Experimental and calculated atomic displacement threshold energies for binary semiconductors

Abstract

A theory for the production of atomic displacements in binary solids by mono-energetic electrons has been developed to yield an expression which may be numerically integrated to give the number of atomic displacements produced at a particular incident electron energy. The theory is applicable to thick samples and for incident electron energies up to the secondary displacement threshold. The variation with incident electron energy of the computed numbers of displaced primary atoms for various displacement threshold energies has been correlated with experimentally induced and determined point defect concentrations and used to give a precise value of the threshold energy for a primary atomic displacement. The atomic displacements were produced by the use of mono-energetic electrons from a 100 to 400 keV Van de Graaff accelerator. The production of point defects was observed experimentally and evaluated quantitatively by photoluminescence or cathodoluminescence techniques. Displacement of tellurium in cadmium telluride was monitored using corresponding changes in the photoluminescence intensity of the 1.13 μ m emission band. No radiation annealing was observed to take place at the electron doses used and a displacement threshold energy of 7.9 ± 0.1 eV was determined for tellurium. Displacement of sulphur in cadmium sulphide was monitored using the changes in the cathodoluminescence intensity of the 1.02 μ m emission band. In this case radiation annealing occurred to such an extent that a phenomenological theory, described here, had to be developed to correct for it. A sulphur displacement threshold energy of 9.6 ± 0.1 eV was determined. In conclusion, it should be stated that direct techniques such as photoluminescence or cathodoluminescence may be used to investigate quantitatively the production of atomic displacements in binary solids and to give a precise determination for displacement threshold energies.