Nitride semiconductor laser device and a method for improving its performance

Description of the invention

The present invention relates to a nitride semiconductor laser device and a method for manufacturing a semiconductor laser device with improved performance for extending its service life. In particular, the method of the invention relates to providing a window layer on a resonator mirror that emits radiation. Such a layer increases the durability of the nitride semiconductor laser device of the invention.

The service life of semiconductor laser devices depends primarily on the quality of the optically active layers, and in particular on the quality of the resonator mirrors of these layers. In the hitherto used semiconductor laser diodes, produced on the basis of GaAs semiconductors, the extended lifetime of the laser diode is achieved by creating special layers on the resonator mirrors. These layers act as antireflection layers or form a window structure. Such a structure is disclosed in Japanese Patent Application No. 10-251577, published under No. 2000-08286.

The energy gap in the layers of semiconductor windows must be wider than the energy gap of the active layer in semiconductor laser structures to extend the life and durability of laser structures protected in this way.

In nitride semiconductor lasers, the resonator mirrors are produced by RIE (Reactive Ion Etching) or cleavage and - due to the narrowing of the energy gap - they absorb the emitted radiation, as a result of which heat is released causing deterioration of the life of laser diodes with a power exceeding 100 mW. Therefore, it has been proposed to create a window structure in nitride semiconductor lasers by covering the resonator mirrors with a semiconductor layer of the AlGaInN formula (Japanese Unexamined Patent Publication No. 249830/1995) or another layer such as an AlN layer (Japanese Unexamined Patent Publication no. 26442/2002).

According to the prior art technology, it is necessary to use temperatures greater than 1000 ° C to form a gallium-containing monocrystalline nitride window layer by gas phase growth methods, for example the most commonly used MOCVD (Metallo-Organic Chemical Vapor Deposition) method. However, such high temperatures damage the active region made of the indium-containing nitride semiconductor previously used in semiconductor nitride lasers. On the other hand, when the nitride layer is produced by the known methods at a temperature which does not damage the active area, the layer thus obtained is amorphous. When an amorphous layer is used to create a window structure, it scatters the emitted light, making the laser beam heterogeneous. Moreover, due to the amorphous coloration, light is absorbed and the mirror is heated, which in turn leads to its accelerated degradation.

Secondly, known nitride-based opto-electronic devices are produced on sapphire or silicon carbide substrates that differ from the layers subsequently applied to these substrates (heteroepitaxy). There are significant differences in the chemical, physical, crystallographic and electrical properties of the indicated substrates and the semiconductor nitride layers deposited thereon by the method of heteroepitaxy, which results in a rather high density of dislocations in the epitaxial semiconductor layers. In order to lower the surface dislocation density and thus increase the stability of the laser semiconductor structures, a buffer layer is first applied to the sapphire or SiC substrates. However, the reduction in surface dislocation density obtained is not greater than up to about 10⁸/ cm².

So far, the reduction of the surface dislocation density has been possible as a result of the ELOG (Epitaxial Lateral Overgrowth) method. According to this method, a GaN layer is first deposited on the sapphire substrate, and then SiO 2 is subsequently applied to it in the form of stripes or a grid. The thus prepared substrate can then be used to conduct lateral growth of GaN, reducing the defect density to about 10⁶/ cm².

A further refinement of the epitaxial nitride forming substrate of a semiconductor laser device was achieved by using the method for producing a bulk monocrystalline nitride layer containing gallium disclosed in WO 02/101120.

PL 216 522 B1

The object of the present invention is to provide a nitride semiconductor laser with a radiation emitting mirror covered with a nitride layer forming a window, without degrading the performance of the laser.

Another object of the present invention is to provide a nitride semiconductor laser structure on a new substrate having a low surface dislocation density, preferably lower than 10⁶/ cm².

It is a further object of the present invention to provide a method for manufacturing a nitride semiconductor laser device, which comprises producing a nitride laser with a satisfactory nitride window layer guaranteeing improved performance of the manufactured device.

These objectives have been achieved by developing a nitride semiconductor laser device and a method for producing such a laser according to the invention, based on the use of Group XIII element nitrides (the Group numbering throughout the documentation is in accordance with the 1989 IUPAC Convention), preferably gallium-containing nitrides of the general formula Al_xGa_1-xyIn_yN, where 0 <x + y <1, 0 <x <1 and 0 <y <1, especially nitrides of the general formula Al_xGa_1-xN (0 <x <1).

The nitride semiconductor laser device of the present invention has the distinguishing features of independent claim 1, and its advantageous features are defined in the corresponding dependent claims 2 to 11. The method of the present invention is defined in claims 12 to 16.

The nitride semiconductor laser device with a window layer on the radiation emitting resonator mirror comprising an active layer of a nitride semiconductor between an n-type nitride semiconductor layer and a p-type nitride semiconductor layer according to the present invention is characterized by:

at least the radiation-emitting mirror of the resonator is covered with a window layer containing a monocrystalline nitride of the general formula AlxGa1-x-yInyN, where 0 <x + y <1, 0 <x <1 and 0 <y <1, especially a nitride of the general formula AlxGa1-xN (0 <x <1) with an energy gap wider than the energy gap of the active layer and produced at low temperature, so that this active layer is not damaged. In the present invention, the term "window layer" means a layer having an energy gap wider than the energy gap of the active layer or quantum well layer formed directly on the radiation emitting resonator mirror in order to avoid problems caused by the narrowing of the energy gap of that resonator's mirror.

The thickness of the window layer on the resonator mirror is preferably greater than 50 A, and more preferably equal to an integer multiple of the wavelength of the emitted radiation (λ).

According to the invention, the window layer on the resonator mirror of the monocrystalline AlxGa1-xN (0 <x <1) is preferably formed in a supercritical ammonia solution.

Preferably, at least the p-type resonator contact layer is covered with a mask when a monocrystalline AlxGa1-x-yN (O <x <1) window layer is formed on the resonator mirror in a supercritical ammonia solution environment.

The window layer on the resonator mirror contains at least one of Group I elements, preferably Li or Na.

Preferably, the active layer of the resonator has a quantum (multi) well structure and comprises at least one well layer of InGaN or InAlGaN.

According to the present invention, the structure of the nitride semiconductor laser device is preferably formed on a substrate selected from the group consisting of a GaN substrate, preferably a monocrystalline GaN substrate, a sapphire, spinel, ZnO, SiC substrate, an ELOG substrate and a nitride semiconductor substrate having a concave surface. -convex. In the present invention, the term "ELOG substrate" means a substrate having a nitride layer or layers deposited by the so-called ELOG (Epitaxial Lateral Over-Growth) method.

