Microdoping compensation of microcrystalline silicon obtained by hot-wire chemical vapour deposition

Undoped hydrogenated microcrystalline silicon was obtained by hot-wire chemical vapour deposition at different silane-to-hydrogen ratios and low temperature (<300°C). As well as technological aspects of the deposition process, we report structural, optical and electrical characterisations of the samples that were used as the active layer for preliminary p–i–n solar cells. Raman spectroscopy indicates that changing the hydrogen dilution can vary the crystalline fraction. From electrical measurements an unwanted n-type character is deduced for this undoped material. This effect could be due to a contaminant, probably oxygen, which is also observed in capacitance–voltage measurements on Schottky structures. The negative effect of contaminants on the device was dramatic and a compensated p–i–n structure was also deposited to enhance the cell performance.