Patent Publication Number: US-8987156-B2

Title: Polycrystalline group III metal nitride with getter and method of making

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&#39;Evelyn, et al. (J. Crystal Growth 300, 11 (2007)), and by Wang, et al. [Crystal Growth &amp; 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&#39;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 NH 4 Cl. 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 10 15  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 10 5  per cubic centimeter, or greater than about 10 5  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 10 10  atoms per cubic centimeter. In one embodiment, the dopant concentration may be in a range of from about 10 10  atoms per cubic centimeter to about 10 15  atoms per cubic centimeter, from about 10 15  atoms per cubic centimeter to about 10 16  atoms per cubic centimeter, from about 10 16  atoms per cubic centimeter to about 10 17  atoms per cubic centimeter, from about 10 17  atoms per cubic centimeter to about 10 18  atoms per cubic centimeter, from about 10 18  atoms per cubic centimeter to about 10 21  atoms per cubic centimeter, or greater than about 10 21  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, Ga 2 O 3 , Al 2 O 3 , and/or In 2 O 3 . The unintentional oxygen impurity may originate from residual oxygen in the metal raw material, from moisture or O 2  present as an impurity in the gaseous raw materials used in the synthesis process, from moisture or O 2  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 Ga 2 O 3  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 Ga 2 O 3  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 polycrystalline group III metal nitride. 
     Referring now to the apparatus that includes an embodiment according to the present disclosure, the apparatus may include sub systems, such as a housing, one or more supply sources, and a control system. 
     The housing may include one or more walls, components, and the like. The walls of the housing may be made of at least one of a metal, a refractory material, or a metal oxide. In one embodiment, the walls of the housing comprise at least one of fused silica, alumina, carbon, iron-based alloy, chromium-based alloy, molybdenum, molybdenum-based alloy, or boron nitride. In one embodiment, the housing may have an inner wall, and an outer wall spaced from the inner wall. An inner surface of the inner wall may define a chamber. 
     The walls of the housing may be configured (e.g., shaped or sized) with reference to processing conditions and the desired end use. The configuration may depend on the size and number of components, and the relative positioning of those components, in the chamber. The chamber may have a pre-determined volume. In one embodiment, the housing may be a rectangular cuboid. In one embodiment, the housing may be cylindrical with an outer diameter in a range of from about 5 centimeters to about 1 meter, and a length of from about 20 centimeters to about 10 meters. The housing may be elongated horizontally, or vertically. The orientation of the elongation may affect one or more processing parameters. For example and as discussed in further detail below, for a horizontal arrangement, a series of crucibles may be arranged in a series such that a stream of reactants flow over the crucibles one after another. In such an arrangement, the concentration and composition of the reactant stream may differ at the first crucible in the series relative to the last crucible in the series. Of course, such an issue may be addressed with such configuration changes as rearrangement of the crucibles, redirection of the reactant stream(s), multiple reactant stream inlets, and the like. 
     A liner may be disposed on the inner surface of the inner wall along the periphery of the chamber. Suitable liner material may include graphite, boron nitride, metal, or graphite coated with a material such as TaC, SiC or pyrolytic boron nitride. The liner and other inner surfaces may not be a source of undesirable contaminants. The liner may prevent or reduce material deposition on the inner surface of the inner wall. The liner may prevent or reduce etching of the walls of the housing by halides of getter metals. Failing the prevention of material deposition, the liner may be removable so as to allow the deposited material to be stripped from the inner wall during a cleaning process and/or replacement of the liner. In another embodiment, the housing may contain an outer wall and an inner wall, and the inner wall may comprise graphite, boron nitride, metal, or graphite coated with a material such as TaC, SiC or pyrolytic boron nitride and may possess one or more of the benefits described above for the liner. 
     Because the inner wall may be concentric to and spaced from the outer wall, the space may define a pathway between the inner wall and the outer wall for environmental control fluid to flow therethrough. Suitable environmental control fluids that may be used for circulation may include inert gases. Environmental control fluid may include gas, liquid or supercritical fluid. An environmental control inlet may extend through the outer wall to the space. A valve may block the environmental control fluid from flowing through the inlet and into the pathway to circulate between the inner and outer walls. In one embodiment, the inlet may be part of a circulation system, which may heat and/or cool the environmental control fluid and may provide a motive force for the fluid. The circulation system may communicate with, and respond to, the control system. Flanges, such as those meant for use in vacuum systems, may provide a leak proof connection for the inlet. 
     Suitable components of the housing may include, for example, one or more inlets (such as raw material inlets, gas inlets, carrier gas inlets, and dopant inlets), one or more outlets, filters, heating elements, cold walls, hot walls, pressure responsive structures, crucibles, baffles, and sensors. Some of the components may couple to one or more of the walls, and some may extend through the walls to communicate with the chamber, even while the housing is otherwise sealed. The inlets and the outlet may further include valves. 
     The inlets and the outlet may be made from one or more materials suitable for semiconductor manufacturing, such as electro-polished stainless steel materials, corrosion-resistant metal alloys (such as Hastelloy™), quartz, or refractory materials. The inlets and/or outlets may be welded or fused to the respective wall, or may be secured to the wall by one or more metal-to-metal, quartz-to-quartz, or metal-to-quartz seals. The inlets may extend into a hot zone in the chamber. Accordingly, the inlets may be composed of multiple materials wherein different materials are used in different regions of the reactor (or chamber). Different inlet materials may be chosen based on the temperature of the region and the chemical exposure. In one embodiment, a hot zone of the chamber may have inlets that comprise graphite, molybdenum, tungsten, or rhenium or one or more of an oxide, a nitride, or an oxynitride of silicon, aluminum, magnesium, boron, or zirconium. In a specific embodiment, the one or more inlets in a hot zone may comprise a non-oxide material, such as boron nitride, silicon carbide, tantalum carbide, or a carbon material such as graphite. Optionally, the inlets and/or outlets may include purifiers. In one embodiment, the purifier includes a getter material that does not become incorporated into the inlet gas stream, for example a zirconium alloy which may react with contaminants in the inlet gas stream to form non-volatile nitrides, oxides and carbides, thus reducing the probability of contamination in the final product. In one embodiment, the purifiers may be placed in the inlets at the entrance to the chamber. For reactions utilizing large quantities of ammonia the main concern for contamination may be the presence of water due to hygroscopic nature of ammonia. The contamination of ammonia drawn from an ammonia tank may increase exponentially as the ammonia tank empties and when 70 percent of ammonia is reached, the tank may be replaced. Alternatively, a point-of-use purifier may be utilized at the inlets. The use of a point-of-use purifier may help in controlling the contamination in ammonia thereby reducing ammonia wastage. Optionally, lower grade ammonia may be utilized along with the point-of-use purifier to obtain a grade of about 99.9999 percent. 
     The shape or structure of the one or more inlets and outlets may be modified to affect and control the flow of fluid therethrough. For example, an inner surface of the inlet/outlet may be rifled. The rifling may spin the gas flowing out through the ends and enhance mixing. In one embodiment, the inlets may be coupled together such that the reactants may pre-mix before they reach a reaction zone or a hot zone. Each of the inlets and outlets may have an inner surface that defines an aperture through which material can flow into, or out of, the chamber. Valve apertures may be adjustable from fully open to fully closed thereby allowing control of the fluid flow through the inlets and the outlets. 
