JP2006041490A - Semiconductor laser device and manufacturing method thereof - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a long-lived semiconductor laser element capable of low threshold current and high output operation in a blue-violet semiconductor laser element using a nitride semiconductor layer.
An n-type GaN layer 2, an n-type AlGaN cladding layer 3, a first n-type GaN guide layer 4 and a p-type AlGaN blocking layer 6 (current blocking layer) are sequentially formed on a GaN substrate 1, and p A stripe-shaped opening is formed in a part of the type AlGaN blocking layer 6, and a second n-type GaN guide layer 5 is formed so as to cover the opening, and an InGaN multiple quantum well active layer 7 is formed thereon. An undoped GaN guide layer 8, a p-type AlGaN electron barrier layer 9, a p-type AlGaN cladding layer 10 and a p-type GaN contact layer 11 are sequentially formed.
[Selection] Figure 1

Description

  The present invention relates to a semiconductor laser device applicable to, for example, a blue-violet semiconductor laser device that can be used as a light source for writing / reading on a high-density optical disk, and a manufacturing method thereof.

  III-V compound semiconductor laser elements are widely used as light sources for reading / writing optical disks such as CD (Compact Disk) and DVD (Digital Versatile Disk). As the density of optical disks increases, the wavelength of the light source needs to be shortened, and so far, the light has shifted from 780 nm in the infrared region to 650 nm in the red region. A light source with a shorter wavelength is required to achieve higher density, and a GaN-based III-V group nitride semiconductor (denoted as InGaAlN) is expected as a material that can realize this. To date, blue-violet laser elements with a power of several tens of mW have already been commercialized, and research and development have been actively conducted toward the practical application of next-generation high-density optical disc systems (Blu-ray Discs). In the optical disk system, it is indispensable to increase the output of the light source for its high-speed writing operation, and research aimed at increasing the output of GaN-based semiconductor laser devices composed of GaN-based III-V nitride semiconductors Development is also active.

  Usually, a semiconductor laser element used in an optical disk system has a stripe-shaped waveguide that is positioned in the vicinity of an active layer that emits light and confines light, and a resonator mirror that is formed by cleavage. Factors that hinder high output of such semiconductor laser elements include end face destruction, kinks due to spatial hole burning (observed in current-light output characteristics), output saturation due to heat generation, and so on. The red semiconductor laser device has solved these problems and has been increasing its output. On the other hand, in the current GaN-based blue-violet semiconductor laser element expected for the next generation, the biggest issue is the development of a waveguide structure mainly for raising the kink level, rather than problems of end face destruction and heat dissipation. Development of higher output is being promoted by dimensional design and control of the waveguide structure.

  Hereinafter, a laser structure of a high-power infrared semiconductor laser device reported so far and an example in which the laser structure of the high-power infrared semiconductor laser device is applied to a GaN blue-violet semiconductor laser device will be described.

FIG. 5 is a cross-sectional view showing a laser structure of a conventional GaAs infrared semiconductor laser device.
This GaAs-based infrared semiconductor laser device includes an n-type GaAs substrate 23, an n-type AlGaAs cladding layer 24, an undoped AlGaAs active layer 25, a first p-type AlGaAs cladding layer 26, an n-type AlGaAs blocking layer 27, The second p-type AlGaAs cladding layer 28, the p-type GaAs contact layer 29, the AuGeNi / Au ohmic electrode 30, and the Ti / Pt / Au ohmic electrode 31.

  In this GaAs infrared semiconductor laser device, high power operation is realized by controlling optical confinement in the waveguide by precisely controlling the mixed crystal ratio of AlGaAs or GaAs using epitaxial regrowth technology. . On the n-type GaAs substrate 23, an n-type AlGaAs cladding layer 24, an undoped AlGaAs active layer 25, and a part of the p-type AlGaAs cladding layer, that is, a first p-type AlGaAs cladding layer 26 are sequentially formed. An n-type AlGaAs block layer 27 is formed on the first p-type AlGaAs cladding layer 26 in a shape having a stripe-shaped opening, and the remaining p-type AlGaAs cladding layer, that is, a second p-type is formed on the opening. An AlGaAs cladding layer 28 and a p-type GaAs contact layer 29 are formed. An AuGeNi / Au ohmic electrode 30 is formed on the back surface of the n-type GaAs substrate 23, and a Ti / Pt / Au ohmic electrode 31 is formed on the p-type GaAs contact layer 29. The refractive index of the second p-type AlGaAs cladding layer 28 formed by the regrowth becomes larger than the refractive index of the n-type AlGaAs blocking layer 27, and light is confined in the stripe portion. At this time, since the n-type AlGaAs block layer 27 does not absorb light and has a real refractive index waveguide structure with small internal loss, low threshold current and high output operation are realized (Patent Document 1 and Non-Patent Document). 1).

  FIG. 6 is a sectional view of a GaN blue-violet semiconductor laser device for explaining the laser structure in an example in which the laser structure of a high-power GaAs-based infrared semiconductor laser device is applied to a GaN-based blue-violet semiconductor laser device. Documents 2, 3 and the like.

  This GaN-based blue-violet semiconductor laser device includes an n-type GaN layer 2, an n-type AlGaN cladding layer 3, an InGaN multiple quantum well active layer 7, a p-type GaN contact layer 11, and a Ti / Al / Ni / Au ohmic contact. Electrode 12, Ti / Au pad electrode 14, sapphire substrate 16, Ni / Au electrode 32, first p-type AlGaN cladding layer 33, n-type AlGaN blocking layer 34, and second p-type AlGaN cladding Layer 35.

In this GaN-based blue-violet semiconductor laser device, a p-type cladding layer is regrown on a part of the p-type cladding layer in the same manner as the GaAs-based infrared semiconductor laser device shown in FIG. By controlling the ratio precisely, it is possible to control optical confinement in the waveguide and realize low threshold current and high output operation.
JP-A-4-370993 JP-A-8-97507 Japanese Patent Laid-Open No. 10-27947 See I O. Imafuji et al., IEEE J. Quantum Electron. QE-29 (1993) p.1889

However, in the GaN-based blue-violet semiconductor laser device having the regrowth step shown in FIG. 6 and the manufacturing method thereof, a concentration distribution such as an increase or decrease in the Mg concentration contained in the p-type AlGaN layer occurs in the vicinity of the regrowth interface. End up. In the p-type AlGaN layer, the resistivity depends on the Mg concentration, and when the concentration exceeds about 5 × 10 ¹⁹ cm ⁻³ , the resistance suddenly becomes high. As a result, Mg is redistributed near the interface. A high resistance portion is formed at the interface. Therefore, the GaN-based blue-violet semiconductor laser device and the manufacturing method thereof have problems that the series resistance is large and the operating voltage is high. That is, since the operating voltage is high, there is a problem that power consumption is large and it is difficult to extend the life as a result. From such a background, the conventional GaN blue-violet laser element does not use a regrowth process, and after the epitaxial growth up to the p-type layer, the p-type AlGaN cladding layer is formed with a convex portion, for example, at the periphery thereof. A semiconductor laser device having a laser structure in which a SiO ₂ passivation film is formed and light is confined by a difference in refractive index between the SiO ₂ passivation film and a p-type AlGaN cladding layer has been reported.

  In view of the above technical problems, an object of the present invention is to provide a semiconductor laser device having a low lifetime and a high life that enables a high output operation and a method for manufacturing the same.

  In order to solve the above-mentioned problems, the semiconductor laser device of the present invention has a configuration described below.

  That is, the semiconductor laser device of the present invention includes a substrate, a p-type or semi-insulating current blocking layer provided with an opening formed on the substrate, and an n formed at least in the opening. And a light emitting layer formed on the current blocking layer.

  With such a configuration, when the n-type substrate is used, the current blocking layer is p-type and the semiconductor layer is n-type, so that the n-type semiconductor layer is re-applied on the n-type semiconductor layer. Since the semiconductor laser element can be formed by growth, the interface resistance at the regrowth interface can be reduced, and a semiconductor laser element with low series resistance and low voltage operation can be realized. In addition, since a real refractive index waveguide structure with a small internal loss of light can be obtained, a low threshold current and a high output operation are realized.

  Specifically, in the GaN-based semiconductor laser device of the present invention, a first n-type GaN guide layer and a p-type AlGaN blocking layer (current blocking layer) are formed on a substrate, and a part of the p-type AlGaN blocking layer is formed. In this configuration, a second n-type GaN guide layer and an InGaN multiple quantum well active layer are formed so as to cover the opening.

