Alternative ultrathin doped diamond exciton insulator and preparation method thereof

Abstract

The invention discloses an alternating ultrathin doped diamond exciton insulator and a preparation method thereof, and relates to a novel exciton insulator mechanism. According to the method, extra bound electrons and holes are introduced into the diamond alternately-doped ultrathin boron atomic layer and the phosphorus / nitrogen atomic layer, the ultrathin bound exciton layer is formed through layered coupling in the body, the polarizations have the same polarization orientation, and conditions are created for generation of a Bose-Einstein condensed state of the excitons. Furthermore, when the temperature is reduced, strong interaction is formed among excitons, so that the diamond is induced to form an exciton insulator. Alternating ultra-thin doping significantly enhances exciton binding energy through a quantum confinement effect, and at the same time, due to an ultra-high specific surface / volume ratio, regulation and control of exciton properties by factors such as an external electric field and temperature are more flexible, and a solid foundation is provided for application fields such as light emitting diodes and quantum calculation.

Description

Technical Field

[0001] The invention relates to an exciton insulator using ultra-thin diamond doped alternately with boron and phosphorus / nitrogen and a preparation method thereof, belonging to the technical field of semiconductors and condensed matter. Background Art

[0002] Since the exciton was proposed in 1930, the exploration of the Bose-Einstein condensate state of excitons and the exciton insulating state has never stopped. Excitons have also affected the optoelectronic applications of semiconductors in different fields such as photovoltaics and light-emitting diodes. Diamond has excellent physical properties such as electrical conductivity and thermal conductivity, and has been widely studied and applied to various electronic devices. However, the electrical properties of diamond after doping usually behave as conductors or semiconductors, and there has been no report on the exciton insulator of diamond. At present, the most concerned material systems are semiconductor quantum well structures and layered two-dimensional materials, but the former requires specific lattice matching heterojunction materials, and the latter has low interlayer coupling and exciton binding energy. These new materials or topological structures under the action of excitons will bring new evidence of exciton insulation. Although theoretical articles continue to appear, there is still a lack of actual direct and effective experimental verification. Scientists are spending a lot of time looking for practical materials or structures to solve the above problems. However, the diamond structure doped with ultra-thin boron and phosphorus atomic layers alternately deviates from the above two material systems. The exciton binding energy of boron and phosphorus atoms exceeds 2eV, and the donor energy level of phosphorus atoms is 0.58eV below the conduction band; the exciton binding energy of boron and nitrogen atoms exceeds 6eV, and the donor energy level of nitrogen atoms is 1.7eV below the conduction band, and the acceptor energy level of B atoms is 0.37eV above the valence band. Therefore, bound electrons are formed around phosphorus or nitrogen atoms, thereby forming strongly bound excitons with the acceptors of boron atoms, satisfying the conditions for strong exciton binding energy of exciton insulators, driving electrons and holes to form bound excitons in the body, and obtaining new exciton insulators. Summary of the invention

[0003] The object of the present invention is to provide a method for preparing a diamond exciton insulator by effectively realizing the ultra-thin doping technology of alternating boron and phosphorus / nitrogen atoms in diamond.

[0004] The technical solution adopted by the present invention is:

[0005] An alternating ultra-thin doped diamond exciton insulator is prepared by microwave plasma chemical vapor deposition (MPCVD) method. Two doping gases are alternately introduced in different time periods during the preparation process: boron-containing doping gas and phosphorus / nitrogen-containing doping gas, so that the diamond is layered doped with boron elements and phosphorus / nitrogen elements during the growth process, and an alternating ultra-thin heavily doped boron atomic layer and an ultra-thin heavily doped phosphorus / nitrogen atomic layer are formed in the diamond, so that the holes formed by the doped B atoms and the electrons formed by the doped P / N atoms are coupled to form a bound exciton layer. Further, the system temperature is lowered, and strong interactions are formed between the excitons, thereby inducing the diamond to form an exciton insulator. The method of the present invention can increase the insulation transition temperature of the diamond, and the phase transition can be induced by lowering the temperature to below 100K.

[0006] In the above technical solution, the boron-containing doping gas is one or more boron-containing gases such as borane and diborane.

