Method for producing transparent single crystal, transparent single crystal, and production apparatus by solvent moving floating zone melting method.

Abstract

To provide a method for producing a transparent single crystal by a solvent migration floating zone melting method, the method capable of growing a transparent single crystal with cracks reduced, which has been difficult with the conventional IR-FZ method, and also to provide a transparent single crystal and production equipment.SOLUTION: Provided is a method for producing a transparent single crystal by an infrared concentrated heating floating zone melting method, the method including a growth step that forms a molten zone 4 between a raw material rod 1 and a seed crystal 2 by concentrated heating by an infrared irradiation device 3, to thereby make a transparent single crystal gown on the seed crystal. The infrared irradiation device 3 is a device for irradiating the molten zone 4 with infrared rays from a light source 5. The method is characterized in that the direction of the infrared radiation connecting the light source and a focal point 8b on the molten zone is from vertically downward to upward with respect to a line 7 passing through a horizontal plane orthogonal to the vertical direction.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present invention relates to a method for manufacturing a transparent single crystal by a solvent movement floating zone melting method, a transparent single crystal, and a manufacturing apparatus.

Background Art

[0002] Most of the single crystal materials with a large market scale such as silicon and sapphire are mass-produced by the Czochralski method (Cz method) or the Bridgman-Stockbarger method (BS method) in which all of the raw materials are once melted and crystallized from a part thereof. The characteristics of these methods are that although a crucible for holding a large amount of raw material melt is essential, a large-diameter single crystal can be mass-produced by increasing the size of the crucible.

[0003] Due to the normal solidification process in which all of the raw materials are once melted and crystallized from a part thereof, segregation control is difficult. Therefore, it is often difficult or costly to grow crystals with uniformly added different elements or crystals that decompose and melt. Specifically, the growth of a p-type silicon crystal added with boron having a segregation coefficient close to 1 of 0.8 can be grown at low cost, but in the growth of n-type silicon added with phosphorus having a segregation coefficient of at most about 0.3 to 0.4, if all of the melt is crystallized, the phosphorus composition in the grown crystal is greatly different between the initial part and the end part. Therefore, since it is necessary to end the crystal growth while leaving the melt so that the phosphorus composition is within the allowable range, it is more costly than p-type silicon. In lithium niobate and lithium tantalate, it is known that a crystal having a stoichiometric composition of a composition ratio of 1:1 of lithium and niobium or tantalum has excellent characteristics as a surface acoustic wave element, but when a crystal is grown from a stoichiometric melt by the CZ method or the like, the composition ratio in the grown crystal changes. Therefore, crystals having a congruent melting composition in which niobium or tantalum is excessive are mass-produced.

[0004] In addition, due to the necessity of the crucible, the crucible cost and the reaction between the melt and the turbomaterial may become problems. In the case of silicon, since the silicon melt reacts with the quartz crucible, the crucible is disposable. For the growth of oxide crystals such as lithium niobate and lithium tantalate, it is necessary to use precious metals such as platinum and iridium as the crucible. Not only is the ingot itself expensive, but it also deforms during use, resulting in the cost of periodic remelting. That is, the crystal materials currently in mass production are limited to those that have a suitable crucible material for holding the melt and do not have segregation problems. It is difficult to industrially utilize single crystals of substances with high melt reactivity for which no suitable crucible has been found.

[0005] The infrared concentric heating floating zone melting method (IR-FZ method) according to the present invention is a growth method that is one of the floating zone melting methods and does not require a crucible (see Patent Document 1). Therefore, crystal growth is possible even if the melt reactivity is high. By making the composition of the molten zone formed between the raw material rod and the seed crystal different from that of the raw material rod as needed, it is possible in principle to grow a long crystal with a uniform composition. However, since it has been difficult to grow large-diameter crystals, there has been little industrial use so far, and only compound single crystals required for physical property research have been grown by this method.

