Semiconductor laser

Abstract

A compound semiconductor multilayer film (2–4) is formed on a compound semiconductor substrate (1) and has a ridge-shaped stripe (5) and a resonator end surface (6) that is a cleavage surface that is orthogonal to the long-side direction of the stripe (5). A first Au electrode (8) is formed on the stripe (5) to the resonator end surface (6). A second Au electrode (9) is formed on the first Au electrode (8) in a region that excludes a region adjacent to the resonator end surface (6). A metal layer (10) that is harder than Au is formed on the first Au electrode (8) in the region adjacent to the resonator end surface (6). A coating film (12) is formed at the resonator end surface (6).

Description

[Technical field]

[0001] The present disclosure relates to a semiconductor laser having a coating film formed on a resonator end face, which is a cleavage plane. [Background technology]

[0002] In a compound semiconductor laser, a ridge-shaped stripe is formed in the compound semiconductor multilayer film that will become the laser structure. Electrodes for passing current to the laser are formed on the stripe. The resonator facets are formed by cleaving the stripe in a direction perpendicular to the long side. A coating film is formed to protect the resonator facets and obtain the desired facet reflectance.

[0003] The electrode on the stripe also plays a role in extending the life of the laser by dissipating heat generated inside the laser to the outside through the pad electrode formed on the electrode. Therefore, Au electrodes with high thermal conductivity are used as the electrodes. Forming Au electrodes on the stripe up to the resonator end face is effective in increasing the heat dissipation of the laser and manufacturing highly reliable laser elements. However, in order to form Au electrodes up to the resonator end face, it is necessary to cleave the area on the stripe where the Au electrodes are formed. Since Au is highly malleable, when an attempt is made to cleave a compound semiconductor together with the Au electrodes, the Au electrodes stretch and are torn off when they are cut, and hang down so as to cover the resonator end face.

[0004] When the coating film is formed, the sagging parts of the Au get in the way, creating cavities between the coating film and the resonator end faces. If moisture penetrates through these cavities, the laser characteristics change. When using a multilayer film as the coating film, the moisture resistance of the entire coating film is increased by using a highly moisture-resistant film as the final layer of the multilayer film. However, if there are cavities as described above, moisture from the air will penetrate directly through the cavities into the inner layers of the coating film, which have lower moisture resistance than the final layer, significantly worsening the moisture resistance of the laser.

[0005] In response to this, a technique has been disclosed in which the Au electrode at the cleavage position is made thinner than other portions to improve cleavage properties (see, for example, Patent Document 1). [Prior art documents] [Patent documents]

[0006] [Patent Document 1] Japanese Patent Publication No. 2000-22272 Summary of the Invention [Problem to be solved by the invention]

[0007] However, simply thinning the Au electrode at the cleavage position was not enough to prevent the Au from sagging onto the cavity facets, and moisture penetrated through the cavities caused by the Au sagging, reducing the moisture resistance of the laser.

[0008] The present disclosure has been made to solve the problems described above, and its purpose is to obtain a semiconductor laser that can sufficiently suppress the sagging of Au onto the cavity end faces and prevent deterioration of moisture resistance. [Means for solving the problem]

[0009] The semiconductor laser according to the present disclosure is characterized in comprising: a compound semiconductor substrate; a compound semiconductor multilayer film formed on the compound semiconductor substrate and having a ridge-shaped stripe and a resonator facet which is a cleavage plane perpendicular to a long side direction of the stripe; a first Au electrode formed on the stripe up to the resonator facet; a second Au electrode formed on the first Au electrode in a region excluding a region adjacent to the resonator facet; a metal layer having a harder than Au formed on the first Au electrode in a region adjacent to the resonator facet; and a coating film formed on the resonator facet. Effect of the Invention

[0010] In the present disclosure, instead of forming a second Au electrode in the region adjacent to the resonator facet, a metal layer having a harder property than Au is formed. This sufficiently prevents Au from sagging down to the resonator facet during cleavage. Since it is possible to prevent cavities caused by Au sagging, it is possible to prevent deterioration of moisture resistance. [Brief description of the drawings]

