Optical semiconductor device

Abstract

To provide an optical semiconductor device including an improved novel structure in which, for example, the reliability of a heater layer can be improved.SOLUTION: An optical semiconductor device includes, for example, a mesa protruding from a surface of a base in a first direction and extending in a direction intersecting with the first direction, and a heater layer including a top wall on the opposite side of the base with respect to a top surface of the mesa and extending along the mesa. The mesa includes a first mesa extending in a second direction, and a plurality of second mesas branched from the first mesa and extending to separate from each other in a third direction as the mesa goes from the first mesa in the second direction. The second mesa includes a first side surface close to another second mesa adjacent in the third direction, and a second side surface far from the adjacent other second mesa. The heater layer includes a first side wall extending away from the first mesa along the first side surface from a position away from the first mesa in at least one second mesa.SELECTED DRAWING: Figure 3

Description

Technical Field

[0001] The present invention relates to an optical semiconductor device.

Background Art

[0002] Conventionally, an optical semiconductor device having a heater layer on a mesa has been known (Patent Document 1).

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] In this type of optical semiconductor device, for example, it would be beneficial if an inconvenient event caused by the provision of a heater layer could be avoided and the reliability could be improved.

[0005] Therefore, one of the problems of the present invention is to obtain an optical semiconductor device having an improved novel configuration that can, for example, improve the reliability.

Means for Solving the Problems

[0006] The optical semiconductor device of the present invention includes, for example, a base having a surface intersecting a first direction, a mesa protruding from the surface in the first direction, having a top surface and two side surfaces, and extending in a direction intersecting the first direction along the surface, and a heater layer having a top wall located on the side opposite to the base with respect to the top surface and extending along the mesa. The mesa has a first mesa extending in a second direction intersecting the first direction, and a plurality of second mesas branching from the first mesa and extending away from each other in a third direction intersecting the first direction and the second direction as they go from the first mesa in the second direction. The second mesa has a first side surface close to another second mesa adjacent in the third direction and a second side surface far from the adjacent other second mesa. The heater layer has a first side wall extending away from the first mesa along the first side surface from a position away from the first mesa in at least one of the second mesas.

[0007] The semiconductor device may include a coating layer covering the heater layer.

[0008] In the optical semiconductor device, the first side wall may be spaced apart from another second mesa adjacent to the second mesa provided with the first side wall or a heater layer provided on the another second mesa.

[0009] In the optical semiconductor device, the heater layer may have, in the second mesa, a first portion away from the first mesa and having the first side wall, and a second portion closer to the first mesa than the first portion and not having the first side wall.

[0010] In the optical semiconductor device, the heater layer may have a second side wall extending along the second side surface opposite to the first side surface.

[0011] In the optical semiconductor device, the heater layer includes a first heater layer extending along the first mesa, and a second heater layer connected to the first heater layer and extending along the second mesa. The second heater layer may be provided at an end of the second mesa where the second heater layer is provided, adjacent to the first mesa, with a gap from another adjacent second mesa or a heater layer provided on the other second mesa.

[0012] In the optical semiconductor device, when viewed in the direction opposite to the first direction, the second heater layer has a first edge in the width direction closer to the first side surface than the second side surface, a second edge in the width direction closer to the second side surface than the first side surface, a third part away from the first mesa, and a fourth part located between the third part and the first mesa and having the first edge closer to the second side surface than the third part.

[0013] In the optical semiconductor device, when viewed in the direction opposite to the first direction, the second heater layer has a first edge in the width direction closer to the first side surface than the second side surface and a second edge in the width direction closer to the second side surface than the first side surface, and the first edge may approach the second side surface as it approaches the first mesa.

[0014] In the optical semiconductor device, when viewed in the direction opposite to the first direction, the second heater layer may be positioned away from the first side surface and closer to the second side surface throughout the entire area of the second heater layer.

[0015] In the optical semiconductor device, when viewed in the direction opposite to the first direction, the first heater layer may extend along the first mesa with a wider width than the second heater layer.

[0016] The optical semiconductor device of the present invention includes, for example, a base having a surface intersecting a first direction, a mesa protruding in the first direction from the surface, having a top surface and two side surfaces, and extending in a direction intersecting the first direction along the surface, and a heater layer having a top wall located on the side opposite to the base with respect to the top surface and extending along the mesa. The mesa includes a first mesa extending in a second direction intersecting the first direction, a plurality of second mesas branching from the first mesa at an end of the first mesa in the second direction and extending away from each other in a third direction intersecting the first and second directions as they go from the first mesa in the second direction, and a plurality of third mesas branching from the first mesa at an end of the first mesa in the direction opposite to the second direction and extending away from each other in the third direction as they go from the first mesa in the direction opposite to the second direction. The second and third mesas each have a first side surface close to another second or third mesa adjacent in the third direction and a second side surface far from the adjacent other second or third mesa. The heater layer is not provided on the first mesa and includes a second heater layer provided at a portion of the second mesa away from the first mesa and a third heater layer provided at a portion of the third mesa away from the first mesa. The second and third heater layers have at least one of a first side wall extending along the first side surface and a second side wall extending along the second side surface.

[0017] In the optical semiconductor device, the heater layer is made of a thermoelectric material, and the second heater layer and the third heater layer may be electrically connected in series or in parallel.

[0018] The optical semiconductor device may include a wiring layer extending along the first mesa and electrically connecting the second heater layer and the third heater layer.

