CAPACITANCE AND CONDUCTANCE OF ZNXCD1-XS/ZNTE HETEROJUNCTIONS

Capacitance-voltage and conductance-voltage characteristics of RF-sputtered ZnCdS films on ZnTe single crystals were studied as a function of frequency up to 1 MHz. It has been found that the measured capacitance decreases with frequency while the conductance increases. A physical circuit model of the junction is proposed which can explain satisfactorily this dependence. We derived a relationship relating the junction capacitance to the polycrystalline film properties and the built-in voltage of the junction. One of the main results of this relationship is that the junction capacitance is related to the average carrier concentration rather than the doping concentration of the polycrystalline material. From a C-2 versus V plot we obtained an average carrier concentration in the films which is in good agreement with that obtained by Hall measurement. The lower average electron concentration in the ZnCdS film near the substrate is due to either interdiffusion of Cd from the film into substrate or due to higher density of grain boundary states in the starting deposition portion of the film.