Annealing-dependent optical response of two-step-grown Be-doped AlGaAs/GaAsBi quantum wells: confined transitions and defect-related contributions

Post-growth annealing can modify the optical response of dilute-bismide quantum wells by altering confinement, alloy disorder, and localized states. We investigate a two-step-grown Be-doped Al 0 . 12 Ga 0 . 88 As/GaAs 0 . 96 Bi 0 . 04 single quantum well using room-temperature photomodulated reflectance (PR) and electronic band-structure calculations that incorporate strain. Spectra of the as-grown sample and samples annealed at 550, 600, and 650 °C for 60 s are analyzed using the third-derivative functional form (TDFF). The fitted resonances are compared with calculated confined-state transitions and with energy separations involving phenomenological localized levels. Annealing at 600 °C yields the clearest overall spectral separation, whereas 650 °C produces renewed broadening and overlap. From the as-grown sample to 600 °C, the low-energy TDFF resonance center redshifts by 53 meV, and its broadening parameter decreases from 180 to 53.9 meV. A common coupling parameterization for the as-grown, 550, and 600 °C samples yields an unchanged fundamental transition energy at fixed composition, geometry, and strain. This calculation therefore does not reproduce the observed resonance-center shift as a shift of the fundamental transition. Published microscopy of the same wafer and literature trap spectroscopy support consideration of interfacial and defect-related contributions, although their optical assignments remain non-unique. The results indicate that spectral separation and compatibility with calculated transition energies should be considered together when interpreting overlapping PR resonances.