USRE47114E1 - Polycrystalline group III metal nitride with getter and method of making - Google Patents

Polycrystalline group III metal nitride with getter and method of making Download PDF

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USRE47114E1
USRE47114E1 US15/469,196 US201715469196A USRE47114E US RE47114 E1 USRE47114 E1 US RE47114E1 US 201715469196 A US201715469196 A US 201715469196A US RE47114 E USRE47114 E US RE47114E
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gallium
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getter
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Mark P. D'Evelyn
Derrick S. Kamber
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SLT Technologies Inc
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    • C01B21/00Nitrogen; Compounds thereof
    • C01B21/06Binary compounds of nitrogen with metals, with silicon, or with boron, or with carbon, i.e. nitrides; Compounds of nitrogen with more than one metal, silicon or boron
    • C01B21/0632Binary compounds of nitrogen with metals, with silicon, or with boron, or with carbon, i.e. nitrides; Compounds of nitrogen with more than one metal, silicon or boron with gallium, indium or thallium
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    • C01B21/0602Binary compounds of nitrogen with metals, with silicon, or with boron, or with carbon, i.e. nitrides; Compounds of nitrogen with more than one metal, silicon or boron with two or more other elements chosen from metals, silicon or boron
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    • C01B21/072Binary compounds of nitrogen with metals, with silicon, or with boron, or with carbon, i.e. nitrides; Compounds of nitrogen with more than one metal, silicon or boron with aluminium
    • C01B21/0722Preparation by direct nitridation of aluminium
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    • C30B28/00Production of homogeneous polycrystalline material with defined structure
    • C30B28/04Production of homogeneous polycrystalline material with defined structure from liquids
    • C30B28/06Production of homogeneous polycrystalline material with defined structure from liquids by normal freezing or freezing under temperature gradient
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    • 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
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    • C30B35/00Apparatus in general, specially adapted for the growth, production or after-treatment of single crystals or a homogeneous polycrystalline material with defined structure
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    • 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
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    • 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
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    • C30B9/00Single-crystal growth from melt solutions using molten solvents

Abstract

A gettered polycrystalline group III metal nitride is formed by heating a group III metal with an added getter in a nitrogen-containing gas. Most of the residual oxygen in the gettered polycrystalline nitride is chemically bound by the getter. The gettered polycrystalline group III metal nitride is useful as a raw material for ammonothermal growth of bulk group III nitride crystals.

Description

This application is a continuation-in-part of U.S. patent application Ser. No. 12/634,665, filed on Dec. 9, 2009, now allowed, which claims priority to U.S. Patent Application No. 61/122,332, filed on Dec. 12, 2008, each of which is incorporated by reference in its entirety.

BACKGROUND

The present disclosure generally relates to processing of materials for growth of crystals. More particularly, the present disclosure provides a crystalline nitride material suitable for use as a raw material for crystal growth of a gallium-containing nitride crystal by an ammonobasic or ammonoacidic technique, but there can be others. In other embodiments, the present disclosure provides methods suitable for synthesis of polycrystalline nitride materials, but it would be recognized that other crystals and materials can also be processed. Such crystals and materials include, but are not limited to, GaN, AN, InN, InGaN, AlGaN, and AlInGaN, and others for manufacture of bulk or patterned substrates. Such bulk or patterned substrates can be used for a variety of applications including optoelectronic devices, lasers, light emitting diodes, solar cells, photoelectrochemical water splitting and hydrogen generation, photodetectors, integrated circuits, and transistors, among other devices.

Gallium nitride containing crystalline materials serve as substrates for manufacture of conventional optoelectronic devices, such as blue light emitting diodes and lasers. Such optoelectronic devices have been commonly manufactured on sapphire or silicon carbide substrates that differ in composition from the deposited nitride layers. In the conventional Metal-Organic Chemical Vapor Deposition (MOCVD) method, deposition of GaN is performed from ammonia and organometallic compounds in the gas phase. Although successful, conventional growth rates achieved make it difficult to provide a bulk layer of GaN material. Additionally, dislocation densities are also high and lead to poorer optoelectronic device performance.

