Chemical Vapor Deposited Diamond Films Research Articles

Distribution of 1.68 eV emission from diamond films

Free-standing polycrystalline chemical vapor deposition diamond films grown on a silicon wafer, with electrical behavior similar to values currently mentioned in the literature, present microheterogeneity. A detailed analysis by micro Raman shows how the diamond and nondiamond phases are distributed within the film and also the distribution of the silicon related luminescence. This luminescence is discussed in terms of two emitting centers close in energy. Absolute intensity of the diamond peak is not correlated with the good quality of the film as assessed by the Raman linewidth and ratio of this line to the nondiamond Raman lines.

Measurement of the substitutional nitrogen activation energy in diamond films

We show that the electrical properties of nitrogen-doped nominally undoped polycrystalline chemical vapor deposited diamond films are modified by post-deposition heating in an oxidizing atmosphere. We found that the first heating cycle in air in the temperature range of 300–673 K decreased the graphitization content still present in the diamond surface and that after the second heating cycle the electrical resistance versus temperature curves became stabilized. Using a flow of argon with residues of oxygen over the surface of the sample during the heating cycles, the stabilization of the resistance-temperature dependence also occurred but only after the fourth heating cycle. The results suggest the existence of an oxidation mechanism of the nondiamond carbon atoms present at the diamond surface. After stabilization, the deep donor ionization energy was found to be Ed=1.62±0.02 eV. All results brought together strongly suggest that this level is due to single nitrogen atoms that occupy substitutional lattice sites in diamond.

Field-emission current from diamond film deposited on molybdenum

Field-emission current from chemical vapor deposited diamond film on molybdenum wafer has been investigated experimentally and theoretically. The Fowler–Nordheim plot exhibits three linear regimes, corresponding to low, middle, and high electric field, respectively. A potential barrier model, based on a fact that metal carbide, Mo2C, exists at the interface between diamond and substrate, is presented. In terms of this model, the expression of field-emission current from diamond on Mo has been derived. The theoretical results agree qualitatively with the experimental observation and indicate that the emission current is related to the thickness of Mo2C and diamond under low and middle electric field, however, no similar relationship is found under high field.

Stress distribution around the ion-induced channels in chemical vapor deposited diamond films: a micro-Raman study

Stress distribution around the ion-induced channels in chemical vapor deposited diamond films: a micro-Raman study

Methane-induced texturing of chemical vapor deposition diamond films and correlation with UV photoresponse

The aim of the present work was to investigate the correlation between response to UV photons and crystal orientation in diamond films. Some chemical vapor deposition diamond samples were exposed to UV radiation (4–6 eV) and the photocurrent measured applying several electric fields. The orientation of diamond films has been checked by X-ray diffraction and the resulting spectra were used to define the percentage of texture. The results of our experiments show a clear correlation between UV photoresponse and film texture, obtained by varying the methane concentration in the growth plasma. Also, less oriented polycrystalline films have a better response than highly (100) textured films in terms of photocurrent and signal to noise ratio.

Stress distribution around the ion‐induced channels in chemical vapor deposited diamond films: a micro-Raman study

Stress distribution around the ion‐induced channels in chemical vapor deposited diamond films: a micro-Raman study

CVD diamond films as photon detectors

We present an overview of our research on Chemical Vapour Deposited (CVD) diamond films as photon detectors. Samples are grown in our laboratories using three different methods: microwave plasma enhanced CVD (MWPECVD), DC glow discharge CVD (DCGDCVD) and hot filament CVD (HFCVD). We present the photoelectrical properties of these samples having contacts in planar and sandwich configuration, taking into account the roles of material microstructure and electrical configuration. Their photoresponse has been measured in the whole visible–near UV spectral range with the aim to characterize their UV selectivity and to evaluate their gap-state density.

Thermal instability of a conduction channel in chemical vapor deposition diamond films

Thermal instability of a conduction channel in a nonmetallic field emission regime has been assumed as an origin of cathode-initiated vacuum breakdown process. In this article, details are given of a theoretical study of thermal response of a conduction channel in insulating media to dc fields, which takes into account the effect of temperature rise on field emission from substrates. It is found that this effect can lead to a regenerative process, which will finally cause a thermal runaway. In addition, an analysis was carried out on chemical vapor deposition diamond films, and it reveals that the thermal conductivity of diamond films is a key parameter in deciding the initiating mechanism of thermal instability of a channel in the film.

