Effect of Thermal Cleaning Prior to p-GaN Gate Regrowth for Normally Off High-Electron-Mobility Transistors

This work studied the effect of thermal cleaning in metal-organic chemical vapor deposition (MOCVD) prior to p-GaN gate regrowth for normally off high-electron-mobility transistors. X-ray photoelectron spectroscopy, capacitance-voltage measurement, and atomic force microscopy were employed to identify the effects of thermal cleaning before p-GaN regrowth. It was found that the residual damage was hardly repaired at a relatively low thermal cleaning temperature, while GaN decomposition would occur at an excessively high temperature. Thermal cleaning at 850 °C for 2 min in MOCVD can effectively remove the surface contamination and alleviate the etch damage without causing any significant deterioration of the AlGaN barrier. In addition, the density of interface states ( D_it) in the p-GaN gate was reduced from 10¹²-10¹³ to 10¹¹-10¹² eV^-1·cm^-2, resulting in a low gate reverse leakage of 0.1 nA/mm @ V_DS-OFF = 180 V, a high I_on/ I_off ratio of 4 × 10¹⁰, and a relatively high threshold voltage of +1.7 V @ I_D = 10 μA/mm.