Semiconductor integrated optical element and integrated chip

Abstract

A semiconductor integrated optical element (100) according to the present disclosure comprises: a laser (10) having a first lower cladding layer (12), a first active layer (14), and a first upper cladding layer (16) that are formed on a substrate (50) and are laminated in said order from the side of the laser (10) toward the substrate (50); a modulator (20) having a second lower cladding layer (22), a second active layer (24), and a second upper cladding layer (26) that are formed on the substrate (50) and are laminated in said order from the side of the modulator (20) toward the substrate (50); a conversion unit (30) having a lower waveguide (32) that is continuous with the first active layer (14) between the laser (10) and the modulator (20) and a first upper waveguide (34a) that is continuous with the second active layer (24) between the laser (10) and the modulator (20); and an embedding layer (60) in which the side surface of the first active layer (13) of the laser (10) and the side surface of the conversion unit (30) are embedded, wherein the lower waveguide (32) and the first upper waveguide (34a) form a directional coupler that transfers, to the first upper waveguide (34a), light to be guided from the laser (10) toward the modulator (20) by the lower waveguide (32), and the thickness of the embedding layer (60) in which the side surface of the conversion unit (30) is embedded decreases from the laser (10) toward the modulator (20).

Description

Semiconductor optical integrated device and integrated chip

[0001] The present disclosure relates to semiconductor optical integrated devices and integrated chips.

[0002] Patent Document 1 discloses a semiconductor optical integrated device including a substrate, a laser diode and a modulator integrated on the substrate, and a connecting waveguide that guides light emitted from the laser diode to the modulator. The laser diode employs a buried waveguide in which both sides of the core layer are buried with semiconductor. The modulator employs a high mesa ridge waveguide in which both sides of the core layer are not buried with semiconductor. The connecting waveguide employs a buried waveguide in which both sides of the core layer are buried with semiconductor. The width of the connecting waveguide narrows from the laser diode to the modulator.

[0003] Patent No. 5573386

[0004] When converting from a buried structure to a high mesa structure as in Patent Document 1, the structural dimensions, particularly in the height direction, are generally the same for both the buried structure and the high mesa structure. In this case, depending on the laser structure, it may be necessary to make the modulator layer thickness thicker than necessary, which could impose restrictions on the modulator structure.

[0005] An object of the present disclosure is to provide a semiconductor optical integrated device and an integrated chip that can improve the degree of freedom in the structure of a modulator.

[0006] The semiconductor optical integrated device according to the present disclosure comprises: a substrate; a laser formed on the substrate and having a first lower cladding layer, a first active layer, and a first upper cladding layer stacked in this order from the substrate side; a modulator formed on the substrate and having a second lower cladding layer, a second active layer, and a second upper cladding layer stacked in this order from the substrate side; a conversion section having a lower waveguide continuing to the first active layer between the laser and the modulator, and a first upper waveguide continuing to the second active layer between the laser and the modulator; and a burying layer burying a side surface of the first active layer of the laser and a side surface of the conversion section, wherein the lower waveguide and the first upper waveguide form a directional coupler that transfers light guided in the lower waveguide from the laser to the modulator to the first upper waveguide, and the thickness of the burying layer burying the side surface of the conversion section becomes thinner between the laser and the modulator, from the laser to the modulator.

[0007] In the semiconductor optical integrated device according to the present disclosure, the directional coupler in the conversion section shifts light guided through the lower waveguide to the first upper waveguide, which improves the degree of freedom in the structure of the modulator, such as the thickness of the cladding layer.