Optical properties of microcrystalline materials

We use optical, photocurrent and photothermal deflection spectroscopies to study defects in microcrystalline silicon ( μc-Si) thin films and diamond layers. Enhanced light absorption in μc-Si films and solar cells is due to several contributions: light scattering, change in the optical transition probability for strained and surface atoms and residual amorphous fraction. Low defect density (optical absorption with a coefficient, α, smaller than 0.1 cm −1 at about 0.8 eV, as measured by the constant photocurrent method), amorphous volume fraction below 10% and a distinct surface texture is typical for a material yielding a good efficiency μc-Si solar cells. Main defects in heteroepitaxial chemical vapor deposition diamond films are discussed.

Comparison of infrared, Raman, photoluminescence, and x-ray photoelectron spectroscopy for characterizing arc-jet-deposited diamond films

Impurities and growth-related defect structures are mainly responsible for low thermal conductivity of chemical vapor deposited diamond films. Different quality arc-jet-deposited, free-standing diamond samples were obtained from industry. Fourier transform infrared (FTIR), Raman, and x-ray photoelectron spectroscopy (XPS) were used to determine the quality of these samples. The nondiamond carbon was estimated from the 1560 cm−1 broad peak intensity, the CHx integrated peak absorbance, and the C1s plasmon loss features for Raman, FTIR, and XPS studies, respectively. The diamond quality was also determined from the Raman diamond peak full width at half maximum (FWHM) and XPS valence band spectra. It was observed that the higher the hydrogen content (determined by FTIR), the darker the color of the film, the larger the nondiamond 1560 cm−1 peak intensity, and the larger the FWHM of the Raman diamond peak at 1332 cm−1. Negligible difference in the C1s diamond bulk plasmon loss peak was observed for films of wide ranging quality. The FTIR CHx band exhibited the highest sensitivity to film quality. Impurity-related peaks were observed in the one phonon region of the FTIR spectra and the photoluminescence spectra. The photoluminescence background peak centered at 2.0 eV was found to be strongly related to nondiamond carbon impurities. It is shown that a combination of different analytical tools is required to determine diamond quality.

Thermoluminescence analysis of - and -irradiated chemical vapour deposited diamond films

The thermoluminescent (TL) response of a set of synthetic diamond films obtained by chemical vapour deposition was investigated using gamma and beta radioactive sources over the dose range from 60 mGy to 3.5 Gy. A TL response linear with dose was generally observed. A numerical curve-fitting procedure was applied to deconvolute the complex-structured TL glow curves, which were found to be composed at most by five peaks in the temperature range between C to C. A short preheat treatment after irradiation allowed us to obtain a very stable smooth-shaped glow curve composed of a unique peak close to C. This isolated structure followed first-order kinetics over the whole dose range. The activation energy of the main peak, eV, was determined considering all samples and all irradiation doses using both the peak shape method and the fitting procedure. The corresponding frequency factor was estimated to be within the range -. The TL sensitivity of the diamond films calculated considering the isolated high-temperature peak compares favourably with that measured with a set of LiF TLD100 and TLD700 standard dosimeters.

Modifying chemical vapor deposited diamond films for field emission displays

A systematic investigation of deposition parameters and post-treatments was performed for the development of field emission displays based on flat chemical vapor deposited diamond films. The lowest onset field strengths were obtained for films grown at the highest substrate temperature, highest methane content, and with negatively biased substrate. Intentionally damaging the films by implantation with 50 keV and 100 keV carbon ions as well as with 4.4 MeV silicon ions usually resulted in an enhanced field emission. The emission followed the Fowler–Nordheim law up to 0.5 mA/mm2, and a current carrying ability of more than 100 mA/mm2 was detected. Considerably improved emission was achieved by short and long-term processing at higher current levels.

Surface vacancies in CVD diamond

Abstract Investigation of unpolished, high-quality chemical vapour deposition diamond films has revealed a significant concentration of vacancies within a few microns of the surface, but not in the bulk. Modelling of the growth, diffusion and trapping of vacancies shows that this arises from the growth of vacancies into the surface of the diamond and their subsequent migration and trapping as growth proceeds. Because the temperature at which the vacancies migrate is comparable with that of diamond growth, a unique situation arises: the lattice defects created during growth persist in the crystals.

