A template type substrate and a method of preparing the same

The present invention relates to template substrates for opto-electrical or electrical devices and a method of producing such a substrate. More particularly, the present invention relates to a template substrate for use in opto-electric devices such as light emitting diodes - LEDs and laser diodes - LD or in electrical devices such as MOSFET.

Background of the invention

Currently used gas phase epitaxy substrates typically include sapphire, Sic, GaAs and S, and the resultant epitaxial layers deposited on such a substrate still have an unfavorably high dislocation density, on the order of 10 / cm. Therefore, it was proposed to impose ELOG-type structures on such a substrate, which allowed to reduce the dislocation density to the level of 10⁶/ cm²but even this dislocation density is too high to be able to ensure proper functioning of many electronic and optoelectronic devices, and in particular high power semiconductor lasers. There is also an additional problem that the substrates thus obtained have a reduced epitaxial surface area due to the ELOG structures. For these reasons, we have proposed other methods of obtaining monocrystalline nitrides containing gallium or aluminum, such as those given in the Polish patent application no. P-347918, according to which a method of obtaining volumetric monocrystalline nitrides, an example of which is gallium nitride, has been proposed by recrystallizing them from a supercritical solution. ammonia. A characteristic feature of the volumetric monocrystalline gallium nitrides obtained with the use of the above-mentioned supercritical ammonia solution is the low dislocation density (in the case of volumetric GaN: 10⁴/ cm²). These nitrides are obtained, however, with a low growth rate - in fact several times slower than the growth rate in gas phase growth methods.

The inventors, as a result of intensive research work, that it is possible to significantly reduce the dislocation density of gas-deposited epitaxial layers without the need to use ELOG structures, if the gas-phase growth process is carried out on the surface of a substrate made of a gallium-containing bulk monocrystalline nitride or aluminum produced by crystallization from supercritical ammonia solution, and maintaining the entire major surface of the substrate as a completely Ga-polar surface for a further epitaxial method of fabricating opto-electric and electrical devices. This is clearly different than in the case of the ELOG type substrate.

Disclosure of the Invention

It is therefore an object of the present invention to provide a template substrate and a method for producing a template substrate based on said novel bulk monocrystalline nitride.

In accordance with the present invention, a template substrate for use with optoelectric or electrical devices comprises A) a bulk monocrystalline nitride layer which comprises a gallium or aluminum containing nitride having the general formula Al_xGa_1-xN, where 0 <x <1, and further containing at least one element of the alkali metals (Group I, IUPAC 1989) and B) a layer of nitride defined by the general formula Al_xGa_1-xyIn_yN, where 0 <x <1, 0 <y <1, 0 <x + y <1, embedded by epitaxial gas phase growth, where layer A) and layer B) are connected on the non-N-polar side of the layer A) and the N-polar side of layer B).

Preferably, layer B) is produced on a substrate having layer A) by the MOCVD, HVPE or MBE method.

Even more preferably, layer B) is composed of at least two layers, and the first layer B1) is produced on a substrate having layer A) by the MOCVD or MBE method, and the second layer B2) is produced on the first layer B1) by the HVPE method.

Preferably, the substrate according to the invention comprises a layer A) of bulk monocrystalline nitride produced on a seed having layer B) by crystallization of a nitride with a supercritical ammoniacal solution containing at least one alkali metal element.

Preferably, the substrate of the invention further comprises a gallium or aluminum containing nitride layer C) deposited by a vapor epitaxial growth method, wherein the bulk monocrystalline nitride layer A) containing at least one alkali element (Group I, IUPAC 1989) is formed from both on the non-N-polar surface and on the N-polar surface

The germinal surface of layer B) forms layers A1) and A2), and layer C) is connected to the non-N-polar side of layer A1) with the N-polar side of layer C).

Even more preferably, the gallium or aluminum containing nitride layer C) is produced on the substrate constituting the layer A1) by a MOCVD, HVPE or MBE method.

Even more preferably, layer C) is composed of at least two layers and the first layer C1) is produced on the substrate in the form of a layer A1) by the MOCVD or MBE method, and the second layer C2) is formed on the first layer C1) by the HVPE method.

Preferably, the substrate of the invention comprises chloride and has a major surface which is substantially the Ga polar side.

Preferably, the substrate according to the invention has a dislocation density of 10⁶/ cm² or less.

Preferably, layer A) or layers A1) and A2) are of bulk monocrystalline nitride produced by the crystallization of nitride from a supercritical ammonia solution containing at least one alkali metal element.

Preferably, layer A) having two surfaces lying in plane C and having a diameter of 2.54 cm (1 inch) or more is formed by growth in the A direction from bulk monocrystalline nitride in a supercritical ammonia solution containing at least one alkali metal element.

Most preferably, the substrate of the invention has a dislocation density of the order of 10⁴/ cm² or lower.

Preferably, the concentration of at least one alkali metal in layer B) or C) of gallium or aluminum containing nitride and in layers B1) and B2) or C1) and C2) is lower than the concentration of such metal in layer A) obtained by crystallization of nitride in a supercritical ammonia solution containing at least one element of the alkali metals.

Preferably, the nitride layer A) consists of AlN or GaN.

Even more preferably, layer B), B1), C) or C1) is produced by the MOCVD method and has a thickness of 0.1 to 3 µm.