[0007] The phosphorus / nitrogen doping gas is one or more of phosphine, phosphate, nitrogen, ammonia and the like.

[0008] The preparation of diamond by MPCVD method specifically includes: using clean single crystal diamond as substrate, placing it in MPCVD reaction chamber, introducing hydrogen after vacuuming, and etching the non-diamond phase on the diamond surface; after etching the substrate, introducing carbon source gas and doping gas into the reaction chamber to grow diamond. The vacuuming is to make the background vacuum degree in the reaction chamber not less than 1×10 -3 Torr.

[0009] The carbon source gas is methane or other commonly used carbon source gases. The input power range of the microwave source is controlled to be 1 to 10 kW during the growth process, and the cavity pressure range is 10 to 300 Torr. The doping gases are boron-containing gas and phosphorus / nitrogen-containing gas, respectively, wherein the flow ratio of the carbon source gas to the boron-containing gas is usually 2:1, and the flow ratio of the carbon source gas to the phosphorus / nitrogen-containing gas can usually be 2:1 to 6:1. Among them, the diamond is layered doped by alternately introducing two doping gases at different time periods, for example: first introduce the boron-containing gas for 0.5-10 seconds, and then introduce the phosphorus / nitrogen-containing gas for 0.5-10 seconds, to achieve B-doped and P / N-doped layered co-doped diamond. The acceptor and donor coupling brought by the two types of doping atoms form a bound exciton layer, which can significantly enhance the exciton binding energy through the quantum confinement effect. At the same time, the ultra-high specific surface / volume ratio makes the external electric field, temperature and other factors more sensitive to the regulation of the properties of the bound exciton layer. Furthermore, when the temperature decreases, the Coulomb binding energy of the excitons becomes greater than the energy required for electron excitation, and the excitons in the diamond become unstable, thereby achieving a transition to an insulating state, which promotes theoretical research and practical applications of exciton insulation.

[0010] According to a specific embodiment of the present invention, an alternating ultra-thin diamond-doped excitonic insulator and a preparation method thereof include the following steps: 1) Using single crystal diamond with (100) or (110) crystal orientation as substrate; 2) ultrasonically cleaning the substrate using acetone, isopropanol, ethanol and deionized water before growth on the substrate surface; 3) Using MPCVD equipment to evacuate the diamond, and then introducing hydrogen to etch the non-diamond phase on the diamond surface; 4) During the growth stage, the microwave source input power is maintained at 1-10 kW, the cavity pressure is maintained at 10-300 Torr, and methane gas is used as the main carbon source; 5) In the doping growth stage, the boron-containing doping gas and the phosphorus / nitrogen-containing doping gas are introduced alternately as doping sources, each for 0.5 to 10 seconds, the flow ratio of the carbon source gas to the boron-containing doping gas is 2:1, and the flow ratio of the carbon source gas to the phosphorus / nitrogen-containing doping gas is 2:1 to 6:1; the alternating ultra-thin heavy doping of boron atoms and phosphorus / nitrogen atoms during the diamond growth process is achieved; 6) Lowering the temperature to below 100K allows the excitons in the system to form a Bose-Einstein condensate, inducing a phase transition.

[0011] Compared with the prior art, the present invention has the following beneficial effects: Most traditional diamonds are conductors or semiconductors and lack the ability to change phases. The present invention uses an ultra-thin diamond doped with boron and phosphorus / nitrogen atoms alternately and an exciton insulator and preparation method, based on single crystal diamond, to innovate the exciton material system. It mainly uses the MPCVD equipment to introduce boron acceptors and phosphorus / nitrogen donors in the process of growing single crystal diamond, controls the flow ratio and the introduction time of the doping gas, and forms an ultra-thin heavily doped layer. Different from simultaneous doping, alternating doping means that donors and acceptors can be better paired, thereby introducing a large number of bound excitons with the same orientation, making it easier to form interactions between excitons. When the temperature is lowered, the excitons in the heavily doped diamond form a Bose-Einstein condensate, thereby inducing the diamond to change from a semiconductor phase to an exciton insulator, providing a solid material foundation for the application of diamond materials in light-emitting diodes, quantum detection and other fields. BRIEF DESCRIPTION OF THE DRAWINGS

