On the determination of alloy composition using optical spectroscopy in MOVPE grown InGaN layers on Si(111)

Abstract

Abstract Alloy composition of InxGa1-xN layer is investigated using photoluminescence (PL), and photoluminescence excitation (PLE) techniques. InGaN layers were grown on Si(111) substrates using metal organic vapour phase epitaxy (MOVPE) technique under variable flow of either ammonia (NH3) or trimethyl gallium (TMGa) with corresponding V/III ratios in the range of 3.6 × 103 to 1.2 × 104. We observed that though room temperature PL measurements give an indication about the growth of InGaN, it doesn't help in the estimation of band gap or alloy composition of layer. It is restricted mainly by the presence of multiple peaks in the PL spectra which is rather severe at low temperature. A comparison of PL and reflectivity spectra confirmed that such peaks are attributed to interference oscillations and are not related with multiple compositions of InGaN. Further, in such a scenario PLE is found to be quite effective where the measured PLE spectrum is consisted of a clear onset related to InGaN layer in the sub band gap region of GaN. It is quite helpful in a precise determination of band gap and hence the alloy composition of InGaN layer. The indium composition is estimated to be in the range of 3.5% ≤ x ≤ 20.5%, however its trends with respect to V/III ratio as a function of NH3 or TMGa flow are found to be rather opposite.