More preferably, layer B or C) obtained by the gas phase growth method also has the structure defined by the general formula Al_xGa_1-xyIn_yN, where 0 <x <1.0 <y <1.0 <x + y <1.

Even more preferably, layer B) or C) is a combination of AlGaN and GaN double layers.

Preferably, layer B) or C) is nitride containing gallium or aluminum doped with silicon (Si) or oxygen (O) as the donor dopant.

Preferably, layer B) or C) is nitride containing gallium or aluminum doped with magnesium (Mg) or zinc (Zn) as acceptor dopant.

Most preferably, the dopant concentration in the substrate according to the invention is in the range of 10¹⁷/ cm³ up to 10²¹/ cm³.

The invention further comprises a method of producing a template substrate comprising the steps of:

(a) producing layer A) from a bulk monocrystalline nitride which contains a gallium or aluminum-containing nitride defined by the general formula Al_xGa_1-xN, where 0 <x <1, and furthermore containing at least one element of the alkali metals (Group I, IUPAC 1989), having a thickness appropriate for the substrate by crystallization of nitride containing gallium or aluminum on the nucleus of a supercritical ammonia solution, thereby, that a supercritical ammonia solution containing alkali metal ions is produced in the autoclave, and then at least two zones differing in temperature are generated in the autoclave, wherein the source material containing gallium or aluminum in the dissolution zone at the lower temperature and the seed is placed in the crystallization zone at the higher temperature, and the temperature difference between the dissolution zone and the crystallization zone is controlled to ensure chemical transport by convection in the supercritical solution , where the temperature difference between the dissolution zone and the crystallization zone is greater than 1 ° C, and the supercritical ammoniacal solvent is NH₃ containing alkali metal ions and / or its derivatives, and furthermore the source material consists essentially of gallium or aluminum-containing nitride, or precursors thereof selected from the group consisting of azides, imides, amido-imides, amides, hydrides, metallic compounds and alloys containing gallium or aluminum, as well as metallic gallium, and the seed has at least a crystalline layer of nitride containing gallium or aluminum, or other Group XIII elements (according to IUPAC, 1989), wherein crystallization of the gallium or aluminum-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 appropriate solubilities of the source material and the gallium-containing nitride, or aluminum and molar ratio

The alkali metal ions to the remaining components in the supercritical solvent are controlled in the range from 1: 200 to 1: 2, and (b) the formation of a layer B) of a nitride represented by the general formula A1_xGa₁._x._yIn_yN, where 0 <x <1, 0 <y <1.0 <x + y <1, by epitaxial growth from the gas phase on the Al-polar or Ga-polar side of layer A) to form a substrate comprising layer A) and layer B) connected by the Al-polar or Ga-polar side of layer A) and the N-polar side of layer B).

Preferably, the method of the invention comprises the additional step (c) polishing one of the surfaces of layer B) to obtain a vapor phase epitaxy substrate.

Preferably, the method of the invention comprises the further annealing step of the obtained substrate comprising layers A) and B) in an atmosphere containing no hydrogen but containing oxygen at a temperature ranging between about 600 and 1050 ° C, thereby obtaining a better quality material. crystalline than before this treatment.

Even more preferably, the annealing step in the process according to the invention is carried out in an inert atmosphere with an addition of oxygen ranging from 10 to 30% by volume.

Preferably, the annealing step is carried out in a single step or in multiple steps until the desired level of impurities (such as hydrogen and / or ammonia or ions arising from impurities generated during the crystallization and / or annealing process) is achieved.

Preferably, the method according to the invention comprises the further step of removing impurities from the bulk monocrystalline nitride by scrubbing in a supercritical ammonia solution, water or carbon dioxide, or treating it with gaseous hydrogen, nitrogen or ammonia.

Preferably, the rinsing step of the method according to the invention is carried out with simultaneous application of ultrasound or exposure to an electron beam.

The present invention is illustrated in the accompanying drawing, where

Fig. 1 is a graph of temperature versus time in an autoclave, where p = const., And shows the relationship between the temperature change and the dissolution and crystallization processes for the present invention;

Fig. 2 is a graph of pressure change versus time in an autoclave, where T = const., And shows the relationship between the pressure change and the dissolution and crystallization processes for the present invention;

Fig. 3 is a vertical section through an autoclave with a stack of ovens used in the present invention;

Fig. 4 is a perspective view of an apparatus for obtaining bulk monocrystalline gallium nitride;

Fig. 5 shows a graph of the relationship between the solubility of GaN in supercritical ammonia with the addition of potassium amide (with the ratio of the Mineralizer: NH₃ = 0.07) and pressure for T = 400 ° C and T = 500 ° C;

Fig. 6 shows the temperature variation with time in an autoclave in the process described in the example below;

Fig. 7 schematically shows a section through a first embodiment of template support according to the present invention;

Figures 8A and 8B schematically show cross sections through a second embodiment of a template substrate according to the present invention;

Fig. 9 is a schematic plan view showing the process of making an embryo obtained by growth in the direction of the A axis.

In the present invention, the growth of the gallium or aluminum-containing monocrystalline nitride is achieved by chemical transport in a supercritical solvent containing one or more mineralizers that contribute to its ammoniacal character. It is therefore an ammonium base crystallization technique and the terms used in relation to the present invention should be understood in accordance with the definitions below:

Group XIII element (s) nitride means the nitride of the Group XIII element (s), that is, aluminum, gallium and indium alone or in any combination. The gallium-containing nitride is most preferably such a nitride.

