Efficient surface passivation using two-step ammonium sulfide based treatment for GaN/AlGaN heterojunction phototransistors

The effects of different ammonium sulfide [(NH4)2Sx]-based treatments on the surface passivation of dry-etched and thermally recovered GaN epilayer have been investigated. A two-step treatment using HCl followed by the mixture of (NH4)2Sx and isopropyl alcohol demonstrated a more effective removal of intrinsic oxide layer and formation of sulfide passivation. The compensating centers on both the p- and n+-type GaN surfaces were significantly reduced. The fabricated base-floating GaN/Al0.1GaN heterojunction phototransistors (HPTs) with the surface passivation showed improved I–V and enhanced optical gain due to the effective suppression of surface recombination current. A maximum gain of 1.3 × 105 was obtained at 5 V bias in the HPTs using the two-step treatment.