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Growing a group-iii nitride crystal using a flux growth and then using the group-iii nitride crystal as a seed for an ammonothermal re-growth

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Publication number
WO2013010117A1
Authority
WO
Grant status
Application
Patent type
Prior art keywords
crystal
group
nitride
ill
method
Prior art date
Application number
PCT/US2012/046756
Other languages
French (fr)
Inventor
Siddha Pimputkar
Shuji Nakamura
James S. Speck
Original Assignee
The Regents Of The University Of California
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date

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Classifications

    • CCHEMISTRY; METALLURGY
    • C30CRYSTAL GROWTH
    • C30BSINGLE-CRYSTAL-GROWTH; UNIDIRECTIONAL SOLIDIFICATION OF EUTECTIC MATERIAL OR UNIDIRECTIONAL DEMIXING OF EUTECTOID MATERIAL; REFINING BY ZONE-MELTING OF MATERIAL; PRODUCTION OF A HOMOGENEOUS POLYCRYSTALLINE MATERIAL WITH DEFINED STRUCTURE; SINGLE CRYSTALS OR HOMOGENEOUS POLYCRYSTALLINE MATERIAL WITH DEFINED STRUCTURE; AFTER-TREATMENT OF SINGLE CRYSTALS OR A HOMOGENEOUS POLYCRYSTALLINE MATERIAL WITH DEFINED STRUCTURE; APPARATUS THEREFOR
    • C30B7/00Single-crystal growth from solutions using solvents which are liquid at normal temperature, e.g. aqueous solutions
    • C30B7/10Single-crystal growth from solutions using solvents which are liquid at normal temperature, e.g. aqueous solutions by application of pressure, e.g. hydrothermal processes
    • C30B7/105Single-crystal growth from solutions using solvents which are liquid at normal temperature, e.g. aqueous solutions by application of pressure, e.g. hydrothermal processes using ammonia as solvent, i.e. ammonothermal processes
    • CCHEMISTRY; METALLURGY
    • C30CRYSTAL GROWTH
    • C30BSINGLE-CRYSTAL-GROWTH; UNIDIRECTIONAL SOLIDIFICATION OF EUTECTIC MATERIAL OR UNIDIRECTIONAL DEMIXING OF EUTECTOID MATERIAL; REFINING BY ZONE-MELTING OF MATERIAL; PRODUCTION OF A HOMOGENEOUS POLYCRYSTALLINE MATERIAL WITH DEFINED STRUCTURE; SINGLE CRYSTALS OR HOMOGENEOUS POLYCRYSTALLINE MATERIAL WITH DEFINED STRUCTURE; AFTER-TREATMENT OF SINGLE CRYSTALS OR A HOMOGENEOUS POLYCRYSTALLINE MATERIAL WITH DEFINED STRUCTURE; APPARATUS THEREFOR
    • C30B29/00Single crystals or homogeneous polycrystalline material with defined structure characterised by the material or by their shape
    • C30B29/10Inorganic compounds or compositions
    • C30B29/40AIIIBV compounds wherein A is B, Al, Ga, In or Tl and B is N, P, As, Sb or Bi
    • C30B29/403AIII-nitrides
    • CCHEMISTRY; METALLURGY
    • C30CRYSTAL GROWTH
    • C30BSINGLE-CRYSTAL-GROWTH; UNIDIRECTIONAL SOLIDIFICATION OF EUTECTIC MATERIAL OR UNIDIRECTIONAL DEMIXING OF EUTECTOID MATERIAL; REFINING BY ZONE-MELTING OF MATERIAL; PRODUCTION OF A HOMOGENEOUS POLYCRYSTALLINE MATERIAL WITH DEFINED STRUCTURE; SINGLE CRYSTALS OR HOMOGENEOUS POLYCRYSTALLINE MATERIAL WITH DEFINED STRUCTURE; AFTER-TREATMENT OF SINGLE CRYSTALS OR A HOMOGENEOUS POLYCRYSTALLINE MATERIAL WITH DEFINED STRUCTURE; APPARATUS THEREFOR
    • C30B9/00Single-crystal growth from melt solutions using molten solvents
    • C30B9/04Single-crystal growth from melt solutions using molten solvents by cooling of the solution
    • C30B9/08Single-crystal growth from melt solutions using molten solvents by cooling of the solution using other solvents
    • C30B9/12Salt solvents, e.g. flux growth

Abstract

A method of growing a Group-Ill nitride crystal using a flux growth, wherein a fluid containing at least one Group-Ill metal and at least one alkali metal is contained within a vessel and is subject to conditions that allow for the addition or removal of nitrogen to or from the fluid, and the fluid is brought into contact with one or more surfaces of a seed upon which the Group-Ill nitride crystal is grown. The present invention also discloses a method for using the Group-Ill nitride crystal grown using the flux based method as a seed for re-growth using an ammonothermal method.

