a-Si/a-SiC superlattice-structure films fabricated by a photo-CVD method were investigated as a wide-bandgap material and applied to window layers of a-Si solar cells. As for carrier transport properties vertical to the interfaces in the dark, I-V characteristics based on tunneling emission and Frenkel-Poole emission were observed with low and high bias voltage regions, respectively. Under illumination of AM-1, 100 mW/cm2, ohmic emission was observed in the same bias voltage region. As for device characteristics, a p/i/n a-Si solar cell whose p-layer was a superlattice-structure was studied. A remarkable increase in the collection efficiency of the cell was found, and it is explained by a calculation by assuming that the superlattice-structure p-layer is an active photogenerating layer. To confirm this, a superlattice-structure p/n diode was fabricated, and it was found that the peak value of the collection efficiency of the diode was five times greater than that of a conventional p/n diode. A conversion efficiency of 11.2% was obtained for a glass/TCO/p-superlattice-structure/i/n/metal a-Si solar cell with p-type doping gas of B(CH3)3.