Method of fabrication of eptaxial layer standardized substrate (template type substrates) from voluminal mono-crystalline nitride containing gallium with surface suitable for epitaxy featuring required electric properties

Description of the invention

The present invention relates to a method for producing a template substrate from gallium-containing bulk monocrystalline nitride. In particular, the invention comprises a method for producing a template substrate from a gallium-containing bulk monocrystalline nitride having an epitaxial surface with the desired electrical properties by producing a gallium-containing nitride layer on a monocrystalline volumetric gallium nitride crystallized from a gas phase growth method. supercritical ammonia solution.

In the Polish patent application number P-347918 a method of obtaining monocrystalline volumetric nitrides represented by gallium nitride was proposed by recrystallization from supercritical ammonia solution. A characteristic feature of monocrystalline volumetric nitrides obtained with the use of the above-mentioned supercritical ammonia solution is their low dislocation density (in the case of volumetric GaN it is 10⁴/ cm²) and at the same time high specific resistance (in the case of volumetric GaN on the order of a few Ω · cm), so they do not have the electrical conductivity required for the substrates, such as semiconductor light-emitting diodes (LED) or semiconductor lasers (LD). It is therefore desirable to produce on the substrate obtained by crystallization from supercritical ammonia solution a layer with the desired electrical properties, in particular a layer with high conductivity of the n or p type. However, great difficulties were found in doping with silicon (Si) the above-mentioned monocrystalline volumetric nitrides crystallized from supercritical ammonia solution. . On the other hand, n-type electrical conductivity was obtained in gallium-containing nitrides of the general formula Al_xGa_1-xyIn_yN (0 <x <1, 0 <y <1.0 <x + y <1) represented by gallium nitride and obtained by the vapor phase growth method, in which the carrier content can be increased by doping with Si.

The present inventors have discovered that the n-type electrically conductive layer formed by gas phase growth on a monocrystalline gallium-containing volumetric nitride substrate crystallized from supercritical ammonia solution, compared to bulk layers obtained by gas phase growth on other types of substrates such as sapphire. or GaAs, it has a much lower dislocation density and even after doping with Si, the crystal quality of the gallium-containing nitride layer obtained by the vapor-phase growth method improves. Therefore, the object of the present invention is to propose a method for obtaining a template substrate from a bulk single crystal with the desired electrical properties, in particular a layer with high conductivity of the n or p type, in which a layer is deposited on the bulk monocrystalline substrate obtained from a supercritical ammonia solution by a vapor phase growth method. nitride containing gallium with the desired electrical conductivity.

According to the invention, a method for the production of a template substrate from a gallium-containing bulk monocrystalline nitride, based on the use of known techniques for the production of substrates for the deposition of vapor-phase epitaxial layers and the technique of crystallization from a solution in a solvent containing ammonia and / or its inorganic derivatives and alkali metal ions, in supercritical conditions, in an autoclave, in an ammoniacal environment, with a molar ratio of alkali metal ions to the remaining components in a supercritical solvent not exceeding 1: 2 and involving dissolution of the gallium-containing source material, formation of a supercritical solution, and crystallization of the gallium-containing nitride from this solution on the surface of the embryo at a temperature higher than for dissolution, is characterized by: that when depositing a gallium-containing nitride layer from a supercritical ammonium base solution, a gallium-containing bulk monocrystalline nitride substrate prepared by vapor deposition is used as a seed, and the nucleus is crystallized by the gallium-containing bulk monocrystalline nitride layer on the thus obtained, and a gallium-containing nitride layer having the desired electrical properties is applied to the thus obtained gallium-containing nitride layer by vapor growth by doping with donors to provide n-type conductivity, or by acceptors to provide p-type conductivity.

Preferably, according to this method, using the negative solubility temperature coefficient of the gallium-containing nitride at least in the crystallization zone in which the gallium-containing nitride seed has been placed. by increasing the temperature above the dissolution temperature of the gallium-containing source material, a supersaturation zone is created with respect to the seed, and selective crystallization of gallium-containing nitride is carried out from the supercritical ammonia solution exclusively on the surface of the gallium-containing nitride seed at a temperature higher than the dissolution of the material source, keeping the concentration in this zone at a level that does not cause spontaneous crystallization, and then, on the thus obtained gallium-containing nitride layer, a layer of gallium-containing nitride with the desired electrical properties is applied by the vapor-phase growth method, by doping with donors to provide n-type conductivity, or with acceptors in order to provide p-type conductivity.

