Characterization of semi-polar GaN on GaAs substrates
Cubic GaN was grown on GaAs(0 0 1). The GaN layers were found to exhibit residual strain with a measured a-lattice parameter of 4.4990 Å. The GaN layers were grown on GaAs(1 1 0) forming cubic crystal structure with an a-lattice parameter of 4.4947 Å for the LT-GaN buffer layers and a hexagonal structure with an a-lattice parameter of 2.7463 Å and a c-lattice parameter of 5.5882 Å for the main GaN layers. Comparisons between the two GaAs substrate orientations, GaN on GaAs(1 1 0) showed a smoother surface (R rms of 5.369 nm) than that on GaAs(0 0 1) (R rms of 9.776 nm). It was shown by a TEM investigation that semi-polar GaN layers with low defect densities could be grown by MOCVD on GaAs(1 1 0) substrates. The TEM results indicated GaN//GaAs[1 1 0] and GaN//GaAs(1 1 0) crystal orientations.