[0008] 4 is a perspective view of a semiconductor optical integrated device according to a first embodiment. FIG. 5 is a cross-sectional view of the semiconductor optical integrated device according to the first embodiment. FIG. 6 is a cross-sectional view obtained by cutting FIG. 1 along line A-A. FIG. 7 is a cross-sectional view obtained by cutting FIG. 1 along line B-B or line F-F. FIG. 8 is a cross-sectional view obtained by cutting FIG. 1 along line C-C or line E-E. FIG. 9 is a cross-sectional view obtained by cutting FIG. 1 along line D-D. FIG. 10 is a cross-sectional view illustrating a directional coupler according to the first embodiment. FIG. 4 is a cross-sectional view at point A in FIG. 4. FIG. 4 is a cross-sectional view at point B or F in FIG. 4. FIG. 4 is a cross-sectional view at point C or E in FIG. 4. FIG. 4 is a cross-sectional view at point D in FIG. 4. FIG. 5 is a cross-sectional view illustrating a manufacturing method of a semiconductor optical integrated device according to the first embodiment. FIG. 6 is a cross-sectional view at point A in FIG. 6. FIG. 6 is a cross-sectional view at point B or F in FIG. 6. FIG. 6 is a cross-sectional view at point C or E in FIG. 6. FIG. 6 is a cross-sectional view at point D in FIG. 6. FIG. 7 is a cross-sectional view illustrating a manufacturing method of a semiconductor optical integrated device according to the first embodiment. FIG. 8 is a cross-sectional view at point A in FIG. 8. FIG. 8 is a cross-sectional view at point B or F in FIG. 8. FIG. 8 is a cross-sectional view at point C or E in FIG. 8. FIG. 8 is a cross-sectional view at point D in FIG. 8. 10. A cross-sectional view at point A in FIG. 10. A cross-sectional view at point B or F in FIG. 10. A cross-sectional view at point C or E in FIG. 10. A cross-sectional view at point D in FIG. 10. A cross-sectional view explaining a manufacturing method of a semiconductor optical integrated device according to the first embodiment. A cross-sectional view at point A in FIG. 12. A cross-sectional view at point B or F in FIG. 12. A cross-sectional view at point C or E in FIG. 12. A cross-sectional view at point D in FIG. 12. A cross-sectional view explaining a manufacturing method of a semiconductor optical integrated device according to the first embodiment. A cross-sectional view at point A in FIG. 14. A cross-sectional view at point B or F in FIG. 14. A cross-sectional view at point C or E in FIG. 14. A cross-sectional view at point D in FIG. 14. A cross-sectional view explaining a manufacturing method of a semiconductor optical integrated device according to the first embodiment. A cross-sectional view at point A in FIG. 16. A cross-sectional view at point B or F in FIG. 16. A cross-sectional view at point C or E in FIG. 16. A cross-sectional view at point D in FIG. 16. A cross-sectional view explaining a manufacturing method of a semiconductor optical integrated device according to the first embodiment. A cross-sectional view at point A in FIG. 18. A cross-sectional view at point B or F in FIG. 18. 19 is a cross-sectional view taken at point C or point E in FIG. 18. FIG. 19 is a cross-sectional view taken at point D in FIG.28 is a cross-sectional view illustrating a manufacturing method of a semiconductor optical integrated device according to a first embodiment. 29 is a cross-sectional view at point A in FIG. 20. 30 is a cross-sectional view at point B or point F in FIG. 20. 31 is a cross-sectional view at point C or point E in FIG. 20. 32 is a cross-sectional view at point D in FIG. 20. 33 is a cross-sectional view of a laser in a semiconductor optical integrated device according to a comparative example. 34 is a cross-sectional view of a modulator in a semiconductor optical integrated device according to a comparative example. 35 is a perspective view of a semiconductor optical integrated device according to a second embodiment. 36 is a cross-sectional view of a semiconductor optical integrated device according to a second embodiment. 37 is a cross-sectional view obtained by cutting FIG. 23 along line A-A. 38 is a cross-sectional view obtained by cutting FIG. 23 along line B-B or line F-F. 39 is a cross-sectional view obtained by cutting FIG. 23 along line C-C or line E-E. 40 is a cross-sectional view obtained by cutting FIG. 23 along line D-D. 41 is a cross-sectional view illustrating a directional coupler according to a second embodiment. 42 is a cross-sectional view at point A in FIG. 43. 43 is a cross-sectional view at point B or point F in FIG. 43. 44 is a cross-sectional view at point C or point E in FIG. 44. 45 is a cross-sectional view illustrating a manufacturing method of a semiconductor optical integrated device according to a second embodiment. 46 is a cross-sectional view at point A in FIG. 45. 28. A cross-sectional view taken at point B or point F in FIG. 28. A cross-sectional view taken at point C or point E in FIG. 28. A cross-sectional view taken at point D in FIG. 28. A perspective view of a semiconductor optical integrated device according to embodiment 3. A cross-sectional view of a semiconductor optical integrated device according to embodiment 3. A cross-sectional view obtained by cutting FIG. 30 along line A-A. A cross-sectional view obtained by cutting FIG. 30 along line B-B or line F-F. A cross-sectional view obtained by cutting FIG. 30 along line CC or line E-E. A cross-sectional view obtained by cutting FIG. 30 along line D-D.