In the process of the invention, the gallium-containing nitride produced by crystallization from supercritical ammonia solution is preferably in the form of Al_xGa_1-xN, where 0 <x <1.

In the process of the invention, the gallium-containing nitride layer deposited by gas phase growth on gallium-containing nitride produced by crystallization from supercritical ammonia solution is preferably in the form of Al_xGa_1-xyIn_yN, where 0 <x <1.0 <y <1.0 <x + y <1.

The invention is illustrated in more detail by the attached drawings, in which:

Fig. 1 is a graph of the change in temperature over time in the autoclave with p = const and illustrates the relationship between temperature changes and the dissolution and crystallization processes of the present invention, Fig. 2 is a graph of change over time of the pressure in the autoclave at T = const and illustrates the relationship between the changes of temperature. pressure and the dissolution and crystallization processes of the present invention, Fig. 3 is an axial section of the autoclave and furnace assembly used in the present invention, Fig. 4 is a perspective drawing of a device for obtaining volumetric monocrystalline gallium nitride, Fig. 5 is a graph of the solubility relationship of GaN in supercritical ammonia containing potassium amides (from Mineralizer: NH₃ = 0.07) from the pressure for T = 400 ° C and T = 500 ° C, Fig. 6 is a graph of the change over time in the temperature in the autoclave for the description of Example I, and Figure 7 is an analogous graph for Example II.

The invention consists in ammonobasic crystal growth and makes it possible to obtain monocrystalline gallium-containing nitride selectively deposited on the surface of a seed by creating a chemical transport in a supercritical ammonia solvent containing one or more mineralizers affecting its ammoniacal nature.

This is a method characterized by the fact that it allows to obtain a monocrystalline volumetric template substrate with a conductive layer, in which a layer of gallium-containing nitride with an electrical conductivity of n-type was deposited on the gallium-containing nitride layer by vapor phase growth, due to the fact that the autoclave forms a supercritical solvent containing ammonia and alkali metal ions in which the source material is dissolved, selectively crystallizing the gallium-containing nitride from the solution on the seed surface under conditions of higher temperature and / or lower pressure than in the dissolution process of the gallium-containing source material in the supercritical solvent.

In the first variant, it is crucial in the second process - crystallization, to selectively crystallize on the surface of the seed. Hence, a second variant of this invention relates to the crystallization of a gallium-containing bulk monocrystalline nitride, characterized in that it makes it possible to obtain a monocrystalline bulk template with a conductive layer. in which a layer of ni-conductive gallium nitride was deposited on the gallium containing nitride layer by a vapor phase growth method by dissolving in a supercritical solvent containing ammonia and alkali metal ions, forming a supercritical solution with a negative solubility temperature coefficient of gallium nitride and at least in the zone the autoclave in which the embryo was placed, by appropriately increasing the temperature and / or lowering the pressure, creating a supersaturation zone of the supercritical solution for the seed, and adjusting the concentration so that no spontaneous crystallization occurs, selectively growing the gallium-containing nitride crystal solely on the surface of the autoclave seed.

While in the second variant two zones of dissolution and crystallization are created simultaneously in the autoclave, it is preferable to control the supersaturation of the supercritical solution towards the seed by adjusting the dissolution temperature and the crystallization temperature. In addition, temperature control will be facilitated if the temperature of the crystallization zone is set in the range of 300 to 600 ° C and the temperature difference between the dissolution zone and the crystallization zone in the autoclave is kept below 150 ° C, and more preferably below 100 ° C. The control of supersaturation of the supercritical solution in relation to the embryo can be carried out by placing one or more partitions in the autoclave separating the dissolution zone (low temperature) from the crystallization zone (high temperature e4

In addition, when two zones are formed in the autoclave: dissolution and crystallization with an appropriate temperature difference, the supersaturation of the supercritical solution against the seed can be controlled by using the gallium-containing source material introduced as crystalline GaN, the total area of ​​which is greater than the total area of ​​the nucleus.

In a first variant, the alkali metal ions are introduced in the form of alkali metals and / or alkali metal compounds and / or mixtures thereof, in particular free of Group XVII elements (halogens). Such alkali metal ions may be one or two species selected from the group of Li +, Na + and K +. It is particularly advantageous to introduce them in the form of alkali metals and their amides and azides in a molar ratio to ammonia from 1: 200 to 1: 2. The supercritical solvent-dissolved source material is a gallium-containing nitride or a gallium precursor that can form gallium compounds that are soluble in the supercritical solvent.

