PHOTOCURRENT AND PHOTOREFLECTANCE SPECTRA OF GAAS SAWTOOTH DOPING SUPERLATTICES

Photocurrent and photoreflectance spectra of GaAs δ-doped sawtooth superlattices of various periods are studied experimentally. Both the monotonic exponential part of the photocurrent tail below the bandgap and oscillations of the photoreflectance above the bandgap stem from the Franz-Keldysh effect in the SL built-in electric field. Regular changes of the tail as well as of the above-bandgap oscillations with decreasing SL period are explained by the strengthening of the built-in field. Impurity-related peaks are observed in the photocurrent spectra along with weaker shoulders; the latter may be tentatively attributed to optical transitions between quantum levels in the SL potential. Possible reasons for the blurring of quantum-confined optical transitions and for the impurity-related peaks are discussed. © 1991.