Cathodoluminescence of radiation damage, non-stoichiometric and impurity defects in cadmium telluride

Johnson, P.C. (1981) Cathodoluminescence of radiation damage, non-stoichiometric and impurity defects in cadmium telluride. Doctoral thesis, Preston Polytechnic.

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The effects of atomic displacement, degree of nonstbichiometry and impurity doping on the liquid helium temperature cathodoluminescence of cadmium telluride have been investigated. Under such treatment the responses of the emissions have cast some doubt on the previously accepted significance of the simple cadmium vacancy acceptor in the edge emission spectrum of the material. The nature of the luminescence transitions was revealed by observation of the excitation intensity dependence, time resolved spectroscopy and temperature dependence of the emissions.
Sharp exciton peaks at 778.17nm (1.5930eV) and 781.5nm (1.5862ev) are attributed respectively to the annihilation of excitons bound to neutral Group III impurity donors and to charged donors involving native defects. The previous attribution of the dominant 780.17nm (1.5889eV) cadmium telluride emission to an exciton bound to a simple cadmium vacancy has been shown to be unlikely. However a nearby emission at 779.33nm (1.5906ev) has been shown clearly by selective radiation damage to be due to exciton annihilation at neutral cadmium vacancy acceptors. The ionization energies of these exciton emission centres have been related to the ionization energies of the edge emission centres.
An edge emission at 797.6nm (1.554ev) is attributed to a bound-to-free transition involving a tellurium defectimpurity
centre at Ec - 0.052ev. Emissions at 805.5nm (1.539ev) and 809.5nm. (1.531ev) are shown to be due to free-to-bound and bound-to-bound transitions to the same acceptor at Ev + 0.076ev, with the donor at Ec - 0.024ev.
The effectsof cadmium firing and the implantation of chlorine or indium suggest tentatively that emissions at approximately 830nm (1.493ev) and 854nm (1.452ev) involve complex centres comprising native defects and impurities.
High resolution study of two close emissions at 851nm (1.457ev) and 854nm (1.452ev) has resolved uncertainties
previously reported in this region with time resolved spectroscopy suggesting that the former emission is due to donor - acceptor transitions but not the latter.

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