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The Origin of Midgap States Revisited

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Large-Scale Simulations of a-Si:H: The Origin of Midgap States Revisited

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P. A. Khomyakov, W. Andreoni, N. D. Afify, A. Curioni

Phys. Rev. Lett. 107, 255502 (2011)



The above figure shows a-Si network (transparent grey) with strained (cyan) and highly-strained bonds (red); hole localization (spinden) around highly-strained bonds is given with isosurface.




Large-scale classical and quantum simulations are used to generate a-Si:H structures. The bond-resolved density of the occupied electron states discloses the nature of microscopic defects responsible for levels in the gap. Highly strained bonds give rise to band tails and midgap states. The latter originate mainly from stretched bonds, in addition to dangling bonds, and can act as hole traps. This study provides strong evidence for photoinduced degradation (Staebler-Wronski effect) driven by strain, thus supporting recent work on a-Si, and sheds light on the role of hydrogen.

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