Phosphor single crystal substrate and method for preparing the same, and nitride semiconductor component using the same

The present invention relates to a bulk monocrystalline phosphor substrate prepared by crystallization from a supercritical solution, a method of its preparation and a light emitting device using such a substrate.

Hitherto, a device for converting a wavelength of a nitride semiconductor light emitting device, which is a combination of a gallium nitride light emitting device and a YAG: Ce phosphor, is known to effect the emission of white light from the blue light emitting device. The mechanism used to obtain white light by converting the wavelength of light from the light emitting device, generally includes the step of adding phosphor powder to the semiconductor coating of the LED structure or to the coating resin absorbing part of the light emitted by the phosphor semiconductor structure, the step of excitation of the phosphor, the step of mixing the light from the excited phosphor with unabsorbed light emitted by the semiconductor structure and obtaining colored light.

However, such a method of producing a phosphor layer based on a phosphor mixed with a coating or resin causes some problems: the degree of dispersion of the phosphor in the resin is uneven, due to the sedimentation of the phosphor during curing, it is not possible to obtain a homogeneous mixed color, and the efficiency is very low. .

To overcome these difficulties, attempts have been made to deposit a semiconductor gallium nitride layer directly onto a YAG single crystal substrate to obtain a uniform phosphor layer, however, it has turned out that it is also troublesome to deposit crystalline gallium nitride from the gas phase onto the YAG crystal through the buffer layer.

The present inventors have found a method for producing a bulk nitride single crystal by recrystallization from a supercritical ammonia-containing solution described in Japanese Patent Application No. 2002-143449.

On the other hand, a Zn- or Cd-doped GaN phosphor is disclosed in Japanese Patent Publication No. 51-41686. In the described process, the nitriding reaction of the gallium oxide took place on the grain surface, but it was very difficult to achieve 100% yield. Moreover, the produced phosphor had a low crystal quality and a low spectral reflectance. When this phosphor is excited by ultraviolet radiation or an electron beam, it can emit light with only unsatisfactory properties, and it would be difficult to use such a phosphor in, for example, a fluorescent display.

The object of the present invention is to provide a monocrystalline phosphor substrate on which to support the growth of gallium nitride from the gas phase and also to provide a high efficiency converted wavelength light emitting device that could not be obtained from a powder phosphor.

It is also an object of the invention to provide a bulk monocrystalline nitride phosphor by crystallization from a supercritical ammonia containing solution and to provide a wavelength converted light emitting device having good efficiency by using the inventive phosphor as substrate.

It has now surprisingly been found that when ammonia reacts with metallic gallium or other Group XIII elements (lUPAC 1989) in the presence of an alkali metal or its compounds, a nitride phosphor can be produced by crystallization from a supercritical ammonia-containing solution. The reaction of nitride synthesis, for example GaN, can also be accelerated, which makes it possible to obtain a nitride phosphor with a homogeneous composition, high spectral reflectance and good crystalline quality, and also allows the obtained nitride phosphor to effectively emit light under the influence of UV radiation stimulation or electron beam, which in turn means that such a phosphor is useful in devices such as fluorescent displays.

The set aims were achieved thanks to the solution according to the invention.

The phosphor substrate prepared by crystallization from a supercritical solution containing ammonia, according to the invention, is characterized by the fact that it contains a nitride containing at least one element selected from the elements of Group XIII (lUPAC 1989)

- of the general formula XN in which X represents at least one element chosen from B, Al, Ga and In;

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- of the general formula XN: Y, where X is at least one element selected from B, Al, Ga and In, and Y is at least one element selected from Be, Mg, Ca, Sr, Ba, Zn, Cd and Hg, be

- of the general formula XN: Y, Z, where X is at least one element selected from B, Al, Ga and In, Y is at least one element selected from Be, Mg, Ca, Sr, Ba, Zn, Cd and Hg and Z is at least one element selected from C, Si, Ge, Sn, Pb, O, and S.

The light emitting device comprising an n-type nitride semiconductor layer, an active layer including a nitride semiconductor and a p-type nitride semiconductor layer deposited on a growth substrate, according to the invention, is characterized in that said substrate is a phosphor substrate containing nitride formed by crystallization from a supercritical ammonia-containing solution and containing at least one element selected from Group XIII elements (lUPAC 1989)

- of the general formula XN in which X is at least one element chosen from B, Al, Ga and In;

- of the general formula XN: Y, where X is at least one element selected from B, Al, Ga and In, and Y is at least one element selected from Be, Mg, Ca, Sr, Ba, Zn, Cd and Hg, be

- of the general formula XN: Y, Z, where X is at least one element selected from B, Al, Ga and In, Y is at least one element selected from Be, Mg, Ca, Sr, Ba, Zn, Cd and Hg and Z is at least one element selected from C, Si, Ge, Sn, Pb, O, and S.

The light emitting device of the invention has at least one phosphor layer on the said phosphor substrate.

Preferably, the light emitting device of the invention is a light emitting device of the spherically contact structure type having two electrodes, a p-type electrode, an n-type electrode, formed in the same plane.