Growth of nitride crystals by ammonothermal synthesis has been proposed. Ammonothermal crystal growth methods are expected to be scalable, as described by Dwilinski, et al. (J. Crystal Growth 310, 3911 (2008)), by Ehrentraut, et al. (J. Crystal Growth 305, 204 (2007)), by D'Evelyn, et al. (J. Crystal Growth 300, 11 (2007)), and by Wang, et al. [Crystal Growth & Design 6, 1227 (2006)]. The ammonothermal method generally requires a polycrystalline nitride raw material, which is then recrystallized onto seed crystals. An ongoing challenge of ammonothermally-grown GaN crystals is a significant level of impurities, which cause the crystals to be colored, e.g., yellowish, greenish, grayish, or brownish. The residual impurities may cause optical absorption in light emitting diodes fabricated on such substrates, negatively impacting efficiency, and may also affect the electrical conductivity and/or generate stresses within the crystals. One source of the impurities is the polycrystalline nitride raw material.

For example, gallium nitride crystals grown by hydride vapor phase epitaxy, a relatively more expensive, vapor phase method, have demonstrated very good optical transparency, with an optical absorption coefficient below 2 cm−1 at wavelengths between about 405 nanometers and about 620 nanometers (Oshima, et al., J. Appl. Phys. 98, 103509 (2005)). However, the most transparent ammonothermally-grown gallium nitride crystals of which we are aware were yellowish and had an optical absorption coefficient below 5 cm−1 over the wavelength range between about 465 nanometers and about 700 nanometers (D'Evelyn, et al., J. Crystal Growth 300, 11 (2007) and U.S. Pat. No. 7,078,731).

Several methods for synthesis of polycrystalline nitride materials have been proposed. Callahan, et al. (MRS Internet J. Nitride Semicond. Res. 4, 10 (1999); U.S. Pat. No. 6,406,540)proposed a chemical vapor reaction process involving heating gallium metal in a vapor formed by heating NH4Cl. Related methods have been discussed by Wang, et al. [J. Crystal Growth 286, 50 (2006)) and by Park, et al. [U.S. Application Publication Nos. 2007/0142204, 2007/0151509, and 2007/0141819). The predominant impurity observed was oxygen, at levels varying from about 16 to about 160 parts per million (ppm). The chemical form of the oxygen was not specified. An alternative method, involving heating in ammonia only and producing GaN powder with an oxygen content below 0.07 wt %, was disclosed by Tsuji (U.S. Publication No. 2008/0193363). Yet another alternative method, involving contacting Ga metal with a wetting agent such as Bi and heating in ammonia only, producing GaN powder with an oxygen content below 650 ppm, has been disclosed by Spencer, et al. (U.S. Pat. No. 7,381,391).

What is needed is a method for low-cost manufacturing of polycrystalline nitride materials that are suitable for crystal growth of bulk gallium nitride crystals and do not contribute to impurities in the bulk crystals.

SUMMARY

Disclosed herein are techniques related to processing of materials for growth of crystals are provided. More particularly, the present disclosure provides a crystalline nitride material suitable for use as a raw material for crystal growth of a gallium-containing nitride crystal by an ammonothermal technique, including ammonobasic or ammonoacidic technique, but there can be others. In other embodiments, the present disclosure provides methods suitable for synthesis of polycrystalline nitride materials, but it would be recognized that other crystals and materials can also be processed, including single crystal materials. Such crystals and materials include, but are not limited to, GaN, AN, InN, InGaN, AlGaN, and AlInGaN, and others for manufacture of bulk or patterned substrates. Such bulk or patterned substrates can be used for a variety of applications including optoelectronic devices, lasers, light emitting diodes, solar cells, photoelectrochemical water splitting and hydrogen generation, photodetectors, integrated circuits, and transistors, among other devices.

