Absorption saturation of near-infrared intersubband transition in lattice-matched InGaAs/AlAsSb quantum wells

We report the near-infrared intersubband absorption characteristics in In0.53Ga0.47As/AlAs0.56Sb0.44 heterostructures lattice matched to InP substrate, The intersubband transition energy increases on reducing the quantum-well width and tends to saturate at around 0.65 eV on further reducing the InGaAs layer thickness due to the influence of the interface fluctuations. We present the first report on intersubband absorption saturation in InGaAs/AlAsSb QWs using a femtosecond light source (similar to 200 fs) tuned resonantly to the intersubband transition energy (0.52 eV). We observe a clear absorption saturation behavior of the intersubband transitions. At higher excitation power, a strong absorption due to interband two-photon transitions occurs. The interband two-photon transitions are induced by the intersubband transitions, as the band gap of the InGaAs well layers is resonant to the two-photon transition energy of the intersubband separation of this unique high-conduction band-offset InGaAs/AlAsSb quantum-well system. (C) 2000 Elsevier Science B.V. All rights reserved.