The invention also relates to a method for obtaining a bulk phosphor single crystal in a supercritical solvent autoclave, equipped with convection control means for establishing convection flow, and a furnace assembly equipped with a heating device and a cooling device, which consists in

- the temperature inside the autoclave is regulated by means of the indicated heating device and / or cooling device so as to obtain a given temperature gradient,

- the source material is placed in the dissolution zone and the seed is placed in the crystallization zone, the dissolution and crystallization zones being separated by convection control means including at least one horizontal partition having a central opening and / or peripheral openings between the septum and the inner the autoclave wall, and the dissolution zone is above and the crystallization zone is below this septum,

- the convective flow rate of the supercritical solution between the dissolution zone and the crystallization zone is determined, determined by the degree of opening of the convection control means and the temperature difference between the dissolution zone and the crystallization zone,

- dissolving a nitride having a negative temperature coefficient of solubility in a supercritical solvent containing ammonia and at least alkali metal ions to form a supercritical solution, and the supercritical solution is provided from the dissolution zone to the crystallization zone with a nucleus therein by the indicated convection control measures, yes, that selective growth of the nitride crystal on the seed is achieved by keeping the supersaturation of the supercritical solution with respect to the seed at a predetermined elevated temperature and controlling the concentration below a certain value so as to avoid spontaneous crystallization.

In this mode, an autoclave is preferably used, in which the ratio of the diameter to the total length of the autoclave is in the range of 1/15 to 1/3, and the ratio of the holes in the indicated horizontal partition in terms of the cross-sectional area of ​​the autoclave is set at 30. % or less, and seed growth is performed at a rate of 10 µm / h or greater.

Preferably, at least one element of Li, Na and K and at least one element of Mg and Ca are used as the mineralizer.

The invention is described in detail below with reference to the accompanying drawing of which

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Fig. 1 shows the relationship between pressure and solubility of GaN in supercritical ammonia containing potassium amide (molar ratio KNH2: NH3 = 0.07) at T = 400 ° C and T = 500 ° C.

Fig. 2 is a graph showing the change over time of temperature in an autoclave and the change between the dissolving step and the crystallization step at constant pressure.

Fig. 3 is a graph showing the dependence of the change in pressure in the autoclave over time and the change between the dissolving step and the crystallization step at constant temperature.

4 is a schematic sectional view of an autoclave with a heating furnace used in the practice of the present invention.

Fig. 5 is a schematic perspective view of an apparatus for obtaining a bulk monocrystalline nitride.

Fig. 6 is a graph showing the change over time of temperature in an autoclave and the change between the dissolving step and the crystallization step in Example 1.

Fig. 7 shows the photoluminescent spectrum of the phosphor obtained according to the comparative example by crystallization from a supercritical solution containing ammonia after excitation with UV radiation.

Fig. 8 shows the cathodoliminescence spectrum of a phosphor obtained according to the comparative example by crystallization from a supercritical solution containing ammonia after excitation with an electron beam.

Fig. 9 shows the x-ray diffraction pattern of the phosphor obtained according to the comparative example by crystallization from a supercritical solution containing ammonia.

Fig. 10 shows the spectral reflectance curve of a phosphor obtained according to the comparative example, by the supercritical method.

Fig. 11 shows a schematic sectional view of a first light emitting device manufactured on a phosphor substrate according to the invention.

Fig. 12 is a schematic sectional view of a second light-emitting device produced on the phosphor substrate according to the invention.

Detailed Description of the Invention

As mentioned above, the bulk single crystal of the phosphor substrate according to the invention is a nitride of the general formula XN, XN: Y or XN: Y, Z, where X is at least one element selected from B, Al, Ga and In, Y is at least one element selected from Be, Mg, Ca, Sr, Ba, Zn, Cd and Hg, and Z is at least one element selected from C, Si, Ge, Sn, Pb, O and S.

As far as the process is concerned, the present invention is based on a reaction between ammonia and a Group XIII element or compound thereof at a temperature of not less than 132 ° C and a pressure of not less than 11.2 x 10⁶ Pa (112 bar) in the presence of at least one element selected from Group I and Group II (IUPAC 1989) and / or compounds thereof such as hydrides, imides, amides and nitrides.

When a metal or a compound containing at least one element selected from B, Al, Ga or In reacts with NH3 under conditions above its critical point (132 ° C, 11.2 x 10⁶ Pa), the nitriding reaction essentially takes place, but its rate is not satisfactory. On the other hand, if at least one element selected from Group I and Group II (IUPAC 1989) and / or its compounds such as hydrides, imides, amides and nitrides are introduced into the reaction medium, the nitriding reaction becomes much faster and more efficient. The Group I element may preferably be Li, Na or K, while the Group II element may preferably be Mg or Ca. Group I element nitrides may preferably include Li3N, Na3N, K3N, their amides may include LiNH2, NaNH2 and KNH2, and the imides of Li2NH etc. The group II element nitrides may preferably include Mg3N2, Ca3N2, their amides may include Mg (NH2) 2, Ca (NH2) 2, and imides - CaNH etc. Due to the existence of native nitrogen defects, the nitride phosphor obtained by the method of the invention can emit light even when it is not intentionally doped.

In the case of light emission by a donor-acceptor pair, when the donor contains an spontaneously generated nitrogen defect, the acceptors may preferably be formed with Group II and Group XII elements such as Be, Mg, Ca, Sr, Zn, Cd or Hg .

Preferably, a reaction between NH3 and at least one co-activator element selected from Group XIV and Group XVI (lUPAC 1989) is used, such as C, Si, Ge, Sn, Pb, O, S and / or compounds thereof.

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In the case of light emission by a donor-acceptor pair, the donors may preferably be formed with elements selected from C, Si, Ge, Sn, Pb, O and S, and acceptors may preferably be formed with elements selected from Be, Mg, Ca , Sr, Zn, Cd and Hg.

