Metalorganic chemical vapor deposition of GaN and InGaN on ZnO substrate using Al 2 O 3 as a transition layer

Abstract

Al₂O₃ films were deposited on the Zn face of ZnO (0001) substrates as a transition layer by atomic layer deposition (ALD). The as-deposited 20 and 50nm Al₂O₃ films were transformed to polycrystalline α-Al₂O₃ phase after optimal annealing at 1100°C after 10 and 20 minutes, respectively, as identified by high resolution x-ray diffraction (HRXRD). Furthermore, GaN and InGaN layers were grown on annealed 20 and 50nm Al₂O₃ deposited ZnO substrates by metalorganic chemical vapor deposition (MOCVD) using NH3 as a nitrogen source at high growth temperature. Wurtzite GaN was only seen on the 20nm Al₂O₃/ZnO substrates. Room temperature photoluminescence (RT-PL) shows the near band-edge emission of GaN red-shifted, which might be from oxygen incorporation forming a shallow donor-related level in GaN. Raman scattering also indicated the presence of a wellcrystallized GaN layer on the 20nm Al₂O₃/ZnO substrate. InGaN was grown on bare ZnO as well as Al₂O₃ deposited ZnO substrates. HRXRD measurements revealed that the thin Al₂O₃ layer after annealing was an effective transition layer for the InGaN films grown epitaxially on ZnO substrates. Auger Electron Spectroscopy (AES) atomic depth profile shows a decrease in Zn in the InGaN layer. Moreover, (0002) InGaN layers were successfully grown on 20nm Al₂O₃/ZnO substrates after 10min annealing in a high temperature furnace.