We have used a cascaded-arc expanding thermal plasma (ETP) to produce thin films of amorphous silicon at high growth rates (> 3 nm/s). Here, we present a study of the effect on material properties of hydrogen injection in the nozzle, i.e., at the exit of the arc where the plasma expands into the reactor chamber. The advantage of using extra H2 in the nozzle is that the plasma chemistry and pressure in the arc remain unchanged, whilst higher growth rates and a material with low defect densities can be obtained.
We observe that with an increase of substrate temperature the growth rate decreases due to densification of the material. This densification is accompanied by a reduction of the hydrogen content and of the microstructure parameter. Further we observe that hydrogen content decreases with higher growth rate. A strong relation is found between the light conductivity and the microstructure parameter indicating a large void fraction in samples grown at low temperature.
We have been able to grow a-Si:H material, with H2 in the nozzle, at 350°C and 3 nm/s with a light conductivity of 1.2 × 10−5 Ω1cm−1, which can be suitable for solar-cell application.