The present method of producing a bulk monocrystalline phosphor is based on the use of an ammonium-basic crystal growth technique, which involves chemical transport in a supercritical ammonia-containing solvent with the addition of at least one ammonium-basic mineralizer to achieve nitride single crystal growth. In this technique, impurities such as Zn or Cd introduced into the source material are dissolved in a supercritical solvent followed by recrystallization on a nitride seed, optionally having a main plane to form the desired crystal.

In this regard, the embryo enables the growth of the phosphor substrate.

It has been established that in the technique of crystal growth in an ammonium-base environment, the crystal growth is influenced by the composition and concentration of the supercritical solution containing ammonia, the temperature difference between the dissolution zone and the crystallization zone, the location and surface of the barrier used to control convective flow caused by the temperature difference, filling chambers introduced with ammonia and the ratio of the surface area of ​​the seed to the surface area of ​​the crystals of the source material, etc. Moreover, according to the present invention, the convective flow rate between the dissolution zone 13 and the crystallization zone 14 can be determined by using the convection control measures 2 and the temperature difference indicated, and consequently, it is possible to selectively grow the nitride crystal on the seed by keeping the supercritical solution supersaturated with the seed and keeping the concentration below a certain level to prevent spontaneous crystallization.

In addition, due to the excellent dissolving power of a supercritical solution containing ammonia containing alkali metal ions, it is possible to reduce the level of contaminants entering the environment from the inner walls of the autoclave if the inner walls of the autoclave are covered on the inside with a metal layer such as Ag, Mo, Fe or Ta, or an alloy of these metals.

Convection control measures are used to create a temperature gradient between the dissolution zone and the crystallization zone, and the shape and surface of the convection control means may vary depending on the volume of the autoclave and the ratio of the internal diameter of the autoclave to its total length. Preferably, the convection control means are configured such that they occupy from 70% to 90% of the cross-sectional area of ​​the interior of the retort, and the ratio of the openings in the horizontal partition can be set to 30% or less. The position of the partition wall can be adjusted to the number of crystals to grow, and the partition wall can be positioned in the range of 1/3 to 2/3 of the total length of the inner chamber of the autoclave, and thus arbitrarily set the value of the ratio between the dissolution zone and the crystallization zone. Preferably, the source material is placed in a dissolution zone and the source material is less than half of the dissolution zone filled with the source material. In the case where the source material is metallic gallium, the degree of filling may be about 1/4 of the dissolution zone because the volume of this source material in the crucible may be increased by converting metallic gallium into polycrystalline GaN.

Preferably, a cooling device is installed in the region where the convection control means are located to facilitate the maintenance of a predetermined temperature difference between the dissolution zone and the crystallization zone.

Preferably also, the autoclave is equipped with a cooling device for cooling the bottom of the flow region in the crystallization zone to enable the quench function after crystallization.

By using an autoclave of the above-described structure, the growth rate of the seed crystal can be improved. Preferably, the ratio of the diameter to the total length (height) of the autoclave is set at 1/15 to 1/3, the ratio of the holes in the horizontal partition to the cross-sectional area is kept at 30% or less, and a seed growth rate of 10 μm / h can be obtained. or higher.

According to the results of the research, GaN shows good solubility in NH3 containing alkali metals or their compounds, such as KNH2. The graph of Fig. 1 shows how the solubility of GaN in a supercritical solvent depends on the pressure for temperatures of 400 and 500 ° C. Solubility is defined herein by the mole percent: S._m = GaN^solution : (KNH² + NH₃) x 100%. In this case, the solvent is a supercritical ammonia-containing solution where the molar ratio X = KNH₂ : NH₃ was set at 0.07. Solubility of S._m could be funk6

By means of three parameters: temperature, pressure and molar ratio of the mineralizer, that is Sm = Sm (T, p, X). Minor changes in Sm can be expressed by the relationship:

ΔSm = ^ / δΤ) ρ, χΔΤ + ^ / δρ) τ, χΔρ + ^ / δχ) τ_ψΔχ where the parameters of the partial derivatives, for example each coefficient (5S_m/ 5T)_p,_x and so on, it is defined as the solubility temperature coefficient and the pressure solubility coefficient and the molar ratio coefficient of the mineralizer.

As can be seen from the graph in Fig. 1, the solubility of the indicated nitride in the supercritical ammonia-containing solution is an increasing function of pressure and a decreasing function of temperature. Based on these relationships, it is possible to obtain bulk monocrystalline GaN by dissolving under higher solubility conditions and crystallizing under lower solubility conditions. A negative temperature coefficient of solubility means that in the presence of a temperature gradient, chemical transport of the nitride takes place from the dissolution zone at the lower temperature to the crystallization zone at the higher temperature. Moreover, it has been found that other gallium compounds and gallium metal can be used as the source of GaN complexes.

For example, metallic gallium, which is the simplest form [source] of the Ga complex, can be incorporated into the above-described solution. Subsequently, supersaturation of the solution with respect to the nitride is achieved by changing the physical conditions, for example by heating, whereby a crystal may grow on the seed. According to the present invention, it is possible to nucleate a desired nitride in the form of a bulk single crystal, and also to carry out the stoichiometric growth of GaN obtained in the form of a bulk monocrystalline layer on a nucleus in the form of a GaN crystal.

