Efficient Surface Passivation Using Two-Step Ammonium Sulfide Based Treatment For Gan/Algan Heterojunction Phototransistors

The effects of different ammonium sulfide [(NH4)(2)S-x]-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)(2)S-x 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 1.3x10(5) was obtained at 5V bias in the HPTs using the two-step treatment.