Preferably, the structure of the nitride semiconductor laser device is formed on the C, A or M plane of the monocrystalline GaN substrate.

The structure of the nitride semiconductor laser device is fabricated on the C plane of the monocrystalline GaN substrate, and the window layer on the resonator mirror is deposited on the M or A plane.

The structure of the nitride semiconductor laser device can also be fabricated on the A plane of the monocrystalline GaN substrate, and the window layer is deposited on the C or M plane of the radiation emitting resonator mirror.

PL 216 522 B1

Alternatively, the structure of the nitride semiconductor laser device is formed on the M plane of the monocrystalline GaN substrate, and the window layer is formed on the C or A plane of the light emitting mirror of the resonator.

The present invention also relates to a method of manufacturing a nitride semiconductor laser device having a resonator including an active layer of a nitride semiconductor between an n-type nitride semiconductor layer and a p-type nitride semiconductor layer, wherein a pair of opposing resonator mirrors is exposed in a first process by etching or breaking the structure of the laser device - method characterized by that

- in the second process, the radiation emitting mirror of the resonator is covered with a window layer made of monocrystalline nitride of the general formula Al_xGa_1-xyIn_yN where 0 <x + y <1, 0 <x <1 and 0 <y <1, especially a nitride of the general formula Al_xGa_1-xN (0 <x <1), with an energy gap wider than the energy gap of the active area, at low temperature, so as not to damage this active area.

According to the invention, during the second process, a window layer is preferably deposited on the resonator mirror in a supercritical ammonia solution.

In the method of the present invention, in a second process, the window layer on the resonator mirror is formed after covering at least the top surface of the p-type resonator contact layer with a mask having a higher or the same chemical resistance in a supercritical ammonia solution environment as the chemical resistance of the window layer material on the resonator mirror. .

Preferably, the mask is selected from the group consisting of SiO, SiN, AlN and Ag.

In the method according to the invention, the window layer on the resonator mirror is formed by depositing a monocrystalline nitride layer of the above composition in a supercritical ammonia solution environment at a temperature of 800 ° C or less, preferably at a temperature of 600 ° C or less.

The present invention introduces a significant advance in nitride-based opto-electronics.

The invention is illustrated in the accompanying drawing, in which Fig. 1 shows a cross section of a nitride semiconductor laser according to the invention, Fig. 2 illustrates successive steps of the method according to the invention, Fig. 3 shows a cross section of the structure of a nitride semiconductor laser according to the invention with all non-layers removed. nitrides, Fig. 4 - 6 illustrate a cross-section of the structure of a nitride semiconductor laser, with selected surfaces covered with masking layers, Fig. 7 shows temperature changes as a function of time for the process of example 1, Fig. 8 shows changes in temperature as a function of time for the process of example 7 and Fig. 9-11 illustrate the successive phases of forming three exemplary types of substrates for making the nitride semiconductor laser device of the present invention having a layer of monocrystalline nitride produced by lateral build-up.

The following definitions apply to the present invention:

The active layer of the resonator is the layer of the resonator in which radiation is generated as a result of recombination of electric carriers.

The resonator mirror is the boundary surface of the resonator substantially perpendicular to the direction of the light beam being emitted. The light is at least partially reflected from this surface because the refractive index of the monocrystalline nitrides that make up the resonator is higher than the refractive index of the environment in which the laser is placed (usually air or polymer). Resonator mirrors, with or without window layers, may be coated with reflective layers. Typically, one of these reflecting layers reflects much more light than the other. In this case, the radiation produced by the laser is emitted in substantially one direction defined by the lower reflective layer. Thus, when referring to the resonator mirror corresponding to the layer with lower reflectivity we use the term resonator mirror emitting light or radiation, while the second resonator mirror is termed light reflecting resonator mirror.

Window layer means a layer with an energy gap wider than the energy gap of the active layer or quantum (multi) well layer, deposited directly on the light-emitting resonator mirror in order to avoid problems caused by a narrower energy gap

Resonator mirrors. The window layer thickness is preferably equal to an integer multiple of the wavelength of the emitted light (ηλ). The window layer may be additionally covered with a protective layer.

The gallium containing nitride is the nitride of gallium and possibly another element or other elements of the Group XIII. The term includes, but is not limited to, a GaN binary compound, a ternary compound such as AlGaN, InGaN, and also AlInGaN, in which the ratio of other Group XIII elements to gallium can vary widely.

The C, A, or M planes correspond to and refer to the surfaces of the C, A, or M planes of hexagonal crystals of Group XIII nitrides.

Supercritical ammoniacal solvent means a supercritical fluid. consisting essentially of ammonia and ions of one or more Group I elements to dissolve gallium-containing source material.

The term supercritical solution is used to refer to a supercritical solvent when it contains a Group XIII element or elements, especially gallium - in a soluble form, resulting from dissolution of a source material containing the Group XIII element or elements, in particular gallium.

Complex compounds of a Group XIII element or elements, in particular gallium complex compounds, are complex compounds in which the atom of the Group XIII element or elements, especially gallium, is a coordination center, surrounded by ligands such as NH3 molecules or - -2 derivative groups such as NH2^-, NH^-2 and the like.

An autoclave is a closed container with a reaction chamber in which the ammoniacal window layer deposition process according to the invention is carried out.

According to the invention, a monocrystalline nitride window layer having the general formula AlxGa1-x-yIn_yN, where 0 <x + y <1, 0 <x <1 and 0 <y <1, is produced in a supercritical ammonia solution. The use of this technology avoids the above problems known in the art, since the deposition temperature of the window layer is low enough not to damage the active layer (active region) of the nitride semiconductor laser device.

In the case of an active layer of indium-containing nitride semiconductor, the forming temperature of this active region is typically about 900 ° C. The indium-containing nitride decomposes at about 950 ° C. Deposition of monocrystalline nitride layers by MOCVD or other gas phase epitaxy methods takes place at temperatures higher than 1000 ° C. Under these temperature conditions, the indium-containing nitride active region is damaged. The production temperature of the monocrystalline nitride layer of the general formula AlxGa1-x-yInyN, where 0 <x + y <1, 0 <x <1 and 0 <y <1, in the environment of supercritical ammonia solution is lower than 800 ° C and is typically less than 600 ° C, preferably less than 550 ° C for GaN. Such a low temperature avoids thermal degradation of the indium-containing active region. At the same time, the crystal quality of the window layer deposited in the supercritical ammonia solution environment is very good in view of the evaluation carried out using methods known in the art.