Description

GROWING A GROUP-III NITRIDE CRYSTAL USING A FLUX GROWTH AND THEN USING THE GROUP-III NITRIDE CRYSTAL AS A SEED

FOR AN AMMONOTHERMAL RE-GROWTH CROSS REFERENCE TO RELATED APPLICATIONS

This application claims the benefit under 35 U.S.C. Section 119(e) of copending and commonly-assigned applications:

U.S. Provisional Application Serial No. 61/507,170, filed on July 13, 2011, by Siddha Pimputkar and Shuji Nakamura, entitled "USE OF GROUP-III NITRIDE CRYSTALS GROWN USING A FLUX METHOD AS SEEDS FOR

AMMONOTHERMAL GROWTH OF A GROUP-III NITRIDE CRYSTAL" attorneys' docket number 30794.419-US-P1 (2012-020-1); and

U.S. Provisional Application Serial No. 61/507,187, filed on July 13, 2011, by Siddha Pimputkar and James S. Speck, entitled "METHOD OF GROWING A BULK GROUP-III NITRIDE CRYSTAL USING A FLUX BASED METHOD THROUGH PREPARING THE FLUX PRIOR TO BRINGING IT IN CONTACT WITH THE GROWING CRYSTAL" attorneys' docket number 30794.421 -US-PI (2012-022); both of which applications are incorporated by reference herein.

This application is related to the following co-pending and commonly- assigned patent applications:

U.S. Utility Patent Application Serial No. 13/128,092, filed on May 6, 2011, by Siddha Pimputkar, Derrick S. Kamber, James S. Speck, and Shuji Nakamura, entitled "USING BORON-CONTAINING COMPOUNDS, GASSES AND FLUIDS DURING AMMONOTHERMAL GROWTH OF GROUP-III NITRIDE

CRYSTALS," attorneys docket number 30794.300-US-WO (2009-288-2), which application is a national stage application that claims the benefit of or priority to P.C.T. International Patent Application Serial No. PCT/US09/063233, filed on November 4, 2009, by Siddha Pimputkar, Derrick S. Kamber, James S. Speck, and Shuji Nakamura, entitled "USING BORON-CONTAINING COMPOUNDS, GASSES AND FLUIDS DURING AMMONOTHERMAL GROWTH OF GROUP- III NITRIDE CRYSTALS," attorneys docket number 30794.300-WO-U1 (2009-288- 2), which application claims the benefit under 35 U.S.C. Section 119(e) of U.S.

Provisional Patent Application Serial No. 61/112,550, filed on November 7, 2008, by Siddha Pimputkar, Derrick S. Kamber, James S. Speck, and Shuji Nakamura, entitled "USING BORON-CONTAINING COMPOUNDS, GASSES AND FLUIDS

DURING AMMONOTHERMAL GROWTH OF GROUP-III NITRIDE

CRYSTALS," attorneys docket number 30794.300-US-P1 (2009-288-1);

U.S. Utility Patent Application Serial No. 13/048,179, filed on March 15, 2011, by Siddha Pimputkar, James S. Speck, and Shuji Nakamura, and entitled

"GROUP-III NITRIDE CRYSTAL AMMONOTHERMALLY GROWN USING AN INITIALLY OFF-ORIENTED NONPOLAR OR SEMIPOLAR GROWTH SURFACE OF A GROUP-III NITRIDE SEED CRYSTAL," attorney's docket number 30794.376- US-U1 (2010-585-1), which application claims the benefit under 35 U.S.C. Section 119(e) of co-pending and commonly-assigned U.S. Provisional Patent Application Serial No. 61/314,095, filed on March 15, 2010, by Siddha Pimputkar, James S. Speck, and Shuji Nakamura, and entitled "GROUP-III NITRIDE CRYSTAL

GROWN USING AN INITIALLY OFF-ORIENTED NONPOLAR AND/OR SEMIPOLAR GROUP-III NITRIDE AS A SEED CRYSTAL USING THE

AMMONOTHERMAL METHOD AND METHOD OF PRODUCING THE SAME," attorney's docket number 30794.376-US-P1 (2010-585-1);

