JP5223531B2 - Semiconductor laser element - Google Patents

Description

  The present invention relates to a semiconductor laser device, and more particularly to a semiconductor laser device having a structure in which light is confined by a current blocking layer.

Conventionally, for example, in _{In x Al y Ga 1-xy} N (0 ≦ x, 0 ≦ y, 0 ≦ x + y ≦ 1) blue-violet semiconductor laser comprising a compound semiconductor, the vertical direction of the light in the active layer In order to sufficiently increase the confinement factor, methods for increasing the Al composition of the cladding layer have been studied. However, when the Al composition is increased, there is a problem that strain is inherent in the Al-containing layer due to lattice mismatch with the substrate and other compound semiconductor layers, and cracks are generated.

On the other hand, by disposing a current blocking layer having a stripe-shaped groove and a transparent electrode or metal layer functioning as a cladding layer on the active layer, the growth time of the compound semiconductor layer is shortened, and the compound Semiconductor laser elements that can reduce the generation of cracks in an Al-containing layer by reducing the thickness of the semiconductor layer have been proposed (for example, Patent Documents 1 and 2).
JP 2006-41491 A JP 2007-129236 A

However, when current is injected to the end face of the resonator by such a transparent electrode or metal layer, heat is generated in the vicinity of the end face of the resonator, and particularly in a high output element, heat generation becomes remarkable. There is concern about the decline.
Furthermore, when a transparent electrode or metal layer is formed away from the resonator end face to improve the COD level, the optical confinement factor in the vertical direction near the end face of the resonator fluctuates, and the refractive index distribution changes in the resonator direction. However, the FFP (Far Field Pattern) in the vertical direction is disturbed.

  The present invention has been made in view of the above problems. Even in a high-power semiconductor laser element, heat generation at the cavity end face can be minimized, the COD level can be improved, and a good FFP shape can be obtained. An object of the present invention is to provide a semiconductor laser device that can be obtained, has high reliability, and has a long lifetime.

The semiconductor laser device of the present invention is
A laminate comprising a first conductivity type semiconductor layer, an active layer, and a second conductivity type semiconductor layer, and comprising a resonator;
A stripe-shaped conductive layer provided in contact with the second conductive semiconductor layer;
A first buried layer in contact with the second conductive type semiconductor layer and disposed on an extension line of the conductive layer and having a refractive index equal to or lower than a refractive index of the conductive layer;
A pad electrode disposed on the conductive layer;
The pad electrode is electrically connected to the conductive layer and electrically disconnected from the first buried layer .
Such a semiconductor laser device further includes a second buried layer formed of an insulating material that is in contact with the second conductive type semiconductor layer and is disposed on both sides along the conductive layer. Is preferred.
The first buried layer is preferably arranged separately from the conductive layer.
Further, the conductive layer and the first embedded layer is formed of the same material, the between the conductive layer and the first embedded layer, the second buried layer formed of an insulating material is arranged It is preferable that
Further, it is preferable that the first buried layer has a refractive index different from that of the conductive layer and is disposed on the resonator surface side in contact with the conductive layer.
It is preferable that one end surface of the first buried layer is formed up to a resonator end surface.
The conductive layer is preferably formed of a conductive oxide.
The conductive layer and the first buried layer preferably have a refractive index that is larger than the second buried layer and smaller than that of the active layer.
The second buried layer is preferably formed of a material selected from the group consisting of SiO ₂ , Ga ₂ O ₃ , Al ₂ O ₃ , ZrO ₂ , SiN, AlN, and AlGaN.
The oscillation wavelength is preferably 440 nm or more.

  According to the semiconductor laser device of the present invention, even in a high-power semiconductor laser device, heat generation at the cavity end face can be minimized, the COD level can be improved, and a good FFP can be obtained, It is possible to provide a semiconductor laser element with high reliability and long life.

  The semiconductor laser device of the present invention is constituted by a laminated body including a first conductive semiconductor layer, an active layer, and a second conductive semiconductor layer, and a resonator is formed in the laminated body. In addition, a conductive layer, a first buried layer, and a second buried layer are provided in contact with the second conductive type semiconductor layer.

The first and second conductivity type semiconductor layers are not particularly limited, but are compound semiconductors, and further nitride semiconductors, in particular, the general formula is In _x Al _y Ga _1-xy N (0 ≦ x ≦ 1, 0 ≦ y ≦ 1, 0 ≦ x + y ≦ 1) is preferable. In addition to this, an element in which B is partially substituted as a group III element may be used, or an element in which a part of N is substituted with P or As may be used as a group V element. One of the first conductivity type and the second conductivity type means n-type, and the other means p-type. The n-side semiconductor layer may contain one or more group IV elements or group VI elements such as Si, Ge, Sn, S, O, Ti, Zr, and Cd as n-type impurities. The p-side semiconductor layer contains Mg, Zn, Be, Mn, Ca, Sr, etc. as p-type impurities. The impurities are preferably contained in a concentration range of, for example, about 5 × 10 ¹⁶ / cm ³ to 1 × 10 ²¹ / cm ³ . Note that all of the semiconductor layers constituting the first and second conductivity type semiconductor layers do not necessarily contain impurities.

  The first and / or second conductivity type semiconductor layer preferably has a light guide layer, and further has a SCH (Separate Confinement Heterostructure) structure in which these light guide layers sandwich an active layer. Is preferred. The light guide layers of the first and second conductivity type semiconductor layers may have structures having different compositions and / or film thicknesses.

  For example, a first conductivity type semiconductor layer (hereinafter may be referred to as “n-side semiconductor layer”), an active layer, and a second conductivity type semiconductor layer (hereinafter may be referred to as “p-side semiconductor layer”) are: A single film structure, a multilayer film structure, or a superlattice structure including two layers having different composition ratios may be provided. These layers may be provided with a composition gradient layer and a concentration gradient layer.

