A study of Franz–Keldysh oscillations in the photo reflectance spectrum of the δ‐doped GaAs film

Our photo reflectance (PR) spectroscopy measurements of the δ‐doped GaAs film at 300 K reveal many Franz–Keldysh oscillations (FKOs) above the valence band edge, E0 and the spin‐orbit split energy, E0+Δ0, which enables us to determine the electric field strength from periods of FKOs provided reduced masses of the electron and holes are known. The reduced masses can be determined unambiguously at E0+Δ0, but not at E0, at which the heavy‐ and light‐hole transitions are degenerate. However, the ambiguity at E0 can be resolved by applying the fast Fourier transform to the PR spectrum to separate the contributions from the heavy and light holes.