Comparative study of drain-current collapse in AlGaN/GaN high-electron-mobility transistors on sapphire and semi-insulating SiC

The drain-current collapse at high drain voltage has been studied in AlGaN/GaN high-electron-mobility transistors (HEMTs) on both semi-insulating (SI)–SiC and sapphire substrates using small frequency (120 Hz) sinusoidal wave superimposed dc $I_{\mathrm{DS}}{\mathrm{–V}}_{\mathrm{DS}}$ characteristics. Low drain-current collapses were observed in AlGaN/GaN HEMTs on SI–SiC substrate when compared with the HEMTs on sapphire substrates. Two and three thermally activated deep traps were observed on SiC-based and sapphire-based HEMTs, respectively. The existence of an additional deep trap $\text{(ΔE=0.61\hspace{0.17em}}\mathrm{eV})$ could be associated with the material defects/ dislocations responsible for the severe drain current collapse in sapphire-based HEMTs. The white-light illuminated $I_{\mathrm{DS}}{\mathrm{–V}}_{\mathrm{DS}}$ characteristics support the existence of more number of deep traps in the sapphire-based HEMTs.