Gallium or aluminum containing nitride means gallium (or aluminum) nitride and optionally other Group XIII element (s) (numbering according to IUPAC, 1989). The term includes but does not

The compound is restricted to the GaN (or AIN) binary compound, the AlGaN, InGaN ternary compound or the AlInGaN ternary compound in which the gallium contributes significantly, in any case, higher than the dopant level. The proportion of other elements in its structure in relation to gallium (aluminum) can be changed to an extent that does not interfere with the ammoniacal nature of the crystallization technique. (The above formulas are intended to indicate the components of the nitrides in question. They are not intended to indicate the relative amounts of these ingredients.)

Volumetric monocrystalline nitride containing gallium or aluminum is defined as a monocrystalline gallium-containing nitride substrate on which by MOCVD or epitaxial growth methods such as, for example, HVPE, opto-electronic devices such as light emitting diodes (LEDs) or laser diodes (LD) can be produced.

The C, A or M plane denotes the surfaces of the C, A or M plane of hexagonal crystals of nitrides of Group XIII elements.

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

The gallium or aluminum containing source material is a gallium or aluminum containing nitride or a precursor thereof. GaN (AlN) obtained by any method, for example by flux methods, high pressure HNP method, HVPE method, or polycrystalline GaN (AlN) obtained in situ from metallic gallium (aluminum) by a chemical 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 or aluminum-containing nitride of the source material. The supercritical ammonia solvent may also contain ammonia derivatives and / or mixtures thereof, in particular hydrazine.

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 or aluminum-containing nitride.

Substances containing anaerobic particles which weaken the ammoniacal character of the supercritical solvent are selected from the group consisting of:

(a) compounds of formula A_mB_n, where A is H + and / or metal, preferably alkali, NH4 +, Si, S, P, and B is halogens, S, P and n and m are corresponding stoichiometric ratios of not less than 1 and / or

b) groups of particles such as:

- S4N4, S2N2, SN, S4N2, S11N2, P3N5, P4N6, PN,

- PN2-, PN34-, PN47-, PN-, PN2-,

- PNCl2, P (NH) 2NH2, P4S10, NP (SNH4) 2, NPSNH4SH, NP (SH) 2, PNS,

Sulfur or silicon particles embedded in the gallium-containing nitride crystal lattice act as donors; magnesium, zinc and cadmium are acceptors; dopants such as manganese or chromium in the gallium nitride crystal lattice give it magnetic properties; while phosphorus atoms are isoelectronic to nitrogen atoms, so they create a narrower band gap than that of pure gallium nitride. These particles not only weaken the ammoniacal nature of the supercritical solvent but also change the optical, electrical and magnetic properties of 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 its derivatives such as NH₂-, NH₂- surround the centrally located gal. An analogous definition applies to the term dissolving of aluminum source material.

Supercritical ammonia solution is a solution resulting from dissolving a source material containing gallium or aluminum in a supercritical ammoniacal solvent.

Solubility: Our experience shows that at a sufficiently high temperature and pressure, between a solid, gallium or aluminum-containing nitride, and a supercritical solution of 6

In this condition, an equilibrium state may occur. Therefore, the solubility of gallium or aluminum containing nitride can be defined as the equilibrium concentration of soluble gallium (aluminum) compounds obtained by the above-mentioned dissolution process for gallium or aluminum containing nitride. In this process, the equilibrium concentration, i.e. solubility, can be controlled by changing the solvent composition, temperature and / or pressure.

Negative solubility temperature coefficient (negative TWR) means that while maintaining the stability of all other parameters, the solubility is monotonically decreasing as a function of temperature. Similarly, a positive solubility pressure coefficient (positive CWR) means that while all other parameters are held constant, solubility is a monotonically increasing function of pressure. In our tests, we have shown that the solubility of gallium or aluminum containing nitride in a supercritical ammoniacal solvent, over a temperature range of at least 300 to 550 ° C and a pressure of 100 to 550 MPa, has 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 for 8 days at 400 ° C (i.e. after the dissolution process), recrystallization of gallium nitride can be obtained by increasing the temperature inside the autoclave to 500 ° C and maintaining a constant pressure of 200 MPa (crystallization process ). In turn, according to the diagram of Fig. 2, after dissolving the source material in an autoclave under elevated pressure maintained for 2 days at 350 MPa (i.e. after the dissolution process), 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 (aluminum) compounds in the supercritical ammonia solution is higher than the solubility of the gallium or aluminum containing nitride under the given physico-chemical conditions, the supersaturation of the supercritical ammonia solution with the gallium or aluminum containing nitride under these conditions can be defined as the difference this actual concentration and solubility. By dissolving gallium or aluminum containing nitride in a closed system, supersaturation can be achieved by, for example, increasing the temperature or reducing the pressure.