[0019] The optical semiconductor device of the present invention includes, for example, a base having a surface intersecting a first direction, a mesa protruding from the surface in the first direction and having a top surface and two side surfaces, and extending in a direction intersecting the first direction along the surface. The mesa has a first mesa extending in a second direction intersecting the first direction, and a plurality of second mesas branching from the first mesa and extending away from each other in a third direction intersecting the first direction and the second direction as the second mesas extend in the second direction from the first mesa. The second mesa has a first side surface close to another second mesa adjacent in the third direction and a second side surface far from the adjacent other second mesa. The heater layer has a first heater layer extending along the first mesa and a second heater layer connected to the first heater layer and extending along the second mesa. The second heater layer is provided at an end of the second mesa where the second heater layer is provided, adjacent to the first mesa, with a gap from another adjacent second mesa.

[0020] In the optical semiconductor device, one of the plurality of second mesas may be curved when viewed in the direction opposite to the first direction and may form a part of a circular mesa.

[0021] In the optical semiconductor device, the circular mesa may form a ring resonator.

[0022] In the optical semiconductor device, one of the plurality of second mesas may extend linearly at least at a portion adjacent to the first mesa when viewed in the direction opposite to the first direction.

[0023] In the optical semiconductor device, the first mesa may form a multimode interference waveguide.

Advantages of the Invention

[0024] According to the present invention, for example, an optical semiconductor device with an improved novel configuration capable of improving reliability can be obtained.

Brief Description of the Drawings

[0025]

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[0026] Exemplary embodiments of the present invention will be disclosed below. The configurations of the embodiments shown below, as well as the operations and results (effects) brought about by the configurations, are examples. The present invention can also be realized by configurations other than those disclosed in the following embodiments. Further, according to the present invention, it is possible to obtain at least one of various effects (including derivative effects) obtained by the configuration.

[0027] The plurality of embodiments shown below have the same configurations. Therefore, according to the configurations of each embodiment, the same operations and effects based on the same configurations can be obtained. Further, in the following, the same reference numerals are given to those same configurations, and redundant descriptions may be omitted.

[0028] In this specification, ordinal numbers are given for convenience in distinguishing parts, directions, etc., and do not indicate priorities or orders.

[0029] In each figure, the X direction is represented by arrow X, the Y direction is represented by arrow Y, and the Z direction is represented by arrow Z. The X direction, Y direction, and Z direction intersect with each other and are orthogonal to each other.

[0030] [First Embodiment] FIG. 1 is a plan view of an optical semiconductor device 100A according to the first embodiment. As shown in FIG. 1, the optical semiconductor device 100A includes a base 10 and mesas 20-1, 20-2L, and 20-2C. This optical semiconductor device 100A can constitute a ring resonator as an example.

[0031] The base 10 is, for example, a semiconductor substrate, which intersects and is orthogonal to the Z direction and extends in the X direction and the Y direction. The base 10 has a surface 10a. The surface 10a intersects and is orthogonal to the Z direction and extends in the X direction and the Y direction. The base 10 is made of a III-V semiconductor having a zinc blende structure, such as n-type indium phosphide (InP) for example. The base 10 can also be referred to as a substrate. The surface 10a is an example of a surface.

[0032] The mesas 20-1, 20-2L, and 20-2C have a shape like a wall protruding on the surface 10a and extending along the surface 10a. The Z direction is an example of a first direction.

[0033] The optical semiconductor device 100A has two mesas 20-1, four mesas 20-2L, and two mesas 20-2C. The heights in the Z direction of the plurality of mesas 20-1, 20-2L, and 20-2C included in the optical semiconductor device 100A from the surface 10a are substantially the same.

[0034] As shown in FIG. 1, when viewed in the opposite direction of the Z direction, the two mesas 20-1 have substantially the same shape and dimensions and are arranged in parallel. The mesa 20-1 has a rectangular shape that is long in the X direction. The four mesas 20-2L all extend in the X direction. The mesa 20-2L also has a rectangular shape that is long in the X direction. Further, the two mesas 20-2C have substantially the same shape and dimensions and are curved in a semi-circular arc shape with a substantially constant width. The two mesas 20-2C are arranged symmetrically with respect to the virtual center line passing through the center in the X direction and along the Y direction. The width of the mesa 20-2L and the width of the mesa 20-2C are substantially the same and are approximately half of the width of the mesa 20-1. The two mesas 20-1 and the two mesas 20-2C constitute a substantially oval-shaped circumferential mesa.

[0035] The mesa 20-1 extends in the X direction with a substantially constant width in the Y direction. The mesa 20-1 is an example of a first mesa, and the X direction or the opposite direction of the X direction is an example of a second direction.

[0036] The mesas 20-2L and 20-2C branch off from the mesa 20-1 at the branching portion J and extend away from each other in the Y direction as they go in the X direction or the opposite direction of the X direction from the mesa 20-1. The mesa 20-2L extends linearly in the X direction with a substantially constant width in the Y direction, and the mesa 20-2C extends while curving with a constant width. The mesas 20-2L and 20-2C are an example of a second mesa. The Y direction is an example of a third direction.

[0037] Further, the base 10 and the mesas 20-1, 20-2L, and 20-2C are covered by the coating layer 40. Furthermore, the mesas 20-1 and 20-2C are covered by the heater layer 30 (see FIG. 2), and the heater layer 30 is further covered by the coating layer 41.

[0038] FIG. 2 is a plan view showing the mesas 20-1, 20-2L, 20-2C, the heater layer 30, and the wiring layer 50 of a part of the optical semiconductor device 100A, excluding the coating layers 40 and 41.