[0006] Attempts have been made to improve the grown crystals even with this IR-FZ method. For example, by using the function of moving the rotating ellipsoidal mirror disclosed in Patent Document 2 in the major axis direction and moving the condensing position of the rotating ellipsoidal mirror according to the raw material diameter, the grown crystal has been made larger in diameter. Also, as in Patent Document 3, the main rotating ellipsoidal mirror is inclined upward and the sub-rotating ellipsoidal mirror is inclined downward, and by using the function of concentratingly heating the molten zone from obliquely above and obliquely below, the convex solid-liquid interface between the molten zone and the grown crystal is made closer to flat and the molten zone is stabilized, and for crystals of substances whose solid-liquid interface is convex, the diameter of the grown crystal can be enlarged. However, these conventional IR-FZ methods do not consider growing transparent single crystals such as optical crystals.

Prior Art Documents

Patent Documents

[0007]

Patent Document 1

Patent Document 2

Patent Document 3

Summary of the Invention

Problems to be Solved by the Invention

[0008] When a single crystal of a substance that becomes transparent like an optical crystal is grown by the conventional IR-FZ method, the solid-liquid interface between the melt zone and the grown crystal becomes concave, resulting in a large number of cracks in the grown crystal, and it has been difficult to reduce those cracks. The present invention has been made in view of such circumstances, and provides a method for producing a transparent single crystal by a solvent transfer floating zone melting method, a transparent single crystal, and a production apparatus, which can grow a transparent single crystal in a state where cracks, which were difficult with the conventional IR-FZ method, are reduced.

Means for Solving the Problems

[0009] According to the present invention, there is provided a method for producing a transparent single crystal by an infrared ray focused heating floating zone melting method, including a growth step of forming a melt zone between a raw material rod and a seed crystal by focused heating with an infrared ray irradiating device and growing the transparent single crystal on the seed crystal, wherein the infrared ray irradiating device is a device that irradiates infrared rays from a light source to the melt zone, and the irradiation direction of the infrared rays connecting the light source and the focus point of the melt zone is a direction from vertically downward to vertically upward with respect to a horizontal plane orthogonal to the vertical direction.

[0010] As a result of intensive studies, the inventors of the present invention have found that by setting the irradiation direction of the infrared rays connecting the light source and the condensing point of the molten zone to be a direction from vertically downward to upward with respect to the horizontal plane orthogonal to the vertical direction, it is possible to suppress the concave shape of the molten zone and the solid-liquid interface of the grown crystal. Therefore, even when growing a crystal of a substance that becomes transparent by the IR-FZ method, it is possible to produce a large-diameter and crack-free transparent single crystal, leading to the completion of the present invention.

[0011] According to another aspect of the present invention, there is provided a manufacturing apparatus for manufacturing a transparent single crystal by the infrared ray concentrated heating floating zone melting method, the apparatus comprising: an infrared ray irradiation apparatus that forms a molten zone between a raw material rod and a seed crystal by concentrated heating with infrared rays and grows the transparent single crystal on the seed crystal, the infrared ray irradiation apparatus including a light source, wherein the irradiation direction of the infrared rays connecting the light source and the condensing point of the molten zone is a direction from vertically downward to upward with respect to the horizontal plane orthogonal to the vertical direction.

[0012] Hereinafter, various embodiments of the present invention will be exemplified. The embodiments shown below can be combined with each other. It is possible. Preferably, the transparent single crystal may be an optical crystal. Preferably, in the growth process of the transparent single crystal, the concavity of the interface shape between the transparent single crystal growing on the seed crystal and the molten zone is smaller than when the irradiation direction is in the horizontal plane direction or from vertically upward to downward with respect to the horizontal plane. Preferably, in the growth process, the interface shape between the transparent single crystal growing on the seed crystal and the molten zone is substantially flat. Preferably, the infrared ray irradiation apparatus is characterized in that the irradiation direction can be changed. Preferably, the angle formed by the irradiation direction and the horizontal plane is 10 degrees or more. Preferably, the transparent single crystal is Pr:Lu3Al5O 12 It is characterized by being.

Brief Description of the Drawings

[0013]

Figure 1

Figure 2

Figure 3

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Figure 5

Figure 6

Mode for Carrying Out the Invention

[0014] Hereinafter, embodiments of the present invention will be exemplified and the present invention will be described in detail. The present invention is not limited in any way by these descriptions. The various characteristic matters of the embodiments of the present invention shown below can be combined with each other. Also, an invention can be established independently for each characteristic matter.

