JP2006032925A - Semiconductor laser device, manufacturing method thereof, and optical pickup device - Google Patents

Abstract

In a semiconductor laser device having a buried structure, the crystallinity and surface morphology of a semiconductor layer formed on a current blocking layer can be improved, and a semiconductor laser device having a small laser oscillation threshold current and high reliability can be realized. Like that.
A buffer layer, an n-type cladding layer, an n-type guide layer, an active layer having a multiple quantum well structure, a first p-type guide layer, a current, The block layer 7 is sequentially laminated. The current blocking layer 7 is composed of an n-type Al _0.15 Ga _0.85 N layer 8 and an n-type GaN layer 9, and a stripe-shaped window portion 20 through which a current flows is formed. On the GaN layer 9, a second p-type guide layer 10, a p-type cladding layer 11, and a p-type contact layer 12 are formed. A p-type electrode 13 made of a Ni-based material is formed on the p-type contact layer 12, and an n-type electrode 14 made of a Ti-based material is formed on the back surface of the substrate 1.
[Selection] Figure 1

Description

  The present invention relates to a semiconductor laser device using a nitride semiconductor, a manufacturing method thereof, and an optical pickup device using the same.

  The laser beam in the blue-violet region can reduce the diameter of the focused spot on the optical disc and improve the recording density of the optical disc compared with the light in the red or infrared region. Expected to be a light source. Currently, in order to realize blue-violet laser light, a semiconductor laser device using a nitride semiconductor such as gallium nitride has been developed.

  As a semiconductor laser device using a nitride semiconductor, a device having the following structure has been proposed (see, for example, Patent Document 1). FIG. 6 shows a cross-sectional structure of a conventional semiconductor laser device. As shown in FIG. 6, in the conventional semiconductor laser device, an n-type cladding layer 103 made of n-type aluminum gallium nitride (AlGaN) is formed on a substrate 101 made of sapphire with a low-temperature growth buffer layer 102 interposed. ing. On the n-type cladding layer 103, an n-type guide layer 104 made of n-type gallium nitride (GaN) and a multiplex made of indium gallium nitride (InGaN) so that a part of the n-type cladding layer 103 is exposed. An active layer 105 having a quantum well structure, a first p-type guide layer 106 made of p-type GaN, a current blocking layer 108 made of n-type AlGaN, a second p-type guide layer 107 made of p-type GaN, A p-type cladding layer 109 made of p-type AlGaN and a p-type contact layer 110 made of p-type GaN are sequentially stacked. An n-type electrode 111 is formed on the exposed portion of the n-type cladding layer 103, and a p-type electrode 112 is formed on the p-type contact layer.

  A part of the current blocking layer 108 is removed in a stripe shape, and a window portion through which a current flows is formed. When a voltage is applied between the p-type electrode 112 and the n-type electrode 111, current flows only in the window portion from which the current blocking layer 108 has been removed, so that the active layer 105 has a stripe-shaped portion below the window portion. Only current can be injected. Further, the light emitted from the active layer can be confined by the difference in refractive index between the current blocking layer 108 and the second p-type guide layer 107.

  FIG. 7 shows a method of manufacturing a semiconductor laser device having such a buried structure. First, as shown in FIG. 7A, the first crystal growth is performed, and the layers from the buffer layer 102 to the current blocking layer 108 are sequentially grown on the substrate 101.

  Next, as shown in FIG. 7B, a part of the current blocking layer 108 is selectively removed by etching to form a stripe-shaped recess serving as a window.

  Next, as shown in FIG. 7C, the second crystal growth is performed, and the p-type guide layer 107, the p-type cladding layer 109, and the p-type contact layer 110 are sequentially formed on the current blocking layer 108 in which the recesses are formed. Form. Next, a p-type electrode and an n-type electrode are formed by a normal method.

  When the recess is formed in the current blocking layer 108, dry etching using a chlorine-based gas is generally used. However, when the concave portion is formed by dry etching, the etched portion such as the exposed portion of the p-type guide layer 106 is damaged, so that the absorption of emitted light is increased and the device characteristics are deteriorated. For this reason, it is desirable to form the recess by wet etching.

