Simulation and electrical characterization of GaN/SiC and AlGaN/SiC heterodiodes

Heterojunctions on SiC is an area in rapid development, especially GaN/SiC and AlGaN/SiC heterojunctions. The heterojunction can improve the performance considerably for BJTs and FETs. In this work heterojunction diodes have been manufactured and characterized. The structure was a GaN or AlGaN n-type region on top of a 6H-SiC p-type substrate. Two different approaches of growing the n-type region were tested. The GaN was grown with the MBE technique using a polycrystalline GaN buffer, whereas the AlGaN was grown with CVD and an AlN buffer. The AlGaN had an aluminum mole fraction of around 0.1. Mesa structures were formed using Cl2 RIE of GaN/AlGaN, which showed good selectivity on 6H-SiC (about 1:6). A Ti metallization with subsequent RTA was used as contact to GaN and AlGaN, and the contact to 6H-SiC was liquid InGa. Both I–V and C–V measurements were performed on the heterojunction diode. The ideality factor of the diodes, doping concentration of the SiC, and the band alignment of the heterojunction were extracted.