In nitride semiconductor laser devices, an indium-containing nitride semiconductor resonator with an active region, called an optical waveguide, consists of an active region and a waveguide layer.

The active area should have the structure of a single well or a multi-quantum well, including at least one well layer: InGaN or InAlGaN.

The monocrystalline nitride layer of the general formula AlxGa1-x-yInyN, where 0 <x + y <1, 0 <x <1 and 0 <y <1, deposited on the mirror of the radiation emitting resonator, according to the invention has a composition selected according to the function which this layer is to fulfill.

For example, in nitride semiconductor lasers on the resonator mirrors, the energy gap is narrowed and, consequently, the absorption of radiation by these mirrors increases. The composition of the monocrystalline nitride layer of the general formula AlxGa1-x-yInyN, where 0 <x + y <1, 0 <x <1 and 0 <y <1, is therefore set to widen the energy gap in order to significantly suppress radiation absorption in the region covered by such a layer of the resonator mirror.

Also in the case of nitride semiconductor lasers with the active region of the resonator made of indium-free nitride semiconductor, it is preferable to apply on the resonator mirrors a monocrystalline nitride layer of the general formula AlxGa1-x-yInyN, where 0 <x + y <1, 0 <x <1 and 0 <y <1, in low-temperature conditions, in a supercritical environment roz6

Thus, the width of the energy gap of the material of this layer is selected. be wider than the width of the energy gap of the nitride semiconductor forming the active area of ​​the resonator. The selection of a preferred structure (pattern) for the nitride semiconductor material of the window layer is therefore made based on the desired value of the bandwidth width. The width of the energy gap in nitride semiconductors increases in series: InGaN <<GaN <GaAlN <AlN. In the nitride semiconductor lasers according to the invention, the thickness of the monocrystalline nitride layer of the general formula Al_xGa_1-xyIn_yN, where 0 <x + y <1, 0 <x <1 and 0 <y <1, should be over 50 A (angstroms) and should be equal to ηλ, where λ is the wavelength of radiation emitted by the active area of ​​the laser device and n is an integer.

According to the invention, the resonator mirror covered with a monocrystalline nitride layer of a nitride window of the general formula AlxGa1-x-yInyN, where 0 <x + y <1, 0 <x <1 and 0 <y <1, may be covered with additional protective layers, for example, layers to increase mechanical strength or chemical resistance.

In order to obtain a monocrystalline nitride window layer of the general formula AlxGa1-x-yInyN on the resonator mirror, where 0 <x + y <1, 0 <x <1 and 0 <y <1, at a suitably low temperature, the invention uses the supercritical ammonia solution is used according to the method detailed in WO 02/101120. the full content of which is referred to as a reference. It is a method of producing a monocrystalline nitride layer of the general formula AlxGa1-x-yInyN, where 0 <x + y <1, 0 <x <1 and 0 <y <1, on the surface of the embryo. According to the present invention, at least the resonator mirror surface of the laser device of the present invention corresponds to an embryo from the process disclosed in WO 02/101120.

By using the crystallization method in a supercritical ammonia solution environment, it is possible to form a monocrystalline nitride window layer on the resonator mirror at a temperature of less than 800 ° C, preferably less than 600 ° C, and most preferably less than 550 ° C. This method is carried out in high pressure autoclaves typically made of nickel alloys. Therefore, due to the transfer of the alloy components into the supercritical ammonia solution, the produced monocrystalline nitride layer also contains elements such as Ni, Cr, Co, Ti, Fe, Al, Si or Mn.

Nitride semiconductor laser devices can be produced on a nitride substrate. They can also be produced on multi-component substrates, for example those with spinel on a sapphire plate. ZnO, SiC or Si - after appropriate treatment - a monocrystalline nitride layer was formed on at least one side of such a plate. For each of these materials, a monocrystalline nitride layer may be produced by side build-up. Due to the use of the crystallization method in a supercritical ammonia solution, it is recommended to use a nitride semiconductor substrate. In the case of nitride semiconductor laser devices using a different type of substrate (with a composition different from the composition of the layer covering the resonator mirror), the substrate material may react with the supercritical ammonia solution during the process. Substrate components will then be introduced into the supercritical ammonia solution environment, leading to contamination of the monocrystalline nitride window layer produced.

Therefore, it is recommended that prior to covering the resonator mirror with a monocrystalline layer of a nitride window with the general formula AlxGa1-x-yInyN, where 0 <x + y <1, 0 <x <1 and 0 <y <1, in the environment supercritical ammonia solution, cover the remaining surfaces with an appropriate masking layer.

Particularly good results are achieved when a GaN wafer is used instead of sapphire as primary substrate 1 (Fig. 1) having surfaces susceptible to lateral build-up of crystalline gallium nitride - CiaN (ELOG structures).

The successive phases of producing three exemplary types of substrates (for producing a nitride semiconductor laser device according to the invention by epitaxial methods) with a monocrystalline nitride layer produced by lateral build-up are shown in Figures 9 to 11.

As shown in Fig. 9, surfaces 206 susceptible to lateral growth can be formed by partially coating the nitride primary substrate 203 with the mask layer 204. Over this mask layer 204, a monocrystalline nitride layer 207 is produced by lateral build-up. it is desirable that the mask layer 204 not dissolve or possibly dissolve very poorly in the supercritical ammonia solution. It can, for example, be made of metallic silver - Ag. The masking layer can also protect the remaining - all or some - surfaces of the primary substrate.

As shown in Fig. 10, the monocrystalline nitride layer 207 obtained by the lateral build-up can also be produced on the primary substrate 203 with the stripe-shaped surface 205. In this case, it was formed on the side walls 206 of the strips 205. It is also possible to lead lateral build-up of this layer on selected side walls 206.

As shown in Fig. 11, the monocrystalline nitride layer 207 can only be formed on a portion of the primary substrate 203. As a result, the surface dislocation density of layer 207 is significantly lower than the dislocation density of the primary substrate 203. In this case, the primary substrate 203 was partially covered with the mask layer. 204 and the monocrystalline nitride layer 205 grew from the apertures of the mask layer 204 upwards and to the sides. As a result, nitride semiconductor strips with a T-bar cross section were obtained. After removal of the mask layer 204, only those T-bars remain, on which a further monocrystalline nitride layer 207 is formed by lateral build-up.