[0015] The present invention relates to a method for manufacturing a transparent single crystal and a manufacturing apparatus by a solvent moving floating zone melting method. The IR-FZ method is a kind of FZ method. A solvent having a composition different from that of the raw material rod is installed between the raw material rod and the seed crystal, the solvent is heated and melted, and a part of the raw material rod is dissolved in the solvent to form a melting zone. While supporting the melting zone by surface tension, it is relatively moved with respect to the raw material rod and the seed crystal, and a target transparent single crystal is grown as a grown crystal on the seed crystal. Hereinafter, the method for manufacturing a transparent single crystal by the solvent moving floating zone melting method according to the present invention will be described in detail.

[0016] Figure 1 is a schematic diagram of a transparent single crystal manufacturing apparatus for implementing a crystal growth process by the IR-FZ method according to an embodiment of the present invention. In the transparent single crystal manufacturing apparatus by the IR-FZ method according to an embodiment of the present invention, the raw material rod 1 is supported at its upper part by a mechanism (not shown) and installed. Also, on the extension line of the rotation axis 6 (vertical direction) of the raw material rod 1, a seed crystal 2 serving as a base for growing a single crystal is installed. Before the start of the crystal growth process, a solvent is adhered to the seed crystal side at the end of the raw material rod. After installing the raw material rod 1 and the seed crystal 2, the solvent is heated by an infrared irradiation device 3 which is a heating means, so that the solvent is dissolved, and further a part of the raw material rod in contact with the solvent is dissolved, and a molten zone 4 is formed. A grown crystal 2a (single crystal) is deposited on the seed crystal 2 from the formed molten zone 4. During heating, in order to stabilize the growth of the crystal, the raw material rod 1 and the seed crystal 2 can be rotated relatively in opposite directions to uniformly heat the molten zone 4. As an example, the rotation speed of the raw material rod 1 can be set to 2 to 30 rpm, and the rotation speed of the seed crystal 2 can be set to 20 to 40 rpm.

[0017] The infrared irradiation device 3 may include a light source 5 and a condenser 9. As the light source 5, a halogen lamp or the like can be used. As the condenser 9, a rotating ellipsoidal mirror (hereinafter also simply referred to as a mirror) or the like can be used. Such a heating means can collect infrared rays from the light source at the condensing point of the solvent by the condenser 9 to dissolve the solvent. It is preferable to arrange one of the two foci 8a of the ellipsoidal mirror used for the rotating ellipsoidal mirror to coincide with the light emission center of the halogen lamp, and the other focus 8b to coincide with the condensing point of the molten zone 4, that is, the rotation axis of the molten zone 4. Note that an infrared laser may be used instead of the halogen lamp and the condenser.

[0018] Also, in the manufacturing apparatus according to an embodiment of the present invention, the infrared irradiation device 3 can be inclined downward in the vertical direction with respect to the horizontal plane orthogonal to the vertical direction by a mechanism (not shown). The inclination angle can be changed. In FIG. 1, a straight line connecting the filament of the halogen lamp and the focal point of the mirror (the condensing point of infrared rays in the melting zone 4) is inclined downward at an angle α° with respect to a straight line 7 passing through the horizontal plane orthogonal to the vertical direction. That is, the irradiation direction of the infrared rays connecting the light source and the condensing point of the condenser is inclined at an angle α° with respect to the horizontal plane. The angle α° can be, for example, 2°, 4°, 6°, 8°, 10°, 12°, 14°, 16°, 18°, 20°, 22°, 24°, 26°, 28°, 30°, and can be within the range between any two of the values exemplified here. The same inclination can be made when using an infrared laser instead of the halogen lamp and the condenser.

[0019] FIG. 2 is a schematic diagram of a crystal growth process by the conventional IR-FZ method. Parts common to FIG. 1 are given the same reference numerals. In FIG. 2, the irradiation direction of the infrared rays of the infrared irradiation device 3 is a direction along the horizontal plane. That is, since there is no inclination, the angle α° is 0°.

