JP2009224506A - Semiconductor laser device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a two-wavelength semiconductor laser device that enhances temperature characteristics of an infrared laser and operates with a low voltage. <P>SOLUTION: The semiconductor laser device includes a substrate 10, a first semiconductor laser formed on the substrate 10, and a second semiconductor laser which outputs light having a shorter wavelength than the first semiconductor and is formed on the substrate. The first semiconductor laser includes a first clad layer 12 of a first conductivity type formed above the substrate 10, a first guide layer 13 of the first conductivity type formed on the first clad layer 12, a first active layer 14 formed on the first guide layer 13 and containing AlGaAs, a second guide layer 15g2 and 15g1 of a second conductivity type formed on the active layer 14 and having smaller Al composition at interface parts for the active layer 14 than at upper surface parts, and a clad layer 16 of the second conductivity type formed on the second guide layer 15g1. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a red and infrared semiconductor laser used as a light source required for a pickup light source of an optical disk device, other electronic devices, information processing devices, and the like.

  Currently, high-capacity digital video discs (DVDs) capable of high-density recording and DVD devices for recording the same are on the market, and are attracting attention as products that will continue to grow in demand in the future. Since this DVD has high-density recording, an AlGaInP semiconductor laser having an emission wavelength of 650 nm is used as a laser light source for recording and reproduction. For this reason, the optical pickup of the conventional DVD apparatus cannot reproduce a compact disc (CD) that is reproduced using an AlGaAs semiconductor laser having an emission wavelength of 780 nm.

  In order to solve this problem, an optical pickup equipped with an AlGaInP semiconductor laser chip with an emission wavelength of 650 nm band and an AlGaAs semiconductor laser chip with an emission wavelength of 780 nm band separately packaged is adopted. Has been. However, the optical pickup as described above has a problem that the size of the optical pickup is large because the two packages of the AlGaInP semiconductor laser and the AlGaAs semiconductor laser are mounted, and thus the size of the DVD device also increases. In order to solve this problem, an integrated semiconductor light emitting device having a plurality of types of semiconductor light emitting elements having different light emission wavelengths, in which a light emitting element structure is formed by a semiconductor layer grown on the same substrate, has been proposed. (See Patent Document 1).

  FIG. 12 is a diagram showing an embodiment of a conventional integrated semiconductor laser device. As shown in the figure, in a conventional integrated semiconductor laser device, an AlGaAs semiconductor laser LD1 having an emission wavelength of 700 nm band (for example, 780 nm) and an emission wavelength of 600 nm band are formed on the same n-type GaAs substrate 201. (For example, 650 nm) AlGaInP semiconductor laser LD2 is integrated in a state of being separated from each other. As the n-type GaAs substrate 201, for example, a substrate having a (100) plane orientation or a substrate having a main surface that is off, for example, 5 to 15 ° from the (100) plane is used.

  In the AlGaAs semiconductor laser LD1, an n-type GaAs buffer layer 211, an n-type AlGaAs cladding layer 212, an active layer 213 having a single quantum well (SQW) structure or a multiple quantum well (MQW) structure are formed on an n-type GaAs substrate 201. A p-type AlGaAs cladding layer 214 and a p-type GaAs cap layer 215 are sequentially stacked. The upper part (downward in FIG. 12) of the p-type AlGaAs cladding layer 214 and the p-type GaAs cap layer 215 have a stripe shape extending in one direction. An n-type GaAs current confinement layer 216 is provided on both sides of the stripe portion, thereby forming a current confinement structure. A p-side electrode 217 is in ohmic contact with the p-type GaAs cap layer 215 on the stripe-shaped p-type GaAs cap layer 215 and the n-type GaAs current confinement layer 216 (under the n-type GaAs current confinement layer 216 in FIG. 12). Is provided. As the p-side electrode 217, for example, a Ti / Pt / Au electrode is used.

  In the AlGaInP-based semiconductor laser LD2, an n-type GaAs buffer layer 221, an n-type AlGaInP clad layer 222, an SQW structure or an MQW structure active layer is formed on an n-type GaAs substrate 201 (under the n-type GaAs substrate 201 in FIG. 12). 223, a p-type AlGaInP cladding layer 224, a p-type GaInP intermediate layer 225, and a p-type GaAs cap layer 226 are sequentially stacked. The upper part of the p-type AlGaInP cladding layer 224, the p-type GaInP intermediate layer 225, and the p-type GaAs cap layer 226 have a stripe shape extending in one direction. An n-type GaAs current confinement layer 227 is provided on both sides of the stripe portion, thereby forming a current confinement structure. A p-side electrode 228 is provided in ohmic contact with the p-type GaAs cap layer 226 on the striped p-type GaAs cap layer 226 and the n-type GaAs current confinement layer 227. As the p-side electrode 228, for example, a Ti / Pt / Au electrode is used.

  An n-side electrode 229 is provided on the back surface of the n-type GaAs substrate 201 in ohmic contact with the n-type GaAs substrate 201. As the n-side electrode 229, for example, an AuGe / Ni electrode or an In electrode is used.

  In such a case, the p-side electrode 217 of the AlGaAs-based semiconductor laser LD1 and the p-side electrode 228 of the AlGaInP-based semiconductor laser LD2 are on the heat sinks H1 and H2 provided on the package base 300 in a state of being electrically separated from each other. Each is soldered.

  In this conventional integrated semiconductor laser device configured as described above, the AlGaAs semiconductor laser LD1 can be driven by passing a current between the p-side electrode 217 and the n-side electrode 229, and the p-side The AlGaInP semiconductor laser LD2 can be driven by passing a current between the electrode 228 and the n-side electrode 229. Then, by driving the AlGaAs semiconductor laser LD1, laser light having a wavelength of 700 nm (eg, 780 nm) can be extracted, and by driving the AlGaInP semiconductor laser LD2, laser light having a wavelength of 600 nm (eg, 650 nm). Can be taken out. The selection of whether to drive the AlGaAs semiconductor laser LD1 or the AlGaInP semiconductor laser LD2 can be made by switching an external switch or the like.

