Comparative Analysis of Nano-Scale Structural and Electrical Properties in AlGaN/GaN High Electron Mobility Transistors on SiC and Sapphire Substrates

Abstract

A comparison of AIGaN/GaN HEMTs fabricated on both 4-in SiC and sapphire substrates was performed. Due to the high crystalline quality with one order lower dislocation density of GaN on a SiC substrate, a better two-dimensional electron gas (2DEG) mobility with high values of drain current density (780 mA/mm) and a better extrinsic transconductance (240 mS/mm) were observed. We demonstrate GaN-on-SiC HEMTs with a periphery gate width of 200 microm, exhibiting a unity-gain cut-off frequency (f(T)) = 29.6 GHz, a maximum frequency of oscillation (f(MAX)) = 63.2 GHz, and an output power density of 6.4 W/mm with a 55% power added efficiency (PAE) at 10 GHz. A surface roughness of 0.828 nm and 1.025 nm and an X-ray diffraction (XRD) GaN (0002) full-width at half-maximum (FWHM) of 120 s and 919 s were measured for the SiC and sapphire-based AIGaN/GaN HEMTs, respectively. The SiC substrate has been shown to be an optimal solution for fabricating HEMTs for X-band high-power applications, which require excellent performances.