Controlling interface oxygen for forming Ag ohmic contact to semi-polar (1 1 −2 2) plane p-type GaN

• Control of interfacial oxide to form Ag-based ohmic contacts to semi-polar (1 1 −2 2) p-GaN.
• The annealed Zn/Ag samples showed better ohmic behavior than that of Ag-only contacts.
• Annealing causes the indiffusion of oxygen toward the contact/GaN interface.
• Ohmic mechanisms are attributed to formation of different types of interfacial oxides.

Low-resistance Ag ohmic contacts to semi-polar (1 1 −2 2) p-GaN were developed by controlling interfacial oxide using a Zn layer. The 300 °C-annealed Zn/Ag samples showed ohmic behavior with a contact resistivity of 6.0 × 10−4 Ω cm2 better than that of Ag-only contacts (1.0 × 10−3 Ω cm2). The X-ray photoemission spectroscopy (XPS) results showed that annealing caused the indiffusion of oxygen at the contact/GaN interface, resulting in the formation of different types of interfacial oxides, viz. Ga-oxide and Ga-doped ZnO. Based on the XPS and electrical results, the possible mechanisms underlying the improved electrical properties of the Zn/Ag samples are discussed.