[0009] The semiconductor optical integrated device and the integrated chip according to each embodiment will be described with reference to the drawings. The same or corresponding components are designated by the same reference numerals, and the repeated description may be omitted.

[0010] First Embodiment. Figure 1 is a perspective view of a semiconductor optical integrated device 100 according to a first embodiment. The semiconductor optical integrated device 100 is an EML (Electro-absorption Modulator Integrated Laser Diode). The semiconductor optical integrated device 100 employs a buried structure for the laser 10 that enables high output, and a high mesa structure for the modulator 20 that provides a high optical confinement rate and high extinction characteristics.

[0011] Fig. 2 is a cross-sectional view of the semiconductor optical integrated device 100 according to the first embodiment. Fig. 3A is a cross-sectional view obtained by cutting Fig. 1 along line A-A. Fig. 3B is a cross-sectional view obtained by cutting Fig. 1 along line B-B or line F-F. Fig. 3C is a cross-sectional view obtained by cutting Fig. 1 along line C-C or line E-E. Fig. 3D is a cross-sectional view obtained by cutting Fig. 1 along line D-D. Note that electrodes, insulating films, contact layers on the cladding layers, etc. are omitted in Figs. 2 and 3.

[0012] The semiconductor optical integrated device 100 includes a substrate 50, and a laser 10, a modulator 20, and a conversion section 30 formed on the substrate 50. The laser 10 has a lower cladding layer 12, an active layer 14, and an upper cladding layer 16 stacked in this order from the substrate 50 side. The modulator 20 has a lower cladding layer 22, an active layer 24, and an upper cladding layer 26 stacked in this order from the substrate 50 side. The modulator 20 is an EA (Electro-Absorption) modulator.

[0013] The substrate 50 is made of, for example, n-InP. The lower cladding layers 12 and 22 are made of, for example, n-InP. The upper cladding layers 16 and 26 are made of, for example, p-InP. The active layers 14 and 24 are made of, for example, InGaAsP or AlGaInAs. AlGaInAs is sometimes written as AlInGaAs or InAlGaAs. The active layers 14 and 24 are also called MQW (Multi Quantum Well).

[0014] The conversion section 30 is provided between the laser 10 and the modulator 20, between the modulator 20 and the substrate 50, and on the output side of the modulator 20. Between the laser 10 and the modulator 20, the conversion section 30 has a lower waveguide 32 continuing to the active layer 14, and an upper waveguide 34a continuing to the active layer 24. On the opposite side of the modulator 20 from the laser 10, the conversion section 30 has an upper waveguide 34b continuing to the active layer 24. The lower waveguide 32 passes between the modulator 20 and the substrate 50 and reaches the opposite side of the modulator 20 from the laser 10. Hereinafter, the upper waveguides 34a and 34b may be collectively referred to as the upper waveguide 34.

[0015] An i-clad layer 31 is provided between the substrate 50 and the lower waveguide 32. An i-clad layer 33 is provided between the lower waveguide 32 and the upper waveguides 34a and 34b. An i-clad layer 35 is provided on the upper waveguides 34a and 34b. In this manner, the entire conversion section 30 is undoped. The conversion section 30 has a portion separating the laser 10 from the modulator 20 and a portion separating the modulator 20 from the substrate 50. Therefore, the clad layer of the modulator 20 is independent of the clad layer of the laser 10. Furthermore, the anode electrode 29 and the cathode electrode 21 of the modulator 20 can be provided independently of the anode electrode 19 and the cathode electrode 11 of the laser 10. In other words, the laser 10 and the modulator 20 do not have any common electrodes or layers.

