Photocurrent and photovoltage spectroscopy of amorphous silicon nanoclusters

Photoelectric properties (photocurrent efficiency and photovoltage) of the silicon suboxide films containing amorphous silicon nanoclusters were investigated in the spectral range of 300–1100 nm. A strongly pronounced increase of the photocurrent efficiency of the sandwich-like structures with such films on c-Si substrates was observed in the short-wavelength region. The possible mechanisms of the increase were discussed, and carrier multiplication due to impact ionization of the defect states was considered to be the most probable. Impact ionization of the defect states involves two main steps: (i) trapping of the photogenerated electron in a defect state, and (ii) impact ionization of this state by another photoexcited electron that has got sufficient energy due to absorption of a high-energy photon.

► The structures of amorphous silicon nanoclusters embedded in α-SiOx were studied.
► The structures reveal significant photoresponse in the 300–500 nm region.
► Increase of the efficiency was observed in the short-wavelength region.
► The increase is ascribed to the impact ionization of the traps in the ncl-Si bandgap.