Electronic structure of GaAs/AlAs symmetric superlattices: A high-pressure study near the type-I–type-II crossover

We have measured low-temperature photoluminescence and photoluminescence excitation spectra of (GaAs${)}_{\mathrm{m}}$/(AlAs${)}_{\mathrm{n}}$ symmetric superlattices (m=n) near the type-I-to-type-II crossover under high hydrostatic pressures. For an (m,n)=(15,15) superlattice we observe a type-I band structure which becomes type II at a pressure of ∼0.22 GPa. Based on pressure coefficients, the zero-pressure splitting is extrapolated as 27(4) meV. When (m,n)=(12,12), the superlattice is type II at zero pressure, showing two luminescence bands separated by 46(4) meV which linearly diverge in energy with increasing pressure. This implies the crossover occurs when 12<m,n<15. From intensity measurements on the (m,n)=(15,15) sample, the type-I recombination rate is estimated to be 1000 times slower than scattering into the lowest-energy X-like conduction-band state. We also find the valence-band offset to be dependent on pressure. These measurements then permit us to determine the pressure coefficients of all the lowest-energy confined states relative to the AlAs-like valence band. Near crossover we see no evidence of interaction between the type-I and type-II conduction-band states.