JP4833457B2 - Fabrication method of optical integrated device - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention, respectively, relates to a method for manufacturing a first and second butt junction semiconductor optical device optical integrated device coupled with (butt joint) system having an active layer comprising a quantum well structure, and more particularly, devices characteristics are good, to a method for manufacturing a optimum optical integrated device as an optical data transmission and optical communication field of the light source.
[0002]
[Prior art]
With the progress of the optical communication field, an optical integrated device in which an optical modulator, for example, an EA modulator, is coupled to a semiconductor laser element, for example, a distributed feedback semiconductor laser element (hereinafter referred to as a DFB laser) by a butt joint method, has a modulation characteristic. It is attracting attention as a good light source.
Here, a configuration of an example of an optical integrated device in which a DFB laser is coupled to an EA modulator will be described with reference to FIG. FIG. 3 is a cross-sectional view along the ridge stripe showing the configuration of the optical integrated device.
As shown in FIG. 3, the optical integrated device 10 in which the EA modulator is coupled to the DFB laser by the butt joint method includes a DFB laser 14 formed on the DFB laser region 12a of the common n-InP substrate 12, and an n− The EA modulator 16 is formed on the EA modulator region 12 b of the InP substrate 12 and is optically coupled to the DFB laser 12.
[0003]
The DFB laser 14 includes an n-InP lower cladding layer 18, a diffraction grating 20 made of GaInAsP, and an n-InP cap layer 22 on the diffraction grating 20, which are epitaxially grown sequentially on the DFB laser region 12 a of the n-InP substrate 12. A stacked structure of an n-InP buried layer 24 in which the diffraction grating 20 and the n-InP cap layer 22 are buried, an SCH-MQW active structure 26 made of GaInAsP, a p-InP upper cladding layer 28, and a p-InP contact layer 30. Have. The SCH-MQW active structure 26 has a well layer having five wells.
A p-side electrode 32 is formed on the p-InP contact layer 30, and a common n-side electrode 34 is formed on the back surface of the n-InP substrate 12.
[0004]
The EA modulator 16 includes an n-InP lower cladding layer 36 and a GaInAsP that are sequentially epitaxially grown on the EA modulator region 12b of the n-InP substrate 12, and an SCH-MQW active structure 38 that constitutes a light absorption layer. , A p-InP upper clad layer 40 and a p-InP contact layer 42. The SCH-MQW active structure 38 has an active layer having a band gap wavelength of 1.48 μm, which is a well layer having 18 wells.
A p-side electrode 44 is formed on the p-InP contact layer 42.
[0005]
In order to enhance the high-speed modulation characteristics, the upper layers of the p-InP upper cladding layers 28 and 40 of the DFB laser 14 and the EA modulator 16 are formed into ridge stripes (not shown) to form a waveguide.
Both sides of the ridge stripe are filled with a high resistance layer (not shown) made of Fe-doped InP, and further, regrowth of the p-InP upper cladding layers 28 and 40 on the p-InP upper cladding layers 28 and 40. Layers and p-InP contact layers 30/42 are provided.
[0006]
The SCH-MQW active structure 26 of the DFB laser 14 and the SCH-MQW active structure 38 of the EA modulator 16 are coupled by a butt joint method.
A separation groove 46 is provided between the EA modulator 16 and the DFB laser 14 to electrically separate the EA modulator 16 and the DFB laser 14.
[0007]
4 (a) to 4 (c) and FIGS. 5 (d) to 5 (f) are cross-sectional views along the ridge stripe for each process when the conventional optical integrated device 10 is manufactured by the butt joint method. .
As shown in FIG. 4A, an n-InP lower cladding layer 18, a GaInAsP diffraction grating layer 19, and an n-InP cap layer 22 are epitaxially grown on the entire surface of the n-InP substrate 12 by MOCVD.
Next, as shown in FIG. 4B, the p-InP cap layer 22 and the GaInAsP diffraction grating layer 19 are etched to form a diffraction grating 20. Note that the diffraction grating 20 may be formed only in the DFB laser region 12a.
Subsequently, as shown in FIG. 4C, an n-InP buried layer 24 is grown, the diffraction grating 20 is buried, and an SCH-MQW active structure 26 made of GaInAsP is further formed on the InP buried layer 24, and p. The InP upper cladding layer 28a is grown sequentially.
[0008]
Next, as shown in FIG. 5D, a mask 48 made of a SiN film is formed so as to cover the DFB-LD region 12a and expose the EA modulator region 12b. Subsequently, the EA modulation exposed from the mask 48 is formed. The p-InP upper cladding layer 28a, the SCH-MQW active structure 26, the n-InP buried layer 24, the n-InP cap layer 22, the diffraction grating 20, and the n-InP cladding layer 18 in the vessel region 12b are etched, and n -InP substrate 12 is exposed.
