Optical properties of nanocrystal-silicon thin films on silicon nanopillar arrays after thermal annealing

The optical properties of nanocrystal-silicon (nc-Si) thin films on silicon nanopillar arrays after thermal annealing treatments have been investigated in this paper. The structure was prepared by SiO2 nanosphere lithography, reactive-ion etching, conformal deposition method and thermal annealing treatment, successively. The thickness of nc-Si thin film is about 100 nm, while the diameter, period and height of silicon nanopillar arrays are about 250 nm, 500 nm and 1 μm, respectively. By reflectance and photoluminescence (PL) spectroscopy measurements in visible to near-infrared wavelength range, a minimum reflectivity of about 0.7% has been demonstrated in such a kind of structure, meanwhile, a large variation (from 12.5 times of suppression to 8.8 times of enhancement compared to the flat referential thin films) of the light emission efficiencies of the samples depending on the thermal annealing temperatures has been observed, which is due to the temperature dependent modification of optical constants of nc-Si thin films. By combining the nc-Si with silicon nanopillar array, the structure will be very promising for the design of radial p–i–n junction solar cell devices.