In-situ passivation combined with GaN buffer optimization for extremely low current dispersion and low gate leakage in Si_3N_4/AIGaN/GaN HEMT devices on Si (111)

摘要

Using Si substrates is the sole route towards III-nitrides process on large wafer diameter: flat, crack-free HEMT epiwafers have been grown by MOVPE with diameter up to 150 mm, exhibiting very low sheet resistivity (260 Ω/sq.) and high uniformity (<2%), thanks to in-situ Si3N4 capping (<5 nm). We show here that simultaneous optimization of GaN growth and of device passivation results in a drastic reduction of buffer and surface traps. This has impact onto device performance, assessed by pulse IV measurements. Drain lag is correlated with the appearance of deep defect-related peaks in photolu-minescence spectra (6 K), and completely eliminated by tun-ing growth temperature. Gate formation (Ni/Au) onto MOVPE-grown Si_3N_4, followed by cleaning and PECVD ex-situ passivation, leads to very low gate current dispersion, associated to gate leakage current in μA/mm range. Both dc and pulsed characteristics show a current density in the order of 0.8-1 A/mm, whereas maximal transconductance is 250 mS/mm (L_g= 1 μm).