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

The seed, as already indicated, is essential to obtain the desired volumetric monocrystals of gallium or aluminum containing nitride in the process of the invention. Since it has a major influence on the crystal quality of the gallium or aluminum bulk nitride single crystals produced by the process of the invention, the best possible seed quality should be selected. A variety of structures or surface-modified tiles can also be used. For example, a structure may be used as a nucleus having a series of surfaces, respectively spaced apart, distributed on the primary substrate and susceptible to lateral build-up of crystalline nitrides. Furthermore, an embryo having an n-type electrically conductive homoepitaxial surface, for example doped with Si, may be used. These types of nuclei are produced by methods of growing nitrides containing gallium from the gas phase, such as HVPE or MOCVD, or MBE. Doping with Si during the growth process in an amount of 10 to 10 / cm gives them an electrical conductivity of the n-type. Moreover, a compound seed can be used, and in the case of such a seed, a layer of GaN doped with Si can be deposited directly on the primary substrate or on a buffer layer with, for example, AIN. Moreover, for a particular future application, the growth of bulk single crystals may be carried out by the method of the present invention on homo-seeds having a specific orientation with respect to the hexagonal lattice of the group XIII nitride nitride (s) type vurcite, such as the C plane, the A plane or the M plane of the respective nitride.

PL 224 992 B1

Spontaneous crystallization from supersaturated supercritical ammonia solution is the undesirable process of nucleation and growth of gallium or aluminum containing nitride crystals to occur inside the autoclave anywhere other than the seed surface. 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.

Nuclear 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 MOCVD (Metal-Organic Chemical Vapor Deposition) method is a vapor-phase epitaxial deposition process in which ammonia and gallium organometallic compounds are used as substrates for gallium nitride.

The HVPE (Halide Vapor Phase Epitaxy) method is a method of deposition of epitaxial layers from the gas phase, in which metal halides and ammonia are used as reagents in the production of nitrides.

Autoclave is a closed autoclave having a reaction chamber in which crystallization is carried out in an ammoniacal nature according to the present invention.

According to a first aspect of the present invention, there is provided a template substrate for use with opto-electric or electric devices which comprises A) a bulk monocrystalline nitride layer containing at least one alkali metal element (Group I, IUPAC 1989) and B) a nitride layer embedded by the method of epitaxial growth from the gas phase, wherein layer A) and layer B) are joined on the non-N-polar side of layer A) and on the N-polar side of layer B). As used herein, the term non-polar nitride surface means the polar surface of any element other than nitrogen present in the nitride. In the case of a gallium containing nitride, the non-N-polar surface typically is a Ga-polar surface, and in the case of an aluminum containing nitride it is an Al-polar surface.

According to the present invention, we can obtain an excellent epitaxial layer deposited from the gas phase on the Ga-polar or Al-polar surface of a monocrystalline substrate of formula Al_xGa_1-xN, where 0 <x <1, if the substrate can be obtained using a method based on the use of supercritical ammonia solution and the obtained template substrate containing layers A) and B) is very useful in the production of opto-electric or electrical devices by epitaxial growth from the gas phase.

In the present invention, the layer A) of bulk monocrystalline nitride comprises a gallium or aluminum containing nitride represented by the general formula Al_xGa_1-xN, where 0 <x <1. Layer A) is typically a monocrystalline AlN or GaN substrate which can be obtained by the methods described in WO 02/101120 and WO 02/101124, based on the use of a supercritical ammonia solution. Thus, in the present specification, a method based on the use of supercritical ammonia solution is the technology defined below and in WO 02/101120 and WO 02/101124.

In the present invention, the nitride layer B) deposited by vapor epitaxial growth is defined by the general formula Al_xGa_1-xyIn_yN, where 0 <x <1, 0 <y <1, 0 <x + y <1. Layer B) can be deposited on a substrate having a layer A) by the MOCVD method (Metal Ogranic Chemical Vapor Deposition - i.e. by deposition of layers (epitaxy) from the vapor phase containing organometallic compounds), HVPE (Hydride or Halide Vapor Phase Epitaxy - i.e. by deposition layers (epitaxy) from the gas phase containing metal hydrides or halides) or MBE (Molecular Beam Epitaxy - i.e. by deposition of layers (epitaxy) from the so-called "Molecular beam"), which methods are well known, and one skilled in the art can readily employ this type of well-known vapor phase epitaxy in the present invention, although these methods are not described herein. In the present invention, layer B) typically comprises semiconductor layers of GaN, AlGaN, InGaN and AlGaInN compounds.

PL 224 992 B1

In a preferred embodiment of the present invention, layer B) may consist of at least two layers, and the first layer B1) may be deposited on a substrate having layer A), by the MOCVD or MBE method, and the second layer B2) may be deposited on the first layer B1. ) by the HVPE method as illustrated in Fig. 7.

The thus obtained template substrate may on the one hand consist essentially entirely of the Ga-polar side, that is to say more than 95%, and preferably more than 99% of its area is the Ga-polar side. Compared to the GaN substrate produced by the HVPE method, using the ELOG method, in which the Ga-polar surface is less than 90% of the surface area of ​​one side of the substrate, due to the presence of the N-polar surface on the same side, now a substrate with excellent quality, in terms of the dislocation density and the half-width (FWHM) of the X-ray reflection, as well as due to the fully Ga-polar surface.