U.S. Utility Patent Application Serial No. xx/xxx,xxx, filed on July 13, 2012, by Siddha Pimputkar and James S. Speck, entitled "GROWTH OF BULK GROUP- III NITRIDE CRYSTALS AFTER COATING THEM WITH A GROUP-III METAL AND AN ALKALI METAL" attorneys' docket number 30794.420-US-U1 (2012- 021-2), and P.C.T. International Patent Application Serial No. PCT/US12/xxxxxx, filed on July 13, 2012, by Siddha Pimputkar and James S. Speck, entitled "GROWTH OF BULK GROUP-III NITRIDE CRYSTALS AFTER COATING THEM WITH A GROUP-III METAL AND AN ALKALI METAL" attorneys' docket number 30794.420-WO-U1 (2012-021-2), both of which applications claim the benefit under 35 U.S.C. Section 119(e) of U.S. Provisional Application Serial No. 61/507,182, filed on July 13, 2011, by Siddha Pimputkar and James S. Speck, entitled "GROWTH OF BULK GROUP-III NITRIDE CRYSTALS AFTER COATING THEM WITH A GROUP-III METAL AND AN ALKALI METAL" attorneys' docket number

30794.420-US-P1 (2012-021-1); and

P.C.T. International Patent Application Serial No. PCT/US12/xxxxxx, filed on July 13, 2012, by Siddha Pimputkar, Shuji Nakamura and James S. Speck, entitled "METHOD FOR IMPROVING THE TRANSPARENCY AND QUALITY OF GROUP-III NITRIDE CRYSTALS AMMONOTHERMALLY GROWN IN A HIGH PURITY GROWTH ENVIRONMENT," attorneys' docket number 30794.422-WO- Ul (2012-023-2), which application claims the benefit under 35 U.S.C. Section 119(e) of U.S. Provisional Application Serial No. 61/507,212, filed on July 13, 2011, by Siddha Pimputkar and Shuji Nakamura, entitled "HIGHER PURITY GROWTH ENVIRONMENT FOR THE AMMONOTHERMAL GROWTH OF GROUP-III NITRIDES," attorneys' docket number 30794.422-US-P1 (2012-023-1); U.S.

Provisional Application Serial No. 61/551,835, filed on October 26, 2011, by Siddha Pimputkar, Shuji Nakamura, and James S. Speck, entitled "USE OF BORON TO IMPROVE THE TRANSPARENCY OF AMMONOTHERMALLY GROWN GROUP-III NITRIDE CRYSTALS," attorneys' docket number 30794.438-US-P1 (2012-248-1); and U.S. Provisional Application Serial No. 61/552,276, filed on October 27, 2011, by Siddha Pimputkar, Shuji Nakamura, and James S. Speck, entitled "USE OF SEMIPOLAR SEED CRYSTAL GROWTH SURFACE TO IMPROVE THE QUALITY OF AN AMMONOTHERMALLY GROWN GROUP- III NITRIDE CRYSTAL," attorneys' docket number 30794.439-US-Pl (2012-249-1); all of which applications are incorporated by reference herein. BACKGROUND OF THE INVENTION

1. Field of the Invention.

This invention relates to a method of fabricating Group-Ill nitride crystals and, more specifically, a method of growing a Group-Ill nitride crystal using a flux growth, and then using the Group-Ill nitride crystal as a seed for ammonothermal re- growth of the Group-Ill nitride crystal. The invention also relates to apparatus for performing the method and compositions of matter fabricated using the method.

2. Description of the Related Art.

(Note: This application references a number of different publications as indicated in the specification by one or more reference numbers within brackets, e.g., [x]. A list of these different publications ordered according to these reference numbers can be found below in the section entitled "References." Each of these publications is incorporated by reference herein.)

True bulk Group-Ill nitride crystals can be grown through various means, such as an ammonothermal method, a high pressure nitrogen solution growth method, or other flux methods, such as a sodium flux method, wherein a major component of the flux is elemental sodium. Of all the methods currently proposed to produce bulk Group-Ill nitride crystals, the sodium flux method appears the most promising due to the currently demonstrated growth rates and resulting properties of the crystals.

However, ammonothermal growth of Gallium Nitride (GaN) is currently the only growth method that has demonstrated the growth of truly large bulk Group-Ill nitride crystals up to 2" in size. While the ammonothermal method has proven to be a viable one, it has its shortcomings in that the growth rate in a nonpolar direction is approximately 4-5 times slower than those in a polar direction. Therefore, in order to scale from small seeds to truly large crystals, a significant amount of time is needed to grow out the crystal in nonpolar directions. What is needed in the art, then, is a method that combines the best attributes of both the sodium flux method and the ammonothermal method for the growth of bulk Group-Ill nitride crystals. The present invention satisfies this need.

