Analysis of optical properties of p -type GaAs/AlGaAs superlattices for multiwavelength normal incidence photodetectors

A calculation on intersubband optical transitions including heavy and light hole bands to spin-split-off band in heavily doped p-type GaAs/AlGaAs multi-quantum well (MQW) structures is reported. The analysis is focused on elucidating the recent experimental observation of normal incidence absorption and photocurrent at photon wavelengths of 2–3 μm, in addition to the already-observed absorption at around 8 μm in heavily doped p-type GaAs/AlGaAs MQW structures. The calculation is an extension of our previous study which only includes transitions between heavy and light bands. The analysis, in which Hartree and exchange-correlation many-body interactions are taken into account within one-particle local density approximation, shows that normal incidence absorption occurs in two wavelength regions over the transition energy range higher than the 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 at around 8 μm, and the other has two rather sharp peaks at 2.7 and 3.4 μm with 1800 and 1300 cm−1, respectively. The result agrees reasonable well with the experimental observation in general absorption features. The existence of multiabsorption wavelengths in heavily doped GaAs/AlGaAs MQWs may allow the design of multicolor normal incidence photodetectors.