Bombardment of Cadmium Sulfide Crystals with 30- to 60-kev Electrons

Abstract

The dependence of induced conductivity in CdS crystals on the rate of arrival and the energy of impinging electrons is reported. These results lead to a qualitative picture of the conduction, excitation, and recombination phenomena in CdS which is satisfied by the simple model of a sulfur vacancy, and an analytical expression which involves the mobility of carriers, their effective masses, the number of ground states in the forbidden gap (for pure but not perfect crystals) and their positions as a function of temperature. The red and green luminescence observed under irradiation by electrons is qualitatively explained. The equation for the induced conductivity is derived from the expression for two-carrier conductivity and the definitions of the steady-state Fermi levels for holes and electrons. An empirical fit to the observed data yields $\sigma =\frac{e{\mu }_n{N}_c\exp (kT\alpha I-{E_{\mathrm{fn}}}^0)}{\mathrm{kT}}$ for $I<\mathrm{}{I}_s$ and $\sigma =\frac{e({\mu }_n+{\mu }_p)N_v\exp \left[kT\beta \right(I-I_s)-{E_{\mathrm{fp}}}^0]}{\mathrm{kT}}$ for $I>\mathrm{}{I}_s$. The data reported herein were obtained by using monoenergetic bombarding electrons in the range of 30 to 60 kev. An interesting field effect is reported but no clear interpretation is available to the authors. Corroborating data employing ultraviolet irradiation are described.