[0039] The heater layer 30 is an electric resistor that generates heat when energized, and is made of a thermoelectric material such as tungsten or its alloy. Further, the wiring layer 50 is made of a highly conductive material such as gold, for example.

[0040] As shown in FIG. 2, the heater layer 30 has a section 30-1 extending along the mesa 20-1 and sections 30-21 and 30-22 extending along the mesa 20-2C. The sections 30-1, 30-22, 30-21, 30-22, 30-1 are connected in series in this order, constituting a series of heater layers 30. The section 30-21 is separated from the section 30-1. Further, the section 30-22 is located closer to the section 30-1 than the section 30-21 and is positioned between the section 30-21 and the section 30-1. The section 30-1 is an example of a first heater layer, and the sections 30-21 and 30-22 are examples of a second heater layer. Also, the section 30-21 is an example of a first site and a third site, and the section 30-22 is an example of a second site and a fourth site.

[0041] Wiring layers 50 are connected to the two sections 30-1, respectively. When a predetermined voltage is applied to the two wiring layers 50, the heater layer 30 is energized and generates heat.

[0042] Here, when viewed in the opposite direction of the Z direction, the section 30-1 extends along the mesa 20-1 with a wider width than the sections 30-21 and 30-22. As a result, the cross-sectional area of the heater layer 30 becomes larger in the section 30-1, the electrical resistance can be made smaller, and thus, for example, the heating efficiency by the heater layer 30 can be increased, or the local excessive temperature rise of the optical semiconductor device 100A can be suppressed to improve the reliability, and the like.

[0043] FIG. 3 is a plan view of mesas 20-1, 20-2L, 20-2C and heater layer 30 in the vicinity of branch portion J. FIG. 4 is a cross-sectional view of the optical semiconductor device 100A at the IV-IV position in FIG. 3, FIG. 5 is a cross-sectional view of the optical semiconductor device 100A at the V-V position in FIG. 3, and FIG. 6 is a cross-sectional view of the optical semiconductor device 100A at the VI-VI position in FIG. 3.

[0044] FIG. 4 is a cross-sectional view of mesa 20-2C (20). Mesa 20-2C has a top surface 20a and two side surfaces 20b (20b1, 20b2). In this cross-section, section 30-21 of heater layer 30 is provided in mesa 20-2C.

[0045] The top surface 20a intersects and is orthogonal to the Z direction. The top surface 20a is substantially parallel to the surface 10a.

[0046] The side surface 20b extends in the Z direction. Also, the side surface 20b extends in a direction intersecting the Z direction with a substantially constant width in the Z direction.

[0047] Here, as can be seen by referring to FIG. 3, of the two side surfaces 20b, side surface 20b1 is closer to another mesa 20-2L adjacent in the Y direction at branch portion J, and side surface 20b2 is farther from the other mesa 20-2L. Side surface 20b1 is an example of a first side surface, and side surface 20b2 is an example of a second side surface.

[0048] Also, as shown in FIG. 4, mesa 20-2C has a clad layer 21, a waveguide layer 22, and a clad layer 23. The clad layer 21, the waveguide layer 22, and the clad layer 23 are arranged in this order in the Z direction. That is, the waveguide layer 22 is sandwiched between the clad layers 21 and 23.

[0049] The mesa 20-2C can be fabricated by a known semiconductor manufacturing process. The cladding layers 21 and 23 function as claddings for the waveguide layer 22 as the core. The cladding layers 21 and 23 can be made of a material having a refractive index lower than that of the waveguide layer 22. As an example, when the wavelength of the light guided by the waveguide layer 22 is 1.55 [μm], the cladding layers 21 and 23 are made of InP, and the waveguide layer 22 is made of InGaAsP. Note that the materials of the waveguide layer 22 and the cladding layers 21 and 23 are not limited to this example and can be appropriately set according to the wavelength of the light transmitted by the waveguide layer 22.

[0050] The surface 10a of the base 10, the top surface 20a and the side surface 20b of the mesa 20-2C are covered with a coating layer 40 having insulating properties. The coating layer 40 is formed with a substantially constant thickness on each surface. The coating layer 40 is made of a dielectric such as silicon nitride (SiN x ) or silicon dioxide (SiO2). Further, the heater layer 30 is covered with a coating layer 41 made of the same material as the coating layer 40. In such a configuration, the heater layer 30 is covered with the coating layers 40 and 41.

[0051] The section 30-21(30) of the heater layer 30 has a top wall 31 and two side walls 32 and 33. Thus, by the heater layer 30 having two side walls 32 and 33 in addition to the top wall 31, the cross-sectional area of the heater layer 30 can be made larger and the electrical resistance can be made smaller. As a result, advantages such as increasing the heating efficiency by the heater layer 30 or suppressing a local excessive temperature rise of the optical semiconductor device 100A to improve the reliability can be obtained.

[0052] The top wall 31 is provided on the top surface 20a of the mesa 20-2C via the coating layer 40. The top wall 31 has a substantially constant thickness and a substantially constant width and extends substantially along the top surface 20a of the mesa 20-2C. The top wall 31 is located on the side opposite to the base 10 with respect to the top surface 20a.

[0053] The side walls 32 and 33 are respectively provided on the side surface 20b of the mesa 20-2C via a coating layer 40. The side walls 32 and 33 have a substantially constant thickness and a substantially constant width in the Z direction, and extend along the side surface 20b of the mesa 20-2C. The side wall 32 extending along the side surface 20b1 is an example of a first side wall, and the side wall 33 extending along the side surface 20b2 is an example of a second side wall.

