Low-temperature grown wurtzite InxGa1−xN thin films via hollow cathode plasma-assisted atomic layer deposition
Herein, we report on atomic layer deposition of ternary InxGa1−xN alloys with different indium contents using a remotely integrated hollow cathode plasma source. Depositions were carried out at 200 °C using organometallic Ga and In precursors along with N2/H2 and N2 plasma, respectively. The effect of In content on structural, optical, and morphological properties of InxGa1−xN thin films was investigated. Grazing incidence X-ray diffraction showed that all InxGa1−xN thin films were polycrystalline with a hexagonal wurtzite structure. X-ray photoelectron spectroscopy depicted the peaks of In, Ga, and N in bulk of the film and revealed the presence of relatively low impurity contents. In contents of different InxGa1−xN thin films were determined by energy-dispersive X-ray spectroscopy, X-ray photoelectron spectroscopy, and X-ray diffraction. Transmission electron microscopy also confirmed the polycrystalline structure of InxGa1−xN thin films, and elemental mapping further revealed the uniform distribution of In and Ga within the bulk of InxGa1−xN films. Higher In concentrations resulted in an increase of refractive indices of ternary alloys from 2.28 to 2.42 at a wavelength of 650 nm. The optical band edge of InxGa1−xN films red-shifted with increasing In content, confirming the tunability of the band edge with alloy composition. Photoluminescence measurements exhibited broad spectral features with an In concentration dependent wavelength shift and atomic force microscopy revealed low surface roughness of InxGa1−xN films with a slight increase proportional to In content.