Optical and electrical properties of hydrogenated amorphous Si1-xGex alloy thin films prepared by planar magnetron sputtering

Abstract Thin films of hydrogenated amorphous Si 1- x Ge x were prepared by the r.f. diode planar magnetron sputtering method using composite targets of silicon and germanium in an atmosphere of H 2 diluted with argon. The optical absorption coefficient, d.c. conductivity, photoconductivity and IR transmission spectra were measured, and the dependence of these characteristics on the germanium content x was investigated. For films with x ≈ 0.1, it is found that the dark conductivity decreases and the ratio of the photoconductivity to the dark conductivity increases by about one order of magnitude compared with those for hydrogenated amorphous silicon. This phenomenon seems to be caused by a reorganization of the tetrahedrally bonded structure. Films of this composition are considered to be of interest as an opto-electronic material requiring a high resistance. Photoconductive effects are not observed for films with x > 0.3. This is considered to be due to an alloying effect. The decrease in the amount of bonded hydrogen in the films becomes appreciable for the films with x > 0.6.