Semiconductor laser element

Abstract

Provided is a semiconductor laser element in which peeling of an insulating film and wiring is less likely to occur.　A laser waveguide (200) extends in a first direction (y direction). A groove (190) extending in the first direction (y direction) is formed on a surface of a semiconductor laser element (100). The groove (190) includes a first portion (192) having a relatively narrow width in a second direction (x direction) when viewed in cross-section, and a second portion (194) located deeper than the first portion (192) and having a relatively wide width in the second direction (x direction). In at least a part of the first direction (y direction), a surface of the groove (190) is continuously covered in a direction crossing the groove (190) by metal connection wiring (Lc) or a contact insulation film (160), which is an insulating material.

Description

semiconductor laser element

[0001] The present disclosure relates to a semiconductor laser device.

[0002] Semiconductor lasers are used as light sources in electronic devices such as printers and head-mounted displays (HMDs). To accommodate the increasing resolution of such electronic devices that handle images, multi-beam semiconductor laser elements are being adopted.

[0003] To miniaturize lenses and MEMS mirrors, it is necessary to narrow the beam pitch. If the beam pitch is narrower than the ball diameter for wire bonding or the solder pattern width for die bonding, it becomes impossible to secure an area for direct wire bonding or die bonding to the electrode on the top surface of the laser waveguide. As a result, it becomes necessary to form the electrode pads closer to the edge of the chip (semiconductor substrate). In this case, the connecting wiring (laminated wiring) connecting the electrode pads and the laser waveguide must straddle the laser waveguide (see Patent Document 1).

[0004] Specifically, the connection wiring that connects the power supply electrode (P-side electrode) formed on the top surface of the central laser waveguide to the electrode pad crosses the adjacent laser waveguide. Focusing on the intersection of the connection wiring and the laser waveguide, an interlayer insulating film is inserted between the connection wiring and the power supply electrode of the laser waveguide, forming a laminated wiring structure.

[0005] JP 2000-269601 A JP 2010-135731 A

[0006] The present inventors have studied narrow beam pitch multi-beam semiconductor laser devices and have come to recognize the following problems.

[0007] Forming the connecting wires that intersect with the power supply electrodes requires complex processes, which makes it easy for the interlayer insulating film, connecting wires, etc. Peeling is particularly likely to occur on the upper part of an uneven base, such as on a ridge, or in a location where different materials with different thermal expansion coefficients are crossed.

[0008] Such problems are not limited to the connection wiring in multi-beam semiconductor laser devices, but can occur in wiring, pads, and insulating films in other semiconductor laser devices.

[0009] An aspect of the present disclosure has been made in view of such problems, and one exemplary purpose thereof is to provide a semiconductor laser element in which peeling of insulating films and wiring is unlikely to occur.

[0010] One aspect of the present disclosure relates to a semiconductor laser element. The semiconductor laser element includes a laser waveguide. A groove extending in a first direction is formed on a surface of the semiconductor laser element. When viewed in cross section, the groove includes a first portion having a relatively narrow width in a second direction and a second portion located deeper than the first portion and having a relatively wide width in the second direction. At least a portion of the surface of the groove in the first direction is covered with a metal or insulating material formed so as to cross the groove in the second direction.

[0011] Any combination of the above components, or mutual substitution of the components or expressions of the present disclosure between methods, devices, systems, etc., are also valid aspects of the present disclosure.

[0012] According to an aspect of the present disclosure, a semiconductor laser device can be provided in which peeling of insulating films and wiring is unlikely to occur.

[0013] 1 is a perspective view of a semiconductor laser element according to embodiment 1; a cross-sectional view of a portion of the semiconductor laser element of FIG. 1; an enlarged view of a groove; a cross-sectional view of a groove according to modification 1.1; a cross-sectional view of a groove according to modification 1.2; a cross-sectional view of a semiconductor laser element according to modification 1.3; a cross-sectional view of a semiconductor laser element according to modification 1.4; a cross-sectional view of a semiconductor laser element according to modification 1.5; a cross-sectional view of a semiconductor laser element according to embodiment 2; a cross-sectional view of a groove according to modification 2.1;

[0014] (Summary of the Embodiments) A summary of some exemplary embodiments of the present disclosure will be provided. This summary is intended as a prelude to the detailed description that follows, or to provide a basic understanding of the embodiments. The summary is intended to briefly explain some concepts of one or more embodiments and is not intended to limit the scope of the invention or disclosure. Furthermore, this summary is not an exhaustive overview of all possible embodiments, nor does it limit essential elements of the embodiments. For convenience, the term "one embodiment" may refer to one embodiment (example or variant) or multiple embodiments (examples or variants) disclosed herein.