To obtain a layer of monocrystalline nitride of the general formula Al on the primary substrate_xGa₁._x._yIn_yN in which 0 <x + y <1.0 <x <1 and 0 <y <1, which could be used to epitaxically fabricate the nitride semiconductor laser device of the invention, it is preferable to manufacture at a relatively low temperature. This is possible using the method of crystallization in a supercritical ammonia solution described in WO 02/101120. In the case of preparing the preferred substrate for the nitride semiconductor laser device of the present invention, the crystallization of the desired Group XIII element nitride is performed on surfaces disposed on the primary substrate susceptible to lateral build-up of nitrides. Under these conditions, it is possible to produce a monocrystalline nitride layer on the appropriately shaped primary substrate described above at a temperature lower than 600 ° C, preferably lower than 550 ° C, by lateral build-up. The implementation of the crystallization method in a supercritical ammonia solution in a typical high-pressure autoclave causes that the monocrystalline nitride layer obtained as a result of lateral growth also contains elements such as Ni, Cr, Co, Ti, Fe, Al, Si and Mn. Preferably, the thickness of the monocrystalline nitride layer obtained by side-growing is greater than 1 µm.

The window layers deposited according to the present invention are of both high quality and the desired thickness. Such layers may have an area dislocation density of less than 10⁶/ cm²and a half-width (FWHM) of the X-ray reflex from plane (0002) of 50 arcsec or less.

Due to the conditions of the molding process, the gallium-containing monocrystalline nitride window layer may contain alkali elements (metals), typically in an amount greater than about 0.1 ppm. Typically, it is desirable to keep the content of alkaline elements below 10 ppm.

The gallium-containing monocrystalline nitride window layer may additionally contain traces of Ti, Fe, Co, Cr and Ni introduced during the manufacturing process due to corrosion of the autoclave under the process conditions. Such trace contamination does not adversely affect the properties of the resulting window layer.

In general, halogens are not components specifically introduced into the gallium-containing monocrystalline nitride window layer of the present invention. However, it is also possible that halogens are present in this layer. Typically, it is desirable to keep the halogen level of the gallium-containing nitride at or below about 0.1 ppm.

The window layer on the radiation-emitting mirror of the nitride resonator of the semiconductor laser device of the invention is deposited by dissolving a source material containing Group XIII elements in a supercritical solvent and crystallizing the gallium-containing nitride on the surface of the resonator's mirror, whereby supersaturation of the supercritical solution with respect to the gallium-containing nitride is achieved by changes in the gallium-containing nitride. temperature and / or pressure conditions. In a preferred embodiment, the layer is deposited by a method that includes dissolving the gallium source material in a supercritical solvent and crystallizing

Gallium nitride is deposited on the surface of the resonator mirror at a higher temperature and / or lower pressure than in the dissolution process.

Typically, the supercritical solvent comprises ammonia and / or its derivatives and contains Group I element ions - at least lithium or sodium ions, the source material consists essentially of gallium-containing nitride and / or its precursors selected from the group consisting of azides, imides, amide-imides. , amides, hydrides, gallium-containing metallic compounds and alloys, as well as Group XIII metallic elements, especially gallium metallic.

In the present process, in which a window layer according to the invention of monocrystalline nitride is deposited, the crystallization of gallium-containing nitride takes place in an autoclave at temperatures ranging from 100 ° C to 800 ° C and at a pressure of 10 MPa to 1000 MPa and at a molar ratio of ions of Group I elements to the solvent is usually not more than 1: 2, based on the moles of these metal ions per moles of the solvent (mole ratio). In a preferred embodiment, the concentration is not more than 1: 5, preferably not more than 1:20 (moles of alkali metal ion to moles of solvent used).

As the source of alkali metal ions, alkali metals or alkali metal compounds, with the exception of halogen-containing compounds, are used. The growth of the gallium-containing monocrystalline nitride window layer is controlled by controlling the temperature and pressure in the dissolution step and the temperature and pressure of the crystallization step. The crystallization step requires a temperature in the range of 400 ° C to 600 ° C.

According to the present invention, the gallium-containing monocrystalline nitride window layer is crystallized in an autoclave with two distinct zones - a dissolution zone and a crystallization zone, with a temperature difference between the two zones during crystallization of not more than 150 ° C, preferably not more than 100 ° C. The control of supersaturation of the supercritical solution with respect to gallium-containing nitride in the crystallization zone of the autoclave with two separate zones and the predetermined temperature difference between the two zones is achieved by regulating the chemical transport (mass) between the two zones by using a barrier or baffles separating the two zones and / or by using gallium-containing source material in the form of higher surface area gallium nitride crystals total than the total surface area of ​​the resonator mirror on which the window layer is deposited.

Preferably, the dissolving step and the crystallization step are carried out - at least partially - simultaneously in the same autoclave. In such an embodiment, the pressure is practically uniform throughout the reactor, while the temperature difference between the dissolution zone and the crystallization zone should be at least 1 ° C, and preferably between 5 ° C and 150 ° C. In addition, the temperature difference between the dissolution zone and the crystallization zone must be controlled to ensure chemical transport in the autoclave in a supercritical solution that occurs by convection.

Many materials containing a Group XIII element or elements, especially gallium, which are soluble in a supercritical solvent under the conditions of the present invention, can be used as a source material in the present invention. Typically, the gallium containing material will be a substance or mixture of substances containing at least gallium and optionally alkali metals, another element or other Group XIII element or elements, nitrogen and / or hydrogen such as Group XII elements and intermetallic compounds, hydrides, amides, imides, amides. imides, azides. A suitable gallium-containing source material may be selected from the group consisting of gallium nitride GaN, azides such as Ga (N3) 3, imides such as Ga2 (NH) 3, amideimides such as Ga (NH) NH2, amides such as Ga (NH2) 3, hydrides such as GaH3, alloys containing gallium, metal gallium, and mixtures thereof. The preferred source material is metallic gallium, gallium nitride, and mixtures thereof. Most preferably, the source material is gallium metal or gallium nitride. If other Group XIII elements are to be incorporated into the crystals of the gallium containing nitride, suitable compounds or mixed compounds containing Ga and other Group XIII elements may be used. If the medium is to contain dopants or other additives, their precursors can be added to the source material.