[0009]
Next, as shown in FIG. 5E, using the mask 48 as a selective growth mask, an n-InP lower cladding layer 36 and an active structure 38 made of GaInAsP are formed on the n-InP substrate 12 in the EA modulator region 12b. The p-InP upper cladding layer 40a is epitaxially grown by a selective region growth method.
[0010]
Next, after removing the SiN mask 48, another etching mask having a waveguide pattern is formed to improve high-speed modulation characteristics, and a striped ridge (not shown) is formed by dry etching, and then Fe A high resistance layer (not shown) made of doped InP is grown to fill the ridge.
After removing the waveguide etching mask, the p-InP upper cladding layers 28 and 40 are regrown on the p-InP upper cladding layers 28a and 40a, and then the p-InP contact layers 30/42 are grown.
[0011]
Further, the p-side electrodes 32 and 44 are formed, the back surface of the n-InP substrate 12 is polished and adjusted to a predetermined substrate thickness, and then the n-side electrode 34 is formed on the back surface of the n-InP substrate 12. Also, by forming the separation groove 46, the optical integrated device 10 shown in FIG. 3 can be manufactured.
[0012]
[Problems to be solved by the invention]
However, the conventional optical integrated device manufactured by the butt joint method according to the manufacturing method described above has the following problems.
That is, when the compound semiconductor layer constituting the laminated structure constituting the EA modulator is grown by the selective region growth method by removing the DFB laser laminated structure on the EA modulator region, the boundary region near the selective growth mask, That is, at the junction, the growth conditions of the compound semiconductor layer, particularly the SCH-MQW active structure 38, are different from the growth conditions on the other optical modulator region 12b due to the influence of the selective growth mask.
Therefore, as shown in a circle in FIG. 6, the compound semiconductor layer constituting the SCH-MQW active structure 38 grows abnormally so as to rise, and the composition of the compound semiconductor layer is likely to be modulated.
[0013]
In addition, since the EA modulator obtains a large extinction ratio, the number of wells in the quantum well structure of the EA modulator is generally larger than the number of wells in the DFB laser. For example, as described above, the number of wells in the quantum well structure of the DFB laser is 5 to 6 layers, while the number of wells in the quantum well structure of the EA modulator is 10 or more. In addition, strain is introduced into the well layer and the barrier layer in order to improve the modulation characteristics.
Therefore, when the stacked structure of the EA modulator is regrown on the substrate, the strain is relaxed due to abnormal growth, dislocation occurs, and crystallinity deteriorates.
As a result, there are problems that good device characteristics cannot be obtained, device deterioration after energization is remarkable, and it is difficult to obtain high device reliability.
[0014]
As described above, it is difficult to fabricate an optical integrated device exhibiting good device characteristics by fabricating an optical integrated device by causing the active layer of the DFB laser to butt-join the absorption layer of the optical modulator.
In the above description, the fabrication of the optical integrated device has been described by taking the DFB laser as an example. However, this is not limited to the DFB laser, and this is a universal that occurs when the optical modulator is coupled to the semiconductor laser element by the butt joint method. It is a problem. Furthermore, it is not limited to an optical modulator.
[0015]
Accordingly, an object of the present invention is a method for manufacturing an optical integrated device in which first and second semiconductor optical elements each having an active layer having a quantum well structure are coupled to each other on a common substrate by a butt joint method . An object of the present invention is to provide a method for manufacturing an optical integrated device having good characteristics.
[0016]
[Means for Solving the Problems]
The inventor first forms a first semiconductor optical device stacked structure having a large number of quantum wells and a large strained absorption layer, and then includes a first layer having an active layer with a small number of strains or a small number of quantum wells. The idea was to re-grow the stacked structure of the semiconductor optical elements of 2 and to make a butt joint.
That is, contrary to the conventional method, first, after forming the stacked structure of the EA modulator including the active structure having a large number of wells and a large strain, and then removing the stacked structure of the EA modulator, the number of wells is increased. The idea was to suppress the abnormal growth of the junction by forming a laminated structure of a DFB laser including an active structure with little strain.
And this was confirmed by experiment and came to invent the present invention.