[0020] Note that a transparent single crystal is a single crystal through which light in the visible, ultraviolet, or infrared region passes, and includes optical crystals. An optical crystal is a crystal having various material properties with respect to strong light or coherent light, also called an optoelectronic crystal, and having a wide transmission wavelength range from ultraviolet to infrared. For example, scintillator crystals used in medical device imaging diagnostic apparatuses and radiation measuring instruments, non-linear crystals mainly used for converting the wavelength of laser light to short wavelengths such as 1 / 2, 1 / 3, 1 / 4, etc., laser crystals used for generating laser oscillation in solid-state lasers, magneto-optical crystals used in optical isolators and Faraday rotators, birefringent crystals, etc. are known.

[0021] The scintillator crystal is, for example, Lu3Al5O 12 (abbreviation: LuAG), Gd3(Al,Ga)5O 12(Abbreviation: GAGG), NaI, Ce:LaCl3, Bi4Ge3O 12 (Abbreviation: BGO), CsI, etc. are known. Nonlinear crystals include, for example, KH2PO4 (abbreviation: KDP), KD2PO4 (abbreviation: KD*P), LiNbO3, LiTaO3, LiB3O5 (abbreviation: LBO), β-BaB2O4 (abbreviation: BBO), BiB3O6 (abbreviation: BIBO), MgO:LiNbO3, CsLiB6O 10 (Abbreviation: CLBO), KTiOPO4 (abbreviation: KTP), Gray Track Resistance KTiOPO4 (abbreviation: GTR-KTP), RbTiOPO4 (abbreviation: RTP), KTiOAsO4 (abbreviation: KTA), LiNbO3, LiTaO3, etc. are known. Laser crystals include, for example, Nd:Y3Al5O 12 (Abbreviation: Nd:YAG), Nd:Ce:Y3Al5O 12 (Abbreviation: Nd:Ce:YAG), Nd:LiYF4 (abbreviation: Nd:YLF), Nd:YVO4, Nd:KGd(WO4)2 (abbreviation: Nd:KGW), Nd:GdVO4, Yb:KGd(WO4)2 (abbreviation: Yb:KGW), Ti:Al2O3 (abbreviation: Ti:sapphire), Cr:LiStAlF6 (abbreviation: Cr:LiSAF), Cr:Y3Al5O 12 (Abbreviation: Cr:YAG), Ho:Cr:Tm:Y3Al5O 12 (Abbreviation: Ho:Cr:Tm:YAG), Er:Cr:Y 2.9 Sc 1.4 Ga 3.6 O 12 (Abbreviation: Er:Cr:YSGG), Er:Y3Al5O 12 (Abbreviation: Er:YAG), etc. are known. Magneto-optical crystals include, for example, Tb3Ga5O 12 (Abbreviation: TGG), Tb3Sc2Al3O 12 (Abbreviation: TSAG), etc. are known. Birefringent crystals include, for example, α-BaB2O4 (abbreviation: α-BBO), YVO4, etc. are known

[0022] Note that the term "transparent single crystal and light transmission" includes cases where the transmittance is 100% or less. The transmittance may be such that the above-described single crystal or optical crystal satisfies its function. Further, it suffices that infrared rays can penetrate to the central portion of the melting zone 4 and the temperature of the central portion can rise to the temperature at which the raw material rod melts.

[0023] In one embodiment of the present invention, the principle of manufacturing a large-diameter and crack-free transparent single crystal will be described.

[0024] In crystal growth, it is necessary to form the melting zone 4 in a state where the raw material rod 1 and the growing crystal 2a are separated from each other so as not to contact each other at the central portion of the melting zone 4. The heat required therefor is supplied to the melting zone 4 directly from the infrared rays (radiation light) emitted from the light source 5 and via a condenser 9 such as an ellipsoidal mirror. That is, the melting zone 4, the raw material rod 1, the growing crystal 2a, etc. are heated by radiation. A part of the infrared rays is reflected and scattered on the surface of the melting zone 4, but the heat absorbed on the surface is transmitted toward the vicinity of the central portion 8b by conduction. On the surface of the melting zone 4, not only conduction but also convection acts to transmit heat. Further, if the growing crystal 2a is transparent, not only is it absorbed on the surface of the melting zone 4, but also a part of the condensed radiation light reaches the central portion, so that the central portion of the melting zone 4 becomes hotter than the surface portion. The same applies when an infrared laser is used instead of the halogen lamp and the condenser as the light source.