With such a configuration, light is confined to the second n-type GaN guide layer side due to the refractive index difference between the two layers of the p-type AlGaN block layer and the second n-type GaN guide layer, and etched in a stripe shape. The portion where the second n-type GaN guide layer is buried in the opening of the p-type AlGaN block layer formed in this way forms a waveguide of the blue-violet semiconductor laser device. At this time, by regrowing the second n-type GaN guide layer on the first n-type GaN guide layer, the resistance at the regrowth interface is compared with the case where the p-type layer is regrown on the p-type layer. In addition, since the electrode area on the p-type GaN layer can be increased as compared with the ridge type semiconductor laser device, the series resistance is reduced, and the low voltage operation can be realized. Further, the refractive index difference between the second n-type GaN guide layer and the p-type AlGaN block layer inside the stripe-shaped opening is changed by changing the Al composition of the p-type AlGaN block layer, thereby reducing the refractive index difference by 10 ^−. Since it can be controlled precisely with ^three units, it is possible to suppress the occurrence of kinks in the current-light output characteristics during high output operation and increase the design margin for obtaining a stable high output single transverse mode laser. it can. Further, by precisely controlling the above-described refractive index difference, when the same structure is applied to a self-excited oscillation type low-noise semiconductor laser element, the design margin of the semiconductor laser element can be increased.

  The semiconductor layer preferably has a flat top surface, and the light emitting layer is formed on the semiconductor layer so as to be in contact with the semiconductor layer.

  By adopting such a configuration, since there is no step or unevenness in the surface of the semiconductor layer on which the light emitting layer is formed, the reproducibility of the horizontal divergence angle is improved, so when used as a light source for an optical disc system or the like. This makes it possible to obtain a far field pattern with good reproducibility.

The current blocking layer preferably has a smaller refractive index than the semiconductor layer.
With such a configuration, a waveguide of the semiconductor laser element can be formed by confining light inside the opening due to a difference in refractive index between the current blocking layer having the stripe-shaped opening and the light guide layer. And, by changing the film composition of the current blocking layer, the refractive index difference can be precisely controlled on the order of 10 ⁻³ , thus suppressing the occurrence of kinks in the current-light output characteristics during high output operation, The design margin for obtaining a stable high-power single transverse mode laser can be increased. In addition, by precisely controlling the above-described refractive index difference, when the same structure is applied to a self-excited oscillation type low-noise semiconductor laser element, the design margin of the semiconductor laser element can be increased.

The current blocking layer preferably has a portion to which a plurality of types of impurities are added.
By adopting such a configuration, it is possible to control the loss of light due to absorption in the current blocking layer while maintaining electrical separation, thereby increasing the design margin of a high-power or low-noise semiconductor laser device. Is possible.

The current blocking layer is preferably composed of a plurality of layers having different compositions.
By adopting such a configuration, for example, when the current blocking layer is made of AlGaN, the uppermost layer is made of AlGaN having a large Al composition, and for example, p to the light guide layer or the active layer above the current blocking layer. Since the diffusion of Mg, which is a type impurity, can be suppressed, it is possible to improve the light emission efficiency and realize a semiconductor laser device with a low operating current.

The semiconductor laser device of the present invention is preferably configured such that the concentration of the impurity added to the current blocking layer is 10 ¹⁶ cm ⁻³ or less in the semiconductor layer.

  With such a configuration, it is possible to suppress the diffusion of impurities into the active layer, improve the light emission efficiency, and realize a semiconductor laser device with a low operating current.

  The semiconductor layer includes a first semiconductor layer and a second semiconductor layer formed on the first semiconductor layer so as to be in contact with the first semiconductor layer, and the first semiconductor layer includes the current The second semiconductor layer is formed between the blocking layer and the substrate, the second semiconductor layer is formed between the opening and the current blocking layer and the light emitting layer, and the impurity concentration in the first semiconductor layer is: The light emitting layer side is preferably larger than the substrate side.

  With this configuration, the impurity concentration increases on the surface of the first semiconductor layer where regrowth is performed through the opening. As a result, the redistribution of impurities during re-growth does not result in the formation of parts with low impurities and low carrier concentration. An element can be realized.

The composition of the first semiconductor layer is preferably different from the composition of the second semiconductor layer.
By adopting such a configuration, for example, when the current blocking layer is made of AlGaN, the uppermost layer is made of AlGaN having a large Al composition. For example, Mg of p-type impurity to the upper light guide layer or active layer It is possible to suppress the diffusion, improve the light emission efficiency, and realize a semiconductor laser with a low operating current. Also, the optical confinement factor in the vertical direction can be increased, and a semiconductor laser device with a low threshold current can be realized.

  The impurity concentration distribution of the first semiconductor layer and the second semiconductor layer is preferably a distribution in which a peak is located at an interface between the first semiconductor layer and the second semiconductor layer.

  With this configuration, each of the first semiconductor layer and the second semiconductor layer is made of, for example, Si-doped GaN or InGaN, and the Si doping amount is adjusted so that the Si concentration is increased on the outermost surface of the first semiconductor layer. When crystal growth is performed, the first semiconductor layer and the second semiconductor layer can be formed in a form having a peak in the Si concentration distribution near the regrowth interface, and as a result, the interface resistance can be reduced, and the series resistance and operating voltage can be reduced. A small semiconductor laser device can be realized.

The semiconductor laser device of the present invention, further opening of the current blocking layer, the semiconductor layer constituting the semiconductor laser device, the crystal defect density is formed on the upper portion is 10 ⁷ cm ^-2 or less It is preferable that it is the structure characterized by these.

By adopting such a configuration, the active layer and the waveguide of the semiconductor laser element can be formed in a portion where the crystal defect density is 10 ⁷ cm ⁻² or less, thereby realizing a longer-lived semiconductor laser element. It becomes possible.

  The light emitting layer and the semiconductor layer are preferably composed of a compound semiconductor containing nitrogen.

  By adopting such a configuration, it is possible to realize a blue-violet semiconductor laser element having a low series resistance, a low voltage operation, and a long lifetime.

  The semiconductor laser device of the present invention preferably has a configuration in which Si is further added to the semiconductor layer.

  With such a configuration, for example, a GaN-based semiconductor laser element can be formed by regrowth of an n-type layer containing Si as an impurity on an n-type layer containing Si as an impurity. Therefore, a semiconductor laser element can be formed using a low-resistance n-type GaN-based semiconductor layer, and a blue-violet semiconductor laser element with low series resistance and low voltage operation can be realized.

The semiconductor laser device of the present invention preferably further includes a portion having a Si concentration of 1 × 10 ¹⁸ cm ⁻³ or more in the Si concentration distribution.

  By adopting such a configuration, it is possible to realize a semiconductor laser element with a smaller series resistance and a smaller operating voltage.

Mg is preferably added to the current blocking layer.
With such a configuration, for example, in a GaN-based semiconductor laser element, a p-type GaN-based semiconductor layer having a large carrier concentration can be used as a current blocking layer, so that current is confined in the opening portion of the current blocking layer. can do. In addition, by changing the film composition of the current blocking layer, the refractive index difference can be precisely controlled on the order of 10 ⁻³ , thus suppressing the occurrence of kinks in the current-light output characteristics during high output operation, The design margin for obtaining a stable high-power single transverse mode blue-violet semiconductor laser can be increased. Further, by precisely controlling the refractive index difference, the design margin of the laser can be increased even when the structure is applied to a self-oscillation type low noise blue-violet semiconductor laser element.

The Mg concentration of the current blocking layer is preferably 1 × 10 ¹⁹ cm ⁻³ or less.
By adopting such a configuration, for example, point defects generated in the p-type GaN layer or the p-type AlGaN layer can be suppressed, so that the crystallinity of the active layer formed above the current blocking layer is improved, It is possible to suppress the Mg diffusion concentration in the active layer, and as a result, improve the luminous efficiency of the active layer and realize a semiconductor laser device with a low operating current.

The semiconductor layer is preferably made of GaN.
By adopting such a configuration, when the current blocking layer is made of AlGaN, AlGaN constituting the current blocking layer has a lower refractive index than GaN constituting the semiconductor layer, so that the current is supplied to the current blocking layer. It is possible to constrict at the opening portion. In addition, since the refractive index difference can be precisely controlled on the order of 10 ⁻³ by controlling the Al composition of the current blocking layer, a high-power blue-violet semiconductor laser device and a low-noise blue-violet semiconductor laser device can be obtained. The design margin can be increased.

