Diamond growth rates and quality were studied as a function of source gas composition and correlated with position on the ternary C-H-O diagram. The chemical potentials of carbon and oxygen change dramatically on either side of the H2-CO tie line, leading to large differences in the equilibrium distribution of species. These differences are reflected in the species flux reaching the diamond surface, and hence in the quality and growth rate of the diamond. In situ microbalance measurements in a hot-filament reactor show that the reaction rate is independent of the CO concentration, but decreases with increasing O2. Quality, as measured by Raman spectroscopy, increases as the C/C+O ratio in the source gases is reduced to approach the critical value of 0.5. The stability of the filaments to decarburizing and oxidation are correlated with the carbon and oxygen chemical potentials and hence to the position on the C-H-O diagram. A preliminary ternary diagram for the C-H-F system is presented.

Diamond nucleation has been investigated on a variety of potential heteroepitaxial substrate materials. Previous work in this laboratory has demonstrated heteroepitaxial nucleation on both Si and SiC substrates via bias-enhanced nucleation (BEN). In this study the effects of BEN of diamond on refractory metal substrates is investigated in detail. Initial data suggest a strong correlation between the carbide forming nature of the substrate material and the rate of nucleation during biasing. Our second avenue of research involves low pressure diamond growth on nickel. This material is a promising material due to its close lattice match and recent evidence of epitaxy reported by other researchers. To form heteroepitaxial diamond on nickel a high temperature pretreatment routine has been established and is the basis for this area of research. The relative importance of hydrogen absorption during this routine is explored and correlated to the formation and degree of diamond epitaxy.

Crystallographic defects which form during growth of CVD diamond were studied and their effect on the surface structure of the growing wafer evaluated. The most abundant defects are β=3 twins boundaries whose density is very high at the nucleation side and as low as one twin per 10 /μm at the growth surface. The intersection of these twin boundaries with one another results in a formation of higher order twin boundaries. β=9 as well as β=27 and β=81 boundaries have been analyzed. The surface crystallography of optical quality diamond wafers reveals the role of β=3 twins in promoting fast growth.

We have used an electron cyclotron resonance plasma system to perform chemical vapor deposition experiments on single-crystal, (110) oriented diamond substrates. The depositions were carried out at 0.060 Torr using mixtures of methanol in hydrogen. Substrate temperatures were varied from approximately 620 to 800 °C The film morphology was examined using SEM and microstructural phase determination was attempted using micro-Raman spectroscopy. Based on the results of these experiments, we have determined general trends for the characteristics of films deposited on diamond from the ECR plasma at low pressures and temperatures.

A thick homoepitaxial CVD diamond film was grown on a large high temperature, high pressure (HTHP) Ha diamond to study the defects present in the CVD film. The HTHP diamond had dimensions of 6 mm x 6 mm x 0.44 mm. The thickness of the diamond was increased to 0.84 mm by microwave plasma CVD. X-ray topographs were taken before and after growth to compare the defects in CVD diamond to those in the HTHP diamond. Prior to growth the substrate was unstrained and the characteristic microstructure of stacking faults and dislocations was observed. There was also a surface relief, visible optically, on the substrate of lines along the [100] which are probably due to polishing. After deposition of the CVD film, the crystal was strained with the film in tension. The defect structure observed throughout the CVD film followed the surface relief of the substrate. Cathodoluminescence spectra indicate that the film contains nitrogen defect complexes which are not present in the substrate. Cathodoluminescence also indicates that there are more non-radiative recombination centers in the film than in the substrate. Electrical results from transient photoconductivity measurements indicate that while the mobilities of the film and the substrate are comparable, the lifetime is much shorter in the film, possibly reflecting the higher concentration of non-radiative recombination centers.

Polycrystalline diamond films were synthesized using an oxy-acetylene flame in the open atmosphere and in an enclosed chamber. In the present work, we have shown that the 2.16eV defect band seen in the photoluminescence spectra from the central portion of the films grown in the open atmosphere show a dependence on the growth temperature. Films grown in the open atmosphere all exhibit a decrease in the crystalline quality when moving to the outside edge most likely due to the entrainment of nitrogen into the films.

The present study was done in the enclosed chamber using an oxygen atmosphere via an oxygen flow around the torch. Films have been grown in the enclosed chamber that show only trace amounts of the 2.16eV band. Both the Raman and the photoluminescence spectra show that the films grown in the enclosed chamber are very uniform over the deposition area, which suggests that the degradation of the outer portion of the open atmosphere films may be the result of room air entrainment, and not a temperature variation across the substrate. In addition, when either lower purity oxygen is used or lower growth temperatures, we easily observe the 2.16eV band which may be the result of nitrogen impurities in the source gases.

