Nickel gallate crystal and growth method and application thereof

Abstract

The invention discloses a nickel gallate crystal and a growth method and application thereof, and belongs to the technical field of semiconductor materials. The nickel gallate crystal growth method provided by the invention comprises the following steps: preparing nickel oxide powder and gallium oxide powder according to a stoichiometric ratio, uniformly mixing, pressing, and carrying out solid-phase sintering to obtain a nickel gallate blank; then fixing the nickel gallate blank, and then growing a nickel gallate crystal; the atmosphere adopted in the growth process is a mixed atmosphere of argon and oxygen, and the volume fraction of the oxygen is 5-10%. By selecting the nickel oxide powder and the gallium oxide powder in a specific stoichiometric ratio and the atmosphere during crystal growth, the high-quality nickel gallate crystal is prepared, and the crystal is regular in appearance, green, transparent, bubble-free and polycrystal-free; the method is expected to realize accurate regulation and control of electrical properties of gallium oxide.

Description

Technical Field

[0001] The present invention relates to the technical field of semiconductor materials, and particularly to a nickel gallate crystal, a growth method thereof, and an application thereof. Background Art

[0002] The information disclosed in the background art of the present invention is only intended to increase the understanding of the overall background of the present invention, and is not necessarily regarded as an admission or an implication in any form that this information constitutes the prior art already known to those of ordinary skill in the art.

[0003] Gallium oxide (Ga2O3), as a fourth-generation ultra-wide bandgap semiconductor (bandgap width about 4.9 eV), has a breakdown field strength of up to 8 MV / cm. Its high-voltage resistance ability is 3000 times that of silicon and 3 times that of silicon carbide. Moreover, its theoretical power quality factor far exceeds that of the third-generation semiconductors, making it suitable for high-frequency and high-power devices. At the same time, its raw material cost is only 1 / 4 of that of silicon carbide, and the substrate growth efficiency is higher, showing significant economy. It has great potential in the fields of power device solar-blind ultraviolet detectors and radio frequency devices.

[0004] However, the gallium oxide material system has long faced the technical bottleneck of difficult p-type doping. This is mainly attributed to the fact that its valence band is mainly composed of the 2p orbitals of oxygen, resulting in small valence band dispersion (i.e., large hole effective mass) and deep energy levels, which severely restricts the hole mobility and the controllability of electrical properties. In the prior art, researchers generally attempt to improve the valence band dispersion by introducing the hybridization of the d orbitals of transition metal elements (such as Ni) with the 2p orbitals of O. For example, single metal oxides such as NiO have been proven to form p-type semiconductors with relatively small hole effective masses. Further research has found that double metal oxides with an AB2O4 spinel structure, due to their unique cation site substitution characteristics, can theoretically achieve the coordinated regulation of n-type and p-type conduction types, which provides a new idea for breaking through the bottleneck of the electrical property regulation of gallium oxide. However, the crystal growth method of nickel gallate crystals has not been reported yet. Summary of the Invention

[0005] In view of this, the present invention provides a nickel gallate crystal, a growth method thereof, and an application thereof. The present invention can prepare nickel gallate crystals with good quality and is expected to achieve the regulation of the electrical properties of gallium oxide.

[0006] In a first aspect, the present invention provides a growth method of a nickel gallate crystal, and the chemical formula of the nickel gallate crystal is Ni x Ga2O 3+x , where 0.99 ≤ x ≤ 1.01; the growth method includes the following steps:

[0007] Mix nickel oxide powder and gallium oxide powder according to the stoichiometric ratio, uniformly mix them, then press them, and then perform solid-phase sintering to obtain a nickel gallate blank;

[0008] Then, the nickel gallate blank is fixed, and then the growth of nickel gallate crystals is carried out. The atmosphere used in the growth process is a mixed atmosphere of argon and oxygen, where the volume fraction of oxygen is 5-10%.

[0009] In a second aspect, the present invention provides nickel gallate crystals obtained by the above growth method.

[0010] In a third aspect, the present invention provides the application of the above nickel gallate crystals in the semiconductor field.

