Comparing buffer leakage in PolarMOSH on SiC and free-standing GaN substrates

GaN MOSHEMT or MOSFET on top of conducting (drift layer and drain electrode) layers is a building block for vertical GaN VDMOS power transistors. GaN MOSHEMTs incorporating a polarization-doped p-AlGaN layer as the back barrier on top of conducting layers is named as PolarMOSH. In this work, we present a comparative study of PolarMOSH fabricated on SiC and free-standing GaN substrates. PolarMOSH wafers epitaxially grown on SiC substrates are found to suffer from large leakage currents, with or without Mg doping in the back barrier. Much lower leakage currents are achieved when PolarMOSH wafers are grown on free-standing GaN substrates. The large reduction of buffer leakage current is attributed to the much reduced dislocation density brought by free-standing GaN substrates. The PolarMOSH fabricated on free-standing GaN substrates has a current On/Off ratio > 10 ¹⁰ thanks to the low leakage current.