Photoinduced intersubband absorption in undoped multi-quantum-well structures

Abstract
We report the first observation of strong intersubband (e1-e2) absorption by photogenerated excitons in GaAs/GaAlAs undoped, multi-quantum-well structures. The origin of the transition is verified by polarization measurements, temperature dependence, and comparison with photoluminescence data. Its oscillator strength is found to be approximately 25 times stronger than that measured for bare electrons in modulation-doped quantum wells. We attribute it to an excitonic enhancement.