[0022]
In order to achieve the above object, based on the above-described knowledge, a method for manufacturing an optical integrated device according to a first invention includes an active layer having a quantum well structure on a common substrate, and includes a first semiconductor. An optical integrated device is obtained by connecting the first and second semiconductor optical elements having a larger number of wells in the quantum well structure of the optical element than the number of wells in the quantum well structure of the second semiconductor optical element by a butt joint method. In the manufacturing method, a first stacking step and a first stacking step of forming at least an active layer and a stacked structure between the active layer and the substrate on the substrate among the stacked structures constituting the first semiconductor optical device. And removing the layered structure on the formation region of the second semiconductor optical element to expose the substrate, and at least active among the layered structure constituting the second semiconductor optical element. layer A second stacking process for forming a stacked structure between the active layer and the substrate on the exposed substrate by selective growth, and a third stacking process for forming the remaining stacked structure of the first and second semiconductor optical devices. has the door, the second semiconductor optical element is a distributed feedback semiconductor laser device having a diffraction grating below the active layer, the first laminating step, the active layer and the substrate of the first semiconductor optical element A diffraction grating layer for forming a diffraction grating of the second semiconductor optical element is grown between them, and in the removing step, the diffraction grating layer is etched to reach a layer where a diffraction grating can be formed. The stacked structure is removed, and in the second stacking step, a diffraction grating is formed, and then the diffraction grating is embedded, and at least the active layer and the stacked structure between the active layer and the diffraction grating are formed by a selective growth method. It is a feature.
[0023]
In addition, the method for fabricating an optical integrated device according to the second invention includes an active layer having a quantum well structure having a well layer in which strain is introduced on a common substrate, and the well of the first semiconductor optical device. In the method of manufacturing an optical integrated device by combining the first and second semiconductor optical elements having a strain larger than that of the well layer of the second semiconductor optical element by a butt joint method, Of the laminated structure constituting the semiconductor optical device, at least the active layer and the laminated structure between the active layer and the substrate are formed on the substrate, among the first laminated step and the laminated structure formed in the first laminated step, The removal step of removing the laminated structure on the formation region of the second semiconductor optical device to expose the substrate, and at least the active layer and the active layer and the substrate of the laminated structure constituting the second semiconductor optical device Laminated structure between The second semiconductor optical device includes a second stacking step that is formed on the exposed substrate by a selective growth method, and a third stacking step that forms the remaining stacked structure of the first and second semiconductor optical devices. a distributed feedback semiconductor laser device having a diffraction grating below the active layer, the first laminating step, the diffraction grating of the second semiconductor optical element between the active layer and the substrate of the first semiconductor optical element Growing the diffraction grating layer to be formed, and in the removal step, the laminated structure on the formation region of the second semiconductor optical element is removed up to the layer capable of forming the diffraction grating by etching the diffraction grating layer. A diffraction grating is formed, and subsequently, the diffraction grating is embedded, and at least an active layer and a laminated structure between the active layer and the diffraction grating are formed by a selective growth method.
[0025]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, embodiments of the present invention will be described specifically and in detail with reference to the accompanying drawings.
Embodiment of optical integrated device In this embodiment, an optical integrated device according to the first and second inventions is applied to an optical integrated device in which a DFB laser and an EA modulator are integrated. FIG. 1 is a schematic cross-sectional view along the ridge stripe showing the configuration of the optical integrated device of this embodiment.
In the optical integrated device 50 according to the present embodiment, as shown in FIG. 1, the laminated structure including the active structure 26 of the DFB laser 14 is butt-jointed to the laminated structure including the absorption structure 38 of the EA modulator 16. The n-InP lower cladding layer 18 of the DFB laser 14 and the n-InP lower cladding layer 36 of the EA modulator 16 are common and the activity of the EA modulator 16 (as shown in the circle in FIG. 1). The structure is the same as that of the conventional optical integrated device 10 except that the GaInAsP diffraction grating layer 19 and the n-InP cap layer 22 are provided between the structure 38 and the n-InP lower cladding layer 36.
[0026]
In the optical integrated device 50 of the present embodiment example, the active structure 26 having a small number of quantum wells in the DFB laser 14 is butt-jointed to the absorption structure 38 having a large number of quantum wells in the EA modulator 16. When forming the laminated structure, the compound semiconductor layer in the region near the selective growth mask (junction) is slightly raised as shown in the circle in FIG. The abnormal growth of is significantly suppressed.
Therefore, compositional modulation of the active structure 26 is difficult to occur, and there is little variation in the device characteristics of the optical integrated device 50.
Further, since the strain introduced into the active structure 26 of the DFB laser 14 is smaller than the strain introduced into the active layer of the EA modulator 16, the active structure is compared with the optical integrated device 10 manufactured by the conventional method. The strain introduced in No. 26 is hardly relaxed, and dislocations are hardly generated. Therefore, crystallinity is good, good device characteristics are obtained, device deterioration after energization is small, and reliability is high.