The following methods are known as wet etching methods for nitride semiconductors. FIG. 8 shows a conventional nitride semiconductor wet etching method. As shown in FIG. 8, a metal mask 112 is formed on the nitride semiconductor layer 111, the metal mask 112 and the platinum cathode 113 are electrically connected, and immersed in an alkaline solution 114. In order to increase the etching efficiency, attempts have been made to irradiate the nitride semiconductor layer 111 with light or to pass a current from the outside.
JP-A-8-97507

  However, the semiconductor laser device having an embedded structure has the following problems. First, due to the device structure, crystal growth must be performed twice, and the second crystal growth must be performed on the current blocking layer 108 made of n-type AlGaN except for the window portion. However, when regrowth is performed on a layer made of AlGaN, the surface morphology and crystallinity are very poor at the initial stage of growth. For this reason, there is a problem that light absorption is increased in a portion having poor crystallinity, and the laser oscillation threshold current is increased.

  Further, when the p-type guide layer 107 made of p-type GaN regrown on the current blocking layer 108 has poor crystallinity, magnesium (Mg) doped in the p-type guide layer passes through defects or the like. It becomes easy to diffuse to the active layer 105. When Mg diffuses into the active layer 105, there is a problem that the reliability of the semiconductor laser device using the nitride material is lowered.

  Furthermore, since the current blocking layer 108 made of n-type AlGaN cannot be etched by the conventional wet etching method, the recesses must be formed by dry etching that damages the current blocking layer 108 and the like. Damage caused to the etched portion when forming the recess is one of the factors that increase the laser oscillation threshold current.

  The present invention solves the above-mentioned conventional problems, improves the crystallinity and surface morphology of a semiconductor layer formed on a current blocking layer in a semiconductor laser device having a buried structure, and reduces the laser oscillation threshold current and It is an object of the present invention to realize a highly reliable semiconductor laser device and a manufacturing method thereof.

  In order to achieve the above object, the semiconductor laser device of the present invention is configured such that the current blocking layer is a laminated film whose uppermost layer is made of gallium nitride.

  Specifically, a semiconductor laser device according to the present invention includes an active layer formed on a substrate, a first semiconductor layer made of a first conductivity type nitride semiconductor formed on the active layer, and a first semiconductor layer. A plurality of thin films including a nitride semiconductor of the second conductivity type are stacked, and a stacked film having a groove extending in one direction is formed on the stacked film so as to fill the groove. And a second semiconductor layer made of a nitride semiconductor of the first conductivity type, and the thin film formed on the top of the laminated film is a thin film made of gallium nitride.

  According to the semiconductor laser device of the present invention, since the thin film deposited on the uppermost part of the laminated film that is the current blocking layer is a thin film made of gallium nitride, the second semiconductor layer is regrown on the laminated film. In this case, a second semiconductor layer having good crystallinity and excellent surface morphology can be formed. Therefore, light absorption in the second semiconductor layer can be suppressed, and as a result, a semiconductor laser device with a small laser oscillation threshold current can be realized. In addition, since the impurity doped in the second semiconductor layer can be prevented from diffusing into the active layer, the reliability of the semiconductor laser device can be improved.

  In the semiconductor laser device of the present invention, at least one of the thin films constituting the laminated film is a thin film containing aluminum, and the concentration of the second conductivity type impurity in the thin film containing aluminum is in the thin film made of gallium nitride. The concentration is preferably lower than the concentration of the second conductivity type impurity. The thin film containing aluminum may be an undoped nitride semiconductor. With such a structure, cracks can be prevented from occurring in the thin film containing aluminum, and the yield can be improved.

In the semiconductor laser device of the present invention, the thin film containing aluminum is preferably a thin film made of a compound represented by a general formula of Al _x Ga _1-x N (0 <X ≦ 1).

  In the semiconductor laser device of the present invention, the thickness of the thin film made of gallium nitride is preferably 5 nm or more and 0.3 μm or less. With such a configuration, the film thickness of the thin film made of gallium nitride can be easily controlled, and the surface after the groove is formed becomes smooth, so that productivity is improved.

