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Matched Legal Cases: ['Application No. 2', 'Application No. 02821230', 'Application No. 02802023', 'Application No. 02801950', 'Application No. 02821231', 'Application No. 02802023', 'Application No. 200580040008', 'Application No. 200580040008', 'Application No. 02', 'application No. 03778841', 'application No. 03733682', 'Application No. 02775396', 'Application No. 2004', 'Application No. 2004', 'Application No. 2004', 'Application No. 2004', 'Application No. 2003', 'Application No. 2003', 'Application No. 2003', 'Application No. 2003', 'Application No. 2004', 'Application No. 02788783']

Patent US7811380 - Process for obtaining bulk mono-crystalline gallium-containing nitride - Google PatenteSuche Bilder Maps Play YouTube News Gmail Drive Mehr » Erweiterte Patentsuche | Webprotokoll | Anmelden Erweiterte Patentsuche PatenteA process for obtaining bulk mono-crystalline gallium-containing nitride, liminating impurities from the obtained crystal and manufacturing substrates made of bulk mono-crystalline gallium-containing nitride has been now proposed. According to the invention, the process for obtaining of mono-crystalline...http://www.google.de/patents/US7811380?utm_source=gb-gplus-sharePatent US7811380 - Process for obtaining bulk mono-crystalline gallium-containing nitride Ver�ffentlichungsnummerUS7811380 B2PublikationstypErteilung Anmeldenummer10/537,804 Ver�ffentlichungsdatum12. Okt. 2010Eingetragen11. Dez. 2003 Priorit�tsdatum11. Dez. 2002Auch ver�ffentlicht unterEP1590509A1US20060037530WO2004053206A1WO2004053206A9 ErfinderRobert DwilinskiRoman DoradzinskiJerzy GarczynskiLeszek SierzputowskiYasuo KanbaraUrspr�nglich Bevollm�chtigterAmmono Sp. Z O.O.Nichia CorporationAmmono. Sp. Z.O.O. US-Klassifikation117/11117/68117/74117/81117/83117/73117/78117/77117/952117/76Internationale KlassifikationC30B11/04C30B9/00 UnternehmensklassifikationC30B29/403C30B7/005C30B7/00C30B29/406 Europ�ische KlassifikationC30B29/40BC30B29/40B2C30B7/00ReferenzenPatentzitate (99)Nichtpatentzitate (139)Externe LinksUSPTO USPTO-Zuordnung EspacenetProcess for obtaining bulk mono-crystalline gallium-containing nitrideUS 7811380 B2 Zusammenfassung A process for obtaining bulk mono-crystalline gallium-containing nitride, liminating impurities from the obtained crystal and manufacturing substrates made of bulk mono-crystalline gallium-containing nitride has been now proposed. According to the invention, the process for obtaining of mono-crystalline gallium-containing nitride from the gallium-containing feedstock in a supercritical ammonia-containing solvent with mineralizer addition is characterized in that the feedstock is in the form of metallic gallium and the mineralizer is in the form of elements of Group I and/or their mixtures, and/or their compounds, especially those containing nitrogen and/or hydrogen, whereas the ammonia-containing solvent is in the form of the mineralizer and ammonia, there are two temperature zones in each step of the process, and the feedstock is placed in the dissolution zone, and at least one mono-crystalline seed is deposited in the crystallization zone, and following the transition of the solvent to the supercritical state, the process comprises the first step of transition of the feedstock from the metallic form to the polycrystalline gallium-containing nitride, and the second step of crystallization of the gallium-containing nitride through gradual dissolution of the feedstock and selective crystallization of gallium-containing nitride on at least one mono-crystalline seed at the temperature higher than that of the dissolution of the feedstock, while all the vital components of the reaction system (including the feedstock, seeds and mineralizer) invariably remain within the system throughout the whole process, and consequently bulk mono-crystalline gallium-containing nitride is obtained. The invention relates also the the post-treatment (slicing, annealing and washing) of the thus obtained crystals.
4. The process according to claim 1, wherein a temperature ramping in the dissolution zone to begin the forming of the polycrystalline gallium-containing nitride feedstock is higher than 0.1 0� C./min, and a temperature in the dissolution zone is subsequently maintained higher than 350� C. during the forming of the polycrystalline gallium-containing nitride feedstock.
16. A process for reducing a level of impurities in a bulk mono-crystalline gallium-containing nitride obtained by the process according to claim 1, wherein the obtained bulk mono-crystalline gallium-containing nitride is subjected to annealing in an atmosphere of inert gas at a temperature between 600� C. and 1050� C.
Opto-electronic devices based on Group XIII element nitrides, such as AlN, GaN, are usually manufactured on sapphire or silicon-carbide substrates that differ from the deposited nitride layers (the so-called heteroepitaxy). In the most often used Metallo-Organic Chemical Vapor Deposition (MOCVD) method, the deposition of GaN is performed from ammonia and metallo-organic compounds in a gaseous phase, while the attained growth rates make it impossible to afford bulk layer. The application of a buffer layer reduces the dislocation density, but not more than to approx. 108/cm2. Another method was proposed for obtaining bulk mono-crystalline gallium nitride. It consists in an epitaxial deposition employing halides in a gaseous phase (Halide Vapor Phase Epitaxy�HVPE) [�Optical patterning of GaN films� M. K. Kelly, O. Ambacher, Appl. Phys. Lett. 69 (12) (1996) and �Fabrication of thin-film InGaN light-emitting diode membranes� W. S. Wrong, T. Sands, Appl. Phys. Lett. 75 (10) (1999)]. This method enables preparation of GaN substrates of a 2-inch diameter. However, their quality is not sufficient for laser diodes, because the dislocation density continues to be approx. 107 to approx. 109/cm2. Recently, the method of lateral epitaxial growth (ELOG) has been used for the reduction of a dislocation density. In this method the GaN layer is first grown on sapphire substrate and then a layer of SiO2 is deposited on it in the form of strips or grids. On the thus prepared substrate, in turn, the lateral growth of GaN, leading to a dislocation density lowering to approx. 107/cm2, may be carried out. The growth of bulk crystals of gallium nitride and other metals of Group XIII (IUPAC, 1989) is extremely difficult. Standard methods of crystallization from melt and sublimation methods are not applicable because of the decomposition of the nitrides into metals and N2.
In the HNP method [�Prospects for high-pressure crystal growth of III-V nitrides� S. Porowski et al., Inst. Phys. Conf. Series, 137, 369 (1998)] this decomposition is inhibited by the use of nitrogen under the high pressure. The growth of crystals is carried out in molten gallium, i.e. in the liquid phase, resulting in the production of GaN platelets of approx. 10 mm in size. Sufficient solubility of nitrogen in gallium requires temperature of approx. 1500� C. and pressure of 1500 MPa.