On nitrogen incorporation during PE-CVD of diamond films

Abstract Nitrogen is one of the most widely studied impurities in diamond films. The reason is that nitrogen takes part in a number of defects and therefore has a deep influence on the optical and electrical properties of diamond films. The mechanism of nitrogen incorporation in diamond is still an open question. This is mainly due to the complexity of the N-incorporation processes, depending not only on experimental parameters (e.g. type and concentration of the N-containing gas, substrate temperature etc.) but also on the surface termination and on the orientation of the chemical vapor deposition (CVD) diamond film. The aim of this paper is to compare nitrogen incorporation in CVD diamond films by addition of small amounts (ppm range) of two different N-containing precursors—nitrogen and vaporised nitromethane—to a conventional CH4/H2 gas mixture during microwave PE-CVD. Optical emission spectroscopy (OES) was used to survey the plasma chemistry during deposition. The relative intensities of the Hβ atomic hydrogen emission line and of the CN and C2 emitting radicals were recorded as a function of the nitrogen fraction added to the plasma. The influence of nitrogen incorporation on the diamond film properties was investigated by a number of complementary techniques such as scanning electron microscopy (SEM), X-ray diffraction (XRD), photothermal deflection spectroscopy (PDS-optical absorption) and Raman spectroscopy.

Multifrequency EPR,1HENDOR, and saturation recovery of paramagnetic defects in diamond films grown by chemical vapor deposition

Paramagnetic defects in free-standing polycrystalline chemical vapor deposition (CVD) diamond films have been studied using multifrequency electron paramagnetic resonance (EPR) (1--35 GHz), electron-nuclear double resonance (ENDOR), saturation recovery, and infrared absorption. The results confirm the ${}^{1}$H hyperfine parameters for the recently identified H1 defect [Zhou et al., Phys. Rev. B 54, 7881 (1996)]. However, in the CVD diamond samples studied here, H1 is always accompanied by another defect at $g=2.0028(1)$. Saturation recovery measurements are consistent with two defects centered on $g=2.0028$. At temperatures below 100 K the spin-lattice relaxation rate of H1 is determined by the direct process and is a factor of 10--100 times more rapid than the single substitutional nitrogen center, which is known to be incorporated into the bulk diamond. ${}^{1}$H matrix ENDOR measurements indicate that the H1 center is in an environment with hydrogen atoms 0.2--1.0 nm from the center. The near-neighbor hydrogen identified by multifrequency EPR was not detected in the ENDOR experiments. The concentration of H1 correlates with the total integrated CH stretch infrared absorption in the samples studied here. All the evidence is consistent with H1 being located at hydrogen decorated grain boundaries (or in intergranular material) rather than in the bulk diamond. A third EPR resonance at $g=2.0028(1)$ has been observed in some of the CVD diamond samples studied. The resonance is distinguished by its temperature-dependent linewidth: above 50 K the line is exchange narrowed, but below 50 K it broadens rapidly with decreasing temperature.

Complementary application of electron microscopy and micro-Raman spectroscopy for microstructure, stress, and bonding defect investigation of heteroepitaxial chemical vapor deposited diamond films

The evolution and interdependence of microstructure, stress, and bonding defects of heteroepitaxial diamond films deposited on silicon substrates has been investigated by applying scanning electron microscopy, transmission electron microscopy (TEM), and micro-Raman spectroscopy to the same places in the films. For this purpose, TEM plane-view specimens were prepared and the same grains in the electron transparent areas were characterized by all three methods that allowed crystalline defects and their relation to spectral features of the Raman spectrum to be identified. To the authors’ knowledge, this is the first successful complementary application of these methods to diamond films. Concerning microstructure evolution, dislocations in the silicon substrate and a residual plastic deformation of the silicon wafer prove that plastic deformation of the silicon substrate had occurred with the presence of mechanical stress during deposition. Evolutionary selection of randomly oriented, highly defective diamond grains observed at a film thickness of 300 nm leads to a textured film at 4 μm (an intermediate state) consisting of truncated pyramids with defect-free {001} growth sectors, bounded by four {111} growth sectors which exhibit a high density of twins and stacking faults. During further growth, merging of {001} growth sectors begins and apart from the formation of low-angle grain boundaries, the formation of partial wedge disclinations takes place, partly accommodating the misorientation between grains by elastic deformation. The latter process is shown to be more favorable than the formation of low-angle grain boundaries below a certain misorientation. Merging of grains introduces a high number of dislocations and mechanical stress into the {001} growth sectors. The comparison of the Raman spectra with electron micrograph images shows that the G band of the Raman spectrum originates exclusively from grain boundaries having an associated {111} growth sector. Very localized luminescence sources have been detected, not correlating to microstructure elements. Stress inhomogeneities measured within single grains and an earlier observed transition of the biaxial stress state in the film plane to a more complicated stress state after grain merging is shown to originate from disclinations.

