High Quality Single Crystal Diamond Research Articles

Single Crystal Boron-Doped Diamond Synthesis

AbstractThe electrical characteristics of high quality single crystal boron-doped diamond are studied. Samples are synthesized in a high power-density microwave plasma-assisted chemical vapor deposition (CVD) reactor at pressures of 130-160 Torr. The boron-doped diamond films are grown using diborane in the feedgas at concentrations of 1 to 50 ppm. The boron acceptor concentration is investigated using infrared absorption and a four point probe is used to study the conductivity. The temperature dependent conductivity is analyzed to determine the boron dopant activation energy.

Study of microwave plasma-assisted chemical vapor deposition of poly-and single-crystalline diamond films

We study conditions for microwave plasma-assisted chemical vapor deposition of high-quality single-crystal diamond films in a CVD reactor. These conditions are studied using the results of homoepitaxial growth of polycrystalline diamond films on diamond substrates and on the basis of numerical simulation of the microwave discharge in a CVD reactor. A high-quality single-crystal diamond layer is synthesized on a synthetic, type Ib diamond substrate. The properties of the obtained monolayer are studied by means of Raman and X-ray diffraction spectroscopy as well as optical and atomic-force microscopy.

Core reconstructions of the 〈100〉 edge dislocation in single crystal CVD diamond

AbstractDislocations are common defects in both natural as well as in CVD‐grown diamond. Recent advances in the growth of high quality single crystal CVD diamond have led to an increased interest in the atomistic and electronic structure of 〈100〉 dislocations. These dislocations are observed as mixed‐type 45° and pure edge dislocations. Previously we investigated both types and found that the 45° is by far lower in core energy than the proposed structure of the edge type. In this work we focus on the straight 〈100〉 dislocation only and present novel core reconstructions. We find a minimum energy structure for the edge‐type dislocation which has a similar core energy as the mixed‐type dislocation. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Ramp oxide termination structure using high-k dielectrics for high voltage diamond Schottky diodes

The promising theoretical properties of diamond, together with the recent advances in producing high-quality single crystal diamond substrates, have increased the interest in using diamond in power electronic devices. This paper presents numerical and experimental off-state results for a diamond Schottky barrier diode (SBD), one of most studied unipolar devices in diamond. Finding a suitable termination structure is an essential step towards designing a high voltage diamond device. The ramp oxide structure shows very encouraging electronic performance when used to terminate diamond SBDs. High-k dielectrics are also considered in order to further improve the reliability and electrical performance of the structure.

Theoretical studies on 〈100〉 dislocations in single crystal CVD diamond

AbstractDislocations are common defects in both natural as well as in CVD‐grown diamond. Recent advances in the growth of high quality single crystal CVD diamond have led to an increased interest in the atomistic and electronic structure of 〈100〉 dislocations. These dislocations are observed as mixed‐type 45° and pure edge dislocations. Hence in this work we present ab initio modelling studies on these two types of dislocations. The 45° dislocation is found to be by far more stable than the pure edge and both dislocations lead to states in the electronic band gap. An alternative structure for the mixed‐type dislocation, which is not straight but kinked and consists of short edge and screw segments, was found slightly higher in energy than the straight structure. (© 2006 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Analysis of trapping–detrapping defects in high quality single crystal diamond films grown by Chemical Vapor Deposition

The photoresponse of high quality single crystal diamond films homoepitaxially grown by Chemical Vapor Deposition (CVD) onto low cost diamond substrates has been studied. The time evolution electrical response to the excitation by 5 ns laser pulses at 215 nm closely reproduces the laser pulse shape. The single crystal diamond response is therefore much faster than the laser pulse duration. The output signal is also very stable and reproducible, without significant priming or memory effects. Single crystal diamond films can therefore be grown by CVD having enough high quality to be used as photodetectors. However, a minor slow component shows up in the charge-integrated sample response. A systematic speed up of this slow component when increasing the detector temperature from − 25 °C to + 50 °C demonstrates its thermally activated origin. The slow component is therefore attributed to detrapping effects from shallow trapping centres. A model of the charge transport mechanism in the presence of trapping–detrapping centres can be developed and the results can be compared to the experimental ones. The activation energy of the shallow defects is accordingly determined as E a = 0.4 eV.

