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

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 [(NH4)2Sx]. This is followed by the second step using BOE. The Pt contact, that was simply BOE treated, yields 2.1(±0.9)×10−2 Ω cm2. However, the contact which was treated sequentially using ultrasonically boiled BOE (10 min) and boiled (NH4)2Sx (10 min), produces a specific contact resistance of 2.0(±3.5)×10−5 Ω cm2. 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.