In another known method, the supercritical ammonia was proposed to lower the temperature and decrease the pressure during the growth process. It was shown in particular that it is possible to obtain the crystalline gallium nitride by a synthesis from gallium and ammonia, provided that the latter contains Group I element amides (KNH2 or LiNH2). The processes were conducted at temperature of up to 550� C. and under the pressure of 500 MPa, yielding crystals about 5 μm in size [�AMMONO method of BN, AlN, and GaN synthesis and crystal growth� R. Dwiliniski et al., Proc. EGW-3, Warsaw, Jun. 22-24, 1998, MRS Internet Journal of Nitride Semiconductor Research, http://nsr.mij.mrs.org/3/25].
The use of supercritical ammonia also enables the re-crystallization of gallium nitride from the feedstock consisting of fine-crystalline GaN [�Crystal Growth of gallium nitride in supercritical ammonia� J. W. Kolis et al., J. Cryst. Growth 222, 431-434 (2001)]. The re-crystallization was made possible by an introduction of amide (KNH2) into the supercritical ammonia, along with a small amount of halide (KI). Processes conducted at 400� C. and under the pressure of 340 MPa gave GaN crystals about 0.5 mm in size. However, no chemical transport processes, and in particular no growth on the seeds, were observed in the supercritical solution.
The ammonobasic method for preparing gallium-containing nitride crystals has recently been disclosed in WO 02/101120. The method allows production of gallium-containing nitride mono-crystals crystallized on at least one crystallization seed in the presence of a Group I element-containing compound (Group numbering according to the IUPAC convention of 1989 throughout this application) in a supercritical ammonia-containing solution. As feedstock for growth of desired crystals, gallium-containing nitrides are used. The thus obtained gallium-containing nitride bulk mono-crystals have surface dislocation density lower than surface dislocation density of seeds used in the process. The bulk mono-crystals have sufficient size and regular shape enhancing industrial use of the crystals�among others�as substrates for epitaxy in opto-electronic devices. The major advantage of the discussed method is that it has enabled to lower dislocation density in the thus grown GaN mono-crystalline layers to less than 106/cm2. Besides, the bulk nitride mono-crystals obtained by that method have high electrical resistivity (in the case of GaN single crystals within a range of several Ω�cm) and high crystalline quality, as demonstrated by a low value of FWHM of the X-ray rocking curve from (0002) plane�less then 60 arcsec for a Cu K α1 beam.
According to the invention, the temperature ramping in the dissolution zone at the beginning of the first step is higher than 0.1� C./min, and then the temperature in the first step in the dissolution zone is maintained higher than 350� C., preferably higher than 400� C.
Preferably, in the process according to the invention, the temperature in the first step in the crystallization zone is not higher than 500� C., preferably not higher than 400� C., most preferably not higher than 300� C.
The temperature ramping in the crystallization zone at the beginning of the second step is higher than 0.5� C./min, and after supersaturation of the supercritical solvent with respect to soluble forms of gallium is obtained in the crystallization zone, the temperature in the crystallization zone is maintained at a fixed level.
Preferably, the temperature in the second step in the crystallization zone is not lower than 350� C., preferably not lower than 400� C., most preferably ranges between 500� C. and 550� C.
The process for reducing the level of impurities in bulk mono-crystalline gallium-containing nitride obtained by a method according to the invention is characterized in that the thus obtained bulk mono-crystalline gallium-containing nitride is subjected to annealing in the atmosphere of inert gas, possibly with an addition of oxygen, at temperature between approx. 600 and 1050� C., thus producing material with higher crystalline quality than before the annealing.
FIG. 3 presents the dependence of solubility of GaN in the supercritical ammonia containing potassium amide (with KNH2:NH3=0.07) on pressure at temperature T=400� C. and T=500� C.
Gallium-containing nitride means a nitride of gallium and optionally other element(s) of Group XIII. It includes, but is not restricted to, the binary compound�GaN, a ternary compound �AlGaN, InGaN or a quaternary compound AlInGaN, preferably containing a substantial portion of gallium, anyhow at the level higher than dopant content. The composition of other elements with respect to gallium may be modified in its structure insofar as it does not collide with the ammono-basic nature of the crystallization technique. (The mentioned formulas are only intended to give the components of the nitrides. They are not intended to indicate their relative amounts.)
Bulk mono-crystal of gallium-containing nitride means a mono-crystal�especially for use as a substrate for epitaxy�made of gallium-containing nitride, to be used in the process for manufacturing various opto-electronic devices such as LED or LD, which can be formed by epitaxial methods, such as MOCVD and HVPE, wherein the thickness of the mono-crystal is preferably at least 1 mm, more preferably at least 3 mm.
Supercritical ammonia-containing solvent is a supercritical solvent consisting at least of ammonia, which contains one or more types of ions of Group I elements, used for dissolution of gallium-containing feedstock. The supercritical ammonia-containing solvent may also contain derivatives of ammonia and/or their mixtures, in particular�hydrazine.
Negative temperature coefficient of solubility (negative TCS) means that solubility is decreasing with temperature while all the other parameters are constant. Whereas a positive pressure coefficient of solubility (positive PCS) means that solubility is increasing with pressure while all the other parameters are constant. Our research allow to state that solubility of gallium-containing nitride in the supercritical ammonia-containing solvent, at least in the temperature range from 300 to 550� C., and pressure from 100 to 550 MPa, shows a negative temperature coefficient and a positive pressure coefficient. This means, for example, that after the feedstock is dissolved in the autoclave and maintained for several days at the temperature of 400� C. (namely after the dissolution process), it is possible to obtain re-crystallization of gallium nitride, if temperature inside the autoclave is increased to 500� C. and pressure is kept constant at the level of 200 MPa (crystallization process). Alternatively, after the feedstock is dissolved in the autoclave under increased pressure maintained for a couple of days at the level of 350 MPa (namely after the dissolution process), it is possible to obtain re-crystallization of gallium nitride by lowering pressure to 200 MPa and maintaining constant temperature of 500� C. (crystallization process).