  The light emitting layer is made of InGaAlN, and the Al composition of the light emitting layer is preferably located above the current blocking layer is larger than the portion located above the opening.

  With such a configuration, for example, a blue-violet semiconductor laser element having a light emitting layer having a multiple quantum well structure made of AlGaN is formed by MOCVD, and the light guide layer and the light emitting layer are formed by regrowth from the opening of the current blocking layer. When Ga is formed, Ga migrates in the vicinity of the opening during the burying regrowth, and as a result, the Al composition of the light emitting layer decreases in the vicinity of the opening. Accordingly, the light is easily confined in the light emitting layer above the opening, and a sufficiently large light confinement can be realized even with a thinner current blocking layer, and a low threshold blue-violet semiconductor laser device can be realized. .

  The In composition of the light emitting layer is preferably such that the portion located above the current blocking layer is smaller than the portion located above the opening.

  By adopting such a configuration, for example, a blue-violet semiconductor laser element having a light emitting layer having a multiple quantum well structure made of InGaN is formed by MOCVD, and the light guide layer and the light emitting layer are formed by regrowth from the opening of the current blocking layer. When In is formed, In migrates in the vicinity of the opening during the burying regrowth, as a result, the In composition of the light emitting layer increases in the vicinity of the opening. Therefore, a longer wavelength semiconductor laser element can be formed with a small amount of In material. Further, the In composition is reduced on the current blocking layer, and the lattice mismatch with the underlying AlGaN or GaN can be further reduced, so that a light emitting layer with fewer crystal defects can be realized.

  The semiconductor laser device of the present invention preferably has a configuration in which Mg and Si are further included in the current blocking layer.

  With this configuration, the loss due to absorption in the current blocking layer can be controlled while maintaining electrical isolation by co-doping with Mg and Si, and the design margin of high-power and low-noise semiconductor laser devices can be expanded. It becomes possible to do.

In the semiconductor laser device of the present invention, it is preferable that the substrate is made of any of sapphire, SiC, GaN, AlN, MgO, LiGaO ₂ , LiAlO ₂ , LiGaO _2, and LiAlO ₂ mixed crystals.

  By adopting such a configuration, a GaN-based semiconductor epitaxial growth layer having excellent crystallinity can be formed on the substrate, so that a blue-violet semiconductor laser device having a smaller series resistance and a low voltage operation can be realized.

The first semiconductor layer is preferably made of In _x Ga _1-x N (0 ≦ x ≦ 1), and the second semiconductor layer is preferably made of GaN.

  With this configuration, InGaN has a higher refractive index than GaN, so using InGaN in the semiconductor layer can increase the vertical optical confinement factor and realize a semiconductor laser device with a low threshold current. Is possible.

The current blocking layer includes a first Al _x Ga _1-x N (0 ≦ x ≦ 1) layer and a second Al _y Ga ₁ formed on the _first Al _x Ga _1-x N layer. _-y N (0≤y≤1, where x <y) layers are preferable.

  With such a configuration, for example, by increasing the Al composition of the first AlGaN layer or the second AlGaN layer, diffusion of Mg added to the AlGaN layer having a small Al composition can be suppressed. Therefore, it is possible to suppress the diffusion of Mg into the active layer, improve the light emission efficiency, and realize a semiconductor laser device with a low operating current.

The current blocking layer is preferably made of Al _x Ga _1-x N (0 ≦ x ≦ 1).
With such a configuration, when the semiconductor layer formed in the opening of the current blocking layer is made of, for example, GaN or InGaN, the AlGaN that forms the current blocking layer is more than the material that forms the semiconductor layer. Since the refractive index is small, the current can be confined in the opening portion of the current blocking layer. In addition, by controlling the Al composition of the current blocking layer, the refractive index difference can be precisely controlled on the order of 10 ⁻³ , thus suppressing the occurrence of kinks in the current-light output characteristics during high output operation, The design margin for obtaining a stable high-power single transverse mode blue-violet semiconductor laser can be increased. Further, by precisely controlling the refractive index difference, the design margin of the laser can be increased even when the structure is applied to a self-oscillation type low noise blue-violet semiconductor laser element.

In the semiconductor laser device of the present invention, it is preferable that the light emitting layer is further composed of a multiple quantum well having a quantum well made of In _x Ga _1-x N (0 ≦ x ≦ 1).

  By adopting such a configuration, the gain and light emission efficiency of the light emitting layer constituting the semiconductor laser element can be sufficiently increased. For example, a blue-violet semiconductor laser element having a low threshold current and a low operating current can be realized. Become.

The semiconductor layer functions as a cladding layer, and the semiconductor laser element is further configured by In _x Ga _1-x N (0 ≦ x ≦ 1) formed between the light emitting layer and the cladding layer. It is preferable to provide a light guide layer.

  With such a configuration, when the current blocking layer is made of AlGaN, a sufficiently large refractive index difference between the current blocking layer and the light guide layer can be obtained with a small Al composition. In general, when an AlGaN layer having a high Al composition is formed by epitaxial growth, there is a problem that the growth rate is slow or cracks are likely to occur, but this can be solved, and a current blocking layer that does not easily cause cracks in the film can be solved. It becomes possible to form.

  The light guide layer preferably has a periodic structure in which InGaN and GaN are periodically arranged.

  By adopting such a configuration, the problem of crystallinity degradation due to In segregation, which was a problem when forming an InGaN optical guide layer, was solved, and as a result, internal loss in the InGaN optical guide layer was reduced and a low threshold value was achieved. A blue-violet semiconductor laser element having a current can be realized.

  In the semiconductor laser device of the present invention, it is preferable that a cladding layer having a forbidden band width larger than that of the semiconductor layer is further formed below the semiconductor layer.

  By adopting such a configuration, the clad layer formed below the semiconductor layer has a low refractive index and can increase the vertical light confinement coefficient in the light emitting layer. As a result, a blue-violet semiconductor laser device having a low threshold current is obtained. It can be realized.

In the semiconductor laser device of the present invention, it is preferable that the cladding layer is further made of Al _x Ga _1-x N (0 ≦ x ≦ 1).

  By adopting such a configuration, when the light guide layer formed on the cladding layer in the waveguide of the semiconductor laser device is formed of GaN or InGaN, AlGaN has a lower refractive index than these, and thus emits light. The vertical light confinement factor in the layer can be increased. Further, the optical confinement factor can be precisely controlled by controlling the Al composition of the clad layer and the AlGaN film thickness, and a blue-violet semiconductor laser device having a low threshold current with good reproducibility can be realized.

  The method for manufacturing a semiconductor laser device of the present invention includes a first semiconductor layer forming step of forming a first semiconductor layer on a substrate, a current blocking layer forming step of forming a current blocking layer on the first semiconductor layer, An opening forming step for forming an opening in the current blocking layer, a second semiconductor layer forming step for forming a second semiconductor layer on the opening, and a light emitting layer for forming a light emitting layer on the second semiconductor layer And a forming step.

  With this configuration, when an n-type substrate is used, the current blocking layer is p-type, and the first semiconductor and the second semiconductor layer are n-type. Since the semiconductor laser device can be formed by regrowth of the n-type semiconductor layer, the interface resistance at the regrowth interface can be reduced, and a semiconductor laser device with low series resistance and low voltage operation can be realized.

  In forming the second semiconductor layer, the second semiconductor layer is formed so that the upper surface is flat, and in the light emitting layer forming step, the light emitting layer is formed on the flat surface of the second semiconductor layer. It is preferable.

  By adopting such a configuration, there is no step or unevenness on the surface of the semiconductor layer on which the light emitting layer is formed, so the reproducibility of the horizontal light confinement is improved and the reproducibility of the horizontal far-field image is improved. Can be made. In addition, since a real refractive index waveguide structure with a small internal loss of light can be obtained, a low threshold current and a high output operation are realized.

  In forming the second semiconductor layer, it is preferable to planarize the surface of the second semiconductor layer by etching or polishing.

  By adopting such a configuration, the thickness of the light guide layer formed between the active layer and the current blocking layer is reduced while maintaining the flatness of the active layer, so that the lateral light confinement can be easily controlled. Therefore, it is possible to increase the design margin of the semiconductor laser device with high output and low noise.