In a specific embodiment, the present disclosure provides a composition for a material. The composition includes a polycrystalline group III metal nitride material having a plurality of grains. Preferably, the plurality of grains are characterized by a columnar structure. In a specific embodiment, one or more of the grains have an average grain size in a range of from about 10 nanometers to about 10 millimeters. The composition has an atomic fraction of a group III metal in the group III metal nitride in a range of from about 0.49 to about 0.55. In one or more embodiments, the metal in the group III metal nitride is selected from at least aluminum, indium, or gallium. The composition also has an oxygen content in the group III metal nitride material provided as a group III metal oxide or as a substitutional impurity within a group III metal nitride less than about 10 parts per million (ppm).

In an alternative specific embodiment, the present disclosure provides a method for forming a crystalline material. The method includes providing a group III metal in at least one crucible. Preferably, the group III metal comprises at least one metal selected from at least aluminum, gallium, and indium. The method includes providing a getter at a level of at least 100 ppm with respect to the group III metal. In a specific embodiment, the getter comprises at least one of alkaline earth metals, boron, carbon, scandium, titanium, vanadium, chromium, yttrium, zirconium, niobium, rare earth metals, hafnium, tantalum, and tungsten. The method also includes providing the group III metal in a crucible and providing the getter into a chamber. This chamber and associated components may also be referred to more generally as a reactor or an apparatus. The method transfers a nitrogen-containing material into the chamber and heats the chamber to a determined temperature. The method includes pressurizing the chamber to a determined pressure and processing the nitrogen-containing material with the group III metal in the chamber. In one or more embodiments, the method forms a polycrystalline group III metal nitride in at least the crucible that contained the group III metal. In one or more embodiments, the method forms a polycrystalline group III metal nitride within the chamber, which may substantially occur within the chamber in one or more regions that do not include the group III metal crucible.

In yet an alternative specific embodiment, the present disclosure provides an alternative method of forming a group III metal nitride containing substrate. The method includes providing a group III metal as a source material, which comprises at least one metal selected from at least aluminum, gallium, and indium. The method includes providing a getter at a level of at least 100 ppm with respect to the group III metal source material and providing the group III metal source material and the getter into a chamber. The method also includes transferring a nitrogen-containing material into the chamber and heating the chamber to a determined temperature. In a specific embodiment, the method includes pressurizing the chamber to a determined pressure and processing the nitrogen-containing material with the group III metal source material in the chamber. In one or more embodiments, the method forms a crystalline group III metal nitride characterized by a wurtzite structure substantially free from any cubic entities and an optical absorption coefficient of about 2 cm−1 and less at wavelengths between about 405 nanometers and about 750 nanometers.

Still further, the present disclosure provides a gallium nitride containing crystal. The crystal has a crystalline substrate member having a length greater than about 5 millimeters and a substantially wurtzite structure characterized to be substantially free of other crystal structures. In a specific embodiment, the other structures are less than about 1% in volume in reference to a volume of the substantially wurtzite structure. The crystal also has an impurity concentration greater than 1015 cm−1 of at least one of Li, Na, K, Rb, Cs, Ca, F, Br, I, and Cl and an optical absorption coefficient of about 2 cm−1 and less at wavelengths between about 405 nanometers and about 750 nanometers.

In certain embodiments, methods of preparing a polycrystalline group III metal nitride material are provided, comprising: providing a source material selected from a group III metal, a group III metal halide, or a combination thereof into a chamber, the source material comprising at least one metal selected from at least aluminum, gallium, and indium; providing a getter at a level of at least 100 ppm with respect to the source material into the chamber such that the getter contacts the g source material; transferring a nitrogen-containing material into the chamber; heating the chamber to a determined temperature; pressurizing the chamber to a determined pressure; processing the nitrogen-containing material with the source material in the chamber; and forming a polycrystalline group III metal nitride material.

