Anisotropic properties of MOVPE-grown m-plane GaN layers on LiAlO2 substrates

Abstract

We used metal organic vapour phase epitaxy (MOVPE) to deposit m-plane GaN layers on LiAlO2 substrates and studied the influence of the V/III ratio during growth. All films exhibit a special surface pattern with pyramidal hillocks elongated in [11–20] direction of GaN and small steps perfectly aligned in the (11–20) plane. For higher V/III ratios, the roughness is reduced while holes on the surface are generated. Polarization-dependent low-temperature (LT) photoluminescence (PL) spectra show GaN excitonic peaks at ∼3.5 eV with a high degree of polarization (DoP) of ∼0.9. Another peak at 3.47 eV is much less intense compared to the excitonic peak and probably related to basal plane stacking faults (BSF). Anisotropic in-plane compressive strain which slightly relaxes for a higher V/III ratio can be detected by high-resolution X-ray diffraction (HRXRD). XRD reciprocal space maps of the symmetric (1–100) reflection show relatively weak broadening for scans taken in the [0001] direction and strong broadening for the perpendicular direction. Anisotropic room temperature electron mobilities are found with average values of 108 and 117 cm2/Vs in [11–20] and [0001] direction of GaN, respectively. We explain the higher values in c-axis direction by the presence of extended planar defects in the prism plane which may be also responsible for the observed surface steps and anisotropic broadening of the XRD RSM.