Electronic and intersubband optical properties of p -type GaAs/AlGaAs superlattices for infrared photodetectors

Existing theories of electronic properties and optical transitions in quantum-well structures are extended to p-type superlattices including the two heavy- and light-hole valence bands. These theories are then used to elucidate the normal incidence optical-absorption mechanisms including the Hartree and exchange-correlation many-body interactions on the basis of the one-particle local density approximation. The effects of doping density and doping configuration on the electronic structure and the intersubband optical properties of heavily doped p-type GaAs/AlGaAs superlattices are investigated for use in infrared photodetectors. It is shown that these many-body interactions cause significant changes to the subband energy structure and the optical-absorption coefficient, and that the doping level and doping configuration have an important effect on the properties of these superlattices. Peak absorption coefficients of 6000–10 000 cm−1 for normal light incidence at photon wavelengths of 8–10 μm are predicted for p-type GaAs/AlGaAs superlattices with well doping of 2×1019 cm−3. Because of the heavier effective mass of holes in the p-type structures, as compared to the n-type structures, a relatively slower degradation of the dark current with increasing doping density is expected. This, in addition to the higher absorption values that can be achieved with heavily doped p-type superlattices, renders them highly promising for normal incidence photodetectors.