     The inlet(s) may be configured to promote mixing of the nitrogen-containing gas and the halide-containing gas upstream of the crucible(s), so as to promote uniform process conditions throughout the volume of the chamber. One or more of the inlets may contain one or more of baffles, apertures, fits, and the like, in order to promote mixing. The apertures, frits, and baffles may be placed within the chamber proximate to the hot zone or crucibles so as to control the flow of gas in the chamber, which may prevent or minimize the formation of solid ammonium halide. The apertures, frits, and baffles may be placed upstream of the nearest crucible, with a distance of separation that is in a range from about 2 cm to about 100 cm, in order for mixing to be complete prior to the onset of reaction with the contents of the crucible. The presence of apertures and baffles may promote higher gas velocities that promote mixing and inhibit back-flow of gases, preventing or minimizing the formation of solid ammonium halide. Furthermore, the inlet(s) may be configured to extend into a hot zone or a reaction zone. 
     One or more crucibles may be placed within the chamber. In one embodiment, the number of crucibles within the chamber is about 6. Depending on the configuration of the chamber, the crucibles may be arranged horizontally and/or vertically within the chamber. The crucible shape and size may be pre-determined based on the end usage of the metal nitride, the raw material types, and the processing conditions. For the polycrystalline composition to be useful as a sputter target, the size of the crucible may be relatively larger than the required size of the sputter target. The excess of the polycrystalline composition may be removed, for example, through etching or cutting to form the sputter target article. Such removal may eliminate surface contamination resulting from contact with the crucible material. 
     The crucible may withstand temperatures in excess of the temperature required for crystalline composition formation while maintaining structural integrity, and chemical inertness. Such temperatures may be greater than about 200 degree Celsius, in a range of from about 200 degree Celsius to about 1300 degree Celsius, or greater than about 1300 degrees Celsius. Accordingly, refractory materials may be suitable for use in the crucible. In one embodiment, the crucible may include a refractory composition including an oxide, a nitride, or an oxynitride. The crucible may be formed from one or more of graphite, molybdenum, tungsten, or rhenium or from one or more of an oxide, a nitride, or an oxynitride of silicon, aluminum, magnesium, boron, or zirconium. In a specific embodiment, the crucible comprises a non-oxide material, such as boron nitride, silicon carbide, tantalum carbide, or a carbon material such as graphite. In one embodiment, a removable liner may be placed inside the crucible so as to facilitate easy removal of a raw material and/orpolycrystalline composition. The removable liner may be formed of graphite or boron nitride. In some embodiments, a getter is added to the crucible in the form of a foil or liner. In one specific embodiment, the getter foil or liner is chosen from at least one of zirconium, hathium, and tantalum. In another embodiment, the crucible composition comprises at least one getter. 
     A quantity of group III metal, comprising at least one of aluminum, gallium, and indium, may be placed in at least one crucible. The group III metal may be added in solid or liquid form. A getter, comprising at least one of the alkaline earth metals, boron, carbon, scandium, titanium, vanadium, chromium, yttrium, zirconium, niobium, the rare earth metals, hafnium, tantalum, and tungsten, may also be placed in the at least one crucible along with the group III metal. In another embodiment, a getter, comprising at least one of the alkaline earth metals, boron, carbon, scandium, titanium, vanadium, chromium, yttrium, zirconium, niobium, the rare earth metals, hafnium, tantalum, and tungsten, may be placed in one more separate crucibles that optionally do not contain a group III metal. The getter may be added at a level greater than 100 ppm, greater than 300 ppm, greater than 0.1%, greater than 0.3%, greater than 1%, greater than 3%, or greater than 10% by weight with respect to the group III metal within the chamber. The getter may be added in the form of a solid, including as a powder, grit, pellet, wire, or foil. The getter may be added in the form of a metal, a nitride, a halide, or a mixture or compound thereof. The getter may contain oxygen. In another embodiment, the group III metal, comprising at least one of aluminum, gallium, and indium, may be introduced into the chamber in a gaseous form, for example, in the form of a metal halide. 
     In one embodiment, at least one wetting agent is also added to the crucible, contacting the group III metal. As used herein, “wetting agent” refers to an element or a compound that facilitates the mixing of or a reaction between an otherwise immiscible liquid mixture at the interface of the two components. The wetting agent can be any metal that facilitates interfacial wetting of a binary liquid metal mixture and does not readily react to form covalent bonds with a Group III element. Any suitable and effective wetting agent compound can be employed. Suitable wetting agents include bismuth (Bi), lead (Pb), germanium (Ge), and tin (Sn). Other suitable wetting agents include antimony (Sb), tellurium (Te), and polonium (Po). The reaction mixture can also include a mixture of two or more wetting agents, in any proportion. The reaction mixture can include a wetting agent compound, such as organometallic compounds containing the wetting agent metal or inorganic compounds containing the wetting agent metal. Suitable wetting agent compounds include, e.g., halides, oxides, hydroxides, and nitrates. Many suitable and effective wetting agents and wetting agent compounds are disclosed, e.g., in Aldrich Handbook of Fine Chemicals, 2003-2004 (Milwaukee, Wis.). As used herein, bismuth, germanium, tin, and lead refer to elemental metals, alloys containing these metals, compounds containing these metals, and mixtures thereof. The Group III metal and the wetting agent can be present in a molar ratio of about 1:1 to about 500:1. Specifically, the Group III element and the wetting agent can be present in a molar ratio of about 2:1, about 5:1, about 20:1, about 100: 1, or about 200:1. 
     In certain embodiments, a group III metal is provided to the chamber in the form of a halide, for example, as one or more of GaCl 3 , GaCl, AlCl 3 , or InCl 3 . The group III metal halide may be generated by passing a halogen-containing gas, for example, hydrogen chloride or chlorine, over a crucible containing at least one group III metal and placed within a second chamber which is placed upstream of the chamber in which the polycrystalline group III metal nitride is synthesized. 
     One or more substrates or surfaces may be placed downstream of a crucible containing a group III metal or of an inlet from which a group III metal halide is provided, that is, between the group III metal source and the outlet of the chamber. The one or more substrates or surfaces may be formed from one or more of graphite, molybdenum, tungsten, or rhenium or from one or more of an oxide, a nitride, or an oxynitride of silicon, aluminum, magnesium, boron, or zirconium. In a specific embodiment, the one or more substrates or surfaces comprises a non-oxide material, such as boron nitride, silicon carbide, tantalum carbide, or a carbon material such as graphite. The substrates or surfaces may comprise flat disks, rods, tubes, cones, annular segments, conical sections, crucibles, or the like. The one or more substrates or surfaces may serve as a location for formation of a polycrystalline group III metal nitride. In one embodiment, the substrates or surfaces may further contain polycrystalline group III nitride which may serve as a location or seed for growth during the growth process, for example, in the form of a powder, a film, or adherent particles. 
     Suitable sensors may include one or more of pressure sensors, temperature sensors, and gas composition sensors. The sensors may be placed within the chamber, within the outlet(s), and/or within the inlet(s), and may communicate the process parameters in the chamber to the control system. 
     Suitable supply sources may include one or more of an energy source, a nitrogen-containing gas source, a carrier gas source, a getter gas source, a halide-containing gas source, a raw material source (sometimes referred to as a reservoir), a dopant gas source, environmental control fluid source, and the like. 