[0016] 3, the semiconductor optical integrated device 100 includes a burying layer 60 that buries the side surfaces of the active layer 14 of the laser 10 and the side surfaces of the conversion section 30. As shown in FIG. 3D, both side surfaces of the active layer 24 of the modulator 20 are exposed from the burying layer 60. Between the laser 10 and the modulator 20, the thickness of the burying layer 60 that buries the side surfaces of the conversion section 30 becomes thinner from the laser 10 toward the modulator 20. Furthermore, on the output side of the modulator 20, the thickness of the burying layer 60 that buries the side surfaces of the upper waveguide 34b of the conversion section 30 becomes thicker the further away from the modulator 20.

[0017] The active layer 14 , the active layer 24 , the lower waveguide 32 and the upper waveguide 34 have the same width, which is basically constant throughout the semiconductor optical integrated device 100 .

[0018] The buried layer 60 is also called a current blocking layer. When the buried layer 60 is realized as a single layer, it is formed of, for example, InP containing Fe or Ru as a dopant. When the buried layer 60 has a multi-layer structure, it is formed by stacking, for example, p-InP, n-InP, and p-InP.

[0019] 2 and 3, anode electrodes 19 and 29 and a cathode electrode 21 of the modulator 20 are provided on the upper cladding layers 16 and 26 via a current contact layer, an insulating film, etc. A cathode electrode 11 of the laser 10 is provided on the underside of the substrate 50. The electrode of the laser 10 and the electrode of the modulator 20 are independent. The current contact layer is made of, for example, p-InGaAsP. The insulating film is made of, for example, SiO2 or SiN. The electrode is made of, for example, Au.

[0020] FIG. 4 is a cross-sectional view illustrating the directional coupler according to the first embodiment. FIG. 5A is a cross-sectional view taken at point A in FIG. 4 . FIG. 5B is a cross-sectional view taken at point B or point F in FIG. 4 . FIG. 5C is a cross-sectional view taken at point C or point E in FIG. 4 . FIG. 5D is a cross-sectional view taken at point D in FIG. 4 . In the conversion unit 30, the lower waveguide 32 and the upper waveguide 34a form a directional coupler that transfers light 80 guided through the lower waveguide 32 from the laser 10 toward the modulator 20 to the upper waveguide 34a. In this manner, the laser 10 and the modulator 20 are connected by a directional coupler. In addition, in the conversion unit 30, the lower waveguide 32 and the upper waveguide 34b form a directional coupler that transfers light 80 guided through the upper waveguide 34b in a direction away from the modulator 20 to the lower waveguide 32.

[0021] The lower waveguide 32 and the upper waveguide 34 are arranged parallel to each other so as to overlap in a plan view. The lower waveguide 32 and the upper waveguide 34 have the same thickness. The lower waveguide 32 is arranged at the same height as the active layer 14 of the laser 10. The upper waveguide 34 is arranged at the same height as the active layer 24. The upper waveguide 34a is arranged at a height such that the guided light 80 moves from the lower waveguide 32 to the upper waveguide 34a. As shown in FIG. 4, the upper waveguide 34a is preferably arranged at a height such that the optical waveguide mode distribution in the laser 10 overlaps the upper waveguide 34a.

[0022] In the conversion section 30, the ridge width W of the upper waveguide 34a continuously narrows at the same time as the light 80 starts to move to the upper waveguide 34a. This reduces the optical waveguide mode diameter, bringing it closer to the optical waveguide mode diameter of the high mesa structure of the modulator 20. Furthermore, as the optical waveguide mode diameter becomes smaller, the light 80 no longer impinges on the lower waveguide 32, and the light does not return to the lower waveguide 32.

[0023] The refractive index of the air outside the burying layer 60 is 1, the refractive index of the upper waveguide 34 is, for example, 3.6, and the refractive index of the i-clad layer 31 and the burying layer 60 is, for example, 3.5. Because the device structure is made of semiconductors, the difference in refractive index between the burying layer 60 and air is the largest. Therefore, by thinning the burying layer 60 and narrowing the ridge width W, the optical waveguide mode can be confined in a layer with a high refractive index, thereby reducing the optical waveguide mode diameter.

[0024] Similarly, at the output side of the modulator 20, the ridge width W of the upper waveguide 34b increases continuously as the light 80 begins to move from the upper waveguide 34b to the lower waveguide 32. This increases the optical waveguide mode diameter.

[0025] In this manner, in this embodiment, conversion between the laser 10 and the modulator 20, and conversion between the modulator 20 and an output conversion section (not shown) are realized by forming a directional coupler and changing the ridge width W.

