Relationships between structure, spin density and electronic transport in `solar-grade' microcrystalline silicon films

Abstract Microcrystalline silicon (μc-Si:H) sfilms produced by very high frequency (95 MHz) plasma enhanced chemical vapour deposition (VHF-PECVD) under deposition conditions used to obtain best solar cells are investigated. The relationship between structure, spin density and conductivity is studied for films deposited under different silane–hydrogen gas compositions and different substrate temperatures. The transition from microcrystalline to amorphous structure induced by the increase in silane concentration is clearly reflected in the spin and transport properties. Within the microcrystalline growth regime, both the spin density and the conductivity show the lowest values close to the transition to amorphous growth, i.e. for material which shows the best performance in solar cells. Also with variation of the substrate temperature a clear correlation between the spin density and maximum solar cell efficiency is found with an optimum temperature of 250 °C.