  In the semiconductor laser device of the present invention, the second semiconductor layer preferably has a higher refractive index than the thin film having the smallest refractive index among the thin films constituting the laminated film. With such a configuration, the emitted light can be reliably confined at the interface between the second semiconductor layer and the laminated film.

  The pickup device of the present invention uses the semiconductor laser device of the present invention. By adopting such a configuration, it is possible to realize a pickup device equipped with a semiconductor laser device having high oscillation efficiency and high reliability.

  A method of manufacturing a semiconductor laser device according to the present invention includes an active layer, a first semiconductor layer made of a first conductivity type nitride semiconductor, and a plurality of thin films containing a second conductivity type nitride semiconductor on a substrate. And a step of sequentially growing a laminated film whose uppermost thin film is a thin film made of gallium nitride, a step of forming a groove portion extending in one direction by selectively removing a part of the laminated film, and a groove portion being formed Forming a second semiconductor layer made of a nitride semiconductor of the first conductivity type on the laminated film.

  According to the method of manufacturing a semiconductor laser device of the present invention, the second semiconductor layer made of the first conductivity type nitride semiconductor is formed on the laminated film whose uppermost thin film is made of gallium nitride. Since the growth step is provided, the crystallinity and surface morphology of the second semiconductor layer can be improved. Therefore, it is possible to realize a semiconductor laser device that absorbs less light in the second semiconductor layer and, as a result, has a small laser oscillation threshold current. Further, since the impurity doped in the second semiconductor layer can be prevented from diffusing into the active layer, the reliability of the semiconductor laser device can be improved.

  In the method for manufacturing a semiconductor laser device of the present invention, at least one of the thin films constituting the laminated film is a thin film containing aluminum, and the concentration of the second conductivity type impurity in the thin film containing aluminum is from gallium nitride. It is preferable that the concentration is lower than the concentration of the second conductivity type impurity in the thin film.

In this case, the thin film containing aluminum is preferably made of a compound represented by a general formula of Al _x Ga _1-x N (0 <X ≦ 1).

  In the method of manufacturing a semiconductor laser device of the present invention, it is preferable that, in the step of forming the groove portion, a metal mask is formed on a thin film made of gallium nitride and then the laminated film is wet etched. With such a structure, etching can be performed without damaging the stacked film, and thus the emission light can be prevented from being absorbed in the stacked film.

  In this case, the metal mask is preferably in ohmic contact with the thin film made of gallium nitride. The metal mask is preferably made of titanium or tantalum. Furthermore, in wet etching, it is preferable to form a metal film having a smaller ionization tendency than hydrogen on the surface of the metal mask, and the metal having a smaller ionization tendency is preferably platinum. With such a configuration, it is possible to form a mask on the entire surface of the wafer and perform wet etching.

  In the method of manufacturing a semiconductor laser device according to the present invention, in the step of forming the groove, the layered film is wet while irradiating the layered film with light having energy larger than the largest bandgap among the bandgap of the thin film constituting the layered film. It is preferable to perform etching.

  In the method for manufacturing a semiconductor laser device of the present invention, in wet etching, an alkaline solution is preferably used as an etchant, and the alkaline solution is preferably a potassium hydroxide solution or a sodium hydroxide solution.

  According to the semiconductor laser device and the manufacturing method thereof according to the present invention, in the semiconductor laser device having a buried structure, the crystallinity and surface morphology of the semiconductor layer formed on the current blocking layer are improved, and the laser oscillation threshold current is increased. A semiconductor laser device having a small size and high reliability and a manufacturing method thereof can be realized.

(First embodiment)
A semiconductor laser device according to a first embodiment of the present invention will be described with reference to the drawings. FIG. 1 shows a cross-sectional structure of the semiconductor laser device according to the first embodiment. As shown in FIG. 1, an n-type GaN layer 2 is formed on a substrate 1 made of 2 inches of GaN. On the GaN layer 2, an n-type cladding layer 3 made of n-type Al _0.06 Ga _0.94 N, an n-type guide layer 4 made of n-type GaN, an active layer 5 having a multiple quantum well structure made of InGaN, A first p-type guide layer 6 made of p-type GaN is sequentially stacked.