In certain embodiments, methods of forming a polycrystalline gallium-containing group III metal nitride material are provided, comprising: providing a gallium-containing group III metal or a group III metal halide source material to a chamber, the gallium-containing group III metal or metal halide source material comprising at least one metal selected from aluminum, gallium, and indium; providing a getter at a level of at least 100 ppm with respect to the source material into the chamber such that the getter contacts the source material; transferring a nitrogen-containing material into the chamber; heating the chamber to a determined temperature; pressurizing the chamber to a determined pressure; processing the nitrogen-containing material with the source material in the chamber to form a polycrystalline gallium-containing group III metal nitride comprising a plurality of grains of a crystalline gallium-containing group III metal nitride; the plurality of grains having an average grain size in a range from about 10 nanometers to about 10 millimeters and defining a plurality of grain boundaries; and the polycrystalline gallium-containing group III metal nitride material having: an atomic fraction of a gallium-containing group III metal in a range from about 0.49 to about 0.55, the gallium-containing group III metal being selected from at least one of aluminum, indium, and gallium; and an oxygen content in the form of a gallium-containing group III metal oxide or a substitutional impurity within the polycrystalline gallium-containing group III metal nitride less than about 10 parts per million (ppm); and a plurality of inclusions within at least one of the plurality of grain boundaries and the plurality of grains, the plurality of inclusions comprising a getter, the getter constituting a distinct phase from the crystalline gallium-containing group III metal nitride and located within individual grains of the crystalline gallium-containing group III metal nitride and/or at the grain boundaries of the crystalline gallium-containing group III metal nitride and being incorporated into the polycrystalline gallium-containing group III metal nitride at a level greater than about 200 parts per million, and; forming a crystalline gallium-containing group III metal nitride crystal from the polycrystalline gallium-containing group III metal nitride characterized by a wurtzite structure substantially free from any cubic entities and an optical absorption coefficient less than or equal to about 2 cm−1 at wavelengths between about 405 nanometers and about 750 nanometers.

Benefits are achieved over pre-existing techniques using the present disclosure. In particular, the present disclosure enables a cost-effective manufacture of crystals that serve as a starting material for high quality gallium nitride containing crystal growth. In a specific embodiment, the present method and apparatus can operate with components that are relatively simple and cost effective to manufacture, such as ceramic and steel tubes. A specific embodiment also takes advantage of a getter material suitable for processing one or more chemicals for manufacture of high quality gallium nitride starting material. Depending upon the embodiment, the present apparatus and method can be manufactured using conventional materials and/or methods according to one of ordinary skill in the art. In specific embodiments, the final crystal structure is substantially clear and free of haze and other features that may be undesirable. Depending upon the embodiment, one or more of these benefits may be achieved. These and other benefits may be described throughout the present specification and more particularly below.

The present disclosure achieves these benefits and others in the context of known process technology. However, a further understanding of the nature and advantages implementing embodiments according to the present disclosure may be realized by reference to the latter portions of the specification and attached drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIGS. 1, 2, and 3 are schematic diagrams illustrating reactors according to embodiments of the present disclosure;

FIG. 4 is a simplified flow diagram of a synthesis method according to an embodiment;

FIG. 5 is a simplified flow diagram of utilization method according to an embodiment; and

FIG. 6 is a simplified system diagram according to an embodiment.

DETAILED DESCRIPTION

According to the present disclosure, techniques related to processing of materials for growth of crystals are provided. More particularly, the present disclosure provides a crystalline nitride material suitable for use as a raw material for crystal growth of a gallium-containing nitride crystal by an ammonothermal technique, including ammonobasic or ammonoacidic technique, but there can be others. In other embodiments, the present disclosure provides methods suitable for synthesis of polycrystalline nitride materials, but it would be recognized that other crystals and materials can also be processed, including single crystal materials. Such crystals and materials include, but are not limited to, GaN, AN, InN, InGaN, AlGaN, and AlInGaN, and others for manufacture of bulk or patterned substrates. Such bulk or patterned substrates can be used for a variety of applications including optoelectronic devices, lasers, light emitting diodes, solar cells, photoelectrochemical water splitting and hydrogen generation, photodetectors, integrated circuits, and transistors, among other devices.