Although the method described in the present invention is based on reactions in a purely ammoniacal environment, it is permissible to use GaN source material obtained by HVPE or other chemical methods, as long as the chlorine or other elements of Group XVII contained therein do not affect negatively on the reaction environment.

The source material may be gallium-containing nitride with a reversible dissolution process in a supercritical ammoniacal solvent. It can also be combined with metallic gallium which reacts irreversibly in a supercritical solvent.

The use of gallium nitride as the gallium nitride facilitates the control of the crystallization process. It is preferable to use monocrystalline GaN nuclei, but also GaN obtained by HVPE, as well as by the flux method, nuclei obtained by the high pressure method or embryos having the surface A (1120), M (1100) or R (1102) cut from a bulk single crystal obtained from supercritical ammonia. The nitrogen side of the C (0001) surface can also be used for crystallization.

In the present invention, the dissolving process and the crystallization process are usually carried out in parallel with their simultaneous spatial separation in an autoclave. In other words, autoclave produces a supercritical ammoniacal solvent containing alkali metal ions, in which the gallium-containing source material is dissolved, and under a higher temperature and / or lower pressure than the dissolution process of the source material, the gallium-containing nitride is crystallized from the supercritical solution on the surface of the embryo.

In a first embodiment, it is preferable to add a separate supercritical solution process to higher temperature and / or lower pressure conditions to the dissolution process of the gallium-containing source material. In this case, at least two zones of differing temperature are formed simultaneously in the autoclave, the gallium-containing source material is placed in the low-temperature dissolution zone and the seed is placed in the high-temperature crystallization zone. The temperature difference between the dissolution zone and the crystallization zone should be adjusted to ensure chemical transport in a supercritical solution, which is essentially by convection. The temperature difference between the dissolution zone and the crystallization zone is greater than 1 ° C, more preferably 5 to 150 ° C, and most preferably less than 100 ° C.

The gallium containing nitride obtained according to the invention is preferably in the form AlxGa1-x-yInyN, where 0 <x <1.0 <y <1.0 <x + y <1. Supercritical solvent is defined as follows: it contains NH₃ and / or its derivatives and the mineralizer in the form of alkali metal ions, at least sodium or potassium ions. The source material consists essentially of gallium-containing nitride or its precursors selected from the group consisting of azides, imides, amido-imides, amides, hydrides, metallic compounds and alloys containing gallium, as well as metallic gallium. The definition of the precursor is provided later in the text.

The embryo according to the invention has at least a crystalline layer of nitride containing gallium or other group XIII elements (IUPAC 1989), and preferably the surface dislocation density of this layer is lower than 10⁶/ cm².

Crystallization of the gallium-containing nitride of the invention may take place at temperatures from 100 to 800 ° C, more preferably from 300 to 600 ° C, and most preferably from 400 to 550 ° C. The pressure during crystallization of the gallium-containing nitride may be from 10 to 1000 MPa, more preferably from 100 to 550 MPa, and most preferably from 150 to 300 MPa.

The alkali metal ion content of the supercritical solvent is adjusted to ensure the correct solubilities of the source material and the gallium containing nitride,

And the molar ratio of alkali metal ions to the remaining components in the supercritical solution is controlled from 1: 200 to 1: 2, more preferably from 1: 100 to 1: 5, and most preferably from 1:20 to 1: 8.

In the present invention, the growth of monocrystalline gallium nitride is obtained by producing chemical transport in a supercritical solvent containing one or more mineralizers affecting its ammoniacal nature. It is therefore a crystallization technique of an ammoniacal nature and the terms used in this invention should be understood according to the definition set out below:

Gallium-containing nitride is a chemical compound with at least a gallium atom and a nitrogen atom in its structure, therefore it is at least a GaN binary compound, AlGaN, InGaN ternary compound and AlInGaN ternary compound, and the composition of other elements relative to gallium in its structure can be changed in to a degree which does not interfere with the ammoniacal nature of the crystallization technique.

Volumetric monocrystalline nitride containing gallium is a monocrystalline gallium-containing nitride substrate on which optoelectronic devices such as light emitting diodes (LEDs) or laser diodes (LD) can be produced by the MOCVD method or epitaxial growth methods such as e.g. HVPE.

A gallium containing nitride precursor is a substance or mixture containing at least gallium, in other words alkali metals, group XIII elements (according to IUPAC 1989), nitrogen and / or hydrogen, and metallic gallium, its alloys or metallic compounds, hydrides, amides, imides, amides - imides and azides which can form gallium compounds soluble in a supercritical ammoniacal solvent as defined below.

