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)(2)S-x]. This is followed by the second step using BOE. The Pt contact, that was simply BOE treated, yields 2.1(+/- 0.9) x 10(-2) Omega cm(2). However, the contact which was treated sequentially using ultrasonically boiled BOE (10 min) and boiled (NH4)(2)S-x (10 min), produces a specific contact resistance of 2.0(+/- 3.5) x 10(-5) Omega cm(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. (C) 1999 American Vacuum Society. [S0734-211X(99)03506-4].