Single Crystal Diamond Films Research Articles

Free-standing Diamond Single Crystal Film for Electronics Applications

AbstractHigh quality single crystal diamond film is an excellent transparent semiconductor material. Combined with its good electrical, optical, thermal and chemical properties, diamond-based semiconductor devices offer the potential of operation at very high voltages (>10 kV), power levels, and temperatures (>400°C) and under extreme radiation conditions.In this paper, we exploit the optical transparent property of MPCVD single crystal diamond films to correlate the quality of the epi-layers with the performance of Schottky barrier diodes fabricated on the layer. We used optical microscopy to observe stress induced birefringence caused by defects/dislocations in the material and micro- Raman/photoluminescence to detect relative amounts of non-diamond carbon and color centers (nitrogen and silicon atom complexes with lattice vacancies) in the material. High structural quality (low stress) is correlated with the properties of Schottky barrier diodes fabricated in the material. Vertical devices made from a 20 µm homo-epi-layer have been shown high breakdown fields of 1.85 MVcm-1 (BV = 3.7 kV) and conduction of 0.6 A/cm2 at 20V forward drop at 290 °C. Through device failure analysis, we can conclude that the 1.85 MVcm-1 field is only a lower limit for the material. Local stresses (dislocations) and point defects appear to be the main reasons for the high voltage failure of our single crystal diamond rectifiers.

Muon spin relaxation in CVD polycrystalline diamond film

The behavior of hydrogen in chemical vapor deposition (CVD) polycrystalline diamond film characterized by Raman spectroscopy, cathode luminescence and electron spin resonance measurements was studied using the longitudinal magnetic field muon spin relaxation technique. The experimental results showed the existence of a diamagnetic muon state (μ +) and two paramagnetic muonium (Mu: μ +e −) states (tetrahedral interstitial (Mu T) and bond-centered (Mu BC)) formed by positive muons implanted into the sample. Moreover, unknown states, generally called missing fraction (MF), were observed. This is the first time in this research that absolute fractions of Mu BC and MF in CVD polycrystalline diamond film have been determined. The absolute fractions of μ +, Mu T, Mu BC and MF in the present sample were 50, 7, 19 and 24%, respectively. The absolute fraction of Mu T for the present sample with crystallite size of 20–70 μm is comparable to that published for natural IIa single crystal diamond and CVD polycrystalline diamond film with average crystallite size of 100 μm. However, the MF of the present sample was much higher than that of IIa single crystal diamond.

Application of Diamond in High Technology

This review focuses on the critical issues and future directions in the application of diamond in high technology. Diamond nuclear radiation detectors, photosensors, photoemitters, spectral windows, active and passive microelectronic components, and microelectromechanical systems are discussed in detail. In Russia, high-technology diamond applications have not yet moved toward the manufacturing stage, even though Russia possesses immense resources of natural diamond and a considerable scientific potential in the field of creating unique synthetic diamonds, polycrystalline and single-crystal diamond films, and diamond-like compounds. We hope that the points raised in this review will provide the impetus for the development of diamond technology in Russia.

Diamond detectors for space applications

This work reviews some general results obtained by our group in the framework of a programme focused on the development and the characterisation of Vacuum-UV (VUV) CVD diamond photodetectors to address the requirements of space missions where pixel and 2-D arrays are used. We discuss the performance of detectors based on single crystal diamond films and CVD polycrystalline diamond films. The performance of these devices in the dark and under illumination was investigated and the results were compared to those from CCD and MCP detectors. The status of diamond detector technology is finally described in order to highlight its advantages over more traditional detectors and the aspects requiring further developments.

Initial growth stage evaluation of high-quality diamond films synthesized by the chamber flame method

The crystallinity of 5-μm-thick polycrystalline and single-crystal diamond films, which was synthesized by the chamber flame method, was evaluated by means of cathodeluminescence spectral analysis. Crystal defects are found in the initial growth grains in the polycrystalline diamond films. However, defect-free high-quality single-crystalline diamond films can be synthesized at the rate of approximately 20 μm/h in the case of homoepitaxial growth.

Analysis of chemical vapour deposited diamond films by X-ray photoelectron spectroscopy

X-ray photoelectron spectroscopy (XPS) for elemental and phase analysis of diamond surfaces is reviewed, including both single crystal natural diamond and polycrystalline chemical vapour deposition (CVD) films. The core C1s peaks, plasmon losses and valence band spectra of sp 2 graphite are compared with those of sp 3 diamond, and briefly with mixed sp 2/sp 3 hard carbon films. Surface reconstructions are reviewed for diamond in the presence of hydrogen or following thermal annealing. Attention is drawn to the destructive effects of argon ion bombardment ‘cleaning’. The synthesis of CVD diamond, including the initial nucleation process, is described and the significance of hydrogen is explained. Chemical modification of the surface of diamond films is discussed, with relevance to sensors and field electron emission. XPS analysis of (111) polycrystalline films treated by atom beams of N, O, H, Cl is described and the influence of unwanted oxygen is emphasised. For both atom beam and furnace oxidation, the oxygen is incorporated into the (111) diamond surface as bridging C–O–C.

