On factors affecting alloy clustering in In0.52Al0.48As layers grown on InP substrates by molecular beam epitaxy

Abstract

Growth of In0.52Al0.48As epilayers on InP (100) substrates by molecular beam epitaxy at a wide range of substrate temperatures (470 - 550 °C) and V/III flux ratios is carried out. Low temperature photoluminescence (PL) and double-axis X-ray diffraction (XRD) measurements showed a strong dependence of the PL and XRD linewidths and lattice-mismatch on the substrate temperature. Minimum PL and XRD linewidths and lattice-mismatch were found to occur at substrate temperatures between ≈ 500 - 520 °C. The XRD intensity ratios (Iepi/Isub) were generally higher within the same substrate temperature range at which the lattice-mismatch was the lowest. XRD rocking-curves of samples grown at low temperatures showed the main epilayer peak to be a composition of smaller peaks which can strongly indicate the presence of alloy clustering. PL spectra taken at increasing temperatures showed the quenching of the main emission peak followed by the evolution of a distinct peak at lower energy, possibly associated with carrier localization due to the presence of lattice disorder. Within the range of V/III flux ratios investigated (32 to 266), the lowest PL linewidth of 14 meV was recorded for the samples grown at a V/III ratio of 160. The lattice-mismatch between the epilayer and the substrate for these samples was also found to be relatively insensitive to changes in the V/III flux ratios.