The obtained single crystal may contain alkali metals at a concentration of 0.1 ppm or more, since the single crystal grows in a supercritical ammonia-containing solution in which alkali metal ions are present. In order to maintain the desired ammonium-basic nature of the supercritical solution, and to avoid corrosion of the apparatus, no halogens are specifically introduced into the supercritical solvent. According to the present invention, 0.001 to 0.50 Ga of aluminum or indium can be deliberately replaced. The crystal lattice constants of the obtained nitride can be adjusted by appropriately modifying the composition. The volumetric monocrystalline GaN obtained by the method according to the invention can also be deliberately doped with donor dopants (such as C, Si, Ge, Sn, Pb, O or S etc), acceptor dopants (such as Be, Mg, Ca, Sr, Zn, Cd, Hg, etc.) or magnetic impurities (such as Mn, Cr, etc.) in concentrations from 10¹⁷ up to 10²¹/ cm³. The indicated dopants change the optical, electrical and magnetic properties of the nitride. Regarding other physical properties, the bulk GaN single crystal, deposited under the given conditions, has a surface dislocation density of 10⁶/ cm² or less, preferably 10⁵/ cm² or less, and more preferably 10⁴/ cm² or less and at the same time has a half-width (FWHM) of the X-ray reflection from plane (0002) less than 600 arcsec or less, preferably 300 arcsec or less, and more preferably 60 arcsec or less. It is possible to produce / grow a bulk monocrystalline gallium nitride which, under the most favorable conditions, has a surface dislocation density below 10⁴/ cm²and at the same time the half-width (FWHM) of the X-ray reflex from plane (0002) less than 60 arcsec or less.

The device for obtaining a volumetric single crystal comprises an autoclave 1 for supercritical solvent conversion, with means 2 for controlling convection, for establishing convection flow, and around the autoclave, at least one set of ovens 4 is equipped with heating devices 5 and cooling devices 6. The set of ovens has a higher temperature zone 14, provided with a heater 4, which corresponds to the crystallization zone in the autoclave, and a lower temperature zone 13, provided with a heater, which corresponds to the dissolution zone in the autoclave. It is also possible to use a combination of ovens with a higher temperature zone equipped with a heating device and / or a cooling device and a lower temperature zone equipped with a heating device and / or a cooling device. The convection control means for establishing convective flow consists of at least one horizontal partition having a central opening and / or peripheral openings separating the crystallization zone from the dissolution zone. Inside the autoclave, the source material is placed in the dissolution zone and the embryo is placed in the crystallization zone. Convection flow in the supercritical solution between the dissolution and crystallization zones is regulated by the aforementioned convection control measures. The dissolution zone is above the horizontal partition and the crystallization zone is below the horizontal partition.

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The apparatus for obtaining a volumetric single crystal according to the present invention is illustrated in Fig. 4 and Fig. 5. The main component of the apparatus is an autoclave 1 for obtaining a supercritical solvent, provided with a system 2 for obtaining chemical transport in a supercritical solution inside the autoclave 1. The autoclave 1 is placed in the chamber 3 of a group of two furnaces 4 provided with heating 5 and cooling 6 devices. The autoclave 1 is secured in the desired position in relation to the ovens 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 the ovens 4 and beds 8. The bed 8 with the set of ovens 4 is rotatably mounted in 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 approximately 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 12 The source material 16 is introduced into zone 13, and the amount of source material introduced is such that its volume does not exceed 1/2 the volume of the dissolution zone. At the same time, when metallic gallium is introduced as a source material in crucibles, the total volume of the crucibles should not exceed 1/2 the volume of the dissolving zone. The crystallization zone 14, coinciding with the high temperature zone of the furnace 4, is located below the horizontal baffle 12. Seed 17 is embedded in the crystallization zone 14, the seed 17 location being located below the intersection of the convective rising and falling streams, but slightly above the bottom of the crystallization zone. The zone in which the convection flow-regulating installation 2 is located is equipped with a cooling device enabling it to be cooled 6-1. In this way, it is possible to control the temperature difference between the dissolution zone 13 and the crystallization zone 14 at a predetermined level. At the level of the bottom of the crystallization zone there is another cooling device 6-2, used to cool this zone after the end of the process, thanks to which dissolution of the crystal is largely prevented during the cooling of the furnace after the crystallization process.

Temperature difference between the crystallization zone and the dissolution zone

When two zones are formed simultaneously in the autoclave, i.e. a dissolution zone and a crystallization zone, the supersaturation of the supercritical solution to the seed is maintained by controlling the dissolution temperature and the crystallization temperature. Control is found to be not difficult if the temperature of the crystallization zone is set to between 400 and 600 ° C and the temperature difference between the dissolution zone and the crystallization zone in the autoclave is kept at 150 ° C or less, preferably 100 ° C or less. . Preferably, the adjustment of the supersaturation of the supercritical solution to the seed is accomplished by introducing at least one partition separating the interior of the autoclave into a dissolution zone with a lower temperature and a crystallization zone with a higher temperature, and by controlling the convective flow between the dissolution zone and the crystallization zone. Moreover, when two zones are formed within the autoclave, i.e. a dissolution zone and a crystallization zone between which a defined temperature difference is established, the supersaturation of the supercritical solution with respect to the embryo is preferably controlled by using a source material with a total surface area greater than the total surface area of ​​the embryo.