[0011] Compared with the prior art, the present invention has achieved the following beneficial effects:

[0012] By selecting nickel oxide powder and gallium oxide powder with a specific stoichiometric ratio and the atmosphere during crystal growth, the present invention prepares nickel gallate crystals with high quality. The crystal has a regular shape, is green and transparent, has no bubbles and no polycrystals. The grown crystal shows strong carrier absorption in the infrared band, and is expected to realize the regulation of the electrical properties of gallium oxide. Moreover, the preparation method of the present invention is simple and has a low cost. BRIEF DESCRIPTION OF THE DRAWINGS

[0013] The specification drawings constituting a part of the present invention are used to provide a further understanding of the present invention. The schematic embodiments of the present invention and their descriptions are used to explain the present invention and do not constitute an improper limitation of the present invention. Obviously, for those of ordinary skill in the art, other drawings can be obtained based on these drawings without creative efforts.

[0014] Figure 1 It is a picture of the sample of the nickel gallate crystal after cutting and polishing in Example 1 of the present invention;

[0015] Figure 2 It is the X-ray diffraction pattern of the nickel gallate crystal in Example 1 of the present invention;

[0016] Figure 3 It is the infrared transmission spectrum of the nickel gallate crystal in Example 1 of the present invention;

[0017] Figure 4 It is a picture of the sample of the nickel gallate crystal in Comparative Example 1 of the present invention. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0018] It should be noted that the following detailed description is exemplary and is intended to provide further explanation of the present invention. Unless otherwise specified, all technical and scientific terms used herein have the same meaning as commonly understood by those of ordinary skill in the technical field to which the present invention belongs.

[0019] The present invention provides a method for growing nickel gallate crystals, and the chemical formula of the nickel gallate crystal is Ni xGa2O 3+x , 0.99 ≤ x ≤ 1.01; The growth method includes the following steps:

[0020] Mix nickel oxide powder and gallium oxide powder according to the stoichiometric ratio, uniformly mix them, then press them, and then perform solid-phase sintering to obtain a nickel gallate blank;

[0021] Then fix the nickel gallate blank and then grow nickel gallate crystals; The atmosphere used in the growth process is a mixed atmosphere of argon and oxygen, where the volume fraction of oxygen is 5-10%.

[0022] In the present invention, the purity of the nickel oxide powder and the gallium oxide powder is above 99.99%. In one or more embodiments of the present invention, the purity of the nickel oxide powder is 99.99%, and the purity of the gallium oxide powder is 99.999%. High-purity raw materials are the premise for preparing high-quality nickel gallate crystals. The present invention does not impose special restrictions on the source of the above-mentioned high-purity raw materials. They can be obtained commercially, or the commercially available lower-purity nickel oxide or gallium oxide can be purified to obtain high-purity raw materials. The present invention does not impose special restrictions on the specific purification steps, and those skilled in the art can use common means in the art for purification.

[0023] In the present invention, the rotation speed during the mixing process is 30-50 rpm, and the mixing time is 40-100 h, more preferably 70-90 h. In one or more embodiments of the present invention, this mixing process is carried out in a mixer. A longer mixing time ensures that the two are fully mixed, which is beneficial to the subsequent reaction and is also beneficial to the preparation of high-quality gallium oxide crystals with high uniformity.

[0024] The present invention does not impose special restrictions on the pressing process. The present invention preferably presses it into a block by a hydraulic press or into a columnar rod by isostatic pressing. Those skilled in the art can choose according to actual needs. The pressure used in the pressing process is 1800-2200 bar.

[0025] In the present invention, the process of the solid-phase sintering is specifically: place the pressed solid in an air atmosphere at 1200-1400 °C and sinter for 50-70 h. In one or more embodiments of the present invention, the sintering temperature is further preferably 1250-1350 °C, and the sintering time is further preferably 55-65 h.

[0026] In the present invention, the method for growing nickel gallate crystals includes the vertical gradient freezing method, the Czochralski method, the edge-defined film-fed growth method, the optical floating zone method, or the Bridgman method. The present invention does not impose special restrictions on the specific preparation process, and those skilled in the art can grow crystals according to the commonly used crystal growth processes in the art. In the present invention, when using the Czochralski method, the edge-defined film-fed growth method, or the optical floating zone method for crystal growth, a seed crystal in the <111> direction is selected. After the step of selecting a seed crystal in the <111> direction, the steps of cutting, ultrasonic cleaning, and drying are further included.

[0027] In one or more embodiments of the present invention, the specific steps for growing nickel gallate crystals using the vertical gradient freezing method are as follows: placing the nickel gallate blank in an iridium crucible, evacuating, introducing a mixed atmosphere of argon and oxygen, then heating to 1800 - 2000 °C, holding the temperature until the melt is completely melted, and then cooling to obtain nickel gallate crystals. Further, evacuate to a vacuum degree of (2 - 5)×10 -4 Pa; introduce a mixed atmosphere of argon and oxygen until the system pressure is 1 - 1.1 bar. The heating rate is 200 - 300 °C / h, more preferably 240 - 260 °C / h; the cooling rate is 2 - 5 °C / min; the holding time is 1 - 4 h, and the length of the holding time depends on the melting condition of the melt.

