Patent ID: 12247315

DETAILED DESCRIPTION OF THE EMBODIMENTS

Preferred embodiments of the present invention will hereinafter be described in detail with reference to the accompanying drawings, where like numerals of reference designate like elements throughout.

FIG.1shows an apparatus for manufacturing hexagonal crystals according to a first embodiment of the present invention.

The apparatus for manufacturing hexagonal crystal according to the present invention employs a HVPE method for growth of hexagonal crystals. Referring toFIG.1, the apparatus includes a reaction tube100, a reaction boat200disposed in the reaction tube100, a gas supply300for supplying reaction gases to the reaction tube100, and a heater400for heating the interior of the reaction tube100.

The reaction tube100is preferably a quartz tube, and the heater400is preferably a hot wall furnace configured as a general three-heater furnace, but it is not limited thereto.

The reaction boat200is a module of which a source allocating part210and a crystal growth part220are connected. The source allocating part210and the crystal growth part220are arranged vertically.FIG.2shows an exploded perspective view of the reaction boat200ofFIG.1when a cover218is removed.

The source allocating part210has a bottom surface in the shape of a rectangle, but it is not limited thereto. The shape may be circular or other shapes. The source allocating part210has one or more penetration holes500formed on the bottom surface, a first allocating area211disposed around the penetration hole500, and the second allocating area212disposed around the first allocating area211. That is, the first allocating area211is disposed closer to the penetration hole500than the second allocating area212.

The first allocating area211receives aluminum700in a solid state, and the second allocating area212receives a mixture material800of the main material of the hexagonal crystals and gallium. The aluminum700in first allocating area211is placed without blocking the penetration hole500.

Aluminum acts as a catalyst for nucleation required for growing hexagonal crystals. Gallium melts the main material of hexagonal crystals and then accommodates a reaction with the halogenation reaction gas as described later. Gallium also avoids oxidation of materials and then accommodates easy contact with the halogenation reaction gas. Gallium also acts as a catalyst for nucleation required for growing hexagonal Si crystals on the substrate, together with aluminum. Aluminum placed on the first allocating area211around the penetration hole500serves as a main source of nano-absorbers formation.

It is noted that aluminum700should be separated from gallium. That is, aluminum700is placed in the first allocating area211, not in direct contact with gallium in order to prevent melted gallium from directly contacting with aluminum and melting all the aluminum. Rather, GaCl3in gas state acts on the aluminum metal surface to efficiently generate Al-based nano-absorbers.

The main material is in a solid state and is selected from a group consisting of Si, C, Ge, and Ga. One or more materials selected from the group of main materials are used to grow hexagonal crystals. When the hexagonal crystals are hexagonal Si crystals, hexagonal Ge crystals, or hexagonal carbon crystals, one main material among Si, Ge, and C is used. When the hexagonal crystals are SiC crystals, Si and C are used. In the case of hexagonal Ga2O3crystals, Ga and O are selected as main materials. In the case of hexagonal Si1-xGexcrystals (0.35<x<1), Si and Ge are selected as main materials.

When hexagonal crystals are grown, a substrate may be used in a growth mold as described later. When hexagonal silicon crystals or hexagonal Ga2O3crystals@@@ are grown on a substrate which is selected from a group of a SiC substrate, a sapphire substrate, or a GaN substrate, they serve as a material for semiconductors.

A mass ratio of the main material: aluminum:gallium is 0.80-1.5:1.25:1. That is, a ratio of aluminum to the main material ranges from 80%-150%.

FIG.3AtoFIG.3Dshow several examples of the first allocating area211and the second allocating area212of the source allocating part210.

FIG.3Ashows that a rectangular first allocating area211is formed around a penetration hole500, andFIG.3Bshows that a circular first allocating area211is formed around a penetration hole500. The first allocating area211and the second allocating area212may be physically separated by a separation protrusion215, as shown inFIG.3C.

FIG.3DandFIG.3Fshow that a first allocating area211is disposed higher than a second allocating area212by a predetermined height. The first allocating area211having a rectangular shape is disposed with a predetermined height h1from a bottom surface of the source allocating part210, as shown inFIG.3D. The first allocating area211ofFIG.3Fdiffers fromFIG.3Din that the first allocating area211has a circular shape. The first allocating area211may have a separation protrusion around its edge as shown inFIG.3C, although it is not shown.

FIG.3EandFIG.3Gshow that the first allocating areas211′ and211are formed with two steps of heights, h1and h2. The first allocating areas211′ and211having rectangular shapes are disposed with predetermined heights h2and h2from the bottom surfaces of the source allocating part210and the first allocating are211, respectively, as shown inFIG.3E. The first allocating areas211′ and211ofFIG.3Gdiffer fromFIG.3Ein that the first allocating areas211′ and211have circular shapes. Each of the heights h1and h2preferably ranges from 1 mm to 5 mm. Since the first allocating area211or211is disposed higher than the second allocating area212, the melted main material or melted gallium in the second allocating area212is prevented from flowing into the penetration hole500.

