Band gap narrowing in zinc oxide-based semiconductor thin films

摘要

A simple expression is proposed for the band gap narrowing (or shrinkage) in semiconductors using optical absorption measurements of spin coated 1 at. % Ga-doped ZnO (with additional 0-1.5 at. % zinc species) thin films as ΔE_(BGN) = Bn~(1/3) [1 -(nc)~(1/3)], where B is the fitting parameter, n is carrier concentration, and n_e is the critical density required for shrinkage onset. Its uniqueness lies in not only describing variation of ΔE_(BGN) correctly but also allowing deduction of n_e automatically for several M-doped ZnO (M: Ga, Al, In, B, Mo) systems. The physical significance of the term [1 - (n_e)~(1/3)] is discussed in terms of carrier separation.