JP2018101752A - Semiconductor optical device and manufacturing method thereof - Google Patents

Abstract

A semiconductor optical device capable of suppressing abnormal growth of a buried layer and a method for manufacturing the same are provided.
A core layer that includes Al and is provided on a substrate; an intermediate layer that is provided on the core layer and includes Al; and an intermediate layer that is provided on the intermediate layer and is formed of InP. A clad layer that forms a mesa with a layer and the intermediate layer, and buried layers provided on both sides of the mesa, the width of the clad layer being larger than the width of the intermediate layer, The side surface is inclined so as to spread from the core layer to the cladding layer, and the Al composition of the intermediate layer decreases from the core layer side to the cladding layer side.
[Selection] Figure 2

Description

  The present invention relates to a semiconductor optical device and a method for manufacturing the same.

  A quantum cascade laser (QCL) element including aluminum (Al) in a core layer is disclosed (for example, see Patent Document 1).

JP 2009-54637 A

  In a semiconductor optical device, a core layer and a clad layer stacked on a substrate form a mesa, and a high-resistance buried layer is formed on both sides of the mesa. However, the core layer and the cladding layer have different etching rates. For this reason, in the etching for forming the mesa, the etching amount of the core layer is larger than that of the cladding layer, and a step is formed between the core layer and the cladding layer. As a result, the buried layer grows abnormally.

  An object of the present invention is to provide a semiconductor optical device capable of suppressing abnormal growth of a buried layer and a method for manufacturing the same.

  A semiconductor optical device according to the present invention is provided on a substrate, and includes a core layer including Al, an intermediate layer including Al, an intermediate layer including Al, and an intermediate layer including Al. A clad layer that is formed and forms a mesa with the core layer and the intermediate layer, and buried layers provided on both sides of the mesa, and the width of the clad layer is larger than the width of the intermediate layer The side surface of the intermediate layer is inclined so as to spread from the core layer to the cladding layer, and the Al composition of the intermediate layer decreases from the core layer side to the cladding layer side.

  According to the above invention, it is possible to suppress abnormal growth of the buried layer.

1A and 1B are cross-sectional views illustrating a method for manufacturing a semiconductor optical device according to a comparative example. FIG. 2A is a cross-sectional view illustrating the semiconductor optical device according to the first embodiment. FIG. 2B is an enlarged sectional view of the vicinity of the intermediate layer. FIG. 3A and FIG. 3B are cross-sectional views illustrating a method for manufacturing a semiconductor optical device. FIG. 4A and FIG. 4B are cross-sectional views illustrating a method for manufacturing a semiconductor optical device. FIG. 5A and FIG. 5B are cross-sectional views illustrating a method for manufacturing a semiconductor optical device. FIG. 6A and FIG. 6B are cross-sectional views illustrating a method for manufacturing a semiconductor optical device. FIG. 7A and FIG. 7B are cross-sectional views illustrating a method for manufacturing a semiconductor optical device. FIG. 8 is a diagram showing the relationship between the angle, the thickness of the intermediate layer, and the distance between the side surfaces of the core layer and the cladding layer.

[Description of Embodiment of Present Invention]
First, the contents of the embodiments of the present invention will be listed and described.

