Stable Contacts at High Temperature for GaN using Boride-Metal Scheme.

Ohmic contact having boride interlayer (Ti/Al/X/Ti/Au) to n-GaN was studied using contact resistance, scanning electron microscopy and Auger Electron Spectroscopy measurements. X in the metallization scheme was W$_{2}$B, TiB$_{2}$ or CrB$_{2}$. A minimum contact resistance of 7x10$^{-6 }\Omega $.cm$^{2}$ was achieved for W$_{2}$B based scheme at an annealing temperature of 800 \r{ }C. For TiB$_{2}$ it was of 2x10$^{-6 }\Omega $.cm$^{2}$ at 800$^{o}$C and 900$^{o}$C and 8x10$^{-6 }\Omega $.cm$^{2}$ for CrB$_{2}$ at 800$^{o}$C. Contact resistances were found to be essentially independent of measurement temperature, indicating that tunneling plays a dominant role in the current transport. The reliability measurements for the contact resistance of W$_{2}$B based contact showed excellent stability for extended periods at 200\r{ }C which simulates the type of device operating temperature that might be expected for operation of GaN-based power electronic devices.