[0028] The present invention also provides nickel gallate crystals grown by the above growth method. The nickel gallate crystals prepared by the method of the present invention have high quality, with regular crystal shape, green transparency, no bubbles, and no polycrystals.

[0029] The present invention also provides the application of the above nickel gallate crystals in the semiconductor field. The nickel gallate crystals of the present invention are expected to achieve precise regulation of the electrical properties of gallium oxide.

[0030] The technical solution of the present invention will be further described below in conjunction with specific embodiments. The present invention does not impose special restrictions on the sources of the reagents used in the following embodiments, and commercially available products well-known to those skilled in the art can be used.

[0031] Example 1

[0032] This example provides a method for growing nickel gallate crystals by the vertical gradient freezing method. The specific steps are as follows:

[0033] (1) Selection and treatment of raw materials

[0034] Mix nickel oxide powder with a purity of 99.99% and gallium oxide powder with a purity of 99.999% according to the chemical stoichiometry of Ga and Ni in NiGa2O4, mix at 40 rpm for 80 h, then cold press into a block at 2000 bar, and calcine in a corundum crucible at 1300 °C in air for 60 h to obtain a nickel gallate blank.

[0035] (2) Crystal growth

[0036] Load the nickel gallate blank from step (1) into an iridium crucible (height 60 mm, inner diameter 60 mm, wall thickness 2 mm, bottom thickness 3 mm) in the crystal growth furnace. Use an iridium lid with an inner diameter of 30 mm and an outer diameter of 64 mm to reduce evaporation and radiant heat loss. Evacuate the crystal growth furnace to 3×10 -4 Pa, input a mixed gas of argon and oxygen with a volume fraction of 8% (system pressure is 1.02 bar), then heat it in the furnace at a heating rate of 250 °C / h to 1900 °C, keep it in a molten state for about 2 hours. After the melt is completely melted, cool it to room temperature at a cooling rate of 3 °C / min to obtain nickel gallate crystals.

[0037] The picture of the sample of the nickel gallate crystal obtained in this example after cutting and polishing is as Figure 1 shown. It can be seen from Figure 1 that the crystal has a regular shape, is green and transparent, has no bubbles and no polycrystals.

[0038] The spectrum obtained by X-ray diffraction test is as Figure 2 shown. By comparison, it is determined that the grown crystal is a nickel gallate crystal.

[0039] Through EDS test, the chemical formula of the nickel gallate prepared in this example is NiGa 2.02 O 4.1 , and the components are close to the stoichiometric ratio and there is no large deviation.

[0040] The absorption intensity of the crystal in the infrared band has a strong dependence on the free carrier concentration, which means that the higher the carrier concentration, the greater the absorption intensity. The infrared transmission spectrum of the nickel gallate crystal sample in this example is as Figure 3 shown. The highest transmittance of the sample is 35%. From the visible light to the infrared band, the transmittance of NiGa2O4 drops significantly, showing strong free electron absorption. Through infrared spectrum test, the electrical properties of the crystal are indirectly reflected.

[0041] Example 2

[0042] This example provides a method for growing nickel gallate crystals by the Czochralski method. The specific steps are as follows:

[0043] (1) Selection and treatment of raw materials

[0044] Mix nickel oxide powder with a purity of 99.99% and gallium oxide powder with a purity of 99.999% according to the stoichiometric ratio of Ga and Ni in NiGa2O4, mix them at 40 rpm for 80 h, then cold press them into blocks under 2000 bar, and calcine them in a corundum crucible in air at 1300 °C for 60 h to obtain nickel gallate blanks.

[0045] (2) Selection of seed crystal

[0046] The <111>-oriented seed crystal of nickel gallate is selected, cut, ultrasonically cleaned, and dried for later use.