The disclosure discusses embodiments that may relate to a crystalline composition. The disclosure includes embodiments that may relate to an apparatus for making a crystalline composition. The disclosure includes embodiments that may relate to a method of making and/or using the crystalline composition.

Approximating language, as used herein throughout the specification and claims, may be applied to modify any quantitative representation that could permissibly vary without resulting in a change in the basic function to which it may be related. Accordingly, a value modified by a term such as “about” may not be limited to the precise value specified. In at least one instance, the variance indicated by the term about may be determined with reference to the precision of the measuring instrumentation. Similarly, “free” may be combined with a term; and, may include an insubstantial number, or a trace amount, while still being considered free of the modified term unless explicitly stated otherwise.

According to one embodiment according to the present disclosure, a composition of a polycrystalline metal nitride is provided. The polycrystalline metal nitride may have a plurality of grains, and these grains may have a columnar structure. In some embodiments, many grains may be bonded or adhered to one another, forming a polycrystalline plate. In other embodiments, a smaller number of grains may be bonded or adhered to one another, forming a polycrystalline powder.

With reference to the grains, the grains may be characterized by one or more properties. The properties may include a grain dimension. Other properties may include an average number of grains per unit volume, an inter-grain bend strength or a tilt angle of the grains relative to each other.

The grain dimension may refer to either an average grain size or an average grain diameter. The grains may have a columnar structure; in this case they have a major axis, and the average grain size refers to an average length of the grains along the major axis. Perpendicular to the major axis may be one or more minor axes, and the average diameter of each grain may be determined with reference to the minor axes. Collectively, the average diameters of each of the grains may be aggregated and averaged to provide the average grain diameter. An average, as used herein, may refer to the mean value.

The average grain size of the polycrystalline metal nitride may be in a range of greater than about 10 nanometers. In one embodiment, the average grain size may be in a range of from about 0.01 micrometer to about 10 millimeters, while in certain other embodiments, the grain size may be in a range of from about 0.01 micrometer to about 30 micrometers, from about 30 micrometers to about 50 micrometers, from about 50 micrometers to about 100 micrometers, from about 100 micrometers to about 500 micrometers, from about 500 micrometers to about 1 millimeter, from about 1 millimeter to about 3 millimeters, from about 3 millimeters to about 10 millimeters or greater than about 10 millimeters. The average grain diameter may be larger than about 10 micrometers. In one embodiment, the average grain diameter may be in a range of from about 10 micrometers to about 20 micrometer, from about 20 micrometers to about 30 micrometers, from about 30 micrometers to about 50 micrometers, from about 50 micrometers to about 100 micrometers, from about 100 micrometers to about 500 micrometers, from about 500 micrometers to about 1 millimeter, from about 1 millimeter to about 3 millimeters, from about 3 millimeters to about 10 millimeters or greater than about 10 millimeters.

An average number of grains per unit volume of the crystalline composition may indicate a grain average or granularity. The composition may have an average number of grains per unit volume of greater than about 100 per cubic centimeter. In one embodiment, the average number of grains per unit volume may be in a range of from about 100 per cubic centimeter to about 1000 per cubic centimeter, from about 1000 per cubic centimeter to about 10,000 per cubic centimeter, from about 10,000 per cubic centimeter to about 105 per cubic centimeter, or greater than about 105 per cubic centimeter.

The grains may be oriented at a determined angle relative to each other. The orientation may be referred to as the tilt angle, which may be greater than about 1 degree. In one embodiment, the grain orientation or tilt angle may be in a range of from about 1 degree to about 3 degrees, from about 3 degrees to about 5 degrees, from about 5 degrees to about 10 degrees, from about 10 degrees to about 15 degrees, from about 15 degrees to about 30 degrees, or greater than about 30 degrees.

