CHARACTERIZATION OF BORON-CARBIDE THIN-FILMS FABRICATED BY PLASMA ENHANCED CHEMICAL VAPOR-DEPOSITION FROM BORANES

We have fabricated boron carbide thin films on Si(111) and other substrates by plasma-enhanced chemical-vapor deposition (PECVD). The PECVD of boron carbides from nido-cage boranes, specially nido-pentaborane(9) (B5H9), and methane (CH4) is demonstrated. The band gap is closely correlated with the boron to carbon ratio and can range from 0.77 to 1.80 eV and is consistent with the thermal activation barrier of 1.25 eV for conductivity. We have made boron carbide by PECVD from pentaborane and methane that is sufficiently isotropic to obtain resistivities as large as 10(10) OMEGA cm at room temperature. This material is also shown to be suitable for photoactive p-n heterojunction diode fabrication in combination with Si (111).