The n-side semiconductor layer may have a structure of two or more layers having different compositions and / or impurity concentrations.
For example, the first n-side semiconductor layer can be formed of In _x Al _y Ga _1-xy N (0 ≦ x <1, 0 ≦ y ≦ 1, 0 ≦ x + y ≦ 1), preferably Al _x Ga _1-x N (0 ≦ x ≦ 0.5), more preferably Al _x Ga _1-x N (0 <x ≦ 0.3). As specific growth conditions, it is preferable to form the growth temperature in the reactor at 900 ° C. or higher. The first n-side semiconductor layer can function as a cladding layer. A film thickness of about 0.5 to 5 μm is appropriate.
As will be described later, when the striped conductive layer and / or the first / second buried layer is provided in contact with the first conductive type semiconductor layer, the first n-side semiconductor layer can be omitted. .

The second n-side semiconductor layer can function as a light guide layer, and is represented by In _x Al _y Ga _1-xy N (0 ≦ x <1, 0 ≦ y <1, 0 ≦ x + y ≦ 1). Can be formed. The film thickness is suitably from 0.1 to 5 μm. The second n-side semiconductor layer can be omitted.
One or more semiconductor layers may be additionally formed between the n-side semiconductor layers.

The active layer may have either a multiple quantum well structure or a single quantum well structure. The well layer preferably has a general formula In _x Al _y Ga _1-xy N (0 ≦ x ≦ 1, 0 ≦ y <1, 0 ≦ x + y ≦ 1) containing at least In. Increasing the In content makes it possible to emit light in the long wavelength region, and increasing the Al content makes it possible to emit light in the ultraviolet region, and it is possible to emit light in the wavelength region of about 300 nm to 650 nm. Luminous efficiency can be improved by forming the active layer with a quantum well structure.

A p-side semiconductor layer is stacked on the active layer. The p-side semiconductor layer may have a structure of two or more layers having different compositions and / or impurity concentrations.
The first p-side semiconductor layer can be formed of Al _x Ga _1-x N (0 ≦ x ≦ 0.5) containing a p-type impurity. The first p-side semiconductor layer functions as a p-side electron confinement layer.
The second p-side semiconductor layer can function as a light guide layer, and is represented by In _x Al _y Ga _1-xy N (0 ≦ x <1, 0 ≦ y <1, 0 ≦ x + y ≦ 1). Can be formed.
However, the first p-side semiconductor layer and the second p-side semiconductor layer can be omitted.

On the second p-side semiconductor layer, a superlattice layer made of Al _x Ga _1-x N (0 ≦ x ≦ 0.5) or GaN and AlGaN containing a p-type impurity functioning as a cladding layer is formed. This layer can be omitted. By omitting this layer, the growth time of the p-side semiconductor layer after the active layer growth can be omitted. In general, in order to reduce the resistance of the p-side semiconductor layer, the p-side semiconductor layer is preferably stacked at a higher temperature than the n-side semiconductor layer or the active layer. However, when the p-side semiconductor layer is grown at a high temperature, the active layer having a high In mixed crystal ratio may be decomposed. Therefore, by omitting this layer, damage to the active layer caused by growing the p-side semiconductor layer at a high temperature can be reduced. Furthermore, since the number of stacked p-side semiconductor layers having high resistance can be reduced, the operating voltage can be reduced.

The third p-side semiconductor layer can be formed of Al _x Ga _1-x N (0 ≦ x ≦ 1) containing a p-type impurity.
These semiconductor layers may be mixed with In. The thickness of each layer is suitably about 3 nm to 5 μm.
Note that one or more semiconductor layers may be additionally formed between the p-side semiconductor layers.

  In a semiconductor laser having a relatively long wavelength of 440 nm or more, it is necessary to increase the Al mixed crystal in the p-side and / or n-side cladding layer in order to provide a sufficient refractive index difference. In a semiconductor laser that oscillates light in the ultraviolet region of 380 nm or less, light absorption can be prevented by forming a layer with a high Al mixed crystal. However, when a layer having a high Al mixed crystal is formed, cracks are likely to occur in the semiconductor layer. Therefore, by omitting the cladding layer, a highly reliable long-wavelength semiconductor laser with reduced cracks can be realized.

  The growth method of the semiconductor layer is not particularly limited, but MOVPE (metal organic chemical vapor deposition), MOCVD (metal organic chemical vapor deposition), HVPE (hydride vapor deposition), MBE (molecular beam epitaxy), etc. All methods known as nitride semiconductor growth methods can be used. In particular, MOCVD is preferable because it can be grown with good crystallinity under reduced pressure to atmospheric pressure.

In the semiconductor laser device of the present invention, as shown in FIGS. 1A to 1D, stripes are formed on the p-side semiconductor layer (for example, the third p-side semiconductor layer, the p-side contact layer 8) in parallel to the resonator direction. The conductive layer 11 is formed. The conductive layer 11 may be formed so as to be embedded in an opening of a second embedded layer to be described later as long as it is in a stripe shape and in contact with the p-side semiconductor layer (FIG. 2C ′). And may be formed over the second buried layer (see FIG. 4E ′).
The stripe width is not particularly limited as long as it can supply a sufficient current by contact with the second conductivity type semiconductor layer, and can be appropriately adjusted depending on the size of the intended semiconductor laser element. For example, about 0.3-50 micrometers, Preferably about 3-15 micrometers is mentioned. Moreover, when producing a single mode laser, Preferably about 1-5 micrometers is mentioned.