[0026] Next, a method for manufacturing the semiconductor optical integrated device 100 of this embodiment will be described. Fig. 6 is a cross-sectional view illustrating a method for manufacturing the semiconductor optical integrated device 100 according to the first embodiment. Fig. 7A is a cross-sectional view taken at point A in Fig. 6. Fig. 7B is a cross-sectional view taken at point B or F in Fig. 6. Fig. 7C is a cross-sectional view taken at point C or E in Fig. 6. Fig. 7D is a cross-sectional view taken at point D in Fig. 6. First, the lower cladding layer 12, active layer 14, and upper cladding layer 16 that will form the laser 10 are laminated in this order on the substrate 50.

[0027] Next, as shown in FIG. 8, the portions other than the laser 10 are processed down to the substrate 50 by etching or the like. The processing, including subsequent processing, can be performed using a general semiconductor process. For example, the processing is performed in the order of insulating film formation, transfer exposure processing, insulating film processing, and semiconductor processing. FIG. 9A is a cross-sectional view taken at point A in FIG. 8. FIG. 9B is a cross-sectional view taken at point B or point F in FIG. 8. FIG. 9C is a cross-sectional view taken at point C or point E in FIG. 8. FIG. 9D is a cross-sectional view taken at point D in FIG. 8.

[0028] Next, as shown in Fig. 10 , an i-clad layer 31, a lower waveguide 32, an i-clad layer 33, an upper waveguide 34, and an i-clad layer 35, which will become the conversion section 30, are laminated in this order on the substrate 50. Fig. 11A is a cross-sectional view taken at point A in Fig. 10 . Fig. 11B is a cross-sectional view taken at point B or point F in Fig. 10 . Fig. 11C is a cross-sectional view taken at point C or point E in Fig. 10 . Fig. 11D is a cross-sectional view taken at point D in Fig. 10 .

[0029] Next, as shown in Figures 12 and 13, the lower cladding layer 12, active layer 14, upper cladding layer 16, i-cladding layer 31, lower waveguide 32, i-cladding layer 33, upper waveguide 34, and i-cladding layer 35 are processed by etching or the like to form a ridge. Figure 13A is a cross-sectional view taken at point A in Figure 12. Figure 13B is a cross-sectional view taken at point B or point F in Figure 12. Figure 13C is a cross-sectional view taken at point C or point E in Figure 12. Figure 13D is a cross-sectional view taken at point D in Figure 12.

[0030] Next, as shown in Figures 14 and 15, buried layers 60 are formed on both sides of the ridge. Figure 15A is a cross-sectional view taken at point A in Figure 14. Figure 15B is a cross-sectional view taken at point B or F in Figure 14. Figure 15C is a cross-sectional view taken at point C or E in Figure 14. Figure 15D is a cross-sectional view taken at point D in Figure 14.

[0031] Next, as shown in FIG. 16 , the i-clad layer 33, the upper waveguide 34, and a portion of the i-clad layer 35 are processed by etching or the like to form a recess 70 for forming the modulator 20. The recess 70 is formed to a depth at which a portion of the i-clad layer 33 is processed, for example. FIG. 17A is a cross-sectional view taken at point A in FIG. 16 . FIG. 17B is a cross-sectional view taken at point B or point F in FIG. 16 . FIG. 17C is a cross-sectional view taken at point C or point E in FIG. 16 . FIG. 17D is a cross-sectional view taken at point D in FIG. 16 .

[0032] Next, as shown in Fig. 18, a lower cladding layer 22, an active layer 24, and an upper cladding layer 26, which will become the modulator 20, are laminated in this order in the recess 70. Fig. 19A is a cross-sectional view taken at point A in Fig. 18. Fig. 19B is a cross-sectional view taken at point B or point F in Fig. 18. Fig. 19C is a cross-sectional view taken at point C or point E in Fig. 18. Fig. 19D is a cross-sectional view taken at point D in Fig. 18.

