Capacitance Studies of Metastable States in Light-Soaked, Quench-Cooled, and Bias-Annealed N-Type Hydrogenated Amorphous Silicon

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Abstract
We have investigated the metastable states produced in n-type a-Si:H samples by 3 kinds of treatments: light soaking followed by partial annealing, fast (quench) cooling, and bias-annealing. We employed voltage pulse photocapacitance to examine the deep defect state distribution, ND, and drive level capacitance profiling to determine the occupied conduction bandtail states NBT. Our results indicate that: (1) Although the most heavily doped films exhibit a larger increase in ND with light soaking than the corresponding decrease in NBT (consistent with some proposed defect creation reactions), in more lightly doped films we observe significant changes in NBT for much smaller corresponding differences in ND; (2) for quench cooling we observe increases by factors of up to over 2 in NBT without any measurable changes in ND for all samples; and (3) we observe increased NBT in bias annealed samples with no changes in ND. All of these results are inconsistent with a purely silicon bond breaking mechanism for metastable defect creation. We consider a significant contribution from a dopant activation mechanism which does not involve changes in ND).