Effect of the nitridation process on cubic GaN film quality grown on AlGaAs buffer layer by RF‐MBE

Abstract

The effects of the nitridation process on cubic GaN film quality grown on AlGaAs buffer layer by plasma assisted molecular beam epitaxy were investigated. When 10 seconds of nitridation was applied on AlGaAs buffer layer, the surface became very smooth by the suppression of {111} facet formation. The reproducibility and stability of high purity cubic GaN epilayer growth was dramatically improved by reducing the nitridation time. Dominant cubic GaN epilayer (0.8 µm) growth was confirmed by in situ RHEED observation, AFM, PL and X-ray diffraction measurements. 1 Introduction Cubic GaN (c-GaN) is expected to have many advantages in physical properties over those of the hexagonal phase due to its higher crystallographic symmetry. If high quality c-GaN thick film growth is realized, better performance of devices such as light emitting diodes (LEDs) and laser diodes (LDs) will be achievable. We earlier reported that using AlGaN layer formed by nitridation of an Al 0.17 Ga 0.83 As buffer layer was an efficient process for ensuring highly pure c-GaN growth [1]. But there still remain some problems regarding AlGaN nucleation layer growth. The first relates to fluctuations in Al concentration, which in turn significantly affects the purity of the structural phase of the epilayer. The seconds is the difficultly of maintaining high quality stoichiometric growth for extend periods of time due to the need for careful control of the beam fluxes (Al, Ga and As) required. Moreover, in the process of carrying out high quality c-GaN epilayer growth, a small amount of hexagonal GaN (h-GaN) was found to easily grow due to the formation of {111} facets during the nitridation process. Recently, improvements in the crystallinity of nitride crystal growth for short nitridation times have been studied [2,3]. The nitridation process of the initial growth of c-GaN films on GaAs substrate has also been studied [4][5][6].In this work, a dramatic improvement in the reproducibility and stability of c-GaN epilayer growth was achieved by controlling {111} facet formation during the initial stage of growth by optimizing nitridation conditions. The crystallographic properties of the as-grown layers were characterized by reflection high-energy electron diffraction (RHEED) and high resolution X-ray diffraction (HR-XRD). Atomic force microscopy (AFM) and low temperature photoluminescence (PL) measurements were carried out in order to characterize the surface morphology and optical properties, respectively.