[0027]
Embodiment of optical integrated device fabrication method This embodiment is an embodiment in which the optical integrated device fabrication method according to the first and second invention methods is applied to the fabrication of the optical integrated device 50 described above. FIGS. 2A to 2C are schematic cross-sectional views along the ridge stripe in each step when manufacturing an optical integrated device according to the method of this embodiment.
First, as shown in FIG. 2A, an n-InP lower clad layer 36 common to the n-InP lower clad layer 18 of the DFB laser 14 and the number of wells 18 and a band gap wavelength 1 A laminated structure of the EA modulator 16 is formed by growing an absorption structure 38 having a .48 μm quantum well structure and a p-InP upper cladding layer 40a.
For convenience of manufacturing the DFB laser 14, a GaInAsP diffraction grating layer 19 and an n-InP cap layer 22 that form the diffraction grating of the DFB laser 14 are formed between the n-InP lower cladding layer 36 and the quantum well structure 38. Keep it.
[0028]
Next, a SiN film is formed on the p-InP upper cladding layer 40a, and as shown in FIG. 2B, a mask 52 that covers the EA modulator region 12b in the stacked structure of the EA modulator 16 is formed. The p-InP upper cladding layer 40a and the absorption structure 38 on the DFB laser region 12a are etched to expose the n-InP cap layer 22.
Next, as shown in FIG. 2C, a diffraction grating pattern is formed by an EB drawing apparatus, and the n-InP cap layer 22 and the GaInAsP diffraction grating layer 22 are etched to produce a diffraction grating 19.
Using the mask 52 as a selective growth mask, an n-InP layer 24 is grown, the diffraction grating 19 is embedded, and further, an SCH-MQW active structure 26 including a quantum well layer having 5 wells is formed, and p-InP The upper cladding layer 28a is grown.
[0029]
In this embodiment, the active structure 26 of the DFB laser 14 has a small number of quantum wells. Therefore, when the butt joint is used, abnormal growth of the active structure 26 is suppressed, and a good junction can be formed.
Even when the bonded portion is observed with a TEM, dislocations and the like are hardly observed, and the bulge in the vicinity of the mask is suppressed to a small level.
[0030]
Next, the selective growth mask 52 is removed, and another etching mask (not shown) having a waveguide pattern is formed in order to improve high-speed modulation characteristics, and a striped ridge (not shown) is formed by dry etching. To do. Subsequently, a high resistance layer (not shown) made of Fe-doped InP is grown to fill the ridge.
After removing the waveguide mask, the p-InP upper clad layers 28 and 40 are regrown on the p-InP upper clad layers 28a and 40a, and the p-InP contact layers 30/42 are subsequently formed. Grow.
Next, an optical integrated device 50 in which an electrode is formed, a passivation film is formed, an electrical separation groove 46 is formed between the DFB laser 14 and the EA modulator 16, and the DFB laser 14 is butt-joined to the EA modulator 16 is formed. Complete.
[0031]
The optical integrated device 50 has very good device characteristics as compared with the conventional optical integrated device 10, and was able to realize modulation at 10 GHz and transmission of 120 km or more.
In addition, since the butt joint joining can be achieved without dislocation, the reliability of the optical integrated device can be remarkably improved.
[0032]
In the present embodiment, the present invention and the method of the present invention are described by giving an example in which a DFB laser and an EA modulator are butt-jointed. However, the first and second semiconductor optical elements to be butt-joined are DFB lasers. The present invention is not limited to the EA modulator and can be applied to, for example, an optical integrated device in which semiconductor amplifiers and the like are integrated.
In the present embodiment, the example of the optical integrated device in which the diffraction grating of the DFB laser is between the active layer and the substrate has been described. However, the diffraction grating may be on the active layer. However, in this case, it is not necessary to form the diffraction grating layer when growing the laminated structure of the EA modulator, and when the DFB laser laminated structure is regrown, the active layer and the diffraction grating layer are not formed. Growing and then forming a diffraction grating.
[0033]
【The invention's effect】
According to the present invention, the number of wells of the quantum well structure of the first semiconductor optical device is larger than the number of wells of the quantum well structure of the second semiconductor optical device, and the strain of the well layer of the first semiconductor optical device is When the first and second semiconductor optical elements, which are larger than the strain of the well layer of the second semiconductor optical element, are coupled by a butt joint method, the active layer of the second semiconductor optical element is changed to the first semiconductor. By making a butt joint to the active layer of the optical element, the crystallinity of the junction between the first and second semiconductor optical elements is good, good element characteristics are obtained, element deterioration after energization is small, and reliability is high. High optical integrated devices are realized.
