Comparative analysis of nano-scale structural and electrical properties in AlGaN/GaN high electron mobility transistors on sic and sapphire substrates

A comparison of AlGaN/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 m, exhibiting a unity-gain cut-off frequency fT = 296 GHz, a maximum frequency of oscillation fMAX = 632 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 halfmaximum (FWHM) of 120 s and 919 s were measured for the SiC and sapphire-based AlGaN/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.