  The current blocking layer has a p-type or semi-insulating conductivity type, and after forming a part of the current blocking layer by adding an impurity on the first semiconductor layer in the current blocking layer forming step. Preferably, the other part of the current blocking layer is formed on the part of the current blocking layer without adding impurities.

  With such a configuration, for example, when the supply of Mg source is stopped during the formation of the p-type AlGaN current blocking layer and the remaining p-type AlGaN current blocking layer is formed, the p-type formed after the stop is formed. In the AlGaN current blocking layer, added Mg is distributed by diffusion, but the outermost layer can be formed in a form in which Mg does not exist. As a result, Mg diffusion to the light guide layer or the active layer can be suppressed, so that the light emission efficiency can be improved and a semiconductor laser device with a low operating current can be realized.

In the method for manufacturing a semiconductor laser device of the present invention, a mask having an opening is selectively formed on the substrate, and crystal growth is started from the opening, on the opening and the mask. A current blocking layer and a first semiconductor layer are formed, a light emitting layer in the semiconductor laser element is formed above the first semiconductor layer, and a crystal defect density of the active layer above the opening is 10 ⁷ cm ^−. It is preferable that the configuration is ² or less.

By adopting such a configuration, the active layer and the waveguide of the semiconductor laser element can be formed in a portion where the crystal defect density is 10 ⁷ cm ⁻² or less, thereby realizing a longer-lived semiconductor laser element. It becomes possible.

  The light emitting layer, the first semiconductor layer, and the second semiconductor layer are preferably made of a compound semiconductor containing nitrogen.

  By adopting such a configuration, it is possible to realize a blue-violet semiconductor laser element having a low series resistance, a low voltage operation, and a long lifetime.

In the method of manufacturing a semiconductor laser device according to the present invention, the substrate on which the semiconductor laser device is formed may be any of sapphire, SiC, GaN, AlN, MgO, LiGaO ₂ , LiAlO ₂ , LiGaO ₂ and LiAlO ₂ mixed crystal. It is preferable to be configured.

  By adopting such a configuration, a GaN-based semiconductor epitaxial growth layer having excellent crystallinity can be formed on the substrate, so that a blue-violet semiconductor laser device having a smaller series resistance and a low voltage operation can be realized.

  The method of manufacturing a semiconductor laser device further includes a light guide layer forming step of forming a light guide layer by periodically arranging InGaN and GaN between the light emitting layer and the second semiconductor layer, In the optical guide layer forming step, the optical guide layer is preferably formed by crystal growth of the InGaN at a lower temperature than the GaN.

  By adopting such a configuration, it is possible to optimize the crystal growth temperatures of InGaN and GaN individually and realize InGaN with more uniform and good crystallinity. Therefore, the problem of crystallinity degradation due to In segregation, which was a problem when forming an InGaN optical guide layer, was solved, and as a result, the internal loss in the InGaN optical guide layer was reduced, and a blue-violet semiconductor laser having a low threshold current An element can be realized.

  In the method for manufacturing a semiconductor laser device according to the present invention, it is preferable that a portion of the semiconductor laser device above the first semiconductor layer is formed by metal organic chemical vapor deposition.

  By adopting such a configuration, in the regrowth of the current blocking layer on the opening, crystal growth can be realized in such a manner that the step of the opening is buried and flattened, so that the light emitting layer having a flatter surface is formed. realizable. As a result, for example, the uniformity of the film thickness in the multiple quantum well is improved, and the influence of electric field concentration is eliminated, so that a semiconductor laser element with a lower series resistance and a low voltage operation can be realized with good reproducibility. It becomes.

  In the method for manufacturing a semiconductor laser device according to the present invention, the metal laser vapor deposition method, molecular beam epitaxy method, hydride vapor deposition method is used for the portion below the current blocking layer and the second semiconductor layer of the semiconductor laser device. Or it is preferable to form by the combination.

  With this configuration, if a sufficiently thick underlayer of, for example, 100 μm or more is formed below the current blocking layer by hydride vapor phase epitaxy, the crystal defect density is reduced in the underlayer, and a longer-life semiconductor A laser element can be realized. For example, when a thin film buffer layer is inserted for the purpose of relaxing lattice mismatch between the substrate and the semiconductor layer forming the semiconductor laser structure, the thin film buffer layer is formed by molecular beam epitaxy. Therefore, it is possible to realize a semiconductor laser device having a low series resistance and a low voltage operation with good reproducibility.

As described above, according to the semiconductor laser device and the manufacturing method thereof of the present invention, it is possible to obtain a stable high-power single transverse mode laser by suppressing the occurrence of kinks in the current-light output characteristics during high-power operation. The design margin can be increased. Further, by precisely controlling the refractive index difference between the light guide layer and the block layer, the design margin in the laser structure design of the self-excited oscillation type low-noise semiconductor laser element can be increased. Furthermore, since the interface resistance at the regrown portion can be reduced and the electrode area on the p-type GaN layer can be increased, the series resistance is low and low voltage operation is possible. Furthermore, for example, an n-type AlGaN cladding layer is formed below the n-type GaN cladding layer, and a refractive index difference is further provided in the cladding layer, thereby maintaining a high optical confinement coefficient Γ _V perpendicular to the active layer. enables structural design to reduce the vertical divergence angle theta _v, a semiconductor laser device with low threshold current which can obtain high characteristics of the beam utilization efficiency can be realized by optical disks.

  Hereinafter, a semiconductor laser device and a manufacturing method thereof according to embodiments of the present invention will be described with reference to the drawings.

(First embodiment)
FIG. 1 is a cross-sectional view of a GaN blue-violet semiconductor laser device according to the first embodiment of the present invention.

  This semiconductor laser device includes a GaN substrate 1, an n-type GaN layer 2, an n-type AlGaN cladding layer 3, a first n-type GaN guide layer 4, a second n-type GaN guide layer 5, and a p-type. AlGaN blocking layer 6, InGaN multiple quantum well active layer 7, undoped GaN guide layer 8, p-type AlGaN electron barrier layer 9, p-type AlGaN cladding layer 10, p-type GaN contact layer 11, Ti / Al A / Ni / Au ohmic electrode 12, a Ni / Pt / Au ohmic electrode 13, and a Ti / Au pad electrode 14 are formed. The first n-type GaN guide layer 4 and the second n-type GaN guide layer 5 are examples of the semiconductor layer of the present invention, and the first n-type GaN guide layer 4 is the first semiconductor layer of the present invention. As an example, the second n-type GaN guide layer 5 is an example of the second semiconductor layer of the present invention. The InGaN multiple quantum well active layer 7 is an example of the light emitting layer of the present invention, and the p-type AlGaN blocking layer 6 is an example of the current blocking layer of the present invention.

  As shown in FIG. 1, the semiconductor laser device includes a p-type AlGaN blocking layer 6 formed under the InGaN multiple quantum well active layer 7 and a second n-type GaN guide layer on the first n-type GaN guide layer 4. It has a laser structure of a blue-violet semiconductor laser element using a nitride semiconductor formed by re-growing the layer 5. In this laser structure, an n-type GaN layer 2, an n-type AlGaN cladding layer 3, a first n-type GaN guide layer 4 and a p-type AlGaN blocking layer (current blocking layer) 6 are formed on a GaN substrate 1, and further etched. As a result, a stripe-shaped opening is formed in a part of the p-type AlGaN blocking layer 6, and the second n-type GaN guide layer 5, the InGaN multiple quantum well active layer 7, the undoped GaN guide are formed so as to cover the opening. A layer 8, a p-type AlGaN electron barrier layer 9, a p-type AlGaN cladding layer 10, and a p-type GaN contact layer 11 are formed. A Ti / Al / Ni / Au ohmic electrode 12 is formed on the back surface of the GaN substrate 1, and a Ni / Pt / Au ohmic electrode 13 and a Ti / Au pad electrode 14 are formed on the p-type GaN contact layer 11. The InGaN multiple quantum well active layer 7 emits 405 nm blue-violet light by current injection. The n-type layer is doped with Si and the p-type layer is doped with Mg as impurities. The opening portion of the p-type AlGaN block layer 6 etched in a stripe shape, that is, the portion where the second n-type GaN guide layer 5 is embedded has a refractive index larger than that of the p-type AlGaN block layer 6 and is formed of two layers. It functions as a waveguide of a blue-violet semiconductor laser element that confines light on the second n-type GaN guide layer 5 side due to the difference in refractive index.

