JP2004140141A - Semiconductor laser - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a laser structure capable of manufacturing a ridge waveguide type semiconductor laser, excellent in temperature characteristics, in a high yield and with good reproducibility. <P>SOLUTION: The semiconductor laser is constituted of a first clad layer which comprises a first material, an active layer, a second clad layer which comprises the first material and a third clad layer of a ridge structure which comprises a second material different from the first material, which are laminated sequentially while a groove, formed along the direction of lamination from the third clad layer side, arrives at the second clad layer at the chip separating position of the semiconductor laser chip. Further, the semiconductor laser is provided with the active layer, the first clad layer as well as the second clad layer which pinch the active layer, the third clad layer of the ridge structure laminated on the second clad layer and an electrode electrically connected to the third clad layer. The electrode of this laser covers an upper part under a condition separated from the surface of the groove beside the ridge. <P>COPYRIGHT: (C)2004,JPO

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a structure capable of manufacturing a high-performance and highly reliable ridge waveguide semiconductor laser with good reproducibility and high yield, and a manufacturing technique thereof.
[0002]
[Prior art]
In recent years, AlGaInAs / InP-based lasers having excellent temperature characteristics and excellent high-frequency characteristics have been attracting attention as semiconductor lasers for optical fiber communication. Also, as a semiconductor laser for information processing, an AlGaInP / GaAs-based laser having good temperature characteristics and excellent in high-output operation has attracted attention. In these semiconductor lasers, a ridge waveguide type structure having a small number of manufacturing steps is adopted in order to suppress the manufacturing cost.
[0003]
On the other hand, as one means for improving the temperature characteristics, a J-down assembly for assembling a semiconductor laser device (semiconductor laser chip) with the pn junction side down is known. The semiconductor laser chip having the ridge waveguide structure described above is manufactured by adopting the J-down assembly.
[0004]
FIG. 8 is a perspective view of a conventional AlGaInAs / InP ridge waveguide semiconductor laser 180. The laser 180 includes an n-InP substrate 1, an n-InP cladding layer 2 having a thickness of 1 μm, an n-AlInAs cladding layer 3 having a thickness of 0.1 μm, an AlGaInAs-active layer 4, and a p-AlInAs cladding having a thickness of 0.1 μm. Layer 5, 1.75 μm thick p-InP clad layer 6, 0.6 μm thick p-InGaAs contact layer 7, SiO ₂ film 8, P-side electrode (Ti / Au) 9, N-side electrode (AuGe / Ni / Au) 10, a P-side plating electrode 11, a ridge 12, and a chip separation groove 13. The active layer 4 is formed with a multiple quantum well (Multi-Quantum-Well) structure in order to improve luminous efficiency.
[0005]
FIG. 9 is a cross-sectional view showing an ideal state when the above-described ridge waveguide semiconductor laser 180 is assembled by J-down assembly. At this time, the laser 180 has a mount material 14 and a solder material 15 in addition to FIG.
[0006]
As shown in the figure, when the J-down assembly is adopted for the ridge waveguide type semiconductor laser, the laser is bonded to the mount material 14 via the solder material 15 with the active layer 4 side, that is, the ridge 12 side down. Have been. When this assembling is ideally performed, the surface of the semiconductor laser chip 180 other than the top of the ridge 12 is covered with the SiO ₂ film 8 which is an insulating film. A current is injected through the plating electrode 11 and the P-side electrode 9.
[0007]
More specifically, there is a laser in which the entire epitaxial layer in the chip separation groove portion is bent in a concave shape to provide a step, and the surface layer is constituted by a cap layer (contact layer) (see Patent Document 1). Further, there is also known a laser in which solder is confined inside a spacer to prevent short-circuit failure due to swelling of the solder (see Patent Document 2).
[0008]
[Patent Document 1]
JP-A-58-142588 [Patent Document 2]
JP-A-5-110203
[Problems to be solved by the invention]
However, actually, when the J-down assembly is applied to the ridge waveguide semiconductor laser, the following problems are likely to occur.
[0010]
(1) Since the distance between the bonding surface with the solder material 15 and the active layer 4 is close to several μm, the raised solder material 15 comes into contact with an epitaxial layer such as an active layer to cause short-circuit failure or leakage current. It becomes. In the technique according to Patent Document 1 described above, since a cap layer (contact layer) having low contact resistance is provided on the outermost surface of the separation groove, a leak current occurs when a solder material contacts the chip surface.