SUMMARY OF THE INVENTION

To overcome the limitations in the prior art described above, and to overcome other limitations that will become apparent upon reading and understanding the present specification, the present invention discloses a method of growing a Group-Ill nitride crystal using a flux method, wherein a fluid containing at least one Group-Ill metal and at least one alkali metal is contained within a vessel and is subject to conditions that allow for the addition or removal of nitrogen to or from the fluid, and the fluid is brought into contact with one or more surfaces of a seed upon which the Group-Ill nitride crystal is formed. The present invention also discloses a method for using the Group-Ill nitride crystal grown using the flux method as a seed for re- growth using an ammonothermal method.

BRIEF DESCRIPTION OF THE DRAWINGS

Referring now to the drawings in which like reference numbers represent corresponding parts throughout:

FIG. 1 is a schematic of an apparatus used in the sodium flux method according to one embodiment of the present invention.

FIG. 2 illustrates an embodiment of the present invention where the apparatus used in the sodium flux method includes a growth chamber connected to a preparation chamber.

FIG. 3 is a flowchart that illustrates an exemplary process for performing sodium flux growth followed by ammonothermal growth according to one

embodiment of the present invention. DETAILED DESCRIPTION OF THE INVENTION

In the following description of the preferred embodiment, reference is made to the accompanying drawings which form a part hereof, and in which is shown by way of illustration a specific embodiment in which the invention may be practiced. It is to be understood that other embodiments may be utilized and structural changes may be made without departing from the scope of the present invention.

Sodium Flux Growth of Group-Ill Nitride Crystals

In its most fundamental form, the sodium flux method grows Group-Ill nitride crystals in a flux comprising a fluid or melt containing at least one Group-Ill metal, such as Al, Ga and/or In, and at least one alkali metal, such as Na. The fluid is contained within a chamber or vessel, and is subject to conditions that allow for the addition or removal of nitrogen to or from the fluid. For example, the fluid may be placed within a nitrogen-containing atmosphere and heated to a desirable temperature (typically greater than 700°C), wherein the fluid is brought into contact with one or more surfaces of a seed upon which the Group-Ill nitride crystal is formed.

The challenges this growth method faces are primarily related to the solubility of nitrogen into the flux and, once the nitrogen has been dissolved, the diffusion time required for the nitrogen to come into the vicinity of the growing Group-Ill nitride crystal. Multiple methods have been proposed to enhance stirring of the fluid to increase the amount of dissolved nitrogen in close proximity of the crystal and, although these methods may be effective, they are not necessarily scalable and economic. This invention proposes an alternative method of preparing the flux by saturating it with nitrogen prior to coming in contact with the crystal, and furthermore allowing the flux to be prepared under conditions other than those used for the growth of the Group-Ill nitride crystal.

FIG. 1 is a schematic of an apparatus used in the sodium flux method in its most general form. In one embodiment of the present invention, the sodium flux method makes use of a vessel or chamber 100 (which may be open or closed) having a crucible 102 that contains a fluid 104 that is a crystal growth solution comprised of at least one Group-Ill metal, such as Al, Ga and/or In, and at least one alkali metal, such as Na. The fluid 104 may contain any number of additional elements, compounds, or molecules to modify growth characteristics and crystal properties, such as B, Li, K, Rb, Cs, Be, Mg, Ca, Sr, Ba, Sr, C, Bi, Sb, Sn, Be, Si, Ge, Zn, P and/or N.

Additionally, the chamber 100 contains a growth atmosphere 106 in which the fluid 104 is placed that can be a nitrogen-containing atmosphere 106, including, but not limited to, molecules such as diatomic N2, ammonia NH3, hydrazine N2H6, and atomic nitrogen N, or an atmosphere 106 with only trace amounts of nitrogen present, for example, an atmosphere comprised mainly of hydrogen, argon, etc. The atmosphere 106 may be at vacuum, or may have a pressure greater than

approximately 1 atmosphere (arm) and up to approximately 1000 atm.

The crucible 102 may include one or more heaters 108 so that fluid 104 may be heated and then held at one or more set temperatures, and one or more temperature gradients may be established within the chamber 100. In one embodiment, the fluid 104 is held at a temperature greater than approximately 200°C and below

approximately 1200°C during growth.

The chemical potential of the fluid 104 may be raised or lowered with respect to vacuum through the use of a power source operating at arbitrary frequencies (f >= 0Hz) and voltages. The fluid 104 and atmosphere 106 in which it has been placed may be subject to electromagnetic fields, both static and/or dynamic.