Doping Diamond for Electronic Applications

AbstractDiamond exhibits extraordinary physical and chemical properties, many of which have already found application in tribology, thermal management, and optics. Furthermore, diamond is also a wide‐band‐gap semiconductor which, when doped, can lead to the realization of electronic and optoelectronic devices with exceptional properties. Diamond can now be doped p‐type, with boron, both during chemical vapor deposition (CVD) diamond film growth and by ion‐implantation, and n‐type, with phosphorus, during CVD growth. This paper reviews the current status of diamond doping and describes the electronic properties of the doped layers. Some potential applications of doped semiconducting diamond are described.

Nitrogen-Induced Nanocrystallinity of CVD Diamond Films on Ti-6Al-4V Alloys

AbstractMicrowave plasma chemical vapor deposition (CVD) was used to grow nanocrystalline diamond films by adding nitrogen to a high density plasma defined by a high operating pressure (125 Torr) and high methane feedgas concentration (15% in a balance of hydrogen). Films grown at these conditions but without nitrogen exhibited well-faceted, high phase purity crystalline diamond while those grown with added nitrogen showed a nanocrystalline structure and were an order of magnitude smoother. The nitrogen-induced nanocrystalline films are believed to be comprised predominantly of diamond nanocrystallites in a matrix of tetrahedral amorphous carbon. The films were characterized by Raman spectroscopy, grazing-angle x-ray diffraction, surface profilometry, nano-indentation, electron microscopy, and pin-on-disc tribometry. In contrast to standard CVD conditions, the high density plasma results in adhered films on Ti-6AI-4V substrates even at substrate temperatures of 850°C. We present plasma optical emission spectroscopy results which are correlated with changes in the Raman spectra and the film microstructure. The hardness of the films (∼90 GPa), their low rms surface roughness (27 nm), and their good adhesion to the substrate makes these films potentially useful for tribological applications.

Fracture toughness estimation of thin chemical vapor deposition diamond films based on the spontaneous fracture behavior on quartz glass substrates

This article is on the experimental estimation of the fracture toughness of thin diamond film deposited by the microwave plasma chemical vapor deposition method on a quartz glass substrate. Because of their differences in the coefficient of thermal expansion, diamond films on a quartz glass substrate suffer tensile stress at room temperature and show various kinds of spontaneous fracture behavior, reflecting the mechanical properties of the films. On the basis of detailed observation of cracking patterns and also measuring the residual stress with the aid of Raman spectroscopy, the fracture toughness of the film having thickness of around 1 μm has been estimated here satisfactorily without the help of any difficult microscopic experiment. The fracture toughness of the film of thickness 0.35 μm is found to be around half of that obtained with much thicker films.

Reactive Ion Etching of Diamond in O2 and CF4 Plasma, and Fabrication of Porous Diamond for Field Emitter Cathodes

Reactive ion etching (RIE) of synthetic Ib diamond and chemical vapor deposition (CVD) diamond films in O2 and CF4 has been investigated. The large etch rate of up to 2.8 µ m/h and etch rate ratios of 15–20 for diamond (100)/Al were obtained at CF4/O2=10–20%. Numerous columnar structures of approximately 300 nm length and 10 nm width have been made by etching CVD polycrystalline diamond films in O2 plasma. The structures made the diamond film “porous”. A comparative study of field emission characteristics has been made for as-grown diamond films and porous diamond films. The average turn-on field was in the range of 2–3 V/µ m for porous diamond films and 6–8 V/µ m for as-grown diamond films.