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 Ω cm2 was achieved at an annealing temperature of 800 °C. 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 °C, while at 800 °C the Al also began to intermix within the contact. By 1000 °C, 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 °C, which simulates the type of device operating temperature that might be expected for operation of GaN-based power electronic devices.