  The end surface of the conductive layer 11 may be disposed on the inner side of the resonator end surface on one of the light emitting side and the light reflecting side (see FIG. 2C), but is disposed on the inner side on both sides. Preferred (see FIG. 1C). That is, the end surface of the conductive layer 11 is separated from the resonator end surface. In particular, it is preferable that the end face of the conductive layer 11 is separated from the end face of the resonator at the end face on the light emission side.

In the resonator end surface on the light emitting side, the separation distance is not particularly limited. For example, when the resonator length is about 400 to 1500 μm, the length is about 0.001 to 10%, specifically, It is suitable that it is arranged inside the length of about 0.1 to 15 μm.
The side surface along the resonator direction of the conductive layer 11 may coincide with the side surface of the multilayer body, but is preferably disposed inside the side surface of the multilayer body as shown in FIG. 4E ′.

The conductive layer functions as an ohmic electrode by contacting the second conductive type semiconductor layer in a stripe shape. In addition, the conductive layer partially or wholly embedded by the second embedded layer, which will be described later, functions as a cladding layer that confines light in the laser waveguide due to the refractive index difference between the second embedded layer and the conductive layer. .
In order to form a waveguide in the resonator, a conductive layer is disposed. This waveguide is, for example, a refractive index a of a second buried layer described later or smaller than a refractive index d of the active layer. It is preferable to have a refractive index b or satisfy both.

The conductive layer can be formed of, for example, a layer including at least one element selected from the group consisting of zinc (Zn), indium (In), tin (Sn), and magnesium (Mg). The conductive layer is preferably formed of a conductive oxide. Specifically, ZnO (refractive index: about 1.95), In ₂ O ₃ , SnO ₂ , ATO, ITO (in and Sn Composite oxide), MgO, and the like. Of these, ITO (refractive index: about 2.0) is preferable.
In the present specification, the refractive index means a value at a wavelength of 445 nm, and the refractive index usually indicates a value measured by an ellipsometer.

In the case where the conductive layer is formed using a light-transmitting material, it is necessary to consider light absorption by the conductive layer as compared to the case where a metal material having a high reflectance is used. In order to suppress absorption, it is necessary to form a film with good film quality, and a film with high transmittance is said to have good film quality. Therefore, this conductive layer transmits not only visible light but also light with a transmittance of 90% or more, 85% or more, 80% or more without absorbing light with a wavelength of, for example, 360 nm to 650 nm. It is preferable to form it by what is to be made. As a result, the laser beam is hardly absorbed by the conductive layer, and an efficient electrode of the laser element can be formed. Furthermore, for example, the conductive layer preferably has a specific resistance of 1 × 10 ⁻² Ωcm or less, preferably about 1 × 10 ⁻³ to 1 × 10 ⁻⁵ Ωcm. Thereby, it can utilize effectively as an electrode.
The film thickness of the conductive layer is not particularly limited and can be appropriately adjusted depending on the material used, the film thickness of the second buried layer, and the like. For example, about 0.1-4.0 micrometers is mentioned.

Further, in the semiconductor laser device of the present invention, as shown in FIGS. 1A and 1C, at least one of the end portions of the conductive layer on the resonator end face side is substantially the same stripe as the conductive layer on the extension line of the conductive layer. It is preferable that a first buried layer having a width and a refractive index equal to or lower than the refractive index of the conductive layer is formed. As a result, it is possible to prevent fluctuations in the optical confinement factor in the vertical direction in the vicinity of the cavity end face, and in turn, it is possible to prevent changes in the refractive index distribution in the cavity direction and disturbances in the FFP in the vertical direction. For the reason described above, the end portion where the first buried layer is formed is particularly preferably on the light emitting side. Further, in order to prevent the refractive index distribution from fluctuating in the resonator direction, the first buried layer has a refractive index larger than the second buried layer and / or smaller than the active layer, which will be described later, like the conductive layer. It is preferable to have.
Furthermore, by forming the conductive layer and the first buried layer with the same material, a substantially constant refractive index distribution can be obtained in the direction of the resonator, and light can be reliably confined in the waveguide.

The first buried layer may be disposed in contact with the conductive layer. In this case, the first buried layer and the conductive layer are preferably different materials, that is, materials having different refractive indexes.
The first buried layer may be disposed separately from the conductive layer. For example, it is preferable that the second buried layer is disposed between the conductive layer and the first buried layer. The separation distance (D in FIG. 1C) between the conductive layer and the first buried layer only needs to ensure electrical insulation. For example, about 0.1 μm or more, about 0.5 μm or more, and preferably about 1.0 μm or more are exemplified. The length of the first buried layer is not particularly limited. For example, the length is 1/50 or less of the resonator length, preferably the stripe width or less, and the thickness of the conductive layer. It is preferable that it is the above length. Specifically, about 1 to 5 μm and about 2.5 to 4.5 μm are exemplified.

One end surface of the first buried layer is preferably formed to one end surface of the resonator, particularly the end surface on the light emitting side. As a result, optical confinement can be reliably performed in the vicinity of the resonator end face. Note that “up to the end face” means that mismatch, unevenness, and the like due to variations in etching or mask alignment are allowed.
The first buried layer can be formed of a material similar to the material exemplified for the conductive layer. By forming both with the same material, it can be formed in the same process as described later, and the manufacturing process can be simplified. However, the conductive layer and the first buried layer are not necessarily the same.

Generally, when the conductive layer is formed up to the vicinity of the resonator end face, current is injected by the conductive layer up to the vicinity of the resonator end face. As a result, a minute leak is generated near the end face of the resonator, the power consumption increases, the heat generation of the laser element increases, the deterioration rate increases, and the element life is shortened.
Further, when the vicinity of the cavity end face is opened and the semiconductor layer is exposed, the nitride semiconductor laser has a refractive index difference with the semiconductor layer near the cavity face, and the beam emitted from the laser faces downward. Disturbance is seen in the FFP shape.

