JP2007317731A - Semiconductor laser element, optical disk device, and optical transmission system - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a semiconductor laser element having a higher slope efficiency for enabling low power consumption (low threshold current) operation. <P>SOLUTION: A p-side electrode 115 is formed on the element itself 100 of a semiconductor laser element having the oscillation wavelength λ. A first electrode layer 115a of the p-side electrode 115 satisfies the relationships of n<SB>EFF</SB>-n<SB>E1</SB>≥1, d<SB>1</SB>≥λ/(4πk<SB>1</SB>), while a second electrode layer 115b of the p-side electrode 115 satisfies the relationships of n<SB>EFF</SB>-n<SB>E2</SB><1, d<SB>2</SB><λ/(4πk<SB>2</SB>). The character n<SB>EFF</SB>is an effective refractive index of the light having the oscillation wavelength λ of the element itself 100, n<SB>E1</SB>is an effective refractive index of the light having the wavelength λ of the first electrode layer 115a, d<SB>1</SB>is thickness of the first electrode layer 115a, k<SB>1</SB>is an extinction coefficient of the light having the oscillation wavelength λ of the first electrode layer 115a, n<SB>E2</SB>is an effective refractive index of the light having the oscillation wavelength λ of the second electrode layer 115b, d<SB>2</SB>is thickness of the second electrode layer 115b, and k<SB>2</SB>is an extinction coefficient of the light having the oscillation wavelength λ of the second electrode layer 115b. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a semiconductor laser element, and typically relates to a semiconductor laser element suitably used for a pickup of an optical disc apparatus, an optical transmission module part of an optical transmission system, and the like.

  The present invention also relates to an optical disc apparatus and an optical transmission system provided with such a semiconductor laser element.

  Semiconductor laser elements are widely used in optical disk devices and optical transmission systems. Among them, a semiconductor laser element called a ridge embedded type is known as a semiconductor laser element having high reliability and capable of operating with low power consumption (low threshold current).

  However, the ridge-embedded semiconductor laser element forms a current confinement layer in addition to the first crystal growth step performed to form a semiconductor layer including an active layer and a cladding layer on a substrate in the manufacturing process. The second crystal growth step for forming the contact layer and the third crystal growth step for forming the contact layer are required, and the manufacturing process must be performed through a complicated manufacturing process. Therefore, the manufacturing cost is high and the yield is high. There was a problem of being bad.

  Therefore, as a conventional semiconductor laser element that can be easily manufactured at a lower cost, there is a ridge waveguide type semiconductor laser element that has a ridge portion on an active layer and can be manufactured by a single crystal growth process (for example, Patent Document 1). (See JP-A-4-111375).

  FIG. 9 schematically shows a cross section of the ridge waveguide semiconductor laser element. This ridge waveguide type semiconductor laser device is manufactured as follows.

  First, an n-type InGaP cladding layer 402, an InGaAs / GaAs strained quantum well active layer 403, and a p-type InGaP cladding layer are formed on an n-type GaAs substrate 401 by MOCVD (Metal Organic Chemical Vapor Epitaxy). 404 and a p-type InGaAs contact layer 405 are sequentially stacked and etched halfway through the p-type InGaP clad layer 404 by a technique such as photolithography to form a mesa serving as a ridge portion. Pt / Au is sequentially deposited, and AuGe / Ni / Au is sequentially deposited as the n-side electrode 407.

  When a current is passed through the ridge waveguide semiconductor laser device manufactured in this way, a Schottky junction 408 is formed between the p-type InGaP cladding layer 404 and the p-side electrode 406, Current flows only between the p-type InGaAs contact layer 405 and current confinement is performed.

  As described above, the ridge buried type semiconductor laser device requires a total of three crystal growth steps and a complicated manufacturing process, but the ridge waveguide type semiconductor laser device requires only one crystal growth step. In addition, the ridge waveguide semiconductor laser element has a structure that uses a Schottky junction instead of a structure called an air ridge using an insulating film for current confinement with respect to the ridge. There is an advantage that it can be manufactured at a lower cost.

  However, it has been found that the ridge waveguide type semiconductor laser device has the following problems.

  That is, the ridge waveguide type semiconductor laser element is different from a ridge buried type semiconductor laser element or a ridge waveguide type semiconductor laser element having a configuration called an air ridge, and the electrode is in direct contact with the side surface of the ridge portion. In addition, the electrode is in direct contact with the surface of the cladding layer extending outward from the ridge portion. In this case, depending on the relationship between the refractive index of the semiconductor material constituting the ridge waveguide type semiconductor laser element and the refractive index of the metal material constituting the electrode, the oscillated laser light distribution may cause the side surface of the ridge portion and the ridge. It was found that it spreads to the surface of the cladding layer in the vicinity of the portion and leaks to the electrode formed thereon.

  For example, in the ridge waveguide semiconductor laser device of Patent Document 1, the refractive index of the metal material used for the electrode on the ridge portion side is approximately in the range of 650 nm to 1.5 μm for Ti in contact with the semiconductor layer. 3.0 to 3.6, and Pt provided on the upper side of Ti is 2.9 to 5.5 in the same wavelength range of 668 nm to 1.5 μm. On the other hand, the effective refractive index in the direction perpendicular to the substrate outside the ridge is about 3.2.

  Thus, when the effective refractive index in the direction perpendicular to the substrate outside the ridge portion is close to the refractive index of the electrode material directly formed on the semiconductor layer, or from the effective refractive index. However, if the refractive index of the electrode material is larger, the oscillated laser beam may easily leak toward the electrode.

When the laser beam leaks to the electrode, the light absorption coefficient of the metal material constituting the electrode is generally about 10 ⁴ to 10 ⁵ times larger than the light absorption coefficient of the semiconductor material. Absorption occurs, and internal loss is greatly increased.

Accordingly, it has been found that the ridge waveguide semiconductor laser device has problems that the slope efficiency is lowered and the oscillation threshold current value is raised.
Japanese Patent Laid-Open No. 4-111375 (page 3, FIG. 1)

  Accordingly, an object of the present invention is to provide a semiconductor laser device having high slope efficiency and capable of operating with low power consumption (low threshold current).

  Another object of the present invention is to provide an optical disc apparatus and an optical transmission system provided with such a semiconductor laser element.

In order to solve the above problems, the semiconductor laser device of the present invention is
A body having a first conductivity type substrate and a semiconductor layer group formed on the first conductivity type substrate and including at least a first conductivity type cladding layer, an active layer, and a second conductivity type cladding layer. In the semiconductor laser device having the oscillation wavelength λ provided,
An electrode made of a metal material is formed on the semiconductor layer group,
The metal material has a refractive index n _E of the light having the oscillation wavelength λ,
The electrode is
A first electrode layer having an effective refractive index n _E1 of light having the oscillation wavelength λ;
A second electrode layer formed on the first electrode layer, the effective refractive index of the light having the oscillation wavelength λ being n _E2 ;
A third electrode layer made of Au and formed on the second electrode layer;
The first and second electrode layers are
n _EFF −n _E1 ≧ 1
d ₁ ≧ λ / (4πk ₁ )
n _EFF −n _E2 <1
d ₂ <λ / (4πk ₂ )
Where n _{EFF is} the effective refractive index of the light having the oscillation wavelength λ of the main body.
d ₁ : thickness of the first electrode layer [nm]
k ₁ : extinction coefficient of light having the oscillation wavelength λ of the first electrode layer
d ₂ : thickness of the second electrode layer [nm]
k ₂ : It is characterized by satisfying the relationship of the extinction coefficient of the light having the oscillation wavelength λ of the second electrode layer.

  Here, “first conductivity type” refers to one conductivity type of n-type and p-type, and “second conductivity type” refers to the other conductivity type of n-type and p-type. That is, when the first conductivity type is p-type, the second conductivity type indicates n-type, and when the first conductivity type is n-type, the second conductivity type indicates p-type.