The penetration hole500is formed on a bottom surface of the source allocating part210. Preferably, a lower diameter D2of the penetration hole500is smaller than an upper diameter D1of the penetration hole, so that flow rates of gases passing through the penetration hole increase.FIG.4Ashows a penetration hole500in the shape of a funnel, whileFIG.4B-FIG.4Cshow a penetration hole500in a stepped shape, in which a lower diameter D2of the penetration hole500is smaller than an upper diameter D1. The diameters D1and D2of the penetration hole500range from 5 mm to 10 mm, and the ratio of D1:D2is in a range of about 1-2. As such, the lower diameter D2of the penetration hole500is smaller than the upper diameter D1, so flow rates of gases passing through the penetration hole500increase to supply gases to the growth mold240of the crystal growth part220smoothly. The flow rate of gas is inversely proportional to a cross-section through which the gas flows. That is, the smaller an area, the faster a flow rate. Accordingly, gases at the lower point of the penetration hole500are faster, and then enter into the growth mold240smoothly. The stepped shapes of the first allocating area shown inFIGS.4B-4Chave an advantage of preventing melted liquids from directly falling into the growth mold240.

Since the pressure differs at the inside of the penetration hole500from the outside of the penetration hole, a pressure of 0.1-1 GPa is applied to the growth mold240or a substrate in the growth mold.

Preferably, the source allocating part210is covered by a cover218. The cover218has openings through which supply pipes321and331are positioned in the source allocating part210, in order to supply reaction gases.

The crystal growth part220is disposed beneath the source allocating part210and has a rectangular bottom similar to that of the source allocating part210, but is not limited thereto. The crystal growth part220has a depressed growth mold240of a predetermined shape which defines the grown shape of hexagonal crystals. For example, the growth mold240has a depressed circular cylindrical shape or a depressed rectangular cylinder shape, but is not limited thereto. A diameter L (or a length of a side L) or a depth d of the growth mold240shown inFIG.2may be selected according to a desirable shape of hexagonal crystals grown. When the diameter L is selected to be large, it is preferable that the depth d is also selected to be large in proportion thereto. For example, the diameter is selected as 2 inches and 4 inches, the depth d is then selected as 500 μm and 1 mm or more, respectively.

It is preferably that the crystal growth part220including the growth mold240is made of graphite or graphite with a carbon coating. A substrate is not necessary for growing hexagonal crystals, but is preferably employed for manufacturing various semiconductors. A substrate may be selected from various substrates available for industrial use without considering a lattice mismatch of crystals.

For example, hexagonal silicon crystals are preferred to grow on a substrate which is selected from a group consisting of graphite, silicon carbide, silicon, sapphire, quartz, ceramic, and various commercially used substrates such as GaN, GaAs, InP, Ga2O3, etc. Alternatively, a substrate is preferably selected from a SiC substrate such as a space group C46v-P63mc, a-phase 4H—SiC (a=3.0730 Å, b=10.053 Å), and 6H—SiC (a=3.0730 Å, b=10.053 Å), which are Wurtzite crystalline structures. Particularly, when hexagonal silicon crystals grown on a SiC substrate (Si/SiC substrate) are employed for manufacturing an electronic device, it results in an advantage for enhancing thermal characteristics of power semiconductor devices such as Si-based MOSFETs, diodes, and IGBTs, thereby significantly improving efficiency at high temperature and high pressure.

AlthoughFIG.2shows a single growth mold240in the crystal growth part220, it is possible to form two or more growth molds.FIG.5shows three growth molds241,242, and243in a crystal growth part220. It is noted that three growth molds241,242, and243may have different diameters and depths. Therefore, a plurality of crystals in different shapes can be obtained from a single growing process. The three growth molds241,242, and243are in fluid communication with each other in order to maintain internal pressures at the same pressure as shown inFIG.5. It also possible to form the growth molds isolated from each other, as necessary. In line with three growth molds241,242, and243, a source allocating part210has three penetration holes500and three first allocating areas211around the holes. It is possible to further form penetration holes500as necessary.

The source allocating part210and the crystal growth part220are in close contact with each other without a gap, to maintain a predetermined pressure in the growth mold240of the growth mold240of the crystal growth part220, as described later. The source allocating part210is engaged with the crystal growth part220by its own weight, fitting into the crystal growth part, or an engagement holding member, in order to be in close contact.FIG.6Ashows that graphite screws are employed as engagement holding members to engage the source allocating part210with the crystal growth part220.FIG.6Bshows that the source allocating part210is fitted into the crystal growth part220without any engagement holding member. Alternatively, it is possible to engage a source allocating part with a crystal growth part using a clamp.

The gas supply300includes an atmosphere gas supply310for supplying an atmosphere gas such as nitrogen, a nitrification reaction gas supply320for supplying a nitrification reaction gas such as ammonia (NH3), and a halogenation reaction gas supply330for supplying a halogenation reaction gas such as hydrogen chloride (HCl). The gas supplies310,320, and330supply gases to the reaction tube100via pipes311,321, and331, respectively.

The atmosphere gas supply310provides atmospheric gas, e.g., nitrogen, via the pipe311, to form nitrogen as an atmospheric environment in the reaction tube100and the reaction boat200. AlthoughFIG.1shows that the atmosphere gas supply pipe311is disposed outside the reaction boat200, atmosphere gas may be directly supplied into the reaction boat200, as necessary. This makes the atmosphere gas directly carry chloride gas of the main material and metal chloride gases (AlClnand GaCln) which are generated by reaction of the main material, gallium, and aluminum with a halogenation reaction gas to the crystal growth part220through the penetration hole500. The atmospheric gas further maintains stable gas flow in the reaction tube100.

The halogenation reaction gas is directly blown to aluminum disposed on the first allocating area211and main material and gallium disposed on the second allocating area212of the source allocating part210the pipe331connected to the halogenation reaction gas supply330, and accommodates generating chloride gas of the main material and metal chloride gases (AlClnand GaCln).

