PHOTOREFLECTANCE STUDY OF GROWTH MODE IN INAS-GAAS QUASIMONOLAYER SINGLE QUANTUM-WELLS

Photoreflectance measurements have been performed in a number of InAs/ GaAs single-quantum wells with nominal thickness L ranging from 0.6 to 2.0 ML. The InAs growth mode was investigated by analyzing the evolut ion, with increasing coverage, of the optical response associated with the InAs layer. For L less than or equal to 1.6 ML, the experimentall y derived energies for the optical transition originating in the InAs are consistent with those evaluated in a simple square-well envelope-f unction scheme. The dependence of the photoreflectance line shape broa dening on L is well described up to L=1.4 ML in terms of a disordered InAs/GaAs interface made by interconnected InAs and GaAs islands with a typical size of order 2 nm. For L=1.6 Mi,, the quantum well spectral features broaden abruptly and vanish for L=2 ML, suggesting the disap pearance of the InAs 2D layer in favor of a predominant nucleation of large quantum dots. (C) 1998 American Institute of Physics.