The “effective refractive index” is an amount (c: speed of light) that determines the phase velocity (= c / n _EFF ) of the oscillation laser light propagating through the main body, and the “extinction coefficient” is the complex refractive index. N (˜) = imaginary part in n−ik.

According to the semiconductor laser device having the above-described configuration, on the semiconductor layer group including the cladding layer of the second conductivity type, the _first relationship is satisfied so that the relationship of n _EFF −n _E1 ≧ 1 and d ₁ ≧ λ / (4πk ₁ ) is satisfied. 1 is formed, and a second electrode layer is formed on the first electrode layer so as to satisfy the relationship of n _EFF −n _E2 <1 and d ₂ <λ / (4πk ₂ ), By forming the third electrode layer made of Au on the second electrode layer, the oscillated laser beam can be confined in the semiconductor layer group without leaking to the electrode layer.

This is because an oscillation laser beam is formed by forming a metal material having a low refractive index satisfying n _EFF −n _E2 ≧ 1 to a thickness of d ₁ ≧ λ / (4πk ₁ ) as the first electrode layer. This is because the semiconductor layer can be sufficiently confined in the semiconductor layer group.

Further, by limiting the thickness d ₂ of the second electrode layer having a relatively high refractive index such that n _EFF −n _E2 <1, the second electrode layer is limited to d ₂ <λ / (4πk ₂ ). It becomes possible to suppress the influence of light absorption due to.

  As a result, it is possible to provide a semiconductor laser device having a low oscillation threshold current and a high slope efficiency and capable of operating with low power consumption.

  In addition, it is desirable to provide another electrode that forms an ohmic junction with this surface on the surface opposite to the surface on the semiconductor layer group side with respect to the first conductivity type substrate.

  By providing the other electrode, it is possible to easily conduct electricity between the electrode on the semiconductor layer group and the other electrode.

In the semiconductor laser device of one embodiment,
A part of the semiconductor layer group on the electrode side constitutes a striped ridge portion,
The electrode is in contact with the top of the ridge portion, and is in contact with at least one of a side surface of the ridge portion and a surface of the semiconductor layer group excluding the ridge portion and in the vicinity of the ridge portion.

  According to the semiconductor laser device of the above embodiment, at least one of the side surface of the ridge portion and the surface of the semiconductor layer group excluding the ridge portion and in the vicinity of the ridge portion is in contact with the top of the ridge portion. By forming the electrodes so as to be in contact with each other, the crystal growth process at the manufacturing stage can be completed only once as in the case of the ridge waveguide semiconductor laser element of Patent Document 1.

  Therefore, as compared with a general ridge-embedded semiconductor laser element, a manufacturing process can be greatly reduced, and a semiconductor laser element that can be manufactured at low cost can be provided.

In the semiconductor laser device of one embodiment,
The top of the ridge portion forms an ohmic junction with the electrode,
At least one of the side surface of the ridge portion and the surface of the second conductivity type semiconductor layer group excluding the ridge portion and in the vicinity of the ridge portion forms a Schottky junction with the electrode. Yes.

  According to the semiconductor laser device of the above embodiment, the top of the ridge portion forms an ohmic junction with the electrode, and is a region excluding the side surface of the ridge portion and the ridge portion of the second conductivity type semiconductor layer group. Thus, at least one of the surfaces near the ridge portion forms a Schottky junction with the electrode, so that it is not necessary to re-grow a new semiconductor layer or form an insulating film for current confinement. .

  Therefore, in the semiconductor laser device, the manufacturing process can be simplified, and the yield can be improved and the manufacturing cost can be reduced.

  Further, in the semiconductor laser device, even if the electrode is in direct contact with the vicinity of the ridge portion, the oscillated laser beam does not leak to the electrode.

In the semiconductor laser device of one embodiment,
The second electrode layer has a laminated structure in which two or more metal materials are laminated,
Each layer An (n = 1, 2,..., Q, where q is a natural number of 2 or more) of the second electrode layer has a refractive index n _E2n (n = 1, 2, 1) of the light having the oscillation wavelength λ. , ..., q, where q is a natural number of 2 or more)
Each layer of the second electrode layer is
n _EFF -n _E2n <1
Satisfy the relationship
The second electrode layer is
d _total <λ / 4πk _average
d _total : _total thickness [nm] of all the second electrode layers
k _average : satisfies the relationship of the average value of the extinction coefficient of the light having the oscillation wavelength λ of each layer of the second electrode layer.

According to the semiconductor laser device of the above embodiment, when the second electrode layer has a stacked structure in which two or more metal materials are stacked and each layer satisfies n _EFF −n _E2n <1, When the electrode layer is formed so as to satisfy the d _total <λ / 4πk _average , the refractive index close to the effective refractive index n _EFF of the light having the oscillation wavelength λ of the main body or a refractive index larger than the effective refractive index n _EFF is obtained. The influence on the confinement of the oscillation laser light by the second electrode layer made of a metal material having the above can be reduced.

In the semiconductor laser device of one embodiment,
A part of the semiconductor layer group on the electrode side constitutes a striped ridge portion,
The electrode is in contact with the top of the ridge portion, and is in contact with at least one of the side surface of the ridge portion and the surface of the semiconductor layer group excluding the ridge portion and in the vicinity of the ridge portion;
The top of the ridge portion is formed of a high concentration semiconductor layer having a second conductivity type doping concentration of 1 × 10 ¹⁸ cm ⁻³ or more,
At least one of the side surface of the ridge portion and the surface region excluding the ridge portion of the semiconductor layer group includes a low-concentration semiconductor layer having a second conductivity type doping concentration of 1 × 10 ¹⁷ cm ⁻³ or less. ,
A semiconductor layer having a second conductivity type doping concentration of 1 × 10 ¹⁷ cm ⁻³ or more is formed between the low concentration semiconductor layer and the active layer.

According to the semiconductor laser device of the above embodiment, the top of the ridge portion is formed of a high-concentration semiconductor layer having a second conductivity type doping concentration of 1 × 10 ¹⁸ cm ⁻³ or more, thereby realizing a good ohmic junction. it can.

Further, at least one of the side surface of the ridge portion and the surface region excluding the ridge portion of the semiconductor layer group is formed of a low concentration semiconductor layer having a second conductivity type doping concentration of 1 × 10 ¹⁷ cm ⁻³ or less. As a result, a Schottky junction excellent in current confinement and reliability can be obtained.

Further, between the low-concentration semiconductor layer and the active layer above the doping concentration of the second conductivity type is 1 × ¹⁰ 17 ^{cm -3,} the doping concentration of the second conductivity type is 1 × ¹⁰ 17 ^{cm -3} or more By forming the semiconductor layer, in optical design, by changing the layer thickness and composition of the semiconductor layer having the second conductivity type doping concentration of 1 × 10 ¹⁷ cm ⁻³ or more, Schottky junction characteristics The design satisfying the specifications required for the device can be achieved without changing the configuration of the second conductivity type low-concentration semiconductor layer doped to 1 × 10 ¹⁷ cm ⁻³ or less, which affects the above.

In addition, since the semiconductor layer having the second conductivity type doping concentration of 1 × 10 ¹⁷ cm ⁻³ or more is doped to the same concentration or higher than the second conductivity type doping concentration of the low-concentration semiconductor layer, the element An increase in resistance can be suppressed and further reduction in power consumption can be achieved.

In the semiconductor laser device of one embodiment,
At least one of the side surface of the ridge portion and the surface of the second conductivity type semiconductor layer group excluding the ridge portion and in the vicinity of the ridge portion forms a Schottky junction with the electrode,
The substrate is made of GaAs,
The low-concentration semiconductor layer has at least an AlGaAs layer and an InGaAsP layer,
The portion forming the Schottky junction with respect to the second conductivity type semiconductor layer group includes the InGaAsP layer.