  On the other hand, by disposing the first buried layer separately from the conductive layer as in the present invention, that is, by forming the first buried layer in a floating state in the vicinity of the resonator end face. The current flow to the resonator end face can be minimized, the generation of heat at the resonator end face can be suppressed, and the COD level can be improved. In particular, when an attempt is made to increase the output of the laser element, the heat generation becomes large, but the heat generation at the cavity end face where the heat generation is particularly remarkable can be reduced. In addition, by disposing the first buried layer in the vicinity of the resonator end face, it is possible to ensure light confinement particularly in the vicinity of the resonator end face. As a result, distortion of the laser beam emitted from the resonator end face can be prevented, and a good FFP pattern can be obtained.

For example, as shown in FIG. 4C, the conductive layer and the first buried layer are formed on the entire surface of the semiconductor stacked body 24 (11a in FIG. 4C), and a normal method such as photolithography and etching is performed. It can be formed by patterning into a desired shape.
Further, a mask layer having a stripe-shaped first opening and a second opening adjacent to one resonator end face side of the first opening is formed on the semiconductor laminate, and a conductive oxide layer is formed thereon. Then, the conductive layer and the first buried layer may be formed using a lift-off method.
Further, as shown in FIG. 4A, a second embedded layer 9 to be described later is formed on the entire surface of the semiconductor stacked body 24, and the stripe-shaped groove 15 and the groove 15 are adjacent to each other with a distance therebetween. The groove 16 may be formed, and the conductive oxide layer 11a may be embedded in the grooves 15 and 16 to form the conductive layer and the first embedded layers 11 and 10 (see FIGS. 4B ′ to D ′).

  The conductive layer and the first buried layer can be formed by a method known in the art. For example, various methods such as a sputtering method, an ion beam assisted deposition method, an ion implantation method, an ion plating method, a laser ablation method, or a combination of these methods and heat treatment can be used.

Specifically, when the conductive layer or the first embedded layer (for example, ITO film) is formed by sputtering, the sputtering gas is switched from a gas having a low or partial oxygen pressure to a gas having a large oxygen partial pressure, or gradually. A method of increasing the oxygen partial pressure, a method of using a target with a large amount of In or a target with a small amount of oxygen as a target for ITO film formation, and switching to a target with a small amount of In or a target with a large amount of oxygen on the way, sputtering Examples include a method of increasing the input power of the apparatus gradually or rapidly to form a film.
In addition, when a conductive oxide layer, for example, an ITO film is formed by vacuum evaporation, a method for rapidly or gradually increasing or decreasing the temperature of the semiconductor layer, a method for rapidly decreasing the film formation rate, an ion gun And a method of irradiating oxygen ions from the middle of the film formation.

In the semiconductor laser device of the present invention, the second buried layer 9 is formed in contact with the p-side semiconductor layer (for example, the third p-side semiconductor layer, the p-side contact layer 8). In general, the second buried layer 9 is preferably formed as a layer parallel to the active layer 5. The second buried layer 9 is formed so as to surround a part or all of the conductive layer along the stripe-shaped conductive layer 11 described above.
In addition, one end face on the resonator end face side of the second embedded layer 9 (that is, the light exit side end face) is flush with the resonator end face from the viewpoint of preventing minute leaks near the resonator end face. However, a part of the region (that is, the region corresponding to the portion where the conductive layer and the first buried layer are disposed) is formed so as not to reach the end face of the resonator and is located inside the region. (See FIGS. 1A and 1C). That is, the second buried layer is formed so as to straddle the region where the conductive layer is formed. In other words, the stripe-shaped groove (opening) provided in the second buried layer is not completely opened in the resonator direction, and the second buried layer is formed in a part thereof. Yes.
The end surface of the second embedded layer other than in the resonator direction may coincide with the end surface of the stacked body, but is preferably disposed inside the end surface of the stacked body.

The second buried layer includes a semiconductor layer (for example, a refractive index of GaN: about 2.5), in particular, an active layer (for example, a refractive index of InAlGaN: about 2.1 to 3.5) and a first buried layer. It is suitable that the refractive index a is smaller than that. By having such a refractive index, light can be reliably confined in the waveguide.
Alternatively, it is suitable to be made of a material having a barrier higher than the driving voltage of the semiconductor laser element. Here, having a barrier equal to or higher than the driving voltage means that the insulating properties of the semiconductor can be maintained. By having such a barrier, a stable and good electrical characteristic and a long-life semiconductor laser can be expected.

The second buried layer is, for example, an oxide and a nitride, specifically, SiO ₂ (refractive index: about 1.5), Ga ₂ O ₃ , Al ₂ O ₃ , ZrO ₂ , SiN, AlN, and AlGaN. And an insulating material selected from a group including an i-type semiconductor layer. A film thickness is not specifically limited, For example, about 0.05-5 micrometers is mentioned. The second buried layer may be a single layer or a multilayer.

  The second buried layer can be formed by a method known in the art. For example, evaporation method, sputtering method, reactive sputtering method, ECR plasma sputtering method, magnetron sputtering method, ion beam assisted evaporation method, ion plating method, laser ablation method, CVD method, spray method, spin coating method, dip method or Various methods such as a method of combining two or more of these methods or a method of combining these methods and oxidation treatment (heat treatment) can be used.