Seed as it has already been mentioned, is crucial for obtaining desired bulk gallium-containing nitride mono-crystals in a process according to the present invention. In view of the fact that the quality of the seed is crucial for the crystalline quality of the bulk gallium-containing nitride mono-crystals obtained by the process according to the present invention, the seed selected for the process should have possibly high quality. Various structures or wafers having a modified surface can also be used. For example a structure having a number of surfaces spaced adequately far from each other, arranged on a primary substrate and susceptible to the lateral overgrowth of crystalline nitrides may be used as a seed. Moreover, a seed having a homoepitaxial surface, exhibiting n-type electrical conductivity, for example doped with Si, may be used. Such seeds can be produced using processes for gallium-containing nitride crystal growth from gaseous phase, such as HVPE or MOCVD, or else MBE. Doping with Si during the growth process at the level of 1016 to 1021/cm2 ensures n-type electric conductivity. Moreover, a composite seed may be used and in such seed directly on a primary substrate or on a buffer layer made for example of AlN� a layer made of GaN doped with Si may be deposited. Furthermore, for a particular future use, bulk mono-crystals can be grown by the process according to the present invention on homo-seeds having a defined orientation with respect to hexagonal wurzite type crystallographic lattice of the specific Group XIII element(s) nitride, such as C-plane, A-plane or M-plane of the respective nitride.
The main part of the apparatus is the autoclave 1 used for bringing the solvent into a supercritical state. The autoclave is equipped with the installation 2, which enhance chemical transport in the supercritical solution within the autoclave 1. The autoclave 1 is situated in the chamber 3 of the furnace 4, equipped with heating units 5 and cooling means 6. Position of the autoclave 1 within the chamber 3 is secured by a screw blocking device 7. The furnace 4 is embedded in the bed 8 and secured with steel tapes 9 tightly wound around the furnace 4 and the bed 8. The bed 8 with the furnace 4 is pivotally mounted on the supporting base 10 and secured in the desired position by means of a pin securing device 11. By tilting the autoclave during the crystallization process it is possible to influence the convective flow and thus the chemical transport. The convective flow in the autoclave 1 placed in the furnace 4 is established by means of the installation 2 in the form of a horizontal baffle 12 of a size corresponding to not less than 70% of horizontal cross section area of the autoclave 1. The baffle 12 separates the dissolution zone 13 from the crystallization zone 14. The horizontal baffle 12 is located approximately in the middle of the autoclave 1 in terms of longitudinal dimension. Temperature values in individual zones of the autoclave 1, falling within the range from 100� C. to 800� C., are controlled by setting up respective temperature for the furnace 4 by a control unit 15. In the autoclave 1 the dissolution zone 13 corresponding to low temperature zone of the furnace 4 is situated above the horizontal baffle(s) 12. The feedstock 16 is placed in the dissolution zone 13 and the amount of the feedstock 16 is such that its volume does not exceed 50% of volume of the dissolution zone 13. Simultaneously, when metallic gallium is introduced as the feedstock 16 in crucibles, the total volume of the crucible should not exceed 80% of volume of the dissolution zone 13 and the amount of metallic gallium feedstock 16 should match the former requirement (50% of the dissolution zone volume). The crystallization zone 14 corresponds to high temperature zone of the furnace 4 and is situated below the separating baffle(s) 12. In the crystallization zone 14 the seed 17 is located and the specific position in which the seed 17 is placed is below crossing of up-stream convective flow and down-stream convective flow, but still above the bottom of the crystallization zone 14. The separating baffle(s) 12 is/are positioned within the zone of cooling means 6. As the result of cooling the baffle 12 region, the temperature difference between the dissolution zone 13 and the crystallization zone 14 may be controlled. At the level of the bottom of the crystallization zone 14 there is another cooling device 18, used in order to cool down the zone after the process is over, so that the dissolution of the grown crystal(s) during the cooling stage after the process is remarkably reduced.
Gallium nitride exhibits good solubility in supercritical ammonia, provided that the latter contains Group I and optionally Group II elements or their compounds, such as e.g. KNH2. FIG. 3 presents how the solubility of GaN in supercritical ammonia-containing solvent depends on pressure, for temperature 400� C. and 500� C. Here the solubility is defined as the molar percentage: Sm≡[GaNsolution:(KNH2+NH3)]�100%. In this example KNH2 is used in the molar ratio of KNH2:NH3=0.07. In this case Sm is a smooth function of only three parameters: temperature (T), pressure (p), and molar ratio of the mineralizer (x), i.e. Sm=Sm(T, p, x). Small changes of Sm can be expressed as:
ΔS m≈(∂S m /∂T)|p,x ΔT+(∂S m /∂p)|T,x Δp+(∂S m /∂x)|T,p Δx, where the partial derivatives (e.g. (∂Sm/∂T)|p,x) determine the behavior of Sm with variation of its parameters (e.g. T). In this specification these partial derivatives are called �coefficients� (e.g. (∂Sm/∂T)|p,x is a �temperature coefficient of solubility�TCS�).
In the case of the three-step process for obtaining bulk mono-crystalline gallium-containing nitride according to the invention, the application of two forms of the feedstock at the same time�in the form of metallic gallium and mono-crystalline gallium-containing nitride�has a principal advantage since it allows a considerable reduction of the loss of mono-crystalline gallium-containing nitride dissolved in the third step of the process.
Group I and Group II element azides dissolve in a supercritical ammonia-containing solution. The research studies directed to the use of azide mineralizers in processes according to the present invention revealed that under the present process conditions the azide ammonia solution is chemically stable up to a certain temperature, at which the azide starts to decompose (in the case of NaN3 this is ca. 250� C.). Below this temperature the azide ammonia solution is hardly reactive with respect to feedstock and the azide does not act as the ammonobasic mineralizer. However, when the temperature of the supercritical ammonia-containing solution goes high enough (in the case of NaN3�beyond 300� C.), intensive decomposition of azide ion N3 − takes place and molecular nitrogen N2 is released. Only at this stage the azide commences to act as mineralizer, and enhances dissolution of the feedstock and crystallization of gallium-containing nitride on the seed. Thus, during the process according to the present invention realized with metallic gallium as the feedstock, the use of azides makes it easier to control supersaturation and the amount of gallium that does not dissolve.
The main disadvantage of using azides is the extra pressure, originating from the gaseous nitrogen, released during decomposition of azide. The increment of pressure is remarkable and usually undesired, because more durable autoclaves are then needed. However, one can get rid of this effect. There are several ways to do it. The one presented below�as an example�should not be construed as limiting. The azide can be first closed in an empty autoclave (or an autoclave filled with an inert gas), together with the other starting materials (feedstock, seeds etc.) and decomposed by heating to the temperature higher than the decomposition temperature of the azide(s) used. The autoclave contains then a mixture, comprising the (undesired) gaseous nitrogen. Then the temperature should be decreased back below the critical temperature of the mixture, the autoclave should be at least partially evacuated and charged with the solvent (ammonia). Alternatively, all the starting materials (including the mineralizer in the form of azide) and ammonia are placed in the autoclave at the beginning of the process. The autoclave is then heated, so as to transform the ammonia into the supercritical state. In properly controlled temperature distribution the mineralizer reacts with supercritical ammonia, forming supercritical ammonia-containing solvent with ions of Group I elements and molecular nitrogen N2 is released. Metallic gallium, contained in the feedstock, reacts with the supercritical solvent, producing polycrystalline gallium-containing nitride. Then the autoclave should be cooled back below the critical point of the ammonia-containing solution, completely evacuated (with all the vital components of the reaction system, including the feedstock in the form of polycrystalline GaN, seeds and mineralizer in the form of amide(s) of Group I element(s), invariably remaining within the autoclave). The autoclave should be then charged again with the solvent (ammonia) and the two-step or three-step variant of the process for obtaining bulk mono-crystalline gallium-containing nitride according to the invention can be carried on, as described above. Note, that the Group I and optionally Group II element amide(s) remaining in the autoclave after decomposition of their azides may have a very high level of purity, hardly available otherwise.