Diamond nucleation on iridium buffer layers and subsequent textured growth: A route for the realization of single-crystal diamond films

It is shown that diamond nucleation on iridium buffer layers followed by an appropriate textured-growth step offers a viable way to realize single-crystal diamond films. Bias-enhanced nucleation on iridium layers results in heteroepitaxial diamond films with highly improved alignment. By a subsequent textured-growth step, the mosaicity can be further reduced for tilt as well as for twist in sharp contrast to former experiments using silicon substrates. Minimum values of 0.17° and 0.38° have been measured for tilt and twist, respectively. Plan view transmission electron microscopy of these films shows that, for low thicknesses (0.6 μm and 8 μm), the films are polycrystalline, consisting of a closed network of grain boundaries. In contrast, at the highest thickness (34 μm) most of the remaining structural defects are concentrated in bands of limited extension. The absence of an interconnected network of grain boundaries shows that the latter films are no longer polycrystalline.

Epitaxial Ir layers on SrTiO 3 as substrates for diamond nucleation: deposition of the films and modification in the CVD environment

Iridium films on SrTiO3(001) have recently proven to be a superior substrate material for the heteroepitaxy of diamond thin films by chemical vapour deposition in the effort towards the realization of single crystal diamond films. In this paper we report on the growth and structural properties of iridium (Ir) films deposited by electron-beam evaporation on SrTiO3(001) surfaces varying the deposition temperature between 280 and 950°C. The films were studied by scanning electron microscopy, atomic force microscopy and X-ray diffraction. At the highest temperature film growth proceeds via three-dimensional nucleation, coalescence and subsequent layer-by-layer growth. The resulting films show a cube-on-cube orientation relationship with the substrate and a minimum mosaic spread of 0.15°. Towards lower deposition temperatures the orientation spread increases only slightly down to ∼500°C while the surface roughness, after passing through a maximum at ∼860°C, decreases significantly. For the lowest temperatures (below 500°C) the mosaic spread rises accompanied by the occurrence of twins until the epitaxial order is lost. Plasma treatment in the diamond deposition reactor at high temperature (920°C) yields low nucleation densities and modifies the Ir surface. At the same time {111} facets show a significantly higher structural stability as compared with {001} facets. Nucleation at 700°C results in highly aligned diamond grains with low mosaic spread and a vanishing fraction of randomly oriented grains, proving the superior properties of Ir films on SrTiO3 for diamond nucleation as compared with pure silicon substrates.

111 単結晶ダイヤモンド薄膜作製への分子動力学アプローチ

The single crystal diamond film has been drawn attention for new material such as the electronic devices used in higher temperature. So it is important to understand a mechanism of diamond nucleation on silicon substrate by Chemical Vapor Deposition (CVD) method, but the mechanism has not yet been established because of the difficulty of the observation. Fundamental process of the nucleation of the diamond consists of both the adsorption and the reflection of carbon atoms to the silicon substrate. The details of both phenomena have not yet been clear. In this paper, in order to solve fundamental process of the nucleation of the diamond, molecular dynamics simulation of the adsorption of the carbon atom is conducted. The adsorption phenomenon affected by the velocity and angle of incidence of the carbon atom is presented here. It is shown that the adsorption phenomenon is independent of the velocity and the angle of incidence.

Heteroepitaxial growth of {1 1 1}-oriented diamond films on platinum{1 1 1}/sapphire{0 0 0 1} substrates

By microwave enhanced chemical vapor deposition, {1 1 1}-oriented diamond films were heteroepitaxially grown on platinum{1 1 1} films of 4 μm thickness which were sputter-deposited at 600°C on sapphire{0 0 0 1}. It was found that X-ray diffraction rocking curve of diamond{1 1 1} has a full-width at half-maximum value of 2.0°. The films have an intensively coalesced smooth surface consisting of azimuthally aligned diamond{1 1 1}. It was also found using Raman spectroscopy that the diamond films have unexpectedly small residual stress, which is considered to be a major reason why the diamonds are successfully grown without crack or delamination over the entire surface of substrates. While the sample area in this study is only 5×10 mm 2, the present achievements opened a path towards fabrication of large-area single crystal diamond films as sapphire substrates are commercially available in several inches of diameter

Transmission Electron Microscopic Study Of Heteroepitaxial Mechanism Of Cvd-Dlamond Grown On Pt(Lll) Substrate.

Owing to its unique and outstanding physical-chemical properties, diamond is considered to be one of the most important potential materials for applications such as in mechanical, optical, thermal, and electronic devices. Among them, the most attractive application of diamond would be a semiconductor for high temperature and high power electronic devices. To realize such novel devices, a high quality of defect-free single-crystal diamond film is required. Recently, continuous diamond films are found to be able to grow on Pt(lll) substrate. Since the diamond film synthesized on Pt shows a high degree of epitaxy, this approach has drawn the attention of reseafchers in this field and some research results have been reported. However, the heteroepitaxial mechanism is still to be elucidated; in particular, why does diamond grow heteroepitaxially on the Pt substrate and how do the atoms align in the interface between diamond and the Pt substrate? In order to solve those problems, it is very necessary to study the diamond growth mechanism on an atomic scale.