One form of the present invention is (1) provided on a substrate, and includes a core layer including Al, an intermediate layer including Al on the core layer, and provided on the intermediate layer. A clad layer that forms a mesa with the core layer and the intermediate layer, and buried layers provided on both sides of the mesa, and the width of the clad layer is larger than the width of the intermediate layer In the semiconductor optical device, the side surface of the intermediate layer is inclined so as to spread from the core layer to the cladding layer, and the Al composition of the intermediate layer decreases from the core layer side to the cladding layer side. According to this configuration, an inclination is formed in the intermediate layer, and the step between the core layer and the cladding layer becomes gentle. For this reason, stacking faults in the buried layer are suppressed, and the buried layer grows well in a desired direction. Thus, the abnormal growth of the buried layer is suppressed.
(2) The angle formed by the lamination direction of the core layer, the intermediate layer, and the clad layer and the side surface of the intermediate layer may be 50 ° or less. According to this configuration, stacking faults are less likely to occur in the buried layer.
(3) The intermediate layer may be made of Al _x Ga _y In _(1-xy) As and satisfy y = 0.47− (0.47 / 0.48) x. Thereby, since the Al composition decreases toward the cladding layer, the etching rate also decreases, and an inclination is formed in the intermediate layer. The intermediate layer is lattice-matched with the core layer and the cladding layer. Therefore, the crystallinity of the intermediate layer and the cladding layer is improved.
(4) In the portion of the intermediate layer that contacts the core layer, x is 0 or more and 0.1 or less, and in the portion of the intermediate layer that contacts the core layer, x is 0.15 or more, 0. It may be 25 or less. Thereby, since the Al composition decreases toward the cladding layer, the etching rate also decreases, and an inclination is formed in the intermediate layer. The intermediate layer is lattice-matched with the core layer and the cladding layer. Therefore, the crystallinity of the intermediate layer and the cladding layer is improved.
(5) The Al composition in the portion of the intermediate layer in contact with the core layer may be equal to the average Al composition in the core layer. According to this configuration, the etching rate is approximately the same between the intermediate layer and the core layer, and a step is hardly generated between the intermediate layer and the core layer.
(6) The core layer may be formed of GaInAs / AlInAs. According to this configuration, the intermediate layer and the core layer are lattice-matched.
(7) A step of growing a core layer containing Al on the substrate, a step of growing an intermediate layer containing Al on the core layer, and forming a cladding layer of InP on the intermediate layer A step of forming a mesa by etching the core layer, the intermediate layer, and the clad layer, and etching the side surfaces of the core layer, the intermediate layer, and the clad layer after forming the mesa. And a step of growing a buried layer on both sides of the mesa after the etching step, wherein the Al composition of the intermediate layer decreases from the core layer side to the cladding layer side. It is a manufacturing method. According to this configuration, the etching rate of the intermediate layer decreases from the core layer side to the cladding layer side. Accordingly, the mesa side surface is etched to form an inclination in the intermediate layer, and the step between the core layer and the cladding layer becomes gentle. For this reason, stacking faults in the buried layer are suppressed, and the buried layer grows in a desired direction. Thus, the abnormal growth of the buried layer is suppressed.

[Details of the embodiment of the present invention]
Specific examples of the semiconductor optical device and the manufacturing method thereof according to the embodiment of the present invention will be described below with reference to the drawings. In addition, this invention is not limited to these illustrations, is shown by the claim, and intends that all the changes within the meaning and range equivalent to a claim are included.

(Comparative example)
First, a comparative example will be described. 1A and 1B are cross-sectional views illustrating a method for manufacturing a semiconductor optical device according to a comparative example. The XY plane is the (100) plane of the substrate 10, and the Y direction is the [011] direction. The Z direction is the [100] direction, which is the stacking direction of the buffer layer 11 and the like.

As shown in FIG. 1 (a), a buffer layer 11, a diffraction grating layer 12, a spacer layer 13, The core layer 14, the cladding layer 15, and the contact layer 16 are epitaxially grown in this order. The substrate 10, the buffer layer 11, the spacer layer 13, and the cladding layer 15 are made of, for example, n-type indium phosphide (InP). The diffraction grating layer 12 is made of, for example, gallium indium arsenide (GaInAs). The core layer 14 has, for example, a quantum well structure. For example, a well layer made of Ga _0.47 In _0.53 As and a barrier layer made of Al _0.48 In _0.52 As are alternately stacked. It has a structure. As shown in FIG. 1A, a mesa 17 is formed by dry etching these layers. The mesa 17 extends in the [011] direction (the depth direction in FIG. 1A). A damage layer 17a having a thickness of about 0.1 μm is formed on the side surface of each layer (the side surface of the mesa 17) by dry etching.

