LONG-TERM RELAXATION OF THE PHOTOVOLTAGE IN A HETEROEPITAXIAL STRUCTURE

The distribution of the transverse photovoltage has been investigated in samples of a. Ge-GaAs heterostructure with an oxide layer (similar to 15 Angstrom) at the interface. A method of simultaneous excitation with modulated and unmodulated radiation is used to observe the long-t erm relaxation of the photovoltage in these heterostructures. The ener gy barriers responsible for this effect are localized at the surface o f the Ce film and the GaAs substrate, adjacent to the interlying oxide . It is shown that the gradients of the dark carrier concentration in the film and in the substrate are in opposite directions. A transition layer is formed during the growth process and not as a result of the classical heterodiffusion of the components in the film and the substr ate. It is noted that the photoconductivity signal observed at the mod ulation frequency in the field formed at the sample as a result of the unmmodulated illumination must be taken into account in the recorded voltage signal. (C) 1997 American Institute of Physics. [S1063-7850(97 )00706-4].