The present invention relates to the technique of crystal growth in an ammonium-basic medium, comprising the steps of inducing chemical transport in a supercritical solvent containing ammonia with the addition of at least one mineralizer imparting an ammonium-basic character and thereby causing the growth of monocrystalline nitride. Terms used in the present description and claims should be understood in accordance with the definitions given below.

Nitride: The term "nitride phosphor substrate as used herein means a compound containing at least a nitrogen atom as a constituent element. The phosphor substrate comprises a nitride of the general formula XN, XN: Y or XN: Y, Z, where X is at least one element selected from B, Al, Ga and In, Y is at least one element selected from Be, Mg, Ca, Sr, Ba, Zn, Cd and Hg, and Z is at least one element selected from C, Si, Ge, Sn, Pb, O, and S. Furthermore, a nitride of the formula XN can be defined as a compound of the general formula

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Al_xGa_1-xyIn_yN, where 0 & lt; x & lt; 1, 0 & lt; y & lt; 1 and 0 & lt; x + y & lt; 1 and may include at least a binary compound such as GaN or AIN, ternary compounds such as AlGaN, InGaN, and a ternary compound. The term "nitride phosphor substrate" means a monocrystalline substrate that can provide a new light source by converting a luminescent wavelength from LED or LD by combining such substrate with a light emitting device such as LED or LD produced by an epitaxial growth method, for example by MOCVD, HVPE or the like. similar.

Precursor: The term nitride precursor means a substance selected from B, Al, Ga or In and, if necessary, alkali metals, Group XIII elements, nitrogen and / or hydrogen, or mixtures thereof, examples of such precursor include a metal, an alloy or a compound intermetallic as well as hydride, amide, imide, amide-imide and azide which can form a nitride soluble in the supercritical ammonia-containing solvent as defined below.

Source material: The term source material means a target nitride or its precursor. The process of the present invention is based on an ammonium-basic reaction. The source material may be GaN or AIN obtained by HVPE, or GaN or AIN obtained by chemical reaction, which in its original form may contain chlorine, as long as the ammonium-basic nature of the reaction in the supercritical solvent is not disturbed. The combination of an equilibrium soluble nitride in a supercritical ammonia containing solvent and gallium metal and aluminum metal which react irreversibly with the ammonia-containing supercritical solvent can also be used as the source material.

Also an example of a source material are pellets for use in the present invention which are prepared by shaping the powder and sintering it, resulting in a pellet density of 70% or higher. Higher density is preferable. The powder can be used after shaping. Alternatively, a method comprising the steps of producing a metal nitride polycrystalline, dissolving and recrystallizing said polycrystalline in a crucible located in a dissolution zone in a supercritical solution containing ammonia, for example, as well as a method of producing gallium nitride from metallic gallium.

The control of the reactions leading to crystallization is easy when gallium nitride is used as the nitride. In this case, the same monocrystalline nitride is preferably used as the seed. Gallium nitride (GaN) obtained by a fluxing method or by a gas phase synthesis method such as the HVPE method, a polycrystalline gallium nitride crystallized in a supercritical ammonia environment, or a metal gallium can be used as the source material for the production of GaN.

Supercritical solution containing ammonia: As defined below, the supercritical solvent contains NH₃ and / or its derivatives. The mineralizer may contain alkali metal ions, at least lithium, sodium or potassium ions. The term supercritical ammonia-containing solution means a solution that may contain at least ammonia, an ion or ions of at least one alkali metal to dissolve the nitride, and further preferably, alkaline earth metal.

Mineralizer: The term mineralizer means a source that provides one or more types of alkali metal ions to dissolve the nitride in a supercritical solvent containing ammonia. The mineralizer is introduced as an alkali metal compound to introduce the alkali metal or alkali metal ions into the supercritical ammonia-containing solution. For purity reasons, the mineralizer can be advantageously introduced in the form of an alkali metal azide (NaN3, KN3, LiN3, CSN3), an alkali metal amide (LiNH2, KNH2, NaNH2, CsNH2), an alkali metal imide (Li2NH, K2NH, Na2NH, Cs2NH) metal alkali (Na, K, Li, Cs), hydride (LiH, KH, NaH, CsH) or other compound such as Li3N, K3N, Na3N, Cs3N etc., however the alkali metal and the alkali metal compound can be used simultaneously if there is it is required. The concentration of alkali metal ions in the supercritical solution is selected to provide specific solubilities of the source material and the nitride, and the molar ratio of alkali metal ions to other components of the resulting supercritical solution is adjusted in the range from 1: 200 to 1: 2, preferably from 1: 100 to 1: 5, and more preferably from 1:20 to 1: 8. When two or more alkali metal ion components are used in combination, the crystal growth rate and the crystal quality may be improved compared to when only one alkali metal ions are used. Moreover, if necessary, an alkaline earth metal such as Mg, Zn or Cd can be used simultaneously. Additionally, an inert component (alkali metal halide) as well as an acid component (ammonium halide) can be used simultaneously, as long as the ammonium-basic nature of the reaction in a supercritical environment is not disturbed.

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Dissolving source material: Dissolving source material is a reversible or irreversible process whereby the source material takes the form of nitride compounds that are soluble in a supercritical solvent, for example a gallium complex compound or an aluminum complex compound. Gallium complex is a complex compound in which the centrally located gallium atom is surrounded by ligands of the NH3 type or NH3 derivatives, such as NH2^- and NH^2-.