[0033] Next, as shown in Figures 20 and 21, the lower cladding layer 22, the active layer 24, and the upper cladding layer 26 are etched or otherwise processed to a depth equivalent to that of the lower cladding layer 22, thereby forming a high mesa structure. The buried layer 60 is also etched or otherwise processed to obtain the desired ridge width. This results in a buried layer 60 whose thickness varies continuously in the conversion region 30. Figure 21A is a cross-sectional view taken at point A in Figure 20. Figure 21B is a cross-sectional view taken at point B or point F in Figure 20. Figure 21C is a cross-sectional view taken at point C or point E in Figure 20. Figure 21D is a cross-sectional view taken at point D in Figure 20. After this, insulating films and electrodes are formed, but their description will be omitted.

[0034] FIG. 22A is a cross-sectional view of a laser 810 of a semiconductor optical integrated device according to a comparative example. FIG. 22B is a cross-sectional view of a modulator 20 of a semiconductor optical integrated device according to a comparative example. In the comparative example, the laser 810 has a buried structure in which the side surfaces of the active layer 814 are buried with a buried layer 860. The modulator 820 has a high mesa structure in which the side surfaces of the active layer 824 are exposed from the buried layer 860. The laser 810 and the modulator 820 of the comparative example share the cladding layers 812 and 822, and the cladding layers 816 and 826, respectively. The laser 810 and the modulator 820 of the comparative example share the cathode electrodes 11 and 21. A current contact layer 840 and an insulating film 842 are stacked on the cladding layers 816 and 826. The anode electrodes 19 and 29 are in contact with the current contact layer 840 through openings formed in the insulating film 842.

[0035] In such a laser 810, when the optical waveguide mode propagating through the active layer 814 comes into contact with the current contact layer 840, which has a high carrier concentration, optical absorption may occur, resulting in a decrease in optical output. For this reason, the cladding layer 816 is made thick so that the optical waveguide mode propagating through the active layer 814 does not distribute in the current contact layer 840. In this case, depending on the structure of the laser 810, it may be necessary to make the cladding layer 826 of the modulator 820 thicker than necessary, which may impose restrictions on the structure of the modulator 820.

[0036] It is also possible to separate the layer thicknesses of the laser and the modulator. However, a smooth transition of the optical waveguide mode diameter from the buried structure of the laser to the high mesa structure of the modulator, i.e., a transition with low optical loss, requires a continuous structural change. Selective growth technology is one way to continuously change the structure in the thickness direction. However, this requires the placement of special insulating film patterns, which increases the number of steps. Furthermore, processing after growing the layer with a continuously changing structure in the thickness direction requires a step to change the target processing depth for each region. For these reasons, separating the layer thicknesses of the laser and the modulator in a structure like the comparative example may reduce productivity.

[0037] In contrast, in this embodiment, the directional coupler of the conversion section 30 shifts the light guided in the lower waveguide 32 to the upper waveguide 34a, and the ridge width W is made thinner from the laser 10 to the modulator 20. This makes it possible to convert the buried structure of the laser 10 to the high mesa structure of the modulator 20. Furthermore, this structure allows the cladding layer of the modulator 20 to be separated from the cladding layer of the laser 10. Therefore, the thicknesses of the lower cladding layer 22 and the upper cladding layer 26 of the modulator 20 can be freely determined independently of the laser 10, improving the degree of freedom in the structure.

[0038] In particular, because the upper cladding layer 26 of the modulator 20 is independent from the upper cladding layer 16 of the laser 10, the thickness of the upper cladding layer 26 can be set independently from the upper cladding layer 16 of the laser 10. This improves the degree of freedom in the structure of the modulator 20. For example, by setting the upper cladding layer 26 to a required thickness, a low-capacity high mesa structure can be realized, enabling high-speed operation. Furthermore, the laser 10 can also be freely designed independently from the modulator 20.

[0039] Furthermore, the anode electrode 29 and the cathode electrode 21 of the modulator 20 can be made independent of the anode electrode 19 and the cathode electrode 11 of the laser 10. This allows the modulator 20 to be driven by a differential voltage independent of the laser 10. This allows for low power consumption.

[0040] Furthermore, in this embodiment, the buried structure of the laser 10 can be converted to the high mesa structure of the modulator 20 without adding any special process. Furthermore, a simple process allows for separation of the laser 10 and the modulator 20, particularly the lower cladding layers 12 and 22 below the active layer. Furthermore, in a directional coupler, the light transfer distance is determined by the width and distance between the lower waveguide 32 and the upper waveguide 34. Therefore, light can be transferred with higher precision than when, for example, an MMI (Multi-Mode Interferometer) is used.

