Doping and the Density of States of Amorphous Silicon

Abstract

In the preceding article, Professor Spear has given a brief historical survey of the work that led to the successful doping of a-Si and to the present interest in its application in solar cells, high current diodes, liquid crystal displays, etc., and has discussed a number of fundamental topics of current interest. In this article the methods that have been used to dope a-Si are described. The main reason why a-Si can be doped is its low density of gap states. Probably the most complete information on the density of states function g(ε) comes from the extensive field effect measurements of the Dundee group. Recently a number of papers have raised doubts about the analysis used to calculate g(ε). We therefore review the results of bulk measurements that provide support or otherwise for the features of g(ε) determined from the field effect experiments. Finally the experimental approach used in the field effect experiments has been applied in the development of an insulated-gate field-effect transistor and we briefly review the present stage of this work.