In the preferable embodiment of the process according to the invention (Example I), illustrated in FIG. 4, after the transition of the ammonia-containing solution to the supercritical state, the temperature in the first step, in the upper zone�the dissolution zone of the autoclave 13�is raised to the level of 450� C. and maintained for the set period of time (FIG. 4). At the same time, temperature in the lower zone of the autoclave�the crystallization zone 14�is maintained at the level of about 250� C. Under those conditions metallic gallium is transformed into polycrystalline gallium nitride in the dissolution zone, while dissolution of the seeds in the dissolution zone takes place at negligible rate.
Next, after about 3 days, the second step of the process begins and the crystallization zone is heated to the temperature exceeding the temperature of the dissolution zone, which is maintained principally on the same level as at the end of the first step. After a temperature difference is attained between the zones and the temperature gradient is reversed with respect to that maintained in the first step of the process�dissolution of the feedstock takes place in the dissolution zone, and chemical transport between the zones takes place through convection, and when supersaturation of a supercritical ammonia-containing solution with respect to GaN is attained, crystallization of GaN takes place selectively on the seeds in the crystallization zone.
In another example of this invention (Example III), illustrated in FIG. 5, modification is characterized in that the second step may start before the first step is finished, namely, when a portion of metallic gallium has not yet completely reacted with a supercritical ammonia-containing solvent. In this embodiment of the invention, heating of the crystallization zone of the autoclave begins soon after the constant temperature at the level of about 450� C. is attained in the dissolution zone. Chemical transport between the zones is then initiated, when most of metallic gallium has been transformed into polycrystalline gallium nitride, while the transition of metallic gallium to a solution continues for some time. In other respects, this example of the invention does not differ from the one described above.
The bulk mono-crystalline gallium-containing nitride obtained in the process according to the invention has a very low dislocation density. The best substrate obtained by the method according to the invention has the surface dislocation density close to 104/cm2 with simultaneous half-width of X-ray rocking curve from (0002) plane below 60 arcsec (for Cu Kα1). It may contain Group I elements in concentration of about 0.1 ppm or more than 0.1 ppm�over 1.0 ppm, or even more than 10 ppm of Group I elements. Moreover, even if the concentration of Group I elements is at the level of 500 ppm, the quality of the bulk mono-crystalline gallium-containing nitrides obtained in the process according to the invention is satisfactory. SIMS profiles (Secondary-Ion Mass Spectroscopy) for a product sample obtained directly through the process according to the invention show that Group I elements are present at the level of 106counts/s, which indicates that potassium is present in the order of about 500 ppm. Moreover, some transition metals (Fe, Cr, Ni, Co, Ti), present in the reaction environment, produce a measurable signal at least in the layer near the surface. To compare, analogical profiles for GaN seed crystal obtained by HPVE method show that potassium is present only at the level of about 1 ppm. Whereas, profiles of transition metals are at the level of noise, which proves that there is a very small amount of those elements in the seed crystal obtained by HPVE method.
a) Slicing a bulk single crystal, preferably with a wire saw. b) Rinsing the mono-crystalline gallium-containing nitride obtained from the supercritical solution, in various media, such as supercritical ammonia solution, water, or carbon dioxide, in order to remove impurities from the crystal. c) Annealing the mono-crystalline gallium-containing nitride obtained from the supercritical solution, in the atmosphere of inert gas, optionally with an oxygen addition, at the temperature between approx. 600� C. and 1050� C., thus obtaining the material with better crystalline quality than before the annealing and/or activating the acceptors in the bulk gallium-containing nitride mono-crystal. Slicing: usually a wire saw is used for slicing bulk crystals, but in order to use the wire saw the crystal's thickness should exceed 1 mm, preferably 3 mm. Due to the seed's flexion, the bulk mono-crystal obtained by the HVPE method on the sapphire substrate is not thick enough to be sliced with a wire saw. The method described in this application allows to obtain bulk mono-crystalline gallium nitride with high crystalline quality even if the mono-crystal's thickness does not exceed 1 mm, allowing it to be sliced into wafers. Moreover, the obtained bulk mono-crystalline gallium-containing nitride contains few impurities such as, e.g., oxygen, allowing it to be used in opto-electronic devices based on nitric semiconductors, such as laser diodes. The substrates obtained after slicing the crystal with a wire saw are then polished on both sides. Due to the fact that substrates are intended for the growth process from the gaseous phase, they are situated on a wire saw at an off-angle of between 0.05 and 0.2 degree with respect to the principal axis of the crystal. Since the bulk mono-crystals obtained from supercritical ammonia-containing solution contain, among others, impurities in the form of Group I elements, it is preferable to use the MOCVD method to form a buffer layer or a protective layer preventing the impurities from penetrating from the substrate obtained in the process described in this invention to the layers deposited on that substrate by epitaxial methods, e.g. the MOCVD method. This process is illustrated in Example XIV.
Annealing: bulk mono-crystalline gallium-containing nitride may be subjected to annealing in the atmosphere of inert gas, optionally with an oxygen addition, at the temperature between approx. 600� C. and 1050� C., thus obtaining the material with better crystalline quality than before the annealing. The annealing process allows to remove from the obtained bulk mono-crystalline gallium-containing nitride, at least in the near-surface layer, the impurities formed from the reactions carried out in the first step, such as hydrogen and ammonia, as well as ions from the impurities formed during crystallization and/or annealing. During the annealing process hydrogen, ammonia, and other ions formed during the growth processes, may undergo further changes favors their removal from the bulk crystalline gallium-containing nitride. Other impurities of the mono-crystalline gallium-containing nitride formed in the environment of the reactions which took place during the growth process, such as Group I elements or dopes of Group I elements, introduced to the system as a mineralizer, possibly with trace amounts of Group II elements, as well as other elements such as Ti, Fe, Co, Cr, and Ni from the apparata being used, are not removed in the annealing process.
