Normally-off Al2O3/GaN MOSFET: Role of border traps on the device transport characteristics

Based on the self-terminating gate recess technique, two different processes featuring gate-recess-first (GF) and ohmic-contact-first (OF) were proposed for E-mode Al2O3/GaN MOSFETs. Increased maximum drain current (Idmax) ∼30% (420 vs 325 mA/mm), field-effect mobility (μFEmax) ∼67% (150 vs 90 cm2/Vs) and reduced on-state resistance (Ron) ∼42% (9.7 vs 16.8 Ω·mm) were observed in the devices fabricated by GF process. Such significant performance difference of GF- and OF-devices resulted from the presence of border traps at Al2O3/GaN interface with a time constant ∼7 × 10−6 s. Experimental results indicated that: (1) the near interface border traps in Al2O3 dielectric significantly affect device channel mobility; (2) a high temperature post-deposition annealing process could effective suppress generation of border traps.