Hideyuki Watanabe

n-Type Control by Sulfur Ion Implantation in Homoepitaxial Diamond Films Grown by Chemical Vapor Deposition

n-type control was achieved by sulfur-ion-implantation in homoepitaxial diamond (100) films grown by chemical vapor deposition (CVD) for the first time. Sulfur-implantation was carried out with energies of up to 400 keV at 400°C. The activation energy of the conductivity was 0.19–0.33 eV depending on the conditions of ion implantation. A junction between this layer and a boron-doped p-type layer was fabricated by combining sulfur-implantation with gas-phase boron doping during CVD. The junction exhibited clear pn junction properties. The capacitance of the junction decreased with reverse bias voltage, which confirms that the depletion region of the junction was actually extended with the reverse bias voltage.

High quality homoepitaxial diamond thin film synthesis with high growth rate by a two-step growth method ☆

Abstract Homoepitaxial diamond films grown in the condition of CH 4 /H 2 ratio lower than 0.15% in a microwave-assisted plasma chemical vapor deposition system had excellent electrical and optical properties without any unepitaxial crystallites (UCs). Under such a low CH 4 concentration condition, however, the growth rate becomes too slow to obtain a useful thickness. In order to overcome this problem, we attempted a two-step growth method. In the first step the substrate surface was treated by homoepitaxial growth of diamond in the presence of 0.05% CH 4 in H 2 ; in the second step the CH 4 concentration was increased. By considering the origin of UCs with cross-sectional transmission electron microscope studies, it was found that this method is based on surface improvement of the initial substrate by means of ultra-low CH 4 concentration growth. This method was quite useful for obtaining high quality films, with high growth rate and reproducibility.

Electrical conduction of high-conductivity layers near the surfaces in hydrogenated homoepitaxial diamond films

Abstract In order to clarify the origin of high-conductivity layers (HCL) near the surfaces of hydrogenated diamond films, we have studied the relationship between HCL and surface structure in B-doped homoepitaxial (001) diamond films. Samples annealed in nitrogen environment at various temperatures have been characterized by Hall-effect measurements and reflection high-energy electron diffraction. It was found that HCL disappeared in the films annealed at a temperature higher than 350°C, but the (001)-2×1 surface-structures observed in hydrogenated films remained at 350°C. This indicates that HCL is not related directly with the (001)-2×1 surface-structure. The origin of HCL will be discussed on the basis of the present results.

Spatial uniformity of Schottky contacts between aluminum and hydrogenated homoepitaxial diamond films

Homoepitaxial diamond films prepared under low CH4 concentration conditions (CH4/H2 42 dots) prepared on the same film. This result indicates that the quality of the films with atomically flat surfaces over the whole area of the substrate is actually excellent in a viewpoint of chemical stability as well as electrical characteristic.

Structural properties of sulfur-implanted diamond single crystals

The lattice location of sulfur implanted into diamond single crystals has been investigated using particle induced X-ray emission and ion channeling. Sulfur atoms were implanted into high-quality undoped homoepitaxial diamond [100] film grown by microwave plasma assisted chemical vapor deposition onto high-temperature and high-pressure synthetic Ib diamond [100] substrates, as well as into Ib diamond substrates directly, at 400/spl deg/C up to the concentration of 1/spl times/10/sup 20//cm/sup 3/. They were annealed at 800/spl deg/C in vacuum for 100 min after the implantation. Sulfur dopant was found to occupy preferentially substitutional sites in the host lattice. The possible maximum displacement of sulfur dopant was 0.14 A from <001> axis, and 0.07 A from <011> axis. The substitutional fraction of sulfur was 0.5 and 0.7 along <001> and along <011> direction, respectively. The depth profile of sulfur distribution measured by SIMS coincides with that of simulated vacancy depth profile associated with the sulfur implantation, rather than expected dopant distribution. These results suggest the redistribution of sulfur, and possible sulfur-residual damage (vacancy) coupling in the diamond crystal after the implantation.