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

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 degrees 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 degrees C) is about 1.9 x 10(10) 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 degrees 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. (C) 2021 Elsevier B.V. All rights reserved.

Automated summary

A series of N-polar InN epilayers were grown at various temperatures using plasma-assisted molecular beam epitaxy on GaN/AlN/Al2O3(0001) templates. Different island distributions and shapes were observed at varying growth temperatures, but the samples were identified as single crystalline phase regardless of temperature. Increasing the growth temperature up to 560 degrees C improved the crystalline quality, while excessively high temperatures led to degradation of quality.