On the first p-type guide layer 6, a current blocking layer 7 having a groove part partially removed in a stripe shape is formed. The current blocking layer 7 is configured by sequentially laminating an n-type Al _0.15 Ga _0.85 N layer 8 and an n-type GaN layer 9. A second p-type guide layer 10 made of p-type GaN is formed on the first p-type guide layer 6 and the GaN layer 9 exposed on the bottom surface of the groove, and the groove serves as a window 20 through which current flows. Yes. A clad layer 11 made of p-type Al _0.06 Ga _0.94 N and a contact layer 12 made of p-type GaN are formed on the second p-type guide layer 10. A p-type electrode 13 made of a material mainly containing nickel (Ni) is formed on the p-type GaN contact layer 12, and an n-type made of a material mainly containing titanium (Ti) is formed on the back surface of the GaN substrate 1. An electrode 14 is formed. In this embodiment, a GaN substrate is used as the substrate, but sapphire or another substrate may be used.

Since the n-type current blocking layer 7 is formed between the first p-type guide layer 6 and the second p-type guide layer 10, the first p-type guide layer 6, the current blocking layer 7, The current blocking layer 7 blocks current due to the gap energy of the pn junction formed at the interface between the second p-type guide layer 10 and the current blocking layer 7. Therefore, when a voltage is applied between the p-type electrode 13 and the n-type electrode 14, current is injected into the active layer 5 only from the window portion 20 from which the current blocking layer 7 is removed in a stripe shape. Further, the light emission is confined by the difference in refractive index between the n-type Al _0.15 Ga _0.85 N layer 8 and the second p-type guide layer 10. As a result, a laser beam guided in the region below the window 20 in the active layer 5 is generated.

  A method for manufacturing the semiconductor laser device according to the first embodiment will be described below. FIG. 2 shows a cross-sectional structure in each manufacturing process of the semiconductor device according to this embodiment in the order of processes.

First, as shown in FIG. 2A, an n-type GaN layer 2 having a thickness of 2 μm is formed on a substrate 1 made of GaN using a metal organic chemical vapor deposition (MOVPE) apparatus. An n-type cladding layer 3 made of 1 μm n-type Al _0.06 Ga _0.94 N, an n-type guide layer 4 made of n-type GaN having a thickness of 0.2 μm, and an active layer 5 made of InGaN and having a multiple quantum well structure Then, a first p-type guide layer 6 made of p-type GaN having a thickness of 0.1 μm and a current blocking layer 7 are sequentially grown. The current blocking layer 7 is formed by sequentially growing an Al _0.15 Ga _0.85 N layer 8 having a thickness of _0.15 μm and a GaN layer 9 having a thickness of 0.05 μm.

When depositing each layer, trimethylgallium, trimethylaluminum, and trimethylindium are used as a gallium source, an aluminum source, and an indium source, respectively, and ammonia (NH ₃ ) is used as a nitrogen source. For introducing silicon (Si) as a donor impurity, hydrogen gas (H ₂ ) is used as a carrier gas, and monosilane (SiH ₄ ) is used as a raw material. To introduce magnesium (Mg) as an acceptor impurity, H ₂ is used as a carrier gas, and cyclopentadienyl magnesium is used as a raw material.

  Next, as shown in FIG. 2B, a part of the current blocking layer 7 is etched in a stripe shape to form a groove portion 7a having a width of about 2.0 μm to be the window portion 20. The etching method will be described later.

Next, as shown in FIG. 2C, a semiconductor layer is regrown on the GaN layer 9 and the first p-type guide layer 6 exposed by etching, and a p-thickness of 0.1 μm is formed. Second p-type guide layer 10 made of type GaN, p-type cladding layer 11 made of p-type Al _0.06 Ga _0.94 N having a thickness of 0.5 μm, and p-type GaN having a thickness of 0.1 μm A p-type contact layer 12 is sequentially grown.