The pipe321connected to the nitrification reaction gas supply320provides the crystal growth part220through the penetration hole500with the nitrification reaction gas. Therefore, an outlet of the pipe321is preferably disposed around the penetration hole500, but not limited thereto.

A method for manufacturing hexagonal crystal using the apparatus according to the present invention will now be described. For convenience of explanation, it will be described that the hexagonal crystal is a hexagonal silicon crystal with silicon as the main raw material.

First, aluminum700, which is solid, is disposed on the first allocating area211of the source allocating part210, without blocking the penetration hole500. Solid silicon as main material is mixed with solid gallium to form a mixed source800. The mixed source800are evenly disposed on the second allocating area212. Silicon is main material for growing hexagonal silicon crystal and is metallurgical grade silicon. Aluminum acts as a catalyst for nucleation required for growing hexagonal Si crystal. Aluminum is placed on the first allocating area211around the penetration hole500serves as a main source of nano-absorbers formation. Gallium melts the main material of silicon and then accommodates a reaction with the halogenation reaction gas as described later. Gallium also avoids oxidation of materials and then accommodates easy contact with the halogenation reaction gas. Gallium also acts as a catalyst for nucleation required for growing hexagonal Si crystal on the substrate, together with aluminum.

The mixing ratio of silicon as main material: aluminum:gallium is 0.80-1.5:1.25:1. That is, a ratio of aluminum to main material ranges from 80%-150%.

The crystal growth part220is provided beneath the source allocating part210. It is possible to use an engagement holding member to engage the source allocating part210with crystal growth part220, as necessary.

Next, the heater400is operated to heat the reaction tube100to 1200-1350° C. At this time, an atmospheric gas of nitrogen is provided to flow and a nitrification reaction gas of ammonia is provided to flow a certain amount to the reaction boat200before heating to raise the temperature of the reaction boat200. The pipe321for supplying the nitrification reaction gas is formed of a quartz tube

Next, the temperature of the reaction tube100becomes stable and then a halogenation reaction gas of hydrogen chloride is provided to the source allocating part210. The hydrogen chloride reacts with each of aluminum, silicon and gallium. The silicon reacts with hydrogen chloride to generate trichlorosilane (Si+3HCl→SiHCl3+H2), the aluminum reacts with hydrogen chloride to generate AICl, and the gallium reacts with hydrogen chloride to generate GaCln(n=1, 2, 3 . . . ).

At this time, gallium disperses the surfaces of aluminum and silicon in the mixed source and mostly removes the oxidized layer and the nitrified layer of the surfaces of aluminum and silicon. That is, silicon and aluminum are oxidized and nitrified in a high temperature atmosphere, but a small amount of gallium disperses from their surfaces and removes the oxidized layer and the nitrified layer to activate while raising the temperature. Therefore, gallium activates aluminum to accommodate reactions between aluminum and hydrogen chloride to generate AICl. It is noted that AICl gas which generated from the reaction of aluminum with hydrogen chloride flows into the penetration hole500, and acts as a source of Al-based nano-absorbers in the growth mold240of the crystal growth part220. Gallium further suppresses generation of an oxidized layer and a nitrified layer on the surface of silicon, and accommodates reactions between silicon and hydrogen chloride to generate trichlorosilane (SiHCl3).

Next, SiHCl3, AICl, and GaClngases, which are generated from reactions between each material and hydrogen chloride, flow into the penetration hole500, react with ammonia of the nitrification reaction gas and then form Al-based nano-absorbers which serve as nuclei for the hexagonal Si crystal on the surface of the growth mold240of the crystal growth part220. Al-based nano-absorbers served as nuclei for hexagonal silicon crystal includes Al from AICl gas, N from nitrification reaction gas, and O distributed in the reaction tube100, and other atoms, and have nano-sizes. Adatoms grow on Al-based nano-absorbers and coexist with Si nuclei during early growth. A bond of Al and N is a material with a covalent bond having a Wurtzite structure or a hexagonal 2H structure. Accordingly, it is possible to rapidly grow Si nuclei with a pure hexagonal 2H structure. Trichlorosilane is provided to the depressed growth mold240of the crystal growth part220at the high partial pressure to grow hexagonal Si crystals in a main growth mode. In the present invention, only predetermined amounts of aluminum and gallium in a HVPE method, which differs from a conventional HVPE method or MOCVD in which source material, is continuously supplied. This causes aluminum and gallium in the source allocating part to be exhausted rapidly. In this condition, aluminum and gallium are depleted before Al-based nano-absorbers grow to another nano-crystal completely. Then the concentration of silicon rapidly increases as compared to that of aluminum, so that silicon atoms outcompete aluminum atoms. By this principle, the remaining dopants also can be excluded.

It is noted that predetermined amounts of aluminum and gallium are rapidly exhausted, and then aluminum atoms are substituted by silicon atoms by outcompeting according to the present invention which provides an optimized growth mechanism to hexagonal crystals. Within 10 minutes of growth time, this phenomenon occurs simultaneously, and a relatively excessive amount of SiClnform absorbers such as Al+O+N+C+Si, which can be used to form hexagonal Si crystals.

Nuclei of silicon, which are included in the absorbers, can rapidly grow in a length direction (002) plane, but grow in the growth mold240of the crystal growth part220to form hexagonal silicon crystals. The pressure inside the growth mold240of the crystal growth part220can be obtained by engaging the source allocating part210with the crystal growth part220in vertical disposition.

