Rectifying contacts on semiconducting type IIb diamond crystals are readily established with any conducting material system including elemental metals, highly doped semiconductors, silicides and carbides. However, for a given surface preparation using oxidizing wet chemicals and in the absence of a surface reaction, barrier heights are observed to be constant regardless of the metal work function. In this report it is demonstrated that an adjustment of the barrier height can be achieved by employing a premetallization low-dose low-energy ion-implantation step.

In this study copper and cobalt films have been deposited on natural type IIb single crystal semiconducting diamond (100) surfaces in ultra-high vacuum (UHV). Prior to metal deposition the diamond crystals have been cleaned by a 1150°C anneal in UHV. This treatment resulted in positive electron affinity surfaces. Upon deposition of 2Å of Cu or Co a negative electron affinity (NEA) was observed. Schottky barrier heights of 0.70 eV and 0.35 eV were found for Cu and Co respectively. In-situ Auger electron spectroscopy (AES) was employed to confirm the presence of a metal layer.

The role of intrinsic stresses in diamond films is examined. The films were deposited on (100) Si substrates by microwave plasma-enhanced chemical vapor deposition. The total internal stresses (thermal and intrinsic) were measured at room temperature with the bending plate method. The thermal stresses are compressive and arise due to the mismatch in thermal expansion coefficient of film and substrate. The intinsic stresses were tensile and evolved during the deposition process. These stresses increased with increasing deposition time. A 12 hour intermediate annealing treatment was found to reduce the tensile stresses considerably. The annealing treatment is most effective when the diamond crystallites are undergoing impingement and coalescence. This is consistent with the theory that the maximum tensile stresses are associated with grain boundary energetics.

Defects in the surface conductive layer of CVD-diamond films have been investigated by ESR method. ESR analysis revealed that defect center ( Pac-center: g=2.003, ΔΔ Hpp=8 Oe ) in the non-diamond phase carbon region exists in the surface conductive layer. The Pac-center with a spin density of the order of 1020spins/cm3 or above was formed in the surface layer by hydrogen radical irradiation during the diamond deposition. Formation of the Pac-center causes the resistivity of CVD-diamond to decrease ( from 9 × 108 Ω to 1.8 × 106 Ω )

Scanning Tunneling and Atomic Force Microscopy (STM, AFM) of amorphous tetrahedral carbon films (a-tC) film surfaces grown by pulsed laser deposition indicate extreme flatness and uniform electronic properties.1 This is consistent with the observed predominance of sp3 (diamond-like) bonding in these materials.2 Potential applications of a-tC films may be enhanced with the ability to modify their surfaces on the nanoscale. Exploiting the metastable nature of the sp3 hybridized state of carbon, the high flux electron beam from an STM tip was used to modify ˜100 nm regions; processing in air or in vacuum produces similar results. STM and AFM maps of the modified regions indicate stable morphologic and electronic structures consistent with a local transformation to sp2 (graphitic) hybridization. Surface potentiometric mapping of these regions indicates a correlation between electron dose and a lowering of the surface potential. In addition, spatially-resolved electron energy loss spectroscopy of the modified areas performed with a Scanning Auger Microscope shows plasmon energy shifts that confirm an elevated sp2 content in the modified regions.3

The gas temperature of a radio-frequency thermal plasma has been measured by laser-induced fluorescence along the axis of the plasma jet near the substrate surface. The temperature was determined from the rotational population distribution of OH radicals. From the measured temperature profile, the freestream temperature was found to be about 3400 K and the boundary layer thickness was determined to be about 1 mm. A numerical model including carbonhydrogen- argon kinetics was used to predict species concentrations near the surface of the substrate. The results indicate that all CHa radical concentrations increase with freestream temperature for temperatures between 2500-4000 K. Of the C1 radicals, methyl has the highest concentration in this range in our system, which is consistent with other reports that methyl is an important diamond growth species.

The nucleation stage of diamond on silicon substrates was studied by atomic force microscopy. Samples were grown by hot filament chemical vapor deposition and substrate biases from -200 ν to +75 ν were investigated. The effects of the process on the substrate as well as on the morphology of the crystallites were observed using an atomic force microscope operating in tapping mode. It was observed that both the density and morphology of the diamond crystallites were greatly dependent on the applied bias values. The highest nucleation density was achieved for the -200 ν bias, when a plasma around the substrate holder was formed.

