Saturation behavior of the light-induced defect density in hydrogenated amorphous silicon [solar cells]

The light-induced generation of defects in a-Si:H(F) was saturated by a few hours of illumination with Kr-ion-laser light soaking (λ=647.1 nm) near room temperature. The time to reach saturation scales roughly with 1/G², but the saturation value is essentially independent of the illumination intensity. Therefore, the saturation is not due to thermal annealing. The saturation values of the light-induced defect density in 37 a-Si:H(F) samples which had been grown in six different reactors over a range of conditions were measured. These a-Si:H(F) samples have annealed-state defect densities in the range of 1.1×10¹⁵ to 1.6×10¹⁶ cm^-3, Urbach energies of 42-62 meV, and Tauc optical bandgaps of 1.61 to 1.83 eV. The saturation value rises from 5×10¹⁶ to 2×10¹⁷ cm^-3 with increasing optical gap and total hydrogen content, but it is not correlated with the Urbach energy or with the annealed-state defect density