Diamond is an important semiconductor which has great potential in high temperature, high power device applications. In the fabrication process of diamond electronic device, doping ofdiamond and understanding of diamond/metal interfaces are important. As a Column V element, Sb is a possible dopant for diamond. Early work reported that Sb is incorporated into diamond by ion implantaion [1]. In addition, Sb plays an important role in Si and Ge heteroepitaxial growth. On the Si or Ge surface one ordered monolayer of Sb occupies the epitaxial sites and saturates the surface dangling bonds, which leads to uniform epitaxial growth. While diamond has the same crystal structure as both silicon and germanium, it has a drastically smaller lattice and much stronger bond. This makes it very difficult to extrapolate antimony's behavior on diamond from its behavior on either silicon or germanium. In this work, we have studied the electronic and geometric structure of Sb on diamond surfaces using photoelectron spectroscopy and low energy electron diffraction. While the exact adsorption sites could not be determined, we find that antimony strongly bonds to the diamond surface. Further, antimony behaves very differently on the diamond(100) face as compared to the diamond(111) face. We also find that neither Sb/diamond system behaves like antimony on either silicon or germanium. We attribute these results to the drastically smaller diamond lattice and the stronger C-C bond.

Electrical conductivity measurements were used to study the effects that sample distance from the plasma during growth has on the carrier transport properties of undoped CVD diamond. The films were grown by downstream microwave plasma chemical vapor deposition at distances from 0.5 to 2.0 cm from the edge of plasma glow. Electrical conductivity measurements were performed between room temperature and 1000 °C to gain a better understanding of the CVD growth process and the resulting electrical properties of the diamond film's. Room temperature electrical conductivity was found to vary by over 5 orders of magnitude with increasing growth distance from the plasma, and this is attributed to decreasing hydrogen incorporation efficiencies at further distances from the plasma.

High temperature rectifying contacts have been fabricated on naturally occurring lib semiconducting diamond crystals using highly doped Si. Polycrystalline Si deposited by low pressure chemical vapor deposition (LPCVD) and amorphous Si deposited by sputtering were investigated. Following LPCVD deposition, the polycrystalline Si filn was doped with P by solid state diffusion at a temperature of 900°C using a POCI3 source. Boron doped and As doped Si films were deposited by sputtering from highly doped Si targets. Current-voltage measurements were performed on the fabricated P doped, B doped and As doped Si contacts from room temperature up to ∼400∼C. In all cases, the contacts yielded excellent rectification in the temperature range investigated. Current conduction in doped Si/diamond systems appears to be space charge limited. The position and concentration of deep levels in a natural lib diamond crystal have been determined from an analysis of space charge limited current-voltage (I-V) characteristics.

Low resistance ohmic contacts have been fabricated on a naturally occurring lib diamond crystal and on polycrystalline diamond films by B ion-implantation and subsequent Ti/Au bilayer metallization. A high B concentration was obtained at the surface by ion implantation, a postimplant anneal and a subsequent chemical removal of the graphite layer. A bilayer metallization of Ti followed by Au, annealed at 850°C, yielded specific contact resistance values (as measured using a standard transmission line model (TLM) pattern) of the order of 10-5 Ω cm2 for chemical vapor deposition (CVD) grown polycrystalline films and the natural lib crystal. Specific contact resistance values have also been determined from circular TLM measurements on CVD films and the values compared to those from standard TLM measurements. These contacts were stable to a measurement temperature of ∼400°C and no degradation due to temperature cycling was observed.

Schottky diodes to be used for mechanical stress effect studies were fabricated using aluminum contacts to polycrystalline diamond thin films grown by a hot-filament assisted chemical vapor deposition process. Compressive stress was found to have a large effect on the forward biased current-voltage characteristics of the diode. At selected values of constant forward biased current, a linear relationship between voltage and stress, for stress less than 10 N was observed. The stress sensitivity of the diode was as high as 0.74 V/N at 1 mA forward bias. This study shows that polycrystalline diamond Schottky diodes are stress sensitive devices and have potential as mechanical sensors.

Shock-wave profiles of highly ordered pyrolytic graphite shocked normal to the basal plane of the graphite crystal structure have been measured. For graphite with sufficient orientational order a martensitic transformation to a diamond-like phase is observed with a transition onset pressure 19.6±0.7 GPa, the stability limit of the graphite structure under shock compression. The minimum overpressure required for the transformation is not more than 6 GPa.

A new method for the modelling and measurement of the thermal diffusivity of very thin films is proposed, and is applied to diamond thin film samples grown by chemical vapor deposition using a mixture of methane and hydrogen. This method is based on a two-dimensional model of the heat conduction process in a thin film to which a delta-function heat pulse is applied as a line source. The mathematical solution is specialized to obtain expressions for the temperature pulse propagating through the plane of the film. With suitable approximations, it is shown that the thermal diffusivity of the film can be deduced directly from a measurement of the temperature excursion with time at various points on the films. The advantages and difficulties of the measurement using this method will be discussed.

Hard amorphous carbon films have been deposited by ArF pulsed laser ablation of graphite at room temperature, with the laser power density of 5x108 W/cm2. The films prepared in the high vacuum environment possess remarkable diamond-like properties with a hardness up to 38 GPa and an optical energy band gap of 2.4 eV. The properties of the films doped with nitrogen vary with the nitrogen content, but improve interface adhesion, resulting in the extension of the film thickness limit to a greater range. The results suggest that the properties of the laser ablation deposited diamond-like carbon films depend not only on the laser power density, but also strongly on the laser wavelength or photon energy.

