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

摘要

Using Si substrates is the sole route towards Ill-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 Si_3N_4 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 correlatedrnwith the appearance of deep defect-related peaks in photolu-minescence spectra (6 K), and completely eliminated by tuning 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).