     The energy source may be located proximate to the housing and may supply energy, such as thermal energy, plasma energy, or ionizing energy to the chamber through the walls. The energy source may be present in addition to, or in place of, the heating elements disclosed above. In one embodiment, the energy source may extend along an outward facing surface of the outer wall of the housing. The energy source may provide energy to the chamber. In one embodiment, the energy source may be within the housing and supply energy, such as thermal energy, plasma energy, or ionizing energy to the crucible(s) and reaction region. The energy source may be present in addition to, or in place of, the heating elements disclosed above. In one embodiment, the energy source may extend above, below, or beside the crucible(s) and reaction region. The energy source may provide energy to the chamber. Multiple energy sources may be applied to supply energy. In one embodiment, the multiple energy sources may permit controllable heating of a crucible within the chamber to a particular temperature and heating of a reaction region to a different temperature. In one embodiment, two or more crucibles within the chamber may be heated to a different temperature. 
     The energy source may be a microwave energy source, a thermal energy source, a plasma source, or a laser source. In one embodiment, the thermal energy may be provided by a heater. Suitable heaters may include one or more molybdenum heaters, tube furnaces, split furnace heaters, three-zone split furnaces, graphite heaters, or induction heaters. 
     Sensors may be placed within the chamber. The sensors may be capable of withstanding high temperature and elevated or reduced pressure in the chamber and may be chemically inert. The sensors may be placed proximate to the crucible, and/or may be placed at the inlet(s), outlet(s), or another location within the housing. The sensors may monitor process conditions such as the temperature, pressure, gas composition and concentration within the chamber. 
     The nitrogen-containing gas source may communicate through a first inlet with the chamber. The nitrogen-containing gas source may include one or more filters, purifiers, or driers to purify and/or dry the nitrogen-containing gas. In one embodiment, the nitrogen-containing gas may be produced at the source. The purifier may be able to maintain purity levels of the nitrogen-containing gas up to or above semiconductor grade standards for purity. Suitable nitrogen-containing gases may include ammonia, diatomic nitrogen, and the like. Where the presence of carbon is not problematic, nitrogen-containing organics may be used. 
     Controlling the aperture of the associated valve allows control of the flow rate of the nitrogen-containing gas into the chamber. Unless otherwise specified, flow rate will refer to volumetric flow rate. Processing considerations, sample size, and the like may determine an appropriate flow rate of the gas. The flow rate of nitrogen-containing gas may be greater than about 10 (standard) cubic centimeters per minute. In one embodiment, the flow rate of nitrogen-containing gas may be in a range of from about 10 cubic centimeters per minute to about 100 cubic centimeters per minute, from about 100 cubic centimeters per minute to about 200 cubic centimeters per minute, from about 200 cubic centimeters per minute to about 500 cubic centimeters per minute, from about 500 cubic centimeters per minute to about 1200 cubic centimeters per minute, from about 1200 cubic centimeters per minute to about 2000 cubic centimeters per minute, from about 2000 cubic centimeters per minute to about 3000 cubic centimeters per minute, from about 3000 cubic centimeters per minute to about 4000 cubic centimeters per minute, from about 4000 cubic centimeters per minute to about 5000 cubic centimeters per minute, from about 5 standard liters per minute to about 10 standard liters per minute, from about 10 standard liters per minute to about 20 standard liters per minute, from about 20 standard liters per minute to about 50 standard liters per minute, or greater than about 50 standard liters per minute. In some embodiments, the flow of the nitrogen-containing gas in units of volume per second is chosen to be greater than 1.5 times the volume of the group III metal. In some embodiments, the flow of the nitrogen-containing gas is supplied at a gas flow velocity of at least 0.1 centimeters per second on the surface of the group III metal, at a reaction temperature of at least 700 degrees Celsius and no greater than 1300 degrees Celsius. In some embodiments, the flow of the nitrogen-containing gas is supplied at a gas flow velocity of at least 0.1 centimeters per second and combines with a gaseous source of the group III metal, for example GaCl, at a reaction temperature of at least 700 degrees Celsius and no greater than 1,300 degrees Celsius. 
     The carrier gas source may communicate with the chamber through an inlet, and/or may share the first inlet with the nitrogen-containing gas. Pre-mixing the nitrogen-containing gas with at least one carrier gas may dilute the nitrogen-containing gas to a determined level. Because the nitrogen-containing gas may be diluted with a carrier gas, which may be inert, the likelihood of formation of certain halide solids proximate to the first inlet in the chamber may be reduced. The dilution of the nitrogen-containing gas with a carrier gas may also serve to achieve a desired gas velocity through an inlet or an orifice or tube. Suitable carrier gases may include one or more of argon, helium, nitrogen, hydrogen, or other inert gases. In one embodiment, the carrier gas inlet is positioned so that a stream of carrier gas may impinge on a stream of nitrogen-containing gas exiting the first inlet. Dopants may be entrained in the carrier gas, in one embodiment, for inclusion in the polycrystalline composition. 
     A halide-containing gas source may communicate through a second inlet with the chamber. As with the nitrogen-containing gas source, the halide-containing gas source may include one or more filters, purifiers, driers, and the like, so that the halide-containing gas be purified and/or dried at the source. The halide-containing gas may be produced at the source. Suitable halide-containing gases may include hydrogen chloride, chlorine gas, and the like. In some embodiments, the halide-containing gas is omitted from the process. 
     Controlling the aperture of the associated valve allows control of the flow rate of the halide-containing gas into the chamber. Processing considerations, sample size, and the like, may determine an appropriate flow rate of the gas. The flow rate of halide-containing gas may be greater than about 10 (standard) cubic centimeters per minute. In one embodiment, the flow rate of halide-containing gas may be in a range of from about 10 cubic centimeters per minute to about 50 cubic centimeters per minute, from about 50 cubic centimeters per minute to about 100 cubic centimeters per minute, from about 100 cubic centimeters per minute to about 250 cubic centimeters per minute, from about 250 cubic centimeters per minute to about 500 cubic centimeters per minute, from about 500 cubic centimeters per minute to about 600 cubic centimeters per minute, from about 600 cubic centimeters per minute to about 750 cubic centimeters per minute, from about 750 cubic centimeters per minute to about 1000 cubic centimeters per minute, from about 1000 cubic centimeters per minute to about 1200 cubic centimeters per minute, or greater than about 1200 cubic centimeters per minute. 
     The halide-containing gas may flow into the chamber from the halide-containing gas source through a second inlet. As with the nitrogen-containing gas, the halide-containing gas may be pre-mixed with at least one carrier gas to dilute the halide-containing gas to a determined level. The dilution of the halide-containing gas with an inert, carrier gas may reduce the likelihood of formation of certain halide solids in the second inlet, proximate to the chamber. Such a formation might reduce or block the flow therethrough. The dilution of the halide-containing gas with an inert, carrier gas may also serve to achieve a desired gas velocity through a second inlet, orifice, or tube. Optionally, the carrier gas inlet may be positioned such that a stream of carrier gas may impinge on a stream of halide-containing gas exiting a second inlet or entering the chamber. In one embodiment, dopants may be entrained in the carrier gas for inclusion in the polycrystalline composition. 
     The halide-containing gas and the nitrogen-containing gas may be introduced into the chamber in a manner that determines properties of the polycrystalline composition. The manner may include simultaneous introduction at a full flow rate of each component fluid (gas, liquid, or supercritical fluid). Other suitable introduction manners may include pulsing one or more of the components, varying the concentration and/or flow rate of one or more components, or staggered introductions, for example, to purge the chamber with carrier gas. 
     The halide-containing gas and the nitrogen-containing gas inlets may be disposed such that the exit end is located in the hot zone in the chamber. In one embodiment, one or more inlets are located in a region of the chamber that, during use, has a temperature of greater than about 250 degree Celsius at 1 atmosphere, or a temperature in a range of from about 250 degree Celsius to about 370 degree Celsius, or greater than about 370 degrees Celsius. 