FIG.7shows a schematic view illustrating the growth mechanism of hexagonal crystals using Al-based nano-absorbers according to the present invention. Al metal forms Al-based nano-absorbers for growing hexagonal Si crystals. When the temperature is raised, Al metal reacts with HCl to generate protrusions on its surface. Then nano-nuclei are grown, and Al-based nano-absorbers are generated in the shape of multitudinous downy hairs.

At this time, N which belongs to Group V is provided from the reaction the nitrification reaction gas NH3with the metal chloride gas (AICl and GaCln). Furthermore, since Si, Al, Ga, C, N, and O elements with AICl are provided to Al-based nano-absorbers, Al-based nano-absorbers becomes large in the shape of a hexagonal micro-wire containing Si, Al, Ga, C, N, and O elements. This is a process in which the nuclei of AlN are generated. SiHCl3, AICl, and GaClnreact with ammonia gas to adsorb gallium, aluminum, carbon, etc. in the absorbers, and then the absorbers becomes AlN-based micro-clusters including C and O adsorption. The micro-clusters have hexagonal shapes close to a circle formed of a translucent nanomembrane. They have no intrinsic crystalline structure yet, and take the form of semi crystalline micro-needles in a structurally very weak shell.

FIG.32AandFIG.32Bare SEM pictures of Al-based nano-absorbers in the shape of micro-wires, which is semi-crystalline. It is noted that Al-based nano-absorbers are formed in the shape of a nano-wire.

Al-based nano-absorbers are coupled to NH3of the space group Fm3m to form the hexagonal system which has the Wurtzite crystalline structure in a shape of the space group P63mc. Once the solid materials are set in an initial setting in the manufacturing method according to the present invention, they are not further supplied during the progress of the method. When the amount of AICl rapidly decreases, Al-based nano-absorbers remain and AlN nano-wires are not completely formed.

At this time, large amounts of SiClnare generated, and then Al-based nano-absorbers absorb Si atoms to form Si stems. Si micro-needles have a hexagonal structure having covalent bonds, which are a Wurtzite crystalline structure or a hexagonal 2H structure.

The hexagonal silicon crystals remaining in the shape of a stem (Shape 1: needle) shown inFIG.7become needle-shaped hexagonal silicon crystals.

An Al-based nano-absorber shown in Shape 2 ofFIG.7forms a snowflake shape in which Si branches are formed around a Si stem by increasing its size to form hexagonal silicon crystals.

An Al-based nano-absorber shown in Shape 3 ofFIG.7forms a hexagonal silicon epitaxy on a substrate such as a SiC substrate in the growth mold240, increasing its size transversely.

It is noted that the formation of Al-based nano-absorbers is similar to that of snowflakes. There are several phases of water including ice I h (hexagonal ice crystals), also known as ice-phase-one is the hexagonal crystal form of ordinary ice, or frozen water. Particularly, snow has the most stable crystal structure in a water molecule. During initial formation, water has a shape of a hexagonal plate and changes into branches, and then into various shapes of crystal including snowflakes. This formation process of snowflakes can explain the growth of hexagonal crystal according to the present invention. According to the Wegener-Bergeron-Findeise process, water droplets can coexist with ice in a oversaturated environment, at a constant temperature and pressure in an ice core while water molecules in the air attach to the surface of the ice and consequently grow together. Because water droplets are more than ice crystals, it is possible for water droplets to rapidly grow into snow crystals in large sizes ranging from several micrometers to several millimeters. As such, after Al-based nano-absorbers are generated, activated concentration of the Al-based nano-absorbers can be changed to from a new material. Conventional approaches can obtain hexagonal crystals, particularly hexagonal silicon crystals only at a very high pressure of over 16 GPa. It is rarely reported about pure hexagonal Si crystal independently grown at atmospheric pressure. The present invention has advantages that very stable hexagonal Si single crystals can be grown at atmospheric pressure by generating Al-based nano-absorbers.

FIG.9shows a generation of Al-based nano-absorbers and its roots in a growth mold240of the crystal growth part220. During the generation of Al-based nano-absorbers, SiHCl3, AICl, and GaClngases react with ammonia gas and absorb gallium, aluminum, and carbon to generate Al-based nano-absorbers. Al-based nano-absorbers then form in the shape of a needle which takes the semicrystalline form in a structurally very weak shell. This needles develop into a new shape in a short time in a saturated SiClnatmosphere and then absorb Si atoms served as absorbers. At this time, nuclei have a hexagonal structure having covalent bonds, which are a Wurtzite crystalline structure or a hexagonal 2H structure. While reactions are continued, parasitic Si including Al and N elements explosively grows. Similar to site-competition epitaxy in which doped concentrations of impurities are controlled elements in a space, Si atoms push out Al, N, and C atoms according to the very rapid depletion of aluminum and gallium and finally form Si micro-needles as Si single crystals. As the concentration of Si increases rapidly more than the concentration of Al, Si atoms outcompete Al atoms and then occupy the positions of Al atoms. When silicon crystal grows, Si atoms occupied the hexagonal structure of Al-based nano-absorbers which is the most stable structure to grow hexagonal silicon crystals. Hexagonal silicon crystals are rapidly grown to have a plate shape with a diameter of several tens of μm to several inches and a thickness of several mm. Substituted Al and N atoms are pushed to the surface and discharged by high temperature.

