RU2640788C1 - Method for obtaining doped diamond monocrystal - Google Patents

Abstract

FIELD: chemistry.

SUBSTANCE: method of growing diamond single-crystals doped with nitrogen and phosphorus at high pressures of 5.5-6.0 GPa and temperatures of 1600-1750°C is carried out on the seed crystal, which is pre-pressed into a substrate of cesium chloride and separated from the source of carbon, nitrogen, and phosphorus with the metal-solvent, which is used as an alloy of iron, aluminium, and carbon. Between the source of carbon, nitrogen, and phosphorus and the seed crystal, a temperature difference of 20-50°C is created. The alloy of iron, aluminium, and carbon in the metal-solvent is taken with the following component ratio, wt %: iron 92.5-95.0; aluminium 2.5-0.5; carbon 5.0-4.0. The mixture of the source of carbon, nitrogen, and phosphorus is taken with the following component ratio, wt %: carbon (graphite) 95.0-97.0; phosphorus 5.0-3.0; adsorbed nitrogen 0.001±0.0005. Heating is carried out up to the initial temperature in a zone of growth at 100-250°C higher the melting temperature of the alloy of the metal-solvent, the exposure is produced at this temperature for 50 to 150 h. The mass flow rate of crystal growth is more than 2 mg/h. The technical result consists in the controlled doping the diamond single- crystal grown on the seed with impurities of phosphorus and nitrogen in the conditions of influence of high pressure and temperature.

EFFECT: resulting large diamond single-crystals contain a nitrogen admixture in the concentration of 0,1-17,8 parts per million of carbon atoms and phosphorus in a concentration of 0,5-5 parts per million of carbon atoms.

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Description

The invention relates to the production of single crystals of diamonds, in particular doped with nitrogen and phosphorus, at high pressures and temperatures that can be used in electronic devices. Phosphorus atoms are capable of replacing carbon atoms in the crystal lattice of diamond, similar to how it occurs in silicon. Being an element of group V, phosphorus is a donor impurity in doped silicon. Diamond as a carbon form belongs to the IV group of elements, as well as silicon, and has the same cubic type of crystalline structure as silicon. It is natural that phosphorus is chosen as a donor dopant in the synthesis of diamond crystals with an electronic type of electrical conductivity.

For applications in products of active electronics, optoelectronics and acoustoelectronics, first of all, high-quality synthetic diamond single crystals are required.

A known method of growing single crystals of diamond in the field of its thermodynamic stability on a seed crystal, which is separated from the carbon source by a metal solvent, which is used as an alloy of iron, aluminum and carbon, when creating a temperature gradient between the carbon source and the seed crystal 20-30 ° C, moreover, the alloy of iron, aluminum and carbon is taken in the following ratio of components, weight. %: iron 89-92, aluminum 4-6, carbon 4-5, while heating is carried out to an initial temperature in the growth zone, the value of which is 10-20 ° C higher than the melting point of the metal-solvent alloy, soak at this temperature to 20 hours, and then periodically repeated cycles of temperature change are carried out, including the step of stepwise increase in temperature 10-25 ° C above the initial one and the stage of lowering the temperature to the initial one at a speed of 0.2-3 degrees per minute [S.A. Terentyev, V.D. Blank S.A. Nosukhin, M.S. Kuznetsov. A method of growing single crystals of diamond, RF Patent for the invention No. 2320404, IPC СВВ 31/06, publ. March 27, 2008]. In this way, large single crystals of diamond (weighing more than 3 carats) are grown with a mass growth rate of more than 2 mg / h, containing an admixture of nitrogen of not more than 0.1 parts per million carbon atoms (ppm). Doping of single crystals of diamond with phosphorus by this method of growing is not provided.