Properties that are inherent in or particular to one or more crystalline articles produced according to an embodiment of the present disclosure may include bend strength, density, moisture resistance, and porosity, among others. The properties may be measured using the corresponding ASTM standard test. Example of the ASTM standard test may include ASTM C1499.

The inter-grain bend strength of a film comprising one or more of crystals may be greater than about 20 MegaPascal (MPa). In one embodiment, the inter-grain bend strength may be in a range of from about 20 MegaPascal to about 50 MegaPascal, from about 50 MegaPascal to about 60 MegaPascal, from about 60 MegaPascal to about 70 MegaPascal, from about 70 MegaPascal to about 75 MegaPascal, from about 75 MegaPascal to about 80 MegaPascal, from about 80 MegaPascal to about 90 MegaPascal, or greater than about 90 MegaPascal. The bend strength may indicate the grain to grain relationship at the inter-grain interface and/or the inter-grain strength.

The apparent density of crystalline articles may be greater than about 1 gram per cubic centimeter (g/cc). In one embodiment, the density may be in a range of from about 1 gram per cubic centimeter to about 1.5 grams per cubic centimeter, from about 1.5 grams per cubic centimeter to about 2 grams per cubic centimeter, from about 2 grams per cubic centimeter to about 2.5 grams per cubic centimeter, from about 2.5 grams per cubic centimeter to about 3 grams per cubic centimeter, greater than about 4 grams per cubic centimeter, greater than about 5 grams per cubic centimeter, or greater than about 6 grams per cubic centimeter. The crystalline composition density may be a function of, for example, the porosity or lack thereof, the crystal packing arrangement, and the like.

The crystalline article may be aluminum nitride and may have an apparent density of less than about 3.26 gram per cubic centimeter at standard test conditions. In one embodiment, the aluminum nitride crystalline article may have an apparent density in a range of from about 3.26 gram per cubic centimeter to about 2.93 gram per cubic centimeter, from about 2.93 gram per cubic centimeter to about 2.88 gram per cubic centimeter, from about 2.88 gram per cubic centimeter to about 2.5 gram per cubic centimeter, from about 2.5 gram per cubic centimeter to about 1.96 gram per cubic centimeter, or less than about 1.96 gram per cubic centimeter.

The crystalline article may be gallium nitride and may have an apparent density of less than about 6.2 gram per cubic centimeter at standard test conditions. In one embodiment, the gallium nitride crystalline article may have an apparent density in a range of from about 6.2 gram per cubic centimeter to about 5.49 gram per cubic centimeter, from about 5.49 gram per cubic centimeter to about 4.88 gram per cubic centimeter, from about 4.88 gram per cubic centimeter to about 4.27 gram per cubic centimeter, from about 4.27 gram per cubic centimeter to about 4 gram per cubic centimeter, or less than about 4 gram per cubic centimeter.

The porosity of the polycrystalline composition may be in a range of less than about 30 percent by volume. In one embodiment, the porosity may be in a range of from about 30 percent to about 10 percent, from about 10 percent to about 5 percent, from about 5 percent to about 1 percent, from about 1 percent to about 0.1 percent, or less than about 0.1 percent by volume.

The metal of the metal nitride may include a group III metal. Suitable metals may include one or more of aluminum, gallium, or indium. The “one or more” refers to combination of metals in the metal nitride, and may include compositions such as aluminum gallium nitride (AlGaN), indium gallium nitride (InGaN), aluminum indium nitride (AlInN), aluminum indium gallium nitride (AlInGaN), and the like.

A fraction of the metal, or metals, in the metal nitride may be selected such that there is no excess metal in the metal nitride. In one embodiment, the atomic fraction of the metal may be greater than about 49 percent. In another embodiment, the atomic fraction may be in a range of from about 49 percent to about 50 percent, from about 50 percent to about 51 percent, from about 51 percent to about 53 percent, from about 53 percent to about 55 percent, or greater than about 55 percent.