     The ratio of flow rate of the nitrogen-containing gas to the flow rate of the halide-containing gas may be adjusted to optimize the reaction. In one embodiment, the ratio of flow rate of the nitrogen-containing gas to the flow rate of halide-containing gas may be in a range of greater than 30:1, from about 30:1 to about 15:1, from about 15:1 to about 1:1, from about 1:1 to about 1:10, or from about 1:10 to about 1:15. 
     In certain embodiments, a getter is provided to the chamber in the vapor phase. In a specific embodiment, a metal is provided in an inlet for a halide-containing gas in a region that has an elevated temperature under operating conditions. In one embodiment, the metal may react with the halide-containing gas to form a volatile metal halide, which is transported into the chamber and contacts the group III metal. In another embodiment, the metal may reside in the chamber and react with a halide-containing gas to form a volatile metal halide, which is transported to another part of the chamber. In one embodiment, the metal halide is transported to the reaction zone where it combines with the nitrogen-containing gas and a halide-containing gas that contains a group III metal source. In another embodiment, the getter is provided directly as a compound, for example, as a halide or as a hydride. In certain embodiments, the chemical species formed by reaction of the getter with an undesired impurity, for example, oxygen, is volatile under operating conditions and is carried away out of the chamber. In a specific embodiment, the getter is selected from one of a hydrocarbon (C w H y , where w, y&gt;0), such as methane (CH 4 ) or acetylene (C 2 H 2 ), a halocarbon C w X z , where w, z&gt;0 and X =F, Cl, Br, or I), such as CCl 4 , a halohydrocarbon (C w H y X z , where w, y, z&gt;0 and X=F, Cl, Br, or I), such as chloroform (CHCl 3 ) or methylene chloride (CH 2 Cl 2 ), phosgene (COCl 2 ), thionyl chloride (SOCl 2 ), boron trichloride (BCl 3 ), diborane (B 2 H 6 ), and hydrogen sulfide (H 2 S). In certain embodiments, the chemical species formed by reaction of the getter with an undesired impurity, for example, oxygen, is non-volatile under operating conditions and remains at the mixing or contact point, which may be at a different region than the polycrystalline composition. 
     A raw material source may communicate through a raw material inlet and into the crucible, which is in the chamber. As with the other sources, a raw material source may include one or more filters, driers, and/or purifiers. Particularly with reference to a raw material source, purity of the supplied material may have a disproportionately large impact or effect on the properties of the final polycrystalline composition. A raw material may be produced just prior to use and may be kept in an inert environment to minimize or eliminate contamination associated with atmospheric contact. If, for example, hygroscopic materials are used, or materials that readily form oxides, then a raw material may be processed and/or stored such that the raw material does not contact moisture or oxygen. Further, because the raw material can be melted and flowed into the chamber during processing, in one embodiment, differing materials may be used in a continuous process than might be available for use relative to a batch process. At least some of such differences are disclosed herein below. 
     Suitable raw materials may include one or more of gallium, indium, or aluminum. In one embodiment, the raw material may have a purity of 99.9999 percent or greater. In another embodiment, the purity may be greater than about 99.99999 percent. The raw material may be a gas; a liquid solution, suspension or slurry; or a molten liquid. The residual oxygen in a raw material, particularly a metal, may further be reduced by heating under a reducing atmosphere, such as one containing hydrogen, or under vacuum. 
     In certain embodiments, one or more crucibles and/or raw materials are loaded into the chamber from a glove box, dry box, desiccator, or other inert atmosphere environment. In certain embodiments, a polycrystalline group III metal nitride is removed from the chamber following a synthesis run directly into a glove box, dry box, desiccator, or other inert atmosphere environment. For convenience, an inert atmosphere may generally be referred to as a glove box for the purposes of this document. 
     While all of the materials needed for production may be sealed in the chamber during operation in one embodiment; in another embodiment, various materials may be added during the process. For example, a raw material may flow through a raw material inlet, out of an exit end, and into a crucible within the chamber. Where there is a plurality of crucibles, multiple raw material inlets, or one inlet having multiple exit ends, may be used to flow raw material into individual crucibles. In one embodiment, a raw material inlet may be mounted on a linear motion feed-through structure. Such feed-through structures may allow the translation of the exit end of a raw material inlet from crucible to crucible. 
     The flow and the flow rate of raw material to, and through, a raw material inlet may be controlled by a valve. The valve may be responsive to control signals from the control system. While the flow rate of a raw material may be determined based on application specific parameters, suitable flow rates may be larger than about 0.1 kilogram per hour. In one embodiment, the flow rate may be in a range of from about 0.1 kilogram per hour to about 1 kilogram per hour, from about 1 kilogram per hour to about 5 kilograms per hour, or greater than about 5 kilograms per hour. 
     A dopant inlet may be in communication with a reservoir containing dopants and the chamber. The reservoir may be made of material compliant to semiconductor grade standards. The reservoir may have provisions to purify/dry the dopants. In one embodiment, the reservoir may have liners. The liners may prevent corrosion of the reservoir material, or reduce the likelihood of contamination of the dopants by the reservoir. 
     A dopant source may be separate, or may be co-located with one or more of the other materials being added during processing. If added separately, the dopants may flow directly into a crucible by exiting an end of the dopant inlet. As mentioned, the dopant may be introduced by pre-mixing with, for example, a raw material, a carrier gas, a halide-containing gas, or a nitrogen-containing gas. Metering of the dopant may control the dopant concentration levels in the polycrystalline composition. Similarly, the placement of the dopant in the polycrystalline composition may be obtained by, for example, pulsing, cycling, or timing the addition of the dopant. 
     Suitable dopants may include dopant precursors. For example, silicon may be introduced as SiCl 4  SiH 4 , or Si 2 H 6 , and germanium may be introduced as GeCl 4  or GeH 4 . Where carbon is a desired dopant, carbon may be introduced as a hydrocarbon, such as methane, methylene chloride, or carbon tetrachloride. Suitable dopants may include a halide or a hydride. In situations where carbon is a desired dopant, or an inconsequential contaminant, metals may be introduced as an organometallic compound. For example, magnesium may be introduced as Mg(C 5 H 5 ) 2 , zinc as Zn(CH 3 ) 2 , and iron as Fe(C 5 H 5 ) 2 . The flow rate of dopant precursors may be greater than about 10 (standard) cubic centimeters per minute. In one embodiment, the flow rate of the dopant precursors may be in a range of from about 10 cubic centimeters per minute to about 100 cubic centimeters per minute, from about 100 cubic centimeters per minute to about 500 cubic centimeters per minute, from about 500 cubic centimeters per minute to about 750 cubic centimeters per minute, from about 750 cubic centimeters per minute to about 1200 cubic centimeters per minute, or greater than about 1200 cubic centimeters per minute. Alternatively, the dopant may be added in elemental form, for example, as an alloy with the raw material or in a separate crucible. Other suitable dopants may comprise one or more of Si, O, Ge, Be, Mg, Zn, Sc, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Y, Zr, Mo, Sn, Ce, Pr, Nd, Pm, Sm, Eu, Dy, Er, Tm, Yb, or Hf. 
     The one or more outlets, and corresponding valves, may control the release of material that is inside of the chamber. The released material may be vented to atmosphere, or may be captured, for example, to recycle the material. The released material may be monitored for composition and/or temperature by an appropriate sensor mounted to the outlet. The sensor may signal information to the control system. Because contamination may be reduced by controlling the flow of material through the chamber in one direction, the polycrystalline composition may be removed from the chamber by an exit structure in the wall at the outlet side. 