[0054] In this embodiment, the top wall 31 and the two side walls 32 and 33 are integrally connected in each cross section. The top wall 31 and the two side walls 32 and 33 have a U-shaped configuration in a cross section orthogonal to the extending direction of the mesa 20-2C, and cover the protruding end of the mesa 20-2C. Also, the top wall 31 and the two side walls 32 and 33 extend along the extending direction of the mesa 20-2C.

[0055] FIG. 5 is a cross-sectional view of the mesa 20-1(20). The mesa 20-1 has a configuration substantially the same as that of the mesa 20-2C although they have different widths. The waveguide layer 22 of the mesa 20-1 and the waveguide layer of the mesa 20-2C are provided at the same position in the Z direction, are connected in the X direction, and are optically connected. A section 30-1 of the heater layer 30 is provided in the mesa 20-1.

[0056] FIG. 6 is a cross-sectional view of the mesas 20-2L and 20-2C(20).

[0057] The mesa 20-2L has a configuration substantially the same as that of the mesa 20-2C. The waveguide layer 22 of the mesa 20-1 and the waveguide layer of the mesa 20-2L are provided at the same position in the Z direction, are connected in the X direction, and are optically connected. Also, the heater layer 30 is not provided in the mesa 20-2L.

[0058] As can be clearly seen by comparing FIG. 6 with FIG. 4, in this part, the section 30-22 of the heater layer 30 in the mesa 20-2C has a different configuration from the section 30-21 of the heater layer 30. Specifically, in the section 30-21 shown in FIG. 4, the heater layer 30 had the side wall 32, whereas in the section 30-22 shown in FIG. 6, the heater layer 30 does not have the side wall 32. Here, as also shown in FIG. 3, the section 30-22 is located closer to the section 30-1 than the section 30-21. That is, the heater layer 30 provided in the mesa 20-2C has a section 30-21 that is away from the mesa 20-1 and has the side wall 32, and a section 30-22 that is closer to the mesa 20-1 than the section 30-21 and does not have the side wall 32.

[0059] In other words, in the mesa 20-2C, the side wall 32 of the heater layer 30 extends along the side surface 20b1 from a position away from the mesa 20-1, so as to be away from the mesa 20-1, along the extending direction of the mesa 20-2C. Further, the side wall 32 is spaced apart from another mesa 20-2L adjacent to the mesa 20-2C.

[0060] Furthermore, as shown in FIG. 3, when viewed in the opposite direction of the Z direction, the sections 30-21, 30-22 of the heater layer 30 have an edge 30a on the side closer to the side surface 20b1 than the side surface 20b2 of the mesa 20-2C, and an edge 30b on the side closer to the side surface 20b2 than the side surface 20b1. And in the section 30-22, the edge 30a approaches the side surface 20b2 as it approaches the mesa 20-1, the section 30-1, and the root of the branch portion J. That is, in the section 30-22, the edge 30a is located closer to the side surface 20b2 than the section 30-21. The edge 30a is an example of a first edge, and the edge 30b is an example of a second edge.

[0061] Thus, in the heater layer 30 (sections 30-21, 30-22) provided in the mesa 20-2C, the section 30-22 as an end portion close to the mesa 20-1 and adjacent to the mesa 20-1 is provided at an interval from the mesa 20-2L.

[0062] FIG. 7 is a cross-sectional view taken at an equivalent position to FIG. 6 of the optical semiconductor device 100R of the reference example. The inventors repeatedly conducted experimental studies on the configuration in which the heater layer 30 is provided on the mesa 20-2C. As a result, in a region where the mesas 20-2L and 20-2C are close to each other in the width direction, as shown in FIG. 7, it is difficult to form the heater layer 30 provided on the mesa 20-2C into the desired shape, and an overhanging portion 30p that protrudes toward the mesa 20-2L beyond the side surface of the mesa 20-2C may be formed. In addition, it was found that such an overhanging portion 30p is more likely to be formed as the distance between the adjacent mesas 20-2L and 20-2C is shorter, and is more likely to be formed as the edge 30a of the heater layer 30 is closer to the mesa 20-2L. Furthermore, it was found that the overhanging portion 30p is even more likely to be formed when an attempt is made to provide a side wall 32 closer to the mesa 20-2L. In addition, it was found that when such an overhanging portion 30p is formed, there is a risk that the overhanging portion 30p will not be covered by the coating layers 40 and 41 and will be partially exposed from the coating layers 40 and 41, making it susceptible to oxidation.

[0063] In addition, when there is a difference in the thermal expansion coefficients between the mesas 20-2L and 20-2C and the heater layer 30, there is a risk that the mesa 20-2L will be damaged due to the overhanging portion 30p pressing against or biting into the mesa 20-2L due to thermal expansion or contraction of the mesas 20-2L and 20-2C and the heater layer 30.

[0064] In this regard, as described above, in the present embodiment, among the heater layers 30 provided on the mesa 20-2C, a section 30-22, which is an end adjacent to and close to the mesa 20-1 near the mesa 20-1, in other words, an end close to the branch portion J, is provided at a distance from the mesa 20-2L. According to such a configuration, for example, a situation where an overhanging portion 30p of the heater layer 30 is formed and the heater layer 30 is likely to be oxidized due to the overhanging portion 30p being exposed from the coating layers 40 and 41, and a situation where the overhanging portion 30p damages the mesa 20-2L due to thermal expansion or thermal contraction can be avoided. That is, according to the present embodiment, for example, an inconvenient event caused by the provision of the heater layer 30 can be avoided, and the reliability of the optical semiconductor device 100A can be improved. Further, according to the present embodiment, for example, an advantage can also be obtained that the variation in the individual differences in the shape of the heater layer 30 in the vicinity of the branch portion J becomes large, and as a result, the variation in the individual differences in the heating performance by the heater layer 30 can be suppressed.