The film formation conditions for the second buried layer include sputtering using silicon oxide or silicon as a target when the second buried layer (for example, SiO ₂ ) is formed. At this time, argon gas, a mixed gas of argon gas and oxygen gas, or the like can be used as appropriate. Also, as a sputtering gas, a method of switching from a gas having a small or zero oxygen partial pressure to a gas having a large oxygen partial pressure, a method of reducing a film formation rate, a method of increasing RF power, or a change in the distance between the target and the substrate And a method of forming a film by a method of reducing the pressure. Furthermore, when forming the protective film by sputtering, a method of increasing or decreasing the temperature of the substrate may be used. Thereafter, an optional heat treatment may be performed.
In the semiconductor laser device of the present invention, the above-mentioned laminated body of semiconductor layers is usually formed on a substrate. The substrate may be an insulating substrate such as sapphire or spinel (MgA1 ₂ O ₄ ), or lithium niobate or neodymium gallate in lattice connection with silicon carbide, silicon, ZnS, ZnO, GaAs, diamond, or nitride semiconductor. The substrate may be an oxide substrate such as a nitride semiconductor substrate (GaN, AlN, etc.).

  More preferably, the nitride semiconductor substrate has, for example, an off angle of about 0.03 to 10 ° on the first main surface and / or the second main surface. The thickness is about 50 μm to 10 mm. The nitride semiconductor substrate can be formed by vapor phase growth methods such as MOCVD method, HVPE method, MBE method, hydrothermal synthesis method for crystal growth in a supercritical fluid, high pressure method, flux method, melting method and the like. A commercially available product may also be used.

  The nitride semiconductor substrate may have a dislocation density periodically or irregularly distributed in a plane, such as stripes or dots, on one surface thereof. For example, a low dislocation density region (for example, a first region) and a high dislocation density region (for example, a second region) are alternately formed in stripes by using the ELO method, and a semiconductor layer is formed on a substrate by lateral growth. By forming and using this semiconductor layer as a substrate, a region in which crystal defect densities, crystal directions, and the like are arranged in a stripe shape can be used. Further, regions having different polarities may be distributed. For example, the polarity may be divided in a stripe shape in the first region and the second region.

Here, the low dislocation density region is a region where the number of dislocations per unit area is 1 × 10 ⁷ / cm ² or less, preferably 5 × 10 ⁶ / cm ² or less. As long as the region has a high dislocation density.
When the first region and the second region alternately form stripes, the width of the first region is 10 μm to 500 μm, further 100 μm to 500 μm, and the width of the second region is 2 μm to 100 μm, 10 μm to 50 μm. It is done. The stripe shape includes a stripe shape. These dislocation measurements can be performed by CL observation, TEM observation, or the like.

  The nitride semiconductor substrate may have different crystal growth surfaces distributed on one surface thereof. For example, if the first area is the (0001) plane, the second area is different from the (0001) plane (000-1) plane, (10-10) plane, (11-20) plane, (10-14) And crystal growth planes such as a plane, a (10-15) plane, and a (11-24) plane. In particular, the (000-1) plane is preferable. By using a substrate having a partially different crystal growth surface in this way, stress and strain generated in the substrate can be relaxed, and a semiconductor layer can be formed without forming a stress relaxation layer on the substrate. Lamination can be performed with a film thickness of 5 μm or more.

As the nitride semiconductor substrate, for example, those described in JP-A-2005-175056, JP-A-2004-158500, JP-A-2003-332244, etc. may be used.
Note that a buffer layer, an intermediate layer, and the like (for example, Al _x Ga _1-x N (0 ≦ x ≦ 1) and the like) are provided over the substrate before forming a stacked body that functions as a laser element. Is preferred.

  In the semiconductor laser device of the present invention, it is preferable to form a side surface protective film that covers at least both sides of the stacked body of semiconductor layers. The side surface protective film is preferably formed over the surface of the conductive layer and / or the first buried layer by opening a region connected to the outside. Note that the side surface protective film can be formed of the same material as that of the second buried layer at the same time. Such a side surface protective film is preferably formed after the conductive layer and the first buried layer are formed and before the pad electrode described later is formed.

  Examples of the material of the side surface protective film include oxides and nitrides such as Ti, Al, Zr, V, Nb, Hf, Ta, Ga, and Si. The method for forming the side surface protective film is known in the art, and can be formed in a single layer or a laminated structure by various methods such as CVD, vapor deposition, ECR (electron cyclotron resonance plasma) sputtering, and magnetron sputtering. . A single-layer film may be formed as a film having the same composition but different film quality by changing the manufacturing method or conditions once or twice or more, or a laminated film of these materials It is good.

  A pad electrode is usually formed on the surface of the conductive layer. The pad electrode is preferably a laminated film made of a metal such as Ni, Ti, Au, Pt, Pd, or W. Specifically, a film formed in the order of W—Pd—Au or Ni—Ti—Au and Ni—Pd—Au from the conductive oxide layer side can be given. The film thickness of the pad electrode is not particularly limited, but the film thickness of the final layer of Au is preferably about 100 nm or more. Further, the width and length of the pad electrode are not particularly limited, and may be formed to a certain extent that can be connected to the outside (for example, wire bonding). For example, it is preferably formed on the conductive layer and the second buried layer and in a region that is not electrically connected to the first buried layer.