[0015] A semiconductor laser device according to one embodiment includes a laser waveguide extending in a first direction. A groove extending in the first direction is formed in a surface of the semiconductor laser device, and the groove includes, in a cross-sectional view, a first portion having a relatively narrow width in a second direction and a second portion located deeper than the first portion and having a relatively wide width in the second direction. At least a portion of the surface of the groove in the first direction is covered with a metal or insulating material formed so as to cross the groove in the second direction.

[0016] In one embodiment, the groove may have a protrusion on the side surface corresponding to the first portion.

[0017] In one embodiment, the trench is formed in a layered growth layer, and the first and second portions may be made of different materials.

[0018] In one embodiment, the first portion may be an active layer.

[0019] In one embodiment, the first portion may be a contact layer.

[0020] In one embodiment, the groove may have a tapered shape in which the width narrows toward the surface when viewed in cross section.

[0021] In one embodiment, the difference in width between the first portion and the second portion may be 10 nm or more and 1 μm or less.

[0022] In one embodiment, the trench may be deeper than the active layer.

[0023] In one embodiment, the trench may be shallower than the active layer.

[0024] In one embodiment, the grooves may be filled with at least one of a metal and an insulating material.

[0025] In one embodiment, the laser waveguide may extend in a first direction.

[0026] In one embodiment, the laser waveguide may extend in the second direction, in which case the groove may be a light-shielding groove.

[0027] In one embodiment, a plurality of laser waveguides may be formed adjacent to each other in the second direction in a laser region on the semiconductor substrate, and a plurality of grooves may be formed adjacent to the plurality of laser waveguides.

[0028] In one embodiment, power supply electrodes may be formed on the plurality of laser waveguides. The semiconductor laser element may further include a plurality of connection wires corresponding to the plurality of laser waveguides, each extending in the second direction and connected to the power supply electrode of the corresponding laser waveguide, and an interlayer insulating film formed including a portion where the connection wires and the power supply electrodes, which should be insulated from each other, intersect. The surface of the groove may be covered with the interlayer insulating film or the connection wires.

[0029] (Embodiments) The present disclosure will be described below based on preferred embodiments with reference to the drawings. The same or equivalent components, parts, and processes shown in each drawing will be given the same reference numerals, and redundant explanations will be omitted as appropriate. Furthermore, the embodiments are examples rather than limitations on the disclosure, and all features and combinations thereof described in the embodiments are not necessarily essential to the disclosure.

[0030] The dimensions (thickness, length, width, etc.) of each member shown in the drawings may be enlarged or reduced as appropriate for ease of understanding. Furthermore, the dimensions of multiple members do not necessarily represent the relative size of each other. Even if a member A is depicted as being thicker than another member B in the drawings, member A may actually be thinner than member B.

[0031] 1 is a perspective view of a semiconductor laser device 100 according to embodiment 1. The semiconductor laser device 100 is an edge-emitting semiconductor laser device, and is a multi-beam semiconductor laser having a plurality of m emitters (m≧3). In this embodiment, the number m of emitters is 4.

[0032] The semiconductor laser device 100 includes an N-type semiconductor substrate 110 and a layered growth layer 102 formed on the N-type semiconductor substrate 110. The layered growth layer 102 includes an N-type cladding layer 120, a light-emitting layer (active layer) 130, a P-type cladding layer 140, and a P-type contact layer 142, which are layered in this order on the N-type semiconductor substrate 110. The light-emitting layer 130 includes an N-type guide layer (lower guide layer), an active layer formed of a quantum well layer, and a P-type guide layer (upper guide layer). The materials for the N-type semiconductor substrate 110 and the layered growth layer 102 may be selected depending on the required oscillation wavelength, and are not particularly limited in the present disclosure.