     An outlet may be coupled to an evacuation system. The evacuation system may be capable of forming a low base pressure or a pressure differential in the chamber relative to the atmospheric pressure. Suitable base pressure may be lower than about 10 −7  millibar. In one embodiment, the base pressure may be in a range of from about 10 −7  millibar to about 10 −5  millibar, or greater than about 10 −5  millibar. In one embodiment, the pressure differential may be in a range of from about 760 Torr to about 50 Torr, 50 Torr to about 1 Torr, from about 1 Torr to about 10 −3  Ton, from about 10 −3  Ton to about 10 −5  Ton, or less than about 10 −5  Ton. The evacuation may be used for pre-cleaning, or may be used during processing. 
     An outlet may be heated to a temperature, which may be maintained, that is greater than the temperature where the vapor pressure of an ammonium halide that might be formed during processing is greater than the process pressure, for example, one bar. By maintaining a temperature above the sublimation point of ammonium halide at the reactor pressure, the ammonium halide might flow into a trap or may be precluded from forming or solidifying near the outlet once formed. 
     The control system may include a controller, a processor in communication with the controller, and a wired or wireless communication system that allows the controller to communicate with sensors, valves, sources, monitoring and evaluating equipment, and the like. 
     The sensors within the chamber may sense conditions within the chamber, such as the temperature, pressure, and/or gas concentration and composition, and may signal information to the controller. Flow rate monitors may signal information about the flow rate through the corresponding inlet or outlet to the controller. The controller (via the processor) may respond to the information received, and may control devices in response to the information and pre-determined instruction parameters. For example, the controller may signal the energy source to provide thermal energy to the chamber. The controller may signal one or more valves to open, close, or open to a determined flow level during the course of polycrystalline composition synthesis. The controller may be programmed to implement a method of growing polycrystalline compositions. 
     The resultant polycrystalline composition may be a group III metal nitride. The metal nitride may be doped to obtain one or more of an n-doped or a p-doped composition. The metal nitride may be a metallic, semiconducting, semi-insulating or insulating material. Further, each of these compositions may be a magnetic or a luminescent material. 
     The working of the apparatus and the function of the various components are described below with reference to illustrated embodiments. Referring to the drawings, the illustrations describe certain illustrative embodiments and do not limit the scope of the claims. 
     An apparatus  100  in accordance with an embodiment is shown in  FIG. 1 . The apparatus  100  may be used for preparing a metal nitride material, and may include a housing  102  having a wall  104 . The wall  104  may have an inner surface  106  that defines a chamber  108 . An energy source  110  may be located proximate to the wall  104 . A first inlet  112  and a second inlet  114  extend through the wall  104 . The inlets  112 ,  114  define apertures through which material can flow into, or out of, the chamber  108 . An outlet  118  extends through the wall  104  to the chamber  108 . A crucible  120  may be disposed in the chamber  108 . A liner (not shown) may line the inner surface  106  of the wall  104 . 
     The energy source  110  may be a thermal energy source, such as a ceramic heater. The inlets  112 ,  114  and the outlet  118  may be electro-polished stainless steel suitable for semiconductor grade manufacturing. In a specific embodiment, the crucible  120  may comprise boron nitride, and the liner may comprise graphite. 
     During operation, a group III metal raw material and a getter may be filled into the crucible  120 , and the crucible may be pre-loaded into the chamber. One or more dopants may be placed in the crucible with the raw material. After loading, the crucible  120  may be sealed by a sealing mechanism (not shown). 
     A nitrogen-containing gas may flow through the first inlet  112  into the chamber  108 . The nitrogen-containing gas may include ammonia, and may include a carrier gas for pre-dilution. A halide-containing gas may flow through the second inlet  114  and into the chamber  108 . The halide-containing gas may include hydrogen chloride and/or chlorine. The halide-containing gas may be pre-diluted with a carrier gas. Unreacted gases and/or other waste materials may be removed from the chamber  108  through the outlet  118 . The chamber  108  may be purged by flowing in gases through the inlets  112 ,  114  and out through the outlet  118  prior to crystalline composition formation. The outflow, optionally, may be monitored to detect the impurity level of the out-flowing gas, which may indicate when a sufficient purge has been achieved. 
     The energy source  110  may be activated. Activating the energy source  110  may increase the temperature within the chamber  108  to pre-determined level and at a pre-determined rate of temperature increase. An area, within the chamber  108  and proximate to the crucible  120 , may define a hot zone or reaction zone (not shown). 
     The raw material, already in the crucible  120 , may respond to contact with the nitrogen-containing gas in the presence of the halide-containing gas, and at the determined temperature, by reacting to form a nitride of the metal, that is, the polycrystalline composition. 
     We believe that the group III metal reacts with a hydrogen halide or halogen to form a volatile group III metal halide. The group III metal halide in turn reacts with the nitrogen-containing gas, for example, ammonia, to form a polycrystalline group III metal nitride. Under typical processing conditions, most of the group III metal may react to form a polycrystalline group III metal nitride and only a small fraction of the group III metal may be transported away from the crucible in the form of a group III metal halide. Under typical reaction conditions, some, most, or all of the getter may be dissolved in the liquid group III metal when the getter is placed within the same crucible as the group III metal. Many of the getters disclosed above are broadly miscible in liquid aluminum, gallium, and indium at temperatures above 500-1300 degrees Celsius. Even the refractory metals Zr, Hf, and Ta are soluble at a level above about 1-2% in gallium at 1300 degrees Celsius. The dissolved getter metal may become well mixed within the molten group III metal. The dissolved getter metal may react with dissolved oxygen within the molten group III metal, forming an oxide of the getter metal. Like the group III metal, the getter metal may form halides and/or nitrides. At temperatures of about 500 to 1300 degrees Celsius, the getter metal halides are relatively volatile and the getter metal nitrides, oxides, and oxynitrides are generally not volatile. In the case of some getters, for example, the alkaline earth metals and yttrium, the halides may be formed predominantly and most of the getter metal transported away from the crucible. During the reaction and transport process, however, the getter metal efficiently ties up or removes oxygen from the group III metal and from sources of oxygen in the gas phase, including O 2  and H 2 O. In the case of other getters, for example, Cr and Ta, the nitrides may be formed predominantly and most of the getter metal may remain in the crucible in the form of nitride, oxynitride, and oxide inclusions within the polycrystalline group III nitride for processes that involve exposure the of the group III metal crucible to a nitrogen-containing source. During the reaction and transport process, the getter metal efficiently ties up or removes oxygen from the group III metal and/or from sources of oxygen in the gas phase. 
     In some embodiments, including those not involving the addition of a hydrogen halide to the reaction, most or all of the getter may become incorporated into the polycrystalline group III nitride composition. 
     Referring to  FIG. 1 , after the polycrystalline composition has been formed, the housing  102  may be opened at an outlet side. Opening on the outlet side may localize any introduced contaminants to the chamber  108  caused by the opening to the chamber side proximate to the outlet  118 . Localizing the contaminants proximate to the outlet  118  may reduce the distance the contaminants must travel to purge from the chamber  108 , and may confine the path of the contaminants to regions in which the contaminants are less likely to contact any grown crystal, or crystalline composition growing surface (such as an inner surface of the crucible  120 ). In addition, not opening the housing on the inlet side may decrease the likelihood of a leak proximate to the inlet during a subsequent run. Thus, such a configuration may reduce the chance of contaminants contaminating the produced crystals. In another embodiment, the housing  102  may be opened on an inlet side of the chamber  108 . In certain embodiments, the housing  102  is connected to a glove box and may be opened without exposing chamber  108  to ambient air. 
