TYPE-I AND TYPE-II STARK-LADDER PHENOMENA IN GA1-XINXAS-GAAS STRAINED-LAYER SUPERLATTICES

We report the observation of well-resolved Stark-ladder structure in the interband photoconductivity spectra of Ga(1-x)In(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.