Improved Electrical Properties of AlGaN/GaN High-Electron-Mobility Transistors by In Situ Tailoring the SiNx Passivation Layer

In situ metal-organic chemical vapor deposition growth of SiNx passivation layers is reported on AlGaN/GaN high-electron-mobility transistors (HEMTs) without surface damage. A higher SiNx growth rate, when produced by higher SiH4 reactant gas flow, enables faster lateral coverage and coalescence of the initial SiNx islands, thereby suppressing SiH4-induced III-nitride etching. The effect of in situ SiNx passivation on the structural properties of AlGaN/GaN HEMTs has been evaluated using high-resolution X-ray diffraction. Electrical properties of the passivated HEMTs were evaluated by clover-leaf van der Pauw Hall measurements. The key findings include (a) a correlation of constituent gas chemistry with SiNx stoichiometry, (b) the degree of suppression of strain relaxation in the barrier layer that can be optimized through the SiNx stoichiometry, and (c) optimum strain relaxation by tailoring the SiNx passivation layer stoichiometry that can result in near-ideal AlGaN/AlN/GaN interfaces. The latter is expected to reduce the carrier scatterings and improve electron mobility. Under optimized conditions, low sheet resistance and high electron mobility are obtained. At 10 K, a sheet resistance of 33 Omega/sq and a mobility of 16,500 cm(2)/V-s are achieved. At 300 K, the sheet resistance is 336 Omega/sq and mobility is 2020 cm(2)/V-s with a sheet charge density of 0.78 x 10(13) cm(-2).

Automated summary

The study demonstrates the in situ metal-organic chemical vapor deposition growth of SiNx passivation layers on AlGaN/GaN HEMTs, showing that higher SiNx growth rates can lead to faster lateral coverage and coalescence of initial SiNx islands, thereby suppressing SiH4-induced III-nitride etching. The SiNx stoichiometry can be optimized to reduce strain relaxation in the barrier layer and achieve near-ideal AlGaN/AlN/GaN interfaces, ultimately improving electron mobility and electrical properties of the HEMTs under optimized conditions.