The electronic structure of the acceptor and its bound exciton in a GaAs/AlGaAs QW

Abstract

We have observed for the first time band-edge photoluminescence (PL) corresponding to the quantum well (QW) first subbands transition (∼1.93 eV) for below-gaps (QWs and barriers) photo-excitation (1.8 – 1.92 eV) in Si: modulation doped multiple QWs (MDMQW) in which barriers are intentionally doped. In order to unambiguously identify this PL to be anti-Stokes PL (ASPL), the MDMQW structure was selected to be in the form of 21 Å Al0.2Ga0.8As quantum wells and Si doped Al0.4Ga0.6As barriers. ASPL observed from MDMQW (1.35 × 1016 cm−3 in Al0.4Ga0.6As barriers) is stronger than bulk Si doped (1.35 × 1016 cm−3) Al0.4Ga0.6As taking into account the total number of Si atoms. A similar band-edge photoluminescence (PL) for below-gap photo-excitation in Si double δ-doped (DDD) (60 Å separation) AlxGa1−xAs (x = 0.35) has been observed. Observation of ASPL at low photon fluence of 20 W cm−2 with linear intensity dependence is a clear indication of hole generation via below gap one photon excitation. Relatively strong ASPL is due to the strong hole confinement and combined influence of spatial and thermal barriers on electronic occupancy of Si-deep centers in the barrier. We will describe temperature dependence, doping concentration dependence and excitation spectrum of this luminescence and correlate its origin to the deep centers within the frame work of small lattice relaxation (SLR) and large lattice relaxation (LLR) models.