Characterization of homoepitaxial diamond for ionizing radiation detectors

Synthetic diamond has been proven as an important material for advanced electronic applications, such as those encountered in high energy physics and astrophysics. In fact, diamond transparency to visible light, its high carrier mobility, high breakdown field and strong resistance to chemical attack and radiation damage have suggested the potential application of this material for ‘solar-blind’ UV detectors which have to operate in extreme environments. To avoid the possible problems connected with the presence of grain boundaries in polycrystalline diamond films, a great effort has been devoted to the optimization of the growth process leading to high-quality single-crystal diamond on diamond substrates (homoepitaxy). In this view, characterization studies play a crucial role, because they provide the feedback for the optimization of the deposition process, in order to obtain the best quality material. In this work, a characterization study of homoepitaxial diamond grown by chemical vapor deposition (CVD) on synthetic diamond substrates is presented. The samples have been deposited in a CVD tubular reactor using a CH4–H2 gas mixture (1–7%) at approximately 560°C substrate temperature. The growth rate ranged between 0.9μm/h and 2.2μm/h, microwave powers between 520W and 720W. The crystalline quality of the diamond layer has been studied by means of Raman spectroscopy. Photoluminescence has been used to study the nature and the distribution of impurities, having energy levels in the diamond band gap, which influence negatively the electronic quality of the material. The results have been compared with electro-optical characterization of UV detectors for astrophysics based on the analyzed diamond samples. The growth parameters which guarantees both high material quality and optimal device response have been determined.

Characterization of three-dimensional microstructures in single-crystal diamond

We report on the Raman and photoluminescence characterization of three-dimensional microstructures fabricated in single crystal diamond with a Focused Ion Beam (FIB) assisted lift-off technique. The fabrication method is based on MeV ion implantation, followed by FIB micropatterning and selective chemical etching. In a previous publication we reported on the fabrication of a micro-bridge structure exhibiting waveguiding behavior [ P. Olivero, S. Rubanov, P. Reichart, B. Gibson, S. Huntington, J. Rabeau, Andrew D. Greentree, J. Salzman, D. Moore, D. N. Jamieson, S. Prawer, Adv. Mater., 17 (20) (2005) 2427]. In the present work, Raman and photoluminescence spectroscopies are employed to characterize the structural quality of such microstructures, particularly as regards the removal of residual damage created during the machining process. Three-dimensional microstructures in high quality single crystal diamond have many applications, ranging from integrated quantum-optical devices to micro-electromechanical assemblies.

Lift -Off Process to get Free-Standing High Quality Single Crystal Diamond Films and Suspended Single Crystal Diamond Devices

ABSTRACTFreestanding and suspended single crystal diamond devices, micro disks and beam structures, have been fabricated on single crystal diamond substrates using a lift-off process employing ion implantation followed by electrochemical etching. The ion implantation created subsurface damage in the diamond while the top surface was sufficiently undamaged that a subsequent homo-epitaxial diamond layer could be grown by chemical vapor deposition (CVD). After the CVD growth and patterning by lithography and reactive ion etching, the underlying damage layer was etched/removed by an electrochemical etch. Different implant ions and energies were simulated and tested to optimize the process. The electrochemical etching process was monitored by an optical video technique. The electrochemical etching process used both ac and dc applied electrical potentials. Photoluminescence (PL), Raman spectra, and polarized light transmission microscopy have been used to characterize the implanted substrate and lift-off films. AFM has been used to monitor the surface changes after mechanical polishing, ion implantation, CVD growth and the lift-off process. This research has revealed that the parameters of ion implantation (implant species, dose and energy) dramatically affect the lift-off process. The etching mechanism and critical parameters are discussed in this work. PL spectroscopy indicated differences between the uppermost layers of the homo-epitaxial film and the lift-off interface. Three principal classes of defects have been observed: growth defects inherent in the diamond substrates (type Ib, HPHT), defects induced by the polishing process and associated stress, and point defects.

Trapping-detrapping defects in single crystal diamond films grown by chemical vapor deposition

High-quality single-crystal diamond films were homoepitaxially grown by chemical vapor deposition onto low cost high-pressure high-temperature diamond substrates. The transport properties of the obtained samples were studied by photoresponse characterization. Fast ultraviolet (5 ns) laser pulses at 215 nm were used as a probe. The time evolution of the photoinduced current was observed to closely reproduce the laser pulse shape, thus indicating a time response lower than the adopted laser pulse duration. Very stable and reproducible response was measured, so that neither priming nor memory effects are observed. However, a minor slow component shows up in the charge-integrated sample response, whose temperature dependence was investigated in a −25–+50°C range. A systematic speed up of this slow component of the sample signal is observed, indicating the presence of shallow centers producing trapping-detrapping effects. The experimental results are discussed in the framework of a trapping-detrapping model affecting the charge transport mechanism and an activation energy of Ea=0.4eV was derived for the shallow trapping centers.

