Effect of the Structural Change of Hydrogenated Microcrystalline Silicon Thin Films Prepared by Hot-Wire Chemical Vapor Deposition

Abstract

Hydrogenated microcrystalline silicon (µc-Si:H) thin films and solar cells were prepared by the hot-wire chemical vapor deposition (HWCVD) with various hydrogen dilution conditions. The surface of the film was observed by scanning electron microscopy (SEM) and the atomic force microscopy (AFM). From the observation, we observed that the films deposited at lower hydrogen dilution ratios [films with lower crystalline volume fractions (XC)] had rough surfaces with large crystalline aggregations with diameters larger than 100 nm. Conversely, the films deposited at higher hydrogen dilution ratios (films with higher XC) had almost smooth surface with smaller aggregations. In other words, the number of boundaries between crystalline aggregations increased with hydrogen dilution ratio. These structural changes agreed with the results of the spin density and ambipolar diffusion length measurements, which showed a tendency to deteriorate with the higher XC. The performance of the fabricated solar cells showed a similar change with hydrogen dilution ratio, i.e., a lower hydrogen dilution ratio resulted in a higher quality device. However, too low a hydrogen dilution ratio resulted in the degradation of the solar cell performance originating from the amorphous incubation layer grown at the p–i interface.