[0011] [Figure 1] 1 is a perspective view showing a semiconductor laser according to a first embodiment. [Diagram 2] 1 is a cross-sectional view showing a semiconductor laser according to a first embodiment. [Diagram 3] 2A to 2C are cross-sectional views illustrating a manufacturing process for the semiconductor laser according to the first embodiment. [Figure 4] 2A to 2C are cross-sectional views illustrating a manufacturing process for the semiconductor laser according to the first embodiment. [Diagram 5] 2A to 2C are cross-sectional views illustrating a manufacturing process for the semiconductor laser according to the first embodiment. [Figure 6] 2A to 2C are cross-sectional views illustrating a manufacturing process for the semiconductor laser according to the first embodiment. [Figure 7] 5A to 5C are cross-sectional views showing a manufacturing process of a semiconductor laser according to a comparative example. [Figure 8] 5A to 5C are cross-sectional views showing a manufacturing process of a semiconductor laser according to a comparative example. [Figure 9] 5A to 5C are cross-sectional views showing a manufacturing process of a semiconductor laser according to a comparative example. [Figure 10] 10 is an enlarged cross-sectional view of a portion of a semiconductor laser according to a second embodiment. FIG. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0012] A semiconductor laser according to an embodiment will be described with reference to the drawings. The same or corresponding components are designated by the same reference numerals, and repeated description may be omitted.

[0013] Embodiment 1 FIG. 1 is a perspective view showing a semiconductor laser according to the first embodiment. FIG. 2 is a cross-sectional view showing the semiconductor laser according to the first embodiment. A compound semiconductor substrate 1 is, for example, an n-InP substrate. An n-InP clad layer 2, an active layer 3, and a p-InP clad layer 4 are formed in this order on the compound semiconductor substrate 1 as a compound semiconductor multilayer film that serves as a laser oscillator. A ridge-shaped stripe 5 and a cavity end face 6 are formed in the compound semiconductor multilayer film. The cavity end face 6 is a cleavage plane perpendicular to the long side direction of the stripe 5. FIG. 2 is a cross-sectional view taken along the long side direction of the stripe 5. Sides perpendicular to the short side direction of the stripe 5 and a part of the top surface are covered with an insulating protective film 7.

[0014] A first Au electrode 8 is formed up to the resonator end face 6 on the upper surface of the stripe 5 exposed from the opening in the insulating protective film 7. That is, the first Au electrode 8 is also formed in a region adjacent to the resonator end face 6. A second Au electrode 9 is formed on the first Au electrode 8 in a region excluding the region adjacent to the resonator end face 6. A metal layer 10 is formed on the first Au electrode 8 in the region adjacent to the resonator end face 6. The metal layer 10 is made of a metal harder than Au, such as Ti, Ni, or Cr.

[0015] A bottom electrode 11 is formed on the bottom surface of the compound semiconductor substrate 1. A coating film 12 is formed on the cavity facet 6. The coating film 12 is a single-layer insulating film, but may be a multi-layer film. The coating film 12 is formed on both the front and rear facets of the semiconductor laser. Note that the coating film 12 is not shown in FIG. 1.

[0016] 3-6 are cross-sectional views showing the manufacturing process of the semiconductor laser according to the first embodiment. First, as shown in FIG. 3, an n-InP cladding layer 2, an active layer 3, and a p-InP cladding layer 4 are formed in order on a compound semiconductor substrate 1 as a compound semiconductor multilayer film. A striped mask layer is formed on the compound semiconductor multilayer film, and a ridge-shaped stripe 5 is formed in the compound semiconductor multilayer film by etching a portion not covered by the mask layer. After removing the mask layer, an insulating protective film 7 is formed so as to cover the upper and side surfaces of the stripe 5. An opening is formed by etching the insulating protective film 7 on the upper surface of the stripe 5. A first Au electrode 8 is formed in the opening by deposition or the like. Next, a second Au electrode 9 is formed on the first Au electrode 8 except for the cleavage position and its adjacent region. As a result, the Au electrode is formed in a stripe shape so that only the cleavage position and its adjacent region are thin. Next, a metal layer 10 is formed on the first Au electrode 8 at the cleavage position and its adjacent region. Thereafter, a lower electrode 11 is formed on the lower surface of the compound semiconductor substrate 1. In addition, the lower electrode 11 is omitted in FIGS.

[0017] Next, as shown in Fig. 4, the compound semiconductor substrate 1 and the compound semiconductor multilayer film are cleaved together with the first Au electrode 8 and the metal layer 10 from the metal layer 10 side toward the compound semiconductor substrate 1 side. Fig. 5 shows the resonator facets 6 formed by cleavage. Next, as shown in Fig. 6, a coating film 12 is formed on the resonator facets 6 by deposition, sputtering, or the like.

[0018] Next, the effect of this embodiment will be described in comparison with a comparative example. Figures 7-9 are cross-sectional views showing the manufacturing process of a semiconductor laser according to the comparative example. In the comparative example, as shown in Figure 7, only Au electrode 13 is formed on stripe 5. Next, as shown in Figure 8, compound semiconductor substrate 1 and compound semiconductor multilayer film are cleaved together with Au electrode 13 from the side of Au electrode 13. Since Au is highly malleable, Au electrode 13 is torn off while stretching, and hangs down so as to cover cavity end face 6.

