Heteroepitaxial Diamond Films
Development of the Scaled Methods for Depositing Heteroepitaxial Doped Diamond Films. Creation and Investigation of Devices Based on the Films
Tech Area / Field
- MAT-SYN/Materials Synthesis and Processing/Materials
- NNE-MEC/Miscellaneous Energy Conversion/Non-Nuclear Energy
8 Project completed
Senior Project Manager
Safronova O N
TRINITI, Russia, Moscow reg., Troitsk
- Moscow State University / Institute of Nuclear Physics, Russia, Moscow\nAll-Russian Scientific Research Institute of Non-Organic Materials named after A. Bochvar, Russia, Moscow
- Teer Coating Ltd., UK, Hartlebury\nNorth Carolina State University, USA, NC, Raleigh\nIntel Corporation, USA, OR, Hillsboro\nINOSTEK Inc., Korea, Geonggi\nUniversity of Bristol / School of Chemistry, UK, Bristol
Project summaryDiamond possesses quite a number of unique physical and chemical properties: record thermal conductivity (more than 2000 W/m-K), high chemical resistance and biocompatibility, unmatched high hardness and low friction coefficient. The diamond is a non-direct-band semiconductor with the band gap of 5.5 eV (the band gap for direct band transition is 7.5 eV) and has high mobility of both electrons and holes.
The hydrogenation process also adds to the uniqueness of diamond: after being hydrogenated some its faces acquire negative affinity to electrons, while the hydrogenated surfaces gain a high p-type conductivity with the holes density up to 1013 cm2 and the secondary electron emission coefficient more than 100. Such a combination of unique properties makes the diamond one of the most perspective materials in a great variety of applications: from vacuum electronics and microelectronics to laser physics and biology.
One of the most essential obstacles to the practical utilization of its unique properties is the lack of available diamond monocrystals of the size exceeding several millimeters. Along with advancement in gas phase deposition techniques the method for heteroepitaxial growth of diamond films on non-diamond substrates is being actively developed. Most widely studied materials as substrates are as follows: silicon, silicone carbide, and boron nitride. However, either textured or only super-thin (fractions of a micron) monocrystal diamond layers have been formed on the silicon surface. Similar results have been got for a number of other substrates as a consequence of considerable difference in the lattices of substrates and diamond. The only exception is the cubic boron nitride whose substrates are, unfortunately, as hard to obtain as diamond substrates.
Iridium (100) boundary is a most suitable crystal structure on which the diamond film can heteroepitaxially be grown. In its turn the (100) iridium face itself can heteroepitaxially be deposited upon the corresponding face of MgO monocrystal. Acceptable for the heteroepitaxial process, the latter substrates of up to 2 inches in linear dimensions are presently widely available. Quite recently it has been revealed that epitaxial iridium films can also be grown on sapphire A- surface, such substrates are much more available and their cost is essentially lower.
The heteroepitaxial deposition of Ir is performed by either thermal or magnetron sputtering on the (MgO or sapphire) substrate having temperature of 600-900 °C. The both methods permit to create homogeneous coatings on the area essentially bigger than 2 inches.
The heteroepitaxial increase in the diamond films thickness can be achieved by employing the CVD process either in the dc discharge or in the microwave discharge. These methods have been used in synthesizing heteroepitaxial films of 2-4 mm in size, which is obviously insufficient for a number of applications, for example, in electron multipliers. Besides, up to the present time there has been no display of possibility in heteroepitaxial deposition of doped diamond films, that consequently has been blocking the constructing of device based on such films.
It has to be noted that the diamond is one of the most perspective materials for sun blind photodetectors which can widely be used in medicine, for amplifiers of electron beams and power and high-temperature transistors.
Bearing in mind the above said the following objectives of the Project are claimed:
1. Advancing the heteroepitaxial deposition methods for diamond films up to 10 mm in diameter.
2. Upgrading the technology for doping boron into heteroepitaxial diamond films.
3. Forming diamond membranes up to 5 mm in diameter.
Mono-crystal diamond films produced during the project implementation will be used for accomplishing the following tasks:
1. Studying the electrical and optical properties of heteroepitaxial diamond films and defining the most perspective fields of their application.
