The Optical Band Gap Problem in Amorphous Semiconductors A Perspective

摘要

In contrast to crystalline semiconductors the physical meaning of the optical energy gap (E_opt) in amorphous semiconductors is still a great problem. The conventional models for the interpretation of this most important parameter in solar - cell design are briefly reviewed. A new and useful perspetive in showing more cleary the complexity of this problem is suggested in this paper. The analysis of the (implied by)_2 (imaginary part of the dielectric function) vs. hw data through its derivative (implied by)_2 behavior, has shown that the deposition conditions of amorphous Si&Ge thin films are quite important, such that films prepared in the same vacuum system showed the same (implied by)_2 vs. hw behavior for the same material, while the change in preparation system severly complicates the matter, so that even the proposed solution fo the problem through the accurate experimental determination of the density of states and the matrix element of transition of a typical sample, may not be helpful for other samples of the same material prepared in different deposition systems, even if they show, for example, the same Tauc plot behavior.