[0011]
(2) During chip separation, the insulating film in the separation groove is chipped and the solder material comes into contact with the epitaxial layer, which causes a leak current.
[0012]
(3) Since the solder material 15 enters the groove beside the ridge, the laser is stressed due to the difference in the thermal expansion coefficient between the solder material 15 and the crystal material, and there is a concern that reliability may be impaired.
[0013]
Hereinafter, these problems will be described in more detail with reference to FIGS. As an example, an AlGaInAs / InP laser is used.
[0014]
FIG. 10 is a diagram illustrating a first problem when the conventional ridge waveguide semiconductor laser 180-1 is manufactured by J-down assembly. Originally, the surface of the semiconductor laser chip 180-1 other than the top of the ridge 12 is covered with the SiO ₂ film 8, so only from the top of the ridge 12 via the solder material 15, the P-side plating electrode 11, and the P-side electrode 9. Current is injected. However, actually, the raised solder material 15 may come into contact with the active layer 4 or the n-AlInAs clad layer 3 or the n-InP clad layer 2 to cause a short circuit failure. When a short circuit occurs, the current flows to the substrate side without passing through the pn junction of the active layer 4, so that laser oscillation does not occur.
[0015]
Further, the raised solder material 15 may come into contact with the p-AlInAs clad layer 5 or the p-InP clad layer 6 to generate a leak current. Since the leak current is a reactive current that does not contribute to oscillation and the like, it causes a decrease in laser characteristics such as an increase in threshold current and operating current and a decrease in efficiency.
[0016]
The leak failure that causes a leak current may also occur in the ridge waveguide semiconductor laser 180-2 in FIG. FIG. 11 is a diagram for explaining a second problem when the conventional ridge waveguide semiconductor laser 180-2 is manufactured by J-down assembly. At the time of chip separation in the manufacturing process, the SiO ₂ film 8 of the separation groove 13 may be chipped at the position 81 and the surface of the semiconductor laser chip 180-2 may not be completely covered with the SiO ₂ film 8. Then, the solder material 15 and the p-InP clad layer 6 come into contact with each other, which may cause a leakage current.
[0017]
Furthermore, when a ridge waveguide type semiconductor laser is manufactured by J-down assembly, there is a concern about reliability other than short-circuit failure and leak failure. Referring again to FIG. 9, the solder material 15 enters the groove beside the ridge of the laser 180, and the inside of the groove is filled with a metal material such as the P-side electrode 9, the P-side plating electrode 11, and the solder material 15. . In this state, the laser is subjected to stress caused by a difference between the thermal expansion coefficient of the metal material and the thermal expansion coefficient of the crystal material because the laser is placed in an environment such as a heat cycle during assembly or heat generation during laser oscillation. . For this reason, there is a concern that the reliability is impaired.
[0018]
When the laser does not oscillate or a leak current occurs as described above, the laser element cannot be used in a product. Therefore, this is a factor that lowers the yield.
[0019]
An object of the present invention is to provide a laser structure capable of producing a ridge waveguide type semiconductor laser having a high yield and excellent temperature characteristics with good reproducibility.
[0020]
[Means for Solving the Problems]
A semiconductor laser according to the present invention includes a first clad layer containing a first material, an active layer, a second clad layer containing the first material, and a second material different from the first material. And a third cladding layer having a ridge structure. In this laser, at the chip separation position of the semiconductor laser chip, a groove formed along the direction in which the semiconductor laser chip is stacked from the third clad layer side reaches the second clad layer. This achieves the above object.
[0021]
The first material is a material that is easily oxidized, for example, aluminum.
[0022]
A semiconductor laser according to the present invention includes an active layer, a first clad layer and a second clad layer sandwiching the active layer, and a third clad layer having a ridge structure laminated on the second clad layer. And a ridge waveguide type semiconductor laser comprising an electrode electrically connected to the third cladding layer. The laser electrode covers the upper side in a state separated from the surface of the groove beside the ridge. This achieves the above object.
[0023]
BEST MODE FOR CARRYING OUT THE INVENTION
Hereinafter, embodiments of the present invention will be described with reference to the accompanying drawings. Components having the same reference numerals are components having the same function.