  As shown in FIG. 1B, the damaged layer 17a is removed by wet etching after the mesa 17 is formed. The wet etching is performed from the side surface of the buffer layer 11 to the side surface of the contact layer 16. However, the etching rate differs between the core layer 14 and the cladding layer 15. Specifically, the core layer 14 containing aluminum (Al) is easily etched, and the clad layer 15 not containing Al is difficult to etch. Therefore, if the etching is performed until the damage layer 17a having a thickness of 0.1 μm of the cladding layer 15 can be removed, for example, the core layer 14 is etched by about 0.3 μm, for example. As a result, a step 17b is formed between the core layer 14 and the clad layer 15 as shown in FIG. A step is also formed between the core layer 14 and the spacer layer 13.

  As shown in FIG. 1B, an InP buried layer 18 doped with iron (Fe) is grown on both sides of the mesa 17 by OMVPE. However, a stacking fault of the buried layer 18 occurs in the step 17b, and the growth direction changes from the [100] direction to the [111] direction. Thus, the buried layer 18 grows abnormally due to the step 17b. Since the step between the core layer 14 and the spacer layer 13 does not have an inverted mesa shape, abnormal growth does not occur. Next, a first embodiment will be described.

(First embodiment)
FIG. 2A is a cross-sectional view illustrating the semiconductor optical device 100 according to the first embodiment. 2A is the [100] direction of the substrate 10, and the depth direction is the [011] direction. The semiconductor optical device is a QCL that oscillates light having a wavelength of 7.4 μm.

  As shown in FIG. 2A, the buffer layer 11, the diffraction grating layer 12, the spacer layer 13, the core layer 14, the intermediate layer 19, the cladding layer 15, and the contact layer 16 are formed on the (100) surface that is the upper surface of the substrate 10. Are sequentially stacked.

  The buffer layer 11, the diffraction grating layer 12, the spacer layer 13, the core layer 14, the intermediate layer 19, the cladding layer 15 and the contact layer 16 form a mesa 17. The mesa 17 has a depth (height from the upper surface of the substrate 10) of, for example, 8 μm and a width of 5 μm. The mesa 17 extends in the [011] direction. A buried layer 18 is provided on both sides of the mesa 17. An insulating film 20 is provided on the upper surface of the buried layer 18. An opening 20a is provided in the insulating film 20, and the upper surface of the contact layer 16 is exposed from the opening 20a. The electrode 21 is provided from the upper surface of the contact layer 16 to the upper surface of the insulating film 20. The electrode 22 is provided on the lower surface of the substrate 10.

The substrate 10 is a semiconductor substrate made of n-type InP doped with, for example, tin (Sn), and has a thickness of 100 μm. The buffer layer 11 is made of, for example, InP doped with silicon (Si) and has a thickness of 500 nm. The buffer layer 11 functions as a lower cladding layer. The diffraction grating layer 12 is made of a material having a refractive index different from that of the buffer layer 11 (for example, Ga _0.47 In _0.53 As), and has an uneven pattern in the [011] direction. The thickness of the diffraction grating layer 12 is, for example, 500 nm. The spacer layer 13 is made of, for example, InP doped with Si and fills the unevenness of the diffraction grating layer 12. The thickness of the spacer layer 13 is, for example, 500 nm. The diffraction grating layer 12 may be provided between the core layer 14 and the cladding layer 15. In addition, the diffraction grating layer 12 may not be provided in a semiconductor laser other than a DFB (Distributed Feedback) laser.

The core layer 14 is a multi-quantum well layer made of a laminate of a total of 500 layers of gallium indium arsenide and aluminum indium arsenide (GaInAs / AlInAs), and has a thickness of 1.5 μm. The core layer 14 includes 27 sets of an injection layer and a light emitting layer (not shown). The injection layer injects carriers (for example, electrons) into the light emitting layer, and the light emitting layer emits light having a wavelength of 7.4 μm. The injection layer includes, for example, five pairs of well layers and barrier layers, and three light emitting layers. The well layer is made of, for example, Ga _0.47 In _0.53 As, and the barrier layer is made of, for example, Al _0.48 In _0.52 As. Any layer has a composition with no distortion with respect to the substrate 10.

