Improved Electrical Properties of AlGaN/GaN High-Electron-Mobility Transistors by In Situ Tailoring the SiN...

In situ metal-organic chemical vapor deposition growth of SiN passivation layers is reported on AlGaN/GaN high-electron-mobility transistors (HEMTs) without surface damage. A higher SiN growth rate, when produced by higher SiH₄ reactant gas flow, enables faster lateral coverage and coalescence of the initial SiN islands, thereby suppressing SiH₄-induced III-nitride etching. The effect of in situ SiN 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 SiN stoichiometry, (b) the degree of suppression of strain relaxation in the barrier layer that can be optimized through the SiN stoichiometry, and (c) optimum strain relaxation by tailoring the SiN 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 Ω/sq and a mobility of 16,500 cm²/V-s are achieved. At 300 K, the sheet resistance is 336 Ω/sq and mobility is 2020 cm²/V-s with a sheet charge density of 0.78 × 10¹³ cm^-2.