The form of the source material is not particularly important and it may be in the form of one or more pieces or in the form of a powder. If the source material is in the form of a powder, care should be taken to ensure that its individual particles are not transported from the dissolution zone to the crystallization zone, where they can cause uncontrolled crystallization. Preferably, the source material is in the form of one or more pieces and the surface area of ​​the source material is greater than that of the seed.

PL 216 522 B1

The nitrogen containing solvent used in the present invention must be capable of forming a supercritical fluid in which gallium can dissolve in the presence of alkali metal ions. Preferably such a solvent is ammonia, its derivatives or mixtures thereof.

An example of a suitable ammonia derivative is hydrazine. Most preferably the solvent is ammonia. In order to reduce the risk of corrosion of the reactor and to avoid side reactions, halogens, for example in the form of halides, are preferably not intentionally introduced into the reactor. Although traces of halogens can be introduced into the system in the form of inevitable impurities in the starting materials, care should be taken to keep the amount of halogens as low as possible. By using a nitrogen containing solvent such as ammonia, it is not necessary to introduce nitride compounds as source material.

It turned out that also other gallium compounds, and even metallic gallium, can be the source of gallium ammonia complexes. For example, the gallium complexes can be introduced into a solvent of the above composition starting from the simplest starting material, that is, metallic gallium. By making use of an appropriate change of conditions (for example an increase in temperature), a supersaturated solution of gallium nitride is produced and nucleating can take place.

The solubility of the source material, i.e., gallium and the corresponding Group XIII elements and / or their compounds, can be significantly improved by the presence of at least one type of alkali metal component as dissolution aid (mineralizer). Lithium or a mixture of lithium and sodium is a preferred source of alkali metals. The mineralizer can be added to the supercritical solvent in elemental form or in the form of an alkali metal compound. Generally, the choice of mineralizer depends on the solvent used in the process.

If the mineralizer is in the form of a compound, preferably the compound is an alkali metal hydride such as MH, an alkali metal nitride such as M3N, an alkali metal amide such as MNH2, an alkali metal imide such as M2NH, or an alkali metal azide such as MN3 (where M is an alkali metal ). The concentration of the mineralizer is not particularly limited, and can be selected to provide the appropriate levels of solubility of the source material (starting material), seed and gallium-containing nitride (product obtained). Usually it does not exceed a value of 1: 2, expressing the number of moles of alkali metal ions per mole of solvent (molar ratio). In a preferred embodiment, the concentration of the mineralizer does not exceed 1: 5. more preferably it is not more than 1:20 (moles of alkali metal ions per mole of solvent).

The presence of an alkali metal in the process can lead to the presence of alkali metal elements in the monocrystalline nitride window layer obtained in this process. It is possible that the amount of the alkali metal elements will be greater than about 0.1 ppm, and even greater than 10 ppm. However, in such amounts, the alkali metals do not adversely affect the properties of the single crystals. It has been found that even with an alkali metal content of 500 ppm, the performance characteristics of the obtained monocrystalline nitride window layer according to the invention are still satisfactory.

The dissolved source material crystallizes in a crystallization step under low solubility conditions on the radiation-emitting mirror of a nitride resonator of a semiconductor laser device placed in an autoclave.

Preferably, the gallium-containing nitride window layer consists essentially of GaN, GaAlN or AlN.

Careful selection of the combination of the above-mentioned process parameters allows to obtain a good quality gallium nitride window layer. Depending on the duration of the process and the dimensions of the autoclave used, it is possible to achieve the desired window layer thickness in excess of 50 A.

Due to the good crystal quality, the obtained window layer according to the invention, made of gallium-containing nitride, significantly improves the service life and durability of nitride semiconductor laser devices, especially nitride lasers and nitride laser diodes.

Hereinafter, a detailed description of the embodiments of the present invention will be provided.

The cross-sectional view of the nitride semiconductor laser according to the invention is shown in the accompanying Fig. 1. Nitride n 2 semiconductor layers and p 4 nitride semiconductor layers are deposited on a sapphire plate or a nitride substrate containing gallium 1. 3 in the form of a quantum well made of a nitride semiconductor

PL 216 522 B1 containing In. Nitride n-type semiconductor layers 2 consist of n-type sub-contact layer 21, anti-crack layer 22, n-type casing (emitter) layer 23 and n-type waveguide layer 24. Nitride p-type semiconductor layers 4 consist of bounding layer 41, waveguide layer p-type 42, p-type cover (emitter) layer 43 and p-type sub-contact layer 44.

In the above structure, the nitride laser resonator is made of the above-mentioned active area of ​​the 3rd n-type waveguide layers 24 and p-type 42 and of the bounding layer 41. The radiation emitting resonator mirror is covered with a monocrystalline nitride layer 5 of general formula Al_xGa_1-xyIn_yN. The application of an analogous layer also on the resonator's mirror from the side reflecting the radiation makes it possible to limit its damage caused by the absorption of the reflected radiation.

The subsequent production phases of a nitride semiconductor laser are illustrated in the schematic drawing of Fig. 2. Thus, a buffer layer 11 produced at low temperatures is deposited on a sapphire plate substrate 1, on which the n-type semiconductor layer is subsequently deposited one after another. 2, active area 3 and p-type nitride semiconductor layer 4.

The resulting nitride semiconductor structure is etched to expose the mirrors of the resonator (Fig. 2-B). The exposed mirrors of the resonator are covered with a monocrystalline layer of nitride of the general formula AlxGa1-x-yInyN in a supercritical ammonia solution. For this purpose, the substrate with the laser structure is placed in a high pressure autoclave together with the source material necessary to form a monocrystalline nitride layer with the general formula AlxGa1-x-yInN and with a mineralizer. The autoclave is closed and filled with liquid ammonia. The solution is made supercritical by adjusting the temperature and pressure accordingly.

In this case, the crystallization of the monocrystalline nitride layer of the general formula AlxGa1-x-yInyN takes place on a laser structure (Fig. 2-B) obtained by applying to the substrate 1 successively: a nitride n-type semiconductor layer 2, an active region 3 and a nitride p-type semiconductor layer 4. This structure is the equivalent of a nucleating agent mentioned in the cited publication No. WO 02/101120. Instead, it is also possible to use structures from which all non-nitride layers have been removed, such as, for example, sapphire (Fig. 3). It is also possible to use laser structures with a resonator, in which only the mirror reflecting the radiation is covered with the masking layer 6 (Fig. 4), or also structures with a resonator, all surfaces of which, except the mirror emitting radiation, are covered with the masking layer 6 (Fig. 5), and finally structures in which the mask layer 6 covers only the exposed surfaces of the sapphire layer 1 (Fig. 6). The aforementioned mask layer 6 can be made of a material which either is not etched in the supercritical ammonia solution or, if it is etched, does not constitute an undesirable admixture in the deposited monocrystalline nitride window layer of the general formula AlxGa1-x-yInN. For example, metallic Ag silver can be used as a material of this type.

