Change of spin-lattice relaxation time with light soaking for defects in hydrogenated amorphous silicon

The spin-lattice ralaxation time (T-t) for high-quality hydrogenated amorphous silicon is measured using a saturation method. T-t for neutral Si dangling bonds (D-0) at 77 K is found to increase rapidly with increasing light-soaking time and then tends to saturate. This behavior is quite different from that of D-0 increase, but is similar to that of the increase in the Urbach energy which reflects the randomness of the amorphous network structure. T-1's for three components of the light-induced ESR (LESR) are also measured at 77 K. It is found that T-1's for both broad and narrow components decrease with light soaking. The film-thickness dependence and the change caused by thermal quenching are also investigated for T-1 of D-0 centers. These results show that the change of T-1 of D-0 centers is not directly related to the density of DO but closely related to the global network structure.