved the maximum output power of 19.6 dBm and upconversion gain of 11 dB at 2 GHz and 13 dBm and 5 dB at 5 GHz. [ABSTRACT FROM AUTHOR]