The structure of “diamond-like” carbon, a-C:H has been studied using the Xray diffraction facilities available at the Synchrotron Radiation Source (Daresbury Lab, UK). The principle advantage of using the SRS is that high fluxes are available at short wavelengths (λ ∼ 0.6Å): it is therefore possible to extract the “diffuse” scattering profile associated with all amorphous systems with considerable precision over a very wide K-range. A novel diffraction technique is also described in which the X-ray beam is incident on an as-deposited thin film at or near the critical angle. In this geometry we demonstrate that it is possible to gather diffraction data on -1μm films in-situ.

We have measured the dependence of the optical bandgap of amorphous hydrogenated carbon as a function of self-bias voltage and external bias voltage. It is observed that there is a much stronger variation in the optical bandgap with self-bias voltage than external bias voltage. We explain this observation in terms of collisions in the plasma between electrons and precursor molecules and ions that break carbon-hydrogen bonds. Increased self-bias voltage causes increased collisions, more broken CH bonds, precursor ions and molecules more deficient in hydrogen, leading to grown films with lower hydrogen concentrations and thus smaller optical bandgaps. This interpretation is further supported by plasma emission spectroscopy where the intensity ratio of CH to H lines decreases with increasing self-bias voltage, demonstrating that increased self-bias voltage does lead to increased electron collisions in the plasma and more broken CH bonds.

Amorphous diamond-like carbon (ADLC) coatings are deposited on cemented carbides, high speed steels (HSS) and other steels, using arc-ion plating. The paper describes both the problems and the potential of this process with its many influencing parameters. It also details a number of properties of hydrogen-free a-C films deposited at coating temperatures of 200°C; as an example, a tribological application is described.

Diamond-like amorphous carbon and hydrogenated amorphous carbon films (DLC) prepared by rf sputtering have been characterized by means of measurements of optical gap, hardness and Young's modulus. Preliminary results of the application of the photothermal displacement technique (PTD) are also reported, confirming that this method can in principle be applied for a more complete characterization of DLC films at room temperature and low temperatures.

Results of a study on internal stress, hardness and structure of nitrogen doped amorphous hydrogenated hard carbon films deposited by r.f. glow discharge on silicon are presented. Films obtained for different bias voltage (Vb), N2 partial pressure and total gas pressure were characterized by Nuclear Reaction (NR), Elastic Recoil Detection (ERD), Rutherford Back-Scattering (RBS), Infrared Spectroscopy (IR) and Raman Scattering. The elemental composition, density and structure are correlated with Vickers hardness, and internal stress values obtained by the substrate bending method. It has been observed that internal stress considerably decreases with increasing nitrogen content, contrary to the behavior shown by hardness, structure and hydrogen concentration, which remain unchanged.

Hydrogenated amorphous carbon (a-C:H) films have been deposited by sputter assisted plasma chemical vapor deposition (CVD). The relative concentration of sp3 and sp2 hybridized carbon in samples is determined by infrared (IR) and nuclear magnetic resonance (NMR) spectroscopies and by a new method through the complex dielectric constant deduced from optical transmittance and reflectance. The results are compared and discussed.

Neutron diffraction data from a large, off-substrate sample of amorphous hydrogenated carbon (a-C:H) is presented and discussed. The material is prepared using a fast-atom deposition system using acetylene as the precursor gas. The experiments were performed on the ISIS pulsed neutron source (Rutherford Appleton Laboratory, UK) which is capable of yielding data over an exceptionally wide dynamic range; this ensures a real-space resolution sufficient to resolve directly, for the first time, contributions from the principle C-C bond types. Precise details on the C-H correlations are also revealed by the data, including the presence of molecular hydrogen trapped within distorted spheroidal cages. Quantitative complementary data on the vibrational states of the bonded hydrogen, derived from inelastic neutron scattering (INS) using a simple force-field model, is also presented. In particular, the INS data is used to provide a reliable estimate of the CH:CH2 ratio.

In addition to being successfully used for ion implantation, the plasma source ion implantation (PSII) technique has been used to produce diamond-like carbon films. Homogeneous, adherent films were obtained on silicon and stainless steel substrates under 2 kV pulse bias voltages and 50 mtorr methane plasma pressure. Chemical composition analysis was made using Auger electron microscopy. Fretting wear tests and scratch tests were performed to study the tribological and adherent properties. Cross sectional TEM samples were prepared. The interfacial microstrucutres and chemical compositions were analyzed using transmission electron microscopy and scanning transmission electron microscopy.

Neutron diffraction data has been used as input to a computer-modelling algorithm based on the “Reverse Monte Carlo” technique. Using this method the positions of ∼ 5000 “atoms” in a box, with full periodicity, are altered until the associated model structure factor agrees with the analogous experimental curve to within errors. It is then possible to estimate the partial pair distribution functions (i.e. those associated with C-C, C-H and H-H correlations), bond angle distributions, coordination number distributions, etc. Whilst X-ray data is well-conditioned for the study of the carbon-carbon network, neutrons are sensitive to the interference terms involving hydrogen. We present an exploratory study of the effectiveness of the RMC method in this context, and suggest viable options for the future use of the method in model building.

Thin films of amorphous, diamond-like carbon (DLC) were deposited on crystalline silicon substrates in a capacitively coupled RF-plasma discharge. The investigations concentrated on I-V and C-V measurements, on photoconductivity and on optical transmission between wavelengths of 2 and 50 microns of the heterostructure DLC/Si. The photoconductivity of the heterostructure is investigated for the first time; it depends on the band gap of the film, the thickness and the doping of the substrate. The DLC/Si heterostructure works like a MIS-photoelectric cell.