Supercritical ammonia-containing solution: The term supercritical ammonia-containing solution means a solution containing a soluble gallium or aluminum compound resulting from dissolving a source material in a supercritical ammonia-containing solvent. Based on our experience, we have found that there is an equilibrium state between the solid metal nitride and the supercritical solution under conditions of sufficiently high temperature and sufficiently high pressure. Therefore, the solubility of soluble nitride can be defined as the equilibrium concentration of the above soluble gallium or aluminum compound in the presence of solid nitride. In such a process, this equilibrium can be shifted by changing the temperature and / or pressure.

Solubility: The negative term solubility temperature coefficient shown by gallium nitride in supercritical ammonia means that while all other parameters are kept constant, its solubility is a monophonic decreasing function of temperature. Similarly, the phrase positive solubility pressure coefficient means that while all other parameters are kept constant, solubility is a monotonically increasing function of temperature. Based on our research, we can conclude that the solubility of the gallium-containing nitride in the supercritical ammonia-containing solvent has a negative temperature coefficient at least in the temperature range from 300 ° C to 550 ° C and a positive pressure coefficient at least in the pressure range of 1 x 10⁸ Pa up to 5.5 x 10⁸ Pa (1 kbar to 5.5 kbar). For example, as shown in Figure 2, after dissolving the source material in the autoclave and holding the temperature at 400 ° C for 8 days (i.e. after the dissolution step), gallium nitride crystallization can be achieved by increasing the temperature inside the autoclave to 500 ° C (step crystallization). On the other hand, as shown in Fig. 3, after dissolving the source material under elevated pressure and holding the elevated pressure in the autoclave for days at 3.5 x 10⁸ Pa (3.5 kbar), i.e. after the dissolution step, it is possible to crystallize the gallium nitride by reducing the pressure in the autoclave to 2 x 10⁸ Pa (2 kbar) - crystallization stage.

Supersaturation: The term supersaturation of a supercritical ammonia containing solution versus nitride means that the concentration of soluble gallium or aluminum compounds in the supercritical ammonia containing solution is higher than the equilibrium concentration, that is, higher than the solubility of the nitride. In the case of dissolving nitride in a closed system, such a supersaturation state, according to the negative temperature coefficient or the positive pressure coefficient of solubility, can be achieved by increasing the temperature or reducing the pressure.

Chemical transport: The phrase chemical transport of nitride in a supercritical ammonia-containing solution is a process comprising sequentially dissolving a gallium-containing source material, transferring soluble nitrides through the supercritical ammonia-containing solution, as well as crystallizing the nitride from a supersaturated supercritical solution containing ammonia. Generally, the chemical transport process occurs due to some driving force such as a temperature gradient, pressure gradient, concentration gradient, chemical or physical difference, properties between the dissolved source material and the crystallization product, or the like. Preferably, in the process according to the invention, the chemical transport is achieved by carrying out the dissolution step and the crystallization step in separate zones, provided that the temperature in the crystallization zone is higher than that in the dissolution zone, so that a volumetric nitride single crystal can be obtained by the process of the invention.

Embryo: The term embryo has been described herein by way of example. The seed provides an area or surface where nitride crystallization can occur, and the quality of crystal growth depends on the quality of the seed. Therefore, a high-quality embryo should be selected. The embryo dislocation density is preferably 10⁵/ cm² or less. As a seed, a natural seed obtained by the flux or high pressure method, as well as a seed with plane A, plane M or plane R obtained from a bulk single crystal can be used. In addition, a Si-doped seed having an n-type electrically conductive surface may be used. Such a seed may be produced using a vapor phase nitride crystal growth method such as HVPE or MOCVD etc. Doping with silicon (Si) during the growth process at the level of 10¹⁶ up to 10²¹cm² provides n-type electrical conductivity. In addition, a complex embryo can be used,

It is produced by depositing an independent phosphor layer on one side of the AIN or GaN substrate and a seed on the other side thereof. Such a seed can be used when a plurality of phosphor layers is required.

Spontaneous crystallization: The term spontaneous crystallization denotes the undesirable phenomenon whereby a nitride core is formed and grows from a supersaturated supercritical solution containing ammonia at any point within the autoclave, and includes the growth of a disoriented crystal on the seed surface.

Selective crystallization: The term selective seed crystallization means the step that allows crystallization at the surface of a seed to be crystallized with essentially no spontaneous growth. Such selective seed crystallization is essential for single crystal volume growth, and is one of the features of the present invention.

Reaction Temperature and Pressure: The temperature distribution in the autoclave, described below in the Examples section, is determined with an empty autoclave, that is, without supercritical ammonia, and thus the supercritical temperature is not the temperature actually measured. On the other hand, the pressure in the autoclave is either measured directly or is determined by a calculation taking into account the amount of ammonia initially introduced and the temperature and volume of the retort.

Light emitting device: The light emitting device deposited on the phosphor substrate can be a homogeneous or heterogeneous structure, or a double heterogeneous structure such as a MIS (metal-insulator-semiconductor) junction, a PIN junction or a PN junction. You can choose different luminescence wavelengths by selecting the components of the semiconductor layer and changing the proportions in the mixtures of crystal components. The semiconductor active layer may have a single quantum well or a multi quantum well structure formed on a thin quantum effect enhancing layer so that the output power of this structure can be improved. Regarding the light emitting device used in the present invention, a semiconductor light emitting device with a light emitting layer capable of emitting light of a wavelength that can effectively excite the phosphor substrate is preferred. According to the present invention, emitted light that is converted into a fixed wavelength phosphor substrate can be obtained provided that the wavelength range of the light emitted by the light emitting layer lies in the ultraviolet range (UV radiation), even when the light emitting layer has defects that change the wavelength of the light emitted. Moreover, the light emitted by the phosphor substrate may be mixed with a portion of the light emitted by the other phosphor so that the total light emitted is white.