At this time, the refractive index difference between the second n-type GaN guide layer 5 and the p-type AlGaN blocking layer 6 inside the opening is 10 ⁻³ by changing the Al composition of the p-type AlGaN blocking layer 6. It can be controlled precisely. For this reason, the generation of kinks in the current-light output characteristics due to spatial hole burning during high output operation can be suppressed, and the design margin for obtaining a stable high output single transverse mode laser can be increased. Further, the Al composition of the p-type AlGaN blocking layer 6 is increased to eliminate absorption of blue-violet light emission (about 405 nm), thereby reducing the internal loss as much as possible. As a result, the blue-violet semiconductor laser device has a low threshold current and a low threshold current. An operating current can be realized. In addition, since the power consumption of the semiconductor laser element can be greatly reduced, a long life can also be realized. Further, by precisely controlling the above-described refractive index difference, when the same structure is applied to a self-excited oscillation type low-noise semiconductor laser element, the design margin of the semiconductor laser element can be increased.

In a conventional refractive index guided semiconductor laser device, which has been reported in the laser structure of a conventional GaAs-based or InGaAlP-based infrared semiconductor laser device, a method in which a p-type cladding layer is regrown on a p-type guide layer is used. However, when this is applied to a nitride semiconductor, the interface resistance increases and the operating voltage of the semiconductor laser element increases. This is because the resistivity of the p-type GaN layer depends on the Mg concentration, and when the concentration exceeds about 5 × 10 ¹⁹ cm ⁻³ , it suddenly becomes high resistance, so near the regrowth interface (A in FIG. 1) This is because Mg is redistributed and a portion with a large Mg concentration is generated, and as a result, a high resistance portion is formed near the regrowth interface. In the laser structure of the GaN-based blue-violet semiconductor laser device in this embodiment, the n-type GaN layer is regrown on the n-type GaN layer, and the Si-doped n-type layer has a high resistance even if the Si doping amount is excessively increased. It will not become. As a result, a high-resistance layer like the p-type layer described above is not formed, the resistance at the regrowth interface is reduced, and as a result, a GaN-based blue-violet semiconductor laser device with a low operating voltage can be realized. It becomes possible. For example, when the Si concentration at the outermost surface of the first n-type GaN guide layer 4 before regrowth is increased to, for example, 4 × 10 ¹⁸ cm ⁻³ , as a result, 4 × 10 ¹⁸ cm ⁻ near the regrowth interface. ^An impurity distribution having a peak of about ³ is formed, and the resistance near the regrowth interface can be reduced.

  When the Al composition in the p-type AlGaN block layer 6 doped with Mg is relatively small, internal loss due to internal absorption in the p-type AlGaN block layer 6 cannot be ignored. In this case, for example, an impurity having a shallow impurity level such as Be may be doped into the p-type AlGaN blocking layer 6 to increase the resistance.

  The GaN-based blue-violet semiconductor laser device of this embodiment can increase the electrode area on the p-type GaN layer as compared with a so-called ridge type semiconductor laser device, which has been reported as a nitride semiconductor laser device, so that the series resistance is reduced. A semiconductor laser element that is smaller than the conventional one and operates at a low voltage can be realized.

In the GaN blue-violet semiconductor laser device of this embodiment, the laser structure is formed on the GaN substrate. However, as long as a dislocation density of, for example, 10 ⁶ cm ⁻² can be realized in the waveguide stripe portion, another laser structure can be used. A laser structure may be formed on the substrate. As a method of forming a waveguide stripe having a low dislocation density, a low-dislocation portion is formed by using lateral growth (Epitaxial Lateral Overgrowth: ELOG) on an insulating film such as SiO ₂ patterned in a stripe shape. There is a method of forming a waveguide stripe in that portion. Therefore, in the GaN-based blue-violet semiconductor laser device of this embodiment, for example, a semiconductor laser structure is formed on a thick AlN layer formed on a sapphire substrate, and the waveguide stripe portion is reduced in dislocation density using the above method. It may be formed by forming.

Here, the p-type AlGaN blocking layer 6 is composed of Al _0.15 Ga _0.85 N with a film thickness of 200 nm and Al _0.3 Ga _0.7 N with a film thickness of 10 nm, for example, with Al _0.3 Ga _0.7 N present in the outermost layer. When the p-type AlGaN block layer 6 is formed by MOCVD, the supply of Mg source is stopped before the formation of Al _0.3 Ga _0.7 N, and Mg diffusion is performed on the outermost surface of the p-type AlGaN block layer 6. And Mg is prevented from diffusing into the InGaN multiple quantum well active layer 7. Here, the Mg concentration of the p-type AlGaN block layer 6 is set to 1 × 10 ¹⁹ cm ⁻³ or less to suppress the generation of crystal defects such as point defects in the p-type AlGaN block layer 6, and the InGaN multiple quantum well active layer 7 may be configured to increase the crystallinity. Further, the p-type AlGaN block layer 6 may be co-doped with Si to control internal loss due to absorption in the p-type AlGaN block layer 6 and to control the kink level. As a result, the degree of freedom in designing a high-power semiconductor laser device can be increased.

When the second n-type GaN light guide layer 5 and the InGaN multiple quantum well active layer 7 are formed on the opening of the p-type AlGaN blocking layer 6, the second n-type GaN light guide layer 5 is formed. For example, the thin film of the second n-type GaN light guide layer 5 can be set by setting the conditions such as setting the growth temperature to 1050 ° C. or higher, controlling the supply ratio of the Group III material and the Group V material, or reducing the growth rate. And flattening the top surface. In addition, after forming the second n-type GaN optical guide layer 5, the surface is flattened by gas etching or polishing with Cl ₂ gas or H ₂ gas, and the active layer is epitaxially grown, whereby the second n-type GaN is grown. The light guide layer 5 may be flattened.

  Therefore, in the present embodiment, a stripe-shaped opening is formed in the p-type AlGaN blocking layer 6 formed on the first n-type GaN guide layer 4, and the second n-type GaN guide layer and InGaN multiple quantum well are further formed. The active layer 7 is regrown to form a laser structure. Therefore, it is possible to realize a GaN-based blue-violet semiconductor laser device having a stable single transverse mode and high output operation or a self-oscillation-type low-noise GaN-based blue-violet semiconductor laser device, and the design margin can be increased. In addition, the interface resistance and series resistance in the vicinity of the regrowth interface can be greatly reduced, and a long-life, low-voltage operation GaN-based blue-violet semiconductor laser device can be realized.

  As a manufacturing method of the GaN-based blue-violet semiconductor laser device having the above structure shown in FIG. 1, for example, the manufacturing method shown in FIG. 2 can be considered. FIG. 2 is a cross-sectional view of a GaN blue-violet semiconductor laser device showing a method of manufacturing the GaN blue-violet semiconductor laser device according to the first embodiment of the present invention.

First, for example, an n-type GaN layer 2 and an n-type layer are formed on the (0001) surface of an n-type GaN substrate 1 having a dislocation density of 10 ⁶ cm ^{−2 by} metal organic chemical vapor deposition (MOCVD). An AlGaN cladding layer 3, a first n-type GaN guide layer 4, and a p-type AlGaN blocking layer 6 are formed in this order (FIG. 2A).

Next, a photoresist 15 is formed on the p-type AlGaN block layer 6 so as to have a striped opening. The width of the stripe is about 2 μm. Using this photoresist 15 as a mask, the p-type AlGaN block layer 6 is selectively removed by dry etching called ICP (Inductive Coupled Plasma) etching using, for example, Cl ₂ gas (FIG. 2B).

Next, after removing the photoresist 15, a second n-type GaN guide layer 5, an InGaN multiple quantum well active layer 7, an undoped GaN guide layer 8, in the stripe-shaped opening and on the p-type AlGaN blocking layer 6, A p-type AlGaN electron barrier layer 9, a p-type AlGaN cladding layer 10, and a p-type GaN contact layer 11 are formed in this order by the MOCVD method (FIG. 2C). After this regrowth process, a Ni / Pt / Au ohmic electrode 13 is formed as an ohmic electrode on the surface of the p-type GaN contact layer 11 by, for example, electron beam evaporation and a lift-off method. Thereafter, in order to reduce the contact resistance between the Ni / Pt / Au ohmic electrode 13 and the p-type layer, for example, sintering is performed at 600 ° C. in an N ₂ atmosphere. Further, after the Ni / Pt / Au ohmic electrode 13 is formed, a Ti / Au pad electrode 14 is formed on the Ni / Pt / Au ohmic electrode 13.