Extreme ultraviolet single-crystal diamond detectors by chemical vapor deposition

High-quality single-crystal diamond films, homoepitaxially grown by microwave chemical vapor deposition, have been used to produce diamond-based photodetectors. Such devices were tested over a very wide spectral range, from the extreme ultraviolet (UV) (20 nm) up to the near IR region (2400 nm). An optical parametric oscillator tunable laser was used to investigate the 210–2400 nm spectral range in pulse mode. In this region, the spectral response shows a UV to visible contrast of about 6 orders of magnitude. A time response shorter than 5 ns, i.e., the laser pulse duration, was observed. By integrating the pulse shape, a minor slow component was evidenced, which can be explained in terms of trapping–detrapping effects. Extreme UV gas sources and a toroidal grating vacuum monochromator were used to measure the device response down to 20 nm in continuous mode. In particular, the extreme UV He spectrum was measured and the He II m, 30.4 nmand He I 58.4 nm emission lines were clearly detected. The measured time response of 0.2 s is totally due to the instrumental readout time constants. In both experimental setups an extremely good stability and reproducibility of the device response were obtained, whereas no persistent photoconductivity nor undesirable pumping effects were observed.

Single crystal diamond for electronic applications

There is significant academic and industrial interest in developing electronic devices for high-frequency, high-power and high-temperature applications. This interest has generated considerable research efforts in wide-bandgap semiconductors. Of these materials diamond has by far the most interesting and extreme properties, i.e. mechanical, optical, thermal as well as electronic. Diamond exhibits the highest breakdown field and thermal conductivity of any material and has the highest carrier mobilities of any wide-bandgap semiconductor, thereby enabling the development of electronic devices with superior performance with regards to power efficiency, power density, high-frequency properties, power loss and cooling. Nevertheless, the breakthrough of diamond-based electronics has not yet happened, largely due to the difficulty of synthesising high-quality single crystal diamond. Recent advances in growing intrinsic and boron-doped single crystal diamond intended for electronic applications have resulted in films with exceptionally low defect densities. In the intrinsic material we have reported measured room temperature drift mobilities of 4500 cm 2/V s for electrons and 3800 cm 2/V s for holes (Science 297 (2002) 1670). These mobility values were determined by using the time-of-flight technique on thick intrinsic diamond plates. For comparison, this experiment was also performed on polycrystalline and natural diamond and on silicon. Here, we describe the details of these low-field drift mobility measurements and the modeling used to describe the space-charge-limited transient current.

Very high growth rate chemical vapor deposition of single-crystal diamond

Diamond possesses extraordinary material properties, a result that has given rise to a broad range of scientific and technological applications. This study reports the successful production of high-quality single-crystal diamond with microwave plasma chemical vapor deposition (MPCVD) techniques. The diamond single crystals have smooth, transparent surfaces and other characteristics identical to that of high-pressure, high-temperature synthetic diamond. In addition, the crystals can be produced at growth rates from 50 to 150 mum/h, which is up to 2 orders of magnitude higher than standard processes for making polycrystalline MPCVD diamond. This high-quality single-crystal MPCVD diamond may find numerous applications in electronic devices as high-strength windows and in a new generation of high-pressure instruments requiring large single-crystal anvils.

Diamond film deposition by a substrate-stabilized flat flame

Abstract A diamond film deposition system with a C2H2H2O2 flat flame was improved to extend the stable region of the flat flame in several deposition factors: the volume ratio of C2H2 to O2 in the reactant gas (C/O ratio), the substrate temperature (Ts), the total reactant gas flow rate (Vg) and the distance between the burner nozzle tip and the substrate (L). Effects of these deposition factors on the deposition rate and the quality of the diamond film were studied. As Ts increased, the deposition rate increased at the expense of the film quality for the C/O ratios of 1.03 and 1.05 while the deposition rate increased without deterioration of the film quality for the C/O ratio of 1.01. The maximum deposition rate was 80–90 μm h−1 for the C/O ratios of 1.03 and 1.05 and 50 μm h−1 for the C/O ratio of 1.01. When the Vg increased by 30%, the deposition rate and the uniformly deposited area increased by ca 90% and 30%, respectively. The uniformly deposited area was found to nearly coincide with the flat flame area. For the thermal stress-free self-standing polycrystalline diamond films, it was found that the full width at half-maximum (FWHM) of the diamond Raman peak at 1332 cm−1 becomes narrower with decreasing the amount of the non-diamond carbon in the films. The narrowest FWHM of 2.6 cm−1 obtained in this work was comparable to that of a high quality single crystal diamond.