In some embodiments, the group III metal nitride comprises a powder. The particle size of the powder may be between about 0.1 micron and about 100 microns. Some powder particles may comprise single crystals. Some powder particles may comprise at least two grains. In other embodiments, the group III metal nitride comprises a grit. The particle size of the grit may be between about 100 microns and about 10 millimeters. Some grit particles may comprise single crystals. Some grit particles may comprise at least two grains.

The metal nitride composition may contain one or more impurities. As used herein, and as is commonly used in the art, the term “impurity” refers to a chemical species that is distinct from the group III metal nitride that constitutes the majority composition of the polycrystalline metal nitride. Several classes of impurities may be distinguished, with respect to chemistry, atomic structure, intent, and effect. Impurities will generally comprise elements distinct from nitrogen, aluminum, gallium, and indium, including oxygen, carbon, halogens, hydrogen, alkali metals, alkaline earth metals, transition metals, and main block elements. The impurity may be present in a number of forms, with different atomic structure. In some cases, the impurity is present as an isolated atom or ion within the crystalline lattice of the group III metal nitride, for example, as a substitutional or interstitial impurity. In other cases, the impurity is present in a distinct phase, for example, as an inclusion within an individual group III metal nitride grain or within a grain boundary of the group III metal nitride. The impurity may be deliberately added, to enhance the properties of the group III metal nitride in some way, or may be unintentional. Finally, the impurity may or may not have a significant effect on the electrical, optical, crystallographic, chemical, or mechanical properties of the group III metal nitride. One skilled in the art will recognize that an inclusion comprising, for example, a getter within a crystal grain is distinguished from a dopant in that an inclusion is present as a distinct phase. An inclusion as a distinct phase has a different crystallographic structure than the crystal lattice in which it is embedded whereas a crystal grain having a dopant dispersed within the crystalline lattice of the crystal grain will exhibit a single crystallographic structure.

As used herein, and as is commonly used in the art, the term “dopant” refers to an impurity that is atomically dispersed within the group III metal nitride, for example, as a substitutional or interstitial impurity, and is typically added intentionally. With regard to dopants and dopant precursors (collectively “dopants” unless otherwise indicated), the electrical properties of the group III metal nitride composition may be controlled by adding one or more of such dopants to the above composition during processing. The dopant may also provide magnetic and/or luminescent properties to the group III metal nitride composition. Suitable dopants may include one or more of s or p block elements, transition metal elements, and rare earth elements. Suitable s and p block elements may include, for example, one or more of silicon, germanium, magnesium, or tin. Other suitable dopants may include one or more of transition group elements. Suitable transition group elements may include one or more of, for example, zinc, iron, or cobalt. Suitable dopants may produce an n-type material, a p-type material, or a semi-insulating material. In some embodiments, oxygen, whether added intentionally or unintentionally, also acts as a dopant.

Suitable dopant concentration levels in the polycrystalline composition may be greater than about 1010 atoms per cubic centimeter. In one embodiment, the dopant concentration may be in a range of from about 1010 atoms per cubic centimeter to about 1015 atoms per cubic centimeter, from about 1015 atoms per cubic centimeter to about 1016 atoms per cubic centimeter, from about 1016 atoms per cubic centimeter to about 1017 atoms per cubic centimeter, from about 1017 atoms per cubic centimeter to about 1018 atoms per cubic centimeter, from about 1018 atoms per cubic centimeter to about 1021 atoms per cubic centimeter, or greater than about 1021 atoms per cubic centimeter.