  After each layer is grown, activation annealing is performed at 780 ° C. for 20 minutes in a nitrogen atmosphere to reduce the resistance of the p-type layer.

  Next, as shown in FIG. 2D, a p-type electrode 13 made of a Ni-based material is formed on the p-type contact layer 12, and then sintered at 650 ° C. for 30 minutes in a nitrogen atmosphere.

  After forming the p-type electrode, the GaN substrate 1 is polished to a thickness of about 150 μm. After polishing, an n-type electrode 14 made of a Ti-based material is formed on the back surface of the GaN substrate 1, and then sintered at 600 ° C. for 30 seconds in a nitrogen atmosphere.

  After the n-type electrode 14 is formed, cleavage is performed to obtain a real refractive index waveguide (RISA) type semiconductor laser device that emits blue-violet light having a wavelength of 405 nm.

As described above, in the semiconductor laser device of this embodiment, since the current blocking layer 7 has a laminated structure of the Al _0.15 Ga _0.85 N layer 8 and the GaN layer 9, the regrowth of the crystal is caused by the groove 7a. Is performed on the GaN layer 9. Therefore, better crystallinity can be obtained even in the initial stage of growth, compared to the case where regrowth is performed on a conventional AlGaN layer. As a result, the absorption of emitted light in the second p-type guide layer 10 and the like can be reduced, and the oscillation threshold current of the semiconductor laser device can be reduced.

  FIG. 3 shows the state of the semiconductor layer when the semiconductor layer is regrown on the current blocking layer of this embodiment, and the case where the semiconductor layer is regrown on the current blocking layer made of only the conventional AlGaN layer. The state of the semiconductor layer is shown in comparison. In addition, for the purpose of confirming the morphology at the initial stage of growth, unlike the actual device structure, only the p-type guide layer 10 is regrown and the surface morphology is compared.

  As shown in FIG. 3B, when a semiconductor layer is regrown on a current blocking layer made of only a conventional AlGaN layer, the surface morphology of the semiconductor layer is poor and the surface is wavy. On the other hand, as shown in FIG. 3A, when the semiconductor layer is regrown on the current blocking layer of this embodiment, a semiconductor layer having a flat surface is formed, and the semiconductor laser of this embodiment is formed. In the device, it is clear that a semiconductor layer with good crystallinity can be regrown on the current blocking layer 7.

  In addition, in the semiconductor laser device, it is known that reliability decreases when Mg diffuses into the active layer. In a layer with poor crystallinity, Mg is likely to diffuse into the active layer through defects or the like. However, in the semiconductor laser device of this embodiment, since the crystallinity of each layer regrown on the current blocking layer 7 is improved, Mg diffusion hardly occurs and reliability is also improved.

Since the current blocking layer 7 uses the gap energy of the pn junction to block the current, it needs to have a conductivity type opposite to that of the upper and lower layers, and usually needs to be doped n-type. However, the AlGaN layer doped with a high concentration of Si is likely to crack. However, in the semiconductor laser device of this embodiment, since the current blocking layer 7 is formed of the Al _0.15 Ga _0.85 N layer 8 and the GaN layer 9, the doping concentration of the GaN layer 9 is increased and Al _0.15 Ga _{0.85 is formed.} It is possible to reduce the doping concentration of the N layer 8. With such a configuration, generation of cracks can be suppressed and the yield of the semiconductor laser device can be improved. Further, the Al _0.15 Ga _0.85 N layer 8 may be undoped, and in this case, generation of cracks can be further suppressed.

-Dry etching-
Hereinafter, a method of using dry etching when forming the groove portion 7a in the current blocking layer 7 composed of the Al _0.15 Ga _0.85 N layer 8 and the GaN layer 9 will be described.

  After forming the current blocking layer 7, a mask having a stripe-shaped opening is formed on the current blocking layer 7 using a photoresist or the like.