Different phosphor: The different phosphor is selected to obtain a source of preferred white light by supplementing with any phosphor substrate such as, without limitation, a powder or a substrate. For example, the nitride phosphor may include (1) N; (2) at least one Group II element selected from the group consisting of Be, Mg, Ca, Sr, Ba and Zn (activated by at least one rare earth element selected from the group consisting of Y, La, Ce, Pr, Nd, Sm , Eu, Gd, Tb, Dy, Ho, Er and Lu) and (3) at least one Group IV element selected from the group consisting of C, Si, Ge, Sn, Ti, Zr and Hf.

The invention is explained in detail in the following working examples.

Comparative example. 1 g of gallium metal and 0.1 g of Zn metal were put into a nickel alloy crucible with an inside diameter of 10 mm, and the crucible was placed in a high pressure autoclave with an inside diameter of 14 mm and a height of 70 mm. Then LiNH2 was poured into the autoclave in a dry glove box, it was tightly closed and the gases were emptied from the inside of the autoclave using a special system, and 4.9 g of ammonia was dropped in the reaction chamber. After resealing the autoclave, it was placed in an oven and heated to a temperature of 550 ° C, at which the pressure inside the autoclave reached a value of the order of 4.0 x 10⁸ Pa (4000 bar). The autoclave was kept in this state for 1 week, after which the temperature was lowered to room temperature, and thus the pressure inside the autoclave dropped to about 1.0 x 10⁶ Pa (10 bar). After emptying the ammonia, the autoclave was placed inside a dry glove box and the crucible was removed. The crucible contents were washed with water to allow hydrolysis and washing of the LiNH2 as a highly water-soluble LiOH. The solid residue from the crucible was dried and the result was a GaN: Zn phosphor in the form of a free flowing white powder. Photograph of the phosphor by a scanning field electron microscope (x25000 magnification) shows many crystallites in the shape of hexagonal bars, which indicates the good crystalline quality of the phosphor.

PL 211 013 B1

The obtained phosphor was illuminated with ultraviolet radiation with a wavelength of 365 nm, and then its luminescence spectrum was measured. The measurement results are shown in Fig. 7. The same phosphor was also inserted into an electron beam with a voltage of 7 kV and a current density of 0.5 μΑ / cm³and the results of the measured cathodoluminescence are given in Figure 8. Both these graphs show that the obtained phosphor can be efficiently excited by ultraviolet radiation or an electron beam and can emit blue light. The emissive luminance obtained by excitation of the phosphor according to the invention with ultraviolet rays or an electron beam was respectively 156% and 160% of the emissive luminance of the GaN: Zn phosphor obtained according to the method described in Japanese Patent Publication No. 51-41686. This means that a very significant improvement in the emission properties of the phosphor was achieved.

For the phosphor obtained in this way, X-ray diffraction analysis was also performed using a powder diffractometer. The obtained diffraction patterns are shown in Fig. 9. They showed that the phosphor has a wurcite crystal structure belonging to the hexagonal system. Regarding the lattice constants, the a-axis length was 3.189 angstroms and the c-axis length was 5.185 angstroms. Then, based on the Scherrer equation, the crystallite diameter in the direction (102) was calculated. The crystallite diameter of the GaN: Zn phosphor obtained by the method described in Japanese Patent Publication No. 51-41686 was 285 angstroms, while the crystallite diameter of the phosphor according to the invention was 857 angstroms. For wavelengths ranging from 380 nm to 730 nm, the spectral reflectance of the obtained phosphor was also measured. The results are shown in Fig. 10, the measurement was relative, that is, it was carried out with the assumption that the spectral reflectance of a typical standard - white barium sulfate - is 100%. Fig. 10 shows that the color of the phosphor according to the invention is white and that the spectral reflectance is not less than 70% in the wavelength range from 430 nm to 730 nm. Thus, since the phosphor according to the invention has a high spectral reflectance and its absorption coefficient is low, it can emit light efficiently.

Example 1.

In a high pressure autoclave (Figure 4 and 5) with an inner diameter of 40 mm, a length of 480 mm (D / L = 1/12) and a volume of 585 cm³, in the dissolution zone 13, the 30 g GaN source material was placed in the crucible, and in the crystallization zone 14, a 2.54 cm (1 inch) diameter seed in the form of GaN obtained by the HVPE method. Thereafter, 1.2 g of 6N-pure gallium and 1.2 g of Zn-metal, and then 7 g of 3N-pure lithium metal (or 23 g of sodium metal) were introduced into autoclave 1 as a mineralizer. Then 238 g of ammonia (5N) were introduced into autoclave 1 and sealed. Autoclave 1 was placed in a set of ovens 4 and heated to 200 ° C for 3 days.

Thereafter, the temperature in the dissolving zone 13 was increased to 425 ° C, and simultaneously in the crystallization zone 14 the temperature was increased to 525 ° C. As a result, the pressure inside the autoclave was about 2.5 x 10⁸ Pa (2.5 kbar). The autoclave was left under these conditions for a further 28 days (Fig. 6). As a result of the process, the source material in the dissolution zone 13 was partially dissolved, and in the crystallization zone 14, an increase in GaN: Zn was observed on the HVPE-GaN seed.