EXAMPLE I Two-step Process for Obtaining Bulk Mono-crystalline Gallium Nitride The high pressure autoclave I of the volume of 36.2 cm3 was charged with 3.16 g (about 45 mmol) of the feedstock in the form of metallic gallium of 6N purity in its dissolution zone, and with three seed crystals in the form of gallium nitride obtained by the HVPE method, each about 200 μm thick and with the total surface area of 3.6 cm2 in the crystallization zone. The autoclave was charged with 1.36 g (about 59 mmol) of metallic sodium (4N). Next, the autoclave was filled with 15.4 g of ammonia (5N), closed and put into the set of furnaces.
By slow heating (at 0.4� C./min) the temperature in the dissolution zone was raised to 450� C., maintaining at the same time the temperature at 250� C. in the crystallization zone. The temperature of 450� C. in the dissolution zone was attained after 1 day (FIG. 4). After the period of 3 days, when partial transition of gallium to a solution and a complete reaction of undissolved gallium to polycrystalline GaN took place, the temperature of the crystallization zone was raised (at about 2� C./min) to 500� C., with pressure inside the autoclave reaching about 260 MPa. Under those conditions (the second step of the process), the autoclave was maintained for the subsequent 8 days (FIG. 4). As a result of the process, partial dissolution of the feedstock (i.e. polycrystalline GaN) took place in the dissolution zone and crystallization of gallium nitride took place on the seeds in the form of two-sided mono-crystalline layers of about 220 μm of total thickness.
EXAMPLE II Two-step Process for Obtaining Bulk Mono-crystalline Gallium Nitride The same procedures were followed as in Example I, with the only exception that instead of using 1.36 g of metallic sodium: a) 0.4 g of metallic lithium (4N) were used, b) 2.3 g of metallic potassium (4N) were used or c) 0.68 g of metallic sodium (4N) were used d) 1.92 g of sodium azide (4N) were used, and after 11 days of the process, growths of bulk mono-crystalline gallium-containing nitride layers were obtained of about a) 70 μm, b) 200 μm, c) 360 μm, and d) 400 μm, respectively.
EXAMPLE III Two-step Process for Obtaining Bulk Mono-crystalline Gallium Nitride The same procedures were followed as in Example I, with the only exception that heating�beginning of the second step of the crystallization zone (at the rate of about 2� C./min)�was initiated when the dissolution zone attained the target temperature of 450� C., i.e. after the period of about 4 hours from the beginning of the process (FIG. 5). After another few hours, temperature in the crystallization zone attained 500� C. This state (i.e. 450� C. in the dissolution zone and 500� C. in the crystallization zone) was maintained till the end of the process. After 8 days, the growth, similar to that in Example I, of bulk mono-crystalline gallium-containing nitride layer was obtained.
EXAMPLE IV Three-step Process for Obtaining Bulk Mono-crystalline Gallium Nitride The high pressure autoclave of 90 cm3 volume was charged in the dissolution zone with 4.51 g (about 65 mmol) of the feedstock in the form of metallic gallium of 6N purity, and with 1.5 g (about 18 mmol) of the feedstock in the form of mono-crystalline gallium-containing wafers obtained by the HVPE method, whereas three seed crystals in the form of gallium nitride of about 200 μm thick each and total surface area of 1.9 cm2 were placed in the crystallization zone. The autoclave was also charged with 5.9 g (about 151 mmol) of metallic potassium (4N). Next, the autoclave was filled with 39.3 g of ammonia (5N), closed and put into the set of furnaces.
By heating at 2� C./min, the temperature in the dissolution zone was raised to 175� C., while in the crystallization�to 225� C. This temperature set was maintained for the next three days (FIG. 6). During that time, the reaction of metallic gallium to a solution went to completion, while the feedstock in the form of mono-crystalline GaN deposited in the dissolution zone did not dissolve in significant degree, nor did the seeds placed in the crystallization zone. At the set temperatures, in the first step, there was practically no convection exchange of mass between the zones. In the second step of the process, the temperature in the dissolution zone was slowly�within 3 days (FIG. 6) raised to 500� C., and maintained at this level until the eight day of the process. The temperature in the crystallization zone was maintained at the unchanged level of 225� C. This enabled crystallization of gallium nitride from the supercritical solvent on the feedstock deposited in the dissolution zone. Seed crystals in the crystallization (lower) zone did not significantly dissolve. In the third step of the process, the temperature was gradient reversed (at approx. 2� C./min.) in the autoclave (the temperature in the dissolution zone was set at the level of 425� C., whereas in the crystallization zone at the level of 500� C.). Due to this, the process of dissolution of polycrystalline GaN was initiated in the dissolution zone, chemical transport of the material to the crystallization zone started, and crystallization of GaN took place on the seeds. In this step of the process the pressure inside the autoclave was about 260 MPa. In those conditions, the autoclave was maintained for the next 8 days (FIG. 6). As a result of the process, partial dissolution of the feedstock took place (i.e. complete dissolution of the layer obtained in the second step, and partial dissolution of mono-crystalline gallium-containing nitride introduced as the feedstock in the form of wafers crystallized by HVPE methods) in the dissolution zone, and crystallization of gallium nitride took place on the seeds with obtaining two-sided mono-crystalline layers of the total thickness of about 300 μm.
EXAMPLE V Composed Mineralizer The dissolution zone of a 600 cm3 high pressure autoclave, having the inner diameter of 40 mm and length of 480 mm, was charged with 53.0 g of feedstock in the form of metallic gallium (6N). The crystallization zone of the same autoclave was charged with a seed crystal in the form of a gallium nitride wafer (having the diameter of about 1 inch and the mass of 2.0 g) obtained by the HVPE method. As the mineralizer, 12.0 g of 4N metallic sodium as well as 19.5 g of 4N metallic potassium were put into the autoclave. Next, the autoclave was filled with 255.0 g of ammonia (5N), tightly closed and put into a set of furnaces. The temperature of the dissolution zone was raised to 450� C. (at 1� C./min, FIG. 7), while the crystallization zone was not heated and its temperature did not exceed 250� C. In this way, supercritical ammonia-containing solution was obtained with the following molar ratio: KNH2:NH3=0.035; NaNH2:NH3=0.035. This temperature distribution was maintained in the autoclave for 4 days (FIG. 7), during which partial dissolution of gallium and a complete reaction of undissolved gallium to polycrystalline GaN took place.
Next, the temperature of the dissolution zone was increased to 500� C. (at 1� C./min), the temperature of the crystallization zone was slowly increased to 550� C. (at 0.1� C./min, FIG. 7), with the pressure inside the autoclave reaching about 280 MPa. The autoclave was kept under those conditions (the second step of the process) for the subsequent 20 days (FIG. 7). As a result of the process, partial dissolution of the feedstock (i.e. polycrystalline GaN) was observed in the dissolution zone and crystallization of gallium nitride on the HVPE seed took place in the crystallization zone. The gallium nitride crystallized on both sides of the seed in the form of mono-crystalline layers with the total thickness of about 2 mm.