To conduct phosphorus into diamond, the growth method was used on a seed in the graphite-phosphorus reaction system at high pressures of more than 6.5 GPa and a high temperature of 1800-2200 ° C [Akaishi M .; Kanda N .; Yamaoka S. Phosphorus - An elemental catalyst for diamond synthesis and growth. Science 1993, 259, P. 1592-1593; Michau D .; Kanda H .; Yamaoka S. Crystal growth of diamond from a phosphorus solvent under high pressure-high temperature conditions. - Diam. Relat. Mater. 1999, 8, P. 1125-1129; JP 5123562 (A), IPC: B01J 3/06, publ. 1993.05.21]. In the Fe-Ni-PC reaction system, diamond single crystals with maximum cross-sectional sizes up to 4 × 4 mm ^{2 were} grown at a pressure of 5.4-5.8 GPa and a temperature of 1280-1360 ° C [N.M. - Hua, B. Ning, L. Shang-Sheng, S. Tai-Chao, ZA - Guo, H. Qiang, J. Xiao-Peng, M. Hong-An. Effects of FeNi-phosphorus-carbon system on crystal growth of diamond under high pressure and high temperature conditions. Chin. Phys. B, 2015, 24, No. 3, 038101]. However, the phosphorus concentration in the grown crystals has not been studied.

Phosphorus-doped diamonds are obtained by chemical vapor deposition containing phosphorus [Koizumi S .; Kamo M .; Sato Y .; Ozaki H .; Inuzuka T. Growth and characterization of phosphorous doped {111} homoepitaxial diamond thin films. - Appl. Phys. Lett., 1997, 71, P. 1065-1067] and by the method of ion implantation of phosphorus ions in diamond crystals [R.S. Nelson, D.A. Hudson, D.D. Maisy, A method of obtaining a semiconductor diamond, patent SU 1083915 A, IPC C30B 31/22, publ. 06/01/1978; US patent 5609926, IPC СВВ 31/06, publ. 11/03/1997].

Moreover, despite the pertinent analogy of doping diamond with phosphorus like silicon, in reality, the entry of phosphorus atoms into the diamond crystal lattice is very difficult due to the significant mismatch of the atomic radii of carbon and phosphorus, in contrast to the silicon-phosphorus system. In this connection, the introduction of phosphorus atoms into the crystal lattice of diamond is accompanied by the appearance of various structural defects, which affects the optical and electronic properties of crystals.

To compensate for local stresses near phosphorus atoms and improve the crystal structure of phosphorus-doped diamond crystals grown by the growth method at high pressure and temperature, a technique was proposed for doping with phosphorus and nitrogen simultaneously [B. Yan, X. Jia, S. Fang, N. Chen, Y. Li, S. Sun, HA Ma, The effect of phosphorus and nitrogen co-doped on the synthesis of diamond at high pressure and high temperature, Int. J. Refractory Metals and Hard Materials, 2016, 54, P. 309-314]. In this way, single crystals of diamond were grown with a maximum cross-sectional size of up to 3 × 3 mm ² in the NiMnCo-C system with the addition of P ₃ N ₅ at a concentration of up to 0.4 wt. % and with the addition of up to 1.5 weight. % phosphorus in a system with powdered carbonyl iron. A sufficiently high nitrogen concentration in the obtained crystals was determined by IR spectroscopy, which amounted to 860 ppm (parts per million) in the form of nitrogen pairs and 1260 ppm in the form of single substituting atoms. However, the phosphorus concentration has not been determined.

The closest of the known analogues technical solution, selected as a prototype, is a method for producing phosphorus doped diamond, including the action of high pressure and temperature on the reaction system from graphite and phosphorus, characterized in that the reaction system from graphite and phosphorus is preliminarily annealed in a stream of hydrogen at temperatures of 200-280 ° C and carry out the synthesis of diamond in the temperature range of 1450-1650 ° C and in the pressure range of 6.3-7.5 GPa, limited at 6.3 GPa with an interval of 1550-1650 ° C, and at 7.5 GPa limited interval scrap 1450-1550 ° С with a duration of at least 40 hours [Palyanov Yu.N., Kupriyanov I.N., Sokol A.G., Khokhryakov A.F., Borzdov Yu.M., Kalinin A.A. A method of obtaining a diamond doped with phosphorus (options), patent RU 2476375 C1, IPC СВВ 31/06, СВВ 29/04, publ. 02/27/2013]. The technical result of this invention is to improve the quality of diamond crystals and reduce the temperature and pressure of the growth of diamonds with a size of 200-300 microns with different concentrations of impurities obtained in the phosphorus-carbon system.

