Epitaxially-grown GaN junction field effect transistors

Junction field effect transistors (JFET's) are fabricated on a GaN epitaxia l structure grown by metal organic chemical raper deposition (MOCVD), The d e and microwave characteristics of the device are presented. A junction bre akdown voltage of 56 V is obtained corresponding to the theoretical limit o f the breakdown field in GaN for the doping levels used, A maximum extrinsi c 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 th ese devices are 6 GHz and 12 GHz, respectively. These JFET's exhibit a sign ificant current reduction after a high drain bias is applied, which is attr ibuted to a partially depleted channel caused by trapped hot-electrons in t he semi-insulating GaN buffer layer. A theoretical model describing the cur rent collapse is presented, and an estimate for the length of the trapped e lectron region is given.