Electronic Energy States of Dislocations in CdS-Type Semiconductors

Abstract

It is shown that electronic energy bands are associated with dislocations in wide-band-gap, compound semiconductors. The eigenvalue problem for the dislocation band edge is solved for CdS-type crystals, and the occupation of the band is calculated. The Fermi energy is then determined for crystals containing many deep-lying discrete levels as well as dislocation bands. It is predicted that when a crystal is illuminated with light of appropriate wavelength and increasing intensity, the thermal activation energy governing the electrical conductivity passes through a series of energy plateaus which are equal to the energy of the discrete levels. In a dislocation-free crystal, these plateaus are connected by step changes, while in a crystal with dislocations they are connected by broad transition regions. In order to study the predictions, the thermal activation energy was measured as a function of light intensity in both deformed and undeformed samples of CdS. In all cases, plateaus at 0.80±0.02 and 0.06±0.02 were observed. The transition between these plateaus was sharp in the case of the undeformed samples and broad in the case of the deformed samples. These results confirm the predictions mentioned above.