Amorphous silicon-germanium alloy multilayers for solar cells

The perpendicular transport of electrons and holes in a-Si:H,F/a-SiGe:H,F multilayers is reported. Particular emphasis is placed on a-SiGe:H,F layers with low (E_opt<1.4 eV) gaps. The transport properties include the photoconductivity, the time-of-flight ( mu tau ) for electrons, and the DC mu tau for holes. The basic multilayer material reflects the transport properties of the barrier and well materials, modified by quantum confinement, and thermionic emission over or tunneling through the barriers. At short (d_Gamma Gamma >or approximately=300 AA) periods, the transport properties are improved beyond the baseline values. At short periods the transport properties are improved above the first-order behavior by a reduction in the density of recombination centers. At long periods the transport properties are improved by an effect whose nature is not understood at present.