Guidelines for finer lines in thick film circuitry : P. J. B. Bertrams, W. Keuper, G. Koch and J. H. C. van Mourik. Electrocomponent Sci. Technol.10, 237 (1983)

Synthetic diamond has been proven as an important material for advanced electronic applications, such as those encountered in high energy physics and astrophysics. In fact, diamond transparency to visible light, its high carrier mobility, high breakdown field and strong resistance to chemical attack and radiation damage have suggested the potential application of this material for ‘solar-blind’ UV detectors which have to operate in extreme environments. To avoid the possible problems connected with the presence of grain boundaries in polycrystalline diamond films, a great effort has been devoted to the optimization of the growth process leading to high-quality single-crystal diamond on diamond substrates (homoepitaxy). In this view, characterization studies play a crucial role, because they provide the feedback for the optimization of the deposition process, in order to obtain the best quality material. In this work, a characterization study of homoepitaxial diamond grown by chemical vapor deposition (CVD) on synthetic diamond substrates is presented. The samples have been deposited in a CVD tubular reactor using a CH4–H2 gas mixture (1–7%) at approximately 560 °C substrate temperature. The growth rate ranged between 0.9 μm/h and 2.2 μm/h, microwave powers between 520 W and 720 W. The crystalline quality of the diamond layer has been studied by means of Raman spectroscopy. Photoluminescence has been used to study the nature and the distribution of impurities, having energy levels in the diamond band gap, which influence negatively the electronic quality of the material. The results have been compared with electro-optical characterization of UV detectors for astrophysics based on the analyzed diamond samples. The growth parameters which guarantees both high material quality and optimal device response have been determined.

Automated thermal reliability analysis of hybrids : Gerald N. Morrison and Sally M. Moite. Proc. A. Reliab. Maintainab. Symp. 251 (1983)

Synthetic diamond has been proven as an important material for advanced electronic applications, such as those encountered in high energy physics and astrophysics. In fact, diamond transparency to visible light, its high carrier mobility, high breakdown field and strong resistance to chemical attack and radiation damage have suggested the potential application of this material for ‘solar-blind’ UV detectors which have to operate in extreme environments. To avoid the possible problems connected with the presence of grain boundaries in polycrystalline diamond films, a great effort has been devoted to the optimization of the growth process leading to high-quality single-crystal diamond on diamond substrates (homoepitaxy). In this view, characterization studies play a crucial role, because they provide the feedback for the optimization of the deposition process, in order to obtain the best quality material. In this work, a characterization study of homoepitaxial diamond grown by chemical vapor deposition (CVD) on synthetic diamond substrates is presented. The samples have been deposited in a CVD tubular reactor using a CH4–H2 gas mixture (1–7%) at approximately 560 °C substrate temperature. The growth rate ranged between 0.9 μm/h and 2.2 μm/h, microwave powers between 520 W and 720 W. The crystalline quality of the diamond layer has been studied by means of Raman spectroscopy. Photoluminescence has been used to study the nature and the distribution of impurities, having energy levels in the diamond band gap, which influence negatively the electronic quality of the material. The results have been compared with electro-optical characterization of UV detectors for astrophysics based on the analyzed diamond samples. The growth parameters which guarantees both high material quality and optimal device response have been determined.

Interaction of atomic hydrogen with certain molecular compounds in rarefied zone of hydrogen flame

Microwave plasma assisted chemical vapor deposition (MPCVD) is the established technique to produce high quality single crystal diamond (SCD). While typical pressures for SCD growth regimes in methane-hydrogen plasma are currently within 100–300 Torr, a transition to much high pressures promises enhanced growth rates. Here, we report on successful SCD synthesis by MPCVD in CH4-H2 gas mixtures at pressures up to 600 Tорр. A strong change of the plasma shape and volume (the latter shrinks by 10 times at fixed MW power) with pressure rise from 100 to 600 Torr was observed, still keeping the plasma stable. The record high absorbed MW power density of ≈1800 W/cm3 was achieved at 600 Torr. Optical emission spectroscopy (OES) was used for the plasma analysis via monitoring emission intensities of radicals Hα, C2 and CH. The gas temperature Tg determined from analysis of rotational fine structure of OES Swan transitions of dimer C2 (516 nm) turned out to be essentially constant ∼ 3100 ± 150 K over the pressure range explored. The diamond growth rate is found to increase by an order of magnitude with pressure to achieve 57 μm/h at 500 Torr at relatively low (4%) CH4 concentration, as measured in situ using low-coherence interferometry, but declined at further pressure increase. The produced films were characterized with SEM, XRD, Raman and photoluminescence spectroscopy, and a high/moderate quality of the obtained material was confirmed.