Optimization of selective-area regrown n-GaN via MOCVD for high-frequency HEMT

The selective-area regrowth (SAG) n-type GaN source/drain electrode has been widely used in high electron mobility transistors (HEMTs) for high-frequency applications. Previous studies focused only on device performances, but not on SAG n+-GaN in devices. This paper studies electron concentration and mobility of SAG n+-GaN on InAlN/GaN HEMTs via metal-organic chemical vapor deposition (MOCVD). It is revealed that electron mobility of SAG GaN is significantly affected by thickness. The decrease in mobility in a thin GaN may be attributed to regrowth interface defects. A gas flow model on the regrowth region is proposed to guide the regrowth of SAG GaN for improving the electron mobility. A high electron mobility of 138 cm2/V s with an electron concentration of 5.2 × 1019/cm3 is obtained from an 80-nm n+-GaN with the regrowth width of 10 μm. Due to the high doping level, the nonalloy metal-semiconductor contact resistance (Rm-GaN) is as low as 0.041 Ω mm. The interface resistance (Rint) between GaN and 2DEG is extracted using transfer length measurement (TLM) models and found to be 0.106 Ω mm. The on-resistance (Ron) is 0.753 Ω mm for InAlN/GaN HEMT with a source-drain metal spacing (Lsd metal) of 2 μm.