[0012] Figure 1 The low temperature resistance of the exciton insulator doped with diamond using boron and phosphorus atoms obtained by the method of Example 1 varies with temperature. The test range is 2K to 300K. When the temperature gradually decreases to 6.68K, the resistance of the exciton insulator device begins to increase exponentially. The maximum resistance of the device exciton insulation is 4873 times that at room temperature (298.15K). Figure 2The low temperature resistance of the exciton insulator doped with diamond using boron and phosphorus atoms obtained by the method of Example 2 varies with temperature. The test range is 10K to 300K. When the temperature gradually decreases to 17.21K, the resistance of the exciton insulator device begins to increase exponentially. The maximum resistance of the device exciton insulation is 2785 times that at room temperature (298.15K). Figure 3 A schematic diagram of the structure of an alternating ultra-thin diamond-doped exciton insulator prepared by the method of Example 3; Figure 4 This is a graph showing the relationship between the low-temperature resistance of an exciton insulator using ultra-thin diamond doped with alternating boron and phosphorus atoms obtained by the method of Example 3 and temperature. The test range is 50K to 300K. When the temperature gradually decreases to 51.3K, the resistance of the exciton insulator device begins to increase exponentially, and the maximum resistance of the device exciton insulation is 4615 times that at room temperature (298.15K). DETAILED DESCRIPTION

[0013] The present invention will be further described below in conjunction with the accompanying drawings and specific embodiments.

[0014] Reference Figure 3 , the present invention is an exciton insulator that uses boron, phosphorus / nitrogen atoms to alternately dope diamond ultra-thinly. In the process of preparing diamond by MPCVD growth, borane gas and phosphorus and / or nitrogen-containing gas are used for doping respectively to obtain a single crystal diamond material that is alternately doped ultra-thinly with boron and phosphorus / nitrogen. Boron elements and phosphorus / nitrogen elements are layered doped in diamond to introduce holes and electrons as carriers, and layered coupling is performed in the body to form exciton layers with roughly consistent orientations, so that there is a strong interaction between the excitons. When the temperature is reduced, compared with the exciton insulator in which boron and phosphorus atoms are simultaneously doped with diamond in Example 1, the excitons in the exciton insulator in which diamond is alternately doped ultra-thinly in Example 3 can form a Bose-Einstein condensate at a relatively higher temperature, inducing the diamond to change from a semiconductor phase to an exciton insulator. The present invention is an alternately ultra-thin doped diamond exciton insulator, which can effectively provide an experimental basis for the theory of exciton insulation, promote the development of condensed matter theory and its application in diamond quantum detection.

[0015] Embodiment 1: 1) Take a single crystal diamond with a (100) crystal orientation and a size of 9 mm × 9 mm as a substrate, and polish the growth surface to ensure that the growth surface is smooth and flat; 2) The substrate was ultrasonically cleaned in acetone, isopropanol, ethanol and deionized water in turn, and each solvent was used for 10 minutes to remove organic impurities attached to the surface, and then dried with N2; 3) Use MPCVD equipment to evacuate to 10-3 Torr, hydrogen was introduced to etch the substrate surface, and the chamber pressure was maintained at 100 Torr, the temperature was maintained at 820°C, and the etching time was maintained at 30 min to remove the non-diamond phase on the substrate surface; 4) During the growth stage, the microwave source input power was maintained at 5 kW, the cavity pressure was maintained at 140 Torr, the growth temperature was maintained at 920° C., methane gas was used as the main carbon source, and the gas flow rate was maintained at 30 sccm. 5) During the growth stage, a mixed gas of borane and phosphine is introduced as a direct doping source, wherein the gas flow rates of borane and phosphine are 15 sccm and 5 sccm, respectively, to achieve co-doping of diamond with boron atoms and phosphorus atoms. The relationship between the resistance value and temperature of the boron-phosphorus co-doped diamond prepared in this example is as follows: Figure 1 As shown in the figure, when the ambient temperature drops to 6.68K, the resistance increases exponentially. According to the relationship diagram of the diamond resistance value changing with temperature, it can be seen that the present invention uses boron and phosphorus atoms to co-dope diamond as an exciton insulator, and utilizes the interaction between the boron element and the phosphorus element in the diamond to couple to form excitons. When the temperature drops, strong interactions are formed between the excitons to form a Bose-Einstein condensate, resulting in an exponential increase in resistance, thereby realizing an exciton insulator.

