Effects of doping and indium inclusions on the structural and optical properties of InN thin films grown by MOCVD

Abstract

High-resolution x-ray diffraction (HRXRD), Raman scattering and photoluminescence (PL) are used to investigate the structural and optical properties of InN thin films grown by metalorganic chemical vapour deposition (MOCVD). They reveal that the phonon frequency ϖ (in cm−1) of varies with residual biaxial strains εxx (in %) induced by Mg doping, Zn doping and In inclusions as ϖ = 488.9–43.9 × εxx, relating to a Raman factor of 10.8 cm−1 GPa−1. They also reveal a strong correlation between PL energies and electron concentrations due to bandgap renormalization and band-filling effects. The evolution of HRXRD, due to chemical etching, provides evidence that the In inclusions not only appear on the surface and/or at grain boundaries but are also embedded in the InN crystals. Optical absorptions and PL spectra exhibit no apparent changes upon chemical etching, confirming the absence or minor effect of coupling on In-related plasmonic resonance and/or interband transitions, especially for those In inclusions present on the surface and/or at the grain boundaries of InN.