Nanoscale-controlled Plasma CVD of Metal-doped Semiconducting DLC Films

点击翻译按钮获取中文摘要

We synthesized metal-doped diamond like carbon (DLC) films by rf plasma-enhanced chemical vapor deposition (PECVD) using methane, hydrogen and an organometallic compound as gas sources. First, we used tetramethyltin (TMT) as a dopant source and investigated the film properties of tin-doped DLC films. Tin-carbon direct bonds are formed in the films, which is confirmed with X-ray photoelectron spectroscopy. The tin concentration in the films can be controlled by TMT partial pressure ratio, R (= (P_<TMT>/P_<Total>)*100 [%]). When R is over 0.2%, nanometer-size clusters of beta-tin phase are formed in the deposited films with random orientation. To avoid the formation of the clusters and dope tin at atomic size, the R value should be less than 0.2%, which led to the maximum Sn/C concentration ratio of 0.1 in the films. The electrical resistivity of the tin-doped DLC films is-10^3OMEGAcm, much lower than that of pure DLC films (-10^7OMEGAcm). Higher R value causes lower transmittance in infrared region.Next, we prepared gold-or copper-doped DLC films by a hybrid process of rf PECVD and rf sputtering. In the gold-doped DLC films, gold exists only in the state of metallic cluster. Gold-carbon direct bonds are not formed. On the other hand, small amount of copper-carbon bonds are found in the copper-doped films. The concentration of the dopant metal can be controlled by the number of metal tips located on an rf electrode. The electrical resistivity decreased drastically from 10^7OMEGAcm up to 1OMEGAcm with the increase in the metal concentration. We can vary the electrical resistivity of DLC films over a wide range of 8 order by doping a metallic element.These results mean that the doped metal can change the electrical properties of DLC films from insulating to semiconducting. This study reveals the possible application of DLC films to active electronic devices.