Microcrystalline silicon deposited by the hot-wire CVD technique

Hot-wire chemical vapour deposition (HW-CVD) is a well-known technique to deposit amorphous silicon with high deposition rates from the decomposition of silane and hydrogen gases. By changing the hydrogen and silane flow rates, it is possible to observe a transition from amorphous silicon (a-Si:H) to microcrystalline silicon (μc-Si:H). In this study, structural and electrical properties of layers deposited as a function of silane concentration in the gas are presented. Ellipsometry and X-ray diffractometry have been used to assess the structure of the films. Steady-state photoconductivity, steady-state photocarrier grating, and modulated photocurrent experiments have been carried out to characterise both majority and minority carrier transport properties. Finally, the addition of phosphine and diborane in the reactor allows the deposition of n- and p-type layers with conductivities up to 10 and 1 s cm−1, respectively, making possible the realisation of HW-CVD solar cells.