The theory of multiple quantum-well GaAs-AlGaAs infrared detectors

Abstract

The theory of multiple quantum-well GaAs-AlGaAs IR detectors based on the principle of quantum well photoionization is presented. The expression for the photoionization probability of the symmetric quantum-well is found to be exact in the effective mass approximation. Depolarization effects in the optical absorption spectra are discussed. We demonstrate that the depolarization shift of the spectrum maximum and its broadening lead to non-monotonic dependence of the photodetector detectivity on the electron concentration in wells in the background limited IR performance condition. The optimal factor of quantum-well filling, corresponding to the maximum of detectivity is rather small, and for the photoresistor with boundary wavelength λ 1 = 10 μm, is θ =0.10. We have also performed calculations for the concentration dependence of the transition temperature for background limited IR performance and found that for optimal concentrations it is about T = 83 K (for λ 1 = 10 μm). The lifetime of non-equilibrium electrons is determined by capturing processes into the wells accompanied by emission of polar optical phonons and is τ ≅ 2 × 10 −11 s. The gain, along with the photoresistor sensitivity, is maximal for structures with a single quantum well.