JP2008060180A - Semiconductor laser device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a semiconductor laser device with a highly reliable ridge waveguide structure by reducing distortion applied to the ridge waveguide while keeping productivity. <P>SOLUTION: An electrode formed on a submount 2 is separated into an electrode 4 connected with the ridge waveguide, and electrodes 5 connected with an element electrode of a semiconductor laser element 1 formed on both sides of the waveguide, with a partial connecting region left over. The ridge waveguide is connected with the corresponding electrode 4 via a thick Au film, and only an element electrode is fixed and joined to the corresponding electrodes 5 via solder 6, thereby preventing the solder 6 from flowing out to the waveguide part. Thus, the semiconductor laser device with a highly reliable ridge waveguide structure can be provided by reducing the distortion applied to the ridge waveguide and keeping heat dissipating efficiency of the waveguide while the productivity is secured. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a semiconductor laser device having a ridge waveguide structure and mounting a semiconductor laser element used for optical information processing and optical communication on a mounting substrate.

  In recent years, the demand for semiconductor laser devices is increasing more and more in the field of optical information processing devices such as optical disks and in the field of optical communication. In the field of optical discs, the demand for higher light output of semiconductor lasers has been unresolved due to the demand for higher writing speed. For example, 8 × speed writing on a dual-layer DVD (digital versatile disk) requires an optical output of 300 mW or more at a wavelength of 660 nm.

  As the output of a semiconductor laser increases, the lifetime of the element is shortened, and ensuring reliability is a major issue. The factor that deteriorates the reliability is that the temperature rises due to heat generation of the element due to a large current, and heat radiation becomes very important.

In order to improve the heat radiation of the semiconductor laser element, a method is well known in which an element is adhered to a heat sink having a good thermal conductivity and fixed with a solder material.
Hereinafter, a conventional semiconductor laser device will be described with reference to FIG.

FIG. 4 is a cross-sectional view showing a configuration of a conventional semiconductor laser device.
As shown in FIG. 4, the conventional semiconductor laser device has a configuration in which a semiconductor laser element 101, a submount 102 that acts as a heat sink, and a base 103 that acts as a heat sink are laminated and fixed with a solder material or the like. The semiconductor laser element 101 is a semiconductor laminate in which a back electrode 104 composed of a plurality of layers and a front electrode 105 composed of a plurality of layers are formed.

  The submount 102 has a material having a high thermal conductivity and an electrically insulating material, a front surface electrode 106 composed of a plurality of layers, a solder layer 107, a back surface electrode 108 composed of a plurality of layers, and a solder layer 109. Further, the base 103 has a metal heat radiating body with good thermal conductivity and an electrode layer 110 composed of a plurality of layers.

  The semiconductor element 101 and the submount 102 and the submount 102 and the base 103 are melted and fixed by solder layers 107 and 109 therebetween, and the semiconductor laser device shown in FIG. 4 is manufactured. For the base 103, a metal heat dissipating body in which a metal film of Ni and Au is coated by plating or the like on a metal having good thermal conductivity such as Cu or Ag is used.

  In addition, the submount 102 is required to be made of a material having a thermal expansion coefficient close to that of the semiconductor laser element 101 and good thermal conductivity. The reason for this is that when the solder layer is heated and melted and bonded, and cooled to room temperature after bonding, the semiconductor laser element is accompanied by a dimensional change of both materials due to the difference in thermal expansion coefficient between the semiconductor laser element and the submount. This is because strain is accumulated in the semiconductor laser, which becomes stress and greatly reduces the reliability of the semiconductor laser.

Therefore, the material used for the submount is an electrically insulating material such as AlN, SiC, diamond, or Si when electrical insulation is not required.
As an electrode material of the semiconductor element 101, a metal that makes ohmic contact with the semiconductor material (for example, an Au—Ge—Ni alloy in the case of an n-type semiconductor, Cr or Ti in the case of a p-type semiconductor) and a solder such as Pt or Mo. A metal multilayer film made of Au and a metal serving as a barrier of the layer is used. As the electrode material of the submount 102, a metal multilayer film composed of Cr or Ti for enhancing the adhesion, Pt or Mo serving as a barrier, and Au is used.