The gallium-containing source material is a gallium-containing nitride or a precursor thereof. GaN obtained by flux methods or polycrystalline GaN obtained from metallic gallium by reaction in a supercritical ammonia solvent can be used as the source material.

A supercritical ammoniacal solvent is a supercritical solvent consisting of at least ammonia in which one or more types of alkali metal ions are included to dissolve the gallium-containing nitride.

A mineralizer is a substance that provides one or more types of alkali metal ions to the supercritical ammoniacal solvent to assist in dissolving the gallium-containing nitride.

Dissolving gallium-containing source material is a reversible or irreversible process for the source material to form supercritical solvent-soluble gallium compounds, for example, gallium complexes. Gallium complexes are complex chemical compounds in which ligands of the NH type₃ or NH derivatives thereof₂^-, NH ^- surround the centrally located gal.

Supercritical ammoniacal solution means the solution resulting from dissolving gallium-containing source material in a supercritical ammonia solvent.

Solubility: Our experience shows that at a sufficiently high temperature and pressure, an equilibrium state can occur between the solid, gallium-containing nitride, and the supercritical solution. Therefore, the solubility of the gallium-containing nitride can be defined as the equilibrium concentration of the soluble gallium compounds obtained in the above-mentioned dissolution process of the gallium-containing nitride. In this process, the equilibrium concentration, i.e. Solubility can be controlled by varying the solvent composition, temperature and / or pressure.

Temperature and pressure coefficient of solubility: A negative temperature coefficient of solubility means that with all other parameters met, solubility is a decreasing function of temperature. On the other hand, a positive solubility pressure coefficient means that with all other parameters maintained, the solubility is increasing in pressure. Our research shows that the solubility of gallium-containing nitride in the supercritical ammonia 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 according to the diagram of Fig. 1, after dissolving the source material in an autoclave kept at 400 ° C for 8 days (i.e. after the dissolution process), gallium nitride re-crystallization can be obtained by increasing the temperature inside the furnace to 500 ° C and maintaining a constant pressure of 200 MPa (process crystallization). In turn, according to the diagram of Fig. 2, after dissolving the source material in an autoclave under the conditions of increased pressure maintained for 2 days at the level of 350 MPa (i.e. after the

After dissolution), recrystallization of gallium nitride can be obtained by reducing the pressure to 200 MPa and maintaining a constant temperature of 500 ° C (crystallization process).

Supersaturation: If the concentration of soluble gallium compounds in the supercritical ammonia solution is higher than the solubility of the gallium-containing nitride under the given physicochemical conditions, the supersaturation of the supercritical ammoniacal solution with respect to the gallium-containing nitride under these conditions can be defined as the difference in concentration and solubility. By dissolving gallium-containing nitride in a closed system, supersaturation can be achieved by, for example, increasing the temperature or reducing the pressure.

Chemical transport of gallium-containing nitride in supercritical ammoniacal solution is a continuous process involving dissolution of a gallium-containing source material in a supercritical solution, transport of soluble gallium compounds through the supercritical solution, as well as crystallization of gallium-containing nitride from a supersaturated supercritical solution. In general, the driving force of chemical transport can be a temperature difference, a pressure difference, a concentration difference, or a chemical or physical difference between the source material being dissolved and the crystallization product. By means of the process of the invention, bulky monocrystalline nitride containing gallium can be obtained by chemical transport under temperature differential conditions, it being necessary to maintain a higher temperature in the crystallization zone than in the dissolution zone.

The embryo was mentioned in the description. Since it has a major influence on the quality of the crystallized gallium-containing nitride, the seed with the best possible quality should be selected. In particular, an embryo having an n-type electrically conductive homoepitaxial surface, e.g. doped with Si, may be used. These types of nuclei are produced by methods of growing nitrides containing gas from the gas phase, such as HVPE or MOCVD, and doping with Si during the growth process in an amount of 10 to 10 / cm gives them n-type electrical conductivity. a SiC-type substrate, directly or via an AIN buffer layer, a Si-doped GaN layer was deposited.

Spontaneous crystallization from supersaturated supercritical ammonia solution represents the undesirable process of nucleation and growth of gallium-containing nitride crystals appearing inside the autoclave at any location except on the surface of the seed. However, the definition also includes growth on the surface of a seed in which the resulting crystal has an orientation different from that of the seed.

