An Improved Theoretical Model to Explain Electronic and Optical Properties of p-Type GaAs/AlGaAs Superlattices for Multi-Wavelength Normal Incidence Photodetectors

We extend our previous theoretical analysis of electronic and optical properties of p-type quantum well structures based on the two heavy- and light-hole system to include all the three valence bands. These theories are then used to clarify the origin of the normal incidence absorption and photocurrent at photon wavelengths of 2 - 3 μm, which was observed in addition to the absorption around 8 μm by a recent experimental investigation with heavily doped p-type GaAs/AlGaAs multi-quantum well (MQW) structures. In the theoretical analysis, the Hartree and exchange-correlation many-body interactions are taken into account within one-particle local density approximation, and it is shown that normal incidence absorption occurs in two wavelength regions over the transition energy range higher than barrier height for p-type GaAs/AlGaAs superlattices with well doping of 2 × 10¹⁹ cm⁻³; one region has broad absorption peaks with coefficients of about 5000 cm⁻⁻¹ around 8 μm, and the other has two rather sharp peaks at 2.7 μm and 3.4 μm with 1800 cm⁻⁻¹ and 1300 cm⁻⁻¹, respectively. The result indicates that the theory explains the experimental observation well, as the theoretical and experimental results are in close agreement in general absorption features.