FIG.8shows a picture illustrating growth of hexagonal silicon crystals in the source allocating part210according to the present invention, in which an area of Al-based nano-absorbers and an area of hexagonal silicon crystals are divided.

FIG.10shows nuclei of Si crystals in which Al-based nano-absorbers in the shape of nano-clusters absorb Si atoms. As shown, Si nuclei are formed among the nano-clusters which are clumped together like downy hairs.

Table 1 shows generation conditions for hexagonal silicon crystal and Al-based nano-absorbers and experimental data according to an embodiment of the present invention.

TABLE 1ConditionsExperimentsTemperature of reaction1200-1350°C.1200°C.tubeHydrogen chloride gas200-1000sccm500sccmGrowth time1-5h10-80minAmount of silicon10 g-100 g15 g-30 gAmount of gallium10-100 g or less20gAmount of aluminum10-100 g or less25 g or lessAmmonia gas200-1000sccm500sccmNitrogen gas1000-5000sccm5000sccmDoping materialMg, Te, Ge, B, P, Sb—Efficiency forming Al-150% (Al/Si ratio)100% in growthbased nano-absorberstime of 10 min80% (Al/Si ratio)60% in growthtime of 10 min

Growth conditions of hexagonal Si crystals of Table 1 and results will now be described. Hydrogen chloride, ammonia, and nitrogen gases were uniformly provided at 500 sccm, 500 sccm, and 5000 sccm, respectively. Growth temperature and growth time were set to 1200° C. and 10-80 min, respectively. When Al/Si ratio were 150% and 80%, efficiencies forming Al-based nano-absorbers were 100% and 60% at maximum, respectively, in growth time of 10 min. A mass ratio of silicon: aluminum:gallium is 0.80-1.5:1.25:1. That is, a ratio of aluminum to silicon ranges from 80%-150%.

FIG.11is a picture showing nuclei of Si crystal in which Al-based nano-absorbers in the shape of nano-wires absorb Si atoms. As shown, Al-based nano-absorbers grow to have a micro-size and absorb silicon atoms.

FIG.12shows a picture and spectrum results of Energy Dispersive X-ray Spectroscopy (EDS) inside Al-based nano-absorbers in the shape of nano-wires. It is noted that the elements of C, O, Si, S, etc. exist around Al. In this regard, this material is named Al-based nano-absorbers by the inventors of the present invention.

FIG.13shows results of X-Ray Diffraction (XRD) of Al-based nano-absorbers in the shape of nano-wires. It is noted that peaks relating to the EDS results ofFIG.12are found among various peaks. That is, the origination of 6 peaks is explained referring to the EDS results.

The peaks [44-46] relate to S, the peaks [47-50] relate to Si and Al, the peaks [51-54] relate to C, the peaks [55] relate to SiC, and the peaks [56] relate to AlN.

REFERENCES

[44] Awwad A M, Salem N M, Abdeen A O 2015 Novel Approach For Synthesis Sulfur (S—NPs) Nanoparticles UsingAlbizia julibrissinFruits Extract. Adv. Mater. Lett. 6, 432-435.[45] Deshpande A S, Khomane R B, Vaidya B K, Joshi R M, Harle A S and Kulkarni B D 2008 Sulfur Nanoparticles Synthesis and Characterization from H2S Gas, Using Novel Biodegradable Iron Chelates in W/O Microemulsion. Nanoscale Res Lett. 3, 221-229.[46] Radhika G, Subadevi R, Krishnaveni K, Liu W R and Sivakumar M 2018 Synthesis and Electrochemical Performance of PEG-MnO2-Sulfur Composites Cathode Materials for Lithium-Sulfur Batteries. J. Nanosci. Nanotechnol. 18, 127-131.[47] Wen J Z, Ringuette S, Bohlouli-Zanjani G, Hu A, Nguyen N H, Persic J, Petre C F and Zhou Y N 2013 Characterization of thermochemical properties of Al nanoparticle and NiO nanowire composites. Nanoscale Res Lett. 8, 184-193.[48] Cava S, Tebcherani S M, Souza I A, Pianaro S A, Paskocimas C A, Longo E and Varela J A 2007 Structural characterization of phase transition of Al2O3 nanopowders obtained by polymeric precursor method. Mater. Chem. Phys. 103, 394-399.[49] Krause B et al 2018 Characterization of aluminum, aluminum oxide and titanium dioxide nanomaterials using a combination of methods for particle surface and size analysis. RSC Adv. 8 14377-14388.[50] Du X, Gao T, Qian Z, Wu Y and Liu X 2018 The in-situ synthesis and strengthening mechanism of the multi-scale SiC particles in Al—Si—C alloys. J. Alloys Compd. 750, 935-944.[51] Zhang H, Quan L and Xu L 2017 Effects of Amino-Functionalized Carbon Nanotubes on the Crystal Structure and Thermal Properties of Polyacrylonitrile Homopolymer Microspheres. Polymers 9, 332-344.[52] Wu T M, Lin Y W and Liao C S 2005 Preparation and characterization of polyaniline/multi-walled carbon nanotube composites. Carbon 43, 734-740.[53] Muller C, Golberg D, Leonhardt A, Hampel S and Buchner B 2006 Growth studies, TEM and XRD investigations of iron-filled carbon nanotubes. phys. stat. sol. (a) 203, 1064-1068.[54] Gascho J L S, Costa S F, Recco A C and Pezzin S H 2019 Graphene Oxide Films Obtained by Vacuum Filtration: X-Ray Diffraction Evidence of Crystalline Reorganization. J. Nanomater 2019, 1-12[55] Brauer G, Anwand W, Eichhorn F, Skorupa W, Hofer C, Teichert C, Kuriplach J, Cizek J, Prochazka I, Coleman P G, Nozawa T and Kohyama A 2006 Characterization of a SiC/SiC composite by X-ray diffraction, atomic force microscopy and positron spectroscopies. Appl. Surf. Sci. 252, 3342-3351.[56] Al Tahtamouni T M, Li J, Lin J Y and Jiang H X 2012 Surfactant effects of gallium on quality of AlN epilayers grown via metal-organic chemical-vapour deposition on SiC substrates. J. Phys. D: Appl. Phys. 45, 285103 1-4.

