Intersubband transitions in strained In0.07Ga0.93As/Al0.40Ga0.60As multiple quantum wells and their application to a two-colors photodetector

Infrared absorption spectroscopy is used to study the conduction band intersubband transitions in Si-doped In0.07Ga0.93As/Al0.40Ga0.60As multiple quantum-well structures with the doping being restricted to the well region. The chemical potential determined by the electron density is designed to be above the second subband edge for samples with certain well widths, so that two absorption peaks with a different wavelength would be observed as one of the requirements for a two-colors photodetector. The optical absorption spectra are calculated from which the peak position energies are extracted and compared with the experimental measurements for different well widths. Good agreement between numerical results and experimental data is achieved. In our theory, self-consistent screened Hartree-Fock calculations were performed, which includes the effects of the z-dependent electron effective mass, dielectric constant, and the nonparabolic dispersion. The strain effect is also taken into consideration by the deformation theory. In addition, the calculated optical absorption spectra included the many-body depolarization and excitonlike shifts.