The intermediate layer 19 is in contact with the upper surface of the core layer 14. The thickness of the intermediate layer 19 is, for example, 350 to 500 nm. The intermediate layer 19 is formed of, for example, (Al _0.48 In _0.52 As) _z (Ga _0.47 In _0.53 As) _1-z (z = 0 to 0.4). From the core layer 14 side to the cladding layer 15 side, z in the above chemical formula decreases. In other words, the Al composition (0.48 × z) of the intermediate layer 19 decreases from the core layer 14 side to the cladding layer 15 side. In the portion where the intermediate layer 19 and the core layer 14 are in contact, for example, z = 0.4, and the composition is close to Al _0.19 Ga _0.28 In _0.53 As. The Al composition of the intermediate layer 19 in the portion in contact with the core layer 14 is equal to the average Al composition in the core layer 14. In the portion where the intermediate layer 19 and the cladding layer 15 are in contact, for example, z = 0, that is, the Al composition of the intermediate layer 19 is zero, and the composition is Ga _0.47 In _0.53 As. The energy gap of the intermediate layer 19 is larger than the core layer 14.

  FIG. 2B is an enlarged cross-sectional view of the vicinity of the intermediate layer 19. As shown in FIGS. 2A and 2B, the side surface 19a of the intermediate layer 19 is inclined so as to spread from the core layer 14 side to the cladding layer 15 side. That is, the width of the intermediate layer 19 increases from the bottom to the top. A line segment L1 shown in FIG. 2B is a line segment extending from the side surface of the cladding layer 15 in the Z direction (layer stacking direction). The triangle formed by the side surface 19a and the line segments L1 and L2 is a right triangle. The angle θ between the side surface 19a and the line segment L1 is the thickness T1 of the intermediate layer 19 (the length of the line segment L1) and the distance T2 in the X direction between the side surface of the core layer 14 and the side surface of the cladding layer 15 (line segment). L2 length). θ is, for example, 50 ° or less.

The clad layer 15 shown in FIG. 2A is made of, for example, Si-doped n-type InP and has a thickness of 3000 nm. The clad layer 15 is in contact with the upper surface of the intermediate layer 19. The contact layer 16 is made of Ga _0.47 In _0.53 As and has a thickness of 100 nm. The clad layer 15 and the buffer layer 11 confine light generated from the core layer 14. The buried layer 18 is made of, for example, semi-insulating InP doped with Fe. The insulating film 20 is a silicon nitride (SiN) film, for example, and has a thickness of 300 nm. The electrode 21 is formed by, for example, laminating titanium / platinum / gold (Ti / Pt / Au) from the contact layer 16 side, and contacts the upper surface of the contact layer 16. The electrode 22 is formed of, for example, a laminate (AuGe / Au) of a gold / germanium alloy (AuGe) and Au, and contacts the lower surface of the substrate 10.

(Method for manufacturing semiconductor optical device)
Next, a method for manufacturing the semiconductor optical device 100 will be described. FIG. 3A to FIG. 7B are cross-sectional views illustrating a method for manufacturing the semiconductor optical device 100.

As shown in FIG. 3A, the buffer layer 11 and the diffraction grating layer 12 are epitaxially grown on the (100) plane (upper surface) of the substrate 10 in a wafer state by the OMVPE method. For example, the growth pressure is 100 mbar, the growth temperature is 670 ° C., and the inside of the OMVPE furnace is a phosphine (PH ₃ ) atmosphere. After growth, the substrate 10 is removed from the OMVPE furnace.

  FIG. 3B is a view in which FIG. 3A is rotated by 90 ° and the YZ plane is the front. As shown in FIG. 3B, the diffraction grating layer 12 is dry-etched using a SiN mask 23 to form a diffraction grating extending in the [011] direction. The pitch of the diffraction grating is, for example, 1 μm, the duty ratio is 0.5, and the depth is 200 nm. After the dry etching, the mask 23 is removed.

