Recovery Process of Light-Induced Spins in Hydrogenated Amorphous Silicon-Nitrogen Alloy Films
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JINYAN ZHANG, QING ZHANG, MINORU KUMEDA and TATSUO SHIMIZU Faculty of Engineering, Kanazawa University, Kanazawa 920, Japan ABSTRACT The influences of sub-gap illumination and thermal annealing on the light-induced neutral dangling bonds(DB's) created in the fast process (FDB's) and those created in the slow process (SDB's) are prominently different in Si-rich a-Si,.xN. :H. The results of photobleaching show that the sub-gap illumination annihilates FDB's, more effectively at 77 K, whereas it appears not to affect SDB's, suggesting that FDB's are produced by a carrier capture at preexisting charged DB's. The annealing behaviors for both FDB's and SDB's are in agreement with the monomolecular kinetics. The attempt-to-anneal frequency, 1)o, is _.103 Hz for FDB's and -107 Hz for SDB's. Annealing-time dependence of the density of light-induced spins at various annealing temperatures can be fit with a distribution of annealing activation energies. In addition, clearly separated peaks of the distribution of annealing activation energies related to FDB's and SDB's are observed. A comparison indicates that SDB's have a nature similar to the lightinduced metastable spins in a-Si:H, which are likely to be produced by a creation of new defects. INTRODUCTION Light-induced degradation of the properties in hydrogenated amorphous silicon (a-Si:H) and a-Si based materials is a key issue for their applications. In spite of the extensive investigations on the microscopic mechanism of the light-induced defects in recent years, it is still controversial about the nature and the microscopic origin of the creation of these defects. It is known that the origin of the light-induced DB's in N-rich a-Si1 ..N.:H alloy films is related to a carrier capture[l4]. In Si-rich a-Si1 -xN.:H alloy films, however, two creation-processes are observed under strong band-gap illumination [5-7]. It is proposed that the two creation-processes arise from different mechanisms: namely, the fast and slow processes correspond to a photoexcited-carrier capture at preexisting charged DB's and a breaking of weak Si-Si bonds, respectively[51. In order to clarify the microscopic origins of the light-induced spins arising from neutral DB's in the two creation processes, the influences of sub-gap illumination and thermal annealing on the light-induced spins created by strong band-gap illumination for various illumination times(ti) at room temperature (RT) are investigated. We obtain the, distributions of annealing activation energies for FDB's and SDB's by analyzing the annealing behavior of the lightinduced spins. Our results demonstrate unambiguous difference in the nature between FDB's and SDB's, supporting that the FDB's and SDB's are related to two different origins. The relevant creation mechanisms for FDB's and SDB's are discussed in the text. EXPERIMENTAL a-Si1 .,Nx:H films were deposited on fused-quartz substrates at a substrate temperature of 350 9C and at a pressure of 76 mTorr. A mixture of undiluted SiH 4 and NH 3 gasses was used as a decomposition source
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