DEFECT STRUCTURE AND CONDUCTIVITY IN TETRAHEDRALLY COORDINATED METAL CHALCOGENIDE AMORPHOUS-SEMICONDUCTORS

We examined the paramagnetic defects and the electrical conductivity m echanisms in thin films of amorphous Cu6As4S9 deposited using rf sputt ering. Electron-spin-resonance (ESR) measurements show that the defect s are mainly sulfur dangling bonds. The ESR spin density is independen t of temperature, a fact that suggests that the effective electron-ele ctron correlation energies are positive for these defects. Additional ESR centers can be created by optical excitation at low temperatures. These optically induced centers anneal at temperatures above about 100 K. The electrical conductivity scales with the ESR spin density. Tran sient, optically induced changes in the photoconductivity and the dark conductivity are accompanied by similar transient, optically induced changes in the ESR. These results provide strong experimental evidence that the transport mechanism is controlled by S-dangling-bond defects thar supply holes to the valence band for transport. [S0163-1829(97)1 0240-5].