  When the substrate is a conductive substrate, for example, an n-side electrode is preferably formed on the back surface of the substrate. The n-side electrode can be formed by, for example, sputtering, CVD, vapor deposition, or the like. As the n-side electrode, for example, the total film thickness is about 1 μm or less, and from the substrate side, V (film thickness 100 mm) -Pt (film thickness 2000 mm) -Au (film thickness 3000 mm), Ti (100 mm) -Al (5000 mm) ), Ti (60Å) -Pt (1000Å) -Au (3000 （), Ti (60Å) -Mo (500Å) -Pt (1000Å) -Au (2100Å), Ti (60Å) -Hf (60Å) -Pt (1000Å) ) -Au (3000 Å), Ti (60 Å) -Mo (500 Å) -Ti (500 Å) -Pt (1000 Å) -Au (2100 Å), W-Pt-Au, W-Al-W-Au, or Hf- Al, Ti—W—Pt—Au, Ti—Pd—Pt—Au, Pd—Pt—Au, Ti—W—Ti—Pt—Au, Mo—Pt—Au, Mo—Ti—Pt—Au, W— Pt- Examples of films include u, V-Pt-Au, V-Mo-Pt-Au, VW-Pt-Au, Cr-Pt-Au, Cr-Mo-Pt-Au, Cr-W-Pt-Au Is done.

  Further, a metallized electrode may optionally be formed on the n-side electrode. The metallized electrodes are, for example, Ti—Pt—Au— (Au / Sn), Ti—Pt—Au— (Au / Si), Ti—Pt—Au— (Au / Ge), Ti—Pt—Au—In, It can be formed of Au—Sn, In, Au—Si, Au—Ge, or the like. The film thickness of the metallized electrode is not particularly limited.

In the semiconductor laser device of the present invention, the resonator end face is usually formed by cleaving the substrate and the laminate.
Optionally, an end face protective film made of a dielectric film is preferably formed on the resonator end face, that is, on the light reflection side and / or the light exit face of the resonator face. The dielectric film is preferably a single layer film or a multilayer film made of oxides and nitrides such as SiO ₂ , ZrO ₂ , TiO ₂ , Al ₂ O ₃ , Nb ₂ O ₅ , AlN, and AlGaN. When the resonance surface is formed by cleavage, the dielectric film can be formed with good reproducibility.

Further, as shown in FIG. 5, the semiconductor laser device of the present invention has a structure in which the first and second buried layers and the conductive layer described above are arranged in a pair with the active layer interposed therebetween, that is, the second conductive layer. In addition to the type semiconductor layer side, the first and second buried layers and the conductive layer may be provided on the first conductivity type semiconductor layer side.
In the laser element having such a configuration, for example, after forming a stacked body of semiconductor layers, the substrate is removed or a part of the n-side semiconductor layer (for example, up to the cladding layer or the light guide layer) is removed. Thus, the first and second buried layers and the conductive layer can be formed on the removed side in the same manner as described above. In the first conductivity type semiconductor layer, for example, an n-side pad electrode 22 is formed instead of the p-side pad electrode 12.

Hereinafter, embodiments of the semiconductor laser device of the present invention will be described in detail with reference to the drawings.
Example 1
As shown in FIGS. 1A to 1D, the semiconductor laser device of this embodiment includes an n-side semiconductor layer (n-type cladding layer 3 and n-side light guide layer 4), an active layer 5, and a p-side semiconductor layer on a substrate 1. (Cap layer 6, p-side light guide layer 7, and p-type contact layer 8) are laminated in this order to constitute a laminated body. In this laminate, a resonator having a resonator length of about 800 μm is formed.
Near the center of the p-side semiconductor layer, a stripe-shaped conductive layer 11 is arranged. On the extension line of the conductive layer 11 and on both resonator end faces, the first conductive layer 11 is spaced apart from the conductive layer 11. One buried layer 10 is disposed. Here, the length of the conductive layer 11 is about 787 μm, the width is about 7 μm, the height is about 0.4 μm, the length of the first buried layer 10 is about 5.0 μm, and the conductive layer 11 and the first buried layer are respectively. The distance D between the layers 10 is about 1.5 μm.

Further, a second buried layer 9 is formed in contact with the p-side semiconductor layer so as to bury the conductive layer and the first buried layers 11 and 10. Note that a part of the second buried layer 9 is disposed between the conductive layer 11 and the first buried layer 10, and the two are separated.
A p-side pad electrode 12 electrically connected to the conductive layer 11 is formed on the conductive layer 11 and the second buried layer 9. In this embodiment, the side surface of the p-side pad electrode 12 is not flush with the corresponding side surface of the laminate, but may be flush.
An n-side electrode 14 is formed on the back surface of the substrate 1.

A method for manufacturing this semiconductor laser element will be described below.
First, a substrate 1 made of n-type GaN is set in a MOVPE reaction vessel, and trimethylaluminum (TMA), trimethylgallium (TMG), ammonia (NH ₃ ), silane gas (SiH ₄ ) is used as impurity gas, and Si is doped. The n-type cladding layer 3 made of Al _0.33 Ga _0.67 N is grown.
Subsequently, the n-side light guide layer 4 made of undoped GaN is grown using TMG and ammonia.

Next, a barrier layer made of In _0.02 Ga _0.98 N doped with Si was grown using trimethylindium (TMI), TMG, ammonia, and silane gas. The well layer made of undoped In _0.06 Ga _0.94 N is grown by stopping the silane gas and using TMI, TMG and ammonia. After repeating this twice, a barrier layer made of In _0.02 Ga _0.98 N was grown using TMI, TMG and ammonia, and the active layer 5 made of two pairs of multiple quantum wells (MQW) (refraction) Grow rate: about 2.5).

Stop TMI, use TMA, TMG and ammonia, flow biscyclopentadienylmagnesium (Cp ₂ Mg), grow p-type cap layer 6 made of Mg-doped p-type Al _0.30 Ga _0.70 N Let

Subsequently, Cp ₂ Mg and TMA are stopped, and a p-side light guide layer 7 made of undoped GaN is grown.
Finally, Cp ₂ Mg is flowed thereon using TMG and ammonia to grow a p-type contact layer 8 made of p-type GaN doped with Mg.