According to a second aspect of the present invention, the template substrate may comprise a layer A) of bulk monocrystalline nitride formed on a seed having layer B) by crystallization of nitride with a supercritical ammonia solution containing at least one alkali metal element. In this case, as shown in Fig. 8A, the template substrate may further comprise a gallium or aluminum containing nitride layer C) deposited by a gas phase epitaxial growth method, wherein the bulk monocrystalline nitride layer A) containing at least one alkali metal element (Group I, IUPAC 1989) is formed on both a non-N-polar surface, such as the Ga-polar or Al-polar surface, and on the N-polar surface of the germinal layer B), forming layers A1) and A2), and layer C) is connected to the non-N-polar side of layer A1) with the N-polar side of layer C). Thus, layer C) from gallium or aluminum containing nitride can be obtained on the substrate constituting the layer A1) by the MOCVD, HVPE or MBE method. In a preferred embodiment layer C) may be composed of two layers and the first layer C1) is deposited on the substrate in the form of a layer A1) by the MOCVD or MBE method, and the second layer C2) may be deposited on the first layer C1) by the HVPE method as illustrated. in Figure 8B. According to the invention, the first layer C1) can protect the surface of the substrate A) so as not to interfere with the HVPE process for the layer C2) and can also prevent diffusion of alkali metals from the substrate A) into the layer C2). The layer C1) is preferably obtained at a temperature lower than the single crystal formation temperature from which it is formed.

According to the present invention, a template substrate having a dislocation density of the order of 10 can be obtained⁶/ cm² or less and with an X-ray reflex half-width (FWHM) value from plane (002) less than 80 arcsec.

In the supercritical ammonia solution process, we found that the A-axis growth is 4 times or more than 4 times faster than the C-axis growth and that the A-axis growth in the Supercritical Ammonia Growth method results in an excessive reduction in dislocation density compared to the C-axis growth in the same method of growth from supercritical ammonia solution. Thus, according to a novel aspect of the present invention, we can obtain a template substrate as illustrated in Fig. 9, where layer A) is a substrate having two surfaces lying in plane C and a diameter of 2.54 cm (1 inch) or more, made of the original substrate in dashed lines obtained by growth in the A-axis from bulk monocrystalline nitride in supercritical ammonia solution containing at least one element of alkali metals. Surprisingly, the original substrate has a dislocation density of the order of 10⁴/ cm² or lower.

The template substrate of the present invention is characterized in that even if the concentration of alkali metal in layer B) or C) of gallium or aluminum containing nitride and in layers B1) and B2) or C1) and C2) is lower than the concentration in layer A) obtained by the crystallization of nitride in a supercritical ammonia solution containing at least one element among the alkali metals, since the alkali metal content depends on the diffusion from layer A) during the deposition process of layer B) or C) and layers B1) and B2) or C1) and C2). In this case, the layer B), B1), C) or C1) can be produced by the MOCVD or MBE method and preferably has a thickness of 0.1 to 3 µm.

In the case of the template substrate of the present invention, the layer C) obtained by the gas phase growth method also has a structure defined by the general formula AlxGa1-x-yInyN, where

0 <x <1, 0 <y <1.0 <x + y <1, as defined by layer B). Thus, in a preferred embodiment of the invention, layer B) or C) may be a combination of AlGaN and GaN double layers. In the case of the first AlGaN layer B1) or C1) prepared at a temperature lower than the temperature of the single crystal, the second GaN gallium nitride layer B2) or C2) will improve the quality of the crystallinity.

In the case of the template substrate of the present invention, layer B) or C) is nitride containing gallium or aluminum doped with silicon (Si) or oxygen (O) as the donor dopant, or nitride containing gallium or aluminum doped with magnesium (Mg) or zinc (Zn) ), as an acceptor dopant, deposited as a result of epitaxial growth from the gas phase. The concentration of impurities is preferably in the range from 10 / cm to 10 / cm.

According to a third aspect of the present invention, there is provided a method of producing a template substrate comprising the steps of:

(a) preparation of layer A) from bulk monocrystalline nitride containing at least one alkali metal element (Group I, IUPAC 1989), with a substrate thickness by crystallization of gallium or aluminum containing nitride in a seed from supercritical ammonia solution, and (b) producing the nitride layer B) by epitaxial growth from the gas phase on the Al-polar or Ga-polar surface of layer A) to form a substrate comprising layer A) and layer B) connected by the Al-polar or Ga-polar surface of layer A) and the N-polar surface of layer B).

In a preferred embodiment of the present invention, an additional step (c) of polishing one of the surfaces of layer B) may be needed to obtain a vapor phase epitaxy substrate, allowing good surface properties for further epitaxial growth. The resulting template substrate comprising layers A) and B) can be subjected to a heat annealing treatment in a hydrogen-free atmosphere at a temperature ranging between about 600 and 1050 ° C, thereby obtaining a material of better crystalline quality than before this treatment. The annealing step is preferably carried out in an inert gas atmosphere with the addition of oxygen ranging from 10 to 30% by volume, and the annealing may be carried out in one step or in multiple steps until the desired level of impurities (such as hydrogen and / or ammonia or ions resulting from these is obtained) impurities during crystallization and / or annealing process).

In addition, there is occasionally a need to remove impurities from the bulk monocrystalline nitride by scrubbing in a supercritical ammonia solution, water or carbon dioxide, or treating it with gaseous hydrogen, nitrogen or ammonia. In such a case, the rinsing step is preferably carried out with simultaneous application of ultrasound or exposure to an electron beam.

The present invention is based on the process of ammoniacal crystal growth and allows the preparation of a monocrystalline nitride containing gallium or aluminum, deposited selectively on the surface of a seed by chemical transport in a supercritical ammoniacal solvent containing one or more mineralizers influencing its ammoniacal nature.

