JP7640273B2 - Optical semiconductor device and method for manufacturing the same - Google Patents

Description

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

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 the power consumption caused by heat generation in the heater layer could be reduced.

Therefore, one of the objectives of the present invention is to obtain an optical semiconductor device and a method for manufacturing the optical semiconductor device that have an improved new configuration, for example, that can suppress power consumption due to heat generation in the heater layer.

The optical semiconductor device of the present invention has, for example, a base having a base surface intersecting a first direction, which is a crystal orientation [100] direction; a mesa protruding from the base surface in the first direction, extending along the base surface, and having an end face in the first direction; a waveguide layer provided on the mesa at a position away from the end face in the opposite direction to the first direction so as to extend along the base surface; and a heater layer provided on the mesa at a position away from the waveguide layer in the first direction, which generates heat when supplied with power. A cavity including a groove recessed in the first direction and extending in a second direction intersecting with the first direction is provided at a position of the mesa away from the waveguide layer in the opposite direction to the first direction, and the second direction intersects the crystal orientation [011] direction of the base at an angle difference of 45° or less.

In the optical semiconductor device, the absolute value of the angle difference may be in a direction that is greater than or equal to 10° and less than or equal to 45°.

In the optical semiconductor device, the groove may be V-shaped in the first direction and extend in the second direction.

In the optical semiconductor device, the cavity may be located at an end of the cavity in the opposite direction to the first direction and may have a bottom surface that intersects with the first direction and extends in the second direction.

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

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

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

In the optical semiconductor device, the mesa may have two side surfaces as an end surface in the third direction and an end surface in the opposite direction to the third direction, and the cavity may include a cavity that is open in the third direction on each of the two side surfaces.

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

In the optical semiconductor device, the cavity may include a cavity having a bottom surface located at an end of the cavity in the opposite direction to the first direction, intersecting the first direction and extending in the second direction, and a coating layer covering the bottom surface.

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

The optical semiconductor device may have a thermal resistance layer having a lower thermal conductivity than adjacent portions at a position on the mesa opposite the heater layer with respect to the waveguide layer and aligned with the cavity in a third direction intersecting the first direction and the second direction.

In the optical semiconductor device, the thermal resistance layer may be located 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 cavity is provided so that both ends of the cavity in the extension direction overlap with both ends of the diffraction grating layer in the extension direction in the first direction, or may be provided so as to protrude beyond the diffraction grating layer on both sides in the extension direction.

The optical semiconductor device of the present invention has, for example, a base having a base surface intersecting a first direction, a mesa protruding 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 at a position of the mesa away from the end surface in the opposite direction to the first direction so as to extend along the extension direction of the base surface of the mesa, and a heater layer provided at a position of the mesa away from the waveguide layer in the first direction and generating heat when supplied with power, and a cavity portion including a groove that is V-shaped in the first direction and extends in a second direction intersecting the first direction is provided at a position of the mesa away from the waveguide layer in the opposite direction to the first direction.

The optical semiconductor device of the present invention has, for example, a base having a base surface intersecting a first direction, a mesa protruding 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 at a position of the mesa away from the end surface in the opposite direction to the first direction so as to extend along the extension direction along the base surface of the mesa, and a heater layer provided at a position of the mesa away from the waveguide layer in the first direction and which generates heat when supplied with power, and a cavity portion closed within the mesa is provided at a position of the mesa away from the waveguide layer in the opposite direction to the first direction.

In the optical semiconductor device, the cavity may extend in a direction parallel to the base surface of the mesa.

In the optical semiconductor device, the cavity may be V-shaped in the first direction and extend along the extension direction.

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

The method for manufacturing an optical semiconductor device of the present invention includes, for example, the steps of providing a coating layer extending in a second direction intersecting with a first direction of the base on a base surface intersecting with the first direction, forming a laminate by epitaxial growth in which crystal grains grow in the first direction on the base surface, forming a mesa by partially removing the laminate, and forming a heater layer that generates heat when supplied with power on the end face of the mesa in the first direction. In the step of forming the laminate, the laminate is formed in such a state that a cavity portion including a groove recessed in the first direction on the coating layer and extending in the second direction is provided therein.

The present invention provides an optical semiconductor device and a method for manufacturing an optical semiconductor device with an improved new configuration that can suppress power consumption due to heat generation in the heater layer, for example.

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

Below, exemplary embodiments of the present invention are disclosed. The configurations of the embodiments shown below, and the actions and results (effects) brought about by said configurations, are merely examples. The present invention can also be realized with configurations other than those disclosed in the following embodiments. Furthermore, according to the present invention, it is possible to obtain at least one of the various effects (including derivative effects) obtained by the configurations.

The multiple embodiments described below have similar configurations. Therefore, according to the configuration of each embodiment, similar actions and effects based on the similar configurations can be obtained. Furthermore, below, the similar configurations are given the same reference numerals, and duplicate explanations may be omitted.

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

In addition, in each figure, the X direction is represented by an arrow X, the Y direction is represented by an arrow Y, and the Z direction is represented by an arrow Z. The X direction, Y direction, and Z direction intersect with each other and are perpendicular to each other.

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

The base 11 is a semiconductor substrate, and extends in the X and Y directions, intersecting and perpendicular to the Z direction. The base 11 has a base surface 11a. The base surface 11a intersects and perpendicular to the Z direction, and extends in the X and Y directions. The base 11 is made of a III-V semiconductor having a zinc blende structure, such as n-type indium phosphide (InP). The 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 extension direction of the mesa 12, the Y direction is also referred to as the width direction of the mesa 12, and the Z direction can also be referred to as the height direction or protruding direction of the mesa 12. The Z direction is an example of the 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 to the Y direction, in other words, the end surfaces on both sides in the width direction of the mesa 12. The side surfaces 12a intersect and are perpendicular to the Y direction, and extend in the X direction and Z direction. The side surfaces 12a extend in the X direction at a substantially constant height in the Z direction. The two side surfaces 12a are also substantially parallel.

The top surface 12b is located at the end of the mesa 12 in the Z direction. The top surface 12b intersects and is perpendicular 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. The top surface 12b is also substantially parallel to the base surface 11a. The top surface 12b is an example of an end surface.

Mesa 12 has a waveguide layer 14 and cladding layers 13 and 15. In mesa 12, cladding layer 13, waveguide layer 14, and cladding layer 15 are stacked in this order in the Z direction. Note that mesa 12 may have a different configuration from that shown in FIG. 1, for example, by having more layers.

The waveguide layer 14 is provided at a position away from the top surface 12b in the opposite direction of the Z direction, is located at 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, and extends in a band shape in the X direction with a substantially constant thickness in the Z direction. The waveguide layer 14 also spans between the two side surfaces 12a of the mesa 12.

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

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

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

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

As shown in FIG. 1, a cavity 12c is provided in the mesa 12 on the opposite side of the heater layer 16 with respect to the waveguide layer 14, in other words, at a position away from the waveguide layer 14 in the opposite Z direction. The cavity 12c is provided at the base of the mesa 12. Note that the position of the cavity 12c in the Z direction may be between the base surface 11a and the waveguide layer 14, and is not limited to the base of the mesa 12.

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

Figure 2 is a cross-sectional view taken along line II-II of Figure 1, and Figure 3 is a cross-sectional view taken along line III-III of Figure 1. The cavity 12c is surrounded by a bottom surface 12c1 and two side surfaces 12c21. The bottom surface 12c1 is located at the end of the cavity 12c opposite the Z direction, intersects with 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, a 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 toward the Z direction. The cavity 12c having the cross-sectional shape shown in Figure 2 extends in the X direction as shown in Figures 1 and 3. That is, the cavity 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-groove. The recessed line 12c22 provided at the Z-direction end of the groove 12c2 extends in the X-direction. The X-direction is an example of the second direction. The side surface 12c21 can also be referred to as an inclined surface. As shown in Figures 1 and 3, in this embodiment, both ends of the cavity 12c (12c-1) in the extension direction, i.e., 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 extends along the base surface 11a in the X direction and is an example of a first portion.

A coating layer 17 is provided on the bottom surface 12c1 of the cavity 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 function of the coating layer 17 will be described later. In this embodiment, the coating layer 17 is present in the cavity 12c, but the coating layer 17 may disappear during the manufacturing process of the mesa 12.

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 power is transmitted in the opposite direction of the Z direction in the cladding layer 15 and reaches the waveguide layer 14. This heat is further transmitted in the opposite direction of the Z direction from the waveguide layer 14 in the cladding layer 13 and escapes to the base 11. If the amount of heat that escapes from the waveguide layer 14 to the base 11 via the cladding layer 13 is large, the heating efficiency of the heater layer 16 decreases, which is one of the factors that increases power consumption.

In this respect, in this embodiment, as described above, the cavity 12c is provided in the mesa 12, and as shown in FIG. 2, the width of the mesa 12 in the Y direction is narrowed on both sides of the cavity 12c in the Y direction at the base portion of the mesa 12 close to the base 11. That is, the mesa 12 has a narrowed portion at the position where the cavity 12c is provided, whose cross-sectional area intersecting the Z direction is narrower than other portions. Therefore, according to this embodiment, heat is less likely to escape from the waveguide layer 14 to the base 11 via the cladding layer 13, i.e., the mesa 12, and therefore the heating efficiency of the heater layer 16 is prevented from decreasing, and power consumption can be reduced.

[Formation of Cavity]
4 is a plan view showing the wafer WF that becomes the base 11 and the covering layer 17 provided on the wafer WF. In this embodiment, the portion that becomes the mesa 12, such as the cladding layer 13, is formed by epitaxial growth on the surface of the wafer WF that becomes 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 can also be called the growth direction or the stacking direction. The orientation flat OF of the wafer WF is aligned with the [01-1] direction of the crystal orientation of the wafer WF.

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

The inventors, through extensive research, have discovered that when the cladding layer 13 grows by epitaxial growth on an exposed region outside the coating layer 17, if the coating layer 17 extends in a direction (X direction) that intersects the crystal orientation [011] at an angle θ of 45° or less, as shown in FIG. 4, a cavity 12c adjacent to the coating layer 17 in the Z direction is formed in the growth layer, i.e., in the cladding layer 13. Note that the cavity 12c has a finite height in the Z direction and is closed in the Z direction.

Figures 5 to 7 are cross-sectional views of the base 11 and the cladding layer 13, showing the difference in the growth state of the cladding layer 13 depending on the magnitude of the angle difference θ between the crystal orientation [011] direction and the X direction. Figure 5 shows the case where the angle difference θ in Figure 4 is 0°, Figure 6 shows the case where the angle difference θ is greater than 0° and less than 10°, and Figure 7 shows the case where the angle difference θ is greater than 10° and less than 45°.

As shown in FIG. 5, when the angle difference θ is 0°, in epitaxial growth, two inclined surfaces 13a are formed in the cladding layer 13 that move away from each other in the Y direction as they move in the Z direction from both ends of the coating layer 17 in the Y direction. Therefore, when the angle difference is 0°, it is difficult to form a cavity 12c with a finite height in the Z direction on the coating layer 17 in the cladding layer 13.

As shown in FIG. 6, when the angle difference θ is greater than 0° and less than 10°, in the epitaxial growth, two inclined surfaces are formed in the cladding layer 13 from both ends of the coating layer 17 in the Y direction toward each other in the Z direction, and then, from the middle, inclined surfaces are formed toward each other in the Y direction toward the Z direction. In other words, the two cladding layers 13 adjacent to each other on both sides of the coating layer 17 in the Y direction have protrusions 13b protruding toward each other in the Y direction at the middle position in the Z direction. In this case, by appropriately setting the width Wm of the coating layer 17 relative to the thickness (height) H of the cladding layer 13 in the Z direction, a cavity 12c with a finite height in the Z direction can be formed on the coating layer 17 by configuring the peaks 13p of the two protrusions 13b to be in contact or connected to each other.

Here, the acute angle (hereinafter referred to as the inward inclination 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 protrusion 13b is α, the protrusion height (width) in the Y direction of the protrusion 13b from the Y-direction end of the coating layer 17 is Wp, the Y-direction width of the coating layer 17 is Wm, the Z-direction height from the base surface 11a to the peak 13p (hereinafter referred to as the peak height) is Hp, and the Z-direction thickness of the cladding layer 13 is H, and if the thickness of the coating layer 17 is ignored, then if 2·Wp≧Wm, the two peaks 13p will be in contact with or connected to each other. Here, since Hp=Wp·tan α, in this case,
Wm≦2・Hp/tanα...(1)
The width Wm of the covering layer 17 may be set so as to satisfy the following: Note that, according to research by the inventors, it has been found that the inward inclination angle α is in the range of 36° to 45°, 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 depending on the angle difference θ. Figure 8 is a graph showing an experimental correlation between the ratio Hp/H and the angle difference θ. As shown in Figure 8, it has been found that 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 and approaches 1 as the angle difference θ increases. Therefore, by determining the peak height Hp corresponding to the angle difference θ and the thickness H of the cladding layer 13 from the approximation function or map obtained from the correlation shown in Figure 8, and determining the width Wm of the coating layer 17 so as to satisfy the above formula (1), the two peaks 13p are in contact with or connected to each other, and thus a cavity 12c having a finite height in the Z direction can be formed on the coating layer 17.

Furthermore, the inventors' research has revealed that when the angle difference θ is 10° or more and 45° or less, the ratio Hp/H is approximately 1. In this case, in the epitaxial growth, as shown in FIG. 7, a protrusion 13b having two inclined surfaces approaching each other in the Y direction as it approaches the Z direction is formed in the cladding layer 13 from both ends of the coating layer 17 in the Y direction, and the peak 13p of the protrusion 13b appears at the end of the cladding layer 13 in the Z direction. In this case, the width Wm of the coating layer 17 can also be determined so as to satisfy the above-mentioned formula (1). In other words, the Z-direction thickness H of the cladding layer 13 can be secured sufficiently in correspondence with the Y-direction width of the coating layer 17 so that an opening OP does not occur between the protrusions 13b at the end of the cladding layer 13 in the Z direction, or the Y-direction width of the coating layer 17 can be appropriately set within a range that is not too wide in correspondence with the Z-direction thickness H of the cladding layer 13.

Figure 9 shows a state in which 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 a position spaced apart in the Z direction from the coating layer 17, forming a cavity 12c on the coating layer 17 with a finite height in the Z direction. A groove 12c2 is formed in the cavity 12c, which is recessed in the Z direction and extends in the X direction. The groove 12c2 is a V-shaped groove that forms a recessed line 12c22 extending in the X direction.

When the angle difference θ is 10° or more and 45° or less, as shown in FIG. 9, a flat upper surface 13c of the cladding layer 13 is formed at a position away from the cavity 12c in the Z direction. In this case, the process of processing the upper surface 13c into a flat surface after epitaxial growth is not required, which has the advantage that, for example, the mesa 12 provided with the cavity 12c can be manufactured with less effort and at lower cost.

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 recessed line 12c22 as the Z-direction end of the groove 12c2 extend in the X direction (second direction) diagonally intersecting the crystal orientation [011] direction at an angle of 45° or less, which is evidence that the cavity 12c has been formed in the mesa 12 by the above-mentioned epitaxial growth. In addition, the cross section of the cavity 12c intersecting the X direction, as shown in FIG. 2, has a bottom surface 12c1 that intersects with the Z direction and extends in the X direction, and two side surfaces 12c21 that extend in the X direction and are inclined so as to approach each other in the Y direction as they approach the Z direction, is also evidence that the cavity 12c has been formed in the mesa 12 by the above-mentioned epitaxial growth. Each crystal orientation can be determined by analyzing the material of the optical semiconductor device 10A (10).

[Mesa formation]
10 to 12 are cross-sectional views showing the process of forming the mesa 12. First, as shown in FIG. 10, in a state where the covering layer 17 having the above-mentioned angle difference θ is formed on the base surface 11a of the base 11, the laminate L of the cladding layer 13, the waveguide layer 14, and the cladding layer 15 is formed by epitaxial growth. At this time, as described above, the cavity 12c is formed on the covering layer 17. That is, in the process of forming the laminate L by epitaxial growth, the cavity 12c including the groove 12c2 is formed on the covering layer 17 inside the laminate L. In addition, a covering layer 18 (mask) made of a dielectric material or the like is formed on the top surface 12b located at the end of the cladding layer 15 in the Z direction.

11, the exposed portions of the laminate L that are not covered by the covering layer 18 when viewed from the Z direction are removed, for example by dry etching, and the cladding layer 13, the waveguide layer 14, and the cladding layer 15 included in the mesa 12 are formed as portions of the laminate L aligned with the covering layer 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, the covering layer 18 is removed by, for example, wet etching, and then a dielectric layer 12f is formed to cover the side surface 12a, top surface 12b, and base surface 11a of the mesa 12, and a heater layer 16 is formed on the top surface 12b via the 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 a cavity 12c is provided within the mesa 12.

According to this embodiment, the cavity 12c can be formed in the mesa 12 by the relatively simple process described above, which has the advantage that, for example, heat is less likely to escape from the mesa 12 to the base 11, and the optical semiconductor device 10A with higher heating efficiency by the heater layer 16 can be manufactured with less effort and at 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. 3. In the optical semiconductor device 10A of the first embodiment, both ends in the X direction of the cavity 12c-1 (12c) are open, whereas in this embodiment, as shown in Fig. 13, the end 12c3 in the X direction of the cavity 12c-2 (12c) is located within the mesa 12. That is, the cavity 12c-2 is closed within the mesa 12.

The X-direction end 12c3 of the cavity 12c is separated in the X-direction from the X-direction end 16a of the heater layer 16, while the opposite X-direction end 12c3 of the cavity 12c is separated in the opposite X-direction from the opposite X-direction end 16a of the heater layer 16. In other words, the X-direction length Ls of the cavity 12c is longer than the X-direction length Lh of the heater layer 16. Thus, in this embodiment, the cavity 12c is provided to protrude on both sides of the heater layer 16 in the X-direction.

On the contrary, if the heater layer 16 were to protrude on both sides in the X direction relative to the cavity 12c, the heat from the heater layer 16 would be more likely to escape to the base 11 through the parts of the mesa 12 adjacent to both sides in the X direction relative to the cavity 12c. In this regard, in this embodiment, the cavity 12c is provided so as to protrude on both sides in the X direction relative to the heater layer 16, so that the heat from the heater layer 16 is less likely to escape to the base 11, which in turn prevents the heating efficiency of the heater layer 16 from decreasing and reduces power consumption. Note that 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 cavity 12c may be aligned in the Z direction.

In addition, in the optical semiconductor device 10B of this embodiment, the portion 12d adjacent to the cavity 12c in the Z direction is supported at both ends by the portion 12e adjacent to the portion 12d on both sides in the X direction. As a result, even when the cavity 12c is provided, the required shape and posture of the portion 12d adjacent to the cavity 12c in the Z direction can be maintained. With this configuration, the portion 12d can be supported by the portion 12e, which is a part of the mesa 12, so that, for example, compared to a configuration in which a support or the like that supports the portion 12d is provided separately from the mesa 12, the optical semiconductor device 10B can be made smaller and the manufacturing effort and cost can be reduced. In addition, in this embodiment, since the portions on both sides of the cavity 12c in the Y direction also support the portion 12d, the reduction in rigidity and strength of the mesa 12 due to the cavity 12c can be suppressed. 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]
14 is a cross-sectional view of the optical semiconductor device 10C (10) of the third embodiment at the same position as in FIG. 2. As shown in FIG. 14, in the optical semiconductor device 10C of the third embodiment, a thermal resistance layer 19 having a lower thermal conductivity than the clad layer 13 adjacent to the thermal resistance layer 19 is provided between the cavity 12c and the waveguide layer 14 of the clad layer 13, i.e., on the opposite side of the heater layer 16 with respect to the waveguide layer 14. 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, etc. The clad layer 13 is an example of an adjacent portion.

According to this embodiment, the thermal resistance layer 19 makes it even more difficult for heat to escape to the base 11, which has the advantage that, for example, the heating efficiency of the heater layer 16 can be further prevented from decreasing, and power consumption can be further reduced.

[Fourth embodiment]
Fig. 15 is a cross-sectional view of an optical semiconductor device 10D (10) of the fourth embodiment at the same position as in Fig. 2. As shown in Fig. 15, the optical semiconductor device 10D of the fourth embodiment also has a thermal resistance layer 19 on the opposite side of the heater layer 16 with respect to the waveguide layer 14, so as to be aligned with the cavity 12c in the Z direction. However, in this embodiment, the thermal resistance layer 19 is located in the opposite direction from the cavity 12c in the Z direction.

In this embodiment, the thermal resistance layer 19 makes it even more difficult for heat to escape to the base 11, which has the advantage that, for example, the heating efficiency of the heater layer 16 can be further prevented from decreasing, and power consumption can be further reduced.

[Fifth embodiment]
Fig. 16 is a cross-sectional view of an optical semiconductor device 10E (10) of the fifth embodiment at the same position as in Fig. 2. As shown in Fig. 16, the optical semiconductor device 10E of the fifth embodiment also has a thermal resistance layer 19 on the opposite side of the heater layer 16 with respect to the waveguide layer 14. However, in this embodiment, the thermal resistance layer 19 is aligned in the Y direction with respect to the cavity 12c or the covering layer 17.

In this embodiment, the thermal resistance layer 19 makes it even more difficult for heat to escape to the base 11, which has the advantage that, for example, the heating efficiency of the heater layer 16 can be further prevented from decreasing, and power consumption can be further reduced.

Sixth Embodiment
Fig. 17 is a cross-sectional view of an optical semiconductor device 10F (10) according to a sixth embodiment at the same position as in Fig. 2. As shown in Fig. 17, in the optical semiconductor device 10F according to the sixth embodiment, a plurality of cavities 12c aligned in the Y direction are provided in the mesa 12. The Y direction is an example of a third direction.

In this embodiment, the hollow portion 12c makes it difficult for heat to escape from the mesa 12 to the base 11, which has the advantage that, for example, the heating efficiency of the heater layer 16 is prevented from decreasing and power consumption can be reduced.

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, while the other two cavities 12c are open in the Y direction or in the opposite direction to the Y direction on the side surface 12a.

Such a configuration can be obtained, for example, by the following manufacturing process. That is, first, a plurality of coating layers 17 extending in the X direction are arranged on the base surface 11a in a substantially parallel manner with a space therebetween in the Y direction, and a laminate L is formed on the coating layers 17. As a result, a laminate L including a plurality of substantially parallel cavities 12c is obtained. Next, the coating 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 Y direction of the coating layer 18 overlap with different cavities 12c in the Z direction. Next, the exposed portion of the laminate L that is not covered by the coating layer 18 when viewed in the opposite direction to the Z direction is removed by dry etching. In this embodiment, the side surface 12a of the mesa 12 is also aligned with the edges of both sides of the coating layer 18 in the Y direction in the Z direction. Thus, this process results in a mesa 12 as shown in FIG. 17, in which different cavities 12c are opened on the side surfaces 12a located on both sides in the Y direction. Thereafter, a dielectric layer (not shown) and a heater layer 16 are formed, similar to the first embodiment described above.

When the mesa 12 has two open cavities 12c on each side 12a as in this embodiment, as is clear from FIG. 17, the width of the narrowed portion in the mesa 12 is a value corresponding to the width d between adjacent cavities 12c in the Y direction (2d in this embodiment as an example), and is determined by the arrangement of the multiple cavities 12c, i.e., the arrangement of the coating layer 17.

Figure 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 relative to the configuration of Figure 17 in the configuration of this embodiment. As is clear from a comparison of Figures 17 and 18, in this embodiment, even if the position of the hollow portion 12c and the positions of the two side surfaces 12a are shifted in the Y direction, the width (2d) of the narrowed portion does not change. Also, although not shown, even if the width between the two side surfaces 12a changes, according to this embodiment, the width (2d) of the narrowed portion does not change.

That is, in the case where the mesa 12 has an open cavity 12c on each of the two side surfaces 12a as in this embodiment, the width of the narrowed portion in the mesa 12 does not depend on the position of the side surface 12a of the mesa 12, i.e., the positions of both edges in the Y direction of the coating layer 18. Therefore, with this configuration, for example, compared to a case where the width of the narrowed portion depends on both the width d and the position of the side surface 12a, the individual differences (variations) in the width of the narrowed portion can be suppressed, and therefore the amount of heat transfer escaping from the narrowed portion, and therefore the individual differences (variations) in the heating performance of the heater layer 16 can be suppressed.

[Seventh embodiment]
Fig. 19 is a cross-sectional view of an optical semiconductor device 10G (10) of the seventh embodiment at the same position as in Fig. 3. 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 extension direction of the mesa 12, the waveguide layer 14, and the heater layer 16 is the Y direction. A plurality of cavities 12c aligned in the Y direction are provided in the mesa 12. The extension direction of each of the cavities 12c and each of the grooves 12c2 is the X direction.

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

In this embodiment, the hollow portion 12c makes it difficult for heat to escape from the mesa 12 to the base 11, which prevents the heating efficiency of the heater layer 16 from decreasing and reduces power consumption.

[Eighth embodiment]
20 is a cross-sectional view of an optical semiconductor device 10H (10) of the eighth embodiment. The optical semiconductor device 10H of this embodiment is an example of a wavelength tunable laser device having a wavelength tunable laser resonator including a DBR section 20 (DBR: distributed Bragg reflector), a phase adjustment section 30, and a gain section 40. The DBR section 20, the phase adjustment section 30, and the gain section 40 are integrally formed and have a mesa 12 that extends linearly 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 of the reflecting sections of the laser resonator.

The DBR section 20 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 reflection peak in the frequency axis direction.

The phase adjustment unit 30 has a heater layer 16. By heating the heater layer 16, the refractive index of the waveguide layer 14 is changed, and the optical length of the laser resonator can be adjusted. By adjusting the optical length of the laser resonator, the frequency of the resonator mode (cavity mode) can be shifted in the frequency axis direction while being finely adjusted. Fine adjustment of the resonator mode makes it possible to select the resonator mode in laser oscillation and to change the frequency within a small range.

The gain section 40 has an active layer 14A optically connected to the waveguide layer 14. When a current is passed through the active layer 14A, it generates optical gain, which results in laser oscillation. The end face 14a of the active layer 14A forms the other reflecting section of the laser resonator.

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

In the DBR section 20, the X-direction end 12c3 of the cavity 12c is separated in the X-direction from the X-direction end 21a of the diffraction grating layer 21, while the opposite X-direction end 12c3 of the cavity 12c is separated in the opposite X-direction from the opposite X-direction end 21a of the diffraction grating layer 21. That is, the X-direction length Ls of the cavity 12c is longer than the X-direction length Lg of the diffraction grating layer 21. 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 on both sides in the X direction relative to the cavity 12c, the heat from the heater layer 16 would be more likely to escape to the base 11 through the portions of the mesa 12 adjacent to both sides in the X direction relative to the cavity 12c. In this case, a temperature difference (temperature distribution) would occur in the X direction in the diffraction grating layer 21, making it difficult to obtain the desired reflection characteristics. In this regard, in the present embodiment, the cavity 12c is provided so as to protrude on both sides in the X direction relative to the diffraction grating layer 21, making it difficult for the heat from the heater layer 16 to escape to the base 11, and thus making it possible to suppress the occurrence of a temperature difference (temperature distribution) in the X direction in the diffraction grating layer 21, making it difficult to obtain the desired reflection characteristics.

In addition, in both the DBR section 20 and the phase adjustment section 30, as in the second embodiment, both ends of the cavity 12c in the X direction are arranged to overlap both ends of the heater layer 16 in the Z direction, or are arranged to protrude further on both sides in the X direction than the heater layer 16. Therefore, according to this embodiment, it is difficult for heat from the heater layer 16 to escape to the base 11, which in turn prevents the heating efficiency of the heater layer 16 from decreasing, and reduces power consumption.

[Ninth embodiment]
21 is a plan view of an optical semiconductor device 10I (10) of the ninth embodiment. The optical semiconductor device 10I of this 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. The optical semiconductor device 10I is an example of a wavelength-tunable laser device having a wavelength-tunable laser resonator that utilizes the Vernier effect.

The connection section 50 is branched at a branching section, such as a 1x2 MMI coupler, optically connected to the gain section 40, and has two mesas 12 that are bent in a plan view in opposite directions in the Z direction. The waveguide layer 14 of each mesa 12 is optically connected at the coupling section C to the annular waveguide layer 14 of the ring resonator 60 by a 2x2 MMI coupler or the like.

The phase adjustment unit 30 is provided as part of the connection unit 50.

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

The ring resonator 60 also has a heater layer 16. Heating the heater layer 16 changes the refractive index of the waveguide layer 14, which allows the comb-shaped reflection peak to be shifted in the frequency axis direction.

In the mesa 12 of the SG-DBR section 20S, the mesa 12, the cavity 12c-2 with both ends in the extension direction closed, and the recessed line 12c22 of the cavity 12c-2 all extend in the X20 direction (X direction). In the SG-DBR section 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 adjustment unit 30, the mesa 12, the cavity 12c-2 with both ends in the extension direction closed, and the recessed line 12c22 of the cavity 12c-2 all extend in the X30 direction (X direction). In the phase adjustment unit 30, the mesa 12 also extends in the X30 direction. Therefore, the mesa 12 of the phase adjustment unit 30 is an example of the first portion.

The ring-shaped portion of the mesa 12 of the ring resonator 60 has a plurality of cavities 12c-1 with both ends open in the extension direction. The coupling portion C has a cavity 12c-2 that extends along the extension direction of the mesa 12 of the connection portion 50 and has both ends closed in the extension direction. The cavities 12c-1 and 12c-2 and their recessed lines 12c22 all extend in the X60 direction. In contrast, the mesa 12 of the ring resonator 60 extends in a ring shape, intersecting with the X60 direction. Thus, the mesa 12 of the ring resonator 60 is an example of the second portion. The extension direction at each position of the curved mesa 12 is defined as the tangent direction of the extension direction of the mesa 12 at the center position of the mesa 12 in the width direction in a plan view seen in the opposite direction to the Z direction.

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

The X20, X30, and X60 directions all intersect obliquely with the [011] crystal orientation at an angle of 45° or less. Therefore, according to this embodiment, the same effect as in the above embodiment can be obtained by providing the cavities 12c-1 and 12c-2 in the SG-DBR section 20S, the phase adjustment section 30, and the heater layer 16 of the ring resonator 60.

Tenth embodiment
Fig. 22 is a plan view of an optical semiconductor device 10J (10) of the tenth embodiment. As shown in Fig. 22, in this embodiment, the mesa 12 of the ring resonator 60 is provided with only a cavity 12c-2 whose both ends in the extension direction are closed. Except for this point, the optical semiconductor device 10J has a similar configuration to the optical semiconductor device 10I of the ninth embodiment. Although the shape of the cavity 12c-2 is different, this embodiment also provides the same effects as the ninth embodiment.

[Eleventh embodiment]
Fig. 23 is a plan view of an optical semiconductor device 10K (10) according to an eleventh embodiment. As shown in Fig. 23, the optical semiconductor device 10K according to this embodiment has a similar configuration to the optical semiconductor device 10I according to the ninth embodiment, 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.

As shown in FIG. 23, in this embodiment, the X20 direction, the X30 direction, and the X60 direction are all the same direction and cross the crystal orientation [011] diagonally at an angle of 45° or less. Therefore, this embodiment also provides the same effect as the ninth embodiment. In addition, according to this embodiment, since the multiple coating layers 17 extend in parallel in the same direction, there is also the advantage that, for example, the process of forming the coating layers 17 can be performed more easily or more quickly.

Although the above describes the embodiments and variations of the present invention, the above embodiments and variations are merely examples and are not intended to limit the scope of the invention. The above embodiments and variations can be implemented in various other forms, and various omissions, substitutions, combinations, and modifications can be made without departing from the spirit of the invention. Furthermore, the specifications of each configuration, shape, etc. (structure, type, direction, model, size, length, width, thickness, height, number, arrangement, position, material, etc.) can be modified as appropriate.