Once the chamber 100 containing the fluid 104 has been adequately prepared, it can then be brought into contact with a seed 110, wherein the seed 110 is at least partially exposed to the nitrogen-containing atmosphere 106. Once the fluid 104 has been brought into contact with the seed 110, the seed 110 and/or fluid 104 may be subject to mechanical movements 112, such as stirring or agitating, to shorten the time required to saturate the fluid 104 with nitrogen. In a preferred embodiment, the seed 110 is a Group-Ill nitride crystal, such as GaN, and may be a single crystal or a polycrystal. However, this should not be seen as limiting for this invention. This invention specifically includes growing a Group- Ill nitride crystal on an arbitrary material, wherein the seed 110 may be an amorphous solid, a polymer containing material, a metal, a metal alloy, a semiconductor, a ceramic, a non-crystalline solid, a poly-crystalline material, an electronic device, an optoelectronic device.

When the seed 110 is a Group-Ill nitride crystal, it may have one or more facets exposed, including polar, nonpolar and semipolar planes. For example, the Group-Ill nitride seed crystal 110 may have a large polar c-plane {0001 } facet or a

{0001 } approaching facet exposed; or the Group-Ill nitride seed crystal 110 may have a large nonpolar m-plane {10-10} facet or a {10-10} approaching facet exposed; or the Group-Ill nitride seed crystal 110 may have a large semipolar {10-11 } facet or a {10-11 } approaching facet exposed; or the Group-Ill nitride seed crystal 110 may have a large nonpolar a-plane {11-20} facet or a {11-20} approaching facet exposed.

The flux method that is used to coat the seed 110 and form a resulting Group- Ill nitride crystal on the seed 110 is based on evaporation from the fluid 104, but may also include a solid source containing Group-Ill and/or alkali metals, which results in the formation of a layer of Group-Ill and alkali metal on the surfaces of the seed 110. In one example, the flux method used to coat the seed 110 and form the Group-Ill nitride crystal on the seed 110 is based on bringing the seed 1 10 into contact with the fluid 104, intermittently or otherwise, by means of dripping and/or flowing the fluid 104 over one or more surfaces of the seed 110. In another example, the flux method used to coat the seed 110 and form the Group-Ill nitride crystal on the seed 110 involves submersing or submerging the seed 110 within the fluid 104 and placing one facet of the seed 110 within some specified distance, such as 5 mm, of the interface between the fluid 104 and the atmosphere 106. Further, the seed 110 may be rotated and/or moved on a continuous or intermittent basis. The resulting Group-Ill nitride crystal that is grown on the seed 110 is characterized as AlxByGazIn(i_x_y_z)N, where 0 <= x <= 1, 0 <= y <= 1, 0 <= z <= 1 , and x + y + z <= 1. For example, the Group-Ill nitride crystal may be A1N, GaN, InN, AlGaN, AlInN, InGaN, etc. In another example, the Group-Ill nitride crystal may be at least 2 inches in length when measuring along at least one direction. The Group-Ill nitride crystal may also have layers with different compositions, and the Group-Ill nitride crystal may have layers with different structural, electronic, optical, and/or magnetic properties.

As noted above, the seed crystal 110 may be brought into contact with the fluid 104 by moving the crystal 110 into the fluid 104, as shown in FIG. 1.

Alternatively, the seed crystal 110 may be brought into contact with the fluid 104 by transporting the fluid 104 to be in contact with the crystal 110, as shown in FIG. 2.

FIG. 2 illustrates an embodiment where the apparatus used in the sodium flux method includes a growth chamber 200 connected to a preparation chamber 202, where the crystal is grown in the growth chamber 200 and the fluid is prepared in the preparation chamber 202. A pump 204 moves the fluid from the preparation chamber 202 to the growth chamber 200 and a controller 208 controls the operation of a mechanism 208 in the growth chamber 200 for stirring or agitating the fluid, as well as one or more heaters 210 in the growth chamber 200 for heating the fluid. Excess fluid is then returned from the growth chamber 200 to the preparation chamber 202 for possible reuse and recycling.

Since the preparation chamber 202 is separate from the growth chamber 200, it is possible to expose the fluid to conditions that would not be favorable in the presence of a Group-Ill nitride crystal. For example, the preparation chamber 202 may subject the fluid to different conditions, such as different temperatures or pressures. Additional materials may also be added to the fluid, such as nitrogen- containing materials, one or more alkali metals, one or more alkali earth metals, and/or one or more Group-Ill elements. Moreover, the additional material may be added to the fluid in any state of matter, including solid, liquid or gas states, or as a plasma, and at any time during the process. In addition, an electrical field may be applied to the fluid, or the fluid may be agitated to enhance mixing, or to enhance dissolution or evaporation of nitrogen from the fluid.

Given the difference in conditions between the growth chamber 200 and the preparation chamber 202, it is possible to have a fluid with a higher concentration of dissolved nitrogen than would be possible if the fluid was in equilibrium with nitrogen under the growth chamber 200 conditions. If the nitrogen concentration is higher than would be thermodynamically favorable in the growth chamber 200, it is possible to generate a supersaturation of nitrogen in the fluid in the preparation chamber 202, which, in turn, would modify the growth behavior, potentially increasing it.