The present process is characterized by the fact that it produces a bulk monocrystalline template substrate with a layer of high structural quality, in which a gallium or aluminum-containing nitride layer is deposited on the gallium or aluminum-containing nitride layer obtained by the vapor-phase growth process, thanks to which, that the autoclave produces a supercritical ammoniacal solution containing alkali metal ions. This autoclave dissolves the source material and then crystallizes the gallium or aluminum containing nitride from this solution on the surface of the seed at a higher temperature and / or lower pressure than the dissolving process of the gallium containing source material in the supercritical solvent.

The object of the first embodiment is to perform the selective crystallization in the feed during the second process, the crystallization. Thus, a second embodiment of the present invention relates to a gallium or aluminum containing bulk nitride crystallization process, characterized in that it produces a bulk monocrystalline template support with a layer of high structural quality. in which a layer of gallium or aluminum containing nitride of high structural quality is deposited on the gallium or aluminum containing nitride layer obtained by the vapor phase growth method and consists in dissolving in a supercritical solution containing ammonia and alkali metal ions to form a supercritical solution in which the nitride gallium has a negative temperature coefficient of solubility and in at least this zone of the autoclave, in which the embryo is located, a zone is created in which the supercritical solution is supersaturated with respect to

Of the seed and the concentration is adjusted by appropriately increasing the temperature and / or decreasing the pressure to avoid spontaneous crystallization and achieve selective growth of the gallium or aluminum containing nitride crystal solely on the surface of the autoclave seed.

Although in the second embodiment two sides of the autoclave are simultaneously formed: the dissolution zone and the crystallization zone, it is desirable to control the supersaturation of the supercritical solution with respect to the seed by adjusting the dissolution temperature and the crystallization temperature. Moreover, the temperature control will be facilitated if the temperature in the crystallization zone is kept between 300 and 600 ° C and the temperature difference between the dissolution zone and the crystallization zone in the autoclave is kept below 150 ° C, preferably below 100 ° C. The supersaturation of the supercritical solution to the embryo can be controlled by placing one or more baffles in the autoclave separating the dissolution zone (low temperature) from the crystallization zone (high temperature) and controlling the convective flow rate between these zones. Moreover, if two zones are formed in the autoclave: a dissolution zone and a crystallization zone, with a suitable temperature difference, the supersaturation of the supercritical solution with respect to the seed can be controlled by using a gallium or aluminum-containing source material introduced as crystalline GaN whose total surface area is greater than the total surface area of ​​the embryo.

In a first embodiment, the alkali metal ions are introduced in the form of alkali metals and / or alkali metal compounds and / or mixtures thereof, especially those which do not contain Group XVII elements (halogens). Such alkali metal ions may include one or more types of ions selected from the group consisting of Li⁺ On⁺ and K⁺. They are preferably introduced in the form of alkali metals and their amides and azides in a molar ratio to ammonia in the range from 1: 200 to 1: 2. The source material dissolved in the supercritical solution is a gallium or aluminum containing nitride, or a gallium precursor which can form gallium compounds soluble in the supercritical solution.

Although the process described in accordance with the present invention is based on reactions in a strictly ammoniacal environment, the use of GaN source material produced by HVPE or other chemical methods is also acceptable, provided that chlorine and other Group XVII elements do not adversely affect the environment. where said reaction takes place.

The source material can be gallium or aluminum containing nitride which undergoes a reversible dissolution process in a supercritical ammoniacal solvent. It may be combined with metallic gallium which reacts irreversibly with the supercritical solution.

The use of nitride containing gallium or aluminum in the form of gallium nitride facilitates the control of the crystallization process. Preference is given to using monocrystalline GaN nuclei, although the following materials may also be used: GaN obtained by HVPE or by the flux method, media obtained by the high pressure method, nuclei with surfaces A (112 0), M (11 00) or R (11 02) cut from a bulk single crystal obtained from supercritical ammonia. For the purpose of crystallization, it is also possible to use the C (0001) surface having an N polarity.

According to the present invention, the dissolution and crystallization processes are usually carried out in parallel and are spatially separated in an autoclave. In other words, the autoclave produces a supercritical ammoniacal solvent that contains alkali metal ions. This solvent dissolves the gallium or aluminum-containing source material, and from this supercritical solution the gallium or aluminum-containing nitride is crystallized on the surface of the seed at a higher temperature and / or lower pressure than the dissolution process of the indicated source material.

In the first embodiment, it is preferred that the dissolution process of the gallium or aluminum-containing source material be supplemented with a process for transferring the supercritical solution to a location of higher temperature and / or lower pressure. In this case, at least two zones with different temperatures are formed in the autoclave, and the gallium or aluminum-containing source material is placed in the low-temperature dissolution phase, while the seed is placed in the higher-temperature crystallization zone. The temperature difference between the dissolution zone and the crystallization zone should be selected to ensure chemical transport within the supercritical solution, which occurs mainly by convection. The temperature difference between the dissolution zone and the crystallization zone is greater than 1 ° C, preferably 5 to 150 ° C, and most preferably less than 100 ° C.

Preferably, the nitride produced according to the invention has the formula Al_xGa_1-xyIn_yN, 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 or at least sodium or potassium ions. The source material mainly consists of gallium or aluminum containing nitride or its precursors selected from the group consisting of azides, imides, amide-imides, amides, hydrides, metallic compounds and alloys containing gallium or aluminum, as well as metallic gallium. The precursor definition can be found later in this document.