Al has a face centered cubic lattice (FCC) structure with a density of 2.7 g/cm3, and without corresponding atoms, about 26% of the space is empty. Resultantly, this empty space can be occupied by carbon atoms or similar atomic species. When Al is combined with N, a hexagonal structure of a Wurtzite crystalline structure is obtained. Si atoms substitute for Al, N, and C atoms following the rapid depletion of gallium and aluminum, in order to form hexagonal silicon crystals.

FIG.14andFIG.15show SEM photos illustrating Al-based nano-absorbers in the shape of snowflakes in the crystal growth part220. As shown inFIG.7, Al-based nano-absorbers evolve in the shape of snowflakes in a growth time of 30 min or more. After 60 minutes of growth time, some of the snowflakes of Al-based nano-absorbers inFIG.14evolve to the snowflake shape ofFIG.15.

FIG.16shows EDS data of Al-based nano-absorbers ofFIG.13. It is noted that Al-based nano-absorbers change to silicon crystals by the absorption of Si atoms.

FIG.17shows SEM photos showing grown Si nuclei on a 4H—SiC substrate in the growth mold240after generating Al-based nano-absorbers.

FIG.18shows EDS data of Al-based nano-absorbers at a point indicated in a red box ofFIG.17. It is noted that the Al-based nano-absorbers contain 81% or more of Al, and remainders of C, N, O, Ga, Si, and so forth.

FIGS.19A-19Cshow a sample while Si atoms are absorbed by Al-based nano-absorbers in the crystal growth part220, andFIG.19Dshows its Raman data.FIG.19Ais an optical picture of an entire sample, in which a yellow portion of a needle shape at a growth time of 30 min can be confirmed. This yellow portion confirms that Al-based nano-absorbers undergo changes by absorbing Si atoms. That is, two silicon crystal portions are formed on both sides around the yellow portion.FIG.19Bis a FE-SEM picture andFIG.19Cis an optical picture by Raman measuring apparatus with measured positions indicated.

FIG.19Dshows data in which modes relating to AlN at 612 cm−1(A1g), 654 cm−1(E2g), and 666 cm−1(E1g) on the yellow portion. A single peak at 519 cm−1relating to silicon is also observed, although its intensity is low. At the border of the yellow portion, the intensities of a silicon peak at 519 cm−1and AlN peak at 654 cm−1are reversed. This means that Si atoms absorbed by Al-based nano-absorbers are undergoing growth of silicon crystals.

FIG.20shows Raman data of hexagonal Si crystals in the crystal growth part220at early growth. In the case of hexagonal Si single crystals, a peak of an A1gmode is observed at 518 cm−1-519 cm−1. A peak of an E1gmode of single crystal hexagonal Si is observed at 514 cm−1-508 cm−1. In the case of cubic Si crystals, a single Raman peak at 521 cm−1is observed.

The Raman data ofFIG.20were measured to four points of the early growth in a surface of hexagonal silicon crystals. As shown in graphs, the strongest Raman peak was observed at 518 cm−1-519 cm−1, and other peaks are observed at 514 cm−1-508 cm−1and 500 cm−1-495 cm−1. Accordingly, a peak at 500 cm−1-495 cm−1ofFIG.20is a typical E2gpeak, and this confirms that the crystal grown according to the present invention is hexagonal silicon crystals.

FIG.21shows Raman data of hexagonal Si crystals measured at the point of the top flat portion inFIG.20. The Raman data were measured at five points of the top flat portions which were separated from the hexagonal stem. Raman peaks at all five points were observed at 518 cm-1, 508 cm−1-514 cm−1, and 493 cm−1-502 cm−1. This means that a wide Raman peak combines the A1gmode with the E1gmode. In the case of the E2gmode, it were observed at all points and moved by about 9 cm−1. The data confirms that the 518 cm−1peak represents the A1gmode, the 508 cm−1-514 cm−1peak represents the E1gmode, and 4 the 93 cm−1-502 cm−1peak represents the E2gmode. As such, the Raman data confirm that hexagonal silicon crystal grown belongs to the Oh7 (Fd3m) space group, according to the present invention.

FIG.22shows pictures of hexagonal Si crystal grown on a 4H—SiC substrate in the growth mold240of the crystal growth part220, using Al-based nano-absorbers.

FIG.23illustrates Raman data of a sample in the left bottom ofFIG.22, in which the A1gmode and the E1gmode are observed at peaks of 519 cm−1and 512 cm−1, respectively. From the Raman data, hexagonal silicon crystal grown is clearly distinguished from the substrate of 4H—SiC.