We have conducted x-ray diffraction, Raman spectroscopy, and scanning electron microscopy analyses of diamond films grown by hot filament assisted chemical vapor deposition (HFCVD). We present results on the relative abundance of the (111), (220) and (400) faces in polycrystalline diamond films as functions of CH4 concentration. The intensity of the (111) peak can be varied from about 20% to 60% by adjusting CH4 in CH4/H2 mixtures. We also present results on preferred orientation in films grown under varying hydrogen treatments. We discuss correlations between the preferred orientation, FWHM of the diamond peak in the Raman spectrum, and surface morphology of the films.

Smooth diamond films have been grown by hot filament chemical vapor deposition under d.c. bias on mirror-polished Si substrates. Films a few micrometers thick were obtained in 30 minutes. Raman spectra showed very broad diamond peaks. X-ray diffraction showed the presence of diamond and also other carbon phase with a line 2.11 Å. With time, the films apparently underwent a phase transformation.

Microwave plasma has been used to grow diamond films using CH4 and H2 over nickel substrates. Nucleation of the diamond has been achieved by manual scratching and ultrasonic agitation of the substrates. The substrate was left in the H 2 microwave plasma to remove any oxide film present prior to the diamond growth. According to SEM the morphology of the grown films was (100) textured over the entire surface. Our interest is to study the effect of O2 on the growth rate and the morphology of as-deposited diamond films. Infact, O2 has a tendency to preferentially etch the diamond (etch rate: 111 > 110 >100). Injection of O2 into the reaction mixture could enhance the 100 texture further. Raman analysis confirms the deposited films as diamond. Effect of O2 on the nature of the films and the characterization of as-deposited films is described.

We report results from cathodoluminescence spectroscopy of boron nitride films grown on Si (100) substrates by ECR ion source assisted magnetron sputtering of a hexagonal BN target. Three main peaks are observed in the near-bandgap region for hexagonal boron nitride films at energies of 4.90 eV, 5.31 eV, and 5.50 eV. In addition, deep-level emission spectra of predominantly cubic boron nitride films are correlated with sample growth conditions. In particular we show that the emission intensity, position, and linewidth are strongly dependent on the substrate bias voltage used during sample growth.

We report the growth of cubic boron nitride (cBN) films by magnetron sputtering on Si (100) substrates. The films are grown in the presence of negative substrate bias voltages and a nitrogen plasma produced by an electron cyclotron resonance source. We find evidence for a sharp low-voltage threshold in the substrate bias (-105 V) beyond which the samples are predominantly cBN. The structural quality of the cBN films is optimized in a narrow range of voltages near this threshold. We discuss the important role of energetic ions in the formation of cBN in light of recent theoretical findings.

The morphology and interface chemistry occurring during the initial deposition of BN, AlN and GaN films via metal evaporation and N2 decomposition under UHV conditions have been determined. FTIR spectroscopy and TEM revealed the consecutive deposition of an initial 20Å layer of a-BN, 20–60Å of oriented h-BN, and a final layer of polycrystalline c-BN. This sequence is attributed primarily to increasing intrinsic compressive stress in the films. XPS analysis revealed the growth of GaN on sapphire to occur via the Stranski-Krastanov mode; growth on SiC showed characteristics of three-dimensional growth. AlN grew layer-by-layer on both substrates. Vicinal 6H-SiC(0001) substrate surfaces contain closely spaced, single bilayer steps. During deposition of Si and C at 1050°C, 6H layers initially form and step bunching occurs. The latter phenomenon results in more widely spaced steps, the nucleation of 3C-SiC both on the new terraces and at the larger steps and formation of double position boundaries. The C/Si ratio in the gaseous reactants also affects the occurrence of these three phenomena.

The growth morphology and microstructure of SiC/AlN/6H-SiC, SiC/AlN/SiC/Si, and SiC/AlN/Si heterostructures grown by LPCVD were studied using transmission electron microscopy. The SiC/AIN bilayers grown on 6H-SiC substrates were single crystalline and comprised of 3C-SiC and 2H-AlN. The epitaxial relationship between 2H-AlN and 6H-SiC is [0001]AlN//[0001]SiC. The SiC/AlN/SiC trilayers and the SiC/AIN bilayer grown on (001)Si were composed of 3H-SiC and 2H-AlN. However, the 2H-AlN layer was polycrystalline even though the (001)3C-SiC was single crystalline. The preferred orientation of the AlN layers in SiC/AlN/SiC/Si and SiC/AlN/Si are [0112] and [0002], respectively. The AlN/3C-SiC interface is relatively sharp compared to the AIN/Si interface in which an amorphous layer close to the interface was observed. In general, the polycrystalline AlN structure has two distinct layers: (1) nucleation layer and (2) bulk layer. High resolution lattice images of the polycrystalline AlN showed amorphous areas and small misoriented crystallites in the nucleation layer. The bulk layer consists of preferentially oriented large columnar grains.