Determination of conditions for development and growth of a metastable diamond phase of carbon and absence of stable graphite phase

Conditions for development and growth of just a metastable diamond phase of carbon and complete absence of graphite are determined. Based on the results obtained, a method for development of single-crystal diamond films not involving chemical etching of graphite is proposed.

Focused-ion-beam-assisted etching of diamond in XeF2

Ga focused-ion-beam (FIB)-assisted etching of single-crystal diamond and thin film diamond in XeF2 was studied. The etch yield in FIB-assisted etching of diamond in XeF2 is enhanced some six times over the physical sputtering yield. In the crystal orientation dependence of the etch yield in FIB-assisted etching, the (100) face produced the highest etch yield of the three faces—(100), (110), and (111). Thin film diamond produces the lowest etch yield. A diamond field emitter with a tip radius of less than 100 nm was obtained using Ga FIB spot exposure.

Noncontact temperature measurements of diamond by Raman scattering spectroscopy

The possibility of determining the temperature of diamond by noncontact Raman spectroscopy is assessed critically. The intensity ratio of Stokes to anti-Stokes lines is shown to be ill suited for temperatures above ∼750 K. Employing the temperature coefficient of the Raman line position, on the other hand, turns out to be a straightforward and highly reliable means to measure diamond temperatures between 300 and 2000 K with an accuracy of ±10 K. A prerequisite for the application of this method is an empirically developed formula which describes the temperature coefficient of the Raman active phonon frequency with high accuracy. Examples of temperature measurements on single crystal diamond and diamond films grown by chemical vapor deposition are given. The application of this procedure to the temperature measurement of silicon and germanium is demonstrated.

A uniformly cleaved epitaxically grown diamond crystal for synchrotron radiation.

A homoepitaxic single-crystal diamond (111) film grown by microwave-assisted chemical vapour deposition (CVD) and fractured along the [110] directions to form small triangles was investigated by X-ray double-crystal topography. The X-ray topographic image showed that all parts of the cleaved CVD diamond film sections uniformly reflected X-rays at the peak position of the rocking curve, which was measured in the Bragg case. Furthermore, no bending effect was observed and the CVD diamond film appeared to be more perfect than and showed higher integrated intensity than the natural diamond substrate.

Molecular mechanics simulation of the diamond nucleation and growth on silicon (001) and (111) surfaces

The nucleations and growths of diamond on silicon (001) and (111) surfaces according to the models previously proposed by us have been simulated in molecular mechanics optimizations for a series of cluster models. These simulations may provide clear mechanisms of the diamond nucleation and growth on such surfaces and further demonstrate that it may be feasible to grow large, single-crystal diamond film.

Growth and structure of epitaxial diamond films grown on Si(111) single crystals

Experiments on growing single-crystal diamond films on silicon crystals with (111) surface orientation have been performed. Results attesting to the possibility of obtaining thin heteroepitaxial films are presented.

Structural modeling of the possible growth of oriented textured single-crystal diamond film on a silicon (111) surface

A model based on semi-empirical molecular orbital calculations and molecular mechanics is proposed for oriented textured diamond film growth on the Si(111) surface. The diamond <111≳ axis in our model is parallel to the silicon substrate <111≳ while the diamond <11̄0≳ is rotated 10.89° around the <111≳ axis referenced to the <11̄0≳ of the silicon substrate. The atomic density of the grown diamond in one dimension perpendicular to the <111≳ has a ratio 1.003:1 to that of a natural crystal, and thus is much better than the 1:1.015 of the heteroepitaxial diamond on the silicon (001) surface. We conjecture that this improvement in lattice match is important to achieve single-crystal growth. A model for heteroepitaxial growth with a diamond <111≳//Si<111≳ and diamond <11̄0≳//Si<11̄0≳ relationship is also studied but is found to have poorer bonding to the substrate and has a larger residual mismatch of 1:1.015.

Epitaxially oriented growth of diamond on silicon by hot filament chemical vapor deposition

Expitaxially oriented growth of diamond film on Si(001) was achieved using hot filament chemical vapor deposition. The epitaxial relationship between the film and the substrate was confirmed by the observation through scanning electron microscopy and high-resolution transmission electron microscopy (HRTEM) as follows: Dia(001)//Si(001) and Dia〈110〉//Si〈110〉 with a misorientation angle of 9° between Dia(001) and Si(001). This reports the HRTEM observation of the largest area of the diamond/Si interface (larger than 880 Å). It demonstrates that the intermediate β-SiC layer is unnecessary for achieving diamond epitaxy on Si. Discussion reveals that the value of the misorientation angle between Dia(001) and Si(001) is not unique and should be controlled to deposit single-crystal diamond films on Si.

Recent Advances in Producing Cubic BN and Single Crystal Diamond Films by CVD Methods

Recent Advances in Producing Cubic BN and Single Crystal Diamond Films by CVD Methods