  Materials used for the solder layers 107 and 109 include an alloy of Au and Sn (hereinafter referred to as AuSn), an alloy of Ag and Sn (hereinafter referred to as AgSn), and an alloy of Pb and Sn (hereinafter referred to as PbSn). In particular, AuSn is widely used in semiconductor lasers as a solder material that is excellent in corrosion resistance and strength, has low resistance, and does not contain Pb.

  In joining the solder layer 107 and the surface electrode 105 of the semiconductor laser element 101 with the AuSn alloy, the Au of the surface electrode 105 and the AuSn of the solder layer 107 are further alloyed and fixed together. This is also the case with the submount 102 and the base 103 joined via the solder layer 109. In order to obtain sufficient fixing strength, the composition ratio of AuSn and the melting temperature are important. In the eutectic composition of Au (80 wt%)-Sn (20 wt%), the melting point becomes a minimum of 278 ° C., and the melting point increases when deviating from this composition. In order to minimize the strain accumulated in the semiconductor laser element at the time of bonding, the fixing temperature should be low. However, since deviation from the eutectic composition may occur, the temperature is usually higher than 278 ° C. in order to obtain the fixing strength. A sufficiently high temperature, for example, 330 ° C. to 400 ° C. is used. However, as the junction temperature increases, there is a problem that the risk of the reliability of the semiconductor laser device being impaired due to an increase in strain when cooled to room temperature increases.

  In the semiconductor laser device 101 of the semiconductor laser device having the ridge waveguide structure shown in FIG. 4, the light emitting point is in the ridge waveguide 111 portion. The laser with this structure can simplify the manufacturing process, and has the structure of a mainstream semiconductor laser device. In this case, if the solder enters the grooves on both sides of the ridge waveguide 111, a large residual stress is applied to the light emitting point, which is the active region of the semiconductor laser, due to the thermal contraction of the solder, so that the reliability of the semiconductor laser is greatly reduced. There is a problem.

  Besides the reliability, the influence of the strain applied to the ridge waveguide on the semiconductor laser device includes a decrease in the polarization ratio and a deviation in the polarization angle. This is presumably because anisotropy occurs in the refractive index due to strain, and a TM mode component is added to the semiconductor laser light that should originally oscillate in the TE mode. The decrease in the polarization ratio and the deviation in the polarization angle cause a decrease in the light utilization efficiency in the optical disk pickup device using the optical element depending on the polarization, so that the light output required for the semiconductor laser increases. In addition, in the longitudinal single mode laser for optical communication, there is a problem that the single mode property is impaired due to distortion.

  In order to suppress distortion due to solder, a configuration in which the ridge waveguide portion is not bonded with solder has been proposed. According to this method, since only both sides of the ridge are fixed to the submount, the distortion of the laser emission point can be reduced. However, in this method, it is difficult to dissipate the heat generated at the light emitting point of the active layer to the submount directly below, so that the temperature of the semiconductor laser element rises, causing deterioration of characteristics, limitation of the upper limit temperature of operation, and reduction of reliability (For example, refer to Patent Document 1).

  In addition, there has been proposed a method for reducing the mounting distortion by making the ridge portion different from the solder material on both sides of the ridge and making the ridge portion a solder material having a lower melting point. According to this method, heat can be radiated to the submount through the ridge portion. However, in this method, two types of solder materials must be formed on the submount, and conditions such as temperature must be set so that they do not mix at the time of mounting, resulting in a complicated mounting process and an increase in cost. (For example, refer to Patent Document 2).

