Formation of low resistance Pt ohmic contacts to p-type GaN using two-step surface treatment

Abstract

Two-step surface treatment is introduced to obtain low resistance Pt contacts to p-type GaN. The first step is performed after the mesa etching process using buffered oxide etch (BOE) and ammonium sulfide $\mathrm{[(}{\mathrm{NH}}_{\mathrm{4}}{\mathrm{)}}_{\mathrm{2}}{\mathrm{S}}_x\mathrm{].}$ This is followed by the second step using BOE. The Pt contact, that was simply BOE treated, yields ${\text{2.1(±0.9)×10}}^{\text{−2}}$ ${\mathrm{\Omega cm}}^{\mathrm{2}}.$ However, the contact which was treated sequentially using ultrasonically boiled BOE (10 min) and boiled $({\mathrm{NH}}_{\mathrm{4}}{\mathrm{)}}_{\mathrm{2}}{\mathrm{S}}_x$ (10 min), produces a specific contact resistance of ${\text{2.0(±3.5)×10}}^{\text{−5}}$ ${\mathrm{\Omega cm}}^{\mathrm{2}}.$ To the best of our knowledge, this is the lowest contact resistance reported hitherto for the contacts on p-GaN. The effective Schottky barrier heights (SBHs) of the differently surface-treated contacts were determined using the Norde and current–voltage methods. It is shown that the SBHs are dependent upon the surface treatment conditions.