We investigated the effects of the substrate off-angle on the m-plane GaN Schottky diodes. GaN epitaxial layers were grown by metal-organic chemical vapor deposition on m-plane GaN substrates having an off-angle of 0.1, 1.1, 1.7, or 5.1°toward ½0001. The surface of the GaN epitaxial layers on the 0.1°-off substrate consisted of pyramidal hillocks and contained oxygen (>10 17 cm %3 ) and carbon (>10 16 cm %3 ) impurities. The residual carbon and oxygen impurities decreased to <10 16 cm %3 when the off-angle of the m-plane GaN substrate was increased. The leakage current of the 0.1°-off m-plane GaN Schottky diodes originated from the +c facet of the pyramidal hillocks. The leakage current was efficiently suppressed through the use of an off-angle that was observed to be greater than 1.1°. The off-angle of the m-plane GaN substrate is critical in obtaining high-performance Schottky diodes.

In this study, we investigated the deep-level traps in Si-doped GaN epitaxial layers by metal-organic chemical vapor deposition on c-oriented and m-oriented free-standing GaN substrates. The c-oriented and m-oriented epitaxial layers, grown at a temperature of 1000 °C and V/III ratio of 1000, contained carbon atomic concentrations of 1.7×1016 and 4.0×1015 cm–3, respectively. A hole trap was observed at about 0.89 eV above the valence band maximum by minority carrier transient spectroscopy. The trap concentrations in the c-oriented and m-oriented GaN epitaxial layers were consistent with the carbon atomic concentrations from secondary ion mass spectroscopy and the yellow luminescence intensity at 2.21 eV from photoluminescence. The trap concentrations in the m-oriented GaN epitaxial layers were lower than those in the c-oriented GaN. Two electron traps, 0.24 and 0.61 eV below the conduction band (EC) minimum, were observed in the c-oriented GaN epitaxial layer. In contrast, the m-oriented GaN epitaxial layer was free from the electron trap at EC – 0.24 eV, and the trap concentration at EC – 0.61 eV in the m-oriented GaN epitaxial layer was lower than that in the c-oriented GaN epitaxial layer. The m-oriented GaN epitaxial layer exhibited fewer hole and electron traps compared to the c-oriented GaN epitaxial layers.

The electrical properties of m-plane Ni/n-GaN Schottky diodes grown via metalorganic chemical vapor deposition were investigated. Under growth at 1,120 °C with a V/III ratio of 1,000 (growth rate of 100 nm/min), the residual Si, O, and C impurity concentrations in the m-plane GaN layer were below the secondary-ion mass spectroscopy detection limit. The surface of the Si-doped n-GaN epitaxial layer on the 5°-off m-plane GaN substrate consisted of steps and terraces. A linear correlation between the carrier concentration and the Si atomic concentration was clearly observed from 1 × 1017 to 5 × 1015 cm−3. The reverse current–voltage curves were fitted using the thermionic field-emission model at the measured carrier concentration and qϕB. The leakage current of the diodes under a reverse bias was effectively suppressed at a low carrier concentration of 4.6 × 1015 cm−3.

The electrical properties of un-doped and lightly Si-doped GaN grown on cand m-plane GaN substrates by metal organic chemical vapor deposition are investigated. The step-flow growth modes are realized for c-and m-plane GaN epitaxial layer. The carbon contamination in the c-plane GaN and mplane GaN, grown at 1120 C and V/III ¼ 1000, are found to be 1.4 Â 10 16 cm À3 and 5.0 Â 10 15 cm À3 , respectively. The m-plane GaN follows a linear correlation between the carrier concentration and the Si atomic concentration. The Ni/n-GaN (Si; 1 Â 10 16 cm À3 ) Schottky vertical diodes on the c-and m-plane GaN substrates reveal that the reverse current-voltage (I-V) curves are fitted by using the thermionic field emission model under the measured carrier concentration and the Schottky barrier height. The leakage current of the m-plane GaN is three orders of magnitude larger than the c-plane GaN, mostly due to the difference in the Schottky barrier height. status solidi physica a Schottky Diodes www.pss-a.com

The numerical simulation of the AlGaN/GaN HEMT with GIT structure is performed while varying the radiative recombination lifetime of electron and hole, and the conductivity modulation in the channel by the hole injection from the gate electrode is investigated. When the radiative recombination lifetime is long, two peaks in the transconductance curve, gm vs. VG is found, and the hole injection from the gate electrode is enhanced. The accumulation of hole is found in the GaN layer under the channel around the source electrode, and the conductivity modulation is significant at the source‐gate region and at the drain side of the gate electrode. (© 2012 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)