  As described above, according to the conventional integrated semiconductor laser device, the laser light for DVD is obtained by including the AlGaAs semiconductor laser LD1 having an emission wavelength of 700 nm and the AlGaInP semiconductor laser LD2 having an emission wavelength of 600 nm. And CD and MD laser beams can be taken out independently of each other. Therefore, by mounting this integrated semiconductor laser device as a laser light source on the optical pickup of the DVD device, any of DVD, CD, and MD can be reproduced or recorded. Since these AlGaAs semiconductor laser LD1 and AlGaInP semiconductor laser LD2 have a laser structure formed of a semiconductor layer grown on the same n-type GaAs substrate 1, the package of this integrated semiconductor laser device is one. It's enough. For this reason, it is possible to reduce the size of the optical pickup, and thus it is possible to reduce the size of the DVD device.

Further, in a semiconductor laser, in order to rewrite an optical disk at high speed, a light output as high as possible is required even at high temperature operation. For example, in order to rewrite a DVD optical disc at a high speed of 16 times or higher, a high output of 300 mW or more is required as an optical output. In order to obtain such high output, it is necessary to prevent COD (Catastrophic Optical Damage) in which the end face of the semiconductor laser is melted and destroyed by its own light output at the time of high output. In order to prevent COD, it is effective to reduce the light density inside the cavity end face of the laser and suppress heat generation. For this purpose, it is effective to coat the front end face of the semiconductor laser from which the laser light is extracted with a dielectric such as SiO ₂ , Al ₂ O ₃ , or amorphous Si to reduce the reflectance of the front face.

  In general, the reflectance of the cavity end face of a semiconductor laser made of an AlGaInP-based material or an AlGaAs-based material is about 30% when the end face is not coated. In this case, about 30% of the laser light is reflected at the resonator end face and fed back into the resonator, and about 70% of the light is extracted from the front end face. On the other hand, for example, when the dielectric film is coated so that the reflectance of the front surface becomes 10%, 10% of the laser light is reflected at the end face of the resonator and fed back into the resonator, and 90% of the light is fed to the front end It will be taken out from the surface. That is, when the light output extracted from the front end face is the same, the light density at the resonator end face can be reduced by reducing the reflectance of the front face. Therefore, reducing the reflectance of the front surface leads to an increase in the COD level (maximum light output capable of oscillation), and is an effective means for obtaining a high-power laser. Furthermore, if the rear end face reflectance, which is the opposite side of the resonator surface from which the laser light is extracted, is set high, the light extraction efficiency from the front surface of the semiconductor laser can be further increased. Therefore, in high-power semiconductor lasers, end face coating conditions are widely used in which the front-surface reflectance is reduced and the rear-surface reflectance is conversely high. Even in a two-wavelength laser in which semiconductor lasers emitting red and infrared light are integrated on the same substrate, in order to obtain a high output operation, for the reasons described above, low reflectance and high reflectance for red and infrared are used. Are coated on the end face of the laser resonator.

  Further, even if the end face coating as described above is applied, the band gap energy of the active layer at the end face of the laser resonator is affected by the surface level and becomes smaller than the band gap energy of the active layer inside the resonator. That is, when current is injected into the semiconductor laser, the band gap energy of the active layer is reduced due to the effects of Joule heat generation and non-radiative recombination in the active layer. In particular, in a high-power laser, since the reflectance of the front end face is reduced as described above, the light density of the active layer in the vicinity of the front end face is maximized inside the resonator, and the temperature is likely to rise. For this reason, the band gap energy of the active layer in the vicinity of the front end face is further reduced, the absorption loss with respect to the laser light is increased, and heat is further generated. As a result, end face COD occurs. In order to prevent the occurrence of such end face breakdown, the quantum well active layer near the laser end face is disordered by impurity diffusion, an end face window structure is formed, and the band gap energy of the active layer near the end face is increased in advance to generate heat. Thus, even if the band gap of the active layer in the vicinity of the end face is reduced, it is only necessary to maintain a substantially transparent state with respect to the laser oscillation light. As a result, it is possible to increase the light output that generates COD.

  In the future, there will be an increasing demand for light sources for optical disc systems capable of high-speed writing, such as DVDs compatible with 16 × speed recording and CD-Rs compatible with 48 × recording that have recording functions as well as playback. In this case, the laser used as the light source is required to have a high output operation of at least 350 mW even when operating at a high temperature of 85 ° C. or higher.

  In general, in order to realize a high temperature operation, it is necessary to suppress carrier overflow in which electrons injected into the active layer are excited by heat and leak into the p-type cladding layer. In order to suppress this carrier overflow, it is effective to increase the band offset (ΔEc) of the conduction band between the active layer and the p-type cladding layer and to increase the difference in electron potential energy between the active layer and the p-type cladding layer. It is. In the case of a CD-R infrared laser, an AlGaAs-based material is widely used for the active layer in order to obtain laser oscillation light in the 780 nm band. In this structure, using p-type AlGaInP having a larger forbidden band width energy is much more effective in increasing ΔEc than using p-type AlGaAs for the p-type cladding layer.

FIG. 13 is a cross-sectional view showing a two-wavelength semiconductor laser device which is a semiconductor laser device according to a second conventional example. As shown in the figure, the red laser includes an n-type GaAs buffer layer 311, an n-type (Al _0.7 Ga _0.3 ) _0.51 In _0.49 P clad layer 312, barrier layers 313 b 1, 313 b 2, Strain quantum well active layer 313 having well layers 313w1, 313w2, and guide layers 313g1, 313g2, a p-type (Al _0.7 Ga _0.3 ) _0.51 In _0.49 P clad layer 314, and an n-type current It has a block layer 315, a p-type Ga _0.51 In _0.49 P protective layer 316, and a p-type GaAs contact layer 317.