[0065] [Second Embodiment] FIG. 8 is a plan view showing a part of the optical semiconductor device 100B of the second embodiment, including the mesas 20-1, 20-2L, 20-2C, the heater layer 30, and the wiring layer 50. As shown in FIG. 8, in the present embodiment, the heater layer 30 does not have side walls 32 (see FIGS. 4 and 5) throughout its entire area, but has a top wall 31 and side walls 33. Further, when viewed in the opposite direction of the Z direction, the heater layer 30 is located away from the side surface 20b1 of the mesa 20-2C and closer to the side surface 20b2 in the entire area of the section 30-2 on the mesa 20-2C. Furthermore, the edge 30a is located away from the side surface 20b1 of the mesa 20-2C and closer to the side surface 20b2. The section 30-2 is an example of a second heater layer.

[0066] Even in such a configuration, the heater layer 30 provided on the mesa 20-2C is positioned at a distance from the mesa 20-2L at a portion close to the branch portion J. Therefore, also according to the present embodiment, the same effects as those of the first embodiment can be obtained.

[0067] [Embodiment 3] FIG. 9 is a plan view showing a part of the optical semiconductor device 100C according to the third embodiment, including mesas 20-1, 20-2L, 20-2C, 20-3L, 20-3C, a heater layer 30, and a wiring layer 50. As shown in FIG. 9, when viewed in the opposite direction of the Z direction, the mesa 20-2L and the mesa 20-3L, the mesa 20-2C and the mesa 20-3C, and the section 30-2 of the heater layer 30 and the section 30-3 of the heater layer 30 are provided symmetrically with respect to a virtual center line passing through the center in the X direction and extending along the Y direction, respectively.

[0068] The mesas 20-3L and 20-3C branch from the mesa 20-1 at the end in the opposite direction of the X direction of the mesa 20-1, and extend so as to be separated from each other in the Y direction as they go in the opposite direction of the X direction. The mesas 20-3L and 20-3C are an example of a plurality of third mesas.

[0069] The mesa 20-3C has a side surface 20b1 close to the adjacent mesa 20-3L in the Y direction and a side surface 20b2 far from the mesa 20-3L.

[0070] The section 30-3 of the heater layer 30 is provided at a portion of the mesa 20-3C away from the mesa 20-1. The section 30-3 of the heater layer 30 is an example of a third heater layer.

[0071] Also in this embodiment, the heater layers 30 (30-2, 30-3) provided on the mesas 20-2C and 20-3C are separated from the branching portion J and the mesas 20-2L and 20-3L. Therefore, also according to this embodiment, the same effects as those of the first embodiment can be obtained.

[0072] Also in this embodiment, the heater layer 30 has side walls 32 and 33. Therefore, also according to this embodiment, advantages such as increasing the heating efficiency by the heater layer 30 and suppressing the temperature rise per unit area of the surfaces of the mesas 20-2C and 20-3C can be obtained. Note that the heater layer 30 only needs to have at least one of the side walls 32 and 33.

[0073] Furthermore, in the present embodiment, a wiring layer 50 extending along the mesa 20-1 is provided so as to cover the two mesas 20-1, and between the two wiring layers 50, a circuit with the section 30-2 of the heater layer 30 interposed therebetween and a circuit with the section 30-3 of the heater layer 30 interposed therebetween are provided in parallel. According to the present embodiment, for example, the region between the sections 30-2 and 30-3 of the two heater layers 30 on the mesa 20-1 can be effectively utilized as the region for providing the wiring layer 50.

[0074] Note that by separating one of the two wiring layers 50 into two at the intermediate position in the X direction, connecting the positive electrode of the DC power supply to one of the separated parts and the negative electrode to the other, a circuit in which the sections 30-2 and 30-3 of the two heater layers 30 are connected in series can be configured.

[0075] [Fourth Embodiment] FIG. 10 is a plan view showing a part of the optical semiconductor device 100D of the fourth embodiment, including the mesas 20-1, 20-2L, 20-2C, the heater layer 30, and the wiring layer 50. As shown in FIG. 9, in the present embodiment, the optical semiconductor device 100D includes the same heater layer 30 as in the first embodiment and a heater layer 30E provided on the mesa 20-2L.

[0076] As is clear from FIG. 10, the heater layer 30 is separated from the mesa 20-2L where the heater layer 30E is provided and is also separated from the heater layer 30E provided on the mesa 20-2L. Further, the heater layer 30E is separated from the mesa 20-2C where the heater layer 30 is provided and is also separated from the heater layer 30 provided on the mesa 20-2C. Therefore, also in the present embodiment, the same effect as in the first embodiment can be obtained.

[0077] [Fifth Embodiment] FIG. 11 is a plan view of the mesa 20-1, 20-2L, 20-2C and the heater layer 30 in the vicinity of the branch portion J of the optical semiconductor device 100E of the fifth embodiment. As shown in FIG. 11, the heater layer 30 does not have side walls 32, 33. Therefore, when viewed in the opposite direction of the Z direction, the edge 30a is located at the same position as the side surface 20b or inside the side surface 20b in the width direction without protruding in the width direction from the mesa 20-1, 20-2L, 20-2C.