[0024]
(Embodiment 1)
FIG. 1 is a perspective view of an AlGaInAs / InP-based ridge waveguide semiconductor laser 100 according to the first embodiment. The semiconductor laser 100 includes an n-InP substrate 1, an n-InP cladding layer 2 having a thickness of 1 μm, an n-AlInAs cladding layer 3 having a thickness of 0.1 μm, an AlGaInAs-MQW active layer 4, and a p-layer having a thickness of 0.1 μm. AlInAs clad layer 5, p-InP clad layer 6.75 μm thick, p-InGaAs contact layer 7 0.6 μm thick, SiO ₂ film 8, P-side electrode (Ti / Au) 9, N-side electrode ( AuGe / Ni / Au) 10, a P-side plating electrode 11, a ridge 12, and a chip separation groove 13. The MQW active layer 4 is a layer formed with a multiple quantum well (Multi-Quantum-Well) structure in order to improve luminous efficiency. The multiple quantum well structure is a structure in which a quantum well structure in which a layer with a small band gap (well layer) is sandwiched between layers with a large band gap (barrier layer) is stacked in multiple layers.
[0025]
The semiconductor laser 100 having such a structure can be formed by stacking the respective layers by an epitaxial growth method and removing predetermined portions by etching. Examples of the epitaxial growth method include a metal organic chemical vapor deposition (MOCVD) method in which a gas containing an organic metal to be grown is caused to flow toward a substrate, and the organic metal is grown by a chemical reaction on the surface of the substrate. Metal organic molecular beam epitaxy (MOMBE), which evaporates toward the substrate and attaches and grows on the substrate, can be used. The layer grown by the epitaxial growth method is also called an epitaxial layer. Lamination is specifically performed as follows. On an n-InP substrate 1, an n-InP cladding layer 2, an n-AlInAs cladding layer 3, an AlGaInAs-MQW active layer 4, a p-AlInAs cladding layer 5, a p-InP cladding layer 6, and a p-InGaAs contact layer 7 are stacked by an epitaxial growth method. Then, the p-InP cladding layer 6 and the p-InGaAs contact layer 7 are partially removed by etching to form the ridge 12. That is, the ridge 12 is formed by the p-InP cladding layer 6 and the p-InGaAs contact layer 7. Thereafter, P-CVD or sputtering and etching are performed to form the SiO ₂ film 8, and then the P-side electrode 9 is laminated by vapor deposition. After that, the P-side electrode 9 and the N-side electrode 10 are formed. The formed semiconductor laser is separated in the chip separation groove 13.
[0026]
As is clear from the fact that the SiO ₂ film 8 is not provided on the p-InGaAs contact layer 7, the p-InGaAs contact layer 7 is electrically connected to the P-side electrode 9. Holes are injected from the P-side electrode 9 through the ridge 12. On the other hand, electrons are injected from the N-side electrode 10. As a result, in the semiconductor laser 100, light is generated by the combination of holes and electrons in the active layer 4.
[0027]
The feature of the ridge waveguide semiconductor laser 100 according to the first embodiment is that the chip separation groove 13 is formed to a depth at which the p-AlInAs clad layer 5 is exposed. In this structure, the etching time of the p-InP cladding layer 6 and the p-InGaAs contact layer 7 at the position of the chip separation groove 13 may be lengthened.
[0028]
In the conventional semiconductor laser 180 (FIG. 8), the chip separation groove 13 does not reach the p-AlInAs cladding layer 5, and the depth at which the p-InP cladding layer 6 laminated on the p-AlInAs cladding layer 5 is exposed. It was only formed until then. Therefore, conventionally, the depth of the chip separation groove 13 is only about the thickness (about 0.6 μm) corresponding to the thickness of the p-InGaAs contact layer 8. In addition, since the formation of the ridge 12 and the formation of the chip separation groove 13 had to be performed in separate steps, the number of steps was large.
[0029]
However, according to the structure of the semiconductor laser 100 of the present embodiment described above, the ridge 12 and the chip separation groove 13 can be formed simultaneously, so that the number of steps can be reduced. Then, a chip separation groove 13 having a depth (1.75 μm) corresponding to the thickness of the p-InP clad layer 6, specifically, a total depth of about 2.3 μm, is formed. I have. The advantages of providing the chip separation groove 13 having such a depth are as follows.
[0030]
FIG. 2 is a sectional view when the ridge waveguide semiconductor laser 100 is assembled by J-down assembly. When the J-down assembly is adopted for the semiconductor laser 100, the laser 100 is bonded to the mount material 14 via the solder material 15 with the active layer 4 side, that is, the ridge 12 side facing down.
