W2B-based ohmic contacts to n-GaN

Ohmic contact formation on n-GaN using a novel Ti/Al/W2B/Ti/Au metallization scheme was studied using contact resistance, scanning electron microscopy and Auger electron spectroscopy measurements. A minimum specific contact resistivity of 7 10 6 V cm2 was achieved at an annealing temperature of 800 8C. The contact resistance was essentially independent of measurement temperature, indicating that field emission plays a dominant role in the current transport .The Ti began to outdiffuse to the surface at temperatures of 500 8C, while at 800 8C the Al also began to intermix within the contact. By 1000 8C, the contact showed a reacted appearance and AES showed almost complete intermixing of the metallization. The contact resistance showed excellent stability for extended periods at 200 8C, which simulates the type of device operating temperature that might be expected for operation of GaN-based power electronic devices