Analysis of the back-barrier effect in AlGaN/GaN high electron mobility transistor on free-standing GaN substrates

The effect of AlGaN back-barrier on AlGaN/GaN high electron mobility transistors (HEMTs) using free-standing GaN wafer has been investigated in this work. With the introducing back-barrier structure, the leakage path underneath the buffer (native nitrogen-vacancies and GaO_x compounds of the HVPE-grown free-standing GaN surface) layer can be suppressed by lift-up the conduction band. As compared with AlGaN/GaN HEMTs on SiC wafer, AlGaN/GaN HEMTs on free-standing GaN wafer show enhanced drain current (700 mA/mm), improved transconductance (143 mS/mm), less current collapse (12%), higher current gain cut-off frequency (13 GHz), and maximum stable gain cut-off frequency (24 GHz), which is attributed to the higher epi quality layer on free-standing GaN wafer.