As a result of the high pressure autoclave reaction, a monocrystalline nitride layer of the general formula AlxGa1-x-yInN is deposited on the exposed surfaces of the semiconductor nitride laser structure (Fig. 2-C).

The above-mentioned method of producing a monocrystalline nitride layer in a supercritical ammonia solution is based on the use of the negative temperature coefficient of solubility of compounds of the above-defined general formula AlxGa1-x-yInyN in a supercritical ammonia solvent and alkali metal ions.

A negative temperature solubility coefficient means that a specific nitride has lower solubility at high temperatures and higher solubility at low temperatures. Thus, when zones of higher and lower temperatures are created in the autoclave, dissolution of nitride will occur in the zone of lower temperatures, and its crystallization will occur in the zone of higher temperatures. As a result of the convection produced between the lower temperature zone and the higher temperature zone, adequate supersaturation of the solution is maintained in the reaction chamber in the higher temperature zone, which causes a selective growth of nitrides on the seeds.

The laser structure is thus placed in the higher temperature zone (crystallization zone) and the source material in the lower temperature zone of the autoclave (dissolution zone). The source material dissolves in the dissolution zone. Throughout the system, a convective mass flow is produced due to the temperature difference. as a result of which dissolved material

The source is transported to the zone of higher temperatures. Due to the lower solubility at higher temperatures, the supercritical solution becomes supersaturated in the crystallization zone, as a result of which the dissolved source material crystallizes on the laser structure placed in this zone. As a result of the crystallization understood in this way, a window layer of monocrystalline nitride with the general formula AlxGa1-x-yInyN is formed, which is an essential element of the present invention. Moreover, the characteristic feature of this method, compared to the methods of producing gas phase nitride layers at temperatures above 900 ° C, is that it allows the production of monocrystalline nitride layers at temperatures significantly lower than 800 ° C, preferably at temperatures lower than 600 ° C. C, most preferably less than 550 ° C. Thanks to this, in the laser structure located in the zone of higher temperatures, there is no thermal degradation of the active area from the nitride semiconductor containing In.

In a preferred embodiment of the invention, GaN or a precursor thereof can be used as the source material. GaN can be used in the form of plates obtained by gas phase growth methods, such as HVPE (Halide Vopor Phase Epitaxy) or MOCVD (Metallo-Organic Chemical Vapor Deposition), or by embryo crystallization in a supercritical ammonia solution. Compounds selected from gallium azide, gallium amide, gallium metal, or mixtures thereof can be used as the gallium nitride precursor.

In the method of crystallization in a supercritical ammonia solution, alkali metals such as Li, Na, K, Rb, Cs or alkali metal compounds such as hydrides, amides, imides, amido-imides, nitrides or azides can be used as the mineralizer.

According to the invention, it is preferred that the thickness of the monocrystalline nitride window layer 5 of the general formula Al_xGa_1-xyIn_yN was greater than 50 angstroms. If its thickness is less than 50 angstroms, the smoothening effect of the etched surface will also be smaller. On the other hand, the upper limit of the thickness depends on the manufacturing capacity of the manufacturer.

Moreover, according to the present invention, a window layer 5 of monocrystalline nitride having the general formula Al_xGa_1-xyIn_yN is preferably produced on the surface of the stripes and mirrors and on the surface of the n-type contact layer 21, it is advisable to keep the growth of the layer 5 on the surface of the n-type contact layer 21 below 2 μm so that it does not fill the strip-like active area.

In order to improve the leveling effect provided by the window layer 5, it is recommended according to the present invention to have a lower Al content in the monocrystalline nitride layer of the general formula AlxGa1-x-yInN. However, in order to improve the performance of the window structure, a low Al content is desirable. Therefore, the Al content should not be zero and the window layer 5 should preferably be a nitride of formula Al_xGa_1-xN.

By producing the window layer 5 on the etched side surfaces of the strips and on the mirrors of the resonator, they can be brought to a state of high smoothness. In other words, immediately after etching, the surfaces of the strips and the mirror have relatively large uneven surfaces, and the formation of a window layer 5 on them causes the irregularities to be filled and the surface smoothed. Moreover, the window layer 5 can be a homogeneous coating, but it can also consist of several layers differing in composition, especially in the Al content.

After the fabrication of the window layer 5, the subassembly undergoes a further conventional treatment to form a ridge which is then covered with a filler layer 70 of ZrO.₂. A p-type electrode 80 is deposited at the top of the ridges so as to make contact with the p-type sub-contact layer 43 to ensure ohmic contact. Next, n-type electrodes 90 are formed on the surface of the n-type sub-contact layer 21, arranged parallel to the p-type electrodes. Subsequently, p-type 110 and n-120 contact fields are produced. Moreover, an insulating SiO coating is formed.₂/ TiO₂which covers the entire element except the p-type electrode, the n-type electrode and, thanks to the alternating arrangement of the SiO2 and TiO2 layers, acts as a radiation-reflecting layer 100 when excited by the laser. Finally, individual laser semiconductor diodes are cut from the wafer. Thus, a finished nitride laser semiconductor device is obtained (Fig. 1).

Mirrors emitting radiation from nitride semiconductor laser devices of other types than those described above may be coated in the same manner with monocrystalline nitride window layers in the same manner.

The present invention is further illustrated in the following examples. for illustration only. The invention is not limited to the following examples, however.

PL 216 522 B1

Example 1

First, a 2 inch (5.08 cm) diameter sapphire plate 1 with a surface oriented substantially perpendicular to the c-axis is placed in the MOCVD reactor chamber. The temperature is set at 510 ° C. Hydrogen is used as the carrier gas, and the gaseous reactants are ammonia and TMG (trimethylgal). A 200 angstroms thick GaN buffer layer 11 is formed on the sapphire wafer under low temperature growth conditions.

