Plasma-deposited hydrogenated carbon-germanium semiconducting films doped with acceptor and donor centers

Hydrogenated amorphous carbon-germanium (a-GeXCY:H) films were doped with acceptors (boron, aluminum and gallium) and donors (phosphorous). The films were prepared by plasma enhanced chemical vapor deposition (PECVD), using an r.f. (13.56 MHz) reactor with a coplanar electrode geometry. Investigations on electrical conductivity and optical absorption were carried out. All used dopants caused a maximal increase in the conductivity of approximately two orders of magnitude. Based on more thorough examinations performed on the boron and phosphorous-doped films, it has been suggested that both acceptor and donor dopands modify only p-type conductivity of the undoped films and any transition to n-type is not observed. Boron creates an additional band of acceptors whereas phosphorous eliminates the oxygen donor centers reducing thereby the compensation of the native acceptors. (C) 2001 Elsevier Science B.V. All rights reserved.