[0031]
As shown in FIG. 2, the ridge waveguide type semiconductor laser 100 according to the present embodiment has a configuration in which even when the solder material 15 swells, the solder material 15 is applied to the p-AlInAs clad layer 5, the active layer 4, and the like from the side of the laser chip. Difficult to contact the epitaxial layer. This is because the depth of the chip separation groove is as deep as about 2.3 μm, compared with about 0.6 μm in the related art. This makes it difficult for the current to leak, and suppresses the occurrence of a leak failure.
[0032]
FIG. 3 is a cross-sectional view of the semiconductor laser 130 showing an example of manufacturing variation. Normally, it is manufactured like the semiconductor laser 100 shown in FIG. 2, but the SiO ₂ film 8 in the chip separation groove 13 is missing at the position 81 during chip separation. Further, the raised solder material 15 is in contact with the p-AlInAs clad layer 5.
[0033]
Conventionally, such a semiconductor laser is often used as a product having a short-circuit defect or a leak defect. However, such a defect does not occur in the semiconductor laser 130 according to the present embodiment. The reason is that the p-AlInAs cladding layer 5 contains a material (aluminum (Al)) that is easily oxidized, and therefore is oxidized once exposed to the air, and as a result, the contact resistance of the oxidized portion is extremely low. Become higher. Therefore, there is no leakage current from the contact portion between the solder material 15 and the p-AlInAs cladding layer 5, or even if the leakage current flows, it can be suppressed to an extremely small value. As a result, the yield of products is greatly improved.
[0034]
(Embodiment 2)
FIG. 4 is a perspective view of an AlGaInAs / InP-based ridge waveguide semiconductor laser 140 according to the second embodiment. The semiconductor laser 140 is configured by adding a new insulating film 16 to the semiconductor laser 180 (FIG. 8). The insulating film 16 is, for example, water glass. Other manufacturing steps are substantially the same as those described in the first embodiment, except that the chip separation groove 13 is etched so as not to reach the p-AlInAs clad layer 5. Note that, similarly to the semiconductor laser 100 of the first embodiment (FIG. 1), the depth of the chip separation groove 13 may be configured to reach the p-AlInAs clad layer 5.
[0035]
FIG. 5 is a cross-sectional view when the ridge waveguide semiconductor laser 140 is assembled by J-down assembly. The conventional ridge waveguide semiconductor laser 180 (FIG. 8) has a state in which a multilayer epitaxial layer is exposed uncoated on the side surface of the laser chip. However, in the semiconductor laser 140 according to the present embodiment, since the chip side surface is covered with the insulating film, as shown in FIG. No leak failure occurs.
[0036]
(Embodiment 3)
FIG. 6 is a perspective view of an AlGaInAs / InP-based ridge waveguide semiconductor laser 160 according to the third embodiment. The semiconductor laser 160 is configured by newly adding an air bridge type P-side plating electrode 110 instead of the P-side plating electrode 11 of the semiconductor laser 180 (FIG. 8). The air-bridge type P-side plating electrode 110 covers the upper part of the groove on the side of the ridge in a separated state without contacting the surface. This electrode 110 electrically connects the ridge 12 and the electrode pad. That is, unlike Embodiment 1, the P-side electrode 9 is not provided in the groove portion. Also, the chip separation groove 13 is etched so as not to reach the p-AlInAs clad layer 5. Other manufacturing steps are substantially the same as those described in the first embodiment. Note that, similarly to the semiconductor laser 100 of the first embodiment (FIG. 1), the depth of the chip separation groove 13 may be configured to reach the p-AlInAs clad layer 5.
[0037]
FIG. 7 is a cross-sectional view when the ridge waveguide type semiconductor laser 160 is assembled by J-down assembly. As is clear from the figure, in the semiconductor laser 160 according to the present embodiment, the solder material 15 does not enter the groove beside the ridge 12. Therefore, the stress applied to the ridge 12 due to the difference in thermal expansion coefficient between the solder material 15 and the crystal material can be suppressed. Further, since the air-bridge type P-side plating electrode 110 can be higher in the stacking direction than the conventional plating electrode 11 (FIG. 8), it is possible to prevent short-circuit failure and leakage current due to the swelling of the solder material 15.
[0038]
The embodiments of the present invention have been described above. In the first to third embodiments, the case where the crystal material is AlGaInAs / InP has been described. However, if the laser has a ridge waveguide structure, another crystal material (for example, AlGaInP / GaAs or the like) may be used. Even if different materials are used, the same effects as described above can be obtained.