  Finally, the GaN substrate 1 is polished to about 150 μm from the back surface of the GaN substrate 1, and a Ti / Al / Ni / Au ohmic electrode 12 is further formed on the back surface side of the n-type GaN substrate 1, for example, by electron beam evaporation. The GaN blue-violet semiconductor laser shown in FIG. 1 is formed by the lift-off method (FIG. 2D).

  As shown in FIG. 1, the second n-type GaN guide layer 5 and the InGaN multiple quantum well active layer 7 are regrown on the first n-type GaN guide layer 4 by the semiconductor laser device manufacturing method as described above. A simple laser structure is formed. Therefore, in the GaN-based blue-violet semiconductor laser device, the interface resistance and the series resistance at the regrowth interface can be greatly reduced, and low voltage operation and long life can be realized.

  Further, the light emitted from the InGaN multiple quantum well active layer 7 is emitted from the second n-type without internal loss due to the refractive index difference between the second n-type GaN guide layer 5 and the p-type AlGaN blocking layer 6 formed by regrowth. It is confined in the GaN guide layer 5. Therefore, it is possible to realize a GaN-based blue-violet semiconductor laser element having a stable single transverse mode and high output operation or a self-oscillation type low-noise GaN-based blue-violet semiconductor laser element and increasing the design margin. .

  In addition, when an active layer of a semiconductor laser element is formed of an InGaN multiple quantum well and a blue-violet semiconductor laser element is manufactured, in the regrowth growth, In of the active layer migrates in the upper part of the opening depending on the growth conditions. As a result, the In composition increases in the semiconductor layer above the opening, and the In composition decreases in the semiconductor layer above the p-type AlGaN block layer 6. Therefore, for example, when a GaN guide layer is formed below the active layer, crystal growth can be performed with a small lattice mismatch with GaN, so the semiconductor layer formed by regrowth has excellent crystallinity Thus, a long-lived GaN-based blue-violet semiconductor laser element can be realized.

  In addition, when an active layer of a semiconductor laser element is formed of an AlGaN multiple quantum well and a blue-violet semiconductor laser element that emits light at 360 nm, for example, is fabricated, Ga migrates at the upper part of the opening during the burying regrowth. The Al composition at the top of the opening is reduced. Therefore, lateral optical confinement is possible inside the active layer. As a result, a sufficiently large optical confinement can be realized even if the AlGaN blocking layer is thin, and a GaN-based blue-violet semiconductor laser device having a low threshold current. Can be realized.

Further, the first n-type GaN guide layer 4 and the second n-type GaN guide layer 5 may be composed of semiconductor layers having different compositions or materials. For example, the first n-type GaN guide layer 4 is an n-type guide layer made of In _x Ga _1-x N (0 ≦ x ≦ 1), and the second n-type GaN guide layer 5 is made of GaN. An n-type guide layer may be used. As a result, InGaN has a higher refractive index than GaN, and by using a light guide layer composed of InGaN, the optical confinement factor in the vertical direction can be increased, and a GaN blue-violet semiconductor laser with a low threshold current can be realized. It becomes possible.

(Second Embodiment)
FIG. 3 is a cross-sectional view of a GaN blue-violet semiconductor laser device according to the second embodiment of the present invention.

This semiconductor laser device includes an n-type GaN layer 2, an n-type AlGaN cladding layer 3, a p-type AlGaN blocking layer 6, an InGaN multiple quantum well active layer 7, a p-type AlGaN electron barrier layer 9, and a Ti / Al / Ni / Au ohmic electrode 12, Ni / Pt / Au ohmic electrode 13, Ti / Au pad electrode 14, sapphire substrate 16, SiO ₂ mask 17, first n-type GaN cladding layer 18, first 2 n-type GaN cladding layer 19, n-type InGaN guide layer 20, undoped InGaN guide layer 21, and p-type GaN cladding layer 22. The first n-type GaN cladding layer 18 and the second n-type GaN cladding layer 19 are examples of the semiconductor layer of the present invention, and the first n-type GaN cladding layer 18 is the first semiconductor layer of the present invention. The second n-type GaN cladding layer 19 is an example of the second semiconductor layer of the present invention.

As shown in FIG. 3, the semiconductor laser device has a p-type AlGaN blocking layer 6 formed under the InGaN multiple quantum well active layer 7 and a second n-type GaN cladding on the first n-type GaN cladding layer 18. The layer 5 is formed by regrowth, and has a laser structure of a blue-violet semiconductor laser element using a nitride semiconductor having an InGaN layer as a guide layer. In this laser structure, a part of the n-type GaN layer 2 is formed on the sapphire substrate 16, and an SiO ₂ mask 17 having a mask width of 10 μm is formed on the sapphire substrate 16. Further, the remaining n-type GaN layer 2 is formed thereon by lateral growth. In the semiconductor layer above the SiO ₂ mask 17, the dislocation density, which was 10 ⁹ cm ⁻² in the semiconductor layer below the opening, is reduced to 10 ⁶ cm ⁻² . On the n-type GaN layer 2, an n-type AlGaN clad layer 3, a first n-type GaN clad layer 18, and a p-type AlGaN block layer (current blocking layer) 6 are formed, and a p-type AlGaN block is further etched. A stripe-shaped opening is formed in a part of the layer 6. The second n-type GaN cladding layer 19, the n-type InGaN guide layer 20, the InGaN multiple quantum well active layer 7, and undoped so as to cover the opening. An InGaN guide layer 21, a p-type AlGaN electron barrier layer 9, and a p-type GaN cladding layer 22 are formed.

The epitaxial growth layer from the n-type GaN layer 2 to the p-type GaN cladding layer 22 is selectively removed so that the n-type GaN layer 2 is exposed, and Ti / Al / Ni is formed on the exposed n-type GaN layer 2. The Ni / Pt / Au ohmic electrode 13 and the Ti / Au pad electrode 14 are formed above the p-type GaN cladding layer 22. The n-type layer is doped with Si and the p-type layer is doped with Mg as impurities. The opening of the p-type AlGaN block layer 6 etched in a stripe shape is located above the SiO ₂ mask 17 and is formed in a portion having a low dislocation density. Similar to the first embodiment, the opening of the p-type AlGaN blocking layer 6 etched in a stripe shape, that is, the portion where the second n-type GaN cladding layer 19 is embedded is more than the p-type AlGaN blocking layer 6. It has a large refractive index and functions as a waveguide of a blue-violet semiconductor laser device that confines light on the second n-type GaN cladding layer 19 side due to the difference in refractive index between the two layers. Further, the second n-type GaN cladding layer 19 is thinned and the uppermost surface is flattened by setting the conditions for crystal growth, polishing or etching. Furthermore, the first n-type GaN cladding layer 18 and the second n-type GaN cladding layer 19 have an impurity distribution in which the impurity concentration is highest at the interface, that is, the regrowth interface.

At this time, by changing the Al composition of the p-type AlGaN block layer 6, the refractive index difference between the second n-type GaN clad layer 19 and the p-type AlGaN block layer 6 inside the opening is 10 ⁻³ units. It can be controlled precisely. For this reason, the generation of kinks in the current-light output characteristics due to spatial hole burning during high output operation can be suppressed, and the design margin for obtaining a stable high output single transverse mode laser can be increased. Further, the Al composition of the p-type AlGaN blocking layer 6 is increased to eliminate absorption of blue-violet light emission (about 405 nm), thereby reducing the internal loss as much as possible. As a result, the blue-violet semiconductor laser device has a low threshold current and a low threshold current. An operating current can be realized. In addition, since the power consumption of the semiconductor laser element can be greatly reduced, a long life can also be realized. Further, by precisely controlling the above-described refractive index difference, when the same structure is applied to a self-excited oscillation type low-noise semiconductor laser element, the design margin of the semiconductor laser element can be increased.

