Long-term relaxation of the photovoltage in a heteroepitaxial structure

Abstract

The distribution of the transverse photovoltage has been investigated in samples of a Ge-GaAs heterostructure with an oxide layer (∼15 Å) at the interface. A method of simultaneous excitation with modulated and unmodulated radiation is used to observe the long-term relaxation of the photovoltage in these heterostructures. The energy barriers responsible for this effect are localized at the surface of the Ge 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 substrate. It is noted that the photoconductivity signal observed at the modulation 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.