CVD diamond films show both at optical microscope and at SEM a quasi-columnar structure, not homogeneously distributed in the bulk which is agreed to be responsible for the relatively large charge collection lengths measured in the material. In this work, we present the first data on charge collection efficiency distributions as measured directly in the bulk by a 3 Meν proton microbeam. The results indicate that the material is really non-homogeneous, that only few columns are really connecting both electrodes and that, finally, a real connection exists between the morphological structure and the maps of collection efficiency distribution.

The structure and chemistry of annealed and oxygen or hydrogen-terminated low-index (100, 110) diamond surfaces was determined with high resolution electron energy loss spectroscopy (HREELS), low energy electron diffraction (LEED) and other techniques. HREELS revealed carbonyl, hydroxyl and bridge-bonded oxygen groups on oxidized C(100) and C(110) surfaces. The surface chemistry was correlated with secondary electron emission spectra and other data. The oxidized and annealed (reconstructed) surfaces exhibited larger work functions and electron affinity than hydrogenated surfaces, which we attribute to both band-bending and dipole layer effects due to surface oxygen.

The measurement of the optical constants for a rough surface thin film is needed for CVD polycrystalline diamond films which typically have surface roughnesses of the order of tens to hundreds of nm. In this paper, we present a method for determining the optical constants n and k as well as the surface roughness σ for a rough surface diamond thin film. By using the theory of optical reflectance (R) and transmittance (T) for a thin film with incorporation of rough surface scattering factors which are functions of the surface roughness a, the following function can be obtained: R=R(n,k,σ,λ,d), T=T(n,k,σ,λ,d), and Rp=Rp(n,k,σ,λ,d), where λ and d are the incident wavelength and film thickness, respectively. Rp is the reflectance from the smooth back surface of the thin film. From the experimental data for R, T, and Rp in a range of wavelengths, the optical constants n, k, and σ can be extracted by solving the above non-linear equations using a three-dimensional Newton-Raphson technique. Examples of experimental results on diamond films and other examples of simulated results are presented to illustrate the usefulness and validity of this technique.

We have developed diamond heat spreaders and bonding technology to silicon device structure. Diamond films were grown on molybdenum and Si substrates using hot filament chemical vapor deposition. Tin or gold-tin solders were used for bonding. Bonding of silicon on diamond was carried out at 20 Torr with hydrogen ambient and a temperature between 300 to 400°C for half hour. The diamond films were characterized by Raman spectroscopy and scanning electron microscopy. Interfaces between silicon and diamond films Were examined by scanning electron microscopy and energy dispersive spectroscopy. Pull-tests were used to determine the strength of the bonding between the silicon substrate and the diamond film. Bonding is improved with special metallization procedure using Ti and Cu films on the silicon substrate and Ti and Au or Cu films on the diamond film. Mechanisms of improvement of bonding due to metallization layers are discussed.

High quality diamond films have been successfully grown, by step-flow, on (001) diamond substrates using an end-launch type chemical vapor deposition reactor. Electrical properties of as-deposited diamond films as well as the surface morphology and the film crystallinity were investigated. Optical and atomic-force microscope images indicated that diamond films consisted of atomically flat terraces and macroscopic steps running parallel to [110×l and 1×2 double-domain structure. The currentvoltage characteristics of Al-Schottky contacts to these step-flow grown diamond films showed excellent rectification properties, indicating the potential of this material for electronic applications.

Undoped and 10B doped diamond films were neutron irradiated at a moderately high fluence level (thermal neutron fluence of 1.3 × 1020 n/cm2 and a fast neutron (E> 0.1 MeV) fluence of 1.6 × 1020 n/cm2). The unirradiated, irradiated, irradiated and annealed samples were studied using Fourier Transform Infrared (FTIR) and Raman spectroscopies. A dependence of radiation induced stress on the initial boron concentration was observed. The radiation induced stress was lower for the undoped samples. Correlations between FTIR and Raman data were found. The radiation damage was removed after annealing, as measured by Raman and FTIR spectroscopy.

Diamond-like carbon (DLC) films have been prepared by pulsed laser deposition using graphite and cured phenol resin as targets. By comparison with previous reports, it is found that the lower power density (fluence) of irradiated pulsed laser can form DLC. In case of cured phenol resin used as a target, DLC was formed at almost the same wavelength and fluence region as that with graphite.