In a semiconductor laser device for an optical disk system, the vertical optical confinement coefficient Γ _V in the active layer is maintained at a high value, thereby realizing a low threshold current and increasing the light condensing property of the laser light source. It is necessary to reduce the beam divergence angle (hereinafter, vertical divergence angle) θ _v in the direction. Generally when made smaller, the refractive index of the cladding layer to increase the confinement of light gamma _v increases and the threshold current becomes smaller, increases at the same time the vertical divergence angle. In the blue-violet semiconductor laser device shown in the present embodiment, an n-type InGaN guide layer 20 and an undoped InGaN guide layer 21 made of, for example, In _0.02 Ga _0.98 N are formed above and below the InGaN multiple quantum well active layer 7 and outside thereof. A second n-type GaN cladding layer 19 and a p-type GaN cladding layer 22 are formed, and a first n-type GaN cladding comprising, for example, an n-type Al _0.1 Ga _0.9 N layer below the second n-type GaN cladding layer 19. Layer 18 is formed. In this way, by further providing a refractive index difference in the cladding layer, specifically, between the n-type AlGaN cladding layer 3, the first n-type GaN cladding layer 18 and the second n-type GaN cladding layer 19. By providing a refractive index difference, it is possible to design a structure that reduces the vertical divergence angle θ _v while maintaining a high confinement factor Γ _V , and it is possible to obtain characteristics with high beam utilization efficiency in optical disk system applications. A semiconductor laser element having a threshold current can be realized.

The above-described n-type InGaN guide layer 20 made of In _0.02 Ga _0.98 N is intended to reduce the difference in lattice constant between GaN and InGaN or to suppress segregation of In composition by increasing the film thickness. For example, InGaN and GaN are periodically arranged. The InGaN / GaN periodic structure may be provided. In this case, InGaN is grown at a lower temperature than GaN to form the periodic structure. Thereby, the crystallinity of the InGaN multiple quantum well active layer 7 formed on the n-type InGaN guide layer 20 is improved, and a semiconductor laser device having a lower threshold current can be realized.

  In the semiconductor laser device according to the first embodiment, an AlGaN layer is used as a cladding layer and a GaN layer is used as a guide layer. The AlGaN layer generally needs to have a thickness of about 1 μm. There is a problem that cracks are likely to occur due to lattice mismatch. However, the semiconductor laser device of the second embodiment has a structure in which the generation of cracks due to lattice mismatching can be suppressed by making most of the cladding layer of GaN.

In the GaN blue-violet semiconductor laser device of this embodiment, a laser structure has been described in which a low dislocation density portion is formed by lateral growth on a sapphire substrate and a stripe waveguide is formed thereon. For example, the laser structure is not limited to this laser structure as long as a dislocation density of, for example, 10 ⁶ cm ⁻² can be realized in the stripe portion, and the laser structure may be such that a waveguide stripe is formed on a GaN substrate. Further, the laser structure may be reduced in dislocation by, for example, forming a semiconductor laser structure on a thick AlN layer formed on a sapphire substrate.

Further, the first n-type GaN clad layer 18 and the second n-type GaN clad layer 19 may be composed of semiconductor layers having different compositions or materials. For example, the first n-type GaN cladding layer 18 is an n-type cladding layer made of In _x Ga _1-x N (0 ≦ x ≦ 1), and the second n-type GaN cladding layer 19 is made of GaN. An n-type cladding layer may be used. As a result, InGaN has a higher refractive index than GaN and can use a cladding layer made of InGaN to increase the optical confinement factor in the vertical direction, thereby realizing a semiconductor laser with a low threshold current.

  As a manufacturing method of the GaN-based blue-violet semiconductor laser device having the above structure shown in FIG. 3, for example, the manufacturing method shown in FIG. 4 is conceivable. FIG. 4 is a cross-sectional view of a GaN blue-violet semiconductor laser device showing a method of manufacturing a GaN blue-violet semiconductor laser device according to the second embodiment of the present invention.

First, for example, the n-type GaN layer 2 is formed on the (0001) plane of the sapphire substrate 16 by MOCVD. Thereafter, an SiO ₂ film 17 is formed on the n-type GaN layer 2 to a thickness of about 100 nm by, for example, a vapor deposition (Chemical Vapor Deposition: CVD) method using SiH ₄ and O ₂ gas. Subsequently, the SiO ₂ film 17 has a 5 μm wide opening in a stripe shape, and a SiO ₂ stripe having a width of 10 μm is formed, for example, using a photoresist as a mask and a hydrofluoric acid (HF) aqueous solution. _{The two} films 17 are selectively etched (FIG. 4A).

Next, the n-type GaN layer 2, the n-type AlGaN clad layer 3, and the first n-type GaN clad layer 18 are grown by, for example, MOCVD in a form in which the growth occurs from the n-type GaN layer 2 in the opening of the SiO ₂ film 17. Then, a p-type AlGaN blocking layer (current blocking layer) 6 is formed (FIG. 4B). In the crystal growth step by the MOCVD method, the crystal growth is performed in the lateral direction on the SiO ₂ film 17 in which the opening is formed. Therefore, the threading dislocation density is significantly reduced in the semiconductor layer above the SiO ₂ film 17. As a result, a semiconductor layer having a dislocation density of 10 ⁶ cm ⁻² is obtained.

Next, a photoresist 15 is formed on the p-type AlGaN block layer 6 so as to have a striped opening. The width of the stripe is about 2 μm. Using this photoresist 15 as a mask, the p-type AlGaN block layer 6 is selectively removed by dry etching called ICP etching using, for example, Cl ₂ gas (FIG. 4C).

  Next, after removing the photoresist 15, the second n-type GaN cladding layer 19, the n-type InGaN guide layer 20, and the InGaN multiple quantum well active layer 7 are formed in the stripe-shaped opening and on the p-type AlGaN blocking layer 6. Then, the undoped InGaN guide layer 21, the p-type AlGaN electron barrier layer 9, and the p-type GaN cladding layer 22 are formed in this order by the MOCVD method (FIG. 4D). After this regrowth step, a part of the epitaxial growth layer from the n-type GaN layer 2 to the p-type GaN cladding layer 22 is selectively removed so that the n-type GaN layer 2 is exposed (FIG. 4E). For this etching, for example, a dry etching technique such as the aforementioned ICP etching is used. Here, the n-type GaN layer 2 is exposed in a form having an opening parallel to the opening pattern of the p-type AlGaN block layer 6 which is a waveguide stripe.

Next, the Ni / Pt / Au ohmic electrode 13 is formed as an ohmic electrode on the surface of the p-type GaN cladding layer 22 by, for example, electron beam evaporation and a lift-off method. Thereafter, for example, sintering is performed at 600 ° C. in an N ₂ atmosphere for reducing the contact resistance between the Ni / Pt / Au ohmic electrode 13 and the p-type layer, and then Ti / Pt / Au ohmic electrode 13 is subjected to Ti / P An Au pad electrode 14 is formed. Further, a Ti / Al / Ni / Au ohmic electrode 12 is formed on the exposed n-type GaN layer 2 by, for example, electron beam evaporation and a lift-off method, and then a Ti / Au pad electrode 14 is formed thereon (FIG. 4). (F)), a GaN blue-violet semiconductor laser shown in FIG. 3 is formed.

As shown in FIG. 3, the second n-type GaN cladding layer 19 and the InGaN multiple quantum well active layer 7 are regrown on the first n-type GaN cladding layer 18 by the semiconductor laser device manufacturing method as described above. A simple laser structure is formed. Therefore, in the GaN-based blue-violet semiconductor laser device, the resistance near the regrowth interface (A in FIG. 3) can be reduced, and low voltage operation and long life can be realized. InGaN multiple quantum well activity Light emission from the layer 7 is confined in the second n-type GaN cladding layer 19 without internal loss due to the refractive index difference between the second n-type GaN cladding layer 19 and the p-type AlGaN blocking layer 6 formed by regrowth. In addition, it is possible to realize a GaN-based blue-violet semiconductor laser device having a stable single transverse mode and a high output operation or a low-noise GaN-based blue-violet semiconductor laser device of self-excited oscillation, and to increase the design margin.

  Further, the n-type cladding layer has a two-layer structure of AlGaN and GaN, that is, the n-type AlGaN cladding layer 3 is formed below the first n-type GaN cladding layer 18, so that a high optical confinement coefficient and a small vertical It is possible to design a structure capable of satisfying both the divergence angle and to realize a semiconductor laser device having a high beam utilization efficiency and a small threshold current for an optical disk system. As described above, a low operating voltage and a low operating current can be achieved, so that power consumption can be reduced and a long-lived blue-violet semiconductor laser device can be realized.