[0041] The materials of each layer are merely examples and are not limited to those described above. The conductivity types of each layer may be reversed. The conversion section 30 may be provided at least between the laser 10 and the modulator 20.

[0042] The above-described modifications can be applied as appropriate to the semiconductor optical integrated devices and integrated chips according to the following embodiments. Note that the semiconductor optical integrated devices and integrated chips according to the following embodiments have many points in common with the first embodiment, so the following description will focus on the differences from the first embodiment.

[0043] Second Embodiment Fig. 23 is a perspective view of a semiconductor optical integrated device 200 according to a second embodiment. Fig. 24 is a cross-sectional view of the semiconductor optical integrated device 200 according to the second embodiment. Fig. 25A is a cross-sectional view obtained by cutting Fig. 23 along line A-A. Fig. 25B is a cross-sectional view obtained by cutting Fig. 23 along line B-B or line F-F. Fig. 25C is a cross-sectional view obtained by cutting Fig. 23 along line C-C or line E-E. Fig. 25D is a cross-sectional view obtained by cutting Fig. 23 along line D-D.

[0044] In the semiconductor optical integrated device 200 of this embodiment, the laser 10 has a buried structure that allows for high output, and the modulator 220 has a ridge structure that provides a high optical confinement ratio and high extinction characteristics. That is, the semiconductor optical integrated device 200 differs from the semiconductor optical integrated device 100 of the first embodiment in that one side of the active layer 24 of the modulator 220 is exposed from the buried layer 60, and the other side is buried in the buried layer 60. In this way, it is sufficient that at least one side of the active layer 24 of the modulator 220 is exposed from the buried layer 60. The other structures are the same as those of the first embodiment.

[0045] Fig. 26 is a cross-sectional view illustrating a directional coupler according to embodiment 2. Fig. 27A is a cross-sectional view taken at point A in Fig. 26. Fig. 27B is a cross-sectional view taken at point B or point F in Fig. 26. Fig. 27C is a cross-sectional view taken at point C or point E in Fig. 26. Fig. 27D is a cross-sectional view taken at point D in Fig. 26. In this embodiment, as in embodiment 1, conversion between laser 10 and modulator 220, and conversion between modulator 220 and an output conversion unit (not shown) are realized by forming a directional coupler and changing the ridge width W.

[0046] Next, a method for manufacturing the semiconductor optical integrated device 200 of this embodiment will be described. The method for manufacturing the semiconductor optical integrated device 200 of this embodiment is the same as the manufacturing method of embodiment 1 up to the steps shown in Figures 18 and 19. Figure 28 is a cross-sectional view for explaining the manufacturing method of the semiconductor optical integrated device 200 according to embodiment 2. Figure 29A is a cross-sectional view at point A in Figure 28. Figure 29B is a cross-sectional view at point B or point F in Figure 28. Figure 29C is a cross-sectional view at point C or point E in Figure 28. Figure 29D is a cross-sectional view at point D in Figure 28.

[0047] 18, both sides of the upper cladding layer 26 and one side of the active layer 24 are processed by etching or the like to form a ridge structure. The buried layer 60 is also processed by etching or the like to obtain the desired ridge width W. This results in a buried layer 60 whose thickness changes continuously in the conversion region 30.

[0048] In this embodiment, the directional coupler of the conversion section 30 also shifts light guided through the lower waveguide 32 to the upper waveguide 34a, and the ridge width W is reduced from the laser 10 toward the modulator 220. This allows for conversion from the buried structure of the laser 10 to the ridge structure of the modulator 220. As in the first embodiment, the cladding layer of the modulator 220 can be separated from the cladding layer of the laser 10, improving structural flexibility. Setting the upper cladding layer 26 to a required thickness allows for a low-capacity ridge structure, enabling high-speed operation. Furthermore, the modulator 220 can be driven by a differential voltage independent of the laser 10, enabling low power consumption.

[0049] In the first and second embodiments, an example has been described in which at least one side surface of the active layer 24 of the modulator is exposed from the burying layer 60. However, the present invention is not limited to this, and both side surfaces of the active layer 24 of the modulator may be buried in the burying layer 60. For example, a thin burying layer 60 may be disposed on both sides of the active layer 24.