One consequence of this is that nitrogen dissolved within the fluid becomes the driving force to grow a Group-Ill nitride crystal on the seed, as compared to a nitrogen-containing atmosphere. This may result from the fluid being contained in the preparation chamber 202 at higher or lower temperatures and/or higher or lower pressures than the growth chamber 200 in which the Group-Ill nitride crystal is formed.

Finally, those skilled in the art will recognize that the techniques used to bring the fluid into contact with the Group-Ill nitride crystal is not limited in this invention. Possible techniques include:

the dripping, or streaming of the fluid onto one or more surfaces of the Group-Ill nitride crystal, wherein the crystal may be stationary, rotated around one or more axes, moved in any possible direction, and placed at any arbitrary angle with respect to the fluid and any applicable forces, such as the gravitational force;

the dripping or streaming of the fluid onto one or more surfaces of the Group-Ill nitride crystal, wherein the relative positions of the fluid and crystal are configured in such a fashion that gravity pulls the fluid over one or more of the surfaces of the Group-Ill nitride crystal; or the dipping of the Group-Ill nitride crystal into a fluid and sequential removal for extended periods.

Possible Modifications and Variations to the Sodium Flux Growth

Possible modifications and variations to this invention could include the use of a plurality of different preparation chambers, each of which would modify the fluid in a different way. For example, each of the different preparation chambers could modify the temperature or pressure, add or subtract elements or compounds, subject the fluid to electrical fields or mechanical forces, etc. For example, the fluid may be modified, for example, by subjecting it to higher temperature and nitrogen pressures, thereby increasing the amount of dissolved nitrogen in the fluid. Moreover, the plurality of different preparation chambers could be connected serially or in parallel before connecting to the growth chamber, or they could be connected separately to the growth chamber.

Advantages and Improvements of the Sodium Flux Growth

The present invention solves a problem of getting nitrogen through the flux to the crystal. In U.S. Utility Patent Application Serial No. 13/128,092, which is cross- referenced above and incorporated by reference herein, the problem of getting nitrogen through the flux to the crystal may be solved by using a thin layer, wherein the nitrogen goes through the thin layer. In the present invention, nitrogen may already be in the flux (e.g., the fluid is pre-charged with nitrogen), thereby solving the problem of getting nitrogen through the flux to the crystal. In the present invention, any coating (a thin or thick layer) may be used, for example.

The present invention may provide lower cost bulk Group-Ill nitride crystals, with better optical properties, and higher yields. Other benefits of this production method may include the following:

(1) improved uniformity of the flux and dissolved nitrogen; (2) higher purity through separation of the preparation chamber from the growth chamber;

(3) cleaner flux through reducing sources of poly-GaN nucleation;

(4) higher amount of dissolved nitrogen;

(5) alternating the flux material relatively quickly, allowing for layers of different composition or other characteristics (electrical, optical, magnetic); and

(6) easy control of flux composition during extended growths.

Additionally, this invention can be used in reverse, meaning, instead of supplying a high nitrogen containing flux to the crystal surface, a depleted flux layer may be provided, thereby encouraging the Group-III nitride material to be etched. The facets which are formed during the etch may be controlled through modifying the melt and/or growth chamber conditions. This may be useful, for example, for performing an etch-back step prior to growth, or providing a surface roughening layer, which may be useful for enhanced light extraction when applied in optoelectronic devices such as LEDs. Additionally, the surface roughening layer may be useful as an anti-reflection coating as is, for example, useful for solar cell applications.

Furthermore, the surface roughening may be useful for reduction in dislocation density by performing a regrowth on it after etching back. Ammonothermal Re-Growth of Group-III Nitride Crystals

The flux method has shown that significantly enhanced growth rates in the nonpolar direction are possible and hence is a favorable method of growing large Group-III nitride crystals. Additionally, since it is possible to grow large crystals with significantly improved crystal quality and wafer curvature, as compared to Group-III nitride crystals grown using the HVPE (Hydride Vapor Phase Epitaxy) method, it may be financially desirable to use the flux method as a source of seeds for ammonothermal growth. Therefore, the use of Group-III nitride crystals grown using a flux method as seeds for a regrowth using the ammonothermal method also forms the basis of this invention. Specifically, the present invention also includes regrowing a Group-Ill nitride crystal using an ammonothermal method using as a seed the Group-Ill nitride crystal grown using the flux method. The ammonothermal method is well known in the art, as described in, for example, U.S. Utility Patent Application Serial No. 13/128,083, filed on May 6, 2011, by Siddha Pimputkar, Derrick S. Kamber, James S. Speck and Shuji Nakamura, entitled "REACTOR DESIGNS FOR USE IN

AMMONOTHERMAL GROWTH OF GROUP-III NITRIDE CRYSTALS," attorney's docket number 30794.296-US-WO (2009-283-2), which application is incorporated by reference herein, and a similar process and apparatus may be used herein.