     An apparatus  200  in accordance with an embodiment is shown in  FIG. 2 . The apparatus  200  may include a housing  202 , and an energy source  204  proximate to the housing  202 . The housing  202  may include an inner wall  206  and an outer wall  208 . An inlet  209  may extend through the outer wall  208 , but may stop short of the inner wall  206 . The outer wall  208  may have an outward facing surface. An inward facing surface or inner surface  212  of the inner wall  206  may define a chamber  214 . 
     The inner wall  206  may be nested within, and spaced from, the outer wall  208 . The space between the walls  206  and  208  may be used to circulate an environmental control fluid that may enter the space through the inlet  209  configured for that purpose. The outer wall  208  may be formed from metal or quartz, while the inner wall  206  may be made of quartz or from boron nitride. The energy source  204  may be proximate to the outer wall  208 . 
     A first inlet  216 , a second inlet  218 , a raw material inlet  224 , a dopant inlet  232 , and an outlet  226  may extend through the inner and outer walls  206  and  208 . An additional inlet for a vapor phase getter (not shown) may also extend through the inner and outer walls  206  and  208 . A plurality of valves  215 ,  220 ,  223 ,  233  may be disposed, one per tube, within the feed tubes that extend from sources to the corresponding inlets  216 ,  218 ,  224 , and  232 . The individual feed tubes are not identified with reference numbers. And, an outlet  226  may have a valve  227  that may allow or block the flow of fluid therethrough. 
     A first inlet  216  may communicate with a nitrogen-containing gas source  217  and flow a nitrogen-containing gas into the chamber  214 . The nitrogen-containing gas may include ammonia. The nitrogen-containing gas may be diluted with one or more carrier gases. The carrier gas may comprise argon, helium, hydrogen, or nitrogen, and may be controllable separately from the nitrogen-containing gas flow. A second inlet  218  may be in communication with a halide-containing gas source  219 . The second inlet  218  may allow a halide-containing gas to flow from the halide-containing gas source  219  into the chamber  214 . The valve  220  may control the flow of the halide-containing gas from the halide-containing gas source  219  through the second inlet  218  and into the chamber  214 . The halide-containing gas may include hydrogen chloride or chlorine, which may have been diluted with a carrier gas. The raw material inlet  224  may communicate with a raw material reservoir  222 . An exit end of the raw material inlet  224  may be positioned so as to flow raw material leaving the raw material inlet  224  into a crucible  230 . The valve  223  may control the flow of the raw material from the reservoir  222  through the raw material inlet  224  and into the chamber  214 . The raw material may include molten gallium. 
     A dopant source (not shown) may communicate with the chamber  214  through a dopant inlet  232 . A valve  233  may be switched on/off to open or block a flow of dopant from the dopant source into the chamber  214 . In the illustrated embodiment, the dopant may include silicon, which may be in the form of SiCl 4 , or germanium, which may be in the form of GeCl 4 . 
     An outlet  226  may allow for excess material to exit the chamber  214 . A valve  227  may open or close, and by closing, a back pressure might be built up as additional materials are flowed into the chamber  214  and the temperature is increased. 
     A plurality of crucibles  230  may be provided in the chamber  214 . The crucibles  230  may be arranged horizontally relative to each other and/or vertically. One or more sensors  236  and one or more sensors  237  may be provided to monitor the pressure and temperature, or other process parameters within the chamber  214 . 
     As disclosed hereinabove, the environmental control fluid may flow in the space between the walls through the inlet  209 . Inlet  209  may communicate with a circulation system (not shown) to circulate the fluid in the space between the walls. Inlet  209  may include a valve  211  to adjust or optimize the circulation in the space between the walls. Flanges  210  meant for vacuum systems may be used to form a leak proof connection. The fluid circulation system may have provisions to heat or cool the fluid. Chamber  214 , along with its contents, may be cooled or heated through this arrangement. 
     A control system may include a controller  234  that may communicate with the various components as indicated by the communication lines. Through the lines, the controller  234  may receive information, such as signals, from sensors  236 ,  237 . The controller  234  may signal to one or more of the valves  215 ,  220 ,  223 ,  227 ,  233 , which may respond by opening or closing. The valve  211  may communicate with the controller  234 , and through which the controller  234  may control the flow of the environmental control fluid from the circulation system. Thus, the controller  234  may monitor and may control the overall reaction conditions. 
     Prior to operation, the chamber  214  may be evacuated. The controller  234  may activate a valve  227  and a vacuum pump (not shown) to evacuate the chamber  214 . The chamber  214  may be flushed with a gas, including an inert gas or a gas such as hydrogen which may be used to remove one or more contaminants from the chamber  214 . The energy source  204  may be activated to heat, and thereby volatilize, any volatile contaminants. The successive evacuation and purging may remove the contaminants from the chamber  214 . 
     During operation, the controller may activate a valve  223  to start a flow of raw material from a reservoir  222  to the crucibles  230  through a raw material inlet  224 . A dopant may be flowed into the crucible through a dopant inlet  232  in response to the opening of the corresponding valve  233 . The controller may adjust the rates of flow of materials by adjusting the degree to which the corresponding valves are open or closed. The controller  234  may communicate with the sensors  236 ,  237 . The temperature and pressure within the chamber may be raised to determined levels by the controller  234  activating the energy source  204 , and/or adjusting an outlet valve  227 . 
     Once the desired temperature and pressure has been attained, a nitrogen-containing gas may be introduced in the chamber  214  through a first inlet  216 . Alternatively, a nitrogen-containing gas may be introduced in the chamber in the beginning or at any point during the heating cycle. A halide-containing gas may be flowed in through a second inlet  218 . The controller may adjust the flow rate of these gases by controlling the respective valves  215 ,  220 . 
     The raw material including the dopants may react with the nitrogen-containing gas in the presence of the halide-containing gas. The reaction may proceed until the raw material reacts to form the metal nitride. In the illustrated embodiment, a silicon doped gallium nitride may be formed. 
       FIG. 3  is a schematic view of an apparatus  300  detailing the inlets in accordance with an embodiment. The apparatus  300  may include a housing  302  having a wall  304 , the wall  304  may have an inner surface  306  and an outward facing surface  308 , as illustrated in the figure. The wall  304  may be radially spaced from an axis  309 . An energy source  310  may be provided proximate to the outer surface. The inner surface  306  of the wall  304  may define a chamber  312 . 
     The apparatus  300  may further include inlets  316  and  318 . The inlet  316 , in one embodiment, may be a single walled tube, and extends into the chamber  312  through the wall  304 . The inlet  316  may be nested within, and spaced from the inner surface  306  of the wall  304 . An exit end of the inlet  316  may define an aperture  322 . A baffle  324  may adjoin the aperture  322 . The spacing between the inlet  316  and the inner surface  306  of the wall  304  may define the inlet  318 . Further, an aperture or opening  326  may be provided in the inlet  318 . A crucible  330  may be disposed within the chamber  312 . 
     A halide-containing gas may be introduced into the chamber  312  from a source (not shown) through the inlet  316 , and a nitrogen-containing gas may be introduced into the chamber  312  from a source (not shown) through the inlet  318 . The inlets  316  and  318  may be configured such that the baffle  324  provided in the inlet  316  may assist in proper mixing of the gases flowing in to the chamber  312  through the inlets. 
