Franz-Keldysh oscillations in the photomodulated spectra of anIn0.12Ga0.88As/GaAs strained-layer superlattice

The low-temperature photoreflectance and phototransmittance spectra of a 100 Å-period ${\mathrm{In}}_{0.12}$ ${\mathrm{Ga}}_{0.88}$As/GaAs strained-layer superlattice exhibit oscillatory behavior at photon energies above the absorption edge. This behavior can be consistently interpreted in terms of Franz-Keldysh oscillations induced by a built-in electric field of ≃${10}^4$ V/cm and are made possible by a rather large electron miniband dispersion (Δ≃38 meV). The reflectivity spectrum also shows signs of incipient Stark-ladder formation.