Further, as a configuration in which there is no solder in the ridge portion and heat is radiated through the ridge portion, a method of providing a solder suppression film of Ti so that the solder on both sides of the ridge does not spread to the ridge portion has been proposed. Although the solder suppression film has a width of 20 to 30 μm on one side across the ridge, the solder on both sides of the ridge spreads to the ridge portion during mounting, and the grooves on both sides of the ridge are distorted to reduce reliability. There is a possibility (see, for example, Patent Document 3).
JP 2002-314184 A JP 2003-23200 A JP 2004-14659 A

  The present invention has been made in view of the above problems, and an object of the present invention is to provide a highly reliable semiconductor laser device having a ridge waveguide structure by reducing distortion applied to the ridge waveguide while ensuring productivity. And

  In order to achieve the above object, a semiconductor laser device according to claim 1 of the present invention is a semiconductor laser device in which a semiconductor laser element having a ridge waveguide structure is mounted on a submount. A first element electrode formed on both sides in parallel to the cavity length direction of the semiconductor laser element at a predetermined interval from the ridge waveguide, and a second element electrode formed on the ridge waveguide An element electrode, a first electrode formed on the submount and joined to the first element electrode via a first conductive material at the time of mounting, and formed on the submount and at the time of mounting A second electrode connected to the second element electrode via a second conductive material; and one or more connection points connecting the first electrode and the second electrode; The first electrode and the second electrode are It is separated except for the serial connection point, wherein the first conductive material is fed at a said ridge waveguide by a predetermined distance.

  The semiconductor laser device according to claim 2 is the semiconductor laser device according to claim 1, wherein, as the junction point, the first electrode and the second electrode are located behind the semiconductor laser element with respect to a light emitting point of the submount. The electrodes are connected to each other.

  According to a third aspect of the present invention, in the semiconductor laser device according to the first or second aspect, a groove is formed in a separation region between the first electrode and the second electrode. It is characterized by.

  A semiconductor laser device according to a fourth aspect of the present invention is the semiconductor laser device according to the first, second, or third aspect, wherein the first conductive material is solder containing Sn, and the second The conductive material is a thick Au film having such a thickness that the second element electrode and the second electrode are in contact with each other during mounting.

  The semiconductor laser device according to claim 5 is an electrode including a barrier layer for preventing the solder from diffusing inside the semiconductor laser element as the first electrode in the semiconductor laser device according to claim 4. It is characterized by that.

A semiconductor laser device according to a sixth aspect is the semiconductor laser device according to the fifth aspect, wherein the barrier layer is made of Pt.
As described above, it is possible to provide a highly reliable semiconductor laser device having a ridge waveguide structure while reducing the strain applied to the ridge waveguide while maintaining productivity and maintaining the heat dissipation efficiency of the ridge waveguide.

  As described above, the electrode formed on the submount is partially divided into an electrode connected to the ridge waveguide and an electrode connected to the device electrode of the semiconductor laser element formed on both sides of the ridge waveguide. Separation is performed leaving the connection region, and the ridge waveguide part is connected to the corresponding electrode by a thick film of Au, and only the element electrode part is fixedly bonded to the corresponding electrode via solder, so that the solder is in the ridge waveguide part. The semiconductor laser device with a highly reliable ridge waveguide structure that reduces the strain applied to the ridge waveguide while maintaining productivity and maintains the heat dissipation efficiency of the ridge waveguide while ensuring productivity can do.

Hereinafter, embodiments of the semiconductor laser device of the present invention will be described with reference to the drawings.
(Embodiment 1)
FIG. 1 is a diagram showing the structure of the semiconductor laser device according to the first embodiment of the present invention, and shows the structure when the submount is larger than the length of the semiconductor laser element in the resonator direction. 1A is a cross-sectional view of the semiconductor laser device according to the first embodiment, and FIG. 1B is a perspective view of the semiconductor laser device according to the first embodiment.

  1A and 1B, a ridge waveguide type semiconductor laser device 1 is mounted on a submount 2, and a ridge portion 3 has a device electrode formed on the ridge of the submount 2. The first electrode 4 is connected via a conductive material without using solder. The element electrodes formed on both sides of the ridge are fixedly bonded to the second electrode 5 of the submount 2 via the solder 6. The first electrode 4 and the second electrode 5 of the submount 2 are separated along the resonator direction of the semiconductor laser element 1. In addition, although the back electrode of the semiconductor laser element 1, the base, the electrode between the submount 2 and the base, and the solder are omitted, the configuration is the same as that of the conventional semiconductor laser, and the description is omitted in this embodiment. To do.

