The effects of substrate orientation on the optical properties of InGaAs epitaxial layers grown by low-pressure metal organic vapour-phase epitaxy

The effect of substrate orientation on the optical properties of nonpseudomorphic InxGa1–xAs epitaxial layers grown by metal organic vapour-phase epitaxy has been investigated in two series of samples. Series (a) samples were grown on GaAs substrates cut 2° off (001) towards [Formula: see text], and those of series (b) were grown on GaAs substrates cut exactly on (001). The low-temperature photoluminescence spectra of the two series of samples differ drastically. Those of the (a) series are characteristic of highly uniform, fully relaxed ternary layers and are used to determine the composition dependence of the alloy band gap and of the carbon acceptor binding energy. In contrast, those of the (b) series are dominated by an intense, low-energy emission, which is attributed to exciton recombinations in small regions of small band gap. The reduction of the band gap is tentatively assigned to the presence of In-rich regions created by the large strain fields present along dislocations. The density of dislocations is much larger in the samples of the (b) series than in those of the (a) series owing to the combination of three-dimensional growth and slow strain relaxation for layers grown on (001) substrates.