As shown in FIG. 4A, the spacer layer 13 is epitaxially grown by the OMVPE method, and the unevenness of the diffraction grating is buried. On the spacer layer 13, the core layer 14, the intermediate layer 19, the clad layer 15 and the contact layer 16 are epitaxially grown. As described above, the Al composition of the intermediate layer 19 decreases from the lower side to the upper side. Such an Al composition can be realized by reducing the flow rate of the Al source gas from the start to the end of the growth process of the intermediate layer 19. The Al source gas is, for example, trimethyl aluminum (TMA), and the flow rate is, for example, 1.0 to 1.5 sccm. After the contact layer 16 is grown, the inside of the OMVPE furnace is brought to a PH ₃ atmosphere and room temperature, and the substrate 10 is taken out.

  As shown in FIG. 4B, a buffer layer 11, a diffraction grating layer 12, a spacer layer 13, a core layer 14, an intermediate layer 19, and a cladding layer 15 are used by using a reactive ion etching (RIE) apparatus. Then, the mesa 17 is formed by dry etching the contact layer 16. The mesa 17 has a depth (height from the upper surface of the substrate 10) of, for example, 8 μm and a width of 5 μm. At this time, a damage layer 17 a having a thickness of about 0.1 μm remains on the side surface of the mesa 17.

  As shown in FIG. 5A, the damaged layer 17a is removed by wet etching using an acid-based etchant. For example, the etchant is a mixed solution of sulfuric acid and hydrogen peroxide, and the etching time is about 1 minute. The etching amount of the cladding layer 15 having a low etching rate is, for example, about 0.1 μm, and the etching amount of the core layer 14 having a high etching rate is, for example, about 0.3 μm. Since the Al composition of the intermediate layer 19 is small from the core layer 14 side to the cladding layer 15 side, the etching rate is also reduced. Thereby, the side surface 19a of the intermediate layer 19 becomes a slope that spreads toward the cladding layer 15 side. A step is formed between the core layer 14 and the spacer layer 13.

As shown in FIG. 5B, a buried layer 18 is grown on both sides of the mesa 17. The buried layer 18 contacts the side surface of the mesa 17 and reaches the upper surface of the contact layer 16. An example of growth conditions is shown below. 1 sccm = 1.667 × 10 ⁻⁸ m ³ / s.
Growth temperature: 600 ° C
Growth pressure: 100mbar
Source gas: PH ₃ , ferrocene (Cp ₂ Fe), In source gas (for example, trimethylindium, TMI: Trymethyl Indium)
PH ₃ supply amount: 1 × 10 ⁻² mol / min
Cp ₂ Fe supply amount: 10 sccm
In supply amount (amount of In element in source gas): 3 × 10 ⁻⁴ mol / min
Hydrochloric acid (HCl) gas concentration in the atmosphere in the OMVPE furnace: 11 ppm

  As shown in FIG. 6A, the insulating film 20 is formed by, for example, a plasma chemical vapor deposition (CVD) method. As shown in FIG. 6B, an opening 20 a is formed in the insulating film 20. The electrode 21 in contact with the contact layer 16 exposed from the opening 20a is formed by vapor deposition and lift-off. As shown in FIG. 7A, the substrate 10 is polished and thinned to about 100 μm, for example. As shown in FIG. 7B, an electrode 22 is formed on the lower surface of the substrate 10. Further, the semiconductor optical device 100 is formed by dividing the wafer.

  According to the first embodiment, the Al composition of the intermediate layer 19 decreases from the core layer 14 side to the cladding layer 15 side. For this reason, the etching rate of the intermediate layer 19 also decreases from the core layer 14 side to the cladding layer 15 side. Therefore, as shown in FIG. 5A, an inclination is formed in the intermediate layer 19 by etching the damaged layer 17a. Thereby, the level | step difference between the core layer 14 and the clad layer 15 becomes loose. For this reason, the stacking fault of the buried layer 18 is suppressed, and it grows in the [100] direction which is a desired direction. Thus, according to the first embodiment, abnormal growth of the buried layer 18 can be suppressed. Since the step between the core layer 14 and the spacer layer 13 does not have an inverted mesa shape, the buried layer 18 does not grow abnormally.