[0016] Embodiment 2: 1) Take a single crystal diamond with a (111) crystal orientation and a size of 9 mm × 9 mm as a substrate, and polish the growth surface to ensure that the growth surface is smooth and flat; 2) The substrate was ultrasonically cleaned in acetone, isopropanol, ethanol and deionized water in turn, and each solvent was used for 10 minutes to remove organic impurities attached to the surface, and then dried with N2; 3) Use MPCVD equipment to evacuate to 10 -4 Torr, hydrogen was introduced to etch the substrate surface, and the chamber pressure was maintained at 100 Torr, the temperature was maintained at 820°C, and the etching time was maintained at 30 min to remove the non-diamond phase on the substrate surface; 4) During the growth stage, the microwave source input power was maintained at 5 kW, the cavity pressure was maintained at 140 Torr, the growth temperature was maintained at 920° C., methane gas was used as the main carbon source, and the gas flow rate was maintained at 30 sccm. 5) During the growth stage, a mixed gas of borane and phosphine is introduced as a direct doping source, wherein the gas flow rates of borane and phosphine are 15 sccm and 15 sccm respectively, to achieve co-doping of diamond with boron atoms and phosphorus atoms. The relationship between the resistance value of diamond co-doped with boron and phosphorus atoms obtained in 5) and the temperature is as follows: Figure 2 As shown in the figure, when the ambient temperature drops to 17.21K, the resistance increases exponentially. Figure 1 In comparison, after the treatment in step 5), i.e., after increasing the phosphine gas flow rate by 5 sccm during the growth stage, the exciton insulation transition temperature of diamond increases to 17.21 K. Therefore, increasing the phosphine gas doping flow rate is conducive to the coupling of electrons and holes to form excitons, which helps to increase the exciton insulator transition temperature of diamond and achieve exciton insulation.

[0017] Embodiment 3: 1) Take a single crystal diamond with a (110) crystal orientation and a size of 12 mm × 12 mm as a substrate, and polish the growth surface to ensure that the growth surface is smooth and flat; 2) The substrate was ultrasonically cleaned in acetone, isopropanol, ethanol and deionized water in turn, and each solvent was used for 10 minutes to remove organic impurities attached to the surface, and then dried with N2; 3) Use MPCVD equipment to evacuate to 10 -3 Torr, hydrogen was introduced to etch the substrate surface, and the chamber pressure was maintained at 100 Torr, the temperature was maintained at 820°C, and the etching time was maintained at 30 min to remove the non-diamond phase on the substrate surface; 4) During the growth stage, the microwave source input power was maintained at 5 kW, the cavity pressure was maintained at 150 Torr, the growth temperature was maintained at 920° C., methane gas was used as the main carbon source, and the gas flow rate was maintained at 30 sccm. 5) During the growth stage, borane gas and phosphine gas are introduced alternately as direct doping sources, wherein the gas flow rates of borane and phosphine are 15 sccm and 15 sccm, respectively, to achieve alternating ultra-thin doping of diamond with boron atoms and phosphorus atoms. The relationship between the resistance value and temperature of the diamond doped with boron and phosphorus atoms alternately obtained in step 5) is as follows: Figure 4 As shown in the figure, when the ambient temperature drops to 51.3K, the resistance increases exponentially. Figure 2 In comparison, after step 5), alternating doping is used in the growth stage (its structural schematic diagram is shown in FIG. Figure 3 ) after replacing simultaneous doping with boron / phosphorus, the exciton insulating transition temperature of diamond co-doped with boron / phosphorus increases significantly. Therefore, compared with diamond exciton insulators doped with boron / phosphorus simultaneously, alternating ultra-thin doping with boron / phosphorus is conducive to the exciton coupling between boron and phosphorus atomic layers, significantly improving the exciton binding energy through the quantum confinement effect, and contributing to the high-temperature exciton insulator transition of diamond.