  As shown in FIG. 2A, a conductive oxide layer 11a made of ITO is formed with a film thickness of 0.4 μm on the thus formed semiconductor laminate 14 by sputtering.

After that, on the conductive oxide layer 11a, a striped photoresist (stripe width: about 7 μm, a 787 μm long stripe located in the center of the resonator, 1.5 μm apart from the stripe, and resonant on both sides) 5 μm long stripes) up to the vessel end face. Using this photoresist as a mask, the conductive oxide layer 11a exposed from the photoresist is removed by, for example, reactive ion etching (RIE) using hydrogen iodide gas.
As a result, as shown in FIGS. 2B and 2B ′, the stripe-shaped conductive layer 11 and the first buried layer 10 are formed.

Without removing the photoresist as it is, the second buried layer 9 (refractive index: about 1.5) made of SiO ₂ having a thickness of about 400 nm is formed on the exposed semiconductor layer and the photoresist by sputtering. At the same time, a side surface protective film can be formed.
Thereafter, the photoresist and the second buried layer 9 formed thereon are removed.
Thereby, as shown in FIGS. 2C and 2C ′, the second buried layer 9 is formed so as to surround the conductive layer and the first buried layers 11 and 10.

Annealing is performed to reduce the contact resistance of the p-side semiconductor layer.
A p-side pad electrode 12 is formed on the conductive oxide layer 11.
Further, the back surface of the substrate 1 is polished, and an n-side electrode 14 is formed on the polished back surface of the n-type GaN substrate 1.
Thereafter, the wafer is cleaved along a direction perpendicular to the direction of the resonator to form a bar shape, and a resonator surface is produced on the cleaved surface.

Subsequently, a dielectric film is formed as an end face protective film on the resonator surface. On the light emitting side, Al ₂ O ₃ was formed with a film thickness of 70 nm. On the light reflection side, a multilayer dielectric film is formed of a laminated film of ZrO ₂ and SiO ₂ (total film thickness 700 nm).
Finally, it is divided in a direction parallel to the resonator direction, and a bar-shaped wafer is formed into chips to obtain a semiconductor laser element.

  In the semiconductor laser device of this example, by disposing the first buried layer in the vicinity of the resonator end face separately from the conductive layer, problems such as peeling and cleavage of the conductive oxide layer in the vicinity of the resonator end face occur. It is possible to ensure the confinement of light without causing it to occur and to improve the adhesion by the end face with the conductive oxide layer. Therefore, distortion of the laser beam emitted from the cavity end face can be prevented, and a good FFP pattern can be obtained.

In addition, the flow of current to the resonator end face can be minimized, generation of heat at the resonator end face can be suppressed, and the COD level can be improved.
In particular, in the semiconductor laser device of Example 1, as shown in FIGS. 2B and 2B ′, since the conductive layer and the first buried layer can be formed simultaneously by RIE, the shape of the conductive oxide layer and The controllability of the arrangement is good, so that the COD level can be improved.
Further, it is possible to extend the life.

In the semiconductor laser device of Example 1, when the first buried film is not formed, a disturbance in the intensity distribution of the FFP in the vertical direction is observed due to a sudden change in the confinement factor near the resonator surface. It is confirmed that it is difficult to drive the laser element for a long time.
In addition, when the conductive layer is disposed from one end face to the other end face of the resonator without forming the first buried film, end face deterioration due to energization in the vicinity of the end face is induced. A result with a low COD level is obtained, and it is confirmed that it is difficult to drive the laser element for a long time.

Example 2
As shown in FIGS. 3A to 3D, in this semiconductor laser element, the length of the conductive layer 11 is about 793.5 μm, and the resonator end face M on the light reflection side is matched with one end face of the conductive layer 11. Except for the above, the semiconductor laser device has substantially the same configuration as that of the semiconductor laser device of Example 1.

Example 3
As shown in FIG. 4A, a second embedded layer 9 (refractive index: about 1.5) made of SiO _{2 having a} thickness of about 500 nm is formed on the laminate 14 formed in the same manner as in Example 1 by the CVD method. Form.
Subsequently, on the second buried layer 9, a stripe-shaped opening (stripe width: about 7 μm, on one end surface side, a stripe having a length of about 5 μm from the end surface and an adjacent spacing of about 787 μm is provided. 4B and 4B are formed by selectively removing a part of the second buried layer 9 by wet etching using, for example, BHF, using the photoresist as a mask. As shown in FIG. 2, two independent grooves 15 and 16 are formed. Each of these groove portions 15 and 16 is formed such that the bottom thereof reaches the semiconductor layer and is open at the resonator end face. Thereafter, the photoresist is removed.

  Note that dry etching may be used instead of this wet etching. By using dry etching, it becomes easy to control the stripe width and the like, but the surface of the laminate 14 may be damaged. Therefore, it is preferable to select an appropriate etching method in consideration of these.

A conductive oxide layer (refractive index: about 2.0) made of ITO is formed on the entire upper surface of the second buried layer 9 including the grooves 15 and 16. A photoresist having a pattern corresponding to the groove portions 15 and 16 is formed thereon, and etching is performed using the photoresist as a mask. The groove portion 16 close to the resonator end surface corresponding to the light emitting side and the light reflecting side are formed. The conductive layer 11 and the first buried layer 10 are embedded in the groove 15 close to the corresponding resonator end face so as to be electrically separated from each other (see FIGS. 4C and 4C ′).
Subsequently, the mask is removed, and as shown in FIGS. 4D and 4D ′, a conductive material made of ITO is formed on the entire surface of the wafer on which the second embedded layer 9, the conductive layer 11, and the first embedded layer 10 are formed. The oxide layer 11a is formed.
A photoresist having a pattern on part of the conductive layer 11 and the second buried layer 9 is formed thereon, and etching is performed using the photoresist as a mask, so that the groove 15 and the second buried layer 9 are formed. In part, the conductive oxide layer 11 is patterned (see FIG. 4E ′). The patterned conductive oxide layer 11 can function as an ohmic electrode.
Thereafter, a semiconductor laser element is formed in the same manner as in the first embodiment.
Thereby, the same effect as Example 1 can be acquired.