The obtained crystal was subjected to the following processes in order to be used as a substrate:

1) The single crystal deposited on the 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 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 positioned at an angle of 1 degree or less to make it off-angle. Then, the sample was cut into 5 plates by means of a diamond grit, 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 back in the oven and annealed for 1 to 5 hours under a nitrogen atmosphere containing a small amount of oxygen at a temperature of 600 ° C to 900 ° C. (The samples prepared in this way are called GaN: Zn phosphor substrates)

4) The GaN: Zn phosphor substrates were then glued to the polishing plates with glue, placed on a grinding machine manufactured by Logitech Ltd., and the GaN: Zn phosphor substrates were polished sequentially on each side. The polishing process used diamond coating and colloidal silica with a pH from 3 to 6 or an alumina solution with a pH from 9 to 11. As a result, the surface roughness was below 10A.

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5) Then, a GaN or AlGaN protective layer less than a few μm thick was applied to the surface of the GaN: Zn phosphor substrate by the HVPE method under the following conditions, thanks to which a template substrate was obtained.

HVPE terms:

reaction temperature: reaction pressure: NH3 partial pressure: GaCl partial pressure: carrier gas:

1050 ° C, atmospheric pressure approx. 3 x 10⁴ Pa (0.3 atm) approx. 1 x 10 hydrogen

Pa (0.001 atm)

If desired

6) after polishing, the obtained substrate was kept in supercritical ammonia without the addition of mineralizer for 1 day at the temperature of 200 ° C, which resulted in the removal of impurities from the substrate surface.

The obtained phosphor substrate was excited by UV radiation with a wavelength of 365 nm, and its luminescence spectrum was measured. The peak was at a wavelength of 400-480 nm.

7) Next, a UV-emitting LED device was deposited on the phosphor substrate 101. The parameters of the nitride semiconductor 102 are described below. The following steps were taken in turn:

A layer of undoped GaN with a thickness of 5 μm is deposited, a cover layer of the type no thickness of 400 angstroms with Al0.18Ga0.82N doped with Si (Si dopant concentration: 5 x 10¹⁷/ cm³) and the active layer with a total thickness of 420 angstroms comprising a layer of Al0.1Ga0.9N doped with Si with a thickness of 200 angstroms / layer In0.03Al0.02Ga0.95N with a thickness of 70 angstroms / layer of Al0.1Ga0.9N doped with Si and a thickness of 40 angstroms / layer In0.03Al0.02Ga0.95N with a thickness of 70 angstroms / layer of Si-doped Al0.1Ga0.9N, with a thickness of 40 angstroms. Then, a p-type cladding layer is deposited, comprising a layer of Al0.2Ga0.8N doped with Mg, 600 angstroms thick, a p-type contact layer, 0.1 μm thick, with Al0.04Ga0.96N doped with Mg (Mg doping concentration: 1 x 10¹⁹/ cm³) and the Al layer₀.₀₁Ga₀.₉₉N-doped with Mg (concentration of Mg admixture: 2 X 10²¹/ cm³), 0.02 μm thick.

In the resulting LED device (Fig. 11), an n-type electrode and a p-type electrode are formed on the same side. LED device: emits UV light with a wavelength of 373 nm, output power: 4.2 mW and Vf: 3.5V with a forward current of 20 mA. In addition, the wavelength is converted by the phosphor substrate, resulting in a device emitting light with a wavelength of 460 nm. The light emitting device is preferably in the form of a spherically contact structure type device having a light extraction plane on a sidewall of the phosphor substrate indicated.

According to the present invention, the spectral reflectance of the phosphor is high and the absorption rate of the phosphor is low, so it can emit light efficiently.

Example 2 The light emitting device obtained in Example 1 was formed into a spherically contact structured device, and then the light emitting device having a second phosphor was formed. The second phosphor can be formed by covering the surface of the light extraction plane of the phosphor substrate or by forming a resin mixed with the phosphor. According to the present example, the light emitting device (101, 102) is made as a spherically contact structure type device, and the layer 103 of nitride phosphor (Ca_a97Eu_{aci: 3})₂Si₅N₈ is applied by sputtering or screen printing to the surface of the light extraction plane of the phosphor substrate of the light emitting device so as to obtain a white light source (Fig. 12).

Example 3 The light emitting device obtained in Example 1 was made into a spherically contact structured device using a yttrium-gadolinium-aluminum oxide phosphor, an activated ceremony (Y-Gd-Al-O: Ce) as a phosphor to coat the surface of the substrate a light-emitting device by spraying or silk-screening so as to obtain a source of white light.

Example 4. In the light-emitting device obtained in example 1, the surface of the substrate of the light-emitting device is coated with Ca2Si5N7: Eu nitride phosphor with addition B, so as to obtain a white light source.

Example 5 In the light-emitting device obtained in example 1, the substrate surface of the light-emitting device is coated with (Ca0.97Eu0.03) 2Si5N8 and a cerem-activated yttrium-gadolinium-aluminum oxide phosphor (Y-Gd-Al-O: Ce ) to obtain a white light source.

Industrial Applicability: A high quality nitride phosphor substrate can be produced by crystallization from a supercritical solution containing ammonia, thus a light emitting device containing such a substrate can be obtained.