[0033] The semiconductor laser element 100 has a central laser region 902 and pad regions 904 and 906. In the laser region 902, m (m≧3) stripe-shaped laser waveguides 200_1 to 200_m are formed, each extending in a first direction (y direction) and adjacent to each other in a second direction (x direction).

[0034] A waveguide structure for confining light is formed in the layered growth layer 102, and the cleaved surfaces at both ends of this waveguide structure serve as mirrors, forming a Fabry-Perot laser waveguide 200. In this example, four laser waveguides 200_1 to 200_4 are formed, and beams BM1 to BM4 are emitted in the y direction from a front end face (emission end face) S1. The front end face S1 and rear end face S2 of each laser waveguide 200 are coated to provide a desired reflectivity.

[0035] In this embodiment, the waveguide structure is a ridge waveguide, and a ridge structure (mesa structure) 104 extending in the y direction is formed in the P-type cladding layer 140 of the layered growth layer 102 .

[0036] A contact insulating film 160 is formed on the upper surface of the semiconductor laser device 100. A rectangular opening, elongated in the y direction, is formed in the contact insulating film 160 on the upper surface of the laser waveguides 200_1 to 200_n, specifically on the upper surface of the ridge structure 104. A power supply electrode (P-side electrode) 150 is formed along this opening and connected to the P-type contact layer 142. To enable the laser waveguides 200 to be driven independently, the power supply electrodes 150 are electrically insulated from each other. Furthermore, the P-type semiconductor portions have electrical resistance between each emitter, enabling them to be driven independently. In this embodiment, the power supply electrode 150 is a stripe-shaped electrode extending along the y direction on the upper surface of the laser waveguide 200.

[0037] An N-side electrode 152 is formed on the back surface of the laser waveguide 200 .

[0038] To supply power to the laser waveguide 200, a plurality of chip-side electrode pads (hereinafter simply referred to as electrode pads) Pe1 to Pe4 and a plurality of connection wires Lc1 to Lc4 are provided corresponding to the plurality of laser waveguides 200_1 to 200_4.

[0039] A plurality of electrode pads Pe1 to Pe4 are formed in pad regions 904 and 906 adjacent in the x-direction to the laser region 902. Bonding wires are connected to the electrode pads Pe1 to Pe4 in the case of junction-up mounting, and solder is connected to the electrode pads Pe1 to Pe4 in the case of junction-down mounting.

[0040] Each connection wiring Lci (i=1, 2, 3, 4) electrically connects the power supply electrode 150 of the corresponding laser waveguide 200_i to the corresponding electrode pad Pi.

[0041] For the two innermost ones (200_2, 200_3) of the plurality of laser waveguides 200_1 to 200_4, the connection wirings Lc2 and Lc3 cross the power supply electrode 150 of the outer laser waveguide 200. Specifically, the connection wiring Lc2 crosses the power supply electrode 150_1 of the laser waveguide 200_1. Similarly, the connection wiring Lc3 crosses the power supply electrode 150_4 of the laser waveguide 200_4.

[0042] The interlayer insulating film 170 is formed to include the points where the connection wiring Lc and the power supply electrode 150, which should be insulated from each other, intersect, thereby ensuring electrical insulation between the connection wiring Lc2 and the power supply electrode 150_1 and electrical insulation between the connection wiring Lc3 and the power supply electrode 150_4.

[0043] In this embodiment, an interlayer insulating film 170 is provided independently at each location where the connection wiring Lc intersects with the power supply electrode 150. Specifically, the interlayer insulating film 170_1 is provided at the location where the connection wiring Lc2 intersects with the power supply electrode 150_1, and the interlayer insulating film 170_4 is provided at the location where the connection wiring Lc3 intersects with the power supply electrode 150_4.

[0044] At least one stripe-shaped groove 190 extending in a first direction (y direction) is formed on the top surface of the semiconductor laser element 100. In this example, the groove 190 is formed adjacent to each laser waveguide 200. As will be described below, this groove 190 has the function of suppressing peeling of the insulating film, wiring, and pads formed on the top surface of the semiconductor laser element 100. Note that the groove 190 may also serve as a separation groove that thermally and / or electrically separates adjacent laser waveguides 200.