In the present invention, the seed contains at least a crystalline layer of nitride containing gallium or aluminum or other Group XIII elements (lUPAC 1989). Preferably, the surface dislocation density of this layer is lower than 10⁶/ cm².

In the present invention, crystallization of the gallium or aluminum containing nitride may take place at a temperature between 100 and 800 ° C, preferably between 300 and 600 ° C, and most preferably between 400 and 550 ° C. The pressure may be between 10 and 1000 MPa during the crystallization of the gallium or aluminum containing nitride. Preferably between 100 and 550 MPa and most preferably between 150 and 300 MPa.

The concentrations of alkali metal ions in the supercritical solvent are controlled to provide appropriate dissolution properties of the source material and the gallium or aluminum containing nitride, and the molar ratio of alkali metal ions to other molecules in the supercritical solvent is controlled from 1: 200 to 1: 2, preferably from 1: 100 to 1: 5, most preferably from 1:20 to 1: 8.

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

The aforementioned method and apparatus make it possible to obtain a monocrystalline volumetric nitride containing gallium or aluminum. The volumetric single crystal has a low dislocation density (for volumetric GaN it is 10⁴/ cm²). Importantly, the monocrystalline bulk GaN may be over 2.54 cm (1 inch) in diameter and 3 mm (preferably 5 mm) thick. 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 then be used as seeds. In order to improve their n-type electrical conductivity, the concentration of n-type carriers is advantageously increased by doping with Si during the growth from the gas phase.

If the gallium or aluminum containing nitride is deposited by the vapor phase growth method, it is preferred that the gallium or aluminum containing nitride obtained 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. By doping with Si nitride containing gallium or aluminum, Al can be obtained from the gas phase in the growth process_xGa_1-xyIn_yN (0 <x <1, 0 <y <1, 0 <x + y <1) with n-type electrical conductivity, and since it was crystallized on nitride containing gallium or aluminum obtained in supercritical ammonia under the conditions of growth from the gas phase it can produce a template substrate with good crystalline quality and a dislocation density below 10⁵/ cm².

A preferred embodiment of the present invention.

In accordance with step a) of the production of layer A), the process of the invention separates the process of dissolving the source material and the process of converting the supercritical solution to a higher temperature and / or lower pressure, in which the gallium or aluminum containing nitride crystallizes on the seed surface. Moreover, the method includes the possibility of simultaneously creating in the autoclave at least two zones of differing temperature, wherein the gallium or aluminum-containing source material is placed in the lower temperature dissolution zone and the seed is placed in the higher temperature crystallization zone. The temperature difference between the dissolution zone and the crystallization zone is adjusted to provide convection chemical transport in the supercritical solution, the temperature difference between the dissolution zone and the crystallization zone being greater than 1 ° C. The gallium or aluminum-containing nitride obtained in supercritical ammonia has the form Al_xGa_1-xN where 0 <x <1 and the gallium or aluminum 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 or aluminum-containing nitride, or precursors thereof selected from the group consisting of azides, imides, amide-imides, amides, hydrides, metals and alloys containing gallium or aluminum, as well as gallium metal. The embryo has at least a crystalline layer of nitride containing gallium or aluminum or other Group XIII elements (according to IUPAC, 1989).

Crystallization of nitride containing gallium or aluminum takes place at a temperature of 100 to 800 ° C and a pressure of 10 to 1000 MPa, and the content of alkali metal ions in the supercritical solvent

The material is adjusted to provide the correct solubilities of the source material and the gallium or aluminum 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 measurements showed 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 60arcsec, 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 NH₃as 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 for temperatures of 400 and 500 ° C, where the solubility is defined by mole percent: S_m = GaN^solution (KNH₂ + NH₃) x 100%. In the presented case, the solvent is a KNH solution₂ 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 in Sm can be expressed as follows:

AS_m «(5S_m/ 5T)_:::.AT + (5S_m/ 5p) -r, xAp + (5s_m/ 5x)_No.Ax, where the partial derivatives (5s_m/ 5T)_p,_x, (æ? S_m/ æ? p)_T.._x, (5S_m/ 5x)_T.,_p determine the behavior of S._m with the change of individual parameters. In the present description, these derivatives are referred to as "coefficients" (for example (5S_m/ 5T)_p,_x is the "temperature coefficient of solubility (TWR)").

From the graph in Fig. 5 it can be seen that the solubility increases with increasing pressure and decreases with increasing temperature. These relationships make it possible to obtain volumetric monocrystalline nitride containing gallium or aluminum by dissolving it under conditions of higher solubility and crystallizing under conditions of lower solubility. A negative temperature coefficient means that in the presence of a temperature gradient, chemical transport of the gallium or aluminum 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 having the above compositions can be introduced into a solvent based on the simplest substrate, gallium metal. Then, by suitably changing the conditions (for example by increasing the temperature), both a solution supersaturated with gallium or aluminum containing nitride and seed crystallization can be obtained. The process according to the invention makes it possible to obtain a volumetric growth of a monocrystalline nitride containing gallium or aluminum on the seed and leads in particular to the production of a stoichiometric gallium nitride obtained as a monocrystalline volumetric layer on the nucleus of gallium nitride. Due to the fact that such a single crystal is obtained in a supercritical solution containing alkali metal ions, it also contains alkali metals in an amount higher than 0.1 ppm. On the other hand, since it is preferable to maintain the purely basic nature of the supercritical solution (in particular to avoid corrosion of the apparatus), 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 lattice constant of the obtained nitride. Moreover, the bulk monocrystalline GaN can be doped with dopants of the donor (for example Si, O) and / or acceptor (for example Mg, Zn) and / or magnetic (for example Mn, Cr) type in concentrations from 10 to 10 / cm. These admixtures alter the opto-electric, electrical and magnetic properties of the gallium or aluminum 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 surface defect density lower than 10⁴/ cm² and at the same time the half-width of the X-ray reflection from the plane (0002) below 60arcsec (for the Cu Ka beam₁).