Seed selective crystallization means the process of crystallization that occurs at the surface of a seed in the absence of spontaneous crystallization, or when spontaneous crystallization occurs to a negligible degree. It is a necessary process to obtain a bulk single crystal and is one of the elements of the present invention.

Reaction temperature and pressure: In the examples presented in the present invention, the measurement of the temperature distribution inside the autoclave was taken with an empty autoclave, thus without a supercritical ammonia solution. Therefore, these are not the actual temperatures of the supercritical process. The pressure was measured directly or calculated on the basis of the physicochemical data of the ammoniacal solvent for the assumed process temperature and autoclave volume.

The autoclave comprises a closed reaction chamber in which crystallization is carried out in an ammoniacal type environment within the range of temperatures and pressures mentioned above.

For the implementation of the method according to the invention, it is advantageous to use the following device, schematically illustrated in Fig. 3 and Fig. 4, discussed in more detail below.

The above-mentioned method and device allow to obtain a monocrystalline volumetric nitride containing gallium. The volumetric single crystal has a low dislocation density (in the case of volumetric GaN it is 10⁴/ cm². It is important that the monocrystalline bulk GaN has a diameter of more than 1 inch, a thickness of 3 mm, and preferably more than 5 mm. Cutting it with a wire saw into tiles allows to obtain volumetric monocrystalline substrates with a thickness of 0.5 mm. The bulk monocrystalline supports can further be used as seeds. To improve their n-type electrical conductivity, it is worth increasing the concentration of n-type carriers by doping with Si during growth from the gas phase.

In the case of deposition of the gallium containing nitride by the vapor phase growth method, it is preferred that the gallium containing nitride recovered in the supercritical ammonia is of the Al form._xGa_1-xN (0 <x <1) or be a bulk monocrystalline Al_xGa_1-xN (0 <x <1) deposited on GaN. Al can be obtained from the gaseous phase growth process by doping Si-containing nitride with gallium_xGa_1-xyIn_yN

PL 225 424 B1 (0 <x <1.0 <y <1.0 <x + y <1) with n-type electrical conductivity, and since it was crystallized on gallium-containing nitride obtained in supercritical ammonia under the conditions of growth from the phase It can produce a template substrate with good crystalline quality and a dislocation density of less than 10 / cm.

A preferred embodiment of the present invention.

The process of the invention allows for the separation of the source material dissolution process and the supercritical solution process to a higher temperature and / or lower pressure, in which the gallium-containing nitride crystallizes on the seed surface. In addition, it includes the possibility of simultaneously creating in the autoclave at least two zones of differing temperature, wherein the gallium-containing source material is placed in a dissolution zone with a lower temperature, and the seed is placed in a crystallization zone with a higher temperature. The temperature difference between the dissolution zone and the crystallization zone is adjusted to provide chemical transport by convection in the supercritical solution, the temperature difference between the dissolution zone and the crystallization zone being greater than 1 ° C. The gallium-containing nitride recovered from supercritical ammonia is in the form Al_xGa_1-xN where 0 <x <1 and the gallium containing nitride obtained from the gas phase is Al_xGa_1-xyIn_yN where 0 <x <1.0 <y <1, 0 <x + y <1 and may contain impurities of the donor, acceptor or magnetic type. The supercritical solvent may be NH₃ containing alkali metal ions and / or its derivatives. The source material consists essentially of gallium-containing nitride or its precursors selected from the group consisting of azides, imides, amido-imides, amides, hydrides, metallic compounds and alloys containing gallium, as well as metallic gallium. The embryo has at least a crystalline layer of nitride containing gallium or other group XIII elements (according to IUPAC, 1989).

Crystallization of the gallium-containing nitride is carried out at a temperature of 100 to 800 ° C and a pressure of 10 to 1000 MPa, and the alkali metal ion content of the supercritical solvent is adjusted to ensure the correct solubilities of the source material and the gallium-containing nitride. The molar ratio of alkali metal ions to the remaining components in the supercritical solvent is controlled in the range from 1: 200 to 1: 2.

The conducted research has shown that the best obtained volumetric monocrystalline GaN may have a dislocation density lower than 10⁴/ cm² and at the same time the half-width of the X-ray reflection from the plane (0002) below 60 arcsec, which guarantees the appropriate quality and lifetime of semiconductor devices created with its use. At the same time, due to the electrical conductivity of the substrate, an n-type electrode can be applied to it.

