Effect of a deep electron trap with strong lattice relaxation and of interface states on the C super(-2) = f(V) characteristic of Au-CdS Schottky diodes

• Published in: Journal of crystal growth 1982-01, Vol.59 (1-2), p.246-253
• Main Authors: Housin, M, Fialin, M, Bastide, G, Sagnes, G, Rouzeyre, M
• Format: Article
• Language: English
• ISSN: 0022-0248

The occurrence of strong lattice relaxation during the electron capture at a bulk deep localised defect in CdS is demonstrated by TSCAP, DLTS and DLOS experiments. The authors measure its apparent thermal activation energy E sub(a) = 0.925 eV and its capture cross section S sub(a) - 5 x 10 super(-15) cm super(2) as well as its photoionization cross section sigma sub(n) super(0) and its optical ionization energy E sub(n) super(0) = 2.5 eV. An interpretation is given in a one dimensional configuration coordinate diagram on the basis of a large relaxation. The volume density of this trap, hereafter named X centre, in undoped CdS samples is usually larger than the free electron density and its state of charge has a drastic influence on the C super(-2) f(V) characteristic of the Schottky diodes. The inefficiency of the electron capture at low temperatures gives rise to large persistant photocapacitance effects. In addition the role of interface states in Au-CdS diodes, which exhibit either a non-linear C super(-2) = f(V) characteristic, or an abnormally large threshold value, V sub(0), is directly demonstrated by the fact that these interface states are detected by DLTS and that they can be eliminated by a thermal treatment of the crystal surface.