Effect of Deposition-Induced Annealable Defects on Light- Induced Defect Generation in a-Si:H
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EFFECT OF DEPOSITION-INDUCED ANNEALABLE DEFECTS ON LIGHTINDUCED DEFECT GENERATION IN a-Si:H JONG-HWAN YOON Department of Physics, College of Natural Science, Kangwon National University, Chunchon, Kangwon-Do 200-701, Korea ABSTRACT In this paper we present a method to determine the annealable defect density(ANann) present in hydrogenated amorphous silicon(a-Si:H). The effects of the annealable defects on the lightinduced defect generation rate, saturated defect density (Nsat) and the change of defect density in the light-induced saturated state(ANsat) have been studied. Annealable defect density was varied by depositing samples at various substrate temperatures or by post-growth anneals of samples grown at low substrate temperatures. It is found that the generation rate, Nsat and ANsat are well correlated with ANann. In particular, the ANsat is found to follow a relation ANsat --ANann. These results suggest that defect-related microscopic models are appropriate for light-induced metastability. INTRODUCTION It is well known that light-induced metastability occurs in all types of a-Si:H and its alloys. Therefore, it is not only important for technological applications of a-Si:H but also of scientific interest. Since it was discovered by Staebler-Wronski in 1977(S-W effect)[1], various models
for the S-W effect have been proposed. In order to establish a model for the metastability, a particular macroscopic material parameter is introduced into it. Hydrogen and weak Si-Si bond are very important parameters in the hydrogen-induced weak Si-Si bond breaking model[2,3]. Deposition-induced charged defects are also necessary for the charge-trapping model[4,5]. In addition, we can also consider the material parameters, such as hydrogenated microvoids[6], floating bonds[7], as a parameter primarily responsible for light-induced effect. However, it is still unclear what kind of parameter plays the primary role in the metastable defect creation and annealing process. Recent study[8] has shown that the concentration of light-induced defects may be saturated within a few hours by using high-intensity laser light. The saturation effect can provide a more reliable means for the inferring of information about a parameter primarily responsible for light-induced effect, provided that the saturation of the light-induced defect concentration may arise from a small concentration of precursors responsible for defect generation. The finding of a dominant precursor involving in the metastable defect generation should help us to understand the microscopic mechanism for the S-W effect. In this work we present a method to determine the annealable defect density present in the film, and have investigated the effect of annealable defect density on the light-induced effect. Mat. Res. Soc. Symp. Proc. Vol. 297. ©1993 Materials Research Society
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EXPERIMENTAL The a-Si:H films used in this study were prepared from pure SiH 4 gas in a dc-triode glow discharge reactor, which has never been exposed to doping gases. The deposition was carried out
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