GaN shows good solubility in supercritical NH3 as long as alkali metals or their compounds such as KNH are introduced into it₂. The graph of Fig. 5 shows the solubility of GaN in a supercritical solvent as a function of pressure at temperatures of 400 and 500 ° C, where the solubility is defined by mole percent: S_m = GaN^solution : (KNH₂ + NH₃) x100%. In the presented case, the solvent is a solution of KNH2 in supercritical ammonia with a molar ratio x = KNH₂ : NH₃ equal to 0.07. It is expected that the solubility of S._m is a smooth function of temperature, pressure and mineralizer content, expressed by the formula S._m = S._m(T, p, x). Minor changes to S_m can be expressed as follows:

Δ S_m «(5Sm / 5T) p,_x Δ T + (SSm / Sp) T,_x Δ p + (SSm / Sx) T, p Δ x, where partial derivatives (5S_m/ 5T)_p,_x, (5S_m/ 5p)_T.,_x, (5S_m/ 5x)_T.,_p determine the behavior of S._m with the change of individual parameters. In this specification, these derivatives are referred to as "coefficients" (e.g. (5S_m/ 5T)_p,_x is the "temperature coefficient of solubility").

From the graph in Fig. 5 it can be seen that the solubility is an increasing function of pressure and a decreasing function of temperature. These relationships make it possible to obtain volumetric monocrystalline nitride containing gallium by dissolving it under conditions of higher solubility and crystallization under conditions of lower solubility. A negative temperature coefficient means that in the presence of a temperature gradient, chemical transport of the gallium containing nitride will occur from the lower temperature dissolution zone to the higher temperature crystallization zone. It turned out that also other gallium compounds, and even metallic gallium, can be the source of ammonium gallium complexes. For example, gallium complexes can be introduced into a solvent of the above composition starting from the simplest substrate, gallium metal. Then, by suitably changing the conditions (e.g. increasing the temperature), a solution supersaturated with gallium-containing nitride is obtained and seed crystallization is obtained. The method according to the value of a8

The compound allows the growth of the gallium-containing bulk monocrystalline nitride on the seed and leads in particular to the production of a stoichiometric gallium nitride obtained as a monocrystalline volume layer on the nucleus of gallium nitride. Due to the fact that such a crystal is obtained in a supercritical solution containing alkali metal ions, it also contains alkali metals in an amount higher than 0.1 ppm. However, in order to maintain the purely basic character of the supercritical solution, in order to avoid corrosion of the apparatus in the first place, halides are deliberately not introduced into the solvent. The process according to the invention also allows the targeted replacement of 0.05 to 0.5 Ga by Al. The possibility of a smooth change of composition means the possibility of adjusting the constant network of the obtained nitride. Moreover, the bulk monocrystalline GaN can be doped with dopants of the donor type (e.g. Si, O) and / or acceptor (e.g. Mg, Zn) and / or magnetic (e.g. Mn, Cr) in concentrations from 10 to 10 / cm. These dopants alter the optical, electrical and magnetic properties of the gallium-containing nitride. As for other physical properties, the resulting bulk monocrystalline gallium nitride has a surface dislocation density below 10⁶/ cm², more preferably less than 10⁵/ cm²and most preferably less than 10⁴/ cm². Moreover, its X-ray reflection half width from plane (0002) is less than 600 arcsec, more preferably less than 300 arcsec, and most preferably less than 60 arcsec. The best bulk monocrystalline gallium nitride obtained may have a defect density lower than 10⁴/ cm² and at the same time the half-width of the X-ray reflection from the plane (0002) below 60 arcsec (for the Cu K a beam₁).