The objective of this technical solution is the controlled alloying of a single-crystal diamond grown on a seed with impurities of phosphorus and nitrogen under conditions of high pressure and temperature.

The technical result is achieved by the fact that from the reaction system carbon-nitrogen-phosphorus in the form of a mixture of graphite and phosphorus with adsorbed nitrogen in a concentration of about 0.001 ± 0.0005 weight. % with a ratio of phosphorus to carbon 3-5 weight. % prepare the workpiece in the form of a washer and place it on the workpiece in the form of a washer from a metal-solvent alloy, which is used as an alloy of iron, aluminum and carbon with a ratio of components, weight. %: iron - 92.5-95.0, aluminum - 0.5-2.5, carbon - 4-5, under which a cesium chloride substrate is placed with a seed diamond crystal pre-pressed into it, and the seed diamond single crystal is oriented with a face (100) parallel to the plane of the solvent metal washer. As a result of the addition of aluminum to the reaction system, the nitrogen concentration in the grown crystals decreases due to the well-known chemical reaction of the formation of aluminum nitride, and at the same time, phosphorus partially replaces nitrogen in the structure of doped diamond. In the absence of aluminum in the solvent metal, the concentration of phosphorus impurity in the grown diamonds does not exceed 0.1 ppm, and the nitrogen concentration is maximum: about 100 ppm. At an aluminum concentration of more than 2.5 weight. % in the solvent metal, the phosphorus concentration in the grown diamonds also does not exceed 0.1 ppm, while the nitrogen concentration decreases below 0.1 ppm. Only when the concentration of aluminum in the metal solvent is 0.5-2.5 weight. % get diamond crystals in which nitrogen is simultaneously present in an amount of 0.1-17.8 ppm and phosphorus in an amount of 0.5-5 ppm. The temperature in the diamond growth zone is set 100-250 ° C higher than the melting point of the metal-solvent alloy and held at this temperature from 50 to 150 hours, and the diamond is produced in the pressure range 5.5-6.0 GPa and in the temperature range 1600-1750 ° C. Doped diamond single crystals are grown under conditions of a temperature difference between a carbon source and a seed crystal of 20-50 ° C. Under these conditions, diamond crystals are grown weighing more than 0.6 carats with a mass growth rate of more than 2 mg / h. The crystals contain 0.1-17.8 ppm impurities of nitrogen and 0.5-5 ppm impurities of phosphorus.

The technical result of the invention is to grow large single crystals of diamond doped with nitrogen and phosphorus, for use in electronic components.

The solution to the technical problem is confirmed by FIG. 1, 2, which show the grown single crystals of diamonds fixed in an annular holder with a polymer binder (Fig. 1), and the concentration of phosphorus atoms depending on the depth relative to the surface of the crystals according to the mass spectroscopy of secondary SIMS ions (Fig. 2). In the depth range 0-80 nm, the results (Fig. 2) show an overestimated concentration of phosphorus associated with the instrumental measurement error and should not be taken into account. This is evidenced by curve 4, referring to control crystal No. 4 grown without adding phosphorus to the growth medium.

The results of measuring the phosphorus concentration in depth relative to the surface of {111} crystals Nos. 1-4 are shown in FIG. 2. The numbers of the curves correspond to the numbers of the crystals in examples 1-3.

Examples of the method.

Example 1

For the growth of a diamond single crystal doped with nitrogen and phosphorus, a toroid type high-pressure apparatus is used, similarly to [S.A. Terentyev, V.D. Blank S.A. Nosukhin, M.S. Kuznetsov. A method of growing single crystals of diamond, RF Patent for the invention No. 2320404, IPC СВВ 31/06, publ. March 27, 2008], which implements the method of temperature gradient of diamond growth on a seed crystal.