The present findings concern the CVD deposition of diamond films on Ti substrates and the presence of a stratification of other various phases (Titanium Carbide, Titanium Hydride and Graphite) through the thickness of the CVD coatings.

The reflection high energy electron diffraction (RHEED) technique is mainly used to gain insight into the structure of the various phases generated at the diamond/substrate interface.

The experimental results seem to indicate that the structure of the transition layers present at the substrate/film interface play a fundamental role for the control of the heterogeneous nucleation process of the diamond.

Diamond nucleation and growth by CFD were investigated to examine the possibility of engineering diamond growth shapes for practical applications. The results obtained include the following:

a) Evidence supporting certain factors influencing nucleation - useful in controlling nucleation sites and nucleation density.

b) Evidence for a double spiral growth mechanism operating on (111) faces under specific conditions - indicates the possibility of a new mechanism operating for diamond growth from the vapour phase, and the possibility of larger growth rates.

c) Evidence for the enhanced growth in <100= crystallographic direction on a cubooctahedral crystal and its control by varying the process parameters – thus showing the possibility of obtaining diamond needles and tips as engineered growth shapes, for specific applications.

p-type semiconducting boron doped layers have been fabricated on diamond substrates by ion implantation and subsequent annealing. A number of the related published experimental data and theoretical models on electrical properties of boron doped diamond are analyzed with regard to the temperature coefficient of resistance (TCR) of temperature sensors. The dependencies of the conductivity and activation energy on three parameters: (i) boron doping level NA, (ii) electrical compensation ratio ND/NA- C and (iii) duration of the postimplantation annealing time ta are studied. By variation of NA, C and t, an optimized technological regime for the temperature sensor fabrication can be obtained. One can summarize that: 1) the TCR value is not remarkably reduced with the boron concentration up to NA -1019 cm-3, 2) an increase of the electrical compensation decreases the activation energy and consequently the TCR coefficient,3) 1 h annealing at 1500°C is sufficient to remove the compensating radiation defects, 4) the variation of the ta from 1 min to 1 h changes the TCR value by 20% to 30%. Technological steps of the fabrication of a micro temperature sensor are given.

Our studies primarily concern an S=1/2 electron paramagnetic resonance (EPR) at g=2.0028 with a pair of weaker partially resolved satellites that has been observed in polycrystalline diamond grown by chemical vapor deposition (CVD). These satellites can be shown to result from the forbidden Δm=±l nuclear spin flips of hydrogen during the EPR ΔM∼ 2Å away from the unpaired electron spin. It is suggested that hydrogen enters a vacancy-like stretched bond at a grain boundary, allowing the carbons to relax backward, one bonding to the hydrogen, the other with an unpaired electron in its dangling bond.

Changes in electron affinity on the C(001) surface of type Ifb diamonds have been studied using a variety of surface analytical techniques, including ultraviolet photoemission spectroscopy, secondary electron emission spectroscopy and constant initial states photoemission. Following H-plasma exposure, an intense low-energy emission peak was observed with all spectroscopies. The emission intensity associated with the chemisorbed hydrogen was found to be a linear function of surface hydrogen coverage. The proposed mechanism for the hydrogen induced changes in electron affinity is the creation of a dipole on the surface by the addition of hydrogen which opposes the surface potential of the bare surface. A total change in electron affinity of 2.2 eV was measured upon hydrogen termination of the clean 2x1 surface. Constant initial states photoemission demonstrates that the intense low-energy electron emission observed arises from electrons emitted from bulk states at the conduction band edge. Oxygen, as an electronegative species, was found to have the opposite effect and the electron affinity was increased by ∼3.7 eV upon oxygen termination relative to the clean 2x I surface.

The structural phase diagram of the hydrogen terminated diamond-(111) surface, which is of considerable relevance with regard to the low-pressure synthesis of diamond, has been investigated by the highly surface sensitive technique of thermal energy helium atom scattering. A new phase with a (2 × 1) symmetry has been observed to occur upon heating above 940 K, significantly below the well known transition to the hydrogen-free (2 × 1) π-bonded chain structure at 1250 K. It is proposed that the new phase consists of a hydrogen (2 × 1) overlayer on an unreconstructed (1 × 1) diamond substrate. Structural models for this new phase will be presented.