Effect of thermal annealing and hydrogen-plasma treatment in boron-doped microcrystalline silicon

Abstract

We have investigated the effects of temperature (during film growth and post-deposition thermal annealing) and H2-plasma treatment on the electronic and structural properties of p-type microcrystalline silicon films (p-μc-Si:H) for solar cell applications. The highest dark conductivity is obtained in the thermally annealed p-μc-Si:H prepared at low substrate temperature of 50°C. This dark conductivity is decreased by two orders of magnitude when the film is exposed to H2-plasma, being completely restored after thermal annealing. Namely, reversible dual-conductivity cycle is observed between thermally annealed state and H2-plasma-treated state in p-μc-Si:H. The dual-conductivity cycle is accompanied with the reversible change in the infrared-absorption spectrum at around 1845cm−1 assigned as SiHB complex in p-μc-Si:H network structure. Taking into account of the reversible structural change by H2-plasma-exposure and thermal-annealing cycles, necessary process-procedure condition has been proposed for obtaining high photovoltaic performance in thin-film-Si solar cells with high quality p-μc-Si:H.