HALL-EFFECT MEASUREMENTS ON CDTE ELECTRODEPOSITED FROM TRI-N-BUTYLPHOSPHINE TELLURIDE

The carrier transport properties of CdTe electrodeposited from tri-n-butylphosphine telluride have been studied by resistivity and Hall effect measurements as a function of temperature. Argon annealed electrodeposited CdTe was found to be consistently p-type, with resistivity values typically 10(6)-10(7) OMEGA . cm. Various donor and acceptor dopants (Cd, Te, Cu, Ag, In and O2) were incorporated into polycrystalline CdTe films by three methods: electrochemical co-deposition, electromigration and vapour techniques. The carrier concentration of p-type CdTe could be systematically increased by the increasing the current density for the electromigration of copper. The increase in carrier concentration was accompanied by a decrease in resistivity and a decrease in mobility. P --> n conversion of CdTe was achieved by diffusion of Cd at high temperature. The activity of the dopant was dependent on the method that was used for incorporation. The effect of dopant density on the resistivity of the polycrystalline cadmium telluride films can consistently be described by the grain boundary model. In this model charging of grain boundary states decreases the carrier density and results in a barrier. According to the model, dopants accumulated at grain boundaries do not generate carriers and do not affect the density of interface states. Comparison of theory with results indicated that a significant portion of copper dopant was not active. For cadmium dopant, the barrier energy varied from 0.04 to 0.09 eV for crystallite sizes from 14 to 77 nm.