[0050] Embodiment 3. Fig. 30 is a perspective view of an integrated chip 300 according to embodiment 3. Fig. 31 is a cross-sectional view of an integrated chip 300 according to embodiment 3. Fig. 32A is a cross-sectional view obtained by cutting Fig. 30 along line A-A. Fig. 32B is a cross-sectional view obtained by cutting Fig. 30 along line B-B or line F-F. Fig. 32C is a cross-sectional view obtained by cutting Fig. 30 along line C-C or line E-E. Fig. 32D is a cross-sectional view obtained by cutting Fig. 30 along line D-D.

[0051] In the integrated chip 300 according to this embodiment, a plurality of semiconductor optical integrated devices 100 are arranged in a direction perpendicular to the light waveguiding direction. The plurality of semiconductor optical integrated devices 100 are integrated in an array. Here, a plurality of semiconductor optical integrated devices 100 are provided, but the integrated chip 300 may also be made up of a plurality of semiconductor optical integrated devices 200.

[0052] In the first and second embodiments, the modulators 20 and 220 are configured as independent circuits, which makes it possible to obtain an integrated chip 300 in which the modulated electrical signals to the modulators of the respective lanes do not affect each other.

[0053] The technical features described in each embodiment may be used in appropriate combination.

[0054] 10 Laser, 11 Cathode electrode, 12 Lower cladding layer, 14 Active layer, 16 Upper cladding layer, 19 Anode electrode, 20 Modulator, 21 Cathode electrode, 22 Lower cladding layer, 24 Active layer, 26 Upper cladding layer, 29 Anode electrode, 30 Conversion section, 31 i-cladding layer, 32 Lower waveguide, 33 i-cladding layer, 34 Upper waveguide, 34a Upper waveguide, 34b Upper waveguide, 35 i-cladding layer, 50 Substrate, 60 Buried layer, 70 Recess, 80 Light, 100 Semiconductor optical integrated element, 200 Semiconductor optical integrated element, 220 Modulator, 300 Integrated chip, 810 Laser, 812 Cladding layer, 814 Active layer, 816 Cladding layer, 820 Modulator, 822 Cladding layer, 824 Active layer, 826 cladding layer, 840 current contact layer, 842 insulating film, 860 buried layer

Claims

1. A semiconductor optical integrated device comprising: a substrate; a laser formed on the substrate and having a first lower cladding layer, a first active layer, and a first upper cladding layer stacked in this order from the substrate side; a modulator formed on the substrate and having a second lower cladding layer, a second active layer, and a second upper cladding layer stacked in this order from the substrate side; a conversion section having a lower waveguide continuing to the first active layer between the laser and the modulator, and a first upper waveguide continuing to the second active layer between the laser and the modulator; and a burying layer burying a side surface of the first active layer of the laser and a side surface of the conversion section; wherein the lower waveguide and the first upper waveguide form a directional coupler that transfers light guided in the lower waveguide from the laser to the modulator to the first upper waveguide, and the thickness of the burying layer burying the side surface of the conversion section becomes thinner between the laser and the modulator from the laser to the modulator.

2. The semiconductor optical integrated device according to claim 1, wherein the entire conversion section is undoped.

3. The semiconductor optical integrated device according to claim 1 or 2, wherein the conversion section has a portion separating the laser from the modulator and a portion separating the modulator from the substrate.

4. A semiconductor optical integrated device according to any one of claims 1 to 3, characterized in that the conversion section has a second upper waveguide connected to the second active layer on the opposite side of the modulator from the laser, and the lower waveguide passes between the modulator and the substrate and reaches the opposite side of the modulator from the laser.

5. The semiconductor optical integrated device according to claim 4, wherein the thickness of the burying layer burying the side surface of the second upper waveguide of the conversion section increases with increasing distance from the modulator.

6. A semiconductor optical integrated device according to claim 4 or 5, characterized in that the lower waveguide and the second upper waveguide form a directional coupler that transfers light guided through the second upper waveguide in a direction away from the modulator to the lower waveguide.

7. An integrated chip in which a plurality of semiconductor optical integrated devices according to any one of claims 1 to 6 are arranged in a direction perpendicular to the light waveguide direction.

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