[0047] (3) Crystal growth

[0048] The nickel gallate blank in step (1) is loaded into an iridium crucible in the crystal growth furnace. The crystal growth furnace is evacuated to 3×10 -4 Pa, and a mixed gas of argon and oxygen with a volume fraction of 8% (system pressure is 1.02 bar) is input; the nickel gallate blank is heated and melted by medium-frequency induction heating, the melt is superheated by 15 °C, held at a constant temperature for 2 hours to remove bubbles in the melt; then it is cooled to the temperature when the nickel gallate blank is completely melted and held at a constant temperature for 2 hours; the nickel gallate seed crystal is introduced and necked down at 2 °C above the melting point of the melt. When the diameter of the seed crystal is reduced to 2 mm, shoulder formation is carried out. After equal-diameter growth, it enters the finishing stage; the pulling speeds in the necking down, shoulder formation, equal-diameter growth, and finishing stages are: 1 mm / hour, and the rotation speed is: 20 revolutions per minute. After the crystal grows to the required size, the temperature is raised by 25 °C and held at a constant temperature for 30 minutes, and the crystal is lifted out of the melt; after lifting out the crystal, it is cooled to room temperature at a rate of 20 °C / hour, and the nickel gallate single crystal is obtained.

[0049] Example 3

[0050] This example provides a method for growing nickel gallate crystals by the edge-defined film-fed growth (EFG) method. The specific steps are as follows:

[0051] (1) Selection and treatment of raw materials

[0052] Nickel oxide powder with a purity of 99.99% and gallium oxide powder with a purity of 99.999% are proportioned according to the stoichiometric ratio of Ga and Ni in NiGa2O4, mixed at 40 rpm for 80 h, then cold-pressed into blocks at 2000 bar, and calcined in a corundum crucible in air at 1300 °C for 60 h to obtain a nickel gallate blank.

[0053] (2) Selection of seed crystal

[0054] The <111>-oriented seed crystal of nickel gallate is selected, cut, ultrasonically cleaned, and dried for later use.

[0055] (3) Crystal growth

[0056] The nickel gallate blank in step (1) is loaded into an iridium crucible in the crystal growth furnace. An iridium mold is placed in the crucible, and crystal growth is carried out by the EFG method. The crystal growth furnace is evacuated to 3×10 -4Pa, introduce a mixed gas of argon and oxygen with a volume fraction of 8% (system pressure is 1.02 bar); use medium-frequency induction heating to heat the nickel gallate blank until it melts, superheat the melt by 15 °C, keep it at a constant temperature for 2 hours, and remove the bubbles in the melt; then cool it down to the temperature when the nickel gallate blank is completely melted, and keep it at a constant temperature for 2 hours; introduce a nickel gallate seed crystal at 2 °C above the melting point of the melt, make the <111>-direction seed crystal slowly contact the surface of the iridium-gold mold, slightly melt and neck down, and when the diameter of the seed crystal is reduced to 2 mm, perform shoulder opening, enter the finishing stage after equal-diameter growth; the pulling speeds in the necking down, shoulder opening, equal-diameter growth and finishing stages are: 1 mm / hour, and the rotation speed is 20 revolutions per minute. After the crystal grows to the required size, raise the temperature by 25 °C, keep it at a constant temperature for 30 minutes, and lift the crystal out of the melt; after lifting the crystal out, cool it down to room temperature at a rate of 10 - 30 °C / hour to obtain a nickel gallate single crystal.

[0057] Example 4

[0058] This example provides a method for growing nickel gallate crystals by the optical floating zone method. The specific steps are as follows:

[0059] (1) Selection and treatment of raw materials

[0060] Mix nickel oxide powder with a purity of 99.99% and gallium oxide powder with a purity of 99.999% according to the chemical stoichiometric ratio of Ga and Ni in NiGa2O4, mix at 40 rpm for 80 h, then cold press into blocks at 2000 bar, and calcine in a corundum crucible in air at 1300 °C for 60 h to obtain a nickel gallate blank.

[0061] (2) Selection of seed crystal

[0062] Select a <111>-direction nickel gallate seed crystal, cut, ultrasonically clean, and dry it for later use.

[0063] (3) Crystal growth

[0064] Fix the nickel gallate blank obtained in step (1) in a floating zone furnace, evacuate the crystal growth furnace to 3×10 -4 Pa, introduce a flowing atmosphere of a mixed gas of argon and oxygen with a volume fraction of 8% (system pressure is 1.02 bar); raise the temperature to slowly melt the raw materials; introduce a <111>-direction seed crystal at 2 °C above the melting point of the melt to induce crystal growth, perform shoulder opening when the diameter of the seed crystal is reduced to 2 mm, enter the finishing stage after equal-diameter growth; the pulling speeds in the necking down, shoulder opening, equal-diameter growth and finishing stages are 1 mm / hour, and the rotation speed is 20 revolutions per minute; after the crystal grows to the required size, lift the crystal out of the melt at high speed.