  After forming the mask, the substrate 1 is placed on the cathode table in the etching chamber, and the pressure in the etching chamber is reduced by a vacuum pump. After the pressure in the etching chamber is stabilized, plasma is generated by applying high-frequency power while introducing chlorine gas into the etching chamber. By such a method, the current blocking layer 7 having a thickness of 0.2 μm can be etched to expose the first p-type guide layer 6 on the bottom surface of the groove 7a.

  After forming the groove 7a, the substrate 1 is taken out of the etching chamber, the mask is removed by ashing, and then the crystal is regrown using the MOVPE apparatus.

  When the groove 7a is formed using dry etching, the operation is simple and the etching time is short, so that the production efficiency can be increased.

-Wet etching-
Hereinafter, a method of using wet etching when forming the groove 7a in the current blocking layer 7 composed of the Al _0.15 Ga _0.85 N layer 8 and the GaN layer 9 will be described with reference to the drawings.

FIG. 4 shows the steps of wet etching the current blocking layer 7 in the order of steps. First, as shown in FIG. 4A, after a current blocking layer 7 composed of an Al _0.15 Ga _0.85 N layer 8 and a GaN layer 9 is grown, a metal mask 15 is formed on the GaN layer 9. The metal mask 15 is made of Ti, and the GaN layer 9 and the metal mask 15 are in ohmic contact. The metal mask 15 only needs to form an ohmic junction with the GaN layer 9, and tantalum (Ta) or the like may be used instead of titanium (Ti).

Next, as shown in FIG. 4B, the metal mask 15 and the cathode 16 made of platinum (Pt) are connected by a wire and then immersed in an aqueous potassium hydroxide solution 17. At this time, the GaN layer 9 is irradiated with light. The light to be irradiated may be light having energy larger than the band gap of the layers constituting the current blocking layer 7. For example, when the current blocking layer 7 is composed of the Al _0.15 Ga _0.85 N layer 8 and the GaN layer 9, ultraviolet light having a wavelength having energy larger than the band gap of the Al _0.15 Ga _0.85 N layer 8 may be irradiated. .

  By irradiation with light, the current blocking layer 7 absorbs light, and electrons and holes are generated in the current blocking layer 7. The holes react with the nitride semiconductor constituting the current blocking layer 7 and the electrons are released from the cathode 16 into the solution, so that the current blocking layer 7 is etched.

In the conventional semiconductor laser device, since the current blocking layer 7 is made of only Al _0.15 Ga _0.85 N, the metal mask 15 must be formed on Al _0.15 Ga _0.85 N. Since Al _0.15 Ga _0.85 N has a larger band gap than GaN and it is difficult to form an ohmic junction with the metal mask 15, a potential barrier is easily generated between the Al _0.15 Ga _0.85 N and the metal mask 15. Accordingly, it is considered that the electrons generated by the light irradiation cannot exceed the potential barrier and are not easily emitted from the cathode 16 and the current blocking layer 7 is hardly etched.

As in the present embodiment, the current blocking layer 7 is formed of two layers of the Al _0.15 Ga _0.85 N layer 8 and the GaN layer 9, so that the groove 7a can be formed by wet etching, and damage caused to the semiconductor layer. Can be suppressed. As a result, the light absorption loss can be reduced, the laser oscillation threshold current can be further reduced, and a high output operation is possible.

  In the present embodiment, an example is shown in which the metal mask 15 is formed of only Ti, and the metal mask 15 and the cathode 16 made of Pt are electrically connected by a wire. In such a configuration, when a plurality of chips are formed on the wafer and etching is performed on the entire surface of the wafer, all of the metal mask 15 formed on the entire surface of the wafer needs to be electrically connected to the cathode 16. The mask pattern is limited. In order to solve this, Pt may be formed on the surface of the metal mask 15, and the metal mask 15 may be a laminated film of Ti and Pt so that the metal mask 15 itself becomes the cathode. With such a configuration, it is not necessary to wire the metal mask 15 and the cathode 16, and etching can be performed on the entire surface of the wafer using an arbitrary mask pattern.

  Note that a small metal having a smaller ionization tendency than hydrogen may be used for the cathode, and gold or the like may be used instead of platinum. In addition, an alkaline solution may be used for the wet etchant, and a sodium hydroxide solution or the like may be used instead of the potassium hydroxide solution.