  According to the semiconductor laser device of the above embodiment, by forming an AlGaAs layer on the GaAs substrate, the AlGaAs layer can be used as an optical confinement layer (cladding layer).

  Further, by forming an InGaAsP layer on the GaAs substrate, the InGaAsP layer can be used as a layer for forming a Schottky junction.

  In addition, by covering the AlGaAs layer with an InGaAsP layer that does not contain Al, an easily oxidized AlGaAs layer is not exposed to the atmosphere, so that the generation of deep levels due to Al oxidation is suppressed. In addition, long-term reliability can be improved, and absorption due to deep levels can be reduced.

  Further, by covering the AlGaAs layer with an InGaAsP layer that does not contain Al and forming an electrode directly on the InGaAsP layer to form a Schottky junction, the leakage current of the Schottky junction can be greatly reduced. it can.

  There is an InGaP layer as a semiconductor layer that does not contain Al and can be expected to have the same effect as the InGaAsP layer. However, InGaP has a large barrier against holes and has a refractive index due to natural superlattice formation. The InGaAsP semiconductor layer is more preferable than the InGaP layer because of its demerits such as being easily fluctuated.

In the semiconductor laser device of one embodiment,
The metal material constituting the first electrode layer includes at least one element selected from Ag, Al, Au, Cu, Nd, Pb, Rh, and Ta.

According to the semiconductor laser device of the above embodiment, the metal material constituting the first electrode layer is made of at least one element selected from Ag, Al, Au, Cu, Nd, Pb, Rh and Ta. By including, it becomes easy to form the first electrode layer satisfying the equation of n _EFF −n _E1 ≧ 1, and it becomes easy to improve the effect of confining the oscillation laser light in the main body.

In the semiconductor laser device of one embodiment,
The metal material constituting the second electrode layer includes at least one element selected from Cr, Mo, Ni, Os, Pd, Pt, Rd, Sb, Ti, W, and Zn.

According to the semiconductor laser device of the embodiment, the metal material constituting the second electrode layer is selected from Cr, Mo, Ni, Os, Pd, Pt, Rd, Sb, Ti, W, and Zn. Forming a second electrode layer satisfying the formula n _EFF −n _E2 <1 by including at least one element, improving adhesion of the second electrode layer to the first electrode layer, In addition, it becomes easy to prevent Au, which is the metal material of the third electrode layer, from diffusing into the second conductivity type semiconductor layer group.

  Therefore, by forming the second electrode layer with a metal material containing at least one element selected from Cr, Mo, Ni, Os, Pd, Pt, Rd, Sb, Ti, W and Zn, The electrode having the first, second, and third electrode layers can maintain low contact resistance for a long period without deteriorating element characteristics.

  The optical disk apparatus of the present invention is characterized by including the semiconductor laser element of the present invention.

  According to the optical disk apparatus having the above configuration, by using the semiconductor laser element of the present invention, writing can be performed with lower power consumption and cost can be reduced as compared with the conventional optical disk apparatus.

  The optical transmission system of the present invention is characterized by including the semiconductor laser device of the present invention.

  According to the optical transmission system configured as described above, by using the semiconductor laser element of the present invention, it is possible to operate at lower cost and with lower power consumption than the conventional optical transmission system, and to achieve lower cost and higher performance. it can.

  According to the semiconductor laser device of the present invention, the absorption loss of the oscillation laser light by the electrode provided on the ridge portion side (especially, the electrode provided in a region other than the uppermost portion of the ridge portion) can be suppressed. Can be reduced. Moreover, since it has a simple structure, manufacture is easy and a yield can be improved. Therefore, it is possible to provide a semiconductor laser device that has high slope efficiency, can operate with low power consumption (low threshold current), and can be manufactured at low cost.

  According to the optical disk apparatus of the present invention, by using the semiconductor laser element of the present invention, data writing can be performed with low power consumption as compared with the conventional optical disk apparatus, and the structure is more inexpensive.

  According to the optical transmission system of the present invention, by using the semiconductor laser element of the present invention, it is possible to provide an optical transmission module that can be operated at lower cost and with lower power consumption than the conventional one. And high performance can be achieved.

  Hereinafter, a semiconductor laser device, an optical disk device, and an optical transmission system of the present invention will be described in detail with reference to the illustrated embodiments.

  In the following description, “n−” represents the n-type as the first conductivity type, and “p−” represents the p-type as the second conductivity type.

[First Embodiment]
FIG. 1 schematically shows a cross section of the semiconductor laser device according to the first embodiment of the present invention.

  The semiconductor laser element includes a main body 100, a p-side electrode 115 formed on the main body 100, and an n-side electrode 116 formed below the main body 100, and has an oscillation wavelength of 890 nm.

The main body 100 includes an n-GaAs substrate 101, an n-GaAs buffer layer 102, an n-Al _0.5 Ga _0.5 As first lower cladding layer 103, and an n-GaAs buffer layer 102 sequentially stacked on the n-GaAs substrate 101, n -Al _0.422 Ga _0.578 As second lower cladding layer 104, Al _0.25 Ga _0.75 As lower guide layer 105, multiple strain quantum well active layer 106, Al _0.25 Ga _0.75 As first Upper guide layer 107, p-Al _0.4 Ga _0.6 As second upper guide layer 108, p-Al _0.456 Ga _0.544 As first upper cladding layer 109, p-Al _0.456 Ga _{0. 544} As second upper cladding layer 110 and p-In _0.1568 Ga _0.8432 As _0.4 P _0.6 semiconductor layer 111. The n-GaAs substrate 101 is an example of a first conductivity type substrate, the n-Al _0.5 Ga _0.5 As first lower cladding layer 103 is an example of a first conductivity type cladding layer, and n-Al ₀ An example of _.422 Ga _0.578 As an example of the second lower cladding layer 104 is clad layer of the first conductivity type, multiple strained quantum well active layer 106 is an active _layer, p-Al _{0.456 Ga 0.544} As first The upper cladding layer 109 is an example of a second conductivity type cladding layer, and the p-Al _0.456 Ga _0.544 As second upper cladding layer 110 is an example of a second conductivity type cladding layer. In addition, the p-Al _0.456 Ga _0.544 As second upper cladding layer 110 and the p-In _0.1568 Ga _0.8432 As _0.4 P _0.6 semiconductor layer 111 are an example of a low concentration semiconductor layer. Is configured. The p-Al _0.4 Ga _0.6 As second upper guide layer 108 and the p-Al _0.456 Ga _0.544 As first upper cladding layer 109 are composed of a low-concentration semiconductor layer, an active layer, It is an example of the semiconductor layer formed between.

On the p-In _0.1568 Ga _0.8432 As _0.4 P _0.6 semiconductor layer 111, a p-Al _0.5 Ga _0.5 As-th layer is formed so as to form a forward mesa stripe-shaped ridge 130. 3 An upper cladding layer 112, a p-GaAs contact layer 113, and a p ⁺ -GaAs contact layer 114 are provided. The p-Al _0.5 Ga _0.5 As third upper cladding layer 112 is an example of a second conductivity type cladding layer, and the p ⁺ -GaAs contact layer 114 is an example of a high-concentration semiconductor layer. The layers from the n-Al _0.5 Ga _0.5 As first lower cladding layer 103 to the p ⁺ -GaAs contact layer 114 toward the p-side electrode 115 constitute an example of a semiconductor layer group.

  The p-side electrode 115 is provided so as to cover the ridge 130 and the semiconductor layer 111 on both sides of the ridge 130. More specifically, the p-side electrode 115 is in contact with the top and side portions of the ridge 130 and the upper portion of the semiconductor layer 111 below both sides of the ridge 13. The p-side electrode 115 has a configuration in which a first electrode layer 115a made of Ag, a second electrode layer 115b made of Ti and Pt, and a third electrode layer 115c made of Au are sequentially stacked. It has become.