[Brief description of the drawings]
FIG. 1 is a schematic cross-sectional view along a ridge stripe showing a configuration of an optical integrated device according to an embodiment.
FIGS. 2A to 2C are schematic cross-sectional views along the ridge stripe in each step when an optical integrated device is manufactured according to the method of the embodiment. FIG.
FIG. 3 is a cross-sectional view showing a configuration along a ridge stripe of a conventional optical integrated device.
4 (a) to 4 (c) are cross-sectional views taken along a ridge stripe for each process when an optical integrated device is manufactured by a conventional butt joint method, respectively.
FIGS. 5 (d) to 5 (f) are cross-sectional views taken along the ridge stripe for each process in fabricating an optical integrated device by the conventional butt joint method, respectively, following FIG. 4 (c). It is.
FIG. 6 is a cross-sectional view showing a problem of an optical integrated device manufactured by a conventional butt joint method.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 10 Optical integrated device 12 which combined EA modulator with DFB laser by butt joint system 12 n-InP substrate 12a DFB laser region 12b EA modulator region 14 DFB laser 16 EA modulator 18 n-InP lower clad layer 19 Diffraction grating layer 20 Diffraction grating 22 n-InP cap layer 24 n-InP buried layer 26 SCH-MQW active structure 28 p-InP upper cladding layer 30 p-InP contact layer 32 p-side electrode 34 n-side electrode 36 n-InP lower cladding layer 38 SCH -MQW active structure 40 p-InP upper cladding layer 42 p-InP contact layer 44 p-side electrode 46 separation groove 48 mask 50 optical integrated device 52 mask of embodiment example in which DFB laser is coupled to EA modulator by butt joint method

Claims (2)

First and second active layers each having a quantum well structure on a common substrate, wherein the number of wells in the quantum well structure of the first semiconductor optical device is larger than the number of wells in the quantum well structure of the second semiconductor optical device. In a method of manufacturing an optical integrated device by joining two semiconductor optical elements by a butt joint method,
A first stacking step of forming, on the substrate, at least an active layer and a stacked structure between the active layer and the substrate, among the stacked structures constituting the first semiconductor optical device;
A removal step of removing the stacked structure on the formation region of the second semiconductor optical element from the stacked structure formed in the first stacking step to expose the substrate;
A second layering step of forming at least an active layer and a layered structure between the active layer and the substrate among the layered structures constituting the second semiconductor optical device on the exposed substrate by a selective growth method;
A third stacking step for forming the remaining stacked structure of the first and second semiconductor optical devices,
The second semiconductor optical element is a distributed feedback semiconductor laser device having a diffraction grating below the active layer,
In the first stacking step, a diffraction grating layer that forms the diffraction grating of the second semiconductor optical device is grown between the active layer of the first semiconductor optical device and the substrate, and in the removal step, the diffraction grating layer is etched. The layered structure on the formation region of the second semiconductor optical device is removed up to the layer where the diffraction grating can be formed, and in the second layering step, the diffraction grating is formed, and then the diffraction grating is embedded, and at least the active layer and the active layer A method for manufacturing an optical integrated device, comprising forming a stacked structure between a layer and a diffraction grating by a selective growth method. Each includes an active layer having a quantum well structure having a well layer with strain introduced on a common substrate, and the strain of the well layer of the first semiconductor optical device is greater than the strain of the well layer of the second semiconductor optical device. In a method of manufacturing an optical integrated device by joining large first and second semiconductor optical elements by a butt joint method,
A first stacking step of forming, on the substrate, at least an active layer and a stacked structure between the active layer and the substrate, among the stacked structures constituting the first semiconductor optical device;
A removal step of removing the stacked structure on the formation region of the second semiconductor optical element from the stacked structure formed in the first stacking step to expose the substrate;
A second layering step of forming at least an active layer and a layered structure between the active layer and the substrate among the layered structures constituting the second semiconductor optical device on the exposed substrate by a selective growth method;
A third stacking step for forming the remaining stacked structure of the first and second semiconductor optical devices,
The second semiconductor optical element is a distributed feedback semiconductor laser device having a diffraction grating below the active layer,
In the first stacking step, a diffraction grating layer that forms the diffraction grating of the second semiconductor optical device is grown between the active layer of the first semiconductor optical device and the substrate, and in the removal step, the diffraction grating layer is etched. The layered structure on the formation region of the second semiconductor optical device is removed up to the layer where the diffraction grating can be formed, and in the second layering step, the diffraction grating is formed, and then the diffraction grating is embedded, and at least the active layer and the active layer A method for manufacturing an optical integrated device, comprising forming a stacked structure between a layer and a diffraction grating by a selective growth method.

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