High quality non-alloyed 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 [(NH ₄)₂S_x]. This is followed by the second step using BOE. The Pt contact, which was treated sequentially using ultrasonically boiled BOE (10 min) and boiled (NH₄)₂S_x (10 min), produces a specific contact resistance of 3.0 (±3.8)×10 ^-5 Ωcm². However, the contact, that was simply BOE-treated, yields 3.1 (±1.1)×10^-2 Ωcm ². This indicates that the two-step surface treatment is promising technique for obtaining high quality ohmic contacts to p-GaN. Investigation of the electronic transport mechanisms using current-voltage-temperature (I-V-T) data indicates that thermionic field emission is dominant in the surface-treated Pt contacts.