EXAMPLE VI Composed Mineralizer The same procedures were followed as in Example V, with the only exception that instead of using 12.0 g of metallic sodium and 19.5 g of metallic potassium�39.0 g of 4N metallic potassium together with 1.2 of 3N metallic magnesium were used, and after 24 days of the process growth of bulk mono-crystalline gallium-containing nitride layers was obtained of about 2 mm.
EXAMPLE VII Composed Mineralizer The high-pressure autoclave of the diameter of 40 mm, length of 480 mm and volume of 603 cm3, was charged in the dissolution zone with the feedstock in the form of metallic gallium�53 g (about 750 mmol) and 6N purity, and was charged in the crystallization zone with the seed in the form of gallium nitride�at the weight of 0.74 g and diameter of 1 inch�obtained by the HVPE method. Also, 38 g (about 1000 mmol) of metallic potassium (4N) and 5g (50 mmol) of ZnS (4N) were introduced into the autoclave. Next, the autoclave was filled with 260 g of ammonia (5N), closed and put into the set of furnaces.
By heating at 2� C./min, the temperature in the dissolution zone of the autoclave was raised to 425� C. (FIG. 8). Heating of the crystallization zone (at the rate of about 2� C./min) started when the dissolution zone attained the target temperature of 425� C./min, i.e., after the period of about 4 hours from the beginning of the process. After the next few hours temperature in the crystallization zone attained 500� C., with the pressure inside the autoclave being around 260 MPa. In this way, the supercritical ammonia-containing solution was obtained, in which the molar ratio of the mineralizer to ammonia was KNH2:NH3=0.07, whereas the molar ratio of S species to ions of Group I elements was 1:20. This balance (i.e., at 425� C. in the dissolution zone and 500� C. in the crystallization zone) remained till the end of the process, i.e. for about 8 days (FIG. 8).
EXAMPLE VIII Azide Mineralizer Dissolution zone of an 84 cm3 high-pressure autoclave (FIGS. 1 and 2) was charged with 6.0 g of feedstock in the form of gallium nitride wafers obtained by HVPE method, each of 200 μm thickness as well as 0.27 g of 6N metallic gallium, and 0.5 g of GaN seeds obtained also by HVPE method were placed in the crystallization zone of the same autoclave. Then 9.8 g of 5N sodium azide and 39 g of 5N ammonia were placed in the autoclave. The autoclave was closed, put into the chamber of a furnace and heated up to 300� C. This temperature was maintained inside the autoclave for the next two days. During that time the azide was decomposed and the ammonobasic solvent was produced, which enabled complete dissolution of metallic gallium. After two days the temperature in the dissolution zone of the autoclave was increased to 400� C., while the temperature of the crystallization zone was increased to 500� C. This temperature distribution inside the autoclave was maintained for another 14 days (FIG. 9). At such conditions the expected pressure within the autoclave is ca. 230 MPa. The real pressure turned out to be ca. 330 MPa and the observed increment was the effect of gaseous nitrogen, produced during decomposition of the azide. As the result of the process, partial dissolution of the feedstock in the dissolution zone and growth of mono-crystalline gallium nitride layers on both sides of each seed in the crystallization zone was observed. The total thickness of the re-crystallized layers was ca. 800 μm.
EXAMPLE IX Azide Mineralizer Dissolution zone of an 84 cm3 high-pressure autoclave (FIGS. 1 and 2) was charged with 6.0 g of feedstock in the form of gallium nitride wafers obtained by HVPE method, each of 200 μm thickness as well as 1.05 g of 6N metallic gallium, and 0.7 g of GaN seeds obtained also by HVPE method were placed in the crystallization zone of the same autoclave. Then 4.9 g of 5N sodium azide, 2.9 g of 4N metallic potassium and 3 g of 5N ammonia were placed in the autoclave. The autoclave was closed, put into the chamber of a furnace and heated up to 300� C. This temperature was maintained inside the autoclave for the next two days (FIG. 10). During that time the azide was decomposed and the ammonobasic solvent was produced, which enabled complete dissolution of metallic gallium. After two days the temperature in the autoclave was increased to 500� C. for one day. Then the temperature of the dissolution zone was decreased to 450� C., while the temperature of the crystallization zone was increased to 550� C. This temperature distribution inside the autoclave was maintained for another 7 days (FIG. 10). At such conditions the expected pressure within the autoclave is ca. 260 MPa. The real pressure turned out to be ca. 310 MPa and the observed increment was the effect of gaseous nitrogen, produced during decomposition of the azide. As the result of the process, partial dissolution of the feedstock in the dissolution zone and growth of mono-crystalline gallium nitride layers on both sides of each seed in the crystallization zone was observed. The total thickness of the re-crystallized layers was ca. 700 μm.
EXAMPLE X Azide Mineralizer Dissolution zone of an 84 cm3 high-pressure autoclave (FIGS. 1 and 2) was charged with 8.0 g of feedstock in the form of 6N metallic gallium, and 0.5 g of GaN seeds obtained also by HVPE method, each of ca. 250 μm thickness, were placed in the crystallization zone of the same autoclave. Then 4.9 g of 5N sodium azide and 38 g of 5N ammonia were placed in the autoclave. The autoclave was closed and put into the chamber of a furnace. The temperature in the dissolution zone of the autoclave was increased to 500� C. by slow heating (0.35� C./min), while the temperature in the crystallization zone was maintained at the level of 300� C. The target temperature of 500� C. in the dissolution zone was achieved in ca. 1 day (FIG. 11). This temperature distribution was maintained inside the autoclave for the next two days. During that time the azide was decomposed and the ammonobasic solvent was produced, which enabled partial dissolution of metallic gallium and the reaction of all non-dissolved gallium to polycrystalline GaN. After three days the temperature in the crystallization zone was increased (at 2� C./min) to 550� C. This temperature distribution inside the autoclave was maintained for another 14 days (FIG. 11). At such conditions the expected pressure within the autoclave is ca. 270 MPa. The real pressure turned out to be ca. 330 MPa and the observed increment was the effect of gaseous nitrogen, produced during decomposition of the azide. As the result of the process, partial dissolution of the feedstock (i.e. polycrystalline GaN) in the dissolution zone and growth of mono-crystalline gallium nitride layers on both sides of each seed in the crystallization zone was observed. The total thickness of the re-crystallized layers was ca. 1.6 mm.
