Negative magnetoresistance in Cr-containing diamond-like carbon-based heterostructures

We have characterized the local structure around the Cr atom, as a function of Cr content, in films of chromium-doped hydrogenated amorphous diamond-like carbon (Cr-DLC) synthesized by plasma-enhanced chemical vapor deposition (PECVD). The composition appears to be related to the structure and forward bias magnetoresistance in heterojunction devices. Chromium in diamond-like carbon (DLC) has a chemical state much like chromium carbide and, at low Cr content, the Cr is dissolved in an amorphous DLC matrix forming an atomic-scale composite. At higher Cr content, Cr is present as nano-composite and chromium carbide precipitates preferentially form at the surface of the film. In these films of higher chromium concentration, a large coefficient of negative magnetoresistance is observed in heterojunction devices with n-type silicon.