Atomistic nature of heterointerfaces in III-V semiconductor-based quantum-well structures and its consequences for photoluminescence behavior

Abstract

The atomistic nature of heterointerfaces in III-V semiconductor-based quantum-well structures is investigated via a combined effort comprised of (i) systematic experimental investigations of the well-width ($d_w$) dependence of the photoluminescence (PL) linewidth (Γ) of GaAs/${\mathrm{Al}}_{\mathrm{x}}$ ${\mathrm{Ga}}_{1\mathrm{-}\mathrm{x}}$As(100) single quantum wells grown, via molecular-beam epitaxy (MBE), under identical growth conditions, (ii) Monte Carlo simulations of MBE growth, and (iii) comparison of the results of (i) with a new theory of PL linewidths based upon the nature of interfaces suggested by (ii). The measured behavior, Γ∼$d_w^{\mathrm{-}1}$, for $d_w$ in the range of 5 monolayers (ML) to 40 ML investigated is in contradiction to the widely used notion of fluctuations in the well width and demands a new physical model. The growth-kinetics-dependent in-plane Al concentration fluctuations at and near the interfaces revealed by the simulations of MBE growth indicate that band-edge discontinuity fluctuations and short-ranged alloy disorder are likely to be the dominant scattering mechanisms in high-quality quantum-well structures. Thus, a new theory of PL linewidth, based upon (a) short-ranged alloy-disorder scattering potential defined in the usual terms of difference of atomic potentials and (b) fluctuations in band-edge discontinuity over the size of the exciton, is introduced and the variance of these perturbations is calculated over a suitably chosen exciton wave function. The calculated dependence of Γ on $d_w$ is found to be in good agreement with the observed ∼$d_w^{\mathrm{-}1}$ behavior. The much used but hardly ever specified term ‘‘interface roughness’’ is thus demonstrated for the first time to correspond to fluctuations in the crystal potential of alloy-disorder type and band-edge discontinuity fluctuations, rather than the commonly used notion and model of well-width fluctuations.