AlGaN/GaN field effect transistors with C-doped GaN buffer layer as an electrical isolation template grown by molecular beam epitaxy

摘要

The effectiveness of Ammonia Molecular Beam Epitaxy (MBE) grown carbon-doped GaN buffer layer as an electrical isolation template was investigated. AlGaN/GaN field effect transistor structures with a product of sheet electron density and mobility (n_sμ), linearly increasing from 1.5 x 10~(16) V~(-1) s~(-1) to 2 x 10~(16) V~(-1) s~(-1) with n_s, were grown on 2-μm-thick carbon-doped GaN buffer layer over sapphire substrates. The measurement of the gate-to-source voltage (V_(GS)) dependent drain current (I_D) demonstrated excellent dc pinch-off characteristics as revealed by an on-to-off ratio of 10~7 for a drain-source voltage (V_(DS)) up to 15 V. The gate leakage current was less than 1 μA/mm at the subthreshold voltage (V_(th) = - 5.2V). Inter-devices isolation current (I_(ISO)) measurements demonstrated I_(ISO) values in the low pico-amperes ranges indicating a complete suppression of the parallel conduction paths. Small-signal rf measurements demonstrated a f_(max)/f_t ratio as high as 2.9 attesting the absence of charge coupling effects.