Isomerization effect in a-SI: H

Abstract

It is well known that the hydrogenated amorphous silicon (a-Si: H) prepared from SiH₄ gas in a UHV (ultra high vacuum) system nonessentially contains carbon(C) nitrogen (N) and oxygen (O) atoms of about 10¹⁷, 10¹⁶ and 10¹⁸cm^-3, respectively. The electron negativity of C, N and O is 2.5, 3.0 and 3.5, respectively and these values are larger than that of Si, 1.8 and H, 2.1. Therefor, it is expected that the created Si⁺-O^---H⁺, Si⁺-O^---Si⁺ and Si⁺-H^- bond behave as like as ionic like bond. If a negatively (or positively) charged Si atom, T₃- (or T₃⁺) exists vicinity of the H⁺ (or H^-), the H⁺ (or H^-) forms hydrogen bond with the T₃- (or T₃⁺). The density of dangling bonds T₃ defects is 10¹⁴N-10¹⁵cm^-3 in a-Si: H. These ionic like bond and hydrogen-bond make electric dipoles and that creates electronic potential and may act like as a carrier trap, a recombination center and scattering center which strongly affect carrier mobility. In this paper, especially we will discuss a trapping effect due to the ionic like bond and hydrogen bond which is with an isomerization effect of Si⁺-O^---Si⁺ and Si⁺-O^---H⁺ configurations.