In the two-wavelength semiconductor laser according to the second conventional example, the infrared laser includes an n-type GaAs buffer layer 321 and an n-type (Al _0.7 Ga _0.3 ) _0.51 In _0.49 P clad layer. 322, quantum well active layer 323 having barrier layers 323b1, 323b2 made of Al _0.5 Ga _0.5 As, well layers 323w1, 323w2, 323w3 made of GaAs, and guide layers 323g1, 323g2, and p-type (Al _0.7 Ga _0.3 ) _0.51 In _0.49 P clad layer 324. In this conventional example, the temperature characteristics of the infrared laser are improved by increasing ΔEc of the active layer and the p-type cladding layer (see Patent Document 2).

Further, when the semiconductor laser is operated at a high output, the resonator end face (front end face) on the side from which the laser light is extracted and the resonator end face (rear end face) on the opposite side are each low reflectivity of 10% or less. And coating of a dielectric film having a high reflectivity of 85% or more. By performing such low reflectance (AR) / high reflectance (HR) coating, it is possible to improve external differential quantum efficiency (slope efficiency) in current-light output characteristics. Therefore, while realizing a high optical output with a small injection current amount, the quantum well active layer in the vicinity of the end face is disordered by impurity diffusion, thereby generating COD in which the laser end face is melted and destroyed by the optical output of the laser light itself. It is preventing. As a result, an infrared laser capable of a high output operation of 200 mW or more is realized in the two-wavelength laser.
Japanese Patent Laid-Open No. 11-186651 JP 2007-88188 A

  In the conventional infrared laser according to the second conventional example, Zn is used as a p-type impurity. Further, in order to suppress a decrease in luminous efficiency due to the formation of non-radiative recombination centers due to doping of impurities, the quantum well active layer made of an AlGaAs-based material is not doped with impurities. In this case, since the diffusion rate of Zn in the AlGaInP-based material is faster than that of the AlGaAs-based material, Zn diffuses from the p-type AlGaInP to the quantum well active layer, and the low-diffusion rate AlGaAs-based quantum well active layer and the p-type AlGaInP Zn easily piles up at the interface of the cladding layer. Because of the pileup of Zn at this interface, the size of the spike formed in the valence band energy band structure at the interface between the quantum well active layer and the p-type AlGaInP cladding layer increases, so that the active layer from the p-type cladding layer As a result, the resistance of holes injected toward the surface increases and the operating voltage increases.

  At this time, in the infrared laser, since the overflow of electrons can be suppressed by using AlGaInP for the p-type cladding layer, a laser having a high thermal saturation level in the optical output-current characteristic and a good temperature characteristic. However, on the other hand, the operating voltage at the time of high-temperature high-power operation with a pulse of 85 ° C. and 350 mW is about 3.3V. As a result, the operating voltage is almost equal to the supply voltage capacity (up to 3.5V) of the laser driving circuit for driving the laser, and the operating voltage is reduced considering the further high output operation of the 400 mW class. Otherwise, it will cause a serious trouble that the laser cannot be driven.

  An object of the present invention is to provide a two-wavelength semiconductor laser device having an infrared laser capable of enhancing the temperature characteristics of an infrared laser and capable of operating at a low voltage.

  In order to solve the above problems, a first semiconductor laser device of the present invention includes a substrate, a cladding layer made of an AlGaInP-based material, the first semiconductor laser formed on the substrate, and the first semiconductor laser device. And a second semiconductor laser formed on the substrate, wherein the first semiconductor laser is a first conductivity type first electrode formed above the substrate. 1 cladding layer, a first guide layer of the first conductivity type formed on the first cladding layer, a first active layer formed on the first guide layer and containing AlGaAs, and the active layer A second guide layer of the second conductivity type formed on the layer and having an Al composition at the interface with the active layer smaller than the Al composition at the upper surface, and a second conductivity formed on the second guide layer. And a mold cladding layer.

  With this configuration, it is possible to increase the diffusion rate of impurities in the second guide layer in the vicinity of the interface between the second guide layer and the second cladding layer. For example, it occurs at the interface between the AlGaAs-based material and the AlGaInP-based material. It is possible to reduce the magnitude of impurity pileup. As a result, it becomes possible to reduce the size of the spike in the valence band energy band structure formed at the interface between the second cladding layer and the second guide layer, and to reduce the operating voltage. Become.

  The second guide layer is formed on the third guide layer having a Al composition of 0.5 or less and in contact with the active layer, and a second guide layer having an Al composition of 0.55 or more. 4, the size of the spike in the valence band energy band structure formed at the interface between the second cladding layer and the second guide layer is reduced, and impurities are reduced. Diffusion to the active layer can be prevented. For this reason, it is possible to prevent the non-radiative recombination centers from being formed in the active layer due to impurity diffusion, and thus it is possible to suppress a decrease in light emission efficiency.

  If the thickness of the second guide layer is 20 nm or more and 43 nm or less, the vertical divergence angle of the light output from the first semiconductor laser device can be set to 14 ° or more and 18 ° or less. It can be preferably used as a light source.

  The second semiconductor laser device of the present invention is formed on a substrate, a first conductivity type first cladding layer made of an AlGaInP-based material, and formed on the substrate, and on the first cladding layer. A first conductive type first guide layer; a first active layer formed on the first guide layer containing AlGaAs; and formed on the active layer, wherein the Al composition at the interface with the active layer has an Al composition. A second conductivity type second guide layer having an Al composition lower than that of the upper surface portion and a second conductivity type cladding layer formed on the second guide layer and made of an AlGaInP-based material are provided.

  With this configuration, it is possible to increase the diffusion rate of impurities in the second guide layer in the vicinity of the interface between the second guide layer and the second cladding layer. For example, it occurs at the interface between the AlGaAs-based material and the AlGaInP-based material. It is possible to reduce the magnitude of impurity pileup.

