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An uncommon electron spin resonance technique is used to show that a universal distribution of residual carriers exists in tetrahedrally coordinated amorphous semiconductors following optical excitation at low temperatures. This universal behavior at long decay times results because statistical fluctuations in the electron and hole densities cannot occur and therefore do not affect the kinetics. This behavior is confirmed for carrier densities between 10(16) and 10(17) cm (-3) and decay times as long as 10(4) s.

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In hydrogenated amorphous silicon the kinetics of the optically induced production and thermal annealing of silicon dangling bonds have been measured at temperatures between 25 and 480 K using electron spin resonance ͑ESR͒. Below about 150 K the measurement of optically induced silicon dangling bonds is masked by long-lived, band-tail carriers that accumulate with time t as t 1/3 . It is known that these long-lived carriers can be quenched by infrared light. However, optically, it is not possible to completely remove them. The production rate for optically induced silicon dangling bonds decreases with decreasing temperature. Below about 100 K degradation is at most half as efficient as at room temperature and is nearly temperature independent below approximately 100 K. Additionally, defects created by 10 h of irradiation below 100 K almost entirely anneal at TХ300 K. It is common procedure to anneal a-Si:H samples for 30 min at 175°C to restore the as-deposited defect density. However, by repeatedly performing degradation and annealing cycles we find that a small fraction of defects is not restored by annealing at 175°C and that these defects slowly accumulate with degradation. For defects created at all temperatures we find the same ESR fingerprint, indicating that only one dominant type of defect is created, presumably the silicon dangling bond, and we conclude that different, temperature-dependent stabilization processes must exist. These results lead to new constraints for models that attempt to explain the Staebler-Wronski effect.