Carrier diffusion in microcrystalline silicon studied by the picosecond laser induced grating technique

We report on the picosecond laser induced grating technique applied to hydrogenated microcrystalline silicon (μc-Si:H) and aimed at studying the photocarrier diffusion coefficient D. We have studied a series of three samples having a distinctly different content of the crystalline phase, and the microstructure and morphology of which are known in detail. Our results show that the coefficient D scales with the degree of crystallinity of the samples, reaching values up to D=9 cm2 s−1 close to crystalline silicon. The obtained carrier lifetime (≈1 ns) is constant in all measured samples. The extracted diffusion lengths are much greater than the dimensions of the microcrystalline grains in the samples. We conclude that small grain boundaries do not limit substantially the carrier diffusion length in microcrystalline silicon.