  According to the semiconductor laser device of the present invention, for example, in the infrared laser, the size of the spike in the valence band energy band structure formed at the interface between the second guide layer and the second cladding layer is reduced. Therefore, the operating voltage can be reduced.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings.

  FIG. 1 is a cross-sectional view showing the structure of a semiconductor laser device according to an embodiment of the present invention. In this structure, a red laser and an infrared laser are integrated on an n-type GaAs substrate 10 whose main surface is a surface inclined by 10 ° in the [011] direction from the (100) plane. First, the structure of the infrared laser will be described. In addition, the film thickness of each layer shown below is an example, Comprising: It is not limited to this.

The infrared laser includes a buffer layer 11 made of n-type GaAs having a thickness of 0.5 μm provided on the n-type GaAs substrate 10 in order from the bottom, and (Al _0.7 Ga _0.3 ) _0.51 In _0. An n-type cladding layer 12 made of ₄₉ P with a thickness of 2.0 μm, a first guide layer 13 made of Al _0.5 Ga _0.5 As, well layers 14 w 1 and 14 w 2 made of GaAs, and Al _0.5 Ga a quantum well active layer 14 having a barrier layer 14b1 consisting of _{0.5 as,} a second guide layer 15g2 made of Al _{0.5 Ga} 0.5 _as, a third guide comprising a Al 0.6 _{Ga 0.4} as A layer 15g1, a p-type cladding layer 16 made of (Al _0.7 Ga _0.3 ) _0.51 In _0.49 P, and a protective layer made of p-type Ga _0.51 In _0.49 P and having a thickness of 50 nm. 17 and p-type G a contact layer 18 made of aAs and having a thickness of 0.4 μm.

  The upper part of the p-type cladding layer 16, the protective layer 17 and the contact layer 18 constitute a striped ridge. The distance from the top surface of the p-type cladding layer 16 above the ridge to the quantum well active layer 14 is 1.4 μm, and the distance dp from the bottom of the ridge to the quantum well active layer 14 is 0.24 μm.

A current blocking layer 19 made of SiN and having a thickness of 0.3 μm is formed on the side surface of the ridge and on the p-type cladding layer 16. In this structure, the current injected from the contact layer 18 is confined only in the ridge portion by the current blocking layer 19 and is concentrated in the quantum well active layer 14 located below the bottom of the ridge, so that carriers necessary for laser oscillation are obtained. The inversion distribution state of is realized by a small injection current of several tens of mA. For light emitted by recombination of carriers injected into the quantum well active layer 14, light in the vertical direction is formed by the p-type cladding layer 16 and the n-type cladding layer 12 in the direction perpendicular to the upper and lower surfaces of the quantum well active layer 14. In the direction parallel to the upper and lower surfaces of the quantum well active layer 14, the current blocking layer 19 has a refractive index lower than that of the cladding layer, so that horizontal light confinement occurs. Further, since the current blocking layer 19 is transparent to the laser oscillation light, there is no light absorption, and a low-loss waveguide can be realized. Further, since the light propagating through the waveguide can ooze out to the current blocking layer 19, Δn (effective refractive index difference between the inside and outside of the stripe) of the order of 10 ⁻³ suitable for high output operation, like the red laser portion. ) Can be easily obtained, and the size thereof can be precisely controlled by the size of dp (distance from the bottom edge of the ridge to the quantum well active layer 14), similarly on the order of 10 ⁻³ . Therefore, it is possible to obtain a high-power semiconductor laser with a low operating current while precisely controlling the light distribution. In this embodiment, dp is 0.24 μm, and Δn of 4 × 10 ⁻³ is obtained. With this configuration, it is possible to obtain a stable fundamental transverse mode oscillation having a full width at half maximum of 8 ° and 16.2 °, which is suitable for a light source for a recording / reproducing optical disc, as horizontal and vertical spread angles.

The red laser includes, in order from the bottom, a buffer layer 21 made of n-type GaAs formed on the n-type GaAs substrate 10 and having a thickness of 0.5 μm, and (Al _0.7 Ga _0.3 ) _0.51 In _0. An n-type cladding layer 22 made of ₄₉ P with a thickness of 2.0 μm, a first guide layer 23 g 1 made of (Al _0.5 Ga _0.5 ) _0.5 1In _0.49 P, and a well layer 23 w 1 made of GaInP , 23w2, 23w3, and a strained quantum well active layer 23 having barrier layers 23b1 and 23b2 made of AlGaInP, a second guide layer 23g2 made of AlGaInP, and (Al _0.7 Ga _0.3 ) _0.51 In _0.49. A p-type cladding layer 24 made of P, a protective layer 25 made of p-type Ga _0.51 In _0.49 P with a thickness of 50 nm, and a 0.4 μm thick core made of p-type GaAs. Contact layer 26. The distance from the top surface of the p-type cladding layer 24 above the ridge to the strained quantum well active layer 23 is 1.4 μm, and the distance dp from the bottom of the ridge to the strained quantum well active layer 23 is 0.17 μm.