FIG.24shows a picture of hexagonal Si epitaxy on a 4H—SiC substrate, which was further grown in a large area from hexagonal silicon crystals ofFIG.23. The epitaxy of 8 mm×8 mm was grown on a 4H—SiC substrate of 10 mm×10 mm. Since the lattice mismatch between Si crystals and 4H—SiC is about 20%, it is generally difficult to grow a silicon epitaxy on a 4H—SiC substrate without any buffer layer. However, it is possible to grow a crystalline silicon epitaxy on a 4H—SiC substrate without any buffer layer, under atmospheric pressure using Al-based nano-absorbers according to the present invention.

FIG.25shows XRD data measured on hexagonal Si epitaxy ofFIG.24. XRD peaks relating to hexagonal Si crystals are observed at 2θ=28.38°, 47.30°, and 94.81°, while XRD peaks relating to 4H—SiC are observed at 2θ=33.09°, 35.93°, and 37.81°. Furthermore, a peak of 2θ=28.38° represents the (002) plane and a peak of 2θ=94.98° represents the (006) plane, according to ICSD ID 30396 (Physical Review, serie 3. B-condensed Matter (18, 1978-) 1992.46, 10086-10097). This confirms that hexagonal Si crystal grown is a crystal which belongs to the P63mc space group (lattice constant a=3.8 Å, c=6.26 Å).

FIG.26shows a graph relating to growth time and formation of Al-based nano-absorbers. When a ratio of Al/Si is relatively high (that is, 150%), Al-based nano-absorbers are rapidly generated at early growth. When a ratio of Al/Si is relatively low (that is, 80%), it takes about 10 min for Al to be completely exposed to HCl.

FIG.27shows a sample in which Al-based nano-absorbers and hexagonal silicon crystals are mixed in a crystal growth part220. The sample shows that hexagonal silicon crystals are mixed with Al-based nano-absorbers at a growth time of 80 min.

Table 2 shows generation conditions and experimental data for hexagonal SiC crystals according to another embodiment of the present invention.

TABLE 2ConditionExperimentsTemperature of reaction1200-1350°C.1200°C.tubehydrogen chloride gas200-1000sccm500sccmGrowth time1-5h10-80minAmount of silicon10-100g20gAmount of carbon10-100g20gAmount of gallium10-100 g or less20gAmount of aluminum10-100 g or less25 g or lessAmmonia gas200-1000sccm500sccmNitrogen gas1000-5000sccm5000sccmDoping materialMg, Te, Ge, B, P, Sb—Efficiency forming Al-150% (Al/Si ratio)100% in growthbased nano-absorberstime of 10 min80% (Al/Si ratio)60% in growthtime of 10 min

Silicon and carbon are mixed and placed in the source allocating part210of the second allocating area212. It is preferred that silicon is placed under carbon.

Hydrogen chloride, ammonia, and nitrogen gases were uniformly provided at 500 sccm, 500 sccm, and 5000 sccm, respectively, in order to grow hexagonal SiC crystals. Growth temperature and growth time were set to 1200° C. and 10-80 min, respectively. When Al/Si ratio were 150% and 80%, efficiencies forming Al-based nano-absorbers were 100% and 60% at maximum, respectively, in growth time of 10 min. A mass ratio of silicon: carbon: aluminum:gallium is 0.80-1.5:0.80-1.5:1.25:1. That is, a ratio of aluminum to silicon ranges from 80%-150%, while a ratio of aluminum to carbon ranges from 100%-150%.

FIG.28shows EDS data of hexagonal SiC crystals at a point indicated in a red box. It is noted that the hexagonal SiC crystal contain 80% or more of C, 26% of Si, and remainders of N, O, Al, and so forth.

Table 3 shows generation conditions and experimental data for hexagonal Ge crystals according to still another embodiment of the present invention.

TABLE 3ConditionExperimentsTemperature of reaction900-1350°C.1200°C.tubeHydrogen chloride gas200-1000sccm500sccmGrowth time1-5h10-80minAmount of Ge10-250g20gAmount of gallium10-100 g or less20gAmount of aluminum10-100 g or less25 g or lessAmmonia gas200-1000sccm500sccmNitrogen gas1000-5000sccm5000sccmDoping materialMg, Te, Ge, B, P, Sb—Efficiency forming Al-150% (Al/Si ratio)100% in growthbased nano-absorberstime of 10 min80% (Al/Si ratio)60% in growthtime of 10 min

Hydrogen chloride, ammonia, and nitrogen gases were uniformly provided at 500 sccm, 500 sccm, and 5000 sccm, respectively, in order to grow hexagonal Ge crystals. Growth temperature and growth time were set to 1200° C. and 10-80 min, respectively. When Al/Si ratio were 150% and 80%, efficiencies forming Al-based nano-absorbers were 100% and 60% at maximum, respectively, in growth time of 10 min. A mass ratio of Ge:Si:aluminum:gallium is 1.25-2.5:0.1-0.6:1.25: 1. That is, a ratio of Si/Ge ranges from 5%-50%.

FIG.29shows EDS data of hexagonal Ge crystals at a red point. It is noted that the hexagonal Ge crystal contain 22% or more of Ge. From the data, Al is observed at 40% which originated from Al-based nano-absorber. This means that the sample is in a state before complete hexagonal Ge crystallization.

Table 4 shows generation conditions and experimental data for hexagonal carbon crystals according to still another embodiment of the present invention.

