Doped Microcrystalline Silicon Layers for Solar Cells by 13.56MHz Plasma-enhanced Chemical Vapour Deposition

Doped hydrogenated microcrystalline silicon thin films play a critical role in multi-junction thin-film silicon solar cells, because their crystallinity has a large influence on the properties of intrinsic microcrystalline silicon absorber layers grown on them. The doping efficiency of the doped layers depends strongly on their crystallinity and hence a high-crystallinity doped layer is desired. In this study, highly crystalline doped microcrystalline silicon films are formed on 300 mm × 400 mm glass substrates using a conventional parallel-plate PECVD reactor operated at 13.56 MHz. Raman spectroscopy is used to analyse the crystallinity of the films. The conductivity of the films is measured using the co-planar electrode method. The effects of the deposition parameters on the Raman crystallinity and conductivity of the doped films are investigated. The RF power is found to play a key role for achieving a high crystallinity in the doped layers, whereby a high crystallinity can only be obtained within a narrow RF power range. The influence of the RF power on the lateral thickness uniformity of the deposited films is also examined. It is found that the RF power has a strong influence on the lateral uniformity of the deposited films, with intermediate power giving the best thickness uniformity.