On the side surface of the ridge and on the p-type cladding layer 24, a current blocking layer 19 made of SiN and having a thickness of 0.3 μm is formed. In this structure, the current injected from the contact layer 26 is confined only to the ridge portion by the current blocking layer 19 and concentrated and injected into the active layer 23 located below the bottom of the ridge to invert carriers necessary for laser oscillation. The distribution state is realized by a small injection current of several tens of mA. The light emitted by recombination of carriers injected into the strained quantum well active layer 23 is perpendicular to the upper and lower surfaces of the strained quantum well active layer 23 by the n-type cladding layer 22 and the p-type cladding layer 24. In the direction parallel to the upper and lower surfaces of the strained quantum well active layer 23, the current blocking layer 19 has a refractive index lower than that of the cladding layer, so that horizontal light confinement occurs. Further, since the current blocking layer 19 is transparent to the laser oscillation light, there is no light absorption, and a low-loss waveguide can be realized. Further, since the light propagating through the waveguide can ooze out to the current blocking layer 19, Δn on the order of 10 ⁻³ suitable for high output operation can be easily obtained, and the magnitude thereof is dp. The size can be precisely controlled in the same order of 10 ⁻³ . Therefore, it is possible to obtain a high-power semiconductor laser with a low operating current while precisely controlling the light distribution. In this embodiment, dp is 0.17 μm, and Δn of 5 × 10 ⁻³ is obtained. With this configuration, it is possible to obtain a stable fundamental transverse mode oscillation having a full width at half maximum of 9 ° and 16 °, which is suitable for a light source for a recording / reproducing optical disc, as horizontal and vertical spread angles.

  Further, in order to improve heat dissipation during high-temperature operation at 85 ° C., the operating current density is reduced by setting the resonator length to 1500 μm or more in a high-power laser of 350 mW or more. In this embodiment, the resonator length is 1750 μm.

  The front end face and the rear end face of the resonator are coated with a dielectric film so that the reflectance is 7% and 94% for the infrared laser light and the red laser light, respectively. In addition, the portion near the light output end face in the active layer of the infrared laser and the red laser is disordered by impurity diffusion, thereby preventing the occurrence of COD in which the laser end face is melted and destroyed by the light output of the laser light itself. .

  Here, the structure of the guide layer on the well layer in the infrared laser, which is a feature of the semiconductor laser device of this embodiment, will be described.

  First, the Al composition of the third guide layer 15g1 is at least 0.55 or more, preferably 0.6 or more. This makes it difficult for Zn to pile up at the interface between the p-type cladding layer 16 and the third guide layer 15g1, as will be described later, so that the magnitude of the valence band spike at the interface is reduced. Can do. The Al composition of the third guide layer 15g1 is preferably 0.7 or less.

  Further, since the total film thickness of the second guide layer 15g2 and the third guide layer 15g1 is at least 20 nm, preferably 30 nm, the diffusion of impurities into the well layers 14w1 and 14w2 is prevented. Further, since the total film thickness of the second guide layer 15g2 and the third guide layer 15g1 is 43 nm or less, the vertical divergence angle of the semiconductor laser light can be set to 18 ° or less as described later.

  Next, the above features will be described.

  The p-type cladding layer 16 made of AlGaInP is doped with Zn as a p-type impurity. The second guide layer 15g2 formed on the well layer 14w1 is made of an AlGaAs material. In this case, Zn, which is an impurity, is more easily diffused in AlGaInP due to thermal history during crystal growth than in AlGaAs-based materials, so that Zn piles up at the interface between the p-type cladding layer 16 and the third guide layer 15g1. It becomes easy to do. At this time, the magnitude of spike energy formed in the band structure of valence band energy increases as the Zn concentration piles up. This spike increases the resistance and the operating voltage for holes injected from the p-type cladding layer 16 into the quantum well active layer 14.

  2A to 2D are diagrams showing measurement results of Zn concentration distribution when the Al composition of the guide layer is changed from 0.5 to 0.7. In the figure, the relative distance is the distance in the film thickness direction of the laser, and the place where the Zn concentration rapidly decreases is the interface between the p-type cladding layer 16 and the guide layer. Here, it can be seen that the concentration of Zn piled up at this interface decreases as the Al composition of the guide layer increases. This is because Zn diffusion in the AlGaAs layer increases as the Al composition increases, and as a result, Zn diffuses more easily in the guide layer, resulting in a decrease in the Zn concentration piled up at the interface with the p-type cladding layer 16. It is done. Therefore, in order to reduce the magnitude of the valence band spike at the interface between the p-type cladding layer 16 and the guide layer, the Al composition of the guide layer is increased to at least 0.55 or more, preferably 0.6 or more. I understand that I should do it.

  Further, as shown in FIGS. 2A and 2B, it can be seen that the Zn concentration rapidly decreases at a distance of about 20 nm from the interface between the p-type cladding layer 16 and the guide layer into the guide layer. When the impurities reach the well layer, non-radiative recombination centers are formed, the luminous efficiency is lowered, and the temperature characteristics are deteriorated due to an increase in the oscillation threshold value. Therefore, it is necessary to avoid impurity diffusion into the well layer. From the experimental results shown in FIG. 2, in order to avoid the diffusion of impurities to the well layers 14w1 and 14w2 through the guide layer, the thickness of the guide layer is required to be at least 20 nm, preferably about 30 nm. I understand. Therefore, in the semiconductor laser device of this embodiment shown in FIG. 1, the total thickness of the guide layers is set to 30 nm, and the diffusion of impurities to the well layers 14w1 and 14w2 through the third guide layer 15g1 is suppressed.

  Next, FIG. 3 is a diagram showing the relationship between the thickness of the guide layer and the vertical divergence angle of the laser beam when the Al composition (Xg) of the guide layer is changed from 0.5 to 0.7. Here, the relationship between the full width at half maximum in the vertical direction (hereinafter, vertical divergence angle) and the guide layer thickness in FFP (Far Field Pattern) at each film thickness was calculated.

