Influence of Substrate on the RF-related electric characteristics for W-Band AlGaN/GaN HEMTs

Using the same device processing GaN-based High Electron Mobility Transistors (HEMTs) with 90nm T-shaped gate are fabricated on the AlGaN/GaN heterostuctures epitaxially grown on sapphire and SiC substrate, respectively. The DC outputs/transfer and RF characteristics are measured and compared. It's found that the sheet carrier density and electron mobility of AlGaN/GaN heterostucture on SiC substrate are both much higher than the ones on sapphire substrate, indicating better crystal quality for the one on SiC substrate. Moreover, attributed to the better crystal quality and higher thermal conductivity of SiC, the maximum peak transconductance, current gain cut-off frequency (f(T)) and maximum oscillation frequency (f(max)) of AlGaN/GaN HEMT on SiC substrate are much larger than the ones of AlGaN/GaN HEMT on sapphire substrate, respectively.