The ammonothermal growth may use ammonia, ammonia and one or more other gases, or other nitrogen-containing gases, for example. The ammonothermal method may be either acidic, basic, or neutral. The acidic method utilizes one or more halogens containing materials, while the basic method utilizes one or more alkali metals containing materials. The ammonothermally-grown Group -III nitride crystal may be used to fabricate Group-Ill nitride based electronic or optoelectronic devices, for example.

Like the flux method, the resulting Group-Ill nitride crystal that is grown by the ammonothermal method is characterized as AlxByGazIn(i_x_y_z)N, where 0 <= x <= 1, 0 <= y <= 1, 0 <= z <= l, and x + y + z <= 1. For example, the Group- Ill nitride crystal may be A1N, GaN, InN, AlGaN, AlInN, InGaN, etc. In another example, the Group-Ill nitride crystal may be at least 2 inches in length when measuring along one or more directions. Similarly, the Group-Ill nitride crystal may have layers with different compositions, and the Group-Ill nitride crystal may have layers with different structural, electronic, optical, and/or magnetic properties.

Possible Modifications and Variations to the Ammonothermal Re-Growth Note that the Group-Ill nitride crystal used as a seed crystal for the

ammonothermal method does not need to be the as-grown Group-Ill nitride crystal resulting from the flux method. Instead, the Group-Ill nitride crystal resulting from the flux method may be modified before being used as a seed crystal in the ammonothermal method.

Modifications of interest include:

slicing the flux-grown crystal into thin wafers;

polishing the exposed surfaces of the resulting seed;

ion implanting the seed with one or more elements;

removing one or more portions of the inside of the crystal or wafer; cutting the outer and/or inner surfaces along particular crystallographic directions; or

adding material to or removing additional from the seed using one or more techniques, such as MOCVD, MBE, HVPE, sputtering, other deposition techniques, etching techniques, etc.

Advantages and Improvements of the Ammonothermal Re-Growth

The present invention may enable price reduction in cost of producing substrates, and increased throughput and size of grown Group-Ill nitride crystals.

Process Flowchart

FIG. 3 is a flowchart that illustrates an exemplary process for performing the method of sodium flux growth followed by ammonothermal growth according to one embodiment of the present invention.

Block 300 represents the step of growing a Group-Ill nitride crystal using a sodium flux method (or obtaining a Group-Ill nitride crystal grown using a flux method).

Block 302 represents the end result of Block 300, namely a flux-grown Group- Ill nitride crystal. Block 304 represents an (optional) step of modifying the crystal grown using the flux method prior to re-growth using the ammonothermal method. These modifications may include the following:

slicing the flux-grown crystal into thin wafers;

- polishing the exposed surfaces of the crystal;

ion implanting one or more elements into the crystal;

shaping the crystal;

removing one or more portions of the inside of the crystal; cutting the outer and/or inner surfaces of the crystal along particular crystallographic directions; or

adding material to, or removing material from, the crystal, or surfaces of the crystal, using one or more techniques, such as MOCVD, MBE, HVPE, sputtering, other deposition techniques, etching techniques, etc.

Block 306 represents the step of re-growing the Group-Ill nitride crystal ammonothermally, using the flux-grown Group-Ill nitride crystal of Block 302, as modified by Block 304, as a seed crystal for the ammonothermal re-growth.

Finally, Block 308 represents the end result of the process, namely an ammonothermally-grown Group-Ill nitride crystal. Nomenclature

The terms "Group-Ill nitride" or "Ill-nitride" or "nitride" as used herein refer to any composition or material related to (Al,B,Ga,In)N semiconductors having the formula AlwBxGayInzN where 0 < w < l, 0 < x < l, 0 < y < l, 0 < z < l, and w + x + y + z = 1. These terms as used herein are intended to be broadly construed to include respective nitrides of the single species, Al, B, Ga, and In, as well as binary, ternary and quaternary compositions of such Group III metal species. Accordingly, these terms include, but are not limited to, the compounds of AIN, GaN, InN, AlGaN, AlInN, InGaN, and AlGalnN. When two or more of the (Al,B,Ga,In)N component species are present, all possible compositions, including stoichiometric proportions as well as off-stoichiometric proportions (with respect to the relative mole fractions present of each of the (Al,B,Ga,In)N component species that are present in the composition), can be employed within the broad scope of this invention. Further, compositions and materials within the scope of the invention may further include quantities of dopants and/or other impurity materials and/or other inclusional materials.