The device for obtaining a volumetric single crystal is shown in Fig. 3 and Fig. 4. The main component of the device is an autoclave 1 for obtaining a supercritical solvent, provided with an installation 2 for obtaining chemical transport in a supercritical solution inside the autoclave 1. The autoclave 1 is placed in the chamber 3 of a set of two furnaces 4 equipped with heating devices 5 and / or cooling 6 and secured in the desired position with respect to the furnaces 4 by means of a screw locking device 7. The furnaces 4 are mounted on a bed 8 and secured by steel straps 9 wrapped around 4 stoves and beds 8. The bed 8 with the set of ovens 4 is rotatably mounted in the base 10 and secured in the desired angular position by means of a pin lock 11, thanks to which the speed and type of convection flow in the autoclave 1 are controlled. In the autoclave 1 located in the set of ovens 4, there is a convective flow of the supercritical solution, determined by the installation 2, made in the form of a horizontal partition 12 covering over 70% of the cross-sectional area of ​​the autoclave, separating 1 dissolution zone 13 and crystallization zone 14 in the autoclave. at about halfway the length of the autoclave. The temperature of the individual zones in the autoclave 1, in the temperature range from 100 to 800 ° C, is set on the furnaces 4 by means of the control device 15. In the autoclave 1, the dissolution zone 13, coinciding with the low-temperature zone of the furnace group 4, is located above the horizontal partition or horizontal baffles 12 and the source material 16 is introduced into this zone 13. The source material is introduced in an amount such that its volume does not exceed 50% of the volume of the dissolution zone. The source material in the form of metallic gallium is introduced into the crucibles in an amount such that the volume limited by the crucibles does not exceed 80% of the volume of the dissolution zone. The crystallization zone 14 coincides with the high temperature zone of the furnace 4 and is located below the horizontal baffle or horizontal baffles 12. The embryo 17 is embedded in this zone, the embryo 17 being located below the intersection of the convective rising and falling streams, but slightly above the bottom of the furnace. The zone in which the convection flow-regulating plant 2 is located is provided with a cooling device allowing it to be cooled 6. As a result, a certain temperature difference is created between the dissolution zone 13 and the crystallization zone 14. At the level of the bottom of the crystallization zone there is a cooling device 18, which allows it to be quickly cooled after the end of the process and significantly prevents the dissolution of the crystal during the cooling of the furnace after the crystallization process.

The bulk monocrystalline gallium nitride thus obtained may have a dislocation density of less than 10 / cm and an X-ray half width of less than 60 arcsec. After cutting it into plates with a wire saw at an angle of 0.05 to 0.2 degrees from the main axis of the crystal, it can be applied under the following conditions by the HVPE method of 3 mm GaN with n-type electrical conductivity by maintaining the growth rate for 100 hours μm / h.

The thus obtained 5 mm thick bulk monocrystalline GaN is cut with a wire saw for 25 hours into 0.5 mm thick wafers. At least 4 substrates can be obtained in this way. These substrates

Apart from good crystalline quality, they also have electrical conductivity, so they can be used as substrates for optoelectronic devices based on semiconductors, such as laser diodes.

Example I. ₃

In a high pressure autoclave 1 with a diameter of 40 mm, a length of 480 mm and a volume of 600 cm, in the dissolution zone 13, the source material in the form of metallic gallium (6N) weighing 21.0 g and 18.0 g of the source material in the form of monocrystalline plates were placed in the crucible gallium nitride obtained by the HVPE method, and in the crystallization zone 14 a seed 1 inch in diameter and weighing 2.0 g in the form of GaN obtained by the HVPE method. 12.0 g of metallic sodium with a purity of 4N and 19.5 g of metallic potassium 4N were introduced as the mineralizer. Then 255.0 g of ammonia (5N) was introduced into autoclave 1 and sealed. Autoclave 1 was placed in the set of ovens 4 and heated to a temperature of 200 ° C (Fig. 6). After 3 days, the temperature was increased to 450 ° C. The pressure inside the autoclave was about 230 MPa. Thus, a supercritical ammonia solution was obtained with a molar ratio of: KNH₂ : NH₃ = 0.035; NaNH₂ : NH₃ = 0,035.

After 1 day, the temperature of the dissolution zone 13 was reduced to 370 ° C and the temperature of the crystallization zone 14 was increased to 500 ° C. Autoclave 1 was left for a further 20 days under these conditions (Fig. 6). As a result of the process, the source material in the dissolution zone 13 was partially dissolved and gallium nitride crystallized on the HVPE seed in the crystallization zone 14. The total thickness of the monocrystalline layer on both sides of the seed was about 2 mm.

Crystals obtained in a similar manner were subjected to the following processes in order to be used as a substrate:

1) A 5 mm thick monocrystalline layer deposited on a HVPE-GaN seed was placed in an oven and annealed for 1 to 5 hours under a nitrogen atmosphere containing a small amount of oxygen and at a temperature of 600 ° C to 900 ° C.

2) The sample was then placed on a wire saw by Takatori Corp. The sample was angled less than 1 degree to give it an off-angle. Next, the sample was cut into 5 plates with a wire saw, thus obtaining samples with a deviation from the main axis of the crystal from 0.05 to 0.2 degrees.

3) These samples were then placed in an oven and annealed for 1 to 5 hours under a nitrogen atmosphere containing a small amount of oxygen and at a temperature of 600 ° C to 900 ° C. (The samples prepared in this way are called GaN substrates).