[0045] 2 is a cross-sectional view of a portion of the semiconductor laser device 100 of FIG. 1. When viewed in cross section, the groove 190 includes a first portion 192 having a relatively narrow width in the second direction (x direction) and a second portion 194 located deeper than the first portion 192 and having a relatively wide width in the second direction. The first portion 192 has a protruding structure protruding from the side surface of the groove having a rectangular cross section. When the semiconductor laser device 100 is viewed in a plan view along the z direction, a portion of the bottom surface of the groove 190 is hidden by the protruding portion. The difference in width between the first portion 192 and the second portion 194 is preferably 10 nm or more and 1 μm or less.

[0046] In this embodiment, in at least a portion in the y direction, the surface of at least one groove 190 is continuously covered in a direction across the groove 190, i.e., in the x direction, with any of a metal, an inorganic insulating material, or an organic insulating material. In Figure 2, the surfaces of multiple grooves 190a to 190c are covered with a contact insulating film 160. Furthermore, in the grooves 190b and 190c, a connection wiring Lc3 is formed on the contact insulating film 160.

[0047] FIG. 3 is an enlarged view of the groove 190. The groove 190 is formed in the multilayer growth layer 102 of a crystalline material, with the first portion 192 and the second portion 194 being made of different materials. After the multilayer growth layer 102 is formed, the groove 190 is formed by etching before the contact insulating film 160 is formed. By utilizing the difference in etching rates between the different materials, the first portion 192 and the second portion 194, which are protruding structures, can be formed. In the example of FIG. 3, the depth of the groove 190 is deeper than that of the light-emitting layer 130. The first portion 192 is the light-emitting layer 130, and the second portion 194 is the N-type cladding layer 120. Here, the difference in width between the first portion 192 and the second portion 194 is preferably 10 nm or more and 1 μm or less. By keeping the difference in width between first portion 192 and second portion 194 within the above-mentioned range, even if stress is applied to the contact insulating film in the direction toward the chip top surface, the film in the groove is caught on the protrusion in the groove, preventing film peeling. If the difference in width between first portion 192 and second portion 194 is small, sufficient peeling prevention effect cannot be achieved. Furthermore, if the difference in width between first portion 192 and second portion 194 is too large, it becomes difficult to obtain sufficient film coverage at the protrusion, making peeling more likely to occur.

[0048] The above is the configuration of the semiconductor laser device 100.

[0049] In this semiconductor laser device 100, the first portions 192 each having a protruding shape engage with the contact insulating film 160 in the grooves 190a to 190c. That is, the first portions 192 function as anchors that improve connectivity. Therefore, the combination of the first portions 192 and the second portions 194 is called an anchor structure, and the grooves having the anchor structure are also called anchor grooves.

[0050] Furthermore, by forming the contact insulating film 160 thin, it is possible to provide the contact insulating film 160 with irregularities that conform to the shapes of the underlying layers of the grooves 190a to 190c. As a result, in the grooves 190b and 190c, the first portions 192 also function as anchors that improve the adhesion of the connection wiring Lc.

[0051] Next, a modified example will be described.

[0052] (Variation 1.1) FIG. 4 is a cross-sectional view of a groove 190A according to Variation 1.1. In Variation 1.1, the groove 190A is formed in the layered growth layer 102, similar to FIG. 3. The cross-sectional shape of this groove 190A is trapezoidal, and has a tapered shape that becomes wider as it gets deeper. In this structure, the shallowest part of the groove 190A is the first part 192, and the deepest part is the second part 194. In FIG. 4, the depth of the groove 190A is deeper than the light-emitting layer 130, but it may be shallower than the light-emitting layer 130.

[0053] (Modification 1.2) FIG. 5 is a cross-sectional view of a groove 190B according to Modification 1.2. In Modification 1.2, a groove 191 having a rectangular cross section is formed in the layered growth layer 102, and an insulating layer 193 thereon forms an anchor structure consisting of a first portion 192 and a second portion 194. For example, the insulating layer 193 having the anchor structure can be formed of a contact insulating film 160. The contact insulating film 160 may be a CVD insulating film (CVD oxide film) formed by a chemical vapor deposition (CVD) method, or may be formed by a sputtering method or an atomic layer deposition (ALD) method.