In the present embodiment, the current blocking layer 7 is a laminated film in which the Al _0.15 Ga _0.85 N layer 8 and the GaN layer 9 are laminated. The general formula is Al _x Ga _1-x N (0 <x ≦ 1). What is necessary is just to set it as the laminated film of the layer which consists of a compound represented, and a GaN layer. In this case, considering the ease of film formation, x is preferably 0.4 or less. In order to increase the difference in refractive index with the second p-type guide layer 10 and increase the efficiency of confinement of emitted light, x is preferably 0.1 or more. Moreover, it is good also as a laminated film of three or more layers whose uppermost layer is a GaN layer.

  In the present embodiment, the thickness of the GaN layer 9 is 50 nm, but it may be 5 nm or more and 0.3 μm or less. If the thickness of the GaN layer 9 is 5 nm or more, it becomes easy to control the growth of the GaN layer 9, so that the GaN layer 9 can be formed with good reproducibility and the yield is improved. Further, by setting the thickness of the GaN layer 9 to 0.3 μm or less, it is possible to suppress the unevenness generated on the surface after the current blocking layer 7 is etched. As a result, almost no grooves remain on the surface of the regrown semiconductor layer, and the remaining resist can be suppressed in the lithography process.

  In particular, by setting the film thickness of the GaN layer 9 to 10 nm or more, an ohmic junction between the metal mask 15 and the GaN layer 9 can be more reliably formed, and the film thickness of the GaN layer is 100 nm or less. By doing so, it becomes easier to control the transverse mode of the semiconductor laser device.

(Second Embodiment)
Hereinafter, a pickup device according to a second embodiment of the present invention will be described with reference to the drawings. FIG. 5 shows a layout of the pickup device according to the second embodiment. As shown in FIG. 5, the pickup device of this embodiment uses the semiconductor laser device of the present invention. A semiconductor laser device 18 is mounted on a substrate 19 on which a mirror 20 and a light receiving element are formed. The laser light emitted from the semiconductor laser device 18 is reflected by the mirror 20 and passes through the diffraction grating 21. Thereafter, the laser beam is reflected on the surface of the optical disk (not shown) and returns to the diffraction grating 21 again. In the analysis grating 21, the laser light is divided into a plurality of beams, and the divided beams are received by the light receiving elements 22. As described above, by using the semiconductor laser of the present invention, a high-output blue-violet light pickup device can be realized.

  The semiconductor laser device and the manufacturing method thereof according to the present invention improve the crystallinity and surface morphology of the semiconductor layer formed on the current blocking layer in the semiconductor laser device having a buried structure, and reduce the laser oscillation threshold current and It has the effect of realizing a highly reliable semiconductor laser device and a manufacturing method thereof, and is useful as a semiconductor laser device using a nitride semiconductor, a manufacturing method thereof, and an optical pickup device using the same.

1 is a cross-sectional view showing a semiconductor laser device according to a first embodiment of the present invention. It is sectional drawing which shows the manufacturing method of the semiconductor laser apparatus which concerns on the 1st Embodiment of this invention in process order. 4 is an electron micrograph showing a comparison between the surface of a semiconductor layer formed by the method for manufacturing a semiconductor laser device according to the first embodiment of the present invention and the surface of a semiconductor layer formed by a conventional method. It is sectional drawing which shows the wet etching method in the manufacturing method of the semiconductor laser apparatus concerning the 1st Embodiment of this invention in order of a process. It is a layout figure which shows the optical pick-up apparatus which concerns on the 2nd Embodiment of this invention. It is sectional drawing which shows the semiconductor laser apparatus concerning a prior art example. It is sectional drawing which shows the manufacturing method of the semiconductor laser apparatus concerning a prior art example in order of a process. It is sectional drawing which shows the wet etching method of the nitride semiconductor which concerns on a prior art example.

