Thermal degradation of Ohmic contacts on semipolar (11–22) GaN films grown on m-plane (1–100) sapphire substrates

Abstract

Semipolar (11–22) GaN films were grown on m-plane (1–100) sapphire substrates by using metal-organic chemical vapor deposition. The linewidths of the omega rocking curves of the semipolar GaN films were 498 arcsec along the [11–23]_GaN direction and 908 arcsec along the [10–10]_GaN direction. The properties of the Ti/Al/Ni/Au metal contact were investigated using transmission-line-method patterns oriented in both the [11–23]_GaN and the [10–10]_GaN directions of semipolar (11–22) GaN. The minimum specific contact resistance of ∼3.6 × 10⁻⁴ Ω·cm⁻² was obtained on as-deposited metal contacts. The Ohmic contact properties of semipolar (11–22) GaN became degraded with increasing annealing temperature above 400 °C. The thermal degradation of the metal contacts may be attributed to the surface property of N-polarity on the semipolar (11–22) GaN films. Also, the semipolar (11–22) GaN films did not show clear anisotropic behavior of the electrical properties for different azimuthal angles.