  From this result, it can be seen that as Xg increases, the refractive index of the guide layer decreases, so that the confinement action of light in the vertical direction in the active layer decreases and the vertical divergence angle decreases. In order to increase the light coupling efficiency with the optical system, the laser of the light source for optical discs that can be recorded / reproduced needs to have a vertical j divergence angle of 18 ° or less. On the other hand, if the vertical divergence angle is small, the light distribution (NFP: Near Field Pattern) propagating through the waveguide greatly spreads in the vertical direction, so that the spot size can be made sufficiently small when focused by a lens. It becomes impossible to be affected by the bit information of the adjacent track on the optical disc. As a result, the information on the optical disc cannot be read accurately, causing a practical problem. From the above, taking into consideration the coupling efficiency and light condensing property between the optical system and the laser, the vertical divergence angle of the semiconductor laser beam for optical discs that can be recorded and reproduced is usually 14 ° or more and 18 ° or less, particularly preferably about 16 °. It is necessary to. Here, the results shown in FIG. 2 indicate that Xg needs to be at least 0.55 in order to suppress the pileup of impurities at the interface between the guide layer and the p-type cladding layer 16. . Therefore, from the results shown in FIG. 3, it can be seen that if the thickness of the guide layer is 43 nm or less, the vertical divergence angle can be 18 ° or less even when Xg is greater than 0.55.

  In order to suppress the pileup of impurities at the interface between the p-type cladding layer 16 and the guide layer, it is preferable that the Xg of the guide layer near the interface is high, and the impurities diffuse into the well layers 14w1 and 14w2 through the guide layer. In order to prevent this, the lower Xg is better. For this reason, in order to prevent impurity diffusion into the well layers 14w1 and 14w2 while suppressing impurity pileup, Xg in the portion of the guide layer near the interface with the p-type cladding layer 16 is possible. It is preferable to make it as large as possible and make Xg as small as possible in the vicinity of the interface between the well layer 14w1 and the third guide layer 15g2.

  FIG. 4 shows the calculation result of the relationship between the vertical divergence angle of light and the thickness of the guide layer when the guide layer on the well layer is composed of a plurality of layers having the same film thickness and different Al compositions. FIG. Line A is composed of layers having Al compositions of 0.5 and 0.4 on the guide layer on the well layer. Line B is composed of layers of Al and 0.6 on the guide layer on the well layer. In this case, the line C shows a case where the Al composition of the n guide layer on the well layer is composed of 0.7 and 0.6 layers.

  From FIG. 4, when Xg in the vicinity of the interface with the p-type cladding layer 16 in the third guide layer 15g1 is 0.6, in order to make the vertical divergence angle 18 ° or less, the total number of guide layers on the well layer It can be seen that the thickness should be 48 nm or less. Further, in order to avoid the diffusion of impurities to the well layer through the guide layer, the guide layer needs to have a film thickness of at least 20 nm. Therefore, in the guide layer, Xg in the vicinity of the interface with the p-type cladding layer 16 is required. If the total thickness of the guide layer is 20 nm or more and 48 nm or less, the vertical divergence angle is set to 18 ° while preventing the impurity from being piled up at the interface and preventing the impurity from diffusing into the well layer. It is possible to:

  Here, in the semiconductor laser device of the present embodiment shown in FIG. 1, the Al compositions of the third guide layer 15g1 and the second guide layer g2 on the well layer 14w1 are 0.6 and 0.5, respectively. Since the thickness is set to 15 nm and the total film thickness is set to 30 nm, a vertical divergence angle of 16.2 ° suitable as a light source for an optical disk for recording and reproduction is obtained.

  FIG. 5 is a diagram showing measurement results of current-voltage characteristics of an infrared laser in the semiconductor laser device of the present embodiment shown in FIG. 1 and a conventional semiconductor laser device. In the conventional semiconductor laser device, the Al composition of the guide layer on the well layer of the infrared laser is constant at 0.5, and the guide layer thickness is 19 nm in order to obtain a vertical spread angle of 16 °. Here, the temperature of the semiconductor laser device is 85 ° C. As a result, as shown in FIG. 5, in the semiconductor laser device of the present invention, it can be seen that the differential resistance of the infrared laser is lower and the operating voltage is lower than the conventional infrared laser.

  Next, FIG. 6 is a diagram showing measurement results of light output-current characteristics at 85 ° C. of the present embodiment and the conventional infrared laser. From the results shown in the figure, it can be seen that the infrared laser of this embodiment has a low operating current characteristic with a low oscillation threshold current value and high slope efficiency as compared with the conventional infrared laser. This is because, as shown in FIG. 5, in the laser of one embodiment of the present invention, spikes are not easily formed in the valence band energy band structure, and the device resistance is low, so the operating voltage is low and the heat generation during operation is suppressed. This is because it is possible. In addition, in the conventional infrared laser, in order to make the vertical divergence angle near 16 °, the thickness of the guide layer needs to be 20 nm or less, so that impurities doped in the p-type cladding layer are formed in the well layer via the guide layer. As a result of diffusion into the layer 14w1 and formation of non-radiative recombination centers, it is considered that the oscillation threshold current value was increased.

  Next, FIG. 7 is a diagram showing measurement results of voltage-current characteristics of this embodiment shown in FIG. 5 and the conventional infrared laser at 85 ° C., a pulse width of 50 ns, and a duty of 40%. As shown in the figure, it can be seen that the infrared laser of this embodiment has a lower differential resistance and a lower operating voltage than a conventional infrared laser. In particular, when the operating current of the infrared laser of this embodiment is 500 mA, the operating voltage was 3.1 V, which was 0.2 V lower than that of the conventional infrared laser. As a result, according to the semiconductor laser device of the present embodiment, it is possible to widen the margin for the capacity (up to 3.5 V) of the supply voltage of the laser driving circuit that drives the laser, and to perform laser driving at higher output. became.

  Next, FIG. 8 is a diagram showing measurement results of optical output-current characteristics at 85 ° C., a pulse width of 50 ns, and a duty of 40% of the present embodiment and the conventional infrared laser used in FIG. As shown in the figure, the infrared laser of the present embodiment has a low operating current characteristic with a low oscillation threshold current value and high slope efficiency, as in the case of CW drive, compared to a conventional infrared laser. I understand that. As shown in FIG. 5, in the infrared laser of this embodiment, spikes are difficult to form in the valence band energy band structure, and the device resistance is low, so the operating voltage is low, and heat generation during operation is suppressed. This is because it is possible. In addition, in the conventional infrared laser, in order to make the vertical divergence angle near 16 °, the guide layer thickness on the well layer needs to be 20 nm or less. Therefore, impurities doped in the p-type cladding layer pass through the guide layer. It is considered that the diffusion threshold value was increased as a result of diffusion into the well layer and formation of non-radiative recombination centers.

