Electrical properties of GaN grown on a-plane GaN template by plasma-assisted molecular beam epitaxy

Abstract

a-Plane GaN templates were grown on r-plane sapphire substrate by metalorganic vapor phase epitaxy (MOVPE) and then undoped a-plane GaN layers were grown at different growth temperatures on the a-plane GaN templates by plasma-assisted molecular beam epitaxy (PA-MBE). In order to investigate the effect of growth temperature on basal stacking fault (BSF) density and the effect of BSFs on electrical properties of a-plane GaN, background carrier concentration and electron mobility were measured by Hall measurement at room temperature. BSF density and dislocation density were also evaluated by plan-view transmission electron microscope. As the growth temperature increased from 740 to 800 °C, the background carrier concentration decreased from 1.4×10 19 to 3.2×10 17 cm −3. It was observed that the electron mobility ( μ c ) along c-axis [0 0 0 1] direction is larger than that ( μ m ) along m-axis [1 1̄ 0 0] direction except the sample grown at 780 °C. The electron mobility ratio ( μ c / μ m ) is 0.98 for the sample grown at 780 °C. Anisotropic and isotropic electrical property of a-plane GaN grown by PA-MBE is related to the BSF density. As the growth temperature was increased from 740 to 800 °C, the BSF density increased from 4.5×10 5 to 7.91×10 5 cm −1. In the case of isotropic electron mobility of the sample grown at 780 °C, the maximum BSF density was observed. Therefore, isotropic electron mobility results mainly from the carrier scattering by the BSFs along c-axis direction. As the dislocation density was increased, the BSF density also increased.