On the buffer layer, the following layers are successively deposited:

(1) a 4 μm thick contact layer with n-type GaN doped with Si-level

3x10¹⁸/ cm³, (2) a 1.5 Pm thick anti-fracture layer of undoped In_0]06Ga_0]94N, (3) n-type cover layer in the form of superlattice with a total thickness of 1.2 μm. formed by alternating deposition of layers of undoped Inl0.1Ga0.9N with a thickness of 25 angstroms and 19 3 layers of n-type GaN, doped with Si at the level of 1 x 10¹⁹/ cm³, (4) no-type waveguide layer with a thickness of 0.2 μm made of undoped GaN, (5) active area with a total thickness of 380 angstroms in the form of a quantum well with the structure of alternately deposited barrier and well layers, the barrier layer being the In0.05Ga0 layer, 95N with a thickness of 100 angstroms, and the well layer - a layer of undoped In0.1Ga0.9N with a thickness of 40 angstroms, (6) a limiting layer of 300 angstroms thick with Al0.3Ga0.7N p-type, of admixed Mg at the level of 1 x 10²⁰/ cm³, (7) 0.2 μm thick waveguide layer of undoped GaN p-type, (8) p-type cover layer in the form of superlattice with a total thickness of 0.6 μm, formed by alternating layers of undoped In0.16Ga0.84N with a thickness of 25 angstroms and layers of undoped GaN 25 angstroms thick, (9) 150 angstroms sub-contact layer with p-type GaN doped with 20 3 g with Mg at the level of 1 x 10²⁰/ cm³.

After depositing the above layers, the obtained substrate with a nitride semiconductor structure is subjected to annealing in a MOCVD device in a nitrogen atmosphere at a temperature of 700 ° C, which further lowers the resistance of the p-type nitride semiconductor layer.

After annealing, the substrate is removed from the reactor and a mask layer in the form of SiO2 strips is formed on the surface of the uppermost p-type sub-contact layer. Then, by ion etching (RIE), parallel laser structures in the form of strips are produced, thereby exposing the resonator mirrors and the surface of the n-type contact layer. The SiO2 mask layer formed on the surface of the uppermost p-type contact layer is removed by wet etching.

Then, the substrate with the laser structure deposited thereon is placed high in the autoclave₃ pressure with a volume of about 36 cm³ together with the source material in the form of GaN plates (about 0.5 g) obtained by the HVPE method and with a mineralizer in the form of metallic Li (about 0.036 g) with a purity of 3 N.

After filling with ammonia (approximately 14.7 g), the high-pressure autoclave is sealed and heated in a two-zone furnace, with the maximum temperature inside the autoclave not exceeding 550 ° C. The autoclave reaction chamber is divided into two zones: a crystallization zone and a dissolution zone. In the crystallization zone (at a temperature of about 550 ° C) a substrate with a laser structure is located, and in the dissolution zone (at a temperature of about 450 ° C) there is a source material in the form of GaN plaques. The sealed autoclave is kept under constant thermal conditions for 3 days (Fig. 7).

Under the given conditions, in the supercritical ammonia solution environment, the desired monocrystalline GaN 5 layer with a thickness of about 1 μm is deposited on the side walls of the strips and on the exposed surfaces of the n-type sub-contact layer of the p-type-contact layer.

After the monocrystalline GaN layer 5 is formed on the resonator mirror, the monocrystalline GaN deposited on the surface of the uppermost p-type sub-contact layer is removed by etching. Then, the exposed surface of the p-type sub-contact layer is covered with a masking layer in the form of SiO strips.₂ 1.5 μm wide and - the etching is continued deep into the p-type cover layer until the formation of a ridge on the strip portion. The etching is carried out until the thickness of the p-type cover layer on both sides of the ridges is 0.1 μm.

PL 216 522 B1

This creates a 1.5 µm wide ridge.

Then, using the sputtering method, a ZrO2 coating with a thickness of 0.5 µm is formed to cover the surface of the stripes from the top surface of the SiO2 mask layer.

As a result of this heat treatment, a protective filling layer 70 in the form of a ZrO coating is formed on the top surface of the strips, on the side walls of the spines, and on the surface of the p-cladding layer on both sides of the spines.₂. This coating allows to stabilize the side mode at the moment of laser excitation.

Next, a p-type electrode 80 in Ni / Au form is produced on the p-type contact layer so as to create ohmic contact, and on the n-type-sub-contact layer - an n-type electrode 90 in the form of Ti / Al. Then, the semiconductor wafer with such prepared laser structures is subjected to a heat treatment at a temperature of 600 ° C. Next, suitable contact fields in the form of Ni (1000 A) -Ti (1000 A) -Au (8000 A) are applied to the p 80 and n 90 type electrodes. After the radiation reflecting surface 100 is formed in the form of SiO layers₂ and TiO₂, ready-made nitride semiconductor lasers are cut from the substrate plate.

The thus obtained nitride semiconductor lasers are equipped with a heat sink. By increasing the COD (Catastrophic Optical Damage) threshold as a result of covering the resonator's mirror with a monocrystalline nitride layer 5, it is observed that after excitation of the laser in continuous operation - with a threshold current density of 2.0 kA / cm², the output power of 100 mW and the wavelength of light 405 nm - the average lifetime of the laser is significantly extended compared to analogous lasers without such a monocrystalline layer.

Example 2

In the present example 2, only the resonator mirror emitting radiation is covered with the monocrystalline GaN layer. On the other hand, the remaining stages of laser production are carried out as in Example 1. The laser element thus produced was also equipped with a heat pipe. After₂ Similarly to example 1, mean laser lifetime at a threshold current density of 2.0 kA / cm² the output power of 100 mW and the wavelength of light 405 nm have been elongated.

Example 3

In the present example 3, after forming the buffer layer on the sapphire wafer, a 100 µm thick GaN layer was deposited by HVPE. Then, as in Example 1, a n-type nitride semiconductor layer, an active region and a p-type nitride semiconductor layer were formed. The sapphire was then removed, thereby obtaining a homogeneous GaN substrate. In the next steps, as in example 1, the resonator mirrors were exposed and covered with a layer of monocrystalline GaN 0.5 μm thick, crystallized in the environment of supercritical ammonia solution. In the case of a nitride semiconductor laser constructed in this way, the same performance improvement as in example 1 can be expected.

Example 4

The procedure was as in Example 1, with the only difference that the sapphire plate was coated with a metallic silver - Ag coating. In the remaining points, the laser production was analogous to that in example 1.

