PERPENDICULAR TRANSPORT IN A-SI-H/A-SINX-H SINGLE-BARRIER AND DOUBLE-BARRIER STRUCTURES

Current bumps in the current-voltage characteristics of amorphous semiconductor double-barrier structures have previously been associated with a resonant-tunneling process through quantized levels in the well region of the structure. We investigate the perpendicular transport through single- (SB) and double-barrier (DB) structures of hydrogenated amorphous silicon (a-Si:H) and hydrogenated amorphous silicon nitride (a-SiNx:H) grown by glow discharge. The current-voltage characteristics of these structures are studied at 295 and 77 K. Current bumps are observed in the I-V characteristics of both SB and DB structures, which suggests a different transport mechanism than previously proposed. We propose that the first current bump is simply a transition from a low-field (space-charge-limited) transport mechanism to a high-field (multiple-hopping) transport mechanism. The additional bumps are associated with the energy dependence of the density of localized states in the a-SiNx:H and a-Si:H.