Origin of saturated light-induced defect density in hydrogenated amorphous silicon

초록

The saturation of light-induced defect density in hydrogenated amorphous silicon (a-Si:H) has been studied as a function of various material parameters, such as initial defect density N<inf>init</inf>, Urbach energy E<inf>u</inf>, hydrogen content c<inf>H</inf>, hydrogenated void fraction R, and deposition-induced annealable defect density ΔN<inf>ann</inf>. These parameters were varied by depositing samples at various substrate temperatures or by postgrowth anneals of samples grown at low substrate temperatures. It is found that total defect density of saturated light-soaked state N<inf>sat</inf> is well correlated with the N<inf>init</inf>, E<inf>u</inf>, c<inf>H</inf>, R, and ΔN<inf>ann</inf> in the as-grown states but no correlations between N<inf>sat</inf> and parameters other than the N<inf>init</inf>, E<inf>u</inf>, and ΔN<inf>ann</inf> in the annealed states are found. It is also observed that annealing before light soaking reduces the N<inf>sat</inf> substantially. In particular, it is found that the value of N<inf>sat</inf> from the fully annealed state is much lower than that from the as-grown state with similar N<inf>init</inf> and E<inf>u</inf>. A possible parameter that plays a primary role in the saturation of light-induced defects is discussed.