[0039]
【The invention's effect】
According to the semiconductor laser of the present invention, at the chip separation position, the groove formed along the direction in which the third clad layer (p-InP clad layer 6) is laminated is formed in the second clad layer (p-InP clad layer 6). Since it reaches the AlInAs cladding layer 5), a separation groove deeper by the thickness corresponding to the thickness of the third cladding layer can be formed. Therefore, even when the solder material rises when the semiconductor laser is assembled by J-down assembly, it is difficult for the solder material to contact other layers. Therefore, current hardly leaks, and occurrence of leak failure is suppressed.
[0040]
Since the second clad layer (p-AlInAs clad layer 5) is formed of a material that is easily oxidized (for example, aluminum (Al)), the groove formed at the chip separation position is formed by the second clad layer. Even when reaching the layer (p-AlInAs clad layer 5) and being exposed to the air, the contact resistance of the oxidized portion becomes extremely high. Therefore, there is no leakage current in the oxidized portion, or even if leakage current flows, the leakage current can be extremely reduced.
[0041]
According to the laser of the present invention, the electrode electrically connected to the third cladding layer (ridge 12) of the ridge structure covers the upper side while being separated from the surface of the groove beside the ridge. Thus, when the semiconductor laser is assembled by J-down assembly, the solder material does not enter the groove beside the ridge. Therefore, the stress applied to the ridge due to the difference in thermal expansion coefficient between the solder material and the crystal material can be suppressed.
[0042]
As described above, in the ridge waveguide type semiconductor laser according to the present invention, there are characteristics problems such as short-circuit failure and generation of leakage current due to swelling of the solder material during J-down assembly, and the problem of the solder material and the crystal material. The reliability problem caused by the stress due to the difference in thermal expansion coefficient can be solved. Therefore, a significant improvement in yield can be expected.
[Brief description of the drawings]
FIG. 1 is a perspective view of a ridge waveguide semiconductor laser according to a first embodiment.
FIG. 2 is a cross-sectional view when the ridge waveguide type semiconductor laser is assembled by J-down assembly.
FIG. 3 is a cross-sectional view of a semiconductor laser showing an example of manufacturing variations.
FIG. 4 is a perspective view of a ridge waveguide semiconductor laser according to a second embodiment.
FIG. 5 is a cross-sectional view when a ridge waveguide semiconductor laser is assembled by J-down assembly.
FIG. 6 is a perspective view of a ridge waveguide semiconductor laser according to a third embodiment.
FIG. 7 is a cross-sectional view when a ridge waveguide semiconductor laser is assembled by J-down assembly.
FIG. 8 is a perspective view of a conventional ridge waveguide semiconductor laser.
FIG. 9 is a cross-sectional view showing an ideal state when a conventional ridge waveguide type semiconductor laser is assembled by J-down assembly.
FIG. 10 is a diagram illustrating a first problem when a conventional ridge waveguide semiconductor laser is manufactured by J-down assembly.
FIG. 11 is a diagram illustrating a second problem when a conventional ridge waveguide semiconductor laser is manufactured by J-down assembly.
[Explanation of symbols]
Reference Signs List 1 n-InP substrate, 2 n-InP cladding layer, 3 n-AlInAs cladding layer, 4 multiple quantum well active layer, 5 p-AlInAs cladding layer, 6 p-InP cladding layer, 7 p-InGaAs contact layer, 8 SiO ₂ film, 9P side electrode, 10N side electrode, 11P side plating electrode, 12 ridge, 13 chip separation groove, 16 insulating film, 100, 130, 140, 160 semiconductor laser, 110 air bridge type P side plating electrode

Claims (4)

A first cladding layer comprising a first material;
An active layer;
A second cladding layer containing the first material;
A ridge waveguide type semiconductor laser including a second cladding layer having a ridge structure and sequentially including a second material different from the first material,
A semiconductor laser in which a groove formed along a direction stacked from the third clad layer side reaches the second clad layer at a chip separation position of the semiconductor laser. The semiconductor laser according to claim 1, wherein the first material is a material that is easily oxidized. The semiconductor laser according to claim 2, wherein the material is aluminum. An active layer;
A first cladding layer and a second cladding layer sandwiching the active layer;
A third ridge-structured cladding layer laminated to the second cladding layer;
A ridge waveguide type semiconductor laser comprising the third cladding layer and an electrode electrically connected,
A semiconductor laser in which the electrode covers the upper side while being separated from the surface of the groove beside the ridge.

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