Example 4
In the semiconductor laser device of this embodiment, the length of the conductive layer is 777 μm, the length of the first buried layer 10 is 10 μm, and the second buried layer is formed from the cavity end faces on both sides of the first buried layer. The exposed semiconductor layer is buried from the end face of the conductive layer to the end face of the resonator. Other than that, a semiconductor laser element is formed in the same manner as in the first embodiment.
In the semiconductor laser device of this embodiment, the same effect as that of Embodiment 1 can be obtained.

Example 5
In the semiconductor laser device of this embodiment, the length of the conductive layer is 784 μm, the length of the first buried layer 10 is 5 μm from the cavity end faces on both sides of the first buried layer, and the second buried layer is formed. Are spaced apart by about 3 μm, and an exposed semiconductor layer from the end face of the conductive layer to the end face of the resonator is buried. Other than that, a semiconductor laser element is formed in the same manner as in the first embodiment.
In the semiconductor laser device of this embodiment, the same effect as that of Embodiment 1 can be obtained.

Example 6
In the semiconductor laser device of this example, the semiconductor laser device is formed in the same manner as in Example 1 except that the stripe width of the conductive layer and the first buried layers 11 and 10 is 10 μm.
In the semiconductor laser device of this embodiment, in addition to the same effect as that of the first embodiment, it is possible to increase the output by widening the groove.
In other words, when the output of the laser element is increased, heat generation generally increases.However, by widening the groove portion in this way, it is possible to reduce heat generation particularly at the cavity end face where heat generation is remarkable, The COD level can be obtained.

なお、本願表中、「ｎ−」は、ｎ型不純物のドープを示し、「ｐ−」は、ｐ型不純物のドープを示す。
この実施例の半導体レーザ素子では、実施例１と同様の効果を得ることができる。 Example 7
In the semiconductor laser device of this example, each semiconductor layer is configured as shown in the following table, and a laminated body is formed in accordance with Example 1, except that the laser element has an oscillation wavelength of about 440 to 450 nm. A semiconductor laser element is formed in the same manner as described above.

In the table of the present application, “n−” indicates doping of n-type impurities, and “p−” indicates doping of p-type impurities.
In the semiconductor laser device of this embodiment, the same effect as that of Embodiment 1 can be obtained.

  The present invention can be used not only for a laser element but also for a method for manufacturing a light emitting element such as a light emitting diode (LED).

1 is a perspective view A, a front view B, a plan view C, and a side view D showing a structure of a semiconductor laser device of the present invention. It is a schematic manufacturing process figure of the principal part for demonstrating the manufacturing method of the semiconductor laser element of this invention. 4 is a perspective view A, a front view B, a plan view C, and a side view D showing the structure of another semiconductor laser device of the present invention. FIG. It is a schematic manufacturing-process figure of the principal part for demonstrating another manufacturing method of the semiconductor laser element of this invention. 4 is a perspective view A, a front view B, a plan view C, and a side view D showing the structure of another semiconductor laser device of the present invention. FIG.

Explanation of symbols

1 substrate 3 n-type cladding layer 4 n-side light guide layer 5 active layer 6 cap layer 7 p-side light guide layer 8 p-type contact layer 9 second buried layer 10 first buried layer 11 conductive layers 11a and 11b conductive Oxide layer 12 p-side pad electrode 14 n-side electrode 15, 16 groove 22 n-side pad electrode 24 laminate

Claims (10)

A laminate comprising a first conductivity type semiconductor layer, an active layer, and a second conductivity type semiconductor layer, and comprising a resonator;
A stripe-shaped conductive layer provided in contact with the second conductive semiconductor layer;
A first buried layer in contact with the second conductive type semiconductor layer and disposed on an extension line of the conductive layer and having a refractive index equal to or lower than a refractive index of the conductive layer;
A pad electrode disposed on the conductive layer;
The pad electrode is electrically connected to the conductive layer and is not electrically connected to the first buried layer .   2. The semiconductor laser device according to claim 1, further comprising a second buried layer formed of an insulating material in contact with the second conductive semiconductor layer and disposed on both sides along the conductive layer. .   The semiconductor laser device according to claim 1, wherein the first buried layer is disposed separately from the conductive layer. The conductive layer and the first embedded layer is formed of the same material, between the conductive layer and the first embedded layer, the second buried layer formed of an insulating material is disposed The semiconductor laser device according to claim 3.   3. The semiconductor laser device according to claim 1, wherein the first buried layer has a refractive index different from that of the conductive layer and is disposed on a resonator surface side in contact with the conductive layer.   6. The semiconductor laser device according to claim 1, wherein one end face of the first buried layer is formed up to a cavity end face. 7.   The semiconductor laser device according to claim 1, wherein the conductive layer is formed of a conductive oxide. 3. The semiconductor laser device according to claim 2 , wherein the conductive layer and the first buried layer have a refractive index larger than that of the second buried layer and smaller than that of the active layer. The second embedded _layer, according to _{SiO 2, Ga 2 O 3,} Al 2 O 3, ZrO 2, SiN, claim 2 or 8 comprising made of a material selected from the group consisting of AlN and AlGaN Semiconductor laser element.   The semiconductor laser device according to claim 1, wherein the oscillation wavelength is 440 nm or more.

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