Type-I and type-II Stark-ladder phenomena in ${\mathrm{Ga}}_{1\mathrm{-}\mathit{x}}$${\mathrm{In}}_{\mathit{x}}$As-GaAs strained-layer superlattices

We report the observation of well-resolved Stark-ladder structure in the interband photoconductivity spectra of ${\mathrm{Ga}}_{1\mathrm{-}\mathit{x}}$ ${\mathrm{In}}_{\mathit{x}}$As/GaAs (x=0.14) strained-layer superlattices in an axial electric field. For the type-I heavy-hole–to–electron transitions, excitonic peaks corresponding to electron-hole separations of up to two superlattice periods are resolved. The light-hole Stark ladder exhibits characteristic type-II behavior, providing strong evidence for the nature of the light-hole levels in this strained-layer system. The energies of the heavy-hole transitions are shown to be in good agreement with a theoretical model of the exciton states in a superlattice in an axial electric field. The model also gives a good qualitative understanding of the oscillator strengths of the type-I transitions and predicts successfully the behavior of additional ‘‘end-effect’’ peaks that appear in the spectra due to the finite number of periods (ten) of the superlattices investigated. Fitting to the energies of the end-effect peaks provides a sensitive measure of the superlattice miniband width.