OPTICAL CHARACTERIZATION OF SUBMONOLAYER AND MONOLAYER INAS STRUCTURES GROWN IN A GAAS MATRIX ON (100) AND HIGH-INDEX SURFACES

We studied the optical properties of InAs/GaAs heterostructures with InAs average layer thickness ranging from 1 angstrom [one-third of a monolayer (ML)] to 4 ML grown on (100) and (311) surfaces. Extremely high optical quality was revealed for the structures with ultrasmall InAs coverage. We attribute the improvements to the first stage of InAs growth on the GaAs surface which we refer to as submonolayer epitaxy. Optical anisotropy found in photoluminescence (PL), as well as in PL excitation spectra indicates a highly anisotropic growth mode for InAs molecules on the GaAs (100) surface. An InAs/GaAs superlattice composed of submonolayer InAs exhibits greatly improved luminescence efficiency at room temperature and much better nonequilibrium carrier capture compared to either the (In,Ga)As alloy or an InAs/GaAs superlattice composed of monolayer-thick InAs layers with the same average In composition.