The effective refractive index n _EFF for the light having the oscillation wavelength λ (= 890 nm) of the main body 100 is 3.273.

The first electrode layer 115a is the effective refractive index _{n E1} of light of the oscillation wavelength lambda, the effective refractive index _{n E1} meets _n EFF _{-n E1} ≧ 1 the relationship. Specifically, Ag constituting the first electrode layer 115a has a refractive index n _Ag of 0.105 for light in the vicinity of the oscillation wavelength λ.

In the second electrode layer 115b, the effective refractive index of light having the oscillation wavelength λ is n _E2 , and the effective refractive index satisfies the relationship that n _E2 is n _EFF −n _E2 <1. Specifically, in Ti and Pt constituting the second electrode layer 115b, Ti has a refractive index n _Ti for light near the oscillation wavelength λ of 3.25, while Pt is near the oscillation wavelength λ. The refractive index n _Pt for light is 3.16.

  The n-side electrode 116 is made of a multilayer metal thin film of AuGe / Ni / Au, and is in contact with the back surface of the n-GaAs substrate 101 (surface opposite to the surface on the p-side electrode side).

  In FIG. 1, reference numeral 117 denotes a ridge formation region, and 118 denotes a region outside the ridge formation.

  Next, a method for manufacturing the semiconductor laser device will be described with reference to FIGS.

First, as shown in FIG. 2, an n-GaAs buffer layer 102 (layer thickness: 0.5 μm, Si doping concentration: 7.2 × 10 ¹⁷ cm ^{− is formed} on the (100) plane of the n-GaAs substrate 101-1. ³ ), n-Al _0.5 Ga _0.5 As first lower cladding layer 103 (layer thickness: 2.0 μm, Si doping concentration: 5.4 × 10 ¹⁷ cm ⁻³ ), n-Al _0.422 Ga _0.578 As second lower cladding layer 104 (layer thickness: 0.1 μm, Si doping concentration: 5.4 × 10 ¹⁷ cm ⁻³ ), Al _0.25 Ga _0.75 As lower guide layer 105 (layer thickness 3 0.0 nm, non-doped), multiple strain quantum well active layer 106 (non-doped), Al _0.25 Ga _0.75 As first upper guide layer 107 (layer thickness: 3.0 nm, non-doped), p-Al _0.4 Ga _0.6 As second upper Guy Layer 108 (thickness: 0.1 [mu] m, Zn doping _{^{concentration: 1.35 × 10 18 cm -3)}} , p-Al 0.456 Ga 0.544 As first upper cladding layer 109 (thickness: 0.2 [mu] m, Zn doping concentration: 1.35 × 10 ¹⁸ cm ⁻³ ), p-Al _0.456 Ga _0.544 As second upper cladding layer 110 (layer thickness: 0.2 μm, Zn doping concentration: 1 × 10 ¹⁷ cm ^{− 3} ), p-In _0.1568 Ga _0.8432 As _0.4 P _0.6 semiconductor layer 111 (layer thickness: 15.0 nm, Zn doping concentration: 1 × 10 ¹⁷ cm ⁻³ ), p-Al _{0. 5} Ga _0.5 As third upper cladding layer 112-1 (layer thickness: 1.28 μm, Zn doping concentration: 2.4 × 10 ¹⁸ cm ⁻³ ), p-GaAs contact layer 113-1 (layer thickness: 0) .2 μm, Zn Ping ^{concentration: 3 × 10 18 cm -3)} , p + -GaAs contact layer 114-1 (thickness: 0.3 [mu] m, Zn doping concentration: 1 × ¹⁰ 19 ^{cm -3)} in sequence, by MOCVD crystal Grow.

The multi-strain quantum well active layer 106 includes an In _0.1 Ga _0.9 As compressive strain quantum well layer (strain: 0.7%, layer thickness: 4.6 nm × 2 layers) and In _0.24 Ga _{0. 76} As _0.55 P _0.45 Tensile strain barrier layer (strain: 0.1%, band gap Eg≈1.60 eV, film thickness from substrate side: 21.5 nm, 7.9 nm, 21.5 nm in three layers The n-side barrier layer is the closest to the substrate 101 and the p-side barrier layer is the farthest one).

  Next, a resist mask 119 (mask width: 4.2 μm) is formed on the region 117a (see FIG. 1) where the ridge 130 is to be formed by a photolithography process. The resist mask 119 is formed so as to extend in a stripe shape in the <0-11> direction corresponding to the direction in which the ridge 130 to be formed extends.

  Next, using the resist mask 119 as a mask, portions of the third upper cladding layer 112-1 and the contact layers 113-1, 114-1 that overlap with the ridge formation outside region 118 (see FIG. 1) are removed by etching. . As a result, a third upper cladding layer 112 and contact layers 113 and 114 as shown in FIG. 3 are obtained immediately below the resist mask 119. That is, a forward mesa stripe ridge 130 is obtained immediately below the resist mask 119.

  The etching is performed to a position just above the semiconductor layer 111 using a mixed aqueous solution of sulfuric acid and hydrogen peroxide solution, and then overhang portions of the contact layers 113-1 and 114-1 are mixed with a mixed aqueous solution of ammonia and hydrogen peroxide solution. Take. The etching depth is 1.78 μm, and the width of the lowermost portion of the ridge 130 is about 2.7 μm.

  Next, after removing the resist mask 119, as shown in FIG. 4, an Ag layer (layer thickness: 50 nm) and a second electrode layer 115b are formed as the first electrode layer 115a by using an electronic boom deposition method. And a Ti layer (layer thickness: 5 nm) and a Pt layer (layer thickness: 8 nm), and an Au layer (layer thickness: 300 nm) as the third electrode layer 115c in this order. Thereby, the p-side electrode 115 made of the Ag layer, Ti layer, Pt layer, and Au layer is obtained.

  Thereafter, the n-GaAs substrate 101-1 is ground by a lapping method from the back surface side to a desired thickness (here, about 100 μm). Thereby, the n-GaAs substrate 101 shown in FIG. 1 is obtained.

  Then, an AuGe alloy layer (Au: 88% and Ge: 12% alloy, layer thickness: 100 nm), Ni layer (layer thickness: 15 nm) is formed from the back side of the n-GaAs substrate 101 by resistance heating evaporation. And an Au layer (layer thickness: 300 nm) are stacked in this order. As a result, the n-side electrode 116 made of the AuGe alloy layer, Ni layer, and Au layer is obtained.

Subsequently, the n-side electrode 116 is alloyed by heating at 390 ° C. for 1 minute in an N ₂ atmosphere.

  Next, after dividing the n-GaAs substrate 101 into a plurality of bars having a desired resonator length (here, 500 μm), the bar is coated with an end face, and the bars are further formed into chips (500 μm × 250 μm). Divide into The divided chip is fixed on a stem (not shown) using In glue, and an Au wire (not shown) for electrical connection with an external circuit is bonded on the p-side electrode 115. Thus, the semiconductor laser device according to the first embodiment of the present invention is completed.

In the semiconductor laser device manufactured as described above, when a current is passed between the p-side electrode 115 and the n-side electrode 116, a gap between the p-InGaAsP semiconductor layer 111 and the p-side electrode 115 on the side of the ridge 130 is obtained. As a result, a Schottky junction is formed and the current is cut off. At this time, a current flows only through an ohmic junction between the p ⁺ -GaAs contact layer 114 at the top of the ridge 130 and the p-side electrode 115. Thereby, current confinement is realized.

  Since the semiconductor laser device of this embodiment can complete the crystal growth process once in the manufacturing stage, the manufacturing process is greatly reduced compared with a general ridge-embedded semiconductor laser device, and the cost is low. It became possible to produce.