[0019] Next, as shown in Fig. 9, a coating film is formed on the resonator facet 6. During this process, the sagging Au portion gets in the way, creating a cavity 14 between the coating film 12 and the resonator facet 6. Moisture will penetrate through this cavity 14, degrading the moisture resistance of the laser. Note that simply thinning the Au electrode 13 at the cleavage position is not enough to sufficiently prevent the Au from sagging onto the resonator facet 6.

[0020] In contrast, in the present embodiment, the second Au electrode 9 is not formed in the region adjacent to the resonator facet 6, but a metal layer 10 having a harder property than Au is formed instead. This sufficiently prevents Au from sagging onto the resonator facet 6 during cleavage. Since it is possible to prevent the formation of voids 14 caused by Au sagging, it is possible to prevent deterioration of moisture resistance.

[0021] In addition, since the first Au electrode 8 is formed on the upper surface of the stripe 5 up to the cavity facet 6, heat generated at the laser facet is dissipated through the first Au electrode 8. The metal layer 10 also works advantageously in dissipating heat.

[0022] Furthermore, the length from the cavity facets 6 to the second Au electrodes 9 in the long side direction of the stripes 5 is preferably 10 μm to 100 μm. If the length is less than 10 μm, which is the cleavage position accuracy, it becomes difficult to cleave the thin regions of the Au electrodes. On the other hand, if the length is greater than 100 μm, it becomes difficult to ensure heat dissipation in the regions adjacent to the cavity facets 6.

[0023] Furthermore, if the first Au electrode 8 is too thin, there is a risk that the film thickness cannot be controlled when forming it by deposition, for example. Therefore, the thickness of the first Au electrode 8 is preferably 300 Å to 1000 Å. The thickness of the second Au electrode 9 is 1 to 3 μm. The thickness of the metal layer 10 is 300 Å to 2000 Å.

[0024] Embodiment 2 10 is an enlarged cross-sectional view of a portion of a semiconductor laser according to the second embodiment. Instead of the metal layer 10 of the first embodiment, an insulating film 15 is formed on the first Au electrode 8 in a region adjacent to the cavity facet 6. The insulating film 15 and the coating film 12 are made of different materials. The insulating film 15 is, for example, a SiO2 film. The presence of the insulating film 15, which has better cleavage properties than metal, on the first Au electrode 8 at the cleavage position can adequately prevent Au from sagging onto the cavity facet 6 during cleavage. The other configurations and effects are the same as those of the first embodiment.

[0025] The present disclosure is not limited to the above-described embodiments, and various modifications are possible without departing from the spirit of the present disclosure. The present disclosure also includes all combinations of possible configurations among the configurations shown in the respective embodiments. [Explanation of symbols]

[0026] 1 compound semiconductor substrate, 2 n-InP cladding layer (compound semiconductor multilayer film), 3 active layer (compound semiconductor multilayer film), 4 p-InP cladding layer (compound semiconductor multilayer film), 5 stripe, 6 resonator facet, 8 first Au electrode, 9 second Au electrode, 10 metal layer, 12 coating film, 15 insulating film

Claims

1. A compound semiconductor substrate; a compound semiconductor multilayer film formed on the compound semiconductor substrate, the compound semiconductor multilayer film having a ridge-shaped stripe and a cavity end face which is a cleavage surface perpendicular to a long side direction of the stripe; a first Au electrode formed on the stripe up to the cavity end face; a second Au electrode formed on the first Au electrode in a region other than a region adjacent to the cavity end face; a metal layer having a hardness greater than that of Au, the metal layer being formed on the first Au electrode in a region adjacent to the cavity end face; and a coating film formed on the cavity end face.

2. 2. The semiconductor laser according to claim 1, wherein the metal layer is made of Ti, Ni or Cr.

3. A compound semiconductor substrate; a compound semiconductor multilayer film formed on the compound semiconductor substrate, the compound semiconductor multilayer film having a ridge-shaped stripe and a cavity end face which is a cleavage surface perpendicular to a long side direction of the stripe; a first Au electrode formed on the stripe up to the cavity end face; a second Au electrode formed on the first Au electrode in a region other than a region adjacent to the cavity end face; an insulating film formed on the first Au electrode in a region adjacent to the cavity end face; a coating film formed on said cavity end face and made of a material different from said insulating film.

4. 4. The semiconductor laser according to claim 1, wherein the length from the cavity end face to the second Au electrode in the direction of the longer side of the stripe is 10 μm to 100 μm.

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