[0078] The optical semiconductor device 100E of the present embodiment has the same configuration as that of the first embodiment except that it does not have the side walls 32, 33. That is, when viewed in the opposite direction of the Z direction, in the section 30-22, as the edge 30a approaches the mesa 20-1, the section 30-1, and the base of the branch portion J, it approaches the side surface 20b2. That is, in the section 30-22, the edge 30a is located closer to the side surface 20b2 than the section 30-21.

[0079] Also in the present embodiment, the heater layer 30 provided on the mesa 20-2C is separated from the branch portion J and the mesa 20-2L. Therefore, also in the present embodiment, the same effect as that of the first embodiment can be obtained.

[0080] [Sixth Embodiment] FIG. 12 is a plan view of the mesa 20-1, 20-2L, 20-2C and the heater layer 30 in the vicinity of the branch portion J of the optical semiconductor device 100F of the sixth embodiment. As shown in FIG. 12, the heater layer 30 does not have side walls 32, 33. When viewed in the opposite direction of the Z direction, the edge 30a is located at the same position as the side surface 20b or inside the side surface 20b in the width direction without protruding in the width direction from the mesa 20-1, 20-2L, 20-2C.

[0081] The optical semiconductor device 100F of the present embodiment has the same configuration as that of the second embodiment, except that the heater layer 30 does not have side walls 33. That is, when viewed in the opposite direction of the Z direction, the heater layer 30 is located closer to the side closer to the side surface 20b2 from the side surface 20b1 of the mesa 20-2C and away from the side surface 20b1 of the mesa 20-2C over the entire region of the section 30-2 on the mesa 20-2C. Further, the edge 30a is away from the side surface 20b1 of the mesa 20-2C toward the side closer to the side surface 20b2.

[0082] Also in the present embodiment, the heater layer 30 provided on the mesa 20-2C is separated from the branch portion J and the mesa 20-2L. Therefore, also according to the present embodiment, the same effects as those of the first embodiment can be obtained.

[0083] [Seventh Embodiment] FIG. 13 is a cross-sectional view at an equivalent position to FIG. 4 of the optical semiconductor device 100G of the seventh embodiment.

[0084] As is clear from comparing FIG. 13 with FIG. 4, in the present embodiment, the Z-direction lengths of the side walls 32 and 33 in the section 30-21 of the heater layer 30 are longer than those in the first embodiment. Therefore, according to the present embodiment, the cross-sectional area of the heater layer 30 can be made even larger. Thus, for example, advantages such as being able to further improve the heating efficiency by the heater layer 30, being able to further suppress a local excessive temperature rise of the optical semiconductor device 100G and further enhance the reliability can be obtained.

[0085] Also, in the present embodiment, for example, the waveguide layer 22 and the side walls 32 and 33 overlap in the width direction of the mesa 20-2C. And a coating layer 40 is interposed between the waveguide layer 22 and the side walls 32 and 33.

[0086] According to such a configuration, for example, in a configuration where the side walls 32 and 33 extend to a position overlapping the waveguide layer 22 in the Y direction, the coating layer 40 can suppress the leakage of light from the waveguide layer 22 to the side walls 32 and 33 having a relatively high light absorptivity.

[0087] [Eighth Embodiment] FIG. 14 is a cross-sectional view at an equivalent position to FIG. 4 of the optical semiconductor device 100H according to the eighth embodiment.

[0088] In the present embodiment, the lengths in the Z direction of the side walls 32 and 33 of the heater layer 30 are different from each other. Even with such a configuration, the effect of the heater layer 30 having side walls 32 and 33 and increasing the cross-sectional area of the heater layer 30 can be obtained.

[0089] [Ninth Embodiment] FIG. 15 is a cross-sectional view at an equivalent position to FIG. 4 of the optical semiconductor device 100I according to the ninth embodiment.

[0090] In the present embodiment, a slit S is provided between the top wall 31 and the side walls 32 and 33 in the section 30-21 of the heater layer 30. Here, the top wall 31, the side wall 32, and the side wall 33 respectively constitute parallel thermoelectric circuits. Therefore, also in the present embodiment, the effect of the heater layer 30 having side walls 32 and 33 and increasing the cross-sectional area of the heater layer 30 can be obtained.

[0091] [Tenth Embodiment] FIG. 16 is a cross-sectional view at an equivalent position to FIG. 4 of the optical semiconductor device 100J according to the tenth embodiment.

[0092] In the present embodiment, the width of the waveguide layer 22 is shorter than the width of the mesa 20-2C, and both sides in the width direction of the waveguide layer 22 are covered with the cladding layers 21 and 23 of the mesa 20-2C. That is, the mesa 20-2C has a configuration of a so-called buried mesa. Also in the present embodiment, the effect of the heater layer 30 having side walls 32 and 33 and increasing the cross-sectional area of the heater layer 30 can be obtained.

[0093] [Eleventh Embodiment] FIG. 17 is a cross-sectional view at an equivalent position to FIG. 4 of the optical semiconductor device 100K according to the eleventh embodiment.

[0094] In this embodiment, the waveguide layer 22 is provided in the base 10 away from the mesa 20-2C in the opposite direction in the Z direction. That is, the mesa 20-2C has a so-called low mesa configuration. In this case, light is confined and guided by the mesa 20-2C in a region of the waveguide layer 22 located in the opposite direction to the mesa 20-2C in the Z direction. Also according to this embodiment, the effect of the heater layer 30 having side walls 32 and 33 and increasing the cross-sectional area of the heater layer 30 can be obtained.