Example 5

The procedure is as in Example 1, with the only difference that a different mineralizer is used to obtain the window layer 5 of monocrystalline gallium nitride (GaN), deposited by recrystallization from supercritical ammonia solution. Instead of metallic lithium, lithium azide (LiN₃) in an amount of 0.13 g. The gallium nitride window layer 5 produced by this process has a thickness of about 1 µm.

Example 6

The procedure is as in Example 1, with the only difference that a mixture of lithium metal and sodium metal is used as the mineralizer in the deposition of the monocrystalline gallium nitride (GaN) window layer 5 by recrystallization from supercritical ammonia solution. 0.016 g of lithium metal and 0.016 g of sodium metal are introduced into the autoclave, which gives a molar ratio of Li: Na = 9: 1. The gallium nitride window layer 5 deposited by this process has a thickness of about 1 µm.

PL 216 522 B1

Example 7

The procedure is as in Example 1, except that a different source material is used for the deposition of the monocrystalline gallium nitride (GaN) window layer 5 by recrystallization from supercritical ammonia solution. Namely, a substrate with a laser structure deposited on it₃ the hose is placed in a high-pressure autoclave with a volume of about 36 cm³ together with the source material in the form of metallic gallium (approximately 0.6 g) and the mineralizer in the form of metallic lithium (approximately 0.018 g) with a purity of 3 N.

After filling with ammonia (about 14.5 g), the high-pressure autoclave is tightly closed and heated in a two-zone furnace. The autoclave reaction chamber is divided into two zones: a crystallization zone and a dissolution zone. The dissolution zone containing gallium as source material is heated to a temperature of about 450 ° C (at a rate of 2 ° C / min), while the crystallization zone in which the substrate with the laser structure is located is not heated and the temperature in this zone is not much higher than room temperature. The autoclave is kept at this temperature for the next 2 days (Fig. 8), during which the gallium metal source material is completely converted to polycrystalline GaN. The temperature in the crystallization zone is then increased to 550 ° C (at a rate of 2 ° C / min). The autoclave is kept under these thermal conditions for 3 days (Fig. 8).

The gallium nitride window layer 5 deposited by this process on the side surfaces of the ridge and on the unprotected surfaces of the n-type and p-type contact layers has a thickness of about 0.8 µm.

Example 8

The procedure is as in Example 1, with the only difference that the window layer 5 of monocrystalline AlGaN is deposited by recrystallization from supercritical ammonia solution.

In the present example 8, the substrate with the laser structure deposited thereon is placed in the au₃ high-pressure toclave with a volume of about 36 cm³ together with the source material in the form of GaN wafers (about 0.25 g) obtained by the HVPE method, as well as four pieces of polycrystalline AlN (0.83 g) and with a mineralizer in the form of a metal Li (about 0.018 g) with a purity of 3 N.

After filling with ammonia (about 14.5 g), the high-pressure autoclave is sealed and heated in a two-zone furnace, with the maximum temperature inside the autoclave not exceeding 550 ° C. The autoclave reaction chamber is divided into two zones: a crystallization zone and a dissolution zone. In the crystallization zone (at a temperature of about 550 ° C) there is a substrate with a laser structure applied, and in the dissolution zone (at a temperature of about 450 ° C) there is the source material. The sealed autoclave is kept under constant thermal conditions for 3 days (Fig. 7).

The monocrystalline window layer 5 has the composition Al_0]03Ga_0]97In this process, N was deposited on the side surfaces of the ridge and on the unprotected surfaces of the n-type and p-type contact layers. The window layer 5 has a thickness of about 0.9 µm.

Example 9

The procedure is as in Example 1, with the only difference that instead of the sapphire wafer 1, a gallium-containing nitride substrate obtained as follows is used, which results in better performance of the epitaxial nitride semiconductor layers deposited in the manner of Example 1.

First, a buffer layer 202 is deposited on a sapphire wafer 201 with a surface oriented perpendicular to the c axis at a temperature of 500 ° C using hydrogen as a carrier gas, using ammonia and TMG (trimethylgall) as reactants, and a buffer layer 202 is deposited thereon at the usual temperature of growth, the n-type nitride semiconductor layer 203 (Fig. 10-A) is deposited by MOCVD. The thickness of the buffer layer 202 ranges from 50 to 500 angstroms. There are, however, no restrictions on the thickness of the subsequent nitride semiconductive layer 203 other than by the method of depositing the layer employed.

Then, said nitride semiconductor layer 203 is etched to obtain a surface with a parallel stripe structure 205 (Fig. 10-B). Due to the fact that in the environment of supercritical ammonia solution, the sapphire plate 201 reacts with this solution, adversely affecting the quality of the monocrystalline nitride layer formed in this environment, the exposed surfaces of the sapphire 201 should be covered with a protective masking layer 204 made of a material that does not dissolve in the supercritical ammonia solution, or - if it dissolves does not introduce undesirable impurities into the monocrystalline nitride layer produced. Metallic silver is an example of this type of material.

In the next step, the monocrystalline nitride layer 207 is deposited on the primary substrate thus prepared, as a result of lateral build-up by crystallization from a supercritical ammonia solution. To this end, the primary substrate is introduced into a high pressure autoclave of the same type as used in the deposition process of the window layer 5 in Example 1. In addition to the substrate, source material and a mineralizer are introduced into the autoclave to be used to form a monocrystalline nitride layer. After introducing ammonia into the autoclave, it is tightly closed and the solution is made supercritical by proper temperature control.

The nitride plate formed by the lateral build-up of crystalline nitrides is then used as substrate 1 in place of the sapphire plate.

Example 10

The procedure is as in Example 1, with the only difference that instead of sapphire, a SiC plate with surfaces susceptible to lateral growth of crystalline GaN (ELOG structures) is used as the primary substrate. ELOG structures are formed as described in Example 9. The results are comparable to those of Example 1.

As already explained and in accordance with the above-mentioned embodiments of the invention, a particularly significant advantage of the nitride semiconductor lasers according to the invention is the improvement of the operating parameters of these lasers. According to the invention, from the opposing mirrors of the resonator, at least the radiation emitting mirror is covered with a window layer of monocrystalline nitride of the general formula AlxGa1-x-yInyN, deposited at a temperature so low that it does not damage the active region of the nitride semiconductor containing In. Thanks to this, it is possible to widen the energy gap in the area of ​​the mirror emitting radiation. This allows the absorption of radiation to be limited by this mirror and the threshold for the occurrence of COD to be raised. Thanks to this invention, it is possible to produce nitride semiconductor lasers with a power of more than 100 mW, which are characterized by higher reliability and durability.