High cubic phase purity and growth mechanism of cubic InN thin-films by Migration Enhanced Epitaxy

Metastable cubic InN is a promising semiconductor for developing optoelectronic, photovoltaic and electronic devices. The suitable application of the material requires a high crystalline quality and a high cubic phase purity. For this reason, it is important to identify the growth mechanism of both the cubic phase and the structural defects, as well as to quantify the cubic phase purity. In this work, we determine and quantify the cubic phase purity in c-InN samples grown by Migration Enhance Epitaxy (MEE) using Raman spectroscopy. We found, the LO and TO phonon modes attributed to the cubic phase of InN at 589 and 462 cm^{- 1}, respectively. The hexagonal phase inclusions were also identified with the E₂ mode observed at 488 cm^{- 1}. The quantification of the cubic phase purity was performed employing a model that takes into account the intensities of the LO and E₂ modes of the Raman spectra in a depth profile. The highest cubic phase purity obtained was 93.7% for a sample grown at 510 °C. We also analyzed the growth mechanism of c-InN by transmission electron microscopy (TEM), finding the cubic phase, the characteristic planar defects and a small hexagonal inclusion (h-InN). The characteristic planar defects in the samples are the stacking faults (SF). We quantified the SF density using the cross section TEM images. The lowest density was 3.27 × 10⁵ cm^{- 1} for the sample grown at 510 °C. Additionally, the high cubic phase purity in the c-InN samples was identified in a phase map obtained by Precession Electron Diffraction.