In-situ study of the optoelectronic properties of very thin p-type μc-Si:H films and the potential profile at the p-(μc-Si:H)/i-(a-Si:H) interface

In-situ UV-visible ellipsometry and Kelvin probe measurements were performed to study the growth of boron-doped microcrystalline silicon (μc-Si:H) thin films and the band profiling at the p-(μc-Si:H)/i-(a-Si:H) interface. The in-situ UV-visible spectroscopic ellipsometry measurements, combined with dark conductivity measurements, performed at different stages of the growth show that p-type μc-Si:H formation can be achieved for a film thickness below 10 nm. These analyses also reveal that both the optical absorption, and the dark conductivity do not change significantly for a crystalline volume fraction above 50%. Moreover, the contact potential as measured by in-situ Kelvin probe shows a saturation just after the percolation threshold. These results indicate that highly crystallized doped layers are not necessary in device applications. From the Kelvin probe measurements, the potential profile through the p-(μc-Si:H)/i-(a-Si:H) interface was measured. The microcrystalline silicon p-layers were successfully incorporated in single junction solar cells.