As used herein, the term “getter” refers to a substance that is intentionally added to a process or a composition to remove or react with undesired impurities. The getter has a higher chemical affinity for an undesired impurity, for example, oxygen, than the principal metallic constituent of the composition, for example, gallium. The getter may become incorporated into the polycrystalline group III metal nitride in the form of an inclusion, for example, as a metal nitride, a metal halide, a metal oxide, a metal oxyhalide, or as a metal oxynitride. Examples of suitable getters include the alkaline earth metals, boron, carbon, scandium, titanium, vanadium, chromium, yttrium, zirconium, niobium, the rare earth metals (also known as the lanthanides or the lanthanide metals), hafnium, tantalum, and tungsten, and their nitrides, oxynitrides, oxyhalides, and halides. In some embodiments, an elemental composition or substance can act as either a getter or as a dopant, such as magnesium. In other cases, the getter impurity atom has a larger atomic or covalent diameter than gallium and does not become incorporated as a dopant at sufficient levels to modify the electrical properties of the group III metal nitride significantly, and therefore functions predominantly or exclusively as a getter. The getter may be present in the polycrystalline group III metal nitride as a distinct phase, within individual grains of a crystalline group III metal nitride and/or at grain boundaries of a crystalline group III metal nitride, at a level greater than 100 ppm, from about 100 ppm to about 200 ppm, from about 200 ppm to about 500 ppm, from about 500 ppm to about 0.1%, from about 0.1% to about 0.2%, from about 0.2% to about 0.5%, from about 0.5% to about 2%, from about 2% to about 10%, or greater than 10%. Parts per million (ppm) and “%” refer to “by weight” unless otherwise indicated.

In other cases, impurities are unintended and/or undesirable inclusions in the polycrystalline group III metal nitride, and may result from, for example, processing and handling. Other unintentional impurities may result from contaminants in raw materials. Some unintentional impurities may be more closely associated with select raw materials. In some embodiments, the unintentional impurity includes oxygen present as a substitutional impurity, or dopant, in the polycrystalline group III metal nitride at higher than the desired level. In other embodiments, the unintentional impurity includes oxygen present as a group III oxide inclusion, for example, Ga2O3, Al2O3, and/or In2O3. The unintentional oxygen impurity may originate from residual oxygen in the metal raw material, from moisture or O2 present as an impurity in the gaseous raw materials used in the synthesis process, from moisture or O2 generated from outgassing of the reactor components during the synthesis process, from reaction of the gaseous raw materials with one or more of the reactor materials during the synthesis process, or from an air leak in the reactor. In one embodiment, the oxygen content present as Ga2O3 or as a substitutional impurity within the polycrystalline group III metal nitride may be less than about 10 parts per million (ppm). In another embodiment, the oxygen content present as Ga2O3 or as a substitutional impurity within the polycrystalline gallium nitride may be in a range of from about 10 parts per million to about 3 parts per million, from about 3 parts per million to about 1 part per million, from about 1 part per million to about 0.3 parts per million, from about 0.3 part per million to about 0.1 parts per million, or less than about 0.1 part per million.

Getters are often used to purify the gases being used to synthesize polycrystalline gallium-containing group III nitride materials. However in these uses, the incorporation of the getter into the polycrystalline material is avoided. In contrast, it is an object of the invention to deliberately incorporate a getter phase into the polycrystalline group III nitride materials so formed. In some embodiments according to the present disclosure, a getter material is provided in a crucible along with a group III metal. In other embodiments, a getter material is provided to a chamber in which a group III metal or a group III metal halide is to be processed. In some embodiments according to the present disclosure, a getter material is provided in a separate crucible or source from the group III metal crucible and transported to a crucible where a group III metal is to be processed. In some embodiments, a getter material is provided in a separate crucible or source from the group III metal and transported to a region wherein a polycrystalline group III nitride material is formed. In some embodiments, the getter material, or a distinct phase comprising at least one component of the getter material, is incorporated into the polycrystalline group III metal nitride as an inclusion within or between grains of crystalline group III metal nitride. In other embodiments, the getter removes impurities from the growth environment in the gas phase and does not become incorporated into the polycrystalline group III metal nitride. In some embodiments, the getter removes impurities from the growth environment by forming a solid compound that does not become incorporated into the polycrysta