Epitaxially-grown GaN junction field effect transistors

Junction field effect transistors (JFET's) are fabricated on a GaN epitaxial structure grown by metal organic chemical raper deposition (MOCVD), The de and microwave characteristics of the device are presented. A junction breakdown voltage of 56 V is obtained corresponding to the theoretical limit of the breakdown field in GaN for the doping levels used, A maximum extrinsic transconductance (g(m)) of 48 mS/mm and a maximum source-drain current of 270 mA/mm are achieved on a 0.8 mu m gate JFET device at V-GS = 1 V and V-DS = 15 V. The intrinsic transconductance, calculated from the measured g(m) and the source series resistance, is 81 mS/mm, The f(T) and f(max) for these devices are 6 GHz and 12 GHz, respectively. These JFET's exhibit a significant current reduction after a high drain bias is applied, which is attributed to a partially depleted channel caused by trapped hot-electrons in the semi-insulating GaN buffer layer. A theoretical model describing the current collapse is presented, and an estimate for the length of the trapped electron region is given.