Intrinsic microcrystalline silicon (mu c-Si : H) deposited by VHF-GD (veryhigh frequency-glow discharge): a new material for photovoltaics and optoelectronics

The development of mu c-Si:H technology and the introduction of intrinsic [ i] mu c-Si:H as photovotaically active material is retraced. Special emphas is is laid on the use of very high frequency glow discharge as a particular ly propitious deposition method for mu c-Si:H. Thereby, the use of a gas pu rifier to reduce oxygen content and obtain intrinsic layers with 'midgap' c haracter is described. Recent results obtained with single-junction mu c-Si :H solar cells and a-Si:H/mu c-Si:H tandem solar cells are given. The analy sis of carrier collection in single-junction mu c-Si:H solar cells is under taken with the variable intensity measurements method. It yields effective mobility x lifetime (mu tau)(eff) products for the i-layer in p-i-n and n-i -p solar cells in the range 10(-7)-10(-6) cm(2) V-1. Similar values have be en found for mu c-products in individual layers based on photoconductivity and ambipolar diffusion length measurements. Transmission electron microsco py images for mu c-Si:H layers are given. They display a complex microstruc ture not suspected before. On the other hand, atomic force microscopy data reveal a pronounced surface roughness that correlates well with the optical light scattering and with the pronounced enhancement of the apparent optic al absorption coefficient, in the 1-2 eV region, as already observed before . (C) 2000 Elsevier Science S.A. All rights reserved.