[0025] <In the case of the conventional IR-FZ method> Figure 3 is a schematic diagram showing a cross-section along the vertical direction of the raw material rod 1, the seed crystal 2, and the melting zone 4 during the growth of a transparent single crystal by the "conventional IR-FZ method" shown in Figure 2. From above in the vertical direction, there are the raw material rod 1, the raw material rod 1a immersed in the solution (the vertical length thereof is λ), the melting zone 4, the growing crystal 2a, and the seed crystal 2. The interface position between the growing crystal 2a and the melting zone 4 on the surface of the melting zone 4 is 4a, and the interface position between the growing crystal 2a and the melting zone 4 at the center of the melting zone 4 is 4b. Let the vertical length (the distance between the lower end of 1a and 4b) on the surface of the melting zone 4 be L, the vertical length (the distance between the lower end of 1a and 4c) at the center be L', and the radius of the melting zone 4 at the interface position 4a be r. The concavity of the interface shape is defined as concavity of the interface shape = (L' - L) / r.

[0026] As shown in Figure 3, when growing a transparent single crystal by the "conventional IR-FZ method", the vertical length L' at the center of the melting zone 4 is much longer than the vertical length L on the surface of the melting zone 4. That is, the surface shape of the growing crystal 2a becomes concave, so the concavity of the interface shape increases. This is because infrared rays transmit well through the transparent raw material, so the other focal point 8b of the ellipsoidal mirror 9 (the center of the melting zone) becomes hotter. Also, one of the reasons is that the solution absorbs infrared rays more easily than the solid. That is, since the center of the melting zone 4 becomes hotter than the surface part, the crystallization accompanying the descent of the raw material rod starts from the peripheral part in the horizontal cross-section of the interface position 4a of the melting zone 4 and gradually progresses toward the center. Therefore, stress concentrates in the center of the growing crystal 2a and cracks etc. are likely to occur. This is the same even when irradiating infrared rays from both above and below as in Patent Document 3 when growing a transparent single crystal.

[0027] Fig. 5 shows a photograph of Sample 25 obtained by horizontally slicing thinly a scintillator crystal (Pr:LuAG) grown by the "conventional IR-FZ method". The diagonal black lines are the patterns of the placement location of Sample 25, which are for making it easier to see that the crystal is transparent. As described above, in the conventional IR-FZ method, since crystallization proceeds from the peripheral part to the central part of Sample 25, stress concentrates in the central part, and radial cracks 27 and core-shaped cracks 28 are generated. Also, the central part is cloudy.

[0028] Incidentally, in the growth of "non-transparent single crystals" by the conventional IR-FZ method (such as the methods described in Patent Technical Documents 2 and 3), since infrared rays do not penetrate to the inside of the molten part, melting starts from the surface, and crystallization proceeds from the central part. That is, contrary to Fig. 3, the surface shape of the grown crystal is a convex shape, and cracks as shown in Fig. 5 are less likely to occur.

[0029] <In the case of the IR-FZ method according to an embodiment of the present invention> Fig. 4 is a schematic diagram when the raw material rod 1, the seed crystal 2, and the molten zone 4 during the growth of a transparent single crystal by the "IR-FZ method according to an embodiment of the present invention" shown in Fig. 1 are taken as a cross-section along the vertical direction. From above in the vertical direction, they are the raw material rod 1, the raw material rod 1a immersed with the solution, the molten zone 4, the grown crystal 2a, and the seed crystal 2. The interface position with the grown crystal 2a on the surface of the molten zone 4 is 4a, and the interface position with the grown crystal 2a at the central part of the molten zone 4 is 4b. In Fig. 4, the vertical positions of 4a and 4b are almost the same. Let the vertical length on the surface of the molten zone 4 (the distance between the lower end of 1a and 4b) be L, and the vertical length at the central part (the distance between the lower end of 1a and 4c) be L'. In Fig. 4, the difference in the lengths of L and L' is small. That is, the concavity of the interface shape is a smaller value than when the conventional IR-FZ method is used.

