IMPERFECT AMORPHOUS SOLID AND BIPOLARONIC GROUND-STATE

Publisher Website
Google Scholar
Abstract
It is generally considered that the Polk-model of an infinite random network of perfectly bonded amorphous solid does not explain the "real" amorphous silicon which contains dangling bonds, vacancies, voids and fine scale inhomogeneities. The question naturally arises as to the nature of the predominant defect in α-Si that would explain possible Fermi-level pinning and the recombination characteristics. Presuming an isolated dangling bond (T03) to be such a defect, Adler-Elliott have postulated negative U centers on such defects to explain Fermi-level pinning and other properties. Recent experiments as well as detailed calculations do not however support the existence of negative U in α-silicon. In this communication I like to point out that basic defect "unit" is not an isolated dangling bond, but a dangling bond cluster of which the simplest unit is a vacancy center V02 that has only two near-neighbours i.e. a center with two dangling bonds that can locally deform to give bonding. This stable bonded V02 center is a bipolaron and provides all the ingredients to understand a variety of two-electron states phenomena in α-Si. The neutral centers will be deep in the gap. The two related charge states V+2 and V-2 with respectively one and three electrons will also be gap states and are responsible for light induced e.s.r. signal. The V02 centers can trap two hydrogen atoms to give (SiH)2 complexes in contrast to Si-H bonds. A doubly ionised V02 center (V++2) can trap two electrons to go into a metastable He-like configuration and can explain Staebler-Wronski effect. α-Si in general will contain both V02 centers as well as isolated dangling bonds (T03) whose mutual interaction can explain a variety of radiative and non-radiative phenomena. The neutral centers will tend to empty nearby T03 centers, will cause light-induced e.s.r. quenching of the T03 centers. They will be also responsible for Staebler-Wronski effect as well as for quenching of luminescence and photoconductivity

This publication has 0 references indexed in Scilit: