JP2022119325A - Optical semiconductor device and method of manufacturing optical semiconductor device - Google Patents

Abstract

To provide an optical semiconductor device that has improved novel constitution such that, for example, a power consumption for heat generation of a heater layer can be suppressed, and a method of manufacturing the optical semiconductor device.SOLUTION: An optical semiconductor device has, for example; a base which has a base surface crossing a first direction as a crystal azimuth [100]; a mesa which protrudes from the base surface in the first direction to extend along the base surface, and has an end face in the first direction; a waveguide layer which is provided, at a position of the mesa separate from the end face in the opposite direction from the first direction, to extend along the base surface; and a heater layer which is provided at a position of the mesa separate from the waveguide layer in the first direction to generate heat when supplied with electric power, where a cavity part including a groove which is recessed in the first direction and extends in a second direction crossing the first direction is provided at a position of the mesa apart from the waveguide layer in the opposite direction from the first direction, and the second direction crosses a crystal azimuth [011] of the base obliquely at a difference of 45° or less.SELECTED DRAWING: Figure 21

Description

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

2. Description of the Related Art Conventionally, an optical semiconductor device having a heater layer on a mesa is known (Patent Document 1).

JP 2016-054168 A

In this type of optical semiconductor device, it would be beneficial if power consumption due to heat generation of the heater layer could be suppressed.

Accordingly, one of the objects of the present invention is to provide an optical semiconductor device and a method for manufacturing the optical semiconductor device, which have an improved and novel configuration that can suppress power consumption due to heat generation of the heater layer, for example. That is.

An optical semiconductor device of the present invention includes, for example, a base having a base surface that intersects a first direction, which is the crystal orientation [100] direction, and a base surface that protrudes in the first direction from the base surface and extends along the base surface. a mesa having an end face in the first direction; a waveguide layer provided so as to extend along the base face at a position of the mesa separated from the end face in a direction opposite to the first direction; a heater layer that is provided in the mesa at a position away from the waveguide layer in the first direction and that generates heat by being supplied with electric power, the mesa in the opposite direction from the waveguide layer in the first direction; A cavity portion is provided at a position spaced apart in the direction of and obliquely intersect with an angle difference of 45° or less.

In the optical semiconductor device, the absolute value of the angle difference may be in a direction of 10° or more and 45° or less.

In the optical semiconductor device, the groove may be recessed in the first direction in a V shape and extend in the second direction.

In the optical semiconductor device, the hollow portion has a bottom surface located at an end portion of the hollow portion opposite to the first direction and extending in the second direction while intersecting the first direction. You may

In the optical semiconductor device, the mesa may have a first portion whose extending direction along the base surface of the mesa is substantially along the second direction.

In the optical semiconductor device, the mesa may have a second portion where a direction of extension of the mesa along the base surface intersects the second direction.

In the optical semiconductor device, the mesa may be provided with, as the cavity, a plurality of cavities arranged in a third direction crossing the first direction and the second direction.

In the optical semiconductor device, the mesa has two side surfaces as an end surface in the third direction and an end surface in the direction opposite to the third direction, and the hollow portion is formed on each of the two side surfaces. A hollow part opened in the third direction may be included.

In the optical semiconductor device, the cavity may include a cavity closed within the mesa.

In the optical semiconductor device, the hollow portion includes a bottom surface located at an end portion of the hollow portion opposite to the first direction and extending in the second direction intersecting the first direction; and a cavity provided with a cover layer covering the bottom surface.

The optical semiconductor device has a lower thermal conductivity than an adjacent portion at a position of the mesa opposite to the heater layer with respect to the waveguide layer and aligned with the cavity in the first direction. It may have a thermal resistance layer.

The optical semiconductor device is located on the side of the mesa opposite to the heater layer with respect to the waveguide layer, and is aligned with the hollow portion in a third direction crossing the first direction and the second direction. Additionally, it may have a thermal resistance layer having a lower thermal conductivity than the adjacent portion.

In the optical semiconductor device, the thermal resistance layer may be positioned on both sides of the cavity in the third direction.

In the optical semiconductor device, the mesa may have a diffraction grating layer extending along the waveguide layer.

In the optical semiconductor device, the mesa has a diffraction grating layer extending along the waveguide layer, and the hollow portion has both ends of the diffraction grating layer in the extending direction of the hollow portion. It may be provided so as to overlap both ends in the extending direction in the first direction, or may be provided so as to protrude from the diffraction grating layer on both sides in the extending direction.

The optical semiconductor device of the present invention includes, for example, a base having a base surface that intersects with a first direction, a base surface that protrudes in the first direction from the base surface, extends along the base surface, and has an end surface in the first direction. a waveguide layer provided so as to extend along the extending direction along the base surface of the mesa at a position away from the end surface of the mesa in the direction opposite to the first direction; a heater layer that is provided in the mesa at a position away from the waveguide layer in the first direction and that generates heat when supplied with electric power, the mesa in the direction opposite the first direction from the waveguide layer At a position spaced apart from each other, a cavity is provided that includes a groove that is recessed in the first direction in a V-shape and extends in a second direction that intersects the first direction.

The optical semiconductor device of the present invention includes, for example, a base having a base surface that intersects with a first direction, a base surface that protrudes in the first direction from the base surface, extends along the base surface, and has an end surface in the first direction. a waveguide layer provided so as to extend along the extending direction along the base surface of the mesa at a position away from the end surface of the mesa in the direction opposite to the first direction; a heater layer that is provided in the mesa at a position away from the waveguide layer in the first direction and that generates heat when supplied with electric power, the mesa in the direction opposite the first direction from the waveguide layer Cavities are provided which are closed within the mesas at locations spaced apart from each other.

In the optical semiconductor device, the hollow portion may extend along a direction in which the mesa extends along the base surface.

In the optical semiconductor device, the hollow portion may be recessed in the first direction in a V shape and extend along the extension direction.

In the optical semiconductor device, the base and mesa may be made of a III-V group semiconductor having a zincblende structure.

The method for manufacturing an optical semiconductor device of the present invention includes, for example, providing a coating layer extending in a second direction that intersects the first direction on a base surface that intersects the first direction of the base; forming a laminate by epitaxial growth in which crystal grains grow in the first direction; partially removing the laminate to form a mesa; and forming a heater layer that generates heat by supplying a heater layer, wherein in the step of forming the laminate, the laminate is recessed in the first direction on the coating layer in the second direction. is formed with a cavity including a groove extending into the cavity.

According to the present invention, for example, it is possible to obtain an optical semiconductor device and a method of manufacturing the optical semiconductor device having an improved and novel configuration that can suppress power consumption due to heat generation of the heater layer.

FIG. 1 is an exemplary and schematic perspective view of the optical semiconductor device of the first embodiment. FIG. 2 is a cross-sectional view taken along the line II--II in FIG. FIG. 3 is a sectional view taken along line III--III in FIG. FIG. 4 is an exemplary schematic plan view of a wafer serving as a base of the optical semiconductor device of the first embodiment and a coating layer formed on the wafer. FIG. 5 is an exemplary and schematic cross-sectional view showing the base of the optical semiconductor device of the first embodiment and the cladding layer grown on the base, showing the crystal orientation [011] direction and the extending direction of the coating layer. is 0°. FIG. 6 is an exemplary and schematic cross-sectional view showing the base of the optical semiconductor device of the first embodiment and the clad layer grown on the base, showing the crystal orientation [011] direction and the extending direction of the coating layer. is greater than 0° and less than 10°. FIG. 7 is an exemplary and schematic cross-sectional view showing the base of the optical semiconductor device of the first embodiment and the cladding layer grown on the base, showing the crystal orientation [011] direction and the extending direction of the coating layer. is 10° or more and 45° or less. FIG. 8 shows the crystal orientation [011] direction and the extending direction of the coating layer, showing the ratio of the height of the protrusion appearing in the clad layer grown on the base of the optical semiconductor device of the first embodiment to the thickness of the clad layer. 4 is a graph showing changes according to the angle difference from . FIG. 9 is an exemplary and schematic cross-sectional view showing the base of the optical semiconductor device of the first embodiment and the cladding layer grown on the base, showing the crystal orientation [011] direction and the extending direction of the coating layer. 10 is a diagram showing a state in which a finite-length cavity is formed on the coating layer when the angle difference between is 10° or more and 45° or less. FIG. FIG. 10 is an exemplary and schematic cross-sectional view showing one step of the method for manufacturing the optical semiconductor device of the first embodiment. 11A and 11B are exemplary and schematic cross-sectional views showing steps subsequent to FIG. 10 in the method of manufacturing the optical semiconductor device of the first embodiment. 12A and 12B are exemplary and schematic cross-sectional views showing steps subsequent to FIG. 11 in the method for manufacturing the optical semiconductor device of the first embodiment. 13 is an exemplary and schematic cross-sectional view of the optical semiconductor device of the second embodiment at the same position as in FIG. 3. FIG. 14 is an exemplary and schematic cross-sectional view of the optical semiconductor device of the third embodiment at the same position as in FIG. 2. FIG. FIG. 15 is an exemplary and schematic cross-sectional view of the optical semiconductor device of the fourth embodiment at the same position as in FIG. FIG. 16 is an exemplary and schematic cross-sectional view of the optical semiconductor device of the fifth embodiment at the same position as in FIG. FIG. 17 is an exemplary and schematic cross-sectional view of the optical semiconductor device of the sixth embodiment at the same position as in FIG. FIG. 18 is an exemplary and schematic cross-sectional view of the optical semiconductor device of the sixth embodiment at the same position as in FIG. It is a figure which shows. FIG. 19 is an exemplary and schematic cross-sectional view of the optical semiconductor device of the seventh embodiment at the same position as in FIG. FIG. 20 is an exemplary and schematic cross-sectional view of the optical semiconductor device of the eighth embodiment. FIG. 21 is an exemplary and schematic plan view of the optical semiconductor device of the ninth embodiment. FIG. 22 is an exemplary and schematic plan view of the optical semiconductor device of the tenth embodiment. FIG. 23 is an exemplary schematic plan view of the optical semiconductor device of the eleventh embodiment.

Illustrative embodiments of the invention are disclosed below. The configurations of the embodiments shown below and the actions and results (effects) brought about by the configurations are examples. The present invention can be realized by configurations other than those disclosed in the following embodiments. Moreover, according to the present invention, at least one of various effects (including derivative effects) obtained by the configuration can be obtained.

A number of embodiments shown below have similar configurations. Therefore, according to the configuration of each embodiment, similar actions and effects based on the similar configuration can be obtained. Moreover, below, while the same code|symbol is provided to those same structures, the overlapping description may be abbreviate|omitted.

In this specification, ordinal numbers are given for convenience in order to distinguish parts, directions, etc., and do not indicate priority or order.

In each figure, the X direction is indicated by an arrow X, the Y direction is indicated by an arrow Y, and the Z direction is indicated by an arrow Z. The X-, Y-, and Z-directions intersect each other and are orthogonal to each other.

[First embodiment]
FIG. 1 is a perspective view of an optical semiconductor device 10A (10) of the first embodiment. As shown in FIG. 1, the optical semiconductor device 10A includes a base 11 and a mesa 12. As shown in FIG. In the present embodiment, as an example, the mesa 12 extending linearly in the X direction in plan view seen in the direction opposite to the Z direction will be described, but the mesa 12 may be bent or curved in plan view. You may have Also, the mesa 12 may extend in a direction crossing the X direction.

The base 11 is a semiconductor substrate, intersects and is perpendicular to the Z direction, and extends in the X and Y directions. The base 11 has a base surface 11a. The base surface 11a intersects and is orthogonal to the Z direction and extends in the X and Y directions. The base 11 is made of a III-V semiconductor with a zincblende structure, for example n-type indium phosphide (InP). Base 11 may also be referred to as a substrate.

The mesa 12 protrudes in the Z direction from the base surface 11a. The mesa 12 extends in the X direction with a substantially constant height in the Z direction and a substantially constant width in the Y direction. That is, the mesa 12 has a wall-like shape that protrudes above the base surface 11a and extends along the base surface 11a. In this embodiment, the X direction is an example of the extending direction of the mesa 12, the Y direction is also called the width direction of the mesa 12, and the Z direction is also called the height direction or the projecting direction of the mesa 12. sell. The Z direction is an example of a first direction.

The mesa 12 has two side surfaces 12a and a top surface 12b.

The two side surfaces 12a are the end surfaces of the mesa 12 in the Y direction and the opposite direction in the Y direction, in other words, the end surfaces on both sides of the mesa 12 in the width direction. The side surface 12a intersects and is orthogonal to the Y direction and extends in the X and Z directions. The side surface 12a extends in the X direction at a substantially constant height in the Z direction. Also, the two side surfaces 12a are substantially parallel.

The top surface 12b is positioned at the end of the mesa 12 in the Z direction. The top surface 12b intersects and is orthogonal to the Z direction and extends in the X and Y directions. The top surface 12b extends in the X direction with a substantially constant width in the Y direction. Also, the top surface 12b is substantially parallel to the base surface 11a. The top surface 12b is an example of an end surface.

The mesa 12 has a waveguide layer 14 and clad layers 13 and 15 . In the mesa 12, a clad layer 13, a waveguide layer 14, and a clad layer 15 are laminated in this order in the Z direction. It should be noted that the mesa 12 may have a different configuration than in FIG. 1, for example having more layers.

The waveguide layer 14 is provided at a position away from the top surface 12b in the opposite direction in the Z direction, is positioned in the middle of the mesa 12 in the Z direction, and extends along the base surface 11a. The waveguide layer 14 intersects and is perpendicular to the Z direction, has a substantially constant thickness in the Z direction, and extends in a strip shape in the X direction. The waveguide layer 14 also spans between the two sides 12 a of the mesa 12 .

The clad layer 13 is adjacent to the waveguide layer 14 on the opposite side in the Z direction, and the clad layer 15 is adjacent to the waveguide layer 14 in the Z direction. That is, the waveguide layer 14 is located between the clad layer 13 and the clad layer 15 in the Z direction.

The waveguide layer 14 functions as a core that transmits light, and the clad layers 13 and 15 function as clads for the waveguide layer 14 . Materials for the waveguide layer 14 and the clad layers 13 and 15 are set so that the refractive index of the clad layers 13 and 15 is lower than the refractive index of the waveguide layer 14 . As an example, waveguide layer 14 is made of InGaAsP and cladding layers 13 and 15 are made of a III-V semiconductor with a zincblende structure, such as indium phosphide (InP).

The two side surfaces 12a and top surface 12b of the mesa 12 and the base surface 11a are covered with a dielectric layer (not shown).

A heater layer 16 is provided on top surface 12b via a dielectric layer. The heater layer 16 extends in a strip shape in the X direction with a substantially constant thickness in the Z direction at a position away from the waveguide layer 14 in the Z direction. The heater layer 16 is made of an electric resistor that generates heat by being supplied with power from electrodes and conductor wiring (not shown). The heater layer 16 is made of, for example, an alloy containing nickel (Ni) and chromium (Cr) as main components.

As shown in FIG. 1 , in the mesa 12 , a cavity is provided on the opposite side of the waveguide layer 14 from the heater layer 16 , in other words, on the opposite side of the waveguide layer 14 in the Z direction. 12c is provided. The hollow portion 12 c is provided at the root portion of the mesa 12 . The position of the hollow portion 12c in the Z direction is not limited to the root portion of the mesa 12 as long as it is between the base surface 11a and the waveguide layer .

The hollow portion 12c extends in the X direction. The cross section of the hollow portion 12c intersecting the X direction has a triangular shape, more specifically, an isosceles triangular shape whose perpendicular extends along the Z direction.

2 is a sectional view taken along line II-II in FIG. 1, and FIG. 3 is a sectional view taken along line III-III in FIG. The hollow portion 12c is surrounded by a bottom surface 12c1 and two side surfaces 12c21. The bottom surface 12c1 is located at the opposite end of the cavity 12c in the Z direction, intersects the Z direction, and extends in the X direction with a substantially constant width in the Y direction. The bottom surface 12c1 is, for example, part of the base surface 11a. The two side surfaces 12c21 are inclined with respect to the Z direction so as to approach each other in the Y direction from both ends of the bottom surface 12c1 in the Y direction. The hollow portion 12c having the cross-sectional shape shown in FIG. 2 extends in the X direction as shown in FIGS. That is, the hollow portion 12c includes a V-shaped groove 12c2 recessed in the Z direction and extending in the X direction. The groove 12c2 can also be called a V-shaped groove. A concave line 12c22 provided at the end of the groove 12c2 in the Z direction extends in the X direction. The X direction is an example of the second direction. The side surface 12c21 can also be called an inclined surface. As shown in FIGS. 1 and 3, in the present embodiment, both ends of the hollow portion 12c (12c-1) in the extending direction, that is, in the X direction are open.

In this embodiment, the mesa 12 and the cavity 12c extend in the same X direction. The mesa 12 is an example of a first portion, and the extending direction along the base surface 11a is along the X direction.

A covering layer 17 is provided on the bottom surface 12c1 of the hollow portion 12c. The coating layer 17 has a substantially constant thickness in the Z direction and extends in a strip shape in the X direction. The action of the coating layer 17 will be described later. In this embodiment, the coating layer 17 exists in the cavity 12c, but the coating layer 17 may disappear during the manufacturing process of the mesa 12. FIG.

The heater layer 16 described above is provided to heat the waveguide layer 14 . The heat generated in the heater layer 16 by the supply of electric power is transmitted in the direction opposite to the Z direction in the cladding layer 15 and reaches the waveguide layer 14 . This heat is further transmitted from the waveguide layer 14 to the cladding layer 13 in the direction opposite to the Z direction and escapes to the base 11 . If such a large amount of heat escapes from the waveguide layer 14 to the base 11 through the clad layer 13, the heating efficiency of the heater layer 16 is lowered, which contributes to an increase in power consumption.

In this regard, in the present embodiment, as described above, the hollow portion 12c is provided in the mesa 12. Therefore, as shown in FIG. The width of the mesa 12 in the Y direction is narrowed on both sides in the Y direction. That is, the mesa 12 has a constricted portion having a narrower cross-sectional area crossing the Z direction than other portions at the position where the hollow portion 12c is provided. Therefore, according to the present embodiment, heat is less likely to escape from the waveguide layer 14 to the base 11 via the cladding layer 13, that is, the mesa 12, thereby suppressing a decrease in the heating efficiency of the heater layer 16 and increasing the power consumption. Power can be suppressed.

[Formation of cavity]
FIG. 4 is a plan view showing the wafer WF serving as the base 11 and the coating layer 17 provided on the wafer WF. In this embodiment, a portion such as the cladding layer 13 that will become the mesa 12 is formed by epitaxial growth on the surface of the wafer WF that will become the base surface 11a. In this case, the growth direction (stacking direction) of the portion that becomes the mesa 12 is the [100] direction of the crystal orientation of the wafer WF. The [100] direction is the Z direction. The Z direction may also be referred to as the growth direction or stacking direction. The orientation flat OF of the wafer WF is along the [01-1] direction of the crystal orientation of the wafer WF.

In the present embodiment, the coating layer 17 is made of a material that does not allow the cladding layer 13 to grow on the coating layer 17 during epitaxial growth, specifically, for example, silicon dioxide (SiO ₂ ), silicon nitride (SiN _x ), or the like. It is made of a dielectric or a conductor such as tungsten (W). Therefore, in epitaxial growth, the cladding layer 13 grows on exposed regions not covered with the covering layer 17 when viewed in the direction opposite to the Z direction.

Through extensive research, the inventors have found that when the cladding layer 13 is grown by epitaxial growth on the exposed region outside the covering layer 17, the covering layer 17 is aligned with the crystal orientation [011] as shown in FIG. , the growth layer, that is, the cladding layer 13, has a cavity 12c adjacent to the coating layer 17 in the Z direction. found to be formed. It is assumed that the cavity 12c has a finite height in the Z direction and is closed in the Z direction.

5 to 7 are cross-sectional views of the base 11 and the clad layer 13, showing the difference in the growth state of the clad layer 13 due to the difference in the magnitude of the angle difference θ between the crystal orientation [011] direction and the X direction. . 5 shows the results when the angle difference θ in FIG. 4 is 0°, FIG. 6 shows the results when the angle difference θ is greater than 0° and less than 10°, and FIG. The following cases are shown.

As shown in FIG. 5, when the angle difference .theta. Two inclined planes 13a are formed. Therefore, when the angle difference is 0°, it is difficult to form the hollow portion 12c having a finite length in the Z direction above the coating layer 17 in the clad layer 13 .

As shown in FIG. 6, when the angle difference θ is greater than 0° and less than 10°, in the epitaxial growth, the cladding layer 13 has a After two sloped surfaces are formed in the direction of approaching to each other in the Y direction, an sloped surface in the direction of separating from each other in the Y direction is formed halfway along the Z direction. In other words, the two cladding layers 13 adjacent to the coating layer 17 on both sides in the Y direction have protrusions 13b protruding toward each other in the Y direction at intermediate positions in the Z direction. In this case, by appropriately setting the width Wm of the coating layer 17 with respect to the thickness (height) H of the cladding layer 13 in the Z direction, the peaks 13p of the two protrusions 13b are configured to contact or connect with each other. Then, the hollow portion 12c having a finite height in the Z direction can be formed on the covering layer 17. FIG.

Here, the acute angle between the Y-direction end of the coating layer 17 and the base surface 11a of the inclined surface between the peak 13p of the projecting portion 13b (hereinafter referred to as the inward inclination angle) is α, and the projecting portion 13b is Wp is the projection height (width) in the Y direction from the Y-direction end of the coating layer 17, Wm is the Y-direction width of the coating layer 17, and the Z-direction height from the base surface 11a to the peak 13p (hereinafter , peak height) is Hp, the thickness of the cladding layer 13 in the Z direction is H, and the thickness of the coating layer 17 is ignored. or will be connected. Here, since Hp=Wp·tanα, in this case,
Wm≦2·Hp/tanα (1)
The width Wm of the coating layer 17 may be set so as to satisfy The inventors' research has revealed that the inward inclination angle α is 36° or more and 45° or less, and varies depending on the conditions.

Furthermore, the inventors' research has revealed that the ratio Hp/H of the peak height Hp to the thickness H of the cladding layer 13 changes according to the angle difference θ. FIG. 8 is a graph obtained by experimentally obtaining the correlation between the ratio Hp/H and the angle difference θ. As shown in FIG. 8, in the range where the angle difference θ is greater than 0°, 1° or more, and 10° or less, the ratio Hp/H gradually increases as the angle difference θ increases. has been found to approach Therefore, from the approximate function and map obtained from the correlation shown in FIG. 8, the peak height Hp corresponding to the angle difference θ and the thickness H of the clad layer 13 is obtained, By determining the width Wm of the layer 17, the two peaks 13p are in contact with or connected to each other, thereby forming a cavity 12c of finite height in the Z-direction above the covering layer 17. .

Further, the inventors' research has revealed that the ratio Hp/H is approximately 1 when the angle difference θ is 10° or more and 45° or less. In this case, in the epitaxial growth, the cladding layer 13 had two inclined planes from both ends of the coating layer 17 in the Y direction toward each other in the Y direction toward the Z direction, as shown in FIG. A protruding portion 13b is formed, and a peak 13p of the protruding portion 13b appears at the end of the cladding layer 13 in the Z direction. Also in this case, the width Wm of the coating layer 17 can be determined so as to satisfy the above-mentioned formula (1). In other words, the Z-direction thickness H of the cladding layer 13 is set sufficiently corresponding to the Y-direction width of the coating layer 17 so that the opening OP between the projecting portions 13b does not occur at the Z-direction end of the cladding layer 13. Alternatively, the Y-direction width of the covering layer 17 may be appropriately set within a range that is not too wide in accordance with the Z-direction thickness H of the cladding layer 13 .

FIG. 9 shows that the protruding portions 13b of the cladding layer 13 grown from both sides of the coating layer 17 in the Y direction are connected to each other at positions separated from the coating layer 17 in the Z direction, and a finite amount of space is formed on the coating layer 17 in the Z direction. It shows a state in which a hollow portion 12c having a long height is formed. A groove 12c2 recessed in the Z direction and extending in the X direction is formed in the hollow portion 12c. The groove 12c2 is a V-shaped groove forming a concave line 12c22 extending in the X direction.

When the angle difference θ is 10° or more and 45° or less, the flat upper surface 13c of the cladding layer 13 is formed at a position away from the cavity 12c in the Z direction, as shown in FIG. In this case, there is no need to process the upper surface 13c into a flat shape after epitaxial growth, so for example, the mesa 12 provided with the cavity 12c can be manufactured with less labor and at a lower cost. is obtained.

In addition, in the configuration of this embodiment, the coating layer 17 on the bottom surface 12c1 of the cavity 12c, the groove 12c2 recessed in the crystal orientation [100] direction (Z direction) of the cavity 12c, and the Z direction of the groove 12c2 The concave line 12c22 as the end of the extends in the X direction (second direction) that obliquely intersects the crystal orientation [011] direction at 45° or less, because the epitaxial growth described above creates a cavity in the mesa 12. This serves as evidence that the portion 12c has been formed. As shown in FIG. 2, a cross section of the hollow portion 12c intersecting the X direction includes a bottom surface 12c1 that intersects the Z direction and extends in the X direction, and a bottom surface 12c1 that extends in the X direction and extends in the Y direction toward the Z direction. The fact that the two side surfaces 12c21 are slanted toward each other is evidence that the cavity 12c has been formed in the mesa 12 by the epitaxial growth described above. Each crystal orientation can be determined from analysis of the material of the optical semiconductor device 10A (10).

[Mesa Formation]
10-12 are cross-sectional views showing the process of forming the mesa 12. FIG. First, as shown in FIG. 10, the cladding layer 13, the waveguide layer 14, and the cladding layer 13, the waveguide layer 14, and the A laminate L of clad layers 15 is formed. At this time, the cavity 12c is formed on the coating layer 17 as described above. That is, in the step of forming the laminated body L by epitaxial growth, the hollow portion 12c including the groove 12c2 is formed on the covering layer 17 inside the laminated body L. As shown in FIG. Also, a covering layer 18 (mask) made of a dielectric or the like is formed on the top surface 12b located at the end of the cladding layer 15 in the Z direction.

Next, as shown in FIG. 11, for example, dry etching is performed to remove a portion of the laminate L that is not covered with the coating layer 18 and is exposed when viewed from the Z direction, and the coating layer of the laminate L is removed. The cladding layer 13, the waveguide layer 14, and the cladding layer 15 included in the mesa 12 are formed as parts aligned with 18 in the Z direction. The side surfaces 12a of the mesa 12 are aligned in the Z direction with both edges of the covering layer 18 in the Y direction.

Next, as shown in FIG. 12, after removing the coating layer 18 by, for example, wet etching, a dielectric layer 12f is formed to cover the side surface 12a, the top surface 12b, and the base surface 11a of the mesa 12. A heater layer 16 is formed on 12b via a dielectric layer 12f.

Through these steps, an optical semiconductor device 10A (10) is obtained in which the mesa 12 protrudes above the base surface 11a and the hollow portion 12c is provided in the mesa 12. As shown in FIG.

According to the present embodiment, the hollow portion 12c can be formed in the mesa 12 by a relatively simple process as described above. An advantage is obtained that the optical semiconductor device 10A with higher heating efficiency can be manufactured with less labor and at a lower cost.

[Second embodiment]
FIG. 13 is a cross-sectional view of the optical semiconductor device 10B (10) of the second embodiment at the same position as in FIG. In the optical semiconductor device 10A of the first embodiment, both ends of the cavity 12c-1 (12c) in the X direction are open. The X-direction end 12c3 of 2 (12c) is positioned within the mesa 12. As shown in FIG. That is, the cavity 12c-2 is closed within the mesa 12. As shown in FIG.

The X-direction end 12c3 of the hollow portion 12c is separated from the X-direction end 16a of the heater layer 16 in the X-direction, while the opposite X-direction end 12c3 of the hollow portion 12c is located at the heater layer 16. , in the opposite direction in the X direction from the end 16a in the opposite direction in the X direction. That is, the length Ls of the cavity 12c in the X direction is longer than the length Lh of the heater layer 16 in the X direction. Thus, in this embodiment, the cavity 12c is provided so as to protrude on both sides of the heater layer 16 in the X direction.

If, on the contrary, the heater layer 16 protrudes on both sides in the X direction with respect to the cavity 12c, the heat from the heater layer 16 spreads over the cavity 12c of the mesa 12 in the X direction. It becomes easy to escape to the base 11 along the parts adjacent to both sides. In this respect, in the present embodiment, since the cavity 12c is provided so as to protrude from both sides of the heater layer 16 in the X direction, the heat from the heater layer 16 is less likely to escape to the base 11. It is possible to prevent the heating efficiency of the heater layer 16 from being lowered, thereby suppressing the power consumption. The ends 16a on both sides in the X direction of the heater layer 16 and the ends 12c3 on both sides in the X direction of the hollow portion 12c may be aligned in the Z direction.

In the optical semiconductor device 10B of the present embodiment, the portion 12d adjacent to the hollow portion 12c in the Z direction is supported at both ends by the portions 12e adjacent to both sides of the portion 12d in the X direction. there is Thereby, even when the hollow portion 12c is provided, the required shape and posture of the portion 12d adjacent to the hollow portion 12c in the Z direction can be maintained. According to such a configuration, the portion 12d can be supported by the portion 12e which is a part of the mesa 12. Therefore, compared to a configuration in which a post or the like is provided separately from the mesa 12 for supporting the portion 12d, As a result, the optical semiconductor device 10B can be made smaller, and the manufacturing labor and cost can be further reduced. In addition, in the present embodiment, the portions 12d on both sides of the hollow portion 12c in the Y direction also support the portion 12d. Therefore, it is possible to suppress deterioration in rigidity and strength of the mesa 12 due to the hollow portion 12c. The portion 12d can also be called a bridge portion, and the portion 12e can also be called a support portion. In this case, the cavity 12c may be partially open in the Y direction (width direction) on at least one side surface 12a.

[Third embodiment]
FIG. 14 is a cross-sectional view of the optical semiconductor device 10C (10) of the third embodiment at the same position as in FIG. As shown in FIG. 14, in the optical semiconductor device 10C of the third embodiment, the cladding layer 13 is provided between the hollow portion 12c and the waveguide layer 14, that is, between the waveguide layer 14 and the heater layer 16. A thermal resistance layer 19 having a lower thermal conductivity than the clad layer 13 adjacent to the thermal resistance layer 19 is provided on the side of the thermal resistance layer 19 . In this embodiment, the thermal resistance layer 19 is aligned with the cavity 12c in the Z direction. The thermal resistance layer 19 is made of, for example, InGaAs, InGaAsP, AlInAs, or the like. The cladding layer 13 is an example of an adjacent portion.

According to the present embodiment, the thermal resistance layer 19 makes it more difficult for heat to escape to the base 11, so that, for example, a decrease in the heating efficiency of the heater layer 16 can be further suppressed, and power consumption can be further suppressed. You get the advantage of

[Fourth embodiment]
FIG. 15 is a cross-sectional view of the optical semiconductor device 10D (10) of the fourth embodiment at the same position as in FIG. As shown in FIG. 15, also in the optical semiconductor device 10D of the fourth embodiment, the thermal resistance layer 19 is arranged on the side opposite to the heater layer 16 with respect to the waveguide layer 14 so as to be aligned with the cavity 12c in the Z direction. is provided. However, in this embodiment, the thermal resistance layer 19 is located in the opposite direction of the Z direction from the cavity 12c.

Also in the present embodiment, the thermal resistance layer 19 makes it more difficult for heat to escape to the base 11, so that, for example, the lowering of the heating efficiency due to the heater layer 16 can be further suppressed, and the power consumption can be further suppressed. is obtained.

[Fifth embodiment]
FIG. 16 is a cross-sectional view of the optical semiconductor device 10E (10) of the fifth embodiment at the same position as in FIG. As shown in FIG. 16, also in the optical semiconductor device 10E of the fifth embodiment, the thermal resistance layer 19 is provided on the opposite side of the waveguide layer 14 to the heater layer 16. As shown in FIG. However, in the present embodiment, the thermal resistance layer 19 is arranged in the Y direction with respect to the cavity 12c or the covering layer 17 .

Also in the present embodiment, the thermal resistance layer 19 makes it more difficult for heat to escape to the base 11, so that, for example, the lowering of the heating efficiency due to the heater layer 16 can be further suppressed, and the power consumption can be further suppressed. is obtained.

[Sixth embodiment]
FIG. 17 is a cross-sectional view of the optical semiconductor device 10F (10) of the sixth embodiment at the same position as in FIG. As shown in FIG. 17, in an optical semiconductor device 10F of the sixth embodiment, a plurality of cavities 12c arranged in the Y direction are provided inside the mesa 12. As shown in FIG. The Y direction is an example of the third direction.

Also in the present embodiment, since heat is less likely to escape from the mesa 12 to the base 11 due to the provision of the cavity 12c, for example, it is possible to suppress a decrease in the heating efficiency of the heater layer 16, thereby suppressing power consumption. You get the advantage of being able to

However, in this embodiment, of the three cavities 12c provided in the mesa 12, the cavity 12c located in the center in the Y direction is closed in the Y direction, but the other two cavities 12c are closed. , at the side 12a it is open in the Y-direction or in the direction opposite to the Y-direction.

Such a configuration can be obtained, for example, by the following manufacturing steps. That is, first, a plurality of coating layers 17 extending in the X direction are arranged on the base surface 11a substantially parallel to each other at intervals in the Y direction, and the laminate L is formed on the coating layers 17 . Thereby, a laminate L including a plurality of substantially parallel cavities 12c is obtained. Next, the covering layer 18 is formed on the top surface 12b of the laminate L so that the edges extending in the X direction on both sides of the covering layer 18 in the Y direction overlap different cavity portions 12c in the Z direction. Next, dry etching is performed to remove exposed portions of the laminate L that are not covered with the covering layer 18 when viewed in the direction opposite to the Z direction. Also in this embodiment, the side surfaces 12a of the mesa 12 are aligned in the Z direction with the edges on both sides of the coating layer 18 in the Y direction. Therefore, by this process, the mesa 12 shown in FIG. 17 is obtained in which different cavity portions 12c are opened on the side surfaces 12a located on both sides in the Y direction. After that, a dielectric layer (not shown) and a heater layer 16 are formed in the same manner as in the first embodiment.

When the mesa 12 has two open cavities 12c on each side 12a as in the present embodiment, the width of the constricted portion in the mesa 12 is equal to the width of the cavities adjacent to each other in the Y direction, as is apparent from FIG. The value (2d as an example in this embodiment) corresponds to the width d between the portions 12c, and is determined by the arrangement of the plurality of hollow portions 12c, that is, the arrangement of the coating layer 17. FIG.

FIG. 18 shows a case where the position of the hollow portion 12c and the positions of the two side surfaces 12a are shifted in the Y direction with respect to the structure of FIG. 17 in the structure of this embodiment. As can be seen by comparing FIG. 17 and FIG. 18, in the present embodiment, even if the position of the hollow portion 12c and the positions of the two side surfaces 12a are deviated in the Y direction, the width (2d) of the narrowed portion does not change size. Also, although not shown, even if the width between the two side surfaces 12a changes, according to this embodiment, the width (2d) of the constricted portion does not change.

That is, when the mesa 12 is provided with the cavity 12c that is open on each of the two side surfaces 12a as in this embodiment, the width of the constricted portion in the mesa 12 is determined by the position of the side surface 12a of the mesa 12, That is, it does not depend on the positions of the edges on both sides of the coating layer 18 in the Y direction. Therefore, according to such a configuration, individual differences (variation) in the width of the constricted portion are suppressed compared to, for example, the case where the width of the constricted portion depends on both the width d and the position of the side surface 12a. Therefore, there is an advantage that the amount of heat transferred through the constricted portion, and thus the individual difference (variation) in the heating performance of the heater layer 16 can be suppressed.

[Seventh embodiment]
FIG. 19 is a cross-sectional view of the optical semiconductor device 10G (10) of the seventh embodiment at the same position as in FIG. As shown in FIG. 19, in the optical semiconductor device 10G of the seventh embodiment, the mesa 12 extends in the Y direction. That is, the extending direction of the mesa 12, the waveguide layer 14, and the heater layer 16 is the Y direction. A plurality of cavities 12c arranged in the Y direction are provided in the mesa 12 . The extending direction of each cavity 12c and each groove 12c2 is the X direction.

That is, in this embodiment, the cavity 12c extends in the X direction, whereas the mesa 12 extends in the Y direction. The mesa 12 is an example of a second portion, and the extending direction (Y direction) along the base surface 11a intersects the X direction.

Also in the present embodiment, since heat is less likely to escape from the mesa 12 to the base 11 due to the provision of the hollow portion 12c, it is possible to suppress a decrease in the heating efficiency of the heater layer 16 and power consumption. .

[Eighth embodiment]
FIG. 20 is a cross-sectional view of the optical semiconductor device 10H (10) of the eighth embodiment. The optical semiconductor device 10H of the present embodiment is a tunable laser device having a tunable laser resonator including a DBR section 20 (DBR: distributed Bragg reflector), a phase adjustment section 30, and a gain section 40. is an example. The DBR section 20, the phase adjustment section 30, and the gain section 40 have a mesa 12 integrally formed and linearly extending in the X direction.

The DBR section 20 has a laminated structure of a waveguide layer 14 and a diffraction grating layer 21 as a feedback layer. The DBR section 20 has a reflection spectrum characteristic with a peak wavelength determined by the spatial period of the diffraction grating layer 21, and constitutes one reflection section of the laser resonator.

Further, the DBR section 20 has a heater layer 16 . Heating the heater layer 16 changes the refractive index of the waveguide layer 14, thereby shifting the reflection peak in the frequency axis direction.

The phase adjustment section 30 has a heater layer 16 . Heating the heater layer 16 changes the refractive index of the waveguide layer 14, thereby adjusting the optical length of the laser cavity. By adjusting the optical length of the laser resonator, the frequency of the resonator mode (cavity mode) can be finely adjusted and shifted in the frequency axis direction. Fine tuning of the cavity mode allows selection of the cavity mode in lasing and allows frequency variation within a small range.

The gain section 40 has an active layer 14A optically connected to the waveguide layer 14 . The active layer 14A is energized to generate optical gain, thereby causing laser oscillation. The end surface 14a of the active layer 14A constitutes the other reflecting portion of the laser resonator.

In this embodiment, a hollow portion 12 c corresponding to the heater layer 16 is provided for the DBR portion 20 and the mesa 12 of the phase adjustment portion 30 . The cavity 12 c extends in the X direction and is closed within the mesa 12 .

In the DBR portion 20, the X-direction end 12c3 of the cavity 12c is separated from the X-direction end 21a of the diffraction grating layer 21 in the X direction, while the opposite X-direction end 12c3 of the cavity 12c is , away from the opposite end 21a of the diffraction grating layer 21 in the X direction. That is, the length Ls of the cavity 12c in the X direction is longer than the length Lg of the diffraction grating layer 21 in the X direction. Thus, in this embodiment, the cavity 12c is provided so as to protrude on both sides of the diffraction grating layer 21 in the X direction.

Conversely, if the diffraction grating layer 21 were to protrude from both sides of the cavity 12c in the X direction, the heat from the heater layer 16 would be transferred to the cavity 12c of the mesa 12 in the X direction. It becomes easy to escape to the base 11 along the parts adjacent to both sides of the . In this case, a temperature difference (temperature distribution) occurs in the X direction in the diffraction grating layer 21, making it difficult to obtain desired reflection characteristics. In this regard, in this embodiment, since the cavity 12c is provided so as to protrude on both sides in the X direction with respect to the diffraction grating layer 21, the heat from the heater layer 16 is less likely to escape to the base 11. , it is possible to suppress the occurrence of a temperature difference (temperature distribution) in the X direction in the diffraction grating layer 21, which makes it difficult to obtain the desired reflection characteristics.

Moreover, in both the DBR section 20 and the phase adjustment section 30, as in the second embodiment, both ends in the X direction of the hollow portion 12c are provided so as to overlap both ends in the X direction of the heater layer 16 in the Z direction. , or is provided so as to protrude from the heater layer 16 on both sides in the X direction. Therefore, according to the present embodiment, the heat from the heater layer 16 is less likely to escape to the base 11, thereby suppressing a reduction in the heating efficiency of the heater layer 16 and power consumption.

[Ninth Embodiment]
FIG. 21 is a plan view of the optical semiconductor device 10I (10) of the ninth embodiment. The optical semiconductor device 10I of the present embodiment includes a connection section 50 and a ring resonator 60 in addition to an SG-DBR section 20S (SG-DBR: sampled-grating DBR), a phase adjustment section 30, and a gain section 40. ing. The optical semiconductor device 10I is an example of a wavelength tunable laser device having a wavelength tunable laser resonator utilizing the vernier effect.

The connecting portion 50 is branched by a branching portion such as a 1×2 MMI coupler optically connected to the gain portion 40, and includes two mesas 12 each bent in a plan view seen in the opposite direction of the Z direction. there is The waveguide layer 14 of each mesa 12 is optically connected to the annular waveguide layer 14 of the ring resonator 60 at the coupling portion C by a 2×2 MMI coupler or the like.

The phase adjustment section 30 is provided in a part of the connection section 50 .

The ring resonator 60 has a reflection spectrum characteristic having a comb-shaped peak with a period different from that of the SG-DBR portion 20S, and constitutes the other reflection portion of the laser resonator.

The ring resonator 60 also has a heater layer 16 . By heating the heater layer 16, the refractive index of the waveguide layer 14 can be changed, thereby shifting the comb-shaped reflection peak in the frequency axis direction.

In the mesa 12 of the SG-DBR portion 20S, the mesa 12, the hollow portion 12c-2 closed at both ends in the extending direction, and the concave line 12c22 of the hollow portion 12c-2 all extend in the X20 direction (X direction). ing. In the SG-DBR portion 20S, the mesa 12 also extends in the X20 direction. Therefore, the mesa 12 of the SG-DBR section 20S is an example of the first portion.

In the mesa 12 of the phase adjusting portion 30, the mesa 12, the cavity 12c-2 closed at both ends in the extending direction, and the concave line 12c22 of the cavity 12c-2 all extend in the X30 direction (X direction). there is In the phase adjustment portion 30, the mesa 12 also extends in the X30 direction. Therefore, the mesa 12 of the phase adjusting section 30 is an example of the first portion.

Further, a plurality of hollow portions 12c-1, which are open at both ends in the extending direction, are provided in the annular portion of the mesa 12 of the ring resonator 60. As shown in FIG. Further, the connecting portion C is provided with a hollow portion 12c-2 extending along the extending direction of the mesa 12 of the connecting portion 50 and closed at both ends in the extending direction. Both of the cavities 12c-1 and 12c-2 and their concave lines 12c22 extend in the X60 direction. On the other hand, the mesa 12 of the ring resonator 60 extends annularly crossing the X60 direction. Therefore, the mesa 12 of the ring resonator 60 is an example of the second portion. The extending direction at each position of the curved mesa 12 is defined as the tangential direction of the extending direction of the mesa 12 at the center position in the width direction of the mesa 12 in plan view seen in the direction opposite to the Z direction.

As shown in FIG. 21, in this embodiment, the X20 direction and the X60 direction are parallel (same direction), and the X30 direction is a direction (different direction) crossing the X20 direction and the X60 direction.

These X20 direction, X30 direction, and X60 direction all cross at an angle of 45° or less to the crystal orientation [011] direction. Therefore, according to the present embodiment, the SG-DBR section 20S, the phase adjustment section 30, and the heater layer 16 of the ring resonator 60 are provided with the cavity sections 12c-1 and 12c-2 in the same manner as the above embodiment. effect is obtained.

[Tenth embodiment]
FIG. 22 is a plan view of the optical semiconductor device 10J (10) of the tenth embodiment. As shown in FIG. 22, in the present embodiment, the mesa 12 of the ring resonator 60 is provided with only a hollow portion 12c-2 closed at both ends in the extending direction. Except for this point, the optical semiconductor device 10J has the same configuration as the optical semiconductor device 10I of the ninth embodiment. Although the shape of the hollow portion 12c-2 is different, this embodiment also provides the same effects as the ninth embodiment.

[Eleventh embodiment]
FIG. 23 is a plan view of the optical semiconductor device 10K (10) of the eleventh embodiment. As shown in FIG. 23, the optical semiconductor device 10K of the present embodiment differs from the above-described ninth optical semiconductor device 10K except that the shape of the connection portion 50 and the position and direction of the phase adjustment portion 30 provided in the connection portion 50 are different. It has the same configuration as the optical semiconductor device 10I of the embodiment.

As shown in FIG. 23, in the present embodiment, the X20 direction, the X30 direction, and the X60 direction are all the same direction, and intersect the crystal orientation [011] direction at an angle of 45° or less. there is Therefore, according to this embodiment, the same effects as those of the ninth embodiment can be obtained. Moreover, according to this embodiment, since the plurality of coating layers 17 extend in parallel in the same direction, for example, the process of forming the coating layers 17 can be performed more easily or more quickly. is also obtained.

Although the embodiments and modifications of the present invention have been illustrated above, the above-described embodiments and modifications are examples and are not intended to limit the scope of the invention. The above embodiments and modifications can be implemented in various other forms, and various omissions, replacements, combinations, and modifications can be made without departing from the scope of the invention. In addition, specifications such as each configuration and shape (structure, type, direction, model, size, length, width, thickness, height, number, arrangement, position, material, etc.) may be changed as appropriate. can be implemented.

10, 10A to 10K Optical semiconductor device 11 Base 11a Base surface 12 Mesa (first part, second part)
12a side surface 12b top surface 12c, 12c-1, 12c-2 hollow portion 12c1 bottom surface 12c2 groove 12c21 side surface 12c22 concave line 12c3 end portion 12d portion 12e portion 12f dielectric layer 13 clad Layer 13a Inclined surface 13b Protruding portion 13c Upper surface 13p Peak 14 Waveguide layer 14A Active layer 14a End surface 15 Cladding layer 16 Heater layer 16a End 17 Covering layer 18 Covering layer 19 Heat Resistance layer 20 DBR section 20S SG-DBR section 21 Diffraction grating layer 21a End section 30 Phase adjustment section 40 Gain section 50 Connection section 60 Ring resonator C Coupling section d (of the narrowed section) Width L... Laminated body Lg, Lh, Ls... Length H... Thickness of (cladding layer) Hp... Peak height OF... Orientation flat OP... Opening WF... Wafer Wm... Width (of coating layer) Wp... (protruding portion) ) projection height X, X20, X30, X60... direction (second direction)
Y... direction (third direction)
Z direction (first direction)
α: Inward inclination angle θ: Angle difference

Claims (21)

a base having a base surface that intersects the first direction, which is the [100] crystal orientation;
a mesa projecting from the base surface in the first direction, extending along the base surface, and having an end surface in the first direction;
a waveguide layer provided to extend along the base surface at a position away from the end surface of the mesa in a direction opposite to the first direction;
a heater layer provided in the mesa at a position away from the waveguide layer in the first direction and generating heat when supplied with electric power;
has
a hollow portion including a groove recessed in the first direction and extending in a second direction intersecting the first direction is provided at a position of the mesa spaced apart from the waveguide layer in a direction opposite to the first direction;
The optical semiconductor device, wherein the second direction obliquely intersects the crystal orientation [011] direction of the base with an angle difference of 45° or less. 2. The optical semiconductor device according to claim 1, wherein the absolute value of said angular difference is in a direction of 10[deg.] or more and 45[deg.] or less. 3. The optical semiconductor device according to claim 1, wherein said groove is recessed in said first direction in a V shape and extends in said second direction. 4. Among claims 1 to 3, wherein the hollow portion has a bottom surface located at an end opposite to the first direction in the hollow portion and extending in the second direction intersecting the first direction. The optical semiconductor device according to any one of the above. 5. The optical semiconductor device according to claim 1, wherein said mesa has a first portion whose extending direction along said base surface of said mesa is substantially along said second direction. 6. The optical semiconductor device according to claim 1, wherein said mesa has a second portion where a direction of extension of said mesa along said base surface intersects with said second direction. 7. The mesa according to any one of claims 1 to 6, wherein a plurality of cavities arranged in a third direction crossing the first direction and the second direction are provided as the cavities in the mesa. Optical semiconductor device. The mesa has two side surfaces as an end face in the third direction and an end face in the direction opposite to the third direction,
8. The optical semiconductor device according to claim 7, wherein said cavity includes a cavity opened in said third direction on each of said two side surfaces. 9. The optical semiconductor device according to claim 1, wherein said cavity includes a cavity closed within said mesa. The hollow portion has a bottom surface located at an end portion of the hollow portion opposite to the first direction and extending in the second direction intersecting the first direction, and a coating layer covering the bottom surface. 10. The optical semiconductor device according to claim 1, comprising a recessed cavity. The mesa has a thermal resistance layer having a lower thermal conductivity than the adjacent portion at a position on the side opposite to the heater layer with respect to the waveguide layer and aligned with the cavity in the first direction. The optical semiconductor device according to any one of claims 1 to 10. at a position of the mesa opposite to the heater layer with respect to the waveguide layer and aligned with the hollow portion in a third direction intersecting the first direction and the second direction, relative to the adjacent portion; 12. The optical semiconductor device according to any one of claims 1 to 11, further comprising a thermal resistance layer having a thermal conductivity lower than that of adjacent portions. 13. The optical semiconductor device according to claim 12, wherein said thermal resistance layer is positioned on both sides of said cavity in said third direction. 14. The optical semiconductor device according to claim 1, wherein said mesa has a diffraction grating layer extending along said waveguide layer. the mesa having a grating layer extending along the waveguide layer;
The hollow portion is provided so that both ends of the hollow portion in the extending direction overlap with both ends of the diffraction grating layer in the extending direction in the first direction, or 6. The optical semiconductor device according to claim 5, provided so as to protrude from both sides of the . a base having a base surface that intersects the first direction;
a mesa projecting from the base surface in the first direction, extending along the base surface, and having an end surface in the first direction;
a waveguide layer provided so as to extend along the direction in which the mesa extends along the base surface at a position away from the end face of the mesa in the direction opposite to the first direction;
a heater layer provided in the mesa at a position away from the waveguide layer in the first direction and generating heat when supplied with electric power;
has
A hollow portion including a groove that is recessed in the first direction in a V shape and extends in a second direction that intersects with the first direction, at a position of the mesa that is spaced apart from the waveguide layer in the direction opposite to the first direction. An optical semiconductor device provided with a base having a base surface that intersects the first direction;
a mesa projecting from the base surface in the first direction, extending along the base surface, and having an end surface in the first direction;
a waveguide layer provided so as to extend along the direction in which the mesa extends along the base surface at a position away from the end face of the mesa in the direction opposite to the first direction;
a heater layer provided in the mesa at a position away from the waveguide layer in the first direction and generating heat when supplied with electric power;
has
An optical semiconductor device, wherein a cavity closed within the mesa is provided at a position of the mesa spaced apart from the waveguide layer in the direction opposite to the first direction. 18. The optical semiconductor device according to claim 16, wherein said cavity extends in a direction in which said mesa extends along said base surface. 18. The optical semiconductor device according to claim 17, wherein said cavity is recessed in said first direction in a V shape and extends along said extending direction. The optical semiconductor device according to any one of claims 1 to 19, wherein said base and mesa are made of a III-V group semiconductor having a zincblende structure. providing a coating layer extending in a second direction intersecting the first direction on a base surface intersecting the first direction of the base;
forming a laminate by epitaxial growth in which crystal grains grow in a first direction on the base surface;
partially removing the laminate to form a mesa;
forming a heater layer that generates heat when supplied with electric power on the end surface of the mesa in the first direction;
has
In the step of forming the laminate, the laminate is formed in a state in which a hollow portion including a groove recessed in the first direction and extending in the second direction on the coating layer is provided therein. , a method for manufacturing an optical semiconductor device.

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