INFRARED PHOTOCONDUCTIVITY AND LUMINESCENCE OF QUANTUM-WELLS IN MULTILAYER GAAS ALGAAS HETEROSTRUCTURES/

The spectra of the photoconductivity, which is attributable to optical transitions from localized states in GaAs/AlGaAs quantum wells to sta tes in the continuum, have been compared with the cathodoluminescence spectra. The quantum-well structures were made by the MOCVD hydride ep itaxy method. The thickness of the films is in the range 3-6 nm for Ga As and 30-50 nm for AlxGa1-xAs (x=0.28-0.35); the number of periods is up to 70. The photoconductivity spectra with a maximum at wavelengths of 8-10 mum has features which can be explained by assuming the impor tance of the excitation of electrons from the first quantum-size level s in the wells and from the levels of donors or density-of-states tail s in these wells. The main maxima in the luminescence spectra of the s tructures correspond to radiative recombination of electrons at donors with holes in quantum wells. The activation energy of the dark curren t of photodetectors observed at low voltages in the temperature range 40-90 K corresponds to the photoexcitation threshold and amounts to ap proximately 0.12 eV. The responsivity is 0.8 A/W for mesa-structure ph otodetectors which are 200 mum in diameter.1)