Further, in the semiconductor laser device of the present embodiment, the effective refractive index for the light with the oscillation wavelength λ of the main body 100 is n _EFF, and the extinction coefficient for the light with the oscillation wavelength λ of the first electrode layer 115a is k ₁ . when, the first electrode layer 115a satisfies the equation of refractive index _{n E1} is _n EFF _{-n E1} ≧ 1 with respect to light of the oscillation wavelength lambda, the thickness _d 1 [nm] is _{d 1} ≧ λ / _{(4πk 1} ). The first electrode layer 115a is composed of an Ag layer.

On the other hand, the second electrode layer 115b has a refractive index _{n E2} for light of the oscillation wavelength λ is formed so as to satisfy _n EFF _{-n E2} <1 expression. When the extinction coefficient for light of the oscillation wavelength lambda of the second electrode layer 115b was _{k 2,} the thickness _d 2 [nm] of the second electrode layer 115b is _{d 2 <λ / (4πk 2} ) Meet. The second electrode layer 115b is composed of a Ti layer and a Pt layer.

Here, assuming that the extinction coefficients of the Ag layer, Ti layer, and Pt layer with respect to the light having the oscillation wavelength λ are k _Ag , k _Ti , and k _Pt , the thickness d _{Ag of the} Ag layer is d _{Ag Ag} ≧ λ / (4πk _Ag ), The Ti layer thickness d _Ti satisfies the formula d _Ti <λ / (4πk _Ti ), and the Pt layer thickness d _Pt satisfies the formula d _Pt <λ / (4πk _Pt ).

As described above, since the second electrode layer 115b has a two-layer structure including a Ti layer and a Pt layer, the extinction coefficient of the second electrode layer 115b is the same as that of the Ti layer and the Pt layer. The average value k _average of extinction coefficients for light having the oscillation wavelength λ is regarded as k _average (= (d _Ti · k _Ti + d _Pt · k _Pt ) / d _Ti + d _Pt ), and the thickness d _{2 of} the second electrode layer 115b (= d _Ti + d _Pt = d _total ) also satisfies the relationship of d ₂ <λ / (4πk _average ).

Specifically, the effective refractive index n _EFF for the light of the oscillation wavelength λ of the semiconductor laser element is 3.273, the refractive index of the Ag layer for the light of the oscillation wavelength λ is 0.105, and The refractive index of the Ti layer with respect to the light having the oscillation wavelength λ is 3.25, and the refractive index of the Pt layer with respect to the light having the oscillation wavelength λ is 3.16. The extinction coefficient k _Ag of the Ag layer with respect to the light having the oscillation wavelength λ is 6.22, the extinction coefficient k _Ti of the Ti layer with respect to the light having the oscillation wavelength λ is 3.84, and the Pt layer The extinction coefficient k _Pt of the light having the oscillation wavelength λ is 5.38. The average value k _average of the extinction coefficient of the Ti layer with respect to the light having the oscillation wavelength λ and the extinction coefficient of the Pt layer with respect to the light with the oscillation wavelength λ is 4.79.

Accordingly, the Ag layer, Ti layer, the thickness _d Ag of Pt _layer, d _{Ti, d Pt is} filled _{d Ag ≧ 11.4nm, d Ti <} 18.4nm, the d Pt <13.2 nm, and, Ti layer The thickness d _{Ag of the} Ag layer is set to 50 nm so that the thickness d ₂ (= d _Ti + d _Pt ) of the second electrode layer made up of Pt and Pt satisfies d ₂ <14.79 nm. set the thickness _{d Ti} to 5 nm, and set the thickness _{d Pt} of Pt layer 8 nm. Note that the thickness of the Au layer constituting the third electrode layer 115c was set to 300 nm.

As described above, the first electrode layer 115a satisfying the equation n _EFF −n _E1 ≧ 1 is formed so that the thickness d ₁ [nm] satisfies the equation d ₁ ≧ λ / (4πk ₁ ). Thus, the effect of confining the laser light oscillated from the main body 100 in the semiconductor layer is increased, and the light can be prevented from leaking to the first electrode layer 115a. This first electrode layer 115a having a thickness d ₁ having the refractive index n _E1 sufficiently smaller than the effective refractive index n _EFF for light of the oscillation wavelength lambda, the oscillation wavelength of the first electrode layer 115a lambda By forming so that d ₁ ≧ λ / (4πk ₁ ) which is equal to or greater than the reciprocal of the absorption coefficient for light, the effect of preventing the tail portion in the oscillation laser light distribution shape from leaking to the electrode is enhanced. Has been realized.

Further, the second electrode layer 115b satisfying the equation of n _EFF −n _E2 <1 is formed so that the thickness d ₂ [nm] satisfies the equation of d ₂ <λ / (4πk ₂ ). Light absorption by the second electrode layer 115b having a high refractive index can be suppressed. This is because the second electrode layer 115b (thickness: d ₂ , extinction coefficient: k _average ) having a refractive index close to the effective refractive index n _EFF is absorbed by the second electrode layer 115b with respect to the light having the oscillation wavelength λ. By forming d ₂ <λ / (4πk _average ) smaller than the reciprocal of the coefficient, the amount by which the light of wavelength λ is absorbed by the metal material constituting the second electrode layer 115b is 1-1. This can be realized by making it smaller than / e. Note that e is the base of the natural logarithm.

  Therefore, the semiconductor laser device of this embodiment has both a low oscillation threshold current and a high slope efficiency, and can be operated at low power consumption and at low cost.

  The effect of the formation conditions on the first and second electrode layers 115a and 115b is the ridge waveguide semiconductor laser element as in the present embodiment, and further, with respect to the side surface of the ridge and the surface of the upper cladding layer. This is particularly large with respect to those in which electrodes are directly formed.

  The reason for this great effect is that the electrode that acts as an absorber for the oscillation laser beam is formed closer to the light emitting region. In a ridge waveguide semiconductor laser element in which an electrode is formed directly on the surface of the upper cladding layer, it is often difficult to design a semiconductor layer structure that does not leak the oscillation laser light distribution to the electrode. It is.

  In the semiconductor laser device of the present embodiment, the Ti layer of the second electrode layer 115b is formed for the purpose of improving the adhesion of the Au layer that is the third electrode layer 115c. On the other hand, in the Pt layer of the second electrode layer 115b, the Au of the Au layer diffuses to the first electrode layer 115a and the semiconductor layer below it by diffusion, and the threshold current value, efficiency, resistance of the semiconductor laser element It is formed for the purpose of preventing diffusion for preventing the deterioration of the characteristics and reliability.

  Moreover, in the semiconductor laser device of this embodiment, the electrode peeling defect in the manufacturing process is maintained for a long time while maintaining the electrical and optical characteristics of the p-side electrode 115 composed of the Ag layer, Ti layer, Pt layer, and Au layer. Therefore, it is possible to achieve both good device characteristics and good yield. As a result, a semiconductor laser element that can continue to exhibit excellent initial characteristics over a long period of time is provided.

As described above, the effect of configuring the second electrode layer with a plurality of different metals is particularly great when the metal material used as the third electrode layer has poor adhesion and is easily diffused. For example, Au that is suitably used as the electrode material of the third electrode layer is representative of those having poor adhesion and diffusibility. However, the material of the second electrode layer used for this purpose is often a metal having a relatively large refractive index, and the thickness d ₂ of the second electrode layer is set to d ₂ <λ / (4πk as in this embodiment. _If it is not formed so as to satisfy ₂ ), the characteristics of the semiconductor laser element will be deteriorated.

  In the present embodiment, as described above, a Ti layer having a thickness of 5 nm and a Pt layer having a thickness of 8 nm are used. When forming, it is appropriate to set the formation rate (deposition rate) of the metal thin film to about 0.1 to 0.2 nm / second. When the formation rate of the metal thin film is made faster than about 0.2 nm / second, the effect of improving the adhesion of the Ti layer and preventing the diffusion of the Pt layer may be reduced.

