Effect of growth temperature on InGaN/GaN heterostructures grown by MOCVD

Abstract

InGaN/GaN heterostructured samples were grown at different temperatures varying from 680°C to 760°C on c-plane sapphire substrates using a horizontal flow Metal Organic Chemical Vapor Deposition (MOCVD) reactor. Systematic investigation of structural, optical, morphological and electrical properties has been carried out using High Resolution X-Ray Diffraction (HRXRD), Photoluminescence (PL), Atomic Force Microscope (AFM) and Hall Measurement respectively. From the HRXRD results, the respective Indium (In) composition in the InGaN/GaN heterostructures can be calculated using InGaN (0002) peaks. In incorporation is very much sensitive to the temperature and incorporation of In in InGaN epilayer was found to decrease with increase in growth temperature. PL spectra reveal a shift towards higher energy side because of In incorporation with increasing reactor temperature. AFM images of the sample grown at 680°C shows the In rich clusters due to compositional inhomogeneity. With further increase in the growth temperature, decomposition of InN starts and hence decreases the surface roughness. Hall Effect studies confirm that with increasing growth temperature bulk electron concentration of the InGaN thin films decrease and mobility increases. Maximum bulk electron concentration of ~4.5×1019cm−3 and a mobility of ~295cm2/V-s was obtained for 19% of In. Efforts are being made to optimize the incorporation of In content in InGaN/GaN heterostructures for photovoltaic application.