A washer with a total weight of 1.1 g, consisting of 99.99% pure graphite, containing 0.001 ± 0.0005 weight, is placed in the reaction volume of the high-pressure cell. % adsorbed nitrogen, while graphite is 97 weight. % of the puck, and the remaining 3.0 weight. % - phosphorus purity 99.99%. The diameter of the washer is 15 mm, the height is 2.75 mm, a washer of a metal-solvent alloy with a diameter of 15 mm, a height of 4.5 mm and the following ratio of components is placed under it, weight. %: iron - 94.5, aluminum - 0.5, carbon - 5.0. A 0.5 mm diamond seed crystal, weighing about 4 mg, is oriented with a (100) face parallel to the plane of the solvent metal washer and pressed into a cesium chloride substrate, which is placed under the solvent metal washer. The assembled cell is placed in a toroid type pressure chamber, which is placed in the working space of a hydraulic press DO 044. Create a pressure in the reaction volume of 5.5 GPa and, under the control of an automated crystallization process control system, increase the supplied electric power to a value ensuring temperature in the growth zone 100 ° C higher than the melting point of the metal-solvent alloy ~ 1500 ° C, with a temperature difference between the carbon source and the seed crystal of 20 ° C. The temperature difference between the carbon source and the seed crystal (growth zone) is set using the upper and lower end heaters of different heights made of a mixture of graphite and zirconium dioxide. The specified mode is supported by 50 hours. Further, under the control of an automated control system for the crystallization process, a uniform reduction in the input electric power is carried out for 3 hours, thereby reducing the temperature in the reaction volume at a rate of 1 degree per minute. Turn off the supply of electrical power, reduce the pressure, unload the pressure switch, remove the reaction cell. A puck of the solvent metal with the grown diamond is separated and the metal is dissolved in a mixture of hydrochloric and nitric acids (aqua regia) for 30 minutes. The grown diamond is recovered and washed in distilled water with surfactants and deionized water. Crystal weight 123 mg (0.615 carats). The duration of the crystal growth process was 50 hours, and the average mass growth rate was 2.4 mg / h. The concentration of nitrogen impurity N _c calculated from the absorption coefficient at 270 nm α ₂₇₀ in the spectrum recorded on a CARY 4000 spectrometer: N _with [ppm] = 0.517 α ₂₇₀ [cm ^-1 ] is 17.8 ppm. The obtained crystal is fixed in a binder polymer inside the holder for conducting elemental analysis by secondary ion mass spectroscopy (SIMS) (Fig. 1, No. 1). In crystal No. 1 at a depth of more than 200 nm, the phosphorus concentration was about 0.5 ppm.

Example 2

The growth of a diamond single crystal doped with nitrogen and phosphorus, and the analysis of the phosphorus content are carried out analogously to example 1, but with a doubled concentration of aluminum in the solvent alloy: 1.0 weight. % The content of the remaining elements is as follows: 95.0 weight. % Fe, 4.0 weight. % C. They create a pressure in the reaction volume of 5.5 GPa and, under the control of an automated system for controlling the crystallization process, increase the supplied electric power to a value that ensures that the temperature in the growth zone is 100 ° C higher than the melting point of the metal-solvent alloy ~ 1500 ° C, at the temperature difference between the carbon source and the seed crystal 30 ° C. The total duration of the crystal growth process was 150 hours. Further, as in example 1, under the control of an automated control system for the crystallization process, a uniform reduction in the input electric power is carried out for 3 hours, thereby reducing the temperature in the reaction volume at a rate of 1 degree per minute. Analogously to example 1, the washer metal-solvent with the grown diamond is separated and the metal is dissolved in a mixture of hydrochloric and nitric acids (aqua regia) for 30 minutes. The grown diamond is recovered and washed in distilled water with surfactants and deionized water. The weight of the grown crystal was 421 mg (2.1 carats), and the average mass growth rate was 2.8 mg / h. The nitrogen impurity concentration N _c calculated from the absorption coefficient at 270 nm α ₂₇₀ is 1.3 ppm (parts per million). The obtained crystal was fixed in a binder polymer inside the holder for conducting elemental analysis by secondary ion mass spectroscopy (SIMS) (Fig. 1, No. 2). The results of measuring the phosphorus concentration in depth relative to the surface of the {111} crystal are shown in FIG. 2, curve 2. At a depth of more than 200 nm, the phosphorus concentration was about 5 ppm.

