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The frequency dispersion in admittance measurements in AlGaN/GaN high-electron-mobility transistors, which is typically interpreted to result from an interface trap density Dit, is also known to be caused by effects other than Dit. To study the origin of two peaks of conductance component "Gp/ω" as a function of frequency in lateral gated diodes using AlGaN/GaN structures on Si wafers grown by metal–organic chemical vapor deposition, we measured capacitance C and conductance Gp/ω–voltage V as a function of angular frequency ω (C–ω–V and Gp/ω–ω–V, respectively) of long-gate field-effect transistors with a varied gate length. We also simulated the C–ω–V and Gp/ω–ω–V curves using an equivalent circuit that consisted of actually measured component parameters without Dit. We confirmed that the Gp/ω–ω curves show two peaks caused by the two-dimensional electron gas channel resistance and the gate current leakage and quantitatively determined the two ωpeak positions and intensities. We also discussed the effect of acceptor concentration in the GaN channel-layer on lowering of ωpeak at weak inversion. [ABSTRACT FROM AUTHOR]

Contactless photo-electrochemical (CL-PEC) etching was used to fabricate recessed-gate AlGaN/GaN high-electron-mobility transistors (HEMTs). Self-termination of etching was observed during CL-PEC etching on an AlGaN barrier layer whose residual thickness had a uniform value of 6 nm overall on the same chip. After tetramethylammonium hydroxide post-treatment, the root-mean-square roughness of the etched surface was around 0.4 nm, which had smoothness comparable to that of the unetched surface. Recessed-Schottky HEMTs showed a positive shift in Vth, the suppression of drain leakage currents, and an improvement in the subthreshold-slope value as compared with planar-gate HEMTs. By applying a metal–insulator–semiconductor (MIS)-gate structure, the gate and drain leakage currents were significantly reduced, leading to an increased input dynamic range. Furthermore, the standard deviations (σ) of the Vth of CL-PEC-etched recessed-Schottky HEMTs and recessed-MIS HEMTs were very small, 5.5 and 16.7 mV, respectively. These results showed that the CL-PEC etching process is promising for the fabrication of recessed-gate AlGaN/GaN HEMTs having excellent uniformity for normally-off device operations. [ABSTRACT FROM AUTHOR]

GaN films were grown on hydride vapor phase epitaxy (HVPE) AlN/SiC templates by metalorganic CVD (MOCVD) without annealing the reactor to eliminate the memory effect. A step-terrace structure and smooth surface were obtained for the GaN film, which had a thickness of ∼200 nm. Subsequently, AlGaN/GaN heterostructures for application in high electron mobility transistors (HEMTs) with thin GaN channels were fabricated without a C- or Fe-doped GaN buffer layer. The interface quality at the AlGaN/GaN heterostructure was good enough for a two-dimensional electron gas to exhibit Shubnikov–de Haas oscillation in a magnetic field at 1.8 K. The GaN HEMTs with a thin channel on the AlN/SiC templates exhibited both a pinch-off character and conventional properties. In view of both the shorter epitaxial growth time and higher thermal conduction, HVPE AlN/SiC templates are applicable to the fabrication of GaN HEMTs by MOCVD. [ABSTRACT FROM AUTHOR]

We applied scanning internal photoemission microscopy (SIPM) to clarify the electrical characteristics on the electrode periphery of Ni/n-GaN Schottky contacts. Two types of Schottky contacts with different electrode formation methods were prepared. For the samples in which the Ni contacts were evaporated through a metal shadow mask, in the scanning electron microscopes (SEM) observation, the electrode edges were tailed and the tail was divided into two contrasts, a bright region with a width of 15.5 ÎĽ m from the electrode edge followed by a dark region with a width of 32 ÎĽ m. The SIPM signal was obtained from the first 16 ÎĽ m tailing region, and corresponded with the SEM images. For the photolithography sample, a sharp edge less than 1 ÎĽ m wide was obtained and no increase in SIPM signal was detected on the edge. These results indicate SIPM is able to characterize the electrical properties of electrode periphery in conjunction with the structural characteristics. [ABSTRACT FROM AUTHOR]

Precise control of the Al content x in AlxGa1−xN/GaN epitaxial structures is a potentially important technical parameter for power/RF devices. We fabricated five 2 inch diameter high-electron-mobility transistor wafers by metal organic vapor phase epitaxy on free-standing (0001) Ga-face GaN as a substrate. The Al content x of the AlGaN layer was ∼0.2, and the substrate off-angle varied in the range 0.2°–1.0°. The Al content was measured as a function of the substrate off-angle using room-temperature optical reflectance. The values of the AlGaN bandgap energy derived from reflectance spectra were calibrated against the Al content determined by X-ray diffraction beforehand. The Al content in the AlGaN layers was found to be unaffected by the substrate off-angle, and a downward bowing was observed in the relation of the bandgap energy and the Al content, with a bowing parameter of 0.57 eV and a stress-corrected bowing parameter of 0.22 eV. [ABSTRACT FROM AUTHOR]

We have studied the impact of atomic-layer-deposition (ALD) temperature on the HfO2/InGaAs metal-oxide-semiconductor (MOS) interface with a comparison to the Al2O3/InGaAs interface. It is found that the interface properties such as the C-V characteristics and the interface trap density (Dit) and the interface structure of HfO2/InGaAs have strong dependence on the ALD temperature, while the Al2O3/InGaAs interfaces hardly depend on it. As a result, we have achieved the HfO2/InGaAs interfaces with low Dit comparable to that in the Al2O3/InGaAs interface by lowering the ALD temperature down to 200 °C or less. Also, we have found that As2O3 and Ga2O3 formed at the interface during ALD increase with a decrease in the ALD temperature. Combined with the ALD temperature dependence of the electrical characteristics, the better C-V characteristics and the lower Dit obtained at the lower ALD temperature can be explained by the As2O3 and Ga2O3 passivation of the HfO2/InGaAs interfaces, which is consistent with a reported theoretical result on the effective passivation of III-V MOS interfaces by trivalent oxides. [ABSTRACT FROM AUTHOR]

The formation and reduction of pyramidal hillocks on InGaAs/InP(111)A grown by metal organic chemical vapor deposition were investigated. The triangular pyramidal hillocks were observed on the InGaAs surface on on-axis InP (111)A grown at 650 °C. The hillocks disappeared when the vicinal InP (111)A substrates with an off-axis angle >0.4° were applied. The step and terrace surface of InGaAs on 4.0°-off InP (111)A were obtained. InGaAs on on-axis InP (111)A exhibited a hole concentration, mobility of Hall effect measurement, and full width at half-maximum of X-ray diffraction as 1.0 × 1017 cm−3, 56 cm2/V s, and 140 arcsec, respectively. In contrast, InGaAs on 2.0°-off InP (111)A exhibited 2.3-1017 cm−3, 142 cm2/V s, and 63 arcsec, respectively. We suggest that off-axis substrates enable a reduction of stacking faults, which leads to considerable improvement of crystallinity. [ABSTRACT FROM AUTHOR]