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Gap states in non crystalline selenium: roles of d efect ive structure s and impurities



  1. Department of Applied Physics, Graduate School of Engineering, Hokkaido University, Sapporo Kita ku, 060 8628, Japan


After briefly reviewing e lectr onic properties governed by gap states in amorphous and glassy Se we consider the responsible structur es through empirical and ab initio molecular orbital calculations . So far m any fundamental and application oriented studies on Se have been performed , respectively, for melt quenched glasses and evaporated amorphous films, while the atomic structur es producing gap states still remain vague. The calculation for Se clusters such as H n Se H demonstrate s that v ariations of d ihedral angle s and i nter cluster separation s bring substantial fluctuation s in the HOMO energy , which ma y cause hole traps in solid Se . The LUMO energy varies with n which suggests that long n ≥ 5) chain segments behave as electron traps. Small rings and d angling bonds create several gap states , which may work as trap s and absorption centers F or extrinsic defect s, oxygen effects have been emphasized . T he calculation demonstrate s that O atom s behave as potent isoelectronic impurities, being negatively charged , making nearest neighbor Se atoms positive Such an ionic pair can produce a deep LUMO level , which possibly work s as an a cceptor . Compens ation effects of As (and Si) into O contaminated Se are ascribed to the production of stronger As ( O bonds, which are electrically inactive due to wider HOMO LUMO gaps ..


: Amorphous, Selenium, Oxygen, Gap state, Defect, Impurity.

Submitted at: Sept. 17, 2015
Accepted at: Oct. 28, 2015


K. TANAKA, Gap states in non crystalline selenium: roles of d efect ive structure s and impurities, Journal of Optoelectronics and Advanced Materials Vol. 17, Iss. 11-12, pp. 1716-1727 (2015)