Intersubband absorption and infrared modulation in GaAs/AlGaAs single quantum wells

Abstract In this paper we show that intersubband absorption can be observed in single GaAs/AlGaAs quantum wells by using an experimental method similar to that used previously for inversion layers on the surfaces of semiconductors. Absorption spectra are observed in an internal reflection geometry with a metal surface layer which ensures that there is a large radiation field perpendicular to the quantum well as required by the usual selection rules for the intersubband transition. The observed spectra are described well by a multilayer model with the quantum well taken to be an anisotropic Lorentz oscillator. The transition energies and oscillator strengths are shown to agree well with those predicted by an envelope function model, provided that band bending and free carrier polarization effects are taken into account. It is also shown experimentally that the metal overlayer can act as a Schottky gate, which will change the electron population in the quantum well when appropriately biased and thereby modulate the absorption.