Carrier transport mechanism in the SnO2:F/p-type a-Si:H heterojunction

We characterize SnO2:F/p-type a-Si:H/Mo structures by current-voltage (I-V) and capacitance-voltage (C-V) measurements at different temperatures to determine the transport mechanism in the SnO2:F/p-type a-Si:H heterojunction. The experimental I-V curves of these structures, almost symmetric around the origin, are ohmic for |V|< 0.1 V and have a super-linear behavior (power law) for |V|> 0.1 V. The structure can be modeled as two diodes back to back connected so that the main current transport mechanisms are due to the reverse current of the diodes. To explain the measured C-V curves, the capacitance of the heterostructure is modeled as the series connection of the depletion capacitances of the two back to back connected SnO2:F/p-type a-Si:H and Mo/p-type a-Si:H junctions. We simulated the reverse I-V curves of the SnO2:F/p-type a-Si:H heterojunction at different temperatures by using the simulation software SCAPS 2.9.03. In the model the main transport mechanism is generation of holes enhanced by tunneling by acceptor-type interface defects with a trap energy of 0.4 eV above the valence bandedge of the p-type a-Si:H layer and with a density of 4.0 10^13 cm^-2. By using I-V simulations and the proposed C-V model the built-in potential (Vbi) of the SnO2:F/p-type a-Si:H (0.16 V) and p-type a-Si:H/Mo (0.14 V) heterojunctions are extracted and a band diagram of the characterized structure is proposed.