  In FIG. 1B, the dotted line indicates the schematic shape of the semiconductor laser element 1. The first electrode 4 and the second electrode 5 of the submount 2 are connected to the light emitting point of the portion of the submount 2 where the semiconductor laser device 1 is mounted as a connection point 10 at the rear, and the portion where the solder 6 is present Are separated in both side regions of the ridge portion 3. In this way, by sufficiently increasing the distance between the portion where the solder 6 is present and the ridge portion 3, the solder 6 is prevented from flowing to the first electrode 4 of the submount 2 joined to the ridge portion 3 of the semiconductor laser device 1. I can do it. Further, by connecting the second electrode 5 of the submount 2 and the external terminal with a wire, the first electrode 4 and the second electrode 5 are connected at the rear of the semiconductor laser element 1. Can be applied with current.

  The semiconductor laser device 1 is a red semiconductor laser device which has an n-type AlGaInP cladding layer, a GaInP multiple quantum well active layer, a p-type AlGaInP cladding layer, and a p-type GaAs contact layer on an n-type GaAs substrate and oscillates at a wavelength of 660 nm. . An insulating layer made of a semiconductor or a dielectric is provided inside the element so that current flows only through the ridge portion 3. Laser light is emitted from the active layer of the ridge portion 3, and at the same time, heat is generated in this portion. However, since the heat generated in the ridge portion 3 is efficiently radiated to the submount 2 through the first electrode 4 of the submount, the temperature rise of the semiconductor laser device 1 can be suppressed and good temperature characteristics can be obtained. I can do it. At the same time, since the ridge portion 3 is connected to the submount without using solder, and the second electrode 5 and the ridge portion 3 are separated at a sufficient interval, the solder 6 flows into the ridge portion 3. Therefore, distortion of the ridge waveguide due to solder can be suppressed.

  FIG. 2 is a cross-sectional view of the electrode forming process of the semiconductor laser device according to the first embodiment of the present invention, and shows a submount electrode and a solder layer, and the electrode forming process is shown in FIGS. 2 (a) to 2 (c). FIG. 2D shows the configuration of the electrode and solder layer of the submount.

  FIG. 2A shows the semiconductor laser device 1 before forming the device electrode, and the regions of 20 to 30 μm and the depth of 1 to 3 μm on both sides of the ridge portion 3 are removed by etching. With this ridge structure, current and light can be collected in the ridge portion, and laser oscillation can be caused in the active layer of the ridge portion.

  Ti / Pt / Au electrodes 8 are formed as device electrodes on the ridge portion 3 and portions 7 on both sides thereof (hereinafter referred to as wings). Ti is for increasing the adhesion of the electrode and has a thickness of about 50 nm. Pt is a barrier metal that prevents Au from diffusing into the semiconductor and has a thickness of about 150 nm. The uppermost Au layer is formed with a thickness of 500 to 1000 nm. If Au is present in the groove portion between the ridge portion 3 and the wing 7, the solder in the wing portion 7 flows into the ridge portion 3 at the time of mounting. Therefore, the electrode 8 in the groove portion is at least partially removed by a lift-off method or the like ( FIG. 2 (b)).

  Next, as shown in FIG. 2C, Au plating 9 is formed as an example of a thick film by plating only on the ridge portion 3. The film thickness is about 3 to 10 μm, and the first electrode 4 of the submount 2 and the electrode 8 at the ridge portion of the semiconductor laser element are in electrical contact after mounting according to the thickness of the solder 6 layer on the submount 2 side. Adjust to such a thickness. Actually, the film thickness of the solder 6 of the submount and the film thickness of the Au plating 9 of the semiconductor laser element 1 are preferably substantially the same.