[0030] As shown in Fig. 1, in the "IR-FZ method which is an embodiment of the present invention", the irradiation direction of the infrared irradiation device is from vertically downward to upward. That is, the vertical position of the other focus 8b which becomes the hottest is higher compared to the case of Fig. 3. Moreover, since the portion vertically below the surface of the melting zone 4 is irradiated with infrared rays more strongly than in Fig. 3, it is easily melted. Due to the combination of these effects, the concavity of the interface shape at the interface between the melting zone 4 and the grown crystal 2a becomes a small value. That is, crystallization does not progress from the peripheral portion as in the conventional IR-FZ method, so the occurrence of cracks and clouding are suppressed. Note that the concavity of the interface shape may be approximately 0, that is, the interface may be approximately flat. That the interface is approximately flat means that there may be some irregularities, and the difference between L and L' is almost zero.

[0031] Fig. 6 shows a photograph of a sample 26 obtained by thinly cutting out horizontally a scintillator crystal (Pr:LuAG) grown by the "IR-FZ method of an embodiment of the present invention". The diagonal black line is a pattern of the placement location of the sample 26 and is for making it easy to see that the crystal is transparent. As described above, in the IR-FZ method which is an embodiment of the present invention, although radial cracks 27 are visible, the number thereof is small and core-shaped cracks 28 do not occur. Also, clouding is not seen.

[0032] According to an embodiment of the present invention, a melting zone 4 is formed between the raw material rod 1 and the seed crystal 2 by concentrated heating by the infrared irradiation device 3, and a grown crystal 2a which is a transparent single crystal is grown thereon. In the growth process of the grown crystal 2a, by setting the infrared irradiation direction of the infrared irradiation device 3 that irradiates the melting zone 4 with infrared rays to a direction from vertically downward to upward with respect to the horizontal plane orthogonal to the vertical direction, the concavity of the interface shape at the solid-liquid interface between the grown crystal 2a and the melting zone 4 becomes a smaller value than when irradiating infrared rays in the horizontal plane direction or from vertically upward to downward with respect to the horizontal plane as in the conventional IR-FZ method shown in Fig. 3. Therefore, the present invention has a special effect that a transparent single crystal (grown crystal 2a) with a large diameter and few cracks can be manufactured. In other words, in the embodiment of the present invention shown in Fig. 4, it is possible to suppress the solid-liquid interface between the grown crystal 2a and the melting zone 4 from becoming concave.

[0033] In addition to the infrared irradiation device 3, an auxiliary infrared irradiation source (such as a light source and a mirror) that irradiates infrared rays while being inclined downward in the vertical direction with respect to the horizontal plane orthogonal to the vertical direction may be further provided. Even if an auxiliary infrared irradiation source is further provided, the object of the present invention can be achieved if the shape of the solid-liquid interface can be suppressed from becoming concave.

Example

[0034] The scintillator crystal (Pr:LuAG) grown by the "IR-FZ method of an embodiment of the present invention" shown in FIG. 6 was grown by the following method. <Preparation of raw material rod> Pr6O 11 (purity 99.99%) and Lu2O3 (purity 99.99%), α-Al2O3 (purity 99.99%) were used as starting materials. These starting materials were weighed so that the composition was (Pr 0.01 Lu 0.99 )3Al5O 12 and wet-mixed using ethanol. After drying, calcination was performed in air at 1,200 ° C for 12 hours. After calcination, dry mixing was performed, and firing was performed in air at 1,450 ° C for 12 hours. After firing, (Pr 0.01 Lu 0.99 )3Al5O 12 powder was obtained. The obtained powder was formed into a columnar shape by the rubber press method, and sintering was performed in air at 1,500 ° C for 5 hours to obtain a raw material rod. The typical size of the raw material rod was 9 to 11 mm in diameter and 50 to 70 mm in length.

[0035] <Adjustment of seed crystal> As the seed crystal, a part of the sintered rod produced as the raw material rod was used.