EXAMPLE XI Azide Mineralizer Procedures as described in Examples VIII to X have been repeated except that seeds possessing surfaces susceptible to the lateral overgrowth (ELOG structures) were used. In our case, the ELOG structures had the form of ridges, ca. 10 μm high and 7 μm wide. Growth of mono-crystalline gallium nitride layers on the seeds in the crystallization zone was observed and the deposited GaN layers were of good crystalline quality.
EXAMPLE XII Azide Mineralizer Procedures as described in Examples VIII to X have been repeated except that a mixture of sodium azide and magnesium azide in the molar ratio of NaN3:Mg(N3)2=20:1 was used. Similar results were obtained and bulk mono-crystals of GaN deposited on the seeds were of good quality.
EXAMPLE XIII Azide Mineralizer Dissolution zone of an 84 cm3 high-pressure autoclave (FIGS. 1 and 2) was charged with 0.5 g of feedstock in the form of aluminum nitride tablet as well as 0.28 g of 6N metallic gallium, and 1.6 g of GaN seeds obtained also by HVPE method were placed in the crystallization zone of the same autoclave. Then 9.2 g of 4N sodium azide and 36.6 g of 5N ammonia were placed in the autoclave. The autoclave was closed, put into the chamber of a furnace and the temperature inside the autoclave was increased to 325� C. (in the crystallization zone) and to 275� C. (in the dissolution zone) for one day. The azide was decomposed and ammonobasic solvent was produced, which enabled total dissolution of metallic gallium. The temperature of the dissolution zone was then increased to 400� C., while the temperature of the crystallization zone was increased to 500� C. (FIG. 12). After another day the temperature was very slowly (at ca. 2� C./h) increased to 450� C. and 550� C. in the dissolution and crystallization zones respectively. At such conditions the expected pressure within the autoclave is ca. 260 MPa. The real pressure turned out to be ca. 360 MPa and the observed increment was the effect of gaseous nitrogen, produced during decomposition of the azide. At such conditions the autoclave was maintained for another two days (FIG. 12). As the result of the process, partial dissolution of the feedstock (i.e. the AlN tablet) in the dissolution zone and growth of mono-crystalline AlGaN layers on both sides of each seed in the crystallization zone was observed. The total thickness of the re-crystallized layers was ca. 10 μm. The deposited layers of mixed nitride were of good quality and two independent measurement techniques (SEM-EDX and X-ray diffraction) revealed that the composition of the layers was Al0.2Ga0.8N.
EXAMPLE XIV Cutting and Annealing Crystals obtained in similar ways as described above in Examples I-XIII were subjected to the following processes in order to use them as substrates:
3) Next, the samples were placed in the furnace and again subjected to annealing for between 1 and 5 hours in the nitrogen temperature containing low amounts of oxygen and in the temperature between 600� C. and 900� C. (Thus prepared samples are called: GaN substrates)
EXAMPLE XV Washing Ten wafers with the diameter of 1 inch and weight of 15 g were placed in the high-pressure autoclave with the diameter of 40 mm, length 480 mm and the volume of 600 cm3 (FIGS. 1 and 2) in the form of GaN obtained by the growth method from the supercritical ammonia-containing solution. Next, 255.0 g of ammonia (5N) was introduced to the autoclave and the autoclave was tightly closed. The autoclave was then placed in the furnace system and the dissolution zone was heated up to the temperature of 450� C. and the crystallization zone up to the temperature of 550� C. Thus, the ammonia-containing solution was transferred into the supercritical state. After 3 days power was cut off from furnace. In those conditions autoclave was left to cool down by itself (FIG. 13). As a result of this process, the level of impurities in the substrate GaN layer marked as SIMS was considerably reduced.
(a) ions of another Group I element or (b) ions of Group II elements, preferably calcium or magnesium or (c) one or more substances containing oxygen-free species causing the weakening of the ammono-basic nature of the supercritical solvent or (d) ions of Group II elements, preferably calcium or magnesium and one or more substances containing oxygen-free species causing the weakening of the ammono-basic nature of the supercritical solvent. 7. The process according to claim 1 or 2 or 3, characterized in that the mineralizer is in the form of azides of Group I elements. 8. The process according to claim 7, characterized in that said azides of Group I elements are LiN3, NaN3, KN3, CsN3 or their mixtures. 9. The process according to claim 7, characterized in that the molar ratio of the introduced azides of Group I elements to ammonia ranges from 1:200 to 1:2. 10. The process according to claim 1 or 2 or 3, characterized in that the dissolution zone is above the crystallization zone. 11. The process according to any one of the preceding claims 1-3, characterized in that convection and chemical transport between the two zones are suppressed in the first step, and the saturation degree of the supercritical solution with respect to soluble gallium compounds is reduced. 12. The process according to claim 11, characterized in that the reduction of the saturation degree of the supercritical solution with respect to soluble gallium compounds is obtained by adjusting the opening of the crucibles containing metallic gallium, placed in the dissolution zone. 13. The process according to claim 11, characterized in that the temperature ramping in the dissolution zone at the beginning of the first step is higher than 0.1� C./min, and then the temperature in the first step in the dissolution zone is maintained higher than 350� C., preferably higher than 400� C. 14. The process according to claim 11, characterized in that the temperature maintained in the first step in the crystallization zone causes that the seeds do not dissolve or dissolve in negligible degree. 15. The process according to claim 11, characterized in that the temperature in the dissolution zone is maintained higher than the temperature in the crystallization zone in the first step, and in the second step the temperature in the crystallization zone is raised to a higher value than the temperature in the dissolution zone. 16. The process according to claim 15, characterized in that the temperature in the first step in the crystallization zone is not higher than 500� C., preferably not higher than 400� C., most preferably not higher than 300� C. 17. The process according to any one of the preceding claims 1-3, characterized in that the temperature gradient between the zones at the beginning of the second step is reversed and mass transport by convection takes place between the zones. 18. The process according to claim 17, characterized in that the temperature ramping in the crystallization zone at the beginning of the second step enables a certain dissolution of the seed(s). 19. The process according to claim 17, characterized in that the second step begins when the first step is not yet completed. 20. The process according to claim 17, characterized in that in the second step the temperature in the dissolution zone is maintained lower than the temperature in the crystallization zone. 21. The process according to claim 20, characterized in that the temperature in the second step in the crystallization zone is not lower than 350� C., preferably not lower than 400� C., most preferably ranges between 500� C. and 550� C. 22. The process according to claim 20, characterized in that