Example 3

The growth of a diamond single crystal doped with nitrogen and phosphorus, and the analysis of the phosphorus content are carried out analogously to example 1, but with a ratio of graphite and phosphorus in the reaction system of 95.0 weight. % and 5.0 weight. % respectively. The aluminum content in the solvent alloy: 2.5 weight. % The content of the remaining elements is as follows: 92.5 weight. % Fe, 5.0 weight. % C. They create pressure in the reaction volume of 6.0 GPa and, under the control of an automated control system for the crystallization process, increase the supplied electric power to a value that ensures that the temperature in the growth zone is reached by 250 ° C above the melting point of the metal-solvent alloy ~ 1500 ° C, at the temperature difference between the carbon source and the seed crystal 50 ° C. Then, under the control of an automated system for controlling the crystallization process, a uniform reduction in the input electric power is carried out for 5 hours, which ensures a decrease in temperature in the reaction volume at a rate of 1 degree per minute. Analogously to example 1, the washer metal-solvent with the grown diamond is separated and the metal is dissolved in a mixture of hydrochloric and nitric acids (aqua regia) for 30 minutes. The grown diamond is recovered and washed in distilled water with surfactants and deionized water.

The total duration of the growing process was 50 hours, the weight of the grown crystal was 132 mg (0.66 carats), and the average mass growth rate was 2.6 mg / h. The nitrogen impurity concentration N _c calculated from the absorption coefficient at 270 nm α ₂₇₀ is 0.1 ppm (parts per million). The obtained crystal was fixed in a binder polymer inside the holder for conducting elemental analysis by secondary ion mass spectroscopy (SIMS) (Fig. 1, No. 3). The results of measuring the phosphorus concentration in depth relative to the surface of the {111} crystal are shown in FIG. 2, curve 3. At a depth of more than 200 nm, the phosphorus concentration was about 2 ppm.

The proposed technical solution allows to obtain doped single crystals of diamond weighing more than 0.6 carats with a mass growth rate of more than 2 mg / h, containing an admixture of nitrogen at a concentration of 0.1-17.8 ppm and phosphorus at a concentration of 0.5-5 ppm. The obtained doped single crystals of diamond can be used in products of active electronics, optoelectronics and acoustoelectronics.

Claims (1)

A method for producing doped diamond, including the effect of high pressure and temperature on the reaction system from carbon in the form of graphite and phosphorus, characterized in that nitrogen is additionally introduced into the reaction system in the following ratio of components, wt.%: Carbon 95.0-97.0; phosphorus 3.0-5.0; adsorbed nitrogen is 0.001 ± 0.0005, and a blank in the form of a washer is prepared from graphite powders with an admixture of nitrogen and phosphorus and placed on a blank in the form of a washer from an alloy of a metal-solvent made of iron, aluminum and carbon with the following content of components, weight. %: iron 92.5-95.0; aluminum 0.5-2.5; carbon 4.0-5.0, while a cesium chloride substrate is placed under the washer from the metal-solvent alloy, into which a seed diamond single crystal, oriented with face (100) parallel to the plane of the washer-metal washer, is pre-pressed, and the temperature is in the diamond growth zone set at 100-250 ° C above the melting point of the metal-solvent alloy and hold at this temperature from 50 to 150 hours, and the diamond is produced in the pressure range 5.5-6.0 GPa at a temperature difference between the seed crystal and the source ohm-carbon nitrogen-phosphorus 20-50 ° C.

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