In this study, the metal–organic-vapor-phase-epitaxial growth behavior and electrical properties of AlGaN/GaN structures prepared by the growth of an AlGaN layer on a reactive-ion-etched (RIE) GaN surface without regrown GaN layers were investigated. The annealing of RIE-GaN surfaces in NH3 + H2 atmosphere, employed immediately before AlGaN growth, was a key process in obtaining a clean GaN surface for AlGaN growth, that is, in obtaining an electron mobility as high as 1350 cm2 V−1 s−1 in a fabricated AlGaN/RIE-GaN structure. High-electron-mobility transistors (HEMTs) were successfully fabricated with AlGaN/RIE-GaN wafers. With decreasing density of dotlike defects observed on the surfaces of AlGaN/RIE-GaN wafers, both two-dimensional electron gas properties of AlGaN/RIE-GaN structures and DC characteristics of HEMTs were markedly improved. Since dotlike defect density was markedly dependent on RIE lot, rather than on growth lot, surface contaminations of GaN during RIE were believed to be responsible for the formation of dotlike defects and, therefore, for the inferior electrical properties.

In this paper, we report the impact of the HCl treatment of reactive-ion-etching-treated GaN (RIE-treated GaN) surfaces in fabricating AlGaN/GaN structures by regrowing an AlGaN layer directly on the RIE-treated GaN surfaces. By dipping RIE-treated GaN surfaces into a hot HCl solution, a 10-30-nm-thick surface layer, which corresponded to the damaged layer, was etched off. After the annealing of the HCl-treated GaN in NH 3 + H 2 atmosphere, a 30-nm-thick Al 30 Ga 70 N layer was grown on it. The HCl treatment resulted in a decrease in dotlike defect density observed on the AlGaN/GaN surfaces and a marked improvement of electrical data of AlGaN/GaN structures. A clear dependence of electron mobility on sheet carrier concentration was observed, and the highest electron mobility obtained was increased to >1500 cm 2 V %1 s %1 . High-electron-mobility transistors (HEMTs) with excellent performances were successfully fabricated by employing the HCl treatment and metal-insulator-semiconductor (MIS) gate structures.

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In this work, we investigated the effect of shape irregularities of drain electrode on the breakdown voltage of AlGaN/GaN HEMTs. We found that some random devices having rough metal edge definition tend to have lower breakdown voltages. In addition, these devices showed localized high intensity luminescence observed under near pinch-off condition. This is likely due to electric field concentration near irregularities such as sharp edges and corners that were randomly formed at some point during device fabrication. On the other hand, devices that have smooth metal edge definition exhibited uniform faint electroluminescence along the drain electrode edge. We also fabricated AlGaN/GaN HEMTs with intentionally-designed patterns such as sawtooth profiles along the drain edge. Intense luminescence localized at the apexes of sawtooth pattern together with the relatively lower breakdown voltages of these devices confirmed the importance of maintaining smooth drain electrode edge definition for achieving high breakdown performance in AlGaN/GaN HEMTs.