[0054] In this embodiment, after forming the groove 191, a CVD insulating film, which is the contact insulating film 160, is formed. The CVD insulating film has a property that the deposition rate at the corners is higher than the deposition rate at the flat portions. Therefore, the CVD insulating film has a protruding structure at the corners of the entrance of the groove 191, and a narrow first portion 192 can be formed. In FIG. 5, the groove 190B is deeper than the light-emitting layer 130, but this is not limiting, and the groove 190B may be shallower than the light-emitting layer 130.

[0055] Then, by forming another insulating film or wiring 180 on the CVD insulating film having the protruding structure, it becomes difficult for the other insulating film or wiring 180 to peel off. Note that since the CVD insulating film has high adhesion to the underlying semiconductor material, it can obtain sufficient adhesion strength for a groove having a rectangular cross section, and the possibility of peeling off is low.

[0056] 6 is a cross-sectional view of a semiconductor laser device 100C according to Modification 1.3. In this modification, an interlayer insulating film 170 is formed on each laser waveguide 200. An opening is formed in the interlayer insulating film 170_i (i=1, 2, 3, 4) at a position where the corresponding connection wiring Lc_i and the power supply electrode 150_i should be connected.

[0057] According to this modification 1.3, by forming the connection wiring Lc3 along the grooves 190b and 190c, it is possible to improve the adhesiveness to the contact insulating film 160 and make it difficult for the connection wiring Lc3 to peel off.

[0058] (Modification 1.4) Fig. 7 is a cross-sectional view of a semiconductor laser device 100D according to Modification 1.4. In this modification, similar to Fig. 6, a plurality of laser waveguides 200 are covered with an interlayer insulating film 170D. The difference from Fig. 6 is that the interlayer insulating film 170D is continuous.

[0059] In this configuration, the interlayer insulating film 170D is formed along the grooves 190b and 190c. Therefore, the interlayer insulating film 170D is less likely to peel off than in the configuration of Fig. 6. Furthermore, the connection wiring Lc3 is also less likely to peel off because it is formed on the interlayer insulating film 170D along the grooves 190b and 190c.

[0060] (Modification 1.5) Fig. 8 is a cross-sectional view of a semiconductor laser device 100E according to Modification 1.5. In this modification, similar to Fig. 7, an interlayer insulating film 170E is continuously formed across a plurality of laser waveguides 200. The difference from Fig. 7 is that the grooves 190 are filled with the interlayer insulating film 170E. This configuration can further improve the adhesion of the interlayer insulating film 170E to the multilayer growth layer 102.

[0061] Second Embodiment In the first embodiment and its modifications, a ridge-type waveguide has been described, but the structure of the waveguide is not limited to this.

[0062] 9 is a cross-sectional view of a semiconductor laser device 100F according to embodiment 2. In FIG. 9, the laser waveguide 200 does not have the ridge structure 104.

[0063] The structure of the groove 190 in the second embodiment is not particularly limited, and the structure of the groove 190 described in the first embodiment can be adopted.

[0064] According to the second embodiment, peeling of the insulating film and wiring can be prevented, similarly to the first embodiment. Next, modifications related to the second embodiment will be described.

[0065] (Variation 2.1) Fig. 10 is a cross-sectional view of a groove 190G according to Variation 2.1. In the first embodiment and its variations, the groove 190G is formed in the P-type cladding layer 140 in a portion where the P-type contact layer 142 has been removed due to the ridge structure 104. In contrast, in the second embodiment, the P-type contact layer 142 remains on the surface layer of the semiconductor laser device 100. In Variation 2.1, the groove 190G is formed in the multilayer growth layer 102 of a crystalline material including the P-type contact layer 142, and a first portion 192 having a protruding structure is formed by utilizing the P-type contact layer 142.

[0066] The P-type contact layer 142 and the P-type cladding layer 140 are different materials and therefore have different etching rates. For example, the P-type cladding layer 140 is made of GaAs, and the N-type cladding layer 120 is made of AlInP, and the etching rate of GaAs is lower. Therefore, the first portion 192 can be formed by the P-type cladding layer 140.

[0067] (Other Modifications) The above-described embodiment is merely an example, and it will be understood by those skilled in the art that various modifications are possible in the combination of the respective components and the respective processing steps. These modifications will be described below.