  As described above, the GaN-based blue-violet semiconductor laser device and the manufacturing method thereof according to the present invention have been described based on the embodiment, but the present invention is not limited to this embodiment and departs from the scope of the present invention. It goes without saying that various modifications or corrections can be made without doing so.

For example, the GaN substrate and sapphire substrate used in the first and second embodiments may have any plane orientation, and may have a plane orientation with an off-angle from a representative plane such as the (0001) plane. The substrate may be a SiC substrate, a ZnO substrate, a Si substrate, a GaAs substrate, a GaP substrate, an InP substrate, a LiGaO ₂ substrate, a LiAlO ₂ substrate, or a mixed crystal thereof. In addition, the waveguide stripe is preferably formed in a portion having a dislocation density of 10 ⁶ cm ⁻² or less. In addition, the epitaxial growth layer on which the laser structure is formed may have any composition ratio as long as desired laser characteristics can be realized, may include any multilayer structure, and is not MOCVD, for example, molecular beam epitaxy ( A layer formed by a molecular beam epitaxy (MBE) method or a hydride vapor phase epitaxy (HVPE) method may be included. Further, the epitaxial growth layer in which the laser structure is formed may contain a group V element such as As or P or a group III element such as B as a constituent element. The block layer may have a semi-insulating conductivity type.

  The semiconductor laser device according to the present invention is useful as a high-power or low-noise GaN blue-violet semiconductor laser device that can be used as a light source for writing and reading in a high-density optical disk system.

It is sectional drawing which shows the semiconductor laser in the 1st Embodiment of this invention. It is a block diagram which shows the manufacturing method of the semiconductor laser in the 1st Embodiment of this invention. It is sectional drawing which shows the semiconductor laser in the 2nd Embodiment of this invention. It is a block diagram which shows the manufacturing method of the semiconductor laser in the 2nd Embodiment of this invention. It is sectional drawing of the infrared semiconductor laser in a prior art example. It is sectional drawing of the blue-violet semiconductor laser in a prior art example.

Explanation of symbols

1 GaN substrate 2 n-type GaN layer 3 n-type AlGaN cladding layer 4 first n-type GaN guide layer 5 second n-type GaN guide layer 6 p-type AlGaN block layer 7 InGaN multiple quantum well active layer 8 undoped GaN guide layer 9 p-type AlGaN electron barrier layer 10 p-type AlGaN cladding layer 11 p-type GaN contact layer 12 Ti / Al / Ni / Au ohmic electrode 13 Ni / Pt / Au ohmic electrode 14 Ti / Au pad electrode 15 photoresist 16 sapphire substrate 17 SiO ₂ mask 18 First n-type GaN cladding layer 19 Second n-type GaN cladding layer 20 n-type InGaN guide layer 21 undoped InGaN guide layer 22 p-type GaN cladding layer 23 GaAs substrate 24 n-type AlGaAs cladding layer 25 undoped AlGaAs Active layer 26 First p-type AlGaAs cladding layer 27 n-type AlGaAs blocking layer 28 second p-type AlGaAs cladding layer 29 p-type GaAs contact layer 30 AuGeNi / Au ohmic electrode 31 Ti / Pt / Au ohmic electrode 32 Ni / Au electrode 33 First p-type AlGaN cladding layer 34 n-type AlGaN blocking layer 35 Second p-type AlGaN cladding layer

Claims (25)

A substrate,
A p-type or semi-insulating current blocking layer provided on the substrate and provided with an opening;
An n-type semiconductor layer formed at least in the opening;
And a light-emitting layer formed on the current blocking layer. The semiconductor layer has a flat top surface,
The semiconductor laser device according to claim 1, wherein the light emitting layer is formed on the semiconductor layer so as to be in contact with the semiconductor layer. The semiconductor laser device according to claim 2, wherein the current blocking layer has a refractive index smaller than that of the semiconductor layer. The semiconductor laser device according to claim 3, wherein the current blocking layer has a portion to which a plurality of types of impurities are added. The semiconductor laser device according to claim 4, wherein the current blocking layer includes a plurality of layers having different compositions. The semiconductor layer includes a first semiconductor layer and a second semiconductor layer formed on the first semiconductor layer so as to be in contact with the first semiconductor layer;
The first semiconductor layer is formed between the current blocking layer and the substrate;
The second semiconductor layer is formed between the opening and the current blocking layer and the light emitting layer,
The semiconductor laser device according to claim 5, wherein the impurity concentration in the first semiconductor layer is higher on the light emitting layer side than on the substrate side. The semiconductor laser device according to claim 6, wherein the composition of the first semiconductor layer and the composition of the second semiconductor layer are different. 8. The semiconductor laser according to claim 7, wherein the concentration distribution of impurities in the first semiconductor layer and the second semiconductor layer is a distribution in which a peak is located at an interface between the first semiconductor layer and the second semiconductor layer. element. The semiconductor laser device according to claim 8, wherein the light emitting layer and the semiconductor layer are made of a compound semiconductor containing nitrogen. The semiconductor laser device according to claim 9, wherein Mg is added to the current blocking layer. 11. The semiconductor laser device according to claim 10, wherein an Mg concentration of the current blocking layer is 1 × 10 ¹⁹ cm ⁻³ or less. The semiconductor laser device according to claim 11, wherein the semiconductor layer is made of GaN. The light emitting layer is made of InGaAlN,
13. The semiconductor laser device according to claim 12, wherein the Al composition of the light emitting layer is such that a portion located above the current blocking layer is larger than a portion located above the opening. 14. The semiconductor laser device according to claim 13, wherein the In composition of the light emitting layer is such that a portion located above the current blocking layer is smaller than a portion located above the opening. The first semiconductor layer is composed of In _x Ga _1-x N (0 ≦ x ≦ 1),
The semiconductor laser device according to claim 8, wherein the second semiconductor layer is made of GaN. The current blocking layer includes a first Al _x Ga _1-x N (0 ≦ x ≦ 1) layer and a second Al _y Ga ₁ formed on the _first Al _x Ga _1-x N layer. _6. The semiconductor laser device according to claim 5, comprising: _-y N (0≤y≤1, where x <y) layers. The semiconductor laser device according to claim 4, wherein the current blocking layer is made of Al _x Ga _1-x N (0 ≦ x ≦ 1). The semiconductor layer functions as a cladding layer,
The semiconductor laser device further includes a light guide layer made of In _x Ga _1-x N (0 ≦ x ≦ 1) formed between the light emitting layer and the cladding layer. The semiconductor laser device according to claim 1. The semiconductor laser device according to claim 18, wherein the optical guide layer has a periodic structure in which InGaN and GaN are periodically arranged. A first semiconductor layer forming step of forming a first semiconductor layer on a substrate;
Forming a current blocking layer on the first semiconductor layer; and
An opening forming step of forming an opening in the current blocking layer;
A second semiconductor layer forming step of forming a second semiconductor layer on the opening;
And a light emitting layer forming step of forming a light emitting layer on the second semiconductor layer. A method of manufacturing a semiconductor laser device, comprising: In forming the second semiconductor layer, forming the second semiconductor layer so that the upper surface is flat,
21. The method of manufacturing a semiconductor laser device according to claim 20, wherein, in the light emitting layer forming step, the light emitting layer is formed on a flat surface of the second semiconductor layer. The method for manufacturing a semiconductor laser device according to claim 21, wherein in forming the second semiconductor layer, the surface of the second semiconductor layer is planarized by etching or polishing. The current blocking layer has a p-type or semi-insulating conductivity type,
In the current blocking layer forming step, after adding an impurity on the first semiconductor layer to form a part of the current blocking layer, the current blocking layer is added without adding an impurity on a part of the current blocking layer. 23. The method of manufacturing a semiconductor laser device according to claim 22, wherein the other part of the layer is formed. The method for manufacturing a semiconductor laser device according to claim 23, wherein the light emitting layer, the first semiconductor layer, and the second semiconductor layer are made of a compound semiconductor containing nitrogen. The method of manufacturing a semiconductor laser device further includes a light guide layer forming step of forming a light guide layer by periodically arranging InGaN and GaN between the light emitting layer and the second semiconductor layer,
25. The method of manufacturing a semiconductor laser device according to claim 24, wherein in the optical guide layer forming step, the optical guide layer is formed by crystal growth of the InGaN at a temperature lower than that of the GaN.

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