In the semiconductor laser device of this embodiment, the p-side electrode 115 is in ohmic contact with the p ⁺ -GaAs contact layer 114 that forms the top of the ridge portion 130, and the side of the ridge portion 130 and the p− The p-side electrode 115 is in Schottky junction with the InGaAsP semiconductor layer 111. As a result, it is possible to obtain a structure capable of interrupting current to other than the top of the ridge without requiring a regrowth process of the semiconductor buried layer which becomes a current confinement layer and an insulating film forming process. A current flows only through the ohmic junction formed on the top of the semiconductor laser device, and a semiconductor laser device in which current confinement is realized with a very simple configuration can be provided.

Further, in the semiconductor laser device of this embodiment, the p-type doping concentration of the ^p + -GaAs contact layer 114 formed on top of the ridge portion 130, 1 × is ¹⁰ 18 ^{cm -3} or more 1 × ^{10 19} By setting to cm ⁻³ , a good ohmic junction was realized. Note that the upper limit of the p-type doping concentration of the p ⁺ -GaAs contact layer 114 is 1 × 10 ²¹ cm from the viewpoint of preventing crystallinity deterioration due to excessive doping and unnecessary diffusion of the dopant in the active layer direction. ^-3 or less is better.

Further, by setting the p-type doping concentration of the p-InGaAsP semiconductor layer 111 and the p-AlGaAs second upper cladding layer 110 to 1 × 10 ¹⁷ cm ⁻³ , the current confinement property and the long-term reliability are excellent. A Schottky junction can be obtained. The range of the p-type doping concentration of the p-InGaAsP semiconductor layer 111 and the p-AlGaAs second upper cladding layer 110 is to achieve both good current confinement and prevention of deterioration of device resistance more than necessary. 1 × 10 ¹⁶ cm ⁻³ or more and 1 × 10 ¹⁷ cm ⁻³ or less are preferable.

Furthermore, in the semiconductor laser device of this embodiment, between the example of the low concentration semiconductor layer composed of the p-InGaAsP semiconductor layer 111 and the p-AlGaAs second upper cladding layer 110 and the multiple strain quantum well active layer 106, A p-AlGaAs second upper guide layer 108 (Zn doping concentration: 1.35 × 10 ¹⁸ cm ⁻³ ) having a p-type doping concentration of 1 × 10 ¹⁷ cm ⁻³ or more and a p-type doping concentration of 1 × 10 6 ^A p-AlGaAs first upper cladding layer 109 (Zn doping concentration: 1.35 × 10 ¹⁸ cm ⁻³ ) of ¹⁷ cm ⁻³ or more is formed, and the p-AlGaAs second upper guide layer 108 and the p-AlGaAs first are formed. (1) By adjusting the composition and layer thickness of the upper cladding layer 109, the required optical characteristics can be achieved without deteriorating the Schottky junction characteristics. It was made possible to provide a semiconductor laser device suitable for the above-mentioned.

Moreover, the p-type doping concentration of the p-AlGaAs second upper guide layer 108 and the p-AlGaAs first upper cladding layer 109 is 1.35 × 10 ¹⁸ higher than the p-type doping concentration of an example of the low-concentration semiconductor layer. Since it is cm ^−3, it is possible to suppress an increase in element resistance and to further reduce power consumption. The p-type doping concentration of the p-AlGaAs second upper guide layer 108 and the p-AlGaAs first upper cladding layer 109 is at least the p-type doping concentration of the p-InGaAsP semiconductor layer 111 and the p-AlGaAs second upper cladding layer 110. It is appropriate to adjust in the range of 1 × 10 ¹⁷ cm ⁻³ or more and 5 × 10 ¹⁸ cm ⁻³ or less.

  In the semiconductor laser device of this embodiment, an example of the low-concentration semiconductor layer has a structure in which two layers of the p-InGaAsP semiconductor layer 111 and the p-AlGaAs second upper cladding layer 110 are stacked, and the ridge portion 130 is formed. The p-side electrode 115 formed on the side of the p-InGaAsP semiconductor layer 111 forms a Schottky junction. Here, as described above, the p-AlGaAs second upper cladding layer 110 formed on the n-GaAs substrate 101 made of GaAs is suitable as an optical confinement layer (clad layer) from the refractive index and the band gap.

  Further, the p-InGaAsP semiconductor layer 111 is laminated on the upper side (the layer opposite to the substrate) of the p-AlGaAs second upper cladding layer 110, so that the p-type is easily oxidized even after the ridge 130 is formed. Since the AlGaAs second upper cladding layer 110 is not exposed to the atmosphere, generation of deep levels due to Al oxidation is suppressed, long-term reliability is further improved, and due to deep levels. Light absorption can be reduced.

  Further, the p-AlGaAs second upper cladding layer 110 is covered with a p-InGaAsP semiconductor layer 111, and a p-side electrode 115 is directly formed on the p-InGaAsP semiconductor layer 111 to form a Schottky junction. The leakage current of the key junction can be greatly reduced, and there is a remarkable effect in reducing the threshold current value of the semiconductor laser element. As a result, it is possible to provide a semiconductor laser device having a low threshold current value and a high slope efficiency and excellent in long-term reliability.

  In the present embodiment, the semiconductor layer for forming the Schottky junction has a two-layer structure made of InGaAsP and AlGaAs, but it may of course have a one-layer structure or a three-layer structure or more.

  When the semiconductor layer for forming the Schottky junction has a three-layer structure or more, if the uppermost layer of the three-layer structure is an InGaAsP layer that does not contain Al as in this embodiment, the reliability is improved, and GaAs or This is preferable because an effect of enabling highly accurate ridge formation utilizing etching selectivity with respect to AlGaAs can be exhibited.

  In addition, an InGaP semiconductor layer can also be used in that it does not contain Al. However, when used as a p-type semiconductor layer as in this embodiment, InGaAsP is more resistant to holes than InGaP. In addition to the low barrier and the effect of improving hole injection efficiency, InGaP is not preferable because it tends to be a natural superlattice with a change in refractive index depending on crystal growth conditions.

In this embodiment, Ag is used as the material of the first electrode layer 115a, Ti and Pt are used as the material of the second electrode layer 115b, and Au is used as the material of the third electrode layer 115c. However, of course, the present invention is not limited to these. That is, in consideration of the oscillation wavelength and effective refractive index of a desired semiconductor laser element, if the material satisfies n _EFF −n _E1 ≧ 1, the film thickness d ₁ satisfies the relationship of d ₁ ≧ λ / 4πk _1. By doing so, the material can be used as the material of the first electrode layer, and if the material satisfies n _EFF −n _E2 <1, the film thickness d2 is set to satisfy the relationship of d ₂ <λ / 4πk ₂ . It can be used as a material for the second electrode layer by forming so as to satisfy. At this time, as long as the above refractive index condition is satisfied, the layer need not be a single metal element, and may be an alloy or compound composed of a plurality of elements.

  In a semiconductor laser device using a substrate made of any one of GaAs, GaN, and InP, Ag, Al, Au, Cu, Nd, Pb, Rh, and metal materials constituting the first electrode layer can be used. An element selected from Ta or a compound containing the element can be preferably used. The metal material constituting the second electrode layer may be an element selected from Cr, Mo, Ni, Os, Pd, Pt, Rd, Sb, Ti and W, or a compound containing the element Can be preferably used.

  In addition, when Au is used as the third electrode layer, the second electrode layer has an effect of preventing adhesion of Au and a metal layer made of Ti, Cr, or Mo that has an effect of improving adhesion. It is preferable to use a two-layer structure of a metal layer made of Pt, Pd, Rd, or Os. By forming these metal materials so as to conform to the above-described film thickness formation conditions, oscillation with a low resistance and a low refractive index is possible. Uses Au, which has a high effect of confining laser light in the semiconductor layer and is easy to wire bond by pressure welding because it is difficult to oxidize, maintaining its good characteristics for a long time and without reducing the manufacturing yield Will be able to.

