Andrzej Badzian

Crystallization of diamond crystals and films by microwave assisted CVD (Part II)

Results of experiments on crystallization of diamond micro single crystals (∼10μm) and polycrystalline diamond films by microwave plasma assisted chemical vapor deposition are presented. Discussed are problems related to growth mechanisms from CH4H2 plasma: nucleation on different substrates (diamond, graphite, Si, βSiC, SiO2 and Ni), catalytic growth, Raman scattering from deposits and planar defects of diamond structure. Optimal conditions for diamond growth were found in relation to maximum growth rate and exceptional surface phenomena appearing at temperatures close to 1000°C.

The effect of surface treatment on the electrical properties of metal contacts to boron-doped homoepitaxial diamond film

Both doped and undoped homoepitaxial diamond films were fabricated using microwave plasma-enhanced chemical vapor deposition (CVD). The conductivity of the diamond film is strongly affected by the surface treatment. In particular, exposure of film surface to a hydrogen plasma results in the formation of a conductive layer which can be used to obtain linear (ohmic) I-V characteristics of the Au/diamond contacts, regardless of the doping level. It is shown how the proper chemical cleaning of the boron-doped homoepitaxial diamond surface allows the fabrication of Au-gate Schottky diodes with excellent rectifying characteristics at temperatures of at least 400 degrees C.<<ETX>>

Cubic boron nitride - diamond mixed crystals

Mixed crystals of diamond and cubic boron nitride were obtained by the direct phase transformation at a pressure of 14.0 GPa and in temperature about 3300°K of mixed crystals of graphite and hexagonal boron nitride. The crystals, which can be described by the formula (BN)xC1−x, 0 < x < 1, possess sphalerite structure and show short range order expressed by substitution of B-N pair by C-C pair in the first coordination sphere. The phase transformation has a reconstructive character and keeps relation between two structures: 001 plane of graphite — like structure remains parallel to III of diamond — like structure.

Crystallization of diamond from the gas phase; Part 1

Abstract The paper discusses growth mechanisms of diamond from the gas phase taking into account previously presented theory and experimental data. A chemical kinetics model for the deposition of diamond and graphite from hydrocarbon gases is presented, based on the work of Derjaguin, Fedoseev and coworkers. The mechanism proposed by Derjaguin et al. is expanded to consider the relationship between temperature dependence of the growth rate and the atomic reconstruction of the diamond surface. A diamond growth process is proposed which integrates chemical factors (thermodynamics, kinetics, chemisorption) and physical factors (thermal vibrations, surface transformation surface diffusion).

Electrical characteristics of Schottky diodes fabricated using plasma assisted chemical vapor deposited diamond films

Schottky diodes were fabricated using gold and aluminum contacts to thin diamond films obtained by a microwave plasma assisted chemical vapor deposition process. The current‐voltage and capacitance‐voltage‐frequency characteristics of these devices are similar to those fabricated on a crystalline diamond base formed by traditional ultrahigh pressure process.

Silicon carbonitride, a new hard material and its relation to the confusion about ‘harder than diamond’ C3N4

Abstract The claim by Cohen (Science 261 (1993) 307) that powerful computational tools allow us to predict ‘properties of substances even before we have created them’ was made in conjunction with the claim of special properties for a hypothetical phase, C 3 N 4 . Among such properties was hardness, and it was asserted that, the covalent form of C 3 N 4 could be ‘harder than diamond.’ This assumption contradicted what chemists have known since 1816 in their experimentation with carbon nitrides. Never was there a single hint of the existence of a covalent, single bond C–N network. In the last decade some 400 papers have been written about this non-existent material of dubious significance (R.C. DeVries, Mater. Res. Innovat. 1 (1997) 161). No C 3 N 4 material has ever been made and the claims on both the chemical composition and crystal structure are clearly in error. The impact of such exaggerated claims on the scientific enterprise cannot be ignored. In contrast, we report herein on a related but real hard material, silicon carbonitride, with the α -Si 3 N 4 crystal structure modified by the introduction of carbon atoms. Synthesis of this Si–N–C crystalline material was possible by using a CH 4 /H 2 /N 2 microwave plasma etching of solid Si. Films on Si, SiC, Si 3 N 4 and diamond, as well as crystal agglomerates of a few mm 3 volume, have been prepared. This phase possesses a micro-hardness lower than cubic boron nitride and a band gap of 3.8 eV. The present experiments indicate that only 6 at.% of C have been incorporated into α -Si 3 N 4 . We might suggest that ‘first principles’ calculations be undertaken to explain the limited solubility of carbon in the α -Si 3 N 4 phase.

Synthesis of diamond from methane and nitrogen mixture

We have found that diamond can be synthesized from a mixture of CH4 and N2 without adding any H2. This new synthesis is sharply different from the common practice of diamond growth by chemical vapor deposition, which uses a hydrogen‐rich mixture of CH4 and H2. In this new approach, nitrogen becomes an active component of microwave plasma leading to diamond growth. Nitrogen participates in abstraction of hydrogen from the diamond surface. We hypothesize that formation of HCN is an indication of hydrogen abstraction that allows diamond to grow from CH4+N2 mixtures. As a consequence of surface processes, the crystal structure of the grown diamond is distorted. The sequence of tetrahedral layers is mixed (cubic and hexagonal) and it suffers from turbostatic disorder. Diamond films were characterized by x‐ray diffraction, Auger electron spectroscopy, x‐ray photoelectron spectroscopy, and Raman spectroscopy.

Effects of noble gases on diamond deposition from methane‐hydrogen microwave plasmas

The deposition of diamond films by microwave plasmas has been studied in gaseous mixtures of methane, hydrogen, and noble gases. Plasma diagnostic results are compared with growth rates and Raman spectra of the films. The noble gases, which influence the degree of excitation or reactant molecules by energy transfer or charge transfer from their excited and ionic states, are active in the deposition process by inducing additional ion‐molecule and excited atom‐molecule reactions. As a result, enhanced deposition rates have been observed. Small oxygen additions along with the noble gases can suppress the formation of nondiamond carbon phases, leading to an effective way to rapidly deposit diamond films at high methane concentrations while still retaining minimal nondiamond carbon components in the films.

From diamond-like carbon to diamond coatings

Abstract Carbon films deposited by pyrolytic and plasma-activated deposition from hydrocarbon-containing gases encompass a virtual infinity of compositions (hydrogen concentrations) and structures (from amorphous to single crystal and with variable amounts of sp 1 , sp 2 and sp 3 bonding). Coatings which have a high degree of sp 3 bonding generally have properties, especially hardness, close to those of single- crystal diamond and are often referred to as diamond-like carbon. Recently, large grain size diamond crystals and continuous diamond coatings have been prepared by plasma chemical vapor deposition methods. Although such materials are different from the diamond-like carbon class of materials, there is clearly a continuum of materials which is expected to lead to vagueness and confusion in nomenclature. In this paper, such issues are dealt with and a working definition of “diamond” coatings is offered.

High-temperature thin-film diamond field-effect transistor fabricated using a selective growth method

Selective growth of boron-doped homoepitaxial diamond films was achieved using sputtered SiO/sub 2/ as a masking layer. The hole mobility of selectively grown films varied between 210 and 290 cm/sup 2//V-s for hole concentration between 1.0*10/sup 14/ and 6.9*10/sup 14/ cm/sup -3/. The technique was used to fabricate a thin-film diamond field-effect transistor operational at 300 degrees C. The channel resistance of the device is an exponential function of temperature. In combination with the selective growth method, this device can be used as a starting point for the development of high-temperature diamond-based integrated circuits.<<ETX>>