This invention also covers the selection of particular crystal terminations and polarities of Group-Ill nitrides. Many Group-Ill nitride devices are grown along a polar orientation, namely a c-plane {0001 } of the crystal, although this results in an undesirable quantum-confined Stark effect (QCSE), due to the existence of strong piezoelectric and spontaneous polarizations. One approach to decreasing polarization effects in Group-Ill nitride devices is to grow the devices along nonpolar or semipolar orientations of the crystal.

The term "nonpolar" includes the {11-20} planes, known collectively as a- planes, and the {10-10} planes, known collectively as m-planes. Such planes contain equal numbers of Group-Ill and Nitrogen atoms per plane and are charge-neutral. Subsequent nonpolar layers are equivalent to one another, so the bulk crystal will not be polarized along the growth direction.

The term "semipolar" can be used to refer to any plane that cannot be classified as c-plane, a-plane, or m-plane. In crystallographic terms, a semipolar plane would be any plane that has at least two nonzero h, i, or k Miller indices and a nonzero 1 Miller index. Subsequent semipolar layers are equivalent to one another, so the crystal will have reduced polarization along the growth direction.

When identifying orientations using Miller indices, the use of braces, { }, denotes a set of symmetry-equivalent planes, which are represented by the use of parentheses, ( ). The use of brackets, [ ], denotes a direction, while the use of brackets, < >, denotes a set of symmetry-equivalent directions. References

The following references are incorporated by reference herein.

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Conclusion

This concludes the description of the preferred embodiment of the present invention. The foregoing description of one or more embodiments of the invention has been presented for the purposes of illustration and description. It is not intended to be exhaustive or to limit the invention to the precise form disclosed. Many

modifications and variations are possible in light of the above teaching. It is intended that the scope of the invention be limited not by this detailed description, but rather by the claims appended hereto.

Claims

WHAT IS CLAIMED IS:
1. A method for ammonothermal growth, comprising:
(a) growing a Group-Ill nitride crystal using a flux method; and
(b) regrowing the Group-Ill nitride crystal using an ammonothermal method, wherein the Group-Ill nitride crystal grown in step (a) is used as a seed for the regrowth in step (b).
2. The method of claim 1 , wherein the flux method uses one or more Group-Ill metals.
3. The method of claim 2, wherein the Group-Ill metal is one or more of Al, Ga or In.
4. The method of claim 1 , wherein the flux method uses one or more alkali metals.
5. The method of claim 4, wherein the alkali metal is Na.
6. The method of claim 1, wherein the Group-Ill nitride crystal grown using the flux method is at least 2 inches in length when measuring along at least one direction.
7. The method of claim 1, wherein the Group-Ill nitride crystal grown using the flux method is modified prior to the regrowth using the ammonothermal method.
8. The method of claim 7, wherein the Group-Ill nitride crystal is modified by slicing, polishing, ion implanting, or shaping.
9. The method of claim 1, wherein the flux method includes:
(1) a fluid or melt comprised of at least one Group-Ill metal and at least one alkali metal contained within a vessel, that is subject to conditions that allow for addition or removal of nitrogen to or from the fluid or melt; and
(2) the fluid or melt is brought into contact with one or more surfaces of a seed upon which the Group-Ill nitride crystal is grown.
10. The method of claim 9, wherein the growth of the Group-Ill nitride crystal is performed in a vessel other than the one in which the fluid is prepared.
11. The method of claim 9, wherein the conditions under which the fluid is prepared are different than the conditions under which the Group-Ill nitride crystal are grown.
12. The method of claim 11 , wherein the conditions are set such that the dissolved nitrogen has a driving force to grow a Group-Ill nitride crystal on the seed.
13. The method of claim 11, wherein the fluid is agitated to enhance dissolution or evaporation of nitrogen from the fluid.
14. A Group-Ill nitride crystal grown using the method of claim 1.
15. An apparatus for ammonothermal growth, comprising:
(a) a first chamber for growing a Group-Ill nitride crystal using a flux method; and
(b) a second chamber for regrowing the Group-Ill nitride crystal using an ammonothermal method, wherein the Group-Ill nitride crystal grown in the first chamber is used as a seed for the regrowth in the second chamber.
PCT/US2012/046756 2011-07-13 2012-07-13 Growing a group-iii nitride crystal using a flux growth and then using the group-iii nitride crystal as a seed for an ammonothermal re-growth WO2013010117A1 (en)

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