Explanation of symbols

1 substrate 2 GaN layer 3 n-type cladding layer 4 n-type guide layer 5 active layer 6 p-type guide layer 7 current blocking layer 8 Al _0.15 Ga _0.85 N layer 9 GaN layer 10 p-type guide layer 11 p-type cladding layer 12 p-type Contact layer 13 P-type electrode 14 N-type electrode 15 Metal mask 16 Cathode 17 Etching solution aqueous solution 18 Semiconductor laser device 19 Substrate 20 Mirror 21 Diffraction grating 22 Light receiving element

Claims (18)

An active layer formed on a substrate;
A first semiconductor layer made of a first conductivity type nitride semiconductor formed on the active layer;
A laminated film formed on the first semiconductor layer, the laminated film including a plurality of thin films including a second conductivity type nitride semiconductor, and having a groove;
A second semiconductor layer made of a nitride semiconductor of the first conductivity type formed so as to fill the groove on the laminated film,
The semiconductor laser device, wherein the thin film formed on the laminated film is a thin film made of gallium nitride. At least one of the thin films constituting the laminated film is a thin film containing aluminum,
2. The semiconductor laser device according to claim 1, wherein the concentration of the second conductivity type impurity in the thin film containing aluminum is lower than the concentration of the second conductivity type impurity in the thin film made of gallium nitride.   3. The semiconductor laser device according to claim 2, wherein the thin film containing aluminum is made of an undoped nitride semiconductor. The semiconductor laser device according to claim 2, wherein the thin film containing aluminum is a thin film made of a compound represented by a general formula of Al _x Ga _1-x N (0 <X ≦ 1).   5. The semiconductor laser device according to claim 1, wherein a film thickness of the thin film made of gallium nitride is 5 nm or more and 0.3 μm or less.   6. The semiconductor laser according to claim 1, wherein the second semiconductor layer has a higher refractive index than a thin film having the smallest refractive index among the thin films constituting the stacked film. apparatus.   An optical pickup device using the semiconductor laser device according to claim 1. A laminate having an active layer, a first semiconductor layer made of a first conductivity type nitride semiconductor, and a plurality of thin films containing a second conductivity type nitride semiconductor, and a thin film made of gallium nitride on the top. A step of sequentially forming a film;
Forming a groove by selectively removing a part of the laminated film;
And a step of forming a second semiconductor layer made of a first conductivity type nitride semiconductor on the laminated film in which the groove is formed. At least one of the thin films constituting the laminated film is a thin film containing aluminum,
9. The semiconductor laser device according to claim 8, wherein a concentration of the second conductivity type impurity in the thin film containing aluminum is lower than a concentration of the second conductivity type impurity in the thin film made of gallium nitride. Manufacturing method. Thin film containing the aluminum, a method of manufacturing a semiconductor laser device according to claim 9, the general formula is characterized in that it consists of _{Al x Ga 1-x N (} 0 <X ≦ 1) compound represented by the.   The step of forming the groove portion, wherein a metal mask is formed on the thin film made of gallium nitride, and then wet etching is performed on the stacked film using the formed metal mask. The manufacturing method of the semiconductor laser device according to any one of 8 to 10.   The method of manufacturing a semiconductor laser device according to claim 11, wherein the metal mask is in ohmic contact with the thin film made of gallium nitride.   13. The method of manufacturing a semiconductor laser device according to claim 11, wherein the metal mask is made of titanium or tantalum.   14. The step of forming the groove portion, wherein after forming the metal mask, a metal film having a smaller ionization tendency than hydrogen is formed on the surface of the metal mask. A method for manufacturing the semiconductor laser device according to claim 1.   15. The method of manufacturing a semiconductor laser device according to claim 14, wherein the metal having a small ionization tendency is platinum.   16. The step of forming the groove portion includes performing wet etching while irradiating the laminated film with light having energy larger than the largest band gap of the thin film constituting the laminated film. A method of manufacturing a semiconductor laser device according to any one of the above.   17. The method for manufacturing a semiconductor laser device according to claim 11, wherein an alkaline solution is used as an etchant in the wet etching. 18. The method of manufacturing a semiconductor laser device according to claim 17, wherein the alkaline solution is a potassium hydroxide solution or a sodium hydroxide solution.