[0068] The above description has been directed to preventing peeling of the connection wiring Lc and the underlying interlayer insulating film 170 in a multi-beam semiconductor laser element, but the application of the technology disclosed herein is not limited thereto. When there are wirings or insulating films that are prone to peeling in addition to the connection wiring Lc and the interlayer insulating film 170, peeling can be made less likely by forming grooves 190 with anchor structures around the wirings or insulating films and forming the wirings or insulating films continuously along the grooves 190. For example, to prevent peeling of the electrode pads Pe, the grooves 190 may be formed along the formation regions of the electrode pads Pe, and the electrode pads Pe may be formed to extend across the grooves 190.

[0069] The technology according to the present disclosure is applicable not only to multi-beam semiconductor laser elements but also to single-beam semiconductor laser elements when they have wiring or insulating films that are prone to peeling.

[0070] Some semiconductor laser elements have a bank adjacent to the laser waveguide. A light-shielding groove for blocking light leakage from the bank may be provided on the light-emitting end face side. In this case, the light-shielding groove may have an anchor structure, as described in the embodiment.

[0071] Although the embodiments of the present disclosure have been described using specific terms, this description is merely an example to facilitate understanding and does not limit the scope of the present disclosure or the claims. The scope of the present invention is defined by the claims, and therefore, embodiments, examples, and modifications not described herein are also included in the scope of the present invention.

[0072] REFERENCE SIGNS LIST 100 Semiconductor laser element 102 Layered growth layer 104 Ridge structure S1 Front end face S2 Rear end face 902 Laser region 904, 906 Pad region 110 N-type semiconductor substrate 120 N-type cladding layer 130 Light-emitting layer 140 P-type cladding layer 160 Contact insulating film Pe Electrode pad Lc Connection wiring 150 Power supply electrode 152 N-side electrode 154 Contact insulating film 170 Interlayer insulating film 200 Laser waveguide

Claims

1. A semiconductor laser element comprising a laser waveguide, wherein a groove extending in a first direction is formed on a surface of the semiconductor laser element, the groove including, when viewed in cross section, a first portion having a relatively narrow width in a second direction, and a second portion located deeper than the first portion and having a relatively wide width in the second direction, wherein the surface of the groove is covered in at least a portion of the groove in the first direction with a metal or insulating material formed so as to cross the groove in the second direction.

2. A semiconductor laser device according to claim 1, wherein the groove has a protrusion on a side surface thereof corresponding to the first portion.

3. The semiconductor laser device according to claim 2, wherein the groove is formed in a multilayer growth layer, and the first portion and the second portion are made of different materials.

4. The semiconductor laser device according to claim 3, wherein the first portion is an active layer.

5. The semiconductor laser device according to claim 3, wherein the first portion is a contact layer.

6. The semiconductor laser device according to claim 1, wherein the groove has a tapered shape in which the width narrows toward the surface when viewed in cross section.

7. A semiconductor laser device according to any one of claims 1 to 6, wherein the difference in width between the first portion and the second portion is 10 nm or more and 1 µm or less.

8. The semiconductor laser device according to any one of claims 1 to 6, wherein the groove is deeper than the active layer.

9. The semiconductor laser device according to any one of claims 1 to 3, wherein the groove is shallower than the active layer.

10. The semiconductor laser device according to any one of claims 1 to 6, wherein the grooves are filled with at least one of a metal and an insulating material.

11. The semiconductor laser device according to any one of claims 1 to 6, wherein the laser waveguide extends in the first direction.

12. The semiconductor laser device according to claim 11, wherein a plurality of the laser waveguides are formed adjacent to each other in the second direction in a laser region on a semiconductor substrate, and a plurality of the grooves are formed adjacent to the plurality of laser waveguides.

13. A semiconductor laser element according to any one of claims 1 to 6, further comprising: a power supply electrode formed on the plurality of laser waveguides; a plurality of connection wires corresponding to the plurality of laser waveguides, each extending in the second direction and connected to the power supply electrode of the corresponding laser waveguide; and an interlayer insulating film formed including locations where the connection wires and the power supply electrodes, which should be insulated from each other, intersect; and the surface of the groove is covered by the interlayer insulating film or the connection wires.

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