10, 10A to 10K... Optical semiconductor device 11... Base 11a... Base surface 12... Mesa (first portion, second portion)
12a...Side surface 12b...Top surface 12c, 12c-1, 12c-2...Cavity portion 12c1...Bottom surface 12c2...Groove 12c21...Side surface 12c22...Concave line 12c3...End portion 12d...Part 12e...Part 12f...Dielectric layer 13...Ku Rad layer 13a...Slope 13b...Protrusion 13c...Top surface 13p...Peak 14...Waveguide layer 14A...Active layer 14a...End surface 15...Clad layer 16...Heater layer 16a...End 17...Coating layer 18...Coating layer 19...Heat resistance layer 20...DBR section 20S...SG-DBR section 21...diffraction grating layer 21a...end 30...phase adjustment section 40...gain section 50...connection section 60...ring resonator C...coupling section d...(narrowed section) width L...laminated body Lg, Lh, Ls...length H...(cladding layer) thickness Hp...peak height OF...orientation flat OP...opening WF...wafer Wm...(coating layer) width Wp...(protruding section) protrusion height X, X20, X30, X60...direction (second direction)
Y direction (third direction)
Z…direction (first direction)
α: Inward tilt angle θ: Angle difference

Claims (16)

A base having a base surface intersecting a first direction which is a crystal orientation [100] direction;
a mesa protruding from the base surface in the first direction, extending along the base surface, having an end face in the first direction, a cladding layer, and a waveguide layer, and having a cavity partially provided therein ;
a heater layer provided on the end surface and generating heat when supplied with electric power ;
a coating layer covering the base surface, the coating layer being made of a material on which the cladding layer does not epitaxially grow;
having
the waveguide layer is 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,
the cladding layer is provided between the base surface and the waveguide layer and between the waveguide layer and the end surface,
the cavity portion includes a groove that faces a side of the coating layer opposite to the base surface , is V-shaped in the first direction, and extends in a second direction intersecting the first direction;
The second direction obliquely intersects with a [011] crystal orientation of the base at an angle of 45° or less. The optical semiconductor device according to claim 1, wherein the absolute value of the angle difference is in a direction between 10° and 45°. The optical semiconductor device according to claim 1 , wherein the cavity has a bottom surface located at an end of the cavity in a direction opposite to the first direction and extending in the second direction intersecting the first direction. 4. The optical semiconductor device according to claim 1 , wherein the mesa has a first section extending in the second direction and in which the cavity is provided . 5. The optical semiconductor device according to claim 1 , wherein the mesa has a second section extending along the base surface in a direction intersecting the second direction and in which the cavity is provided . 6. The optical semiconductor device according to claim 1 , wherein the mesa is provided with a plurality of cavities arranged in a third direction intersecting the first direction and the second direction as the cavity. the mesa has two side surfaces as an end surface in the third direction and an end surface in a direction opposite to the third direction;
The optical semiconductor device according to claim 6 , wherein the cavity includes a cavity that is open in the third direction on each of the two side surfaces. 8. The optical semiconductor device according to claim 1 , wherein the cavity includes a closed cavity within the mesa. 9. The optical semiconductor device according to claim 1, further comprising a thermal resistance layer having a lower thermal conductivity than an adjacent portion at a position on the mesa opposite to the heater layer with respect to the waveguide layer and aligned with the cavity in the first direction. 10. The optical semiconductor device according to claim 1, further comprising a thermal resistance layer having a lower thermal conductivity than an adjacent portion at a position on the opposite side of the mesa from the heater layer with respect to the waveguide layer and aligned with the cavity in a third direction intersecting the first direction and the second direction. The optical semiconductor device according to claim 10 , wherein the thermal resistance layers are located on both sides of the cavity in the third direction. 12. The optical semiconductor device according to claim 1 , wherein the mesa has a diffraction grating layer extending along the waveguide layer. the mesa has a grating layer extending along the waveguide layer;
5. The optical semiconductor device according to claim 4, wherein the cavity is provided such that both ends of the cavity in the second direction overlap both ends of the diffraction grating layer in the second direction in the first direction, or such that the cavity protrudes beyond the diffraction grating layer on both sides in the second direction. a base having a base surface intersecting the first direction;
a mesa protruding from the base surface in the first direction, extending along the base surface, having an end face in the first direction, a cladding layer, and a waveguide layer, and having a cavity partially provided therein ;
a heater layer provided on the end surface and generating heat when supplied with electric power ;
a coating layer covering the base surface, the coating layer being made of a material on which the cladding layer does not epitaxially grow;
having
the waveguide layer is 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,
the cladding layer is provided between the base surface and the waveguide layer and between the waveguide layer and the end surface,
The cavity portion faces the side of the covering layer opposite the base surface, and includes a groove that is V-shaped in the first direction and extends in a second direction intersecting the first direction. 15. The optical semiconductor device according to claim 1, wherein the base and the mesa are made of a III-V group semiconductor having a zinc blende structure. A method for manufacturing an optical semiconductor device according to any one of claims 1 to 15,
providing the coating layer on the base surface ;
forming a laminate by epitaxial growth of crystal grains on the base surface in the first direction;
removing a portion of the laminate to form the mesa;
forming the heater layer on the end surface of the mesa;
having
The method for manufacturing an optical semiconductor device, wherein the cavity is formed inside the laminate in the step of forming the laminate.

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