Mixing of valence subbands in GaAs/${\mathrm{Al}}_{\mathrm{x}}$${\mathrm{Ga}}_{1\mathrm{-}\mathrm{x}}$As multiple quantum wells by uniaxial stress

The effects of uniaxial stress on the energies of exciton transitions in GaAs/${\mathrm{Al}}_{\mathrm{x}}$ ${\mathrm{Ga}}_{1\mathrm{-}\mathrm{x}}$As multiple quantum wells are investigated both theoretically and experimentally. The valence subbands and the corresponding wave functions are analyzed at the Brillouin-zone center by solving a 4×4 Luttinger-Kohn Hamiltonian in conjunction with a 4×4 strain Hamiltonian in the spin J=(3/2 basis. Appropriate boundary conditions are obtained by integrating the total Hamiltonian across the interfaces of the wells. Good agreement is obtained between numerical calculations on a 22-nm-wide quantum well subjected to a uniaxial stress in the plane of the well and experimental results obtained using photoluminescence excitation spectroscopy at liquid-helium temperatures. Evidence of valence-subband mixing between the light-hole exciton and higher levels of heavy-hole excitons is clearly observed.