Indium Tin Oxide (ITO) based Ohmic Contacts on Bulk n-GaN Substrate

A transparent indium tin oxide (ITO) contact to bulk n-GaN and n-GaN thin film on c-face sapphire with a specific contact resistivity of 8.06 x 10(-4) omega.cm(2) and 3.71 x 10(-4) omega.cm(2) was measured, respectively. Our studies relied on an RF sputtering system for ITO deposition. We have investigated the formation of the ITO-based contacts on untreated and plasma treated samples. A nonlinear I-V curve was observed for ITO deposited on untreated samples. On the other hand, an I-V curve with linear behavior was observed for plasma-treated samples, indicating the formation of ohmic contacts. From the C-V measurements, it was observed that there was also an increase in the carrier concentration in plasma treated samples compared to untreated samples. This can be attributed to the removal of surface oxide layer present on the GaN surface, and increase in nitrogen vacancies after SiCl4 plasma treatment. In addition, the increase in nitrogen vacancies at the GaN surface can also enhance localized surface/sub-surface carriers, thereby reducing the contact resistance further.