Growth temperature effect on physical and mechanical properties of nitrogen rich InN epilayers

Abstract

A set of N-polar InN epilayers has been grown at different temperatures by plasma–assisted molecular beam epitaxy (PA-MBE) on GaN/AlN/Al2O3(0001) templates. The purpose is to understand how the variation of crucial factor, such as the temperature, impacts the growth process and the resulting samples’ properties. The characterization of these InN samples using atomic force microscopy and scanning electron microscopy showed different island distributions and shapes by varying the growth temperature. High resolution-X-ray diffraction (HRXRD) enabled to identify a single crystalline phase (hexagonal wurtzite), whatever the growth temperature. Actually, the increase of growth temperature up to 560 °C has improved the crystalline quality; whereas for high temperature, the crystalline quality degrades. The dislocation density of the epilayer grown at this optimum temperature (around 560 °C) is about 1.9 × 1010 cm−2, which is determined using HRXRD spectra analysis. High compressive residual stress value of 0.54 GPa was derived using Raman spectroscopy. Room temperature photoluminescence (PL) displays a band gap energy around 0.69 eV. Besides, Burstein-Moss effect, the PL band gap energy measured at 10 K is dictated by the biaxial compressive residual stresses. Nanoindentation tests were carried out on InN epilayers. Only, the sample grown at 560 °C exhibited a pop-in event, for which the measured hardness and Young’s modulus are of 4.5 ± 0.5 GPa and of 171 ± 8 GPa, respectively. Accordingly, the growth temperature of InN epilayers influences the resulting physical and mechanical performances, thus a good compromise between physical and mechanical features permits to manufacture efficient devices.