[0095] [Embodiment 12] FIG. 18 is a cross-sectional view at an equivalent position to FIG. 6 of the optical semiconductor device 100L of the 12th embodiment. As shown in FIG. 18, in this embodiment, a coating layer 41 covering the outside of the heater layer 30 is not provided, and the heater layer 30 is exposed. Even in such a configuration, similar to the above-described embodiment, in section 30-22, the edge 30a approaches the side surface 20b2 as it approaches the mesa 20-1, section 30-1, and the root of the branch portion J. That is, in section 30-22, the edge 30a is located closer to the side surface 20b2 than section 30-21. That is, in the heater layer 30 (sections 30-21 and 30-22) provided on the mesa 20-2C, section 30-22 as an end portion adjacent to and close to the mesa 20-1 is provided at an interval from the mesa 20-2L.

[0096] Even in the optical semiconductor device 100L without the coating layer 41 as in this embodiment, the situation where the mesa 20-2L is damaged by the overhanging portion 30p as shown in FIG. 7 can be avoided. That is, even in a configuration where the coating layer 41 is not provided, it is possible to avoid an inconvenient event caused by the provision of the heater layer 30, and the reliability of the optical semiconductor device 100L can be improved. The effects according to the above-described embodiments can be obtained in the same manner even in a configuration where the coating layer 41 is not provided.

[0097] [Embodiment 13] FIG. 19 is a schematic configuration diagram of a wavelength-variable laser device 1 as an optical device according to the 13th embodiment. The wavelength-variable laser device 1 includes a ring resonator 110, an SG-DBR section 120 (SG-DBR: sampled-grating distributed Bragg reflector), a phase adjustment section 130, a gain section 140, and a connection section 150. The wavelength-variable laser device 1 has a wavelength-variable type laser resonator that utilizes the Vernier effect, and constitutes a wavelength-variable light source that outputs laser light with a variable wavelength.

[0098] The wavelength-variable laser device 1 is configured, for example, in a mesa 20 provided on a surface 10a of a base 10 as a semiconductor laminated substrate, to have a predetermined function such as a waveguide layer and an active layer (not shown).

[0099] The ring resonator 110, the SG-DBR section 120, the phase adjustment section 130, the gain section 140, and the connection section 150 are made of, for example, an InP-based semiconductor material.

[0100] The SG-DBR section 120 has a waveguide including a configuration of a sampled grating (SG-DBR) of a distributed Bragg reflection type. The SG-DBR section 120 constitutes one reflection section of the laser resonator.

[0101] The gain section 140 has an active layer. A pair of electrodes (not shown) spaced apart from each other are provided in the gain section 140. By applying a voltage to the pair of electrodes, a current flows through the active layer, and an optical amplification effect is obtained. Thereby, laser oscillation occurs.

[0102] The connection section 150 is branched at a branching section such as a 1×2 MMI coupler optically connected to the gain section 140, and includes two mesas 20 bent in a plan view when viewed in opposite directions in the Z direction. The waveguide layers of the respective mesas 20 are optically connected to the waveguide layer of the oval or annular mesa 20 of the ring resonator 110 by a 2×2 MMI coupler or the like at a coupling section C.

[0103] The ring resonator 110, in combination with the connection part 150, has a reflection spectrum characteristic with a comb-shaped peak having a different period from that of the SG-DBR part 120, and constitutes the other reflection part of the laser resonator.

[0104] The active layer has, for example, a multiple quantum well (MQW) structure made of a GaInAsP-based semiconductor material or an AlGaInAs-based semiconductor material. The passive waveguide is made of, for example, an i-type GaInAsP-based semiconductor material having a bandgap wavelength of 1300 nm. The waveguide having an SG-DBR configuration is made of, for example, a GaInAsP-based semiconductor material or an AlGaInAs-based semiconductor material, and portions having different refractive indices are periodically arranged so as to form a diffraction grating.

[0105] The SG-DBR part 120, the phase adjuster 130, and the mesa 20 of the ring resonator 110 are each provided with a heater layer 30 (not shown in FIG. 19).

[0106] The SG-DBR part 120 has a comb-shaped reflection peak with a periodic frequency interval according to the reciprocal of the period of the diffraction grating. The SG-DBR part 120 and the ring resonator 110 have different periods, and are configured such that the frequency of the laser light can be roughly adjusted by a method called the Vernier type. When the heater layer 30 heats the SG-DBR part 120, the refractive index of the SG-DBR part 120 changes, and thereby the comb-shaped reflection peak shifts in the frequency axis direction. Similarly, when the heater layer 30 heats the ring resonator 110, the refractive index of the ring resonator 110 changes, and the comb-shaped reflection peak shifts in the frequency axis direction.

[0107] Further, by heating the heater layer 30 of the phase adjuster 130, the refractive index of the waveguide layer can be changed, and thereby the optical length of the laser resonator can be adjusted. By adjusting the optical length of the laser resonator, the frequency of the resonator mode (cavity mode) can be shifted in the frequency axis direction while finely adjusting the frequency. By finely adjusting the resonator mode, the selection of the resonator mode in laser oscillation becomes possible, and a change in frequency within a slight range becomes possible. Note that, in this embodiment, the phase adjuster 130 is provided, as an example, in a part of the connection portion 150, but the position where the phase adjuster 130 is provided is not limited to the connection portion 150.