Recent progress in horaoepitaxial growth of 6H-SiC by stop-controlled epitaxy utilizing off-angle substrates is discussed in detail. Features of step-controlled epitaxy and its growth mechanism are described based on experimental results. The growth mode on off-angle substrates is explained by a stagnant layer model. The diffusion length of adatoms on a surface is calculated using a simple surface diffusion model. The critical conditions of two-dimensional nucleation and step-flow growth are predicted based on theoretical calculation and experimental results. Microscopic surface processes such as nucleation and step motion are made clear by observing the grown layer after short-time growth.

Silicon carbide films were deposited by electron cyclotron resonance plasma chemical vapour deposition, using Ditertiary Butyl Silane (SiH2(C4H9)2), a non-corrosive organic compound, liquid at room temperature and stable in air, as precursor. Depositions were carried out in an Ar/H2 plasma at relatively low temperatures, below 400 °C. The influence of deposition parameters such as substrate temperature, gas flow rates, pressure, and microwave power, was systematically investigated and related to the Si:C ratios and the refractive index. The film composition was measured by Auger electron spectroscopy and the surface morphology was examined by scanning electron microscopy. The deposition rates and refractive indexes were extracted from the conventional ellipsometric functions, psi and delta. The results show that high quality silicon carbide of variable Si:C ratios and with very low levels of impurities are obtained.

The growth of SiC epilayers by atmospheric pressure CVD (AP-CVD) is influenced by many chemical gas phase reactions and transport phenomena, and is difficult to study directly due to the high growth temperatures (up to 2100 K). To grow epilayers of good quality, it is necessary to control the silicon and carbon supply, each affected by different mechanisms. The use of graphite as the susceptor material causes a remarkable change in the carbon balance due to reactions between the graphite and the hydrogen carrier gas. This graphite-hydrogen reaction enriches the gas phase with carbon and above a certain critical temperature it is impossible to control the Si:C-ratio in the gas phase by a variation of the carbon containing input gas. The silicon supply is usually treated as transport through a stagnant layer in the gas phase determined by the transport properties of the carrier gas and the temperature gradient in the reactor. A numerical solution of the flow-equations in the reactor shows that the flow characteristics and temperature gradients in the reactor are hardly affected by the gas flow velocity.

Silicon carbide films are grown epitaxially on crystalline silicon substrates heated above 1000 °C, by laser ablation of pure carbon targets to thicknesses between 300 and 400 nm. These films grow on top of the silicon substrate from the carbon in the ablation plume and from the silicon of the substrate. By using a method of alternate ablation of a pure carbon and a pure silicon target, similar epitaxial films can be grown to thicknesses in excess of 1 μm with part of the silicon being supplied by the ablation plume of the silicon target.

As-grown SiC single crystals and as-deposited SiC epilayers often exhibit stacking faults. The most probable fault configurations that occur in 6H- or 15R-SiC crystals are deduced from calculations of the stacking fault energies using a modified Ising model with the Ising parameters taken from earlier ab initio calculations. In this study, experimental TEM observations reveal stacking fault configurations in 6H- and 15R-SiC, and the observed configurations are compared with calculated stacking fault energies.

We present a method for growing low-doped 6H SiC films using chemical vapour deposition in a hot-wall system. The study discusses the influence of temperature, growth rate and C/Si ratio on the purity of the layers. Furthermore, we make a comparison between methane and propane as carbon source, and investigate the influence of bake-out prior to growth. The films are characterised using low temperature photoluminescence. The relative intensity of the free exciton related luminescence as compared to impurity related bound exciton recombination is discussed in terms of material purity. A capacitance-voltage technique is used to determine the doping concentration.

A series of CVD-grown 3C-SiC/Si(100) films of different growth times, and hence film thicknesses, are studied by X-ray photoelectron spectroscopy (XPS) and secondary ion mass spectrometry (SIMS). XPS showed that the surfaces of the samples consist of Si oxides (SiO2 and SiOx where x < 2) and unreacted C.H. Unreacted elemental Si is also present and its amount decreases with increasing growth time. This surface overlayer is further investigated by changing the photoelectron take-off angle and from chemical etching studies. Compositional variations of the SiC films are also studied using SIMS.