2. Developing UV range photo-receivers and photo-transformers as well as photodetectors based on monocrystal diamond films and examining the efficiency of the devices.
3. Investigating the efficiency of the secondary electron emission of a monocrystal diamond membrane in the transmission geometry and estimating the prospects for this membrane utilization in electron multipliers.
4. Studying electrochemical characteristics of the doped heteroepitaxial diamond films, particularly the acid resistance of the films under different overvoltages.
The participants of the Project from the SRC RF TRINITI are well known pioneers in the field of creating diamond detectors. Detectors of this type were recently used for DT neutron spectra measurements on the neutron generators SNEG-13 and NGM-17 in Russia, Frascati Neutron Generator (FNG) in Italy, and Fusion Neutron Source (FNS) in Japan. In addition, diamond detectors were used during tritium experiments on the Tokamak Fusion Test Reactor (TFTR), the Joint European Torus (JET), and during triton burn-up studies on JT-60U. Several diamond detectors were used for fast charge exchange atom spectrometry and flux dynamics measurements during ICRF heating on TFTR and NBI on the Large Helical Device (LHD) and TORE SOPRA.
The participants of the Project from the SRC RF TRINITI are also highly experienced in the field of chemical deposition of diamond films in vapors as well as in the development of methods for diamond film nucleation, in particular, with the use of laser sputtering. Within the frame of ISTC project # 1187 the researchers from SRC RF TRINITI created electron field emitters on the base of nanodiamond materials. The installations created are planned to be used for researching secondary-emission and photo-voltaic processes in mono-crystal diamond films.
The participants of the Project from the SINP MSU are highly experienced in the fields of making and studying new carbon materials, including diamonds. There are over 20 reports presented in international conferences. The basic research works on developing the scaled methods for deposition of heteroepitaxial doped diamond films are under way. Besides, the SINP scientists are also of great experience in both creating devices based on diamond materials and in investigating the operation of these devices. Specimens of polycrystalline diamond films have been produced and studied. The effect of the basic technology parameters such as the substrate temperature, gas composition, the rate of gas flow and activation on the quality of the produced films has been determined. The behavior of diamond films during the process of high electron bombarding has also been examined. The doping method has been worked out and polycrystalline membrane doped specimens from 2 m up to 100 m in thickness have been created.
The participants of the Project from the VNIINM are highly experienced in the field of magnetron deposition of different materials under a wide range of temperatures, including relatively high ones; the latter is to be used while growing transient heteroepitaxial layers on the base of Ir. The VNIINM participants have a number of publications in the leading scientific magazines of this country and in the proceedings of international conferences, received a number of patents.
The participants of the Project from the VNIINM have experimental equipment: installations and test devices for carrying out the research. They are also highly experienced in epitaxial deposition of a number of compositions, including carbides and carbonitrides.
All the above said displays the presence of sound foundation for successful implementation of the project.
The meeting of the above aims and tasks of the project is expected to result in:
- Working out technological regimes for production of heteroepitaxial Ir films on MgO substrates.
- Creating the optimal conditions for growing the epitaxial diamond films on the Ir film specimens.
- Developing the scaled methods for depositing heteroepitaxial doped diamond films.
- Defining optimal technology characteristics for the production of doped diamond films with proper electrophysical properties.
- Finding out the possibility for creating efficient electron multipliers on the base of diamond membranes.
The devices developed on the base of the films produced can be widely used in medicine and biology, electronics, laboratory instrument engineering and industrial electrochemical setups.
Within the frame of the project the collaborators are to take part in the joint research stage, exchange of information, discussions and verifications of the results obtained and estimation of the possibility for practical use of the produced specimens.
The project implementation will make it possible to redirect the experience of the scientists and engineers specialized in weapon development and fabrication to the problems related to new materials investigation.