the mineralizer is introduced into the autoclave and next the feedstock in the form of metallic gallium is placed in the dissolution zone of the autoclave, and at least one seed is mounted in the crystallization zone of the autoclave, and then the autoclave is filled with ammonia; next, in the first step, transition of the solvent to the supercritical state takes place, while temperatures in both zones are maintained different by gradual and selective increase of the temperature in the dissolution zone in order to obtain at least partial reaction between metallic gallium and the supercritical solvent, and at the same time the temperature is maintained in the crystallization zone at which dissolution of seed(s) takes place in negligible degree; next, the temperature is raised in the dissolution zone to the value at which the polycrystalline form of gallium-containing nitride is obtained, and the temperature is maintained in the crystallization zone at which seeds dissolve at negligible rate; after polycrystalline gallium-containing nitride is obtained, at least partially, in the dissolution zone, the average temperature of the crystallization zone is increased to the value higher than the average temperature in the dissolution zone, chemical transport by convection is evoked and re-crystallization of gallium-containing nitride is carried out on the seed(s). 23. The process of controlling the growth rate of the bulk mono-crystalline gallium-containing nitride in the process according to any one of the preceding claims 1-3, characterized in that the process comprises the first step of transition of the feedstock from the metallic form to polycrystalline gallium-containing nitride, while convection and chemical transport are suppressed, and then the second step in which the conditions of dissolution of the feedstock and the saturation degree of the supercritical solution with respect to soluble gallium compounds are controlled, and after convection is evoked, the feedstock gradually dissolves and selective crystallization of gallium nitride on at least one mono-crystalline seed is carried out at the temperature higher than that for the dissolution of the feedstock, as long as the feedstock has completely or partially run out, and bulk mono-crystalline gallium-containing nitride is obtained. 24. The process according to claim 23, characterized in that the dissolution rate of the feedstock in the second step is controlled depending on pressure and temperature of the process through selection of the mineralizer from the Group I elements, including lithium, sodium, potassium and their mixtures and compounds, especially those containing nitrogen and/or hydrogen. 25. The process according to claim 24, characterized in that a preferable molar ratio of the mineralizer to ammonia is used according to the set conditions of the process. 26. The process according to claim 23, characterized in that the dissolution rate of the feedstock in the second step is controlled through adjusting the opening degree of crucibles containing the polycrystalline gallium-containing nitride in the dissolution zone. 27. The process according to claim 23, characterized in that solubility of the feedstock increases in the second step through a decrease of the temperature in the dissolution zone. 28. The process according to claim 23, characterized in that convection is controlled through temperature difference between the zones. 29. The process according to claim 23, characterized in that convection is controlled through controlling the position of the zones with respect to each other. 30. The process according to claim 23, characterized in that convection in the second step is controlled through controlling the opening of the baffle or baffles separating the two zones. 31. The process according to claim 23, characterized in that concentration of soluble gallium-containing compounds in the supercritical solution in the crystallization zone in the second step increases until it attains minimal supersaturation degree with respect to gallium nitride through an increase of the temperature in the crystallization zone. 32. The process according to claim 31, characterized in that supersaturation of the supercritical solution with respect to gallium nitride increases in the crystallization zone through an increase of the temperature in that zone. 33. The process of forming a substrate from bulk mono-crystalline gallium-containing nitride obtained by a method according to any one of the preceding claims 1-3, characterized in that the thus obtained bulk mono-crystalline gallium-containing nitride layer is then sliced and polished. 34. The process according to claim 33, characterized in that the bulk mono-crystalline gallium-containing nitride layer crystallized on the seed has the thickness of over 1 mm, preferably over 3 mm. 35. The process according to claim 33, characterized in that a protective layer is deposited on the thus obtained substrate by the crystallization method from the gaseous phase, preferably using the MOCVD or HVPE method. 36. The process according to claim 35, characterized in that a protective layer from AlxGa1-xN, where 0≦x<1, is deposited on the thus obtained substrate. 37. The process for reducing the level of impurities in bulk mono-crystalline gallium-containing nitride obtained by a method according to any one of the preceding claims 1-3, characterized in that the thus obtained bulk mono-crystalline gallium-containing nitride is subjected to annealing in the atmosphere of inert gas, possibly with an addition of oxygen, at temperature between approx. 600 and 1050� C., thus producing material with higher crystalline quality than before the annealing. 38. The process according to claim 37, characterized in that nitrogen and/or argon serve as inert gas. 39. The process according to claim 37 or 38, characterized in that annealing is carried out in the atmosphere of inert gas with an addition of oxygen between 10 and 30 vol. %. 40. The process according to claim 37, characterized in that the annealing process is carried out in a single step or in multiple steps until the desired level of impurities (such as hydrogen and/or ammonia or ions formed from the impurities formed during the crystallization and/or annealing process) is reached. 41. The process for removing impurities from bulk mono-crystalline gallium-containing nitride obtained by a method according to any one of the preceding claims 1-3, characterized in that the thus obtained mono-crystalline layer of bulk gallium-containing nitride has the thickness of over 1 mm, preferably over 3 mm, and then the layer is sliced into wafers which are
is aided by the application of ultrasounds. 43. The process according to claim 41, characterized in that the process for removing impurities in the gaseous hydrogen, nitrogen or ammonia is aided by exposure to an electron beam. 44. The process according to any one of the preceding claims 33 or 41-43, characterized in that a wire saw is used for slicing bulk mono-crystalline gallium-containing nitride. 45. The process according to claim 6, characterized in that the ammonia-containing solvent produced contains at least ions of Group I elements and ions of acceptors (Group II and Group IV, IUPAC 1989) and the thus obtained bulk mono-crystalline gallium-containing nitride is annealed in the atmosphere that does not contain hydrogen but does contain oxygen. 46. The process according to claim 6, characterized in that elements such as magnesium (Mg), zinc (Zn) or cadmium (Cd) serve as acceptors. 47. The process of obtaining a bulk mono-crystalline gallium-containing nitride from the gallium-containing feedstock in a supercritical ammonia-containing solvent characterized in that the feedstock is in the form of metallic gallium or mono-crystalline gallium-containing nitride, and the ammonia-containing solvent is in the form of ammonia with addition of mineralizer in the form of the Group I (IUPAC, 1989) elements and/or their mixtures, and/or their compounds, especially those containing nitrogen and/or hydrogen, there are two temperature zones in each step of the process, and the feedstock is placed in the dissolution zone and at least one mono-crystalline seed is deposited in the crystallization zone, and following the transition of the solvent to the supercritical state, the process comprises the first step of transition of metallic gallium to the solution at the first temperature, and then the second step of selective crystallization of gallium nitride on the feedstock in the form of mono-crystalline gallium-containing nitride, and then the third step of crystallization of the gallium nitride, through gradual dissolution of the feedstock and selective crystallization of gallium-containing nitride on at least one seed at the temperature higher than that of the dissolution of the feedstock, while all the vital components of the reaction system (including the feedstock, seeds and mineralizer) invariably remain within the system throughout the whole process, and subsequently bulk mono-crystalline gallium-containing nitride is obtained. 48. 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