Modulation spectroscopy of InAs semiconductor nanostructures grown on (631) high index substrates

The molecular beam epitaxial (MBE) growth of InAs nano structures on GaAs(631)-oriented substrates is studied by pho toluminescence (PL) and photoreflectance spectroscopy (PR). First, a corrugated surface conformed by regularly spaced grooves aligned along the [593] azimuth was formed by the GaAs homoepitaxial growth on the (631) substrate. On this template, we proceeded with the deposition of InAs at several thicknesses in the range of 1 to 4.5 monolayers (MLs). An atomic force microscopy (AFM) analysis of samples without GaAs capping, revealed that assemblage of QDs occurs only after the deposition of the equivalent to ∼ 1.9 ML of InAs. On these samples, we observed changes on the PR line-shape in the near-bandgap GaAs region linked to the quantity of InAs deposited. The intensity of the built in electric fields was cor related with the strain state at the heterointerface, as a conse quence of the self induced piezoelectric effect, typical from high index surfaces. On the other hand, when the samples were capped with a 100 Å thick GaAs layer, strong emission of the nanostructures occurs even for deposited quantities of InAs as low as 1 ML. Since for this InAs thickness the self assemblage of QDs is not observed, the optical transitions ob served were associated with the optical emission of self as sembled semiconductor quantum wires, promoted by surface diffusion aniso tropy, characteristic of the (631) plane.