[0018] Obviously, the present invention is not limited to the above-mentioned specific embodiments, and those skilled in the art can make various changes or modifications within the scope of the claims, which does not affect the essence of the present invention. The purpose of selecting and describing the exemplary embodiments is to explain the specific principles of the present invention and its practical application, so that those skilled in the art can realize and utilize various different exemplary embodiments of the present invention and various different options and changes. The scope of the present invention is intended to be limited by the claims and their equivalents.

Claims

1. An alternating ultrathin doped diamond excitonic insulator, characterized in that: Diamond is prepared by microwave plasma chemical vapor deposition (MPCVD). During the preparation process, two doping gases are introduced alternately at different times: a boron-containing doping gas and a phosphorus / nitrogen-containing doping gas, so that the boron element and the phosphorus / nitrogen element are layeredly doped in the diamond during the growth process, and alternating ultra-thin heavily doped boron atomic layers and ultra-thin heavily doped phosphorus / nitrogen atomic layers are formed in the diamond, which are coupled to form bound excitons, thereby realizing the insulating transition of the diamond. The phase transition to an insulator can be induced by lowering the temperature to below 100K. The phosphorus / nitrogen-containing doping gas contains one or more of phosphorus and nitrogen.

2. The alternating ultrathin doped diamond excitonic insulator according to claim 1, characterized in that: The preparation of diamond by MPCVD method specifically includes: using clean single crystal diamond as substrate, placing it in MPCVD reaction chamber, introducing hydrogen after evacuation, and etching the non-diamond phase on the diamond surface; after etching the substrate, introducing carbon source gas into the reaction chamber for diamond growth, and introducing boron-containing doping gas and phosphorus / nitrogen-containing doping gas alternately in time.

3. The alternating ultrathin doped diamond exciton insulator according to claim 2, characterized in that: The vacuuming is performed until the background vacuum degree in the reaction chamber is not less than 1×10 -3 Torr, during the growth process, the input power range of the microwave source is controlled to be 1 to 10 kW, and the cavity pressure range is 10 to 300 Torr.

4. The alternating ultrathin doped diamond excitonic insulator according to claim 2, characterized in that: The carbon source gas is methane, wherein the flow ratio of the carbon source gas to the boron-containing doping gas is 2:1, and the flow ratio of the carbon source gas to the phosphorus / nitrogen-containing doping gas is 2:1-6:

1.

5. The alternating ultrathin doped diamond excitonic insulator according to claim 2, characterized in that: Diamond is doped in layers by alternately introducing two doping gases at different time periods. The introduction time of each doping gas is 0.5-10 seconds to form an ultra-thin doping layer.

6. The alternating ultrathin doped diamond excitonic insulator according to claim 1, characterized in that: The boron-containing doping gas is one or more of borane and diborane.

7. The alternating ultrathin doped diamond excitonic insulator according to claim 1, characterized in that: The phosphorus / nitrogen doping gas is one or more of phosphine, phosphate, ammonia and nitrogen.

8. A method for preparing an alternating ultrathin doped diamond exciton insulator, characterized in that: The steps include: 1) Using single crystal diamond as substrate; 2) ultrasonically cleaning the substrate using acetone, isopropanol, ethanol and deionized water before growth on the substrate surface; 3) Using MPCVD equipment to evacuate the diamond, and then introducing hydrogen to etch the non-diamond phase on the diamond surface; 4) During the growth stage, the microwave source input power is maintained at 1-10 kW, the cavity pressure is maintained at 10-300 Torr, and methane gas is introduced as a carbon source; 5) In the doping growth stage, the boron-containing doping gas and the phosphorus / nitrogen-containing doping gas are introduced alternately as doping sources, each for 0.5 to 10 seconds, the flow ratio of the carbon source gas to the boron-containing doping gas is 2:1, and the flow ratio of the carbon source gas to the phosphorus / nitrogen-containing doping gas is 2:1 to 6:1; the alternating ultra-thin heavy doping of boron atoms and phosphorus / nitrogen atoms during the diamond growth process is achieved; 6) Lowering the temperature to below 100K causes the excitons in the system to form a Bose-Einstein condensate, inducing a phase transition to an insulator.

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