[0108] As is apparent from FIG. 19, for example, the optical semiconductor device 100D of the fourth embodiment described above can be applied to the mesa 20 of the portion where the ring resonator 110 and the mesa 20 of the connection portion 150 are optically connected at the coupling portion C. In this case, the heater layer 30 can be applied to the ring resonator 110, and the heater layer 30E can be applied to the phase adjuster 130. Further, in this case, the mesa 20-1 corresponding to the coupling portion C can be configured as a 2×2 multimode interference waveguide. Note that, instead of the optical semiconductor device 100D, an optical semiconductor device of another embodiment described above may be incorporated in the wavelength variable laser device 1.

[0109] As described above, embodiments of the present invention have been illustrated. However, the above embodiments are merely examples and are not intended to limit the scope of the invention. The above embodiments can be implemented in various other forms, and various omissions, replacements, combinations, and changes can be made without departing from the gist of the invention. Further, each configuration, shape, etc. of the specifications (structure, type, direction, type, size, length, width, thickness, height, number, arrangement, position, material, etc.) can be appropriately changed and implemented.

[0110] For example, the shape of the second mesa is not limited to the above embodiment, and a heater layer may be provided on the second mesa extending linearly. Further, the number of the second mesas may be three or more.

[0111] Also, the coating layer that covers the mesa and the heater layer is not essential.

Explanation of Signs

[0112] 1…Wavelength variable laser device 10…Base 10a…Surface 20…Mesa 20-1…Mesa (first mesa) 20-2C…Mesa (second mesa) 20-2L…Mesa (second mesa) 20-3C…Mesa (third mesa) 20-3L…Mesa (third mesa) 20a…Top surface 20b…Side surface 20b1…Side surface (first side surface) 20b2…Side surface (second side surface) 21…Cladding layer 22…Waveguide layer 23…Cladding layer 30…Heater layer 30-1…Section (first heater layer) 30-2…Section (second heater layer) 30-21…Section (second heater layer, first part, third part) 30-22…Section (second heater layer, second part, fourth part) 30-3…Section (third heater layer) 30a…Edge (first edge) 30b…Edge (second edge) 30E…Heater layer 30p…Overhang 31…Top wall 32…Side wall (first side wall) 33…Side wall (second side wall) 40…Coating layer 41…Coating layer 50…Wiring layer 100A~100L,100R…Optical semiconductor device 110…Ring resonator 120…SG-DBR section 130…Phase adjuster 140…Gain section 150…Connection section C... Joint J... Branch S... Slit X... Direction (Second Direction) Y... Direction (Third Direction) Z... Direction (First Direction)

Claims

1. A base having a surface intersecting a first direction, a mesa protruding from the surface in the first direction, having a top surface and two side surfaces, and extending in a direction intersecting the first direction along the surface, a heater layer having a top wall located on the side opposite to the base with respect to the top surface and extending along the mesa, A photonic semiconductor device comprising: The mesa has a first mesa extending in a second direction intersecting the first direction, and a plurality of second mesas branching from the first mesa and extending away from each other in a third direction intersecting the first direction and the second direction as going from the first mesa in the second direction, The second mesa has a first side surface close to another second mesa adjacent in the third direction and a second side surface far from the adjacent another second mesa, The heater layer has a first side wall extending away from the first mesa along the first side surface from a position away from the first mesa in at least one of the second mesas, The heater layer has a first heater layer extending along the first mesa and a second heater layer connected to the first heater layer and extending along the second mesa, The second heater layer is provided at an end adjacent to the first mesa of the second mesa where the second heater layer is provided, with a gap from another adjacent second mesa or a heater layer provided on the other second mesa, The second heater layer, when viewed in the direction opposite to the first direction, has a first edge in the width direction closer to the first side surface than the second side surface, and a second edge in the width direction closer to the second side surface than the first side surface, and the first edge approaches the second side surface as it approaches the first mesa. A photonic semiconductor device.

2. The second heater layer, when viewed in the direction opposite to the first direction, has a first edge in the width direction closer to the first side surface than the second side surface, a second edge in the width direction closer to the second side surface than the first side surface, a third part away from the first mesa, and a fourth part located between the third part and the first mesa and having the first edge closer to the second side surface than the third part, The photonic semiconductor device according to claim 1, having the above.

3. The photonic semiconductor device according to claim 1 or 2, further comprising a coating layer covering the heater layer.

4. The first side wall is separated from another second mesa adjacent to the second mesa provided with the first side wall or a heater layer provided on the another second mesa, the optical semiconductor device according to any one of claims 1 to 3.

5. In the second mesa, the heater layer has a first portion having the first side wall away from the first mesa and a second portion having no first side wall closer to the first mesa than the first portion, the optical semiconductor device according to any one of claims 1 to 4.

6. The heater layer has a second side wall extending along a second side surface opposite to the first side surface, the optical semiconductor device according to any one of claims 1 to 5.

7. One of the plurality of second mesas is curved when viewed in a direction opposite to the first direction and constitutes a part of a circumferential mesa, the optical semiconductor device according to any one of claims 1 to 6.

8. The circumferential mesa constitutes a ring resonator, the optical semiconductor device according to claim 7.

9. One of the plurality of second mesas extends linearly at least at a portion adjacent to the first mesa when viewed in a direction opposite to the first direction, the optical semiconductor device according to any one of claims 1 to 8.

10. The first mesa constitutes a multimode interference waveguide, the optical semiconductor device according to any one of claims 1 to 9.

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