Mobility-edge shift during diborane doping in hydrogenated amorphous silicon and hydrogenated amorphous silicon carbide

Kelvin probe, ellipsometry and dark-conductivity measurements were made on diborane-doped hydrogenated amorphous silicon (a-Si:H) and hydrogenated amo rphous silicon carbide (a-SiC:H) films. Combining the results of the contac t potential V-k with the activation energies E-a and the optical gap E-g me asurements we reproduced the absolute Fermi level shift and the mobility ed ges evolution with doping in these two materials. The quasi-symmetrical shi ft of the band edges towards midgap is attributed to the different possible boron bonds with the amorphous network. In addition to the optical gap nar rowing, this mobility edge movement makes it possible to interpret the disp arity in the variation of E-a and V-k with doping.