FIG. 9 is a diagram showing the measurement results of the optical output-current characteristics of the red laser according to the present embodiment shown in FIG. 1 at 85 ° C., a pulse width of 50 ns, and a duty of 40%. As shown in the figure, the red laser of this embodiment has a maximum light output of 400 mW or more. This is because SiN, which is almost transparent to laser light, is used for the current blocking layer to reduce the loss of the waveguide, and ΔN is set to 5 × 10 ⁻³ , and the fundamental transverse mode oscillation stable to a high output is achieved. It seems that it became possible by having obtained it.

  FIGS. 10A to 10D and FIGS. 11A to 11D are cross-sectional views illustrating manufacturing processes of the semiconductor laser device according to the embodiment of the present invention.

As shown in FIG. 10A, a buffer layer 11 made of n-type GaAs having a thickness of 0.5 μm is formed on an n-type GaAs substrate 10 using MOCVD or MBE, and (Al _0.7 Ga). _0.3 ) _0.51 In _0.49 P 2.0 μm thick n-type cladding layer 12, Al _0.5 Ga _0.5 As first guide layer 13, GaAs well layer 14W1,14w2, and the _Al 0.5 _{Ga 0.5} quantum well active layer 14 having a barrier layer 14b1 consisting of _as, the second guide layer 15g2 made of _{Al 0.5 Ga} 0.5 _as, Al _0.6 A third guide layer 15g1 made of Ga _0.4 As, a p-type cladding layer 16 made of (Al _0.7 Ga _0.3 ) _0.51 In _0.49 P, and p-type Ga _0.51 In _{0. 49} P A protective layer 17 having a thickness of 50 nm and a contact layer 18 having a thickness of 0.4 μm made of p-type GaAs are formed in this order. In this step, the quantum well active layer 14 forms a strained quantum well, but the quantum well active layer 14 may be composed of an unstrained quantum well or a bulk compound semiconductor. The conductivity type of each layer constituting the quantum well active layer 14 is not particularly described, but may be p-type, n-type, or undoped.

  Next, as shown in FIG. 10B, after removing the substrate from the MOCVD or MBE reactor, a resist pattern 50 is formed by photolithography, and using this pattern as a mask, a sulfuric acid-based or hydrochloric acid-based etching solution is used. The portion of the compound semiconductor layer on the n-type GaAs substrate 10 where the mask is not formed is removed.

Next, as shown in FIG. 10C, after removing the resist pattern 50, the buffer layer 21 made of n-type GaAs and having a thickness of 0.5 μm is formed on the entire surface of the substrate by using the MOCVD method or the MBE method. , (Al _0.7 Ga _0.3 ) _0.51 In _0.49 P and a 2.0 μm thick n-type cladding layer 22, and (Al _0.5 Ga _0.5 ) _0.5 1In _{0. A} first guide layer 23g1 made of 49P, a strained quantum well active layer 23 having barrier layers 23b1, 23b2 made of well layers 23w1, 23w2, 23w3 and AlGaInP made of GaInP, a second guide layer 23g2 made of AlGaInP, _(Al 0.7 _{Ga 0.3)} 0.51 and p-type cladding layer 24 made of _{an In 0.49} P, a p-type _Ga 0.51 _{In 0.49} P thickness A protective layer 25 of 0 nm, are sequentially formed and a contact layer 26 having a thickness of 0.4μm made of p-type GaAs.

  Next, as shown in FIG. 10D, a resist pattern 27 is formed on the contact layer 26 by photolithography, and using this as a mask, a sulfuric acid-based or hydrochloric acid-based etching solution is used, and the portion where the mask is not formed That is, among the buffer layer 21, the n-type cladding layer 22, the first guide layer 23g1, the strained quantum well active layer 23, the second guide layer 23g2, the p-type cladding layer 24, the protective layer 25, and the contact layer 26, an infrared laser The part formed in the part is removed.

  Next, as shown in FIG. 11A, after removing the resist pattern 27, a diffusion source 30 and a cap film are deposited on the contact layers 18 and 26 using an atmospheric pressure thermal CVD method (370 ° C.). After patterning to have a window length set by photolithography and dry etching technology, Zn is diffused into the active layer by thermal annealing to form a window region.

  Next, as shown in FIG. 11B, a silicon oxide film 31 is deposited on the contact layers 18 and 26 so as to have a thickness of 0.3 μm by using an atmospheric pressure thermal CVD method (370 ° C.). The silicon oxide film 31 is patterned by lithography and dry etching technology to form a stripe mask. Subsequently, the contact layers 18 and 26, the protective layers 17 and 25, and the p-type cladding layers 16 and 24 are sequentially and selectively etched using the stripe-shaped silicon oxide film as a mask to form a mesa-like structure on the heterostructure substrate. A ridge is formed.

  Next, as shown in FIG. 11B, the silicon oxide film 31 is removed, and a SiN film is deposited on the entire surface of the substrate by 0.3 μm.

Thereafter, as shown in FIG. 11C, a resist is applied to the entire surface of the substrate, and only the upper portion of the ridge is opened by photolithography, and SiN on the upper portion of the ridge is removed by etching. The current blocking layer 19 made of a dielectric film is a film for making a difference in refractive index from the cladding layer, but SiN, SiO ₂ , TiO ₂ , Al ₂ O ₃ , hydrogenated amorphous Si, or those It is desirable to be composed of a material having a multilayer structure.

