Transient optically induced ESR

Fig. 21. Transient optically induced ESR in undoped and doped a-Si H at 30°K, with illumination at 1.915 eV of 100 mW cm . Three components have been identified in these spectra as detailed in the text. [After Street and Biegelsen (1980a). Copyright North-Holland Publ. Co., Amsterdam, 1980.]...

The occupancy of many of these defects can be altered optically by the application of band-gap light. Three transient optically-induced ESR... 

The first observation of a metastable component to the optically induced ESR in a-Si H was reported by Street ct a/., (1981) in heavily P- and B-doped samples and in doped and compensated samples. [For a recent review of metastable, optically induced effects in a-Si H see Pankove (1982).] As near as can be determined, this metastable signal is a fraction ( 20%) of the transient optically induced response, and the dependences of the line shapes on doping appear to be similar for the two eflFects. These ESR centers can be generated with light intensities of 150 mW cm , and they anneal in a few minutes at 80 ° K. It is particularly surprising that a subset of the photoexcited electrons are trapped in band-tail states or in a Tj configuration in p-type material in which there exists a large density of holes to facilitate rapid recombination. 

Both transient and metastable changes in the ESR are observed with optical excitation by light with energy greater than the band gap. Explanations analogous to those proposed to explain the ESR in doped samples have also been suggested to account for the optically induced changes. 

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