Effects of surface morphology and C concentration in C-doped GaN buffer on breakdown voltage of AlGaN/GaN HEMTs on free-standing GaN substrate

We report on the validity of using a C-doped GaN buffer to achieve high-breakdown-voltage AlGaN/GaN high-electron mobility transistors (HEMTs) on conductive free-standing GaN substrates. We use trimethygallium to dope C into the buffer. We show that breakdown voltage depends not only on the C concentration of the buffer but also on the surface morphology of the HEMT structure. We demonstrate off-state breakdown voltage of over 2 kV by controlling the C concentration of the buffer, thickness of the buffer, and the surface morphology. (C) 2016 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim [GRAPHICS] .