[0065] Example 5

[0066] This example provides a method for growing nickel gallate crystals by the Bridgman method. The specific steps are as follows:

[0067] (1) Selection and treatment of raw materials

[0068] Nickel oxide powder with a purity of 99.99% and gallium oxide powder with a purity of 99.999% are proportioned according to the chemical stoichiometry of Ga and Ni in NiGa2O4, mixed at 40 rpm for 80 h, then cold-pressed into blocks at 2000 bar, and calcined in a corundum crucible in air at 1300 °C for 60 h to obtain nickel gallate blanks.

[0069] (2) Crystal growth

[0070] The nickel gallate blanks from step (1) are loaded into an iridium crucible in a dropping furnace, and the crystal growth furnace is evacuated to 3×10 -4 Pa, and a mixed gas of argon and oxygen with a volume fraction of 8% (system pressure of 1.02 bar) is introduced; the nickel gallate blanks are heated and melted by medium-frequency induction heating, the melt is superheated by 15 °C, and kept at a constant temperature for 2 h to remove the bubbles in the melt; during the crystal growth process, the dropping speed is 1 mm / h. After the crystal growth is completed, it is slowly cooled to room temperature, and the crystal can be taken out.

[0071] Comparative example 1

[0072] Compared with Example 1, the difference in this comparative example is that the atmosphere during the crystal growth process in this comparative example does not contain oxygen.

[0073] The picture of the crystal sample grown in this comparative example is as shown in Figure 4 . It can be seen that there are green impurities on the surface, the crystal quality is poor, and the crystal cannot be used. This is because in an argon atmosphere, the decomposition and volatilization of gallium oxide are relatively serious, which is not conducive to the growth of nickel gallate crystals.

[0074] Comparative example 2

[0075] Compared with Example 1, the difference in this comparative example is that the volume fraction of oxygen in the atmosphere during the crystal growth process in this comparative example is 20%.

[0076] The crystal grown in this comparative example is tested by EDS, and the test results show that the chemical formula of this nickel gallate is NiGa 2.85 O 6.35 , seriously deviating from the chemical stoichiometry.

[0077] The above are only the preferred embodiments of the present invention and are not intended to limit the present invention. For those skilled in the art, the present invention can have various modifications and changes. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention shall be included in the protection scope of the present invention.

Claims

1. A method for growing nickel gallate crystals, characterized in that, The chemical formula of the nickel gallate crystal is Ni x Ga2O 3+x , 0.99 ≤ x ≤ 1.01; The growth method includes the following steps: Nickel oxide powder and gallium oxide powder are proportioned according to the stoichiometric ratio, mixed evenly, then pressed, and then subjected to solid-phase sintering to obtain a nickel gallate blank; Then the nickel gallate blank is fixed, and then the growth of nickel gallate crystals is carried out; the atmosphere used in the growth process is a mixed atmosphere of argon and oxygen, and the volume fraction of oxygen is 5-10%.

2. The growth method according to claim 1, characterized in that, The purity of the nickel oxide powder and gallium oxide powder is above 99.99%.

3. The growth method according to claim 1, characterized in that, The specific process of the solid-phase sintering is: placing the pressed solid in an air atmosphere at 1200-1400 °C and sintering for 50-70 h.

4. The growth method according to claim 1, characterized in that, The method for growing nickel gallate crystals includes the vertical gradient freezing method, the Czochralski method, the edge-defined film-fed growth method, the optical floating zone method or the Bridgman method.

5. The growth method according to claim 4, characterized in that, The specific steps for growing nickel gallate crystals by the vertical gradient freezing method are: placing the nickel gallate blank in an iridium crucible, evacuating, inputting a mixed atmosphere of argon and oxygen, then heating to 1800-2000 °C, holding the temperature until the melt is completely melted, and then cooling to obtain nickel gallate crystals.

6. The growth method according to claim 5, characterized in that, Evacuate to a vacuum degree of (2 - 5)×10 -4 Pa; the input pressure of the mixed atmosphere of argon and oxygen is 1 - 1.1 bar.

7. The growth method according to claim 5, wherein The rotation speed during the mixing process is 30-50 rpm, and the mixing time is 40-100 h; the pressure used in the pressing process is 1800-2200 bar.

8. The growth method according to claim 5, characterized in that The heating rate is 200-300 °C / h, the cooling rate is 2-5 °C / min; the holding time is 1-4 h.

9. A nickel gallate crystal grown by the growth method according to any one of claims 1-8.

10. The application of the nickel gallate crystal according to claim 9 in the semiconductor field.

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