  In order to increase the crystallinity of the buried layer 18, the inclination of the intermediate layer 19 is preferably gentle. When the angle θ shown in FIG. 2B is larger than 54.7 °, the (111) plane becomes dominant on the side surface 19 a of the intermediate layer 19. For this reason, a stacking fault occurs in the buried layer 18 and abnormal growth occurs in the [111] direction. When θ is 54.7 ° or less, the (111) plane and other planes appear alternately on the side surface 19a. For this reason, stacking faults are unlikely to occur in the buried layer 18 and abnormal growth is suppressed. Therefore, the angle θ is 54.7 ° or less, more preferably 50 ° or less.

  The angle θ is determined by the thickness T1 (length of the line segment L1) of the intermediate layer 19 and the distance T2 (length of the line segment L2) in the X direction between the side surface of the core layer 14 and the side surface of the cladding layer 15. The distance T2 is determined by the difference in etching amount between the core layer 14 and the cladding layer 15 in the etching for removing the damaged layer 17a. The thickness T1 and the etching amount of the intermediate layer 19 may be set so that the angle θ is 50 ° or less.

  FIG. 8 is a diagram showing the relationship between the angle θ, the thickness T1 of the intermediate layer 19, and the distance T2 between the side surfaces of the core layer 14 and the cladding layer 15. The horizontal axis represents the angle θ, and the vertical axis represents the thickness T1. A dotted line indicates an example where T2 = 0.1 μm, a solid line indicates T2 = 0.2 μm, and a broken line indicates an example where T2 = 0.3 μm. In any example, the angle θ decreases as the thickness T1 increases. As the angle θ is smaller, the ratio of the (111) plane appearing on the side surface of the mesa after wet etching is reduced, so that stacking faults in the buried layer 18 can be suppressed. In the case of the distance T2 = 0.1 μm, when the thickness T1 is greater than 0.2 μm, the angle θ is 50 ° or less. In the case of the distance T2 = 0.2 μm, when the thickness T1 is larger than 0.35 μm, the angle θ is 50 ° or less. In the case of the distance T2 = 0.3 μm, when the thickness T1 is larger than 0.55 μm, the angle θ is 50 ° or less. For example, θ may be 45 ° or less, 40 ° or less, 35 ° or less, or 30 ° or less. When the angle θ is large, the thick intermediate layer 19 is required, and the height of the mesa 17 is also increased. In order to shorten the time required for crystal growth of the intermediate layer 19 and the time required for growth of the buried layer 18 grown on both sides of the mesa 17, it is preferable that the thickness T1 of the intermediate layer 19 is not too large.

The intermediate layer 19 is made of, for example, (Al _0.48 In _0.52 As) _z (Ga _0.47 In _0.53 As) _1-z . Z decreases from the core layer 14 side to the cladding layer 15 side. For example, z = 0.3 to 0.4 or the like in a portion where the intermediate layer 19 and the core layer 14 are in contact, and z = 0 to 0.2 or the like in a portion where the intermediate layer 19 and the cladding layer 15 are in contact. is there. Thereby, the intermediate layer 19 is lattice-matched with the core layer 14 and the cladding layer 15, and the crystallinity of the intermediate layer 19 and the cladding layer 15 is improved. As a result, the Al composition at the end of each layer is substantially equal to the adjacent layer. Therefore, in the wet etching for removing the damaged layer 17a, the difference in etching rate between the lower end of the intermediate layer 19 and the core layer 14 is small, and the difference in etching rate between the upper end of the intermediate layer 19 and the cladding layer 15 is also small. small. Thereby, the step between the clad layer 15 and the intermediate layer 19 and the step between the intermediate layer 19 and the core layer 14 hardly occur on the side surface of the mesa 17 after wet etching. Further, since the Al composition decreases toward the clad layer 15 side, the etching rate also decreases, and an inclination is formed in the intermediate layer 19.

