Photoconductivity and <i>n</i>- to <i>p</i>-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 1.4×1012 and 8.8×1013 cm−2, as functions of temperature. In all samples, the planar-doped region is placed 0.2 μm 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.

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