The apparatus for obtaining volumetric single crystals is shown in Fig. 3 and Fig. 4. The main component of the apparatus 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 team of two

The furnaces 4 are equipped with heating devices 5 and / or cooling 6 and secured in the desired position in relation 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 strips 9 wrapped around the furnaces 4 and beds 8. The bed 8 with the set of furnaces 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 are regulated. regulated by installation 2, made in the form of a horizontal partition 12 covering more than 70% of the cross-sectional area of ​​the autoclave, separating 1 dissolution zone 13 in the autoclave and a crystallization zone 14. A horizontal baffle 12 is located at about half the length of the autoclave. The temperature value in 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 a control device 15. In the autoclave 1, the dissolution zone 13, coinciding with the low-temperature zone of the furnace assembly 4, is located above the horizontal barrier (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 (or aluminum) 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 installation 2 is located is equipped with a cooling device 6 enabling it to be cooled. Due to the cooling in the area of ​​the partition 12, the temperature difference between the dissolution zone 13 and the crystallization zone 14 can be controlled. At the level of the bottom of the crystallization zone there is a cooling device 18, which allows it to be cooled quickly 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 volume monocrystalline gallium nitride thus obtained may have a surface dislocation density of less than 10 / cm and a half-width of the X-ray reflection from the plane (0002) below 60 arcsec (for the Cu Ka beam)₁). 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, under such conditions, using the HVPE method, a 3 mm layer of GaN with n-type electrical conductivity can be applied to them by maintaining a growth rate of 30 g / m / for 100 hours. hour.

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, also have electrical conductivity, so they can be used as substrates for opto-electronic devices based on semiconductors, such as laser diodes.

In the dissolution zone 13 of the high pressure autoclave 1 with a diameter of 40 mm, a length of 480 mm and a volume of 600 cm, the source material in the form of metallic gallium (6N) with a mass of 53.0 g was placed. In the crystallization zone 14 of the same autoclave, a seed (diameter 2.54 cm-1 inch and weighing 2.0 g) in the form of a GaN wafer obtained by the A-axis growth method in supercritical ammonia, illustrated in Fig. 9 (the embryo is in the form of a plate with the length (L), growth in the direction of the axis A (W) on both sides of the plane A and a circumferential edge in the plane M).

As a mineralizer, 12.0 g of metallic sodium of 4N purity and 19.5 g of metallic potassium 4N were introduced into the autoclave. The autoclave 1 was then filled with 255.0 g of ammonia (5N), sealed and placed in the furnace set 4. The dissolution zone 13 was heated (at a rate of approx. 1 ° C / min) to 450 ° C (Fig. 6). During this time, the crystallization zone was not heated and its temperature did not exceed 250 ° C. Thus, a supercritical ammonia solution with a molar ratio KNH2: NH3 = 0.035 was obtained; 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.

Then the temperature in the dissolution zone was increased to 500 ° C (at a rate of approx. 1 ° C / min), the temperature of the crystallization zone was gently increased to 550 ° C (at a rate of approx. 1 ° C / min, Fig. 6), and the internal pressure was the autoclave reached a value of about 280 MPa. The autoclave was kept under these conditions (second step of the process) for another 20 days (Fig. 6). As a result of this process, partial dissolution of the source material (i.e. polycrystalline GaN) was observed

In the dissolution zone and gallium nitride crystallization on the HVPE seed in the crystallization zone. Gallium nitride crystallized on both sides of the embryo in the form of monocrystalline layers with a total thickness of 2 mm.

Crystals obtained in a similar manner in supercritical ammonia 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, 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 attached to the polishing pads, placed on a Logitech Ltd. grinder, 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 μm was applied to the surface of the GaN substrate by the HVPE or MOCVD method, thanks to which a template substrate was obtained (step b).

6) Alternatively, 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. Using the HVPE method under the following conditions (step b).

After cutting and polishing (step c) according to the methods described above, a template substrate having a thickness of about 0.5 mm was obtained for optoelectronic devices.

The HVPE process conditions were as follows: reaction temperature: 1050 ° C, reaction pressure: atmospheric (0.1MPa), ammonia partial pressure: 0.03MPa, GaCl partial pressure₃: 100 Pa, hydrogen gas carrier.

If necessary, a step of removing impurities from the bulk monocrystalline nitride may be performed by a scrubbing process under supercritical ammonia solvent, water, carbon dioxide, or by treating it with hydrogen, nitrogen or ammonia gas. In such a case, the rinsing step is preferably carried out with the auxiliary use of ultrasound or exposure to an electron beam.

Industrial applicability

The resulting tempIate substrate is very useful as a substrate for epitaxy carried out by a gas phase growth method such as MOCVD, MBE and HVPE, which opens the possibility of producing good opto-electric devices such as laser diodes, high efficiency LEDs and good electrical devices such as MOSFET.