TABLE 4ConditionExperimentsTemperature of reaction1200-1350°C.1200°C.tubehydrogen chloride gas200-1000sccm500sccmGrowth time1-5h10-80minAmount of carbon10-500g100gAmount of gallium10-100 g or less20gAmount of aluminum10-100 g or less25 g or lessAmmonia gas200-1000sccm500sccmNitrogen gas1000-5000sccm5000sccmDoping materialMg, Te, Ge, B, P, Sb—Efficiency forming Al-150% (Al/Si ratio)100% in growthbased nano-absorberstime of 10 min80% (Al/Si ratio)60% in growthtime of 10 min

Hydrogen chloride, ammonia, and nitrogen gases were uniformly provided at 500 sccm, 500 sccm, and 5000 sccm, respectively, in order to grow hexagonal carbon crystals. Growth temperature and growth time were set to 1200° C. and 10-80 min, respectively. When Al/Si ratio were 150% and 80%, efficiencies forming Al-based nano-absorbers were 100% and 60% at maximum, respectively, in growth time of 10 min. A mass ratio of C: aluminum: gallium is 1.25-1.5:1.25:1. That is, a ratio of aluminum/C ranges from 100%-150%.

Table 5 shows generation conditions and experimental data for hexagonal Si1-xGexcrystals according to another embodiment of the present invention.

TABLE 5ConditionExperimentsTemperature of reaction1200-1350°C.1200°C.tubeHydrogen chloride gas200-1000sccm500sccmGrowth time1-5h10-80minAmount of silicon10-100g20gAmount of Ge10-250g20gAmount of gallium10-100 g or less20gAmount of aluminum10-100 g or less25 g or lessAmmonia gas200-1000sccm500sccmNitrogen gas1000-5000sccm5000sccmDoping materialMg, Te, Ge, B, P, Sb—Efficiency forming Al-150% (Al/Si ratio)100% in growthbased nano-absorberstime of 10 min80% (Al/Si ratio)60% in growthtime of 10 min

Hydrogen chloride, ammonia, and nitrogen gases were uniformly provided at 500 sccm, 500 sccm, and 5000 sccm, respectively, in order to grow hexagonal Si1-xGexcrystals. Growth temperature and growth time were set to 1200° C. and 10-80 min, respectively. When Al/Si ratio were 150% and 80%, efficiencies for forming Al-based nano-absorbers were 100% and 60% at maximum, respectively, in growth time of 10 min. A mass ratio of Ge: aluminum: Si is 0.5-1.25:1.25: 0.5-1.25.

FIG.30shows an optical photo of a bar with a length of 1.2 mm and a width of 10-20 μm and Raman data for hexagonal Si1-xGexcrystals (0.35<x<1). It is noted from Raman data that a vibration relating to Ge—Ge is observed at 285 cm−1, a vibration relating to Ge—Si is observed at 482 cm−1, and a vibration relating to Si—Si is observed at 482 cm−1, whose intensities are Ge—Ge>Ge—Si>Si—Si in order. Vibration relating to hexagonal Si1-xGexcrystals (x<0.35) is observed at 516 cm−1for Si—Si, while vibration for Ge—Ge or Ge—Si is hardly observed. When x is at 0.35<x<1, vibration for Si—Si is observed at 480-485 cm−1, vibration for Ge—Ge is observed strongly at −285 cm−1, and vibration for Ge—Si is observed weakly around 482 cm−1. This result indicates that Ge affects low frequency components and Si affects high frequency components. Therefore, the Si—Ge vibration mode, which is an intermediate mode, shows a very strong peak for the composition of 0.4×0.6.

Table 6 shows generation conditions and experimental data for hexagonal Ga2O3crystals according to another embodiment of the present invention.

TABLE 6ConditionExperimentsTemperature of reaction650-1200°C.900°C.tubeHydrogen chloride gas200-1000sccm500sccmGrowth time1-5h10-80minOxygen gas10-500sccm50sccmAmount of gallium10-100 g or less20gAmount of aluminum10-100 g or less25 g or lessAmmonia gas200-1000sccm500sccmnitrogen gas1000-5000sccm5000sccmDoping materialMg, Te, Ge, B, P, Sb—Efficiency forming Al-150% (Al/Si ratio)100% in growthbased nano-absorberstime of 10 min80% (Al/Si ratio)60% in growthtime of 10 min

Oxygen of hexagonal Ga2O3crystals is supplied by nitrogen gas containing mist through bubbling distilled water with nitrogen. Hydrogen chloride, ammonia, and nitrogen gases were uniformly provided at 500 sccm, 500 sccm, and 5000 sccm, respectively, in order to grow hexagonal Ga2O3crystals. Growth temperature and growth time were set to 900° C. and 10-80 min, respectively. When Al/Si ratio were 150% and 80%, efficiencies forming Al-based nano-absorbers were 100% and 60% at maximum, respectively, in growth time of 10 min. A mass ratio of oxygen: aluminum:gallium is 0.5-1.25:1.25:0.5-1.25. That is, a ratio of aluminum/Ga ranges from 5%-100%.

FIG.31shows a SEM photo and EDS data of hexagonal Ga2O3crystals at a point indicated. It is noted that the hexagonal Ga2O3crystal contain 40% or more of Ga, 57% or more of 0, and remainders of N, O, Al, and so forth. From the data, Al is observed at 1.5%, which means that hexagonal Ga2O3crystals are formed from the Al-based nano-absorber.

While this invention has been described in connection with what is presently considered to be practical embodiments, it is to be understood that the invention is not limited to the disclosed embodiments. On the contrary, it is intended to cover various modifications and equivalent arrangements included within the spirit and scope of the appended claims.