Raman Light Scattering from Plasmons in Modulation-Doped Quantum Wells

Abstract

Electronic Raman scattering is a very powerful technique for the contactless optical characterization of quantum wells and heterojunctions and has much promise for the spatially resolved characterization of quantum wire structures. We show that electronic Raman scattering measurements of the plasmon dispersion is a contactless optical alternative to measurements of Shubnikov-de Haas oscillations for the determination of carrier concentractions in modulation-doped single- and multi-quantum wells and heterojunctions. We demonstrate the optical control of carrier density in a single heterojunction with an adjacent δ-layer of acceptors: we use Raman measurements of the plasmon by a probe laser beam to directly determine the change in carrier concentration induced by illumination with a pump laser beam of varying intensity. Using Raman measurements in combination with calculations of the random phase approximation (RPA) dielectric response and self-consistent electronic subband calculations we determine the subband structure, populations, potential and wavefunctions of modulation-doped GaAs/Al_xGa_l-xAs multi-quantum wells with multiple subband occupancy.