     The apparatus  300  may further include components not shown in the figure such as, a control system including a controller which may control the overall reaction, valves for adjusting and/or controlling the flow of materials to and/or from the chamber, inlets for introducing raw materials, getters, and/or dopants into the chamber, sources from where raw materials, getters, and/or dopants may be flowed into the chamber, sensors for monitoring the temperature, pressure and composition within the chamber, and the like. The working of the apparatus may be explained with reference to above described embodiments. 
       FIG. 4  is a flow chart depicting a method for preparing a polycrystalline group III metal nitride in accordance with an embodiment according to the present disclosure. The method starts by providing a group III metal (see step  402 ) and a getter in a crucible (see step  404 ). The crucible containing the group III metal and the getter are then loaded into a chamber or reactor and the chamber is sealed (see step  406 ). The chamber is then evacuated, purged, and otherwise decontaminated to remove trace impurities. The chamber may be evacuated, purged, and otherwise decontaminated prior to or after loading the group III metal and the getter inside (see step  408 ). The environment in the chamber is adjusted to determined levels. The temperature of the chamber may be maintained between about 800 degree Celsius to about 1300 degree Celsius, and the pressure within the chamber may be equal to or greater than about ambient. 
     Dopants may be introduced in the chamber. The dopant may be introduced as a dopant precursor. The dopant precursor may be flowed into the chamber from a dopant source. 
     The temperature within the chamber may be raised to between about 800 degrees Celsius to about 1300 degrees Celsius (see step  412 ), and the pressure may be raised within at least one dimension greater than about 1 meter, for a period greater than about 30 minutes. Next, a nitrogen-containing gas such as ammonia may be introduced in the chamber (see step  410 ). The gas may be flowed from a nitrogen-containing gas source through an inlet into the chamber. The flow rate of the nitrogen-containing gas may be greater than about 250 (standard) cubic centimeters per minute. 
     A halide-containing gas may be introduced into the chamber (see step  414 ). Optionally, the order of the preceding steps may be interchanged. The flow rate of the halide-containing gas may be greater than about 25 cubic centimeters per minute. The ratio of the flow rate of the nitrogen-containing gas to the flow rate of the halide-containing gas may be about 10:1. 
     The group III metal may react with the nitrogen-containing gas in the presence of the halide to form a polycrystalline group III metal nitride from which most residual oxygen has been removed or sequestered by gettering (see step  416 ). The halide affects the reaction between the metal and the nitrogen-containing gas in a determined manner. The getter reacts with oxygen to form a getter metal oxide, oxynitride, or oxyhalide, and additionally with the nitrogen-containing gas to form getter metal nitride and with the hydrogen halide to form getter metal halide. 
     The reaction may proceed through a vapor transport and/or a wicking effect. The metal nitride crust may form on top of the molten metal within the crucible. The crust may be slightly porous. The metal may be vapor transported or, if liquid, wicked to the top of the crust through the pores and react with the nitrogen-containing gas. The reaction may deposit additional metal nitride and add to the crust. The reaction proceeds until virtually all the metal has undergone reaction. Additional metal may be flowed into the chamber from the reservoir. 
     The chamber may be cooled, see  FIG. 5 , as an example (see step  502 ). The excess nitrogen-containing gas and hydrogen halide flows out from the reaction zone and ammonium halide may condense on cooler regions of the chamber or outlet. In one embodiment, the chamber and an outlet may be kept hot so as to facilitate downstream trapping of ammonium halide; or alternatively a cold wall section may be incorporated to facilitate condensation of the ammonium halide. In one embodiment, the chamber may be opened on the outlet side to minimize leakage through the inlet side. The polycrystalline group III metal nitride may be removed through the outlet side (see step  504 ). 
     Optionally, the polycrystalline group III metal nitride formed may be further processed. In one embodiment, at least one surface of the polycrystalline group III metal nitride may be subjected to one or more of scraping, scouring or scarifying. The surface may be further subjected to oxidation in air or in dry oxygen and it may further be boiled in perchloric acid. The residual contamination resulting from the post-processing step may be removed by washing, sonicating, or both. Washing and sonicating may be performed in, for example, organic solvents, acids, bases, oxidizers (such as hydrogen peroxide), and the like. The polycrystalline group III metal nitride may be annealed in an inert, nitriding, or reducing atmosphere. The annealing may also be performed in pure ammonia at a temperature of about 800 degree Celsius to about 1300 degree Celsius for a period of time in a range of from about 30 minutes to about 200 hours. 
     Other processing may be performed for use as a source material for crystalline composition growth. For use as a source material, the polycrystalline group III metal nitride may be pulverized into particulate. The particles may have an average diameter in a range of from about 0.3 millimeters to about 10 millimeters. The pulverizing may be carried out through, for example, compressive fracture, jaw crushing, wire sawing, ball milling, jet milling, laser cutting, or cryo-fracturing. Post pulverization cleaning operations may remove adventitious metal introduced by the pulverization operation, un-reacted metal, and undesirable metal oxide. 
     In some embodiments, the polycrystalline group III metal nitride is used as a source material for ammonothermal growth of at least one group III metal nitride single crystal. The polycrystalline group III metal nitride is placed in an autoclave or a capsule, as described in U.S. Pat. No. 6,656,615, U.S. Patent No. 7,125,453, and U.S. Pat. No. 7,078,731 and in U.S. Patent Application Publication No. 2009/0301388 (see step  506 ). Ammonia and a mineralizer, for example, at least one of an alkali metal, amide, nitride, or azide, an alkaline earth metal, amide, nitride, or azide, ammonium fluoride, ammonium chloride, ammonium bromide, ammonium iodide, a group III metal fluoride, a group III metal chloride, a group III metal bromide, a group III metal iodide, or a reaction product between a group III metal, ammonia, HF, HBr, HI, and HCl are also placed in the autoclave or capsule (see step  508 ). 
     In some embodiments a getter is also placed in the autoclave or capsule. The added getter may be provided in addition to a getter composition that may be present in the polycrystalline group III nitride. The added getter may comprise at least one of alkaline earth metals, Sc, Ti, V, Cr, Y, Zr, Nb, Hf, Ta, W, rare earth metals, and their nitrides, halides, oxynitrides, oxyhalides, amides, imides, and azides. In one specific embodiment, at least a portion of the getter is added in the form of a metal and at least a portion of the mineralizer is added as an azide in such a ratio that the hydrogen generated by reaction of the getter metal with ammonia and the nitrogen generated by decomposition of the azide are present in a ratio of approximately 3:1, as described in U.S. Pat. No. 8,323,405. The added getter may be useful for removing unintentional impurities, for example, oxygen, that are present in the mineralizer or other raw material. In one set of embodiments, the mineralizer comprises an alkali metal and the getter comprises a nitride, imide, or amide of Be, Mg, Ca, Sr, Ba, Sc, Y, a rare earth metal, Ti, Zr, Hf, V, Nb, Ta, Cr, Mo, or W. In another set of embodiments, the mineralizer comprises Cl and the getter comprises a nitride, chloride, oxynitride, or oxychloride of Sc, Ti, Cr, Zr, Nb, a rare earth metal, Hf, Ta, or W. In still another set of embodiments, the mineralizer comprises F and the getter comprises a nitride, fluoride, oxynitride, or oxyfluoride of Ti, V, Cr, Zr, Nb, Hf, Ta, or W. In another set of embodiments, the mineralizer comprises Br and the getter comprises a nitride, bromide, oxynitride, or oxybromide of Sc, Ti, Cr, Y, Zr, Nb, a rare earth metal, Hf, Ta, or W. In another set of embodiments, the mineralizer comprises I and the getter comprises a nitride, iodide, oxynitride, or oxyiodide of Sc, Ti, Cr, Y, Zr, Nb, a rare earth metal, Hf, Ta, or W. 