4) The GaN substrates were then glued with glue to the stands used for polishing, placed on a grinding machine manufactured by Logitech Ltd. and polished sequentially on each side. In the polishing process, diamond grit and colloidal silica or alumina solution (pH 3 to 6 or 9 to 11) were used, resulting in surface roughness below 10A.

5) Then, a GaN or AlGaN protective layer with a thickness of several [mu] m was applied on the surface of the GaN substrate by the HVPE method under the following conditions, thanks to which a template type substrate was obtained. HVPE process conditions: Reaction temperature: 1050 ° C, reaction pressure: atmospheric (0.1 Mpa), ammonia partial pressure: 0.03 MPa, GaCl partial pressure₃: 100 Pa, hydrogen gas carrier.

6) Optionally, on a GaN substrate with the above protective layer or on a GaN substrate without a protective layer, a GaN layer approximately 3 mm thick was produced by the HVPE method. After cutting and polishing according to the methods described above, a template substrate having a thickness of about 0.5 mm was obtained for use in optoelectronic devices.

Example II ₃

In a high pressure autoclave 1 with a diameter of 40 mm, a length of 480 mm and a volume of 600 cm³in the dissolution zone 13, the source material in the form of metallic gallium weighing 53.0 g was placed in the crucible and in the crystallization zone 14 a seed 1 inch in diameter and 2.0 g in the form of GaN obtained by HVPE. 12.0 g of metallic sodium with a purity of 4N and 19.5 g of metallic potassium 4N were introduced as the mineralizer. Then 255.0 g of ammonia (5N) was introduced into autoclave 1 and sealed. Autoclave 1 was placed in the set of ovens 4. The dissolution zone was heated (at a rate of approx. 1 ° C / min) to 450 ° C (Fig. 7). During this time, the crystallization zone was not heated. Thus, a supercritical ammonia solution was obtained with a molar ratio of: KNH₂ : NH₃ = 0.035; NaNH₂ : NH₃ = 0.035. This temperature distribution was maintained in the autoclave for 4 days, during which the gallium was partially dissolved into solution and the undissolved gallium was completely converted to polycrystalline GaN.

PL 225 424 B1

Then the temperature of the dissolving zone 13 was increased (at a rate of about 1 ° C / min) to 500 ° C, and the temperature of the crystallization zone 14 was increased (at a rate of about 0.1 ° C / min) to 550 ° C. The pressure inside the autoclave was about 280 MPa. Autoclave 1 was left for a further 20 days under these conditions (Fig. 7). As a result of the process, the source material (i.e. of polycrystalline GaN) in the dissolution zone and the crystallization of gallium nitride on the HVPE seed in the crystallization zone 14. The total thickness of the monocrystalline layer on both sides of the seed was about 2 mm.

Crystals obtained in a similar manner were subjected to the following processes in order to be used as a substrate:

1) A 5 mm thick monocrystalline layer deposited on a HVPE-GaN seed was placed in an oven and annealed for 1 to 5 hours under a nitrogen atmosphere containing a small amount of oxygen and at a temperature of 600 ° C to 900 ° C.

2) The sample was then placed on a wire saw by Takatori Corp. The sample was angled less than 1 degree to give it an off-angle. Next, the sample was cut into 5 plates with a wire saw, thus obtaining samples with a deviation from the main axis of the crystal from 0.05 to 0.2 degrees.

3) These samples were then placed in an oven and annealed for 1 to 5 hours under a nitrogen atmosphere containing a small amount of oxygen and at a temperature of 600 ° C to 900 ° C. (The samples prepared in this way are called GaN substrates)

4) The GaN substrates were then glued with glue to the stands used for polishing, placed on a grinding machine manufactured by Logitech Ltd. and polished sequentially on each side. In the polishing process, diamond grit and colloidal silica or alumina solution (pH 3 to 6 or 9 to 11) were used, resulting in surface roughness below 10A.

5) Then, a GaN or AlGaN protective layer with a thickness of several [mu] m was applied on the surface of the GaN substrate by the HVPE method under the following conditions, thanks to which a template type substrate was obtained. HVPE process conditions: Reaction temperature: 1050 ° C, reaction pressure: atmospheric (0.1 Mpa), ammonia partial pressure: 0.03 MPa, GaCl partial pressure₃: 100 Pa, hydrogen gas carrier.

6) Optionally, on a GaN substrate with the above protective layer or on a GaN substrate without a protective layer, a GaN layer approximately 3 mm thick was produced by the HVPE method. After cutting and polishing according to the methods described above, a template substrate having a thickness of about 0.5 mm was obtained for use in optoelectronic devices.