  FIG. 2D shows the electrode structure of the submount 2. The submount 2 is an insulating material having a good thermal conductivity, and AlN or SiC having a thermal expansion coefficient close to that of GaAs is used. The first electrode 4 and the second electrode 5 are made of Ti / Pt / Au, and the film thickness thereof is, for example, 50 nm / 200 nm / 600 nm. AuSn solder 6 (Au70% Sn30%) is formed by a method such as plating or vapor deposition at the portion of the second electrode 5 where the semiconductor laser device 1 is bonded to the wing electrode. At the time of mounting, since the Au of the second electrode 5 of the submount 2 and the electrode 8 of the semiconductor laser element 1 melts, the proportion of Au is made smaller than the eutectic composition (Au 80% Sn 20%) that minimizes the melting point. is there. The thickness of the solder 6 layer is approximately the same as that of the Au plating 9 of the semiconductor laser element 1.

  As a mounting method, the semiconductor laser element 1 is brought into contact with the submount 2 by vacuum suction and then brought into contact with the submount 2, and then a load is applied and heated to 300 to 400 ° C. to melt the solder layer 6 and fix bonding. Do. If the solder layer 6 is thin, sufficient adhesive strength cannot be obtained. In addition, when the solder layer 6 is thick, the adhesion of the ridge portion is deteriorated and poor electrical contact and heat dissipation are deteriorated. Therefore, it is important to optimize the thickness of the solder layer according to the mounting conditions.

  As described above, the electrode on the submount 2 is divided into the first electrode 4 that is connected to the ridge portion 3 and the second electrode 5 that is connected to the wing 7. A predetermined interval is provided between the second electrodes 5 so that they are connected to each other at the rear portion of the ridge portion 3, and the wing 7 and the second electrode 5 are joined via the solder 6. By connecting the first electrode 4 via the Au plating 9, the ridge 3 can be thermally connected to the submount 2 while suppressing the solder 6 from flowing into the ridge 3. While ensuring, the strain applied to the ridge waveguide can be reduced, and the heat dissipation efficiency of the ridge waveguide can be maintained to improve the reliability of the semiconductor laser device.

(Embodiment 2)
FIG. 3 is a diagram showing the structure of the semiconductor laser device according to the second embodiment of the present invention, and shows the structure when the length of the semiconductor laser element 1 in the resonator direction and the length of the submount 2 are substantially the same. 3A is a cross-sectional view of the semiconductor laser device according to the second embodiment, and FIG. 3B is a perspective view of the semiconductor laser device according to the second embodiment.

  3A and 3B, in the second embodiment, as in the first embodiment, the ridge waveguide type semiconductor laser device 1 is mounted on the submount 2, and the ridge portion 3 is the sub-mount. The first electrode 4 of the mount 2 is connected. The element electrodes formed on both sides of the ridge are joined to the second electrode 5 of the submount 2 via the solder 6.

  In FIG. 3B, the dotted line indicates the outer shape of the semiconductor laser element 1. The first electrode 4 and the second electrode 5 of the submount 2 are separated along the resonator direction of the semiconductor laser device 1, but have four connecting points 10 connected to each other. As for the connection between the ridge portion 3 and the submount 2, as in the first embodiment, they are connected by Au plating 9 of Au. In this way, the first electrode 4 and the second electrode 5 are separated except for the connection point 10, and only the connection of the second electrode 5 to the submount 2 is performed via the solder 6. It is possible to greatly suppress the solder 6 from flowing to the first electrode 4 of the submount 2 connected to the ridge portion 3 of the element 1. Further, since the first electrode 4 and the second electrode 5 are connected via the four connection points 10 by connecting the second electrode 5 of the submount 2 and the external terminal with a wire, A current can be applied to the ridge portion 13. In the semiconductor laser device shown in FIG. 3, the connection points 10 are provided on both sides of the ridge. However, only the electrode on the side connected to the wire may be used. Also, the number of connection points is not limited to four, and it is sufficient that there is at least one connection point. In this case, the influence of the solder flow can be reduced. In the semiconductor laser device of the second embodiment, the same configuration, manufacturing process, and mounting method as those of the semiconductor laser device of the first embodiment are used except for the points described above.