  In forming the window structure, both the red laser and the infrared laser are formed with the same thermal history. Therefore, the number of element manufacturing steps can be reduced, and the element manufacturing cost can be reduced.

The compositions of the n-type cladding layer 12 and the p-type cladding layer 16 are not limited to those described above (Al _x Ga _1-x ) _y In _1-y P (0 ≦ x ≦ 1, 0 ≦ y ≦ 1). It may be Al _z Ga _1-z As (0 ≦ z ≦ 1).

  In the infrared laser, the Al composition is such that the guide layer on the well layer 14w1 is a single layer, the Al composition on the well layer side of the guide layer is small, and the Al composition increases toward the p-type cladding layer 16 side. May be changed step by step.

  The two-wavelength semiconductor laser device of the present invention is used in various devices such as an optical disk device that perform upper writing and reading using a laser beam.

It is sectional drawing which shows the structure of the semiconductor laser apparatus which concerns on embodiment of this invention. (A)-(d) is a figure which shows the measurement result of Zn density | concentration distribution when changing Al composition of a guide layer from 0.5 to 0.7. It is a figure which shows the relationship between the film thickness of a guide layer, and the vertical divergence angle of a laser beam about the case where Al composition (Xg) of a guide layer is changed to 0.5-0.7. FIG. 6 is a diagram illustrating a calculation result of a relationship between a vertical divergence angle of light and a thickness of the guide layer when the guide layer on the well layer is composed of a plurality of layers having the same film thickness and different Al compositions. is there. It is a figure which shows the measurement result of the current-voltage characteristic of an infrared laser in the semiconductor laser apparatus which concerns on embodiment of this invention shown in FIG. 1, and the conventional semiconductor laser apparatus. It is a figure which shows the measurement result of the optical output-current characteristic in 85 degreeC of embodiment of this invention, and the conventional infrared laser. It is a figure which shows the measurement result of the voltage-current characteristic in 85 degreeC, pulse width 50ns, and duty 40% of embodiment of this invention and the conventional infrared laser. It is a figure which shows the measurement result of the optical output-current characteristic in 85 degreeC, pulse width 50ns, and duty 40% of embodiment of this invention and the conventional infrared laser. It is a figure which shows the measurement result of the optical output-current characteristic in 85 degreeC, pulse width 50ns, and duty 40% of the red laser which concerns on embodiment of this invention. (A)-(d) is sectional drawing which shows the manufacturing process of the semiconductor laser apparatus which concerns on embodiment of this invention. (A)-(d) is sectional drawing which shows the manufacturing process of the semiconductor laser apparatus which concerns on embodiment of this invention. It is a figure which shows one Example of the conventional integrated semiconductor laser apparatus. It is sectional drawing which shows the 2 wavelength semiconductor laser apparatus which is a semiconductor laser apparatus concerning a 2nd prior art example.

Explanation of symbols

10 n-type GaAs substrate
11, 21 Buffer layer
12, 22 n-type cladding layer
13 First guide layer
14 Quantum well active layer
14b1 barrier layer
14w1, 14w2 well layer
15g2 second guide layer
15g1 3rd guide layer
16, 24 p-type cladding layer
17, 25 Protective layer
18, 26 Contact layer
19 Current blocking layer
23 Strained quantum well active layer
23b1, 23b2 barrier layer
23g1 first guide layer
23g2 Second guide layer
23w1, 23w2, 23w3 well layer
25 Protective layer
26 Contact layer
27, 50 resist pattern
30 Diffusion source
31 Silicon oxide film

Claims (9)

A substrate and a clad layer made of an AlGaInP-based material, a first semiconductor laser formed on the substrate, and light having a wavelength shorter than that of the first semiconductor laser are output and formed on the substrate A second semiconductor laser,
The first semiconductor laser is:
A first conductivity type first cladding layer formed above the substrate;
A first guide layer of the first conductivity type formed on the first cladding layer;
A first active layer formed on the first guide layer and comprising AlGaAs;
A second guide layer of a second conductivity type formed on the active layer and having an Al composition at the interface with the active layer smaller than the Al composition at the top surface;
A semiconductor laser device having a second conductivity type cladding layer formed on the second guide layer.   The semiconductor laser device according to claim 1, wherein the second guide layer is made of AlGaAs.   The second guide layer is formed on the third guide layer having an Al composition of 0.5 or less and in contact with the active layer, and a fourth guide layer having an Al composition of 0.55 or more. The semiconductor laser device according to claim 1, further comprising a guide layer.   4. The semiconductor laser device according to claim 3, wherein an Al composition of the fourth guide layer is 0.6 or more.   5. The semiconductor laser device according to claim 1, wherein a film thickness of the second guide layer is 20 nm or more and 43 nm or less. The first clad layer and the second clad layer are composed of (Al _x Ga _1-x ) _y In _1-y P (0 ≦ x ≦ 1, 0 ≦ y ≦ 1). The semiconductor laser device according to any one of claims 1 to 5. The second semiconductor laser includes a second active layer having a quantum well structure including (Al _x Ga _1-x ) _y In _1-y P (0 ≦ x ≦ 1, 0 ≦ y ≦ 1). The semiconductor laser device according to claim 1, wherein the semiconductor laser device is a semiconductor laser device.   The light output end face portion of the first active layer of the first semiconductor laser and the second active layer of the second semiconductor laser are disordered by impurity diffusion. 8. The semiconductor laser device according to 7. A substrate,
A first cladding layer of a first conductivity type formed above the substrate and made of an AlGaInP-based material;
A first guide layer of the first conductivity type formed on the first cladding layer;
A first active layer formed on the first guide layer and comprising AlGaAs;
A second guide layer of a second conductivity type formed on the active layer and having an Al composition at the interface with the active layer smaller than the Al composition at the top surface;
A semiconductor laser device comprising: a second conductivity type cladding layer formed on the second guide layer and made of an AlGaInP-based material.

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