  In the above description, the case where the electrode configuration of the present invention is applied to an ohmic junction and a Schottky junction with respect to a p-type semiconductor layer has been shown as an example. An effect is obtained.

  In the semiconductor laser device of this embodiment, an SCH (Separate Confinement Heterostructure) structure having a light guide layer between the active layer and the cladding layer is used. Of course, the present invention is not limited to the structure described above. Absent. For example, it is a matter of course that each layer thickness, material addition / change, and the like can be added without departing from the spirit of the present invention, such as adding an intermediate layer for smooth crystal growth.

[Second Embodiment]
FIG. 5 schematically shows the configuration of an optical disc apparatus 200 according to the second embodiment of the present invention. In FIG. 5, the optical path of the laser beam is indicated by a dotted line.

  The optical disc device 200 is used for writing data on an optical disc 201 such as a CD-R (writable compact disc) or reproducing data written on the optical disc 201, and is used at that time. As a light emitting element, a semiconductor laser element 202 in which the composition and thickness of the active layer are adjusted so as to oscillate in a wavelength of 780 nm band is provided. The semiconductor laser element 202 has the same configuration as the semiconductor laser element of the first embodiment.

  Hereinafter, the optical disk device 200 will be described in more detail.

  When the optical disc device 200 writes data to the optical disc 201, a laser beam carrying a data signal is emitted from the semiconductor laser element 202. The laser light is converted into parallel light by the collimator lens 203, passes through the beam splitter 204, and the polarization state is adjusted by the λ / 4 polarizing plate 205, and then condensed by the objective lens 206 and applied to the optical disc 201.

  When the optical disc device 200 reads data from the optical disc 201, the optical disc 201 is irradiated with a laser beam carrying a data signal along the same path as that at the time of writing. This laser beam is reflected on the surface of the optical disc 201 on which data is recorded, and after passing through the laser beam irradiation objective lens 206 and the λ / 4 polarizing plate 205, is reflected by the beam splitter 204 so that the optical axis is bent by 90 °. The light is collected by the light receiving element objective lens 207 and enters the signal detecting light receiving element 208. Based on the intensity of the laser light incident on the signal detection light-receiving element 208, the data signal recorded on the optical disc 201 is converted into an electric signal and reproduced by the signal light reproduction circuit 209 to the original signal.

  Since the optical disk device 200 uses the semiconductor laser element 202 that can be manufactured at low cost and operates with high slope efficiency and low threshold current, the power consumption of the device can be greatly reduced. Therefore, an optical disk device with less environmental load can be provided at a lower cost than before.

  In the second embodiment, the example in which the semiconductor laser element 202 having the same configuration as that of the semiconductor laser element of the first embodiment is applied to the recording / reproducing optical disc apparatus has been described. However, the optical disc recording using the same wavelength band of 780 nm is used. Needless to say, the present invention can also be applied to an optical disk apparatus, an optical disk reproducing apparatus, and an optical disk apparatus of another wavelength band (for example, 650 nm band).

[Third Embodiment]
FIG. 6 schematically shows a cross section of an optical transmission module 300 used in the optical transmission system according to the third embodiment of the present invention. FIG. 7 schematically shows a perspective view of the light source portion of the light transmission module 300. FIG. 8 schematically shows a configuration of an optical transmission system including the optical transmission module 300.

  As will be described in detail later, the optical transmission system includes the same optical transmission module 300 on both sides (for example, a terminal and a server) that perform communication, whereby an optical (infrared) signal is transmitted between the optical transmission modules 300. Can be sent and received.

  As shown in FIG. 6, the optical transmission module 300 includes the InGaAs semiconductor laser element 301 that oscillates in the 890 nm band described in the first embodiment as an example of a light source, and is a silicon (Si) pin photodiode. A light receiving element 302 is provided.

  The semiconductor laser element 301 is mounted on a circuit board 306. The circuit board 306 has a pattern of both positive and negative electrodes for driving the semiconductor laser element 301, and a recess 306 a provided in a portion where the semiconductor laser element 301 is mounted.

  A laser mount (mounting material) 310 to which the semiconductor laser element 301 is attached is fixed to the bottom surface of the recess 306a with solder. The recess 306 a has a depth that does not hinder the emission of laser light from the semiconductor laser element 301. Specifically, the depth of the recess 306a is 300 μm. The roughness of the bottom surface of the recess 306a is adjusted so as not to adversely affect the laser beam emission angle.

  The light receiving element 302 is also mounted on the circuit board 306, and an electric signal is taken out by the wire 307B. In addition, an IC (integrated circuit) circuit 308 for laser driving / reception signal processing is mounted on the circuit board 306.

  Further, after fixing the laser mount 310 to the bottom surface of the recess 306a, an appropriate amount of a liquid silicon resin 309 mixed with a filler that diffuses light is dropped into the recess 306a. Then, the silicon resin 309 stays in the recess 306a due to surface tension, covers the laser mount 310, and is fixed to the recess 306a. In the third embodiment, the recess 306a is formed on the surface of the circuit board 306, and the laser mount 310 is fixed to the bottom surface of the recess 306a. However, as described above, the silicon resin 309 is a laser because of surface tension. Since it remains on the chip surface and its vicinity, the recess 306a is not necessarily formed.

  The silicon resin 309 is dropped into the recess 306a and then heated at 80 ° C. for about 5 minutes to be cured until it forms a jelly. The silicon resin 309 is covered with a transparent epoxy resin mold 303. In the epoxy resin mold 303, a lens portion 304 for controlling the radiation angle of laser light and a lens portion 305 for condensing signal light are integrally formed as a mold lens. The lens unit 304 is located above the semiconductor laser element 301, while the lens unit 305 is located above the light receiving element 302.

  Hereinafter, the laser mount 310 will be described with reference to FIG.

  The laser mount 310 has an L-shaped heat sink 311. The semiconductor laser element 301 is die-bonded to the heat sink 311 using In glue. The lower surface 301b of the semiconductor laser element 301 is coated with a high reflection film, while the upper surface 301a of the semiconductor laser element 301 is coated with a low reflection film. These reflective films are also formed to protect the end face of the laser chip.

  A positive electrode 312 is fixed to the base 311 b of the heat sink 311. An insulator is interposed between the positive electrode 312 and the base 311b so that the positive electrode 312 does not conduct to the heat sink 311. The positive electrode 312 and the electrode region 301c provided on the Schottky junction on the surface of the semiconductor laser element 301 are connected by a wire 307C.

  The laser mount 310 is soldered to a laser driving negative electrode portion (not shown) on the circuit board 306. The flat portion 313 of the positive electrode 312 of the laser mount 310 is electrically connected to a laser driving positive electrode portion (not shown) on the circuit board 306 via a wire 307A. By forming such wiring, the optical transmission module 300 that can obtain the laser beam 314 by oscillation is completed.

  Since the optical transmission module 300 uses the semiconductor laser device that can be manufactured at the above-described low cost, and can operate with high efficiency and low power consumption, the power consumption of the module can be kept lower than that of the conventional one. , The module unit price can be greatly reduced. Since the optical transmission system using the optical transmission module 300 operates with low power consumption, the load on the environment can be reduced, and the optical transmission system can be configured at a low price. Furthermore, when this optical transmission system is mounted on a portable device, the battery driving time can be made longer than before, and the portable device can be used more comfortably.

  As shown in FIG. 8, the optical transmission system includes an optical transmission module 300 in a base station 316 installed on the ceiling of a room, and an optical transmission module 350 that is the same as the optical transmission module 300 in a personal computer 315. ing. The optical signal emitted from the light source of the optical transmission module 350 on the personal computer 315 side is received by the light receiving element of the optical transmission module 300 on the base station 316 side. The optical signal emitted from the light source of the optical transmission module 300 on the base station 316 side is received by the light receiving element of the optical transmission module 350 on the personal computer 315 side. In this way, data communication using light (infrared rays) can be realized.

