Development of Heteroepitaxial Diamond Thin Films as Novel Semiconducting Materials

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We produced diamond thin films on (100) and (111) silicon or diamond crystals by microwave plasma-assisted chemical vapor deposition method and developed applications of the films as semiconducting materials.The quality of heteroepitaxial diamond films was strongly affected by orientation of diamond nuclei formed in the very early stage of the deposition. We examined the mechanism of the nucleation in detail, and developed a novel "double-step bias treatment process." We also showed that propylene was superior to methane as the carbon source. By optimizing deposition conditions, we successfully improved the fraction of oriented diamond particles in the nucleation stage up to 60% from the original fraction of 40%.Semiconducting properties of diamond films are dependent on dopants and doping conditions. Although diborane and phosphine are typically used as the boron and phosphorus dopants, respectively, they are very difficult to handle because of toxicity and flammability. We discovered … More that trimethylboron (TMB) and triethylphosphine (TEP) possessed low toxicity and flammability as well as appropriate vapor pressures. We determined the growth rates on the (100) and (111) diamond faces as functions of substrate temperature and methane and TMB or TEP concentrations. B-and P-doped diamond films which were thus formed on (100) and (111) diamond single crystal substrates were characterized by high-resolution scanning electron microscopy, Raman spectroscopy, secondary ion mass spectroscopy and reflection high energy electron diffraction. Semiconductive properties of the films were evaluated by Hall effect examination.Diamond films, which were formed on (100) and (111) diamond crystals using TMB as the boron source were smooth and homoepitaxial. Boron was incorporated in the diamond films homogeneously, and the width of the diamond peak detected by Raman spectroscopy was equivalent to that of natural diamond. The mobility of the TMB-doped film was 300 cm^<2.>V^<-1.>s^<-1> at a hole concentration of 3*10^<13> cm^<-3>, and the activation energy for conductivity in the range of 200-293 K was approximately 0.2eV.Both were lower than those reported with diamond films doped with diborane. The TEP-doped diamond film showed a high resistivity. These results will be improved by further optimizing deposition conditions. Less