Electronic properties and optical-absorption spectra of GaAs-${\mathrm{Al}}_{\mathrm{x}}$${\mathrm{Ga}}_{1\mathrm{-}\mathrm{x}}$As quantum wells in externally applied electric fields

A study of the electronic and optical properties of GaAs-${\mathrm{Al}}_{\mathrm{x}}$ ${\mathrm{Ga}}_{1\mathrm{-}\mathrm{x}}$As quantum wells in external electric fields is presented using a theory which incorporates valence-subband-mixing effects. Electric-field-induced changes in the conduction- and valence-subband structure, exciton binding energies, exciton oscillator strengths of both allowed (Δn=0) and forbidden (Δ≠0) transitions, and the total absorption spectrum are calculated. Optical transitions associated with several conduction and valence subbands are considered. Computed electronic and optical properties are found to be the result of an interplay between the effects of the overlap of electron and hole envelope wave functions and the valence-subband mixing. Valence-subband mixing results in a large splitting of the Kramer’s degeneracy in a quantum-well system in the presence of an electric field. The electric-field-induced changes in the computed exciton binding energies and oscillator strengths are caused mainly by the variation of the degree of overlap between the electron and hole wave functions. The foregoing results are compared with those obtained assuming no valence-band-mixing effects and are shown to be both qualitatively and quantitatively different. A brief comparison of our results with available experimental data is presented.