     After all the raw materials have been added to the autoclave or capsule, the autoclave or capsule is sealed. 
     The capsule, if employed, is then placed within a suitable high pressure apparatus. In one embodiment, the high pressure apparatus comprises an autoclave, as described by U.S. Pat. No. 7,335,262. In another embodiment, the high pressure apparatus is an internally heated high pressure apparatus, as described in U.S. Pat. No. 7,125,453, U.S. Pat. No. 8,097,081, and in U.S. Application Publication No. 2006/0177362A1. The polycrystalline group III metal nitride is then processed in supercritical ammonia at a temperature greater than about 400 degrees Celsius and a pressure greater than about 0.02 gigaPascal (GPa), during which at least a portion of the polycrystalline group III metal nitride is etched away and recrystallized onto at least one group III nitride crystal with a wurtzite structure (see step  510 ). In some embodiments, the polycrystalline group III metal nitride is processed in supercritical ammonia at a temperature greater than about 500 degrees Celsius, greater than about 550 degrees Celsius, greater than about 600 degrees Celsius, greater than about 650 degrees Celsius, greater than about 700 degrees Celsius, or greater than about 750 degrees Celsius. In some embodiments, the polycrystalline group III metal nitride is processed in supercritical ammonia at a pressure greater than about 0.02 GPa, greater than about 0.05 GPa, greater than about 0.1 GPa, greater than about 0.2 GPa, greater than about 0.3 GPa, greater than about 0.4 GPa, greater than about 0.5 GPa, greater than about 0.6 GPa, greater than about 0.7 GPa, or greater than about 0.8 GPa. 
     Residual getter in the polycrystalline group III metal nitride is released into solution gradually, as the polycrystalline group III metal nitride is etched. Once in solution, the getter may react to form a getter metal nitride, amide, or halide. The getter may also be chemically bound to oxygen. The getter may remove residual oxygen in the supercritical ammonia solution, enabling growth of group III nitride single crystals with improved purity. 
     In some embodiments, the added getter is annealed and/or coarsened prior to substantial ammonothermal growth of a group III metal nitride. In some embodiments, the getter may be added as a fine powder or may form a fine powder during heating in ammonia with a mineralizer present, which may undergo undesirable convection throughout the crystal growth environment and/or become incorporated into a crystalline group III metal nitride as an inclusion. The getter may be consolidated by holding at a temperature lower than that at which significant group III metal nitride crystal growth occurs, for example, between about 200 degrees Celsius and about 500 degrees Celsius, for a period of time between about 10 minutes and about 48 hours. 
     The ammonothermally-grown crystalline group III metal nitride may be characterized by a wurtzite structure substantially free from any cubic entities and have an optical absorption coefficient of about 2 cm −1  and less at wavelengths between about 405 nanometers and about 750 nanometers. An ammonothermally-grown gallium nitride crystal may comprise a crystalline substrate member having a length greater than about 5 millimeters, have a wurtzite structure and be substantially free of other crystal structures, the other structures being less than about 0.1% in volume in reference to the substantially wurtzite structure, an impurity concentration greater than 10 14  cm −1 , greater than 10 15  cm −1 , or greater than 10 16  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. The ammonothermally-grown gallium nitride crystal may be semi-insulating, with a resistivity greater than 10 7  Ω-cm. The ammonothermally-grown gallium nitride crystal may be an n-type semiconductor, with a carrier concentration n between about 10 16  cm −3  and 10 20  cm −3  and a carrier mobility η, in units of centimeters squared per volt-second, such that the logarithm to the base 10 of η is greater than about −0.018557 n 3 +1.0671 n 2 −20.599 n+135.49. The ammonothermally-grown gallium nitride crystal may be a p-type semiconductor, with a carrier concentration n between about 10 16  cm −3  and 10 20  cm −3  and a carrier mobility η, in units of centimeters squared per volt-second, such that the logarithm to the base 10 of η is greater than about −0.6546 n+12.809. 
     By growing for a suitable period of time, the ammonothermally-grown crystalline group III metal nitride may have a thickness of greater than about 1 millimeter and a length, or diameter, greater than about 20 millimeters. In a specific embodiment, the length is greater than about 50 millimeters or greater than about 100 millimeters. The crystalline group III nitride may be characterized by crystallographic radius of curvature of greater than 1 meter, greater than 10 meters, greater than 100 meters, greater than 1000 meter, or be greater than can be readily measured (infinite). After growth, the ammonothermally-grown crystalline group III metal nitride may be sliced, lapped, polished, and chemical-mechanically polished according to methods that are known in the art to form one or more wafers or crystalline substrate members. In a specific embodiment, the root-mean-square surface roughness of the at least one wafer or crystalline substrate member is less than about one nanometer, for example, as measured by atomic force microscopy over an area of at least about 10 micrometers by 10 micrometers. 
     In another embodiment, the polycrystalline group III metal nitride is used as a source material for flux growth of at least one group III metal nitride single crystal, as described in U.S. Pat. 7,063,741 and in U.S. Patent Application 2006/0037529. The polycrystalline group III metal nitride and at least one flux are placed in a crucible and inserted into a furnace. The furnace is heated and the polycrystalline group III metal nitride is processed in a molten flux at a temperature greater than about 400 degrees Celsius and a pressure greater than about one atmosphere, during which at least a portion of the polycrystalline group III metal nitride is etched away and recrystallized onto at least one group III nitride crystal. Residual getter in the polycrystalline group III metal nitride is released into solution gradually, as the polycrystalline group III metal nitride is etched. Once in solution, the getter may react to form a getter metal nitride, amide, or halide. The getter may also be chemically bound to oxygen. The getter may remove residual oxygen in the molten flux, enabling growth of group III nitride single crystals with improved purity. 
       FIG. 6  depicts a block diagram of a system to perform certain operations within the context of the architecture and functionality of the embodiments described herein. Of course, however, the system  600  or any operation therein may be carried out in any desired environment. As shown, an operation can be implemented in whole or in part using program instructions accessible by a module. The modules are connected to a communication path  605 , and any operation can communicate with other operations over communication path  605 . The modules of the system can, individually or in combination, perform method operations within system  600 . Any operations performed within system  600  may be performed in any order unless as may be specified in the claims. The embodiment of  FIG. 6  implements a portion of a computer or control system, shown as system  600 , comprising modules for accessing memory to hold program code instructions to perform: providing a gallium-containing group III metal or a gallium-containing group III metal halide into a chamber, the gallium-containing group III metal or metal halide comprising at least one metal selected from at least aluminum, gallium, and indium (see module  620 ); providing a getter at a level of at least 100 ppm with respect to the gallium-containing group III metal into the chamber such that the getter contacts the gallium-containing group III metal or the gallium-containing group III metal halide (see module  630 ); transferring a nitrogen-containing material into the chamber (see module  640 ); heating the chamber to a determined temperature (see module  650 ); pressurizing the chamber to a determined pressure (see module  660 ); processing the nitrogen-containing material with the gallium-containing group III metal or metal halide in the chamber (see module  670 ); and forming a polycrystalline gallium-containing group III metal nitride material (see module  680 ). 
     While the above is a full description of the specific embodiments, various modifications, alternative constructions and equivalents may be used. Therefore, the above description and illustrations should not be taken as limiting the scope of the present disclosure which is defined by the appended claims.