  The preferred embodiments according to the present invention have been described above, but the present invention is not limited to these embodiments. The submount is not limited to AlN or SiC, and a material having good thermal conductivity such as ceramic such as sapphire or alumina, or diamond can be used. Needless to say, a material having a thermal expansion coefficient close to that of GaAs is more preferable.

  In addition to the configuration of the first embodiment and the second embodiment, a groove may be formed in the separation portion between the first and second electrodes of the submount. Rather, this is more preferable because there is no fear of spreading to the first electrode portion even when the solder on the second electrode of the submount protrudes.

Although the case where the solder is formed on the second electrode of the submount has been shown, it may be formed on the electrode of the wing portion on the semiconductor laser element side by an appropriate method.
In the above embodiment, the ridge waveguide type semiconductor laser on the GaAs substrate having the AlGaInP-based semiconductor has been described. However, the present invention is not limited to this material, and the AlGaAs-based semiconductor on the GaAs substrate or the InP substrate is used. The present invention can also be applied to a ridge waveguide type semiconductor laser element made of an InGaAsP semiconductor and a GaN semiconductor material.

  In the embodiment of the present invention, an example in which AuSn solder is used as the solder material has been described. However, AuSi solder, PbSn solder, AgSn solder, or the like may be used.

  The present invention can provide a highly reliable semiconductor laser device having a ridge waveguide structure while reducing the strain applied to the ridge waveguide and maintaining the heat dissipation efficiency of the ridge waveguide, thereby providing a highly reliable ridge waveguide structure. It is useful for a semiconductor laser device in which a semiconductor laser element used for optical information processing and optical communication is mounted on a mounting substrate.

The figure which shows the structure of the semiconductor laser apparatus in Embodiment 1 of this invention Sectional view of electrode formation process of semiconductor laser device in Embodiment 1 of the present invention, and figure showing electrodes and solder layers of submount The figure which shows the structure of the semiconductor laser apparatus in Embodiment 2 of this invention Sectional view showing the structure of a conventional semiconductor laser device

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Semiconductor laser element 2 Submount 3 Ridge part 4 1st electrode 5 2nd electrode 6 Solder 7 Wing 8 Electrode 9 Au plating 10 Connection point 101 Semiconductor laser element 102 Submount 103 Base 104 Back surface electrode 105 Surface electrode 106 Surface electrode 107 Solder layer 108 Back electrode 109 Solder layer 110 Electrode layer 111 Ridge waveguide

Claims (6)

A semiconductor laser device in which a semiconductor laser element having a ridge waveguide structure is mounted on a submount,
A first element electrode formed in parallel to the cavity length direction of the semiconductor laser element at a predetermined interval on both sides of the ridge waveguide;
A second element electrode formed on the ridge waveguide;
A first electrode formed on the submount and bonded to the first element electrode via a first conductive material during mounting;
A second electrode formed on the submount and connected to the second element electrode via a second conductive material during mounting;
One or more connection points connecting the first electrode and the second electrode, and the first electrode and the second electrode are separated except for the connection point; The semiconductor laser device, wherein the first conductive material is supplied at a predetermined distance from the ridge waveguide.   2. The semiconductor laser according to claim 1, wherein the first electrode and the second electrode are connected to the light emitting point of the submount behind the semiconductor laser element as the junction point. apparatus.   The semiconductor laser device according to claim 1, wherein a groove is formed in a separation region between the first electrode and the second electrode.   The first conductive material is a solder containing Sn, and the second conductive material is a thick Au film having a thickness such that the second element electrode and the second electrode are in contact with each other during mounting. The semiconductor laser device according to claim 1, wherein the semiconductor laser device is characterized by the following.   5. The semiconductor laser device according to claim 4, wherein the first electrode is an electrode including a barrier layer for preventing the solder from diffusing into the semiconductor laser element.   6. The semiconductor laser device according to claim 5, wherein the barrier layer is made of Pt.

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