PHOTOCONDUCTIVITY AND N-TYPE TO P-TYPE TRANSITION IN SILICON PLANAR-DOPED GAAS STRUCTURES WITH A DOPED CAP LAYER

Photoconductivity, photo-Hall free carrier concentrations and mobilities were measured on molecular beam epitaxy-grown silicon planar-doped GaAs samples, with silicon concentrations between 1.4 x 10(12) and 8.8 x 10(13) cm(-2), as functions of temperature. In all samples, the planar-doped region is placed 0.2 mu m below a n(+)-doped cap layer at the surface. We perform a systematic investigation of the persistent as well as nonpersistent photoconductivity effects which are present in all samples. A phenomenological analysis shows the presence of two distinct conduction channels, one with n characteristics and the other with p characteristics. These channels can present either bulk or two-dimensional characteristics, depending on the light intensity and on the temperature. A model based on spatial separation between electrons and holes is proposed to account for the persistence of the photoconductivity effect. (C) 1995 American Institute of Physics.