[0036] <Manufacture of oxide single crystal> Using the raw material rod obtained above, (Pr 0.01 Lu 0.99 )3Al5O 12Crystals were produced. For crystal production, a modified elliptical mirror type infrared focused heating furnace (FZ-T-10000-H-TY-1 manufactured by Crystal System) was used. Four halogen lamps with a rated output of 2.5 kW were installed as heating light sources. The growth atmosphere was an argon atmosphere, and argon gas was flowed at a flow rate of 0.2 L / min. The raw material supply rate and the crystal growth rate were set to 7.5 mm / h and 5.0 mm / h, respectively. The rotation speeds of the raw material and the crystal were set to 3 rpm and 40 rpm, respectively, and they were rotated in opposite directions. Crystal growth was carried out under two conditions of the mirror tilt angle α being 0° and -10°, and the changes in the interface shape between the molten zone 4 during growth and the grown crystal 2 and the changes in the grown crystal were examined.

[0037] In addition to the fact that the temperature of the molten zone during growth cannot be directly measured and is easily expected to have variations, it was maintained at 2043 °C or higher, which is the melting point.

[0038] In addition, a sample that had been rapidly cooled by stopping the infrared irradiation during growth was cut vertically, and the concavity of the interface shape was measured, and it was 0.375.

[0039] The difference between the method for manufacturing a scintillator crystal (Pr:LuAG) grown by the "conventional IR-FZ method" shown in Fig. 5 and the IR-FZ method of one embodiment of the present invention described above is only the mirror tilt angle. In one embodiment of the present invention, the mirror tilt angle was inclined 10° upward from the vertical downward direction for irradiation, while the conventional IR-FZ method irradiated at a tilt angle of 0°. Similarly, a sample that had been rapidly cooled by stopping the infrared irradiation during growth was cut, and the concavity of the interface shape was measured, and it was 1.8. It can be seen that the IR-FZ method of one embodiment of the present invention clearly has a smaller concavity of the interface shape and can suppress the interface shape from becoming concave.

Explanation of Reference Signs

[0040] 1…starting rod, 1a…molten zone infiltrated with solution, 2…seed crystal, 2a…grown crystal, 3…infrared irradiation device, 4…molten zone, 4a…interface position with the grown crystal 2a on the surface of the molten zone 4, 4b…interface position with the grown crystal 2a at the center of the molten zone 4, 5…light source, 6…rotation axis, 7…horizontal axis, 8a…focus of the elliptical mirror, 8b…focus of the elliptical mirror, 9…condenser, 25…sample grown by the conventional method, 26…sample grown in one embodiment of the present invention, 27…radial crack, 28…core crack

Claims

**Claim 1** A method for manufacturing a transparent single crystal by an infrared-ray concentrated heating floating zone melting method, including a growth step of forming a molten zone between a raw material rod and a seed crystal by concentrated heating with an infrared-ray irradiating device and growing the transparent single crystal on the seed crystal, wherein the infrared-ray irradiating device is a device for irradiating infrared rays from a light source onto the molten zone, and the irradiation direction of the infrared rays connecting the light source and the focus point of the molten zone is a direction from below upward in the vertical direction with respect to a horizontal plane orthogonal to the vertical direction. A method for manufacturing a transparent single crystal. **Claim 2** The method for manufacturing a transparent single crystal according to claim 1, wherein the irradiation direction makes an angle of 10 degrees or more with the horizontal plane. A method for manufacturing a transparent single crystal. **Claim 3** A manufacturing apparatus for manufacturing a transparent single crystal by an infrared-ray concentrated heating floating zone melting method, comprising an infrared-ray irradiating device for forming a molten zone between a raw material rod and a seed crystal by concentrated heating with infrared rays and growing the transparent single crystal on the seed crystal, wherein the infrared-ray irradiating device includes a light source, and the irradiation direction of the infrared rays connecting the light source and the focus point of the molten zone is a direction from below upward in the vertical direction with respect to a horizontal plane orthogonal to the vertical direction. **Claim 4** The manufacturing apparatus according to claim 3, wherein the irradiation direction makes an angle of 10 degrees or more with the horizontal plane. A manufacturing apparatus.

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