  The semiconductor laser device, the optical disc apparatus, and the optical transmission system of the present invention are not limited to the above illustrated examples. For example, the semiconductor laser element can be variously modified within the range not departing from the paper of the present invention, such as the thickness and the number of the well layers and barrier layers.

  For example, an Au wire can be used as the wires 307A, 307B, and 307C.

FIG. 1 is a schematic cross-sectional view of a semiconductor laser device according to a first embodiment of the present invention. FIG. 2 is a schematic cross-sectional view for explaining a manufacturing process for the semiconductor laser device according to the first embodiment of the present invention. FIG. 3 is a schematic cross-sectional view for explaining a manufacturing process for the semiconductor laser device according to the first embodiment of the present invention. FIG. 4 is a schematic cross-sectional view for explaining a manufacturing process for the semiconductor laser device according to the first embodiment of the present invention. FIG. 5 is a schematic configuration diagram of an optical disc apparatus according to a second embodiment of the present invention. FIG. 6 is a schematic cross-sectional view of an optical transmission module used in the optical transmission system according to the third embodiment of the present invention. FIG. 7 is a schematic perspective view of a light source portion of the optical transmission module according to the third embodiment of the present invention. FIG. 8 is a schematic configuration diagram of the optical transmission system according to the third embodiment of the present invention. It is a schematic cross section of a conventional ridge waveguide type semiconductor laser device.

Explanation of symbols

DESCRIPTION OF SYMBOLS 100 Main body 101 n-GaAs substrate 102 n-GaAs buffer layer 103 n-AlGaAs first lower cladding layer 104 n-AlGaAs second lower cladding layer 105 AlGaAs lower guide layer 106 Multiple strain quantum well active layer 107 AlGaAs first upper guide layer 108 p-AlGaAs second upper guide layer 109 p-AlGaAs first upper cladding layer 110 p-AlGaAs second upper cladding layer 111 p-InGaAsP semiconductor layer 112 p-AlGaAs third upper cladding layer 113 p-GaAs contact layer 114 p ⁺ -GaAs contact layer 115 p-side electrode 115a first electrode layer 115b the second electrode layer 115c third electrode layer 116 n-side electrode 117a ridge formation region 117b ridge formed outside regions 119 resist mask 130 ridge 200 optical disc Device 201 Optical disk 202 Semiconductor laser element 203 Collimator lens 204 Beam splitter 205 λ / 4 polarizing plate 206 Objective lens 207 Light receiving element objective lens 208 Signal detection light receiving element 209 Signal light reproducing circuit 300, 350 Optical transmission module 301 Semiconductor laser element 302 Light receiving element 303 Epoxy resin mold 304, 305 Lens portion 306 Circuit board 306a Recess 307A, 307B, 307C Wire 308 IC circuit 309 Silicon resin 310 Laser mount 311 Heat sink 311b Base 312 Positive electrode 313 Flat portion 314 Laser beam 315 Personal computer 316 Base station

Claims (10)

A body having a first conductivity type substrate and a semiconductor layer group formed on the first conductivity type substrate and including at least a first conductivity type cladding layer, an active layer, and a second conductivity type cladding layer. In the semiconductor laser device having the oscillation wavelength λ provided,
An electrode made of a metal material is formed on the semiconductor layer group,
The metal material has a refractive index n _E of the light having the oscillation wavelength λ,
The electrode is
A first electrode layer having an effective refractive index n _E1 of light having the oscillation wavelength λ;
A second electrode layer formed on the first electrode layer, the effective refractive index of the light having the oscillation wavelength λ being n _E2 ;
A third electrode layer made of Au and formed on the second electrode layer;
The first and second electrode layers are
n _EFF −n _E1 ≧ 1
d ₁ ≧ λ / (4πk ₁ )
n _EFF −n _E2 <1
d ₂ <λ / (4πk ₂ )
Where n _{EFF is} the effective refractive index of the light having the oscillation wavelength λ of the main body.
d ₁ : thickness of the first electrode layer [nm]
k ₁ : extinction coefficient of light having the oscillation wavelength λ of the first electrode layer
d ₂ : thickness of the second electrode layer [nm]
k ₂ : A semiconductor laser element satisfying the relationship of the extinction coefficient of the light having the oscillation wavelength λ of the second electrode layer. The semiconductor laser device according to claim 1,
A part of the semiconductor layer group on the electrode side constitutes a striped ridge portion,
The electrode is in contact with the top of the ridge, and is in contact with at least one of the side surface of the ridge and the surface of the semiconductor layer group excluding the ridge in the vicinity of the ridge. A semiconductor laser device. The semiconductor laser device according to claim 2,
The top of the ridge portion forms an ohmic junction with the electrode,
At least one of the side surface of the ridge portion and the surface of the second conductivity type semiconductor layer group excluding the ridge portion and in the vicinity of the ridge portion forms a Schottky junction with the electrode. A semiconductor laser device comprising: The semiconductor laser device according to claim 1,
The second electrode layer has a laminated structure in which two or more metal materials are laminated,
Each layer An (n = 1, 2,..., Q, where q is a natural number of 2 or more) of the second electrode layer has a refractive index n _E2n (n = 1, 2, 1) of the light having the oscillation wavelength λ. , ..., q, where q is a natural number of 2 or more)
Each layer of the second electrode layer is
n _EFF -n _E2n <1
Satisfy the relationship
The second electrode layer is
d _total <λ / 4πk _average
d _total : _total thickness [nm] of all the second electrode layers
k- _average : A semiconductor laser element satisfying the relationship of the average value of the extinction coefficient of the light having the oscillation wavelength λ of each layer of the second electrode layer. The semiconductor laser device according to claim 4,
A part of the semiconductor layer group on the electrode side constitutes a striped ridge portion,
The electrode is in contact with the top of the ridge portion, and is in contact with at least one of the side surface of the ridge portion and the surface of the semiconductor layer group excluding the ridge portion and in the vicinity of the ridge portion;
The top of the ridge portion is formed of a high concentration semiconductor layer having a second conductivity type doping concentration of 1 × 10 ¹⁸ cm ⁻³ or more,
At least one of the side surface of the ridge portion and the surface region excluding the ridge portion of the semiconductor layer group includes a low-concentration semiconductor layer having a second conductivity type doping concentration of 1 × 10 ¹⁷ cm ⁻³ or less. ,
A semiconductor laser device, wherein a semiconductor layer having a second conductivity type doping concentration of 1 × 10 ¹⁷ cm ⁻³ or more is formed between the low-concentration semiconductor layer and the active layer. The semiconductor laser device according to claim 5, wherein
At least one of the side surface of the ridge portion and the surface of the second conductivity type semiconductor layer group excluding the ridge portion and in the vicinity of the ridge portion forms a Schottky junction with the electrode,
The substrate is made of GaAs,
The low-concentration semiconductor layer has at least an AlGaAs layer and an InGaAsP layer,
The semiconductor laser device, wherein the portion forming the Schottky junction with respect to the second conductivity type semiconductor layer group includes the InGaAsP layer. The semiconductor laser device according to claim 1,
A semiconductor laser device, wherein the metal material constituting the first electrode layer contains at least one element selected from Ag, Al, Au, Cu, Nd, Pb, Rh and Ta. The semiconductor laser device according to claim 1,
The metal material constituting the second electrode layer includes at least one element selected from Cr, Mo, Ni, Os, Pd, Pt, Rd, Sb, Ti, W, and Zn. A semiconductor laser device.   An optical disc apparatus comprising the semiconductor laser element according to claim 1. An optical transmission system comprising the semiconductor laser device according to claim 1.

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