Effect of chemical annealing on the optical properties of hydrogenated amorphous silicon films

The influence of atomic hydrogen in chemical annealing of a-Si:H films on its optical parameters was studied using spectrophotometric measurements of the film transmittance and reflectance in the wavelength range 200 – 3000 nm. In this chemical annealing, the deposition of a thin layer and treatment with atomic hydrogen were repeated alternately, where both the thickness of the thin cyclic layer, dcyc, and the treatment time for each cycle, tca, were kept fixed for each sample. A series of different samples with average thickness of 0.5 μm were prepared with different dcyc and tca. It was found that the refractive index, n, and the optical energy gap, Eg, increase as the treatment time,tca, increases from 0 to 60 seconds, while at tca = 90 second both n & Eg decrease. Also, both the refractive index and the optical energy gap decrease with increasing the relative diffusion length of hydrogen, √tca/dcyc from 0.39 to 0.77. The widening of Eg is due to the structural relaxation resulting from impingement of atomic hydrogen on the growing surface. So, a good quality a-Si:H with the optical energy gap of 1.78 eV exhibiting high stability against light soaking was successfully prepared.