The composition of the intermediate layer 19 can also be expressed as, for example, Al _x Ga _y In _(1-xy) As. The composition ratios x and y satisfy y = 0.47− (0.47 / 0.48) x. X and y decrease from the core layer 14 side to the cladding layer 15 side. For example, x = 0.15 to 0.25 (0.15 or more and 0.25 or less) where the intermediate layer 19 and the core layer 14 are in contact, and the intermediate layer 19 and the cladding layer 15 are in contact with each other. Then, x = 0 to 0.1 (0 or more and 0.1 or less). As the Al composition (x) decreases from the core layer 14 side to the cladding layer 15 side, the etching rate of the intermediate layer 19 decreases and a slope is formed. The intermediate layer 19 is lattice-matched with the core layer 14 and the cladding layer 15.

The Al composition in the portion of the intermediate layer 19 in contact with the core layer 14 may be equal to the average Al composition in the core layer 14 (for example, 0.192). As a result, the intermediate layer 19 and the core layer 14 have the same etching rate, and a step is not easily formed between the intermediate layer 19 and the core layer 14 on the side surface of the mesa 17 after the wet etching. Calculating the average Al composition in the core layer 14, for _example, Al _{0.48 an In 0.52} As the Al composition × _Al 0.48 _{In 0.52} As total thickness / core layer 14 thickness of from Is done.

  The Al composition in the portion of the intermediate layer 19 that contacts the cladding layer 15 is, for example, zero (x = 0). On the side surface of the mesa 17 after the wet etching, a step is hardly generated between the cladding layer 15 and the intermediate layer 19.

  The core layer 14 is formed of GaInAs / AlInAs. As a result, the intermediate layer 19 and the cladding layer 15 have the same etching rate, and a step is not easily formed between the intermediate layer 19 and the cladding layer 15 on the side surface of the mesa 17 after the wet etching. The numbers of the injection layer, the light emitting layer, the well layer, and the barrier layer of the core layer 14 may be changed.

DESCRIPTION OF SYMBOLS 10 Substrate 11 Buffer layer 12 Diffraction grating layer 13 Spacer layer 14 Core layer 15 Cladding layer 16 Contact layer 17 Mesa layer 17a Damaged layer 18 Buried layer 19 Intermediate layer 19a Side surface 20 Insulating film 20a Openings 21, 22 Electrode 23 Mask 100 Semiconductor light element

Claims (7)

A core layer provided on the substrate and containing Al;
An intermediate layer provided on the core layer and containing Al;
A cladding layer provided on the intermediate layer, formed of InP, and forming a mesa with the core layer and the intermediate layer;
Embedded layers provided on both sides of the mesa,
The width of the cladding layer is larger than the width of the intermediate layer,
The side surface of the intermediate layer is inclined so as to spread from the core layer to the cladding layer,
A semiconductor optical device in which the Al composition of the intermediate layer decreases from the core layer side to the cladding layer side.   2. The semiconductor optical device according to claim 1, wherein an angle formed by a stacking direction of the core layer, the intermediate layer, and the cladding layer and a side surface of the intermediate layer is 50 ° or less. 3. The semiconductor optical device according to claim 1, wherein the intermediate layer is formed of Al _x Ga _y In _(1-xy) As and satisfies y = 0.47− (0.47 / 0.48) x. . In the portion of the intermediate layer that contacts the core layer, x is 0 or more and 0.1 or less,
4. The semiconductor optical device according to claim 3, wherein x is 0.15 or more and 0.25 or less in a portion of the intermediate layer that contacts the core layer.   5. The semiconductor optical device according to claim 1, wherein an Al composition in a portion of the intermediate layer in contact with the core layer is equal to an average Al composition in the core layer.   The semiconductor optical device according to claim 1, wherein the core layer is formed of GaInAs / AlInAs. Growing a core layer containing Al on the substrate;
Growing an intermediate layer containing Al on the core layer;
Forming an InP cladding layer on the intermediate layer;
Forming a mesa by etching the core layer, the intermediate layer and the cladding layer;
Etching the side surfaces of the core layer, the intermediate layer, and the cladding layer after forming the mesa;
And after the etching step, growing a buried layer on both sides of the mesa,
The method for manufacturing a semiconductor optical device, wherein the Al composition of the intermediate layer decreases from the core layer side to the cladding layer side.

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