JP2013191589A - Semiconductor device and manufacturing method of the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To achieve a diffraction grating having a large coupling constant with good controllability by suppressing composition non-uniformity of an AlGaAs layer while suppressing mass transport of a GaAs layer to ensure a refractive index difference of the diffraction grating in which regions having different refractive indexes are alternately arranged.SOLUTION: A semiconductor device comprises a diffraction grating 6X including a first region 6Y and a second region 6Z having a refractive index higher than that of the first region which are alternately arranged. The first region includes a first AlGaAs layer 6D. The second region includes: a GaAs layer 6A; a second AlGaAs layer 6B having a refractive index lower than that of the first AlGaAs layer; and a third AlGaAs layer 6C which is provided on the second AlGaAs layer and which has a refractive index higher than that of the second AlGaAs layer.

Description

  The present invention relates to a semiconductor device and a manufacturing method thereof.

Conventionally, in the field of optoelectronics, diffraction gratings are used in optical elements (optical circuit elements) such as filters, optical couplers, distributed feedback (DFB) lasers, and distributed Bragg reflector (DBR) lasers. It is used.
In particular, in semiconductor lasers such as DFB lasers and DBR lasers, the diffraction grating is used for wavelength control or wavelength tuning, so parameters such as the diffraction grating period, shape, depth, refractive index difference, coupling constant, etc. This greatly affects laser characteristics such as the threshold. For this reason, it is important to manufacture a highly accurate diffraction grating with good controllability.

  For example, after forming a concavo-convex structure on the surface of a GaAs layer, the concavo-convex structure is embedded with an AlGaAs layer to produce a diffraction grating. Further, for example, after dividing the GaAs layer into a thin line shape, the diffraction grating is fabricated by embedding the GaAs layer with an AlGaAs layer. In this way, a diffraction grating is manufactured by embedding GaAs layers periodically provided at intervals from each other with an AlGaAs layer.

L. Hoffmann et al., “Patterned growth of (AlGa) As using metalorganic vapor-phase epitaxy”, Journal of Crystal Growth 206 (1999) 255-262

  By the way, when the GaAs layer constituting the diffraction grating is exposed to a high temperature, mass transport occurs, and its shape and thickness, that is, the shape and depth of the diffraction grating change, so that it is difficult to control the coupling constant. It is. For this reason, in order to suppress the mass transport of the GaAs layer when the GaAs layer is buried with the AlGaAs layer to form the diffraction grating, it is necessary to set the growth temperature to a low temperature of about 650 ° C. or less.

On the other hand, when the AlGaAs layer is grown at a low temperature of about 650 ° C. or lower, the compositional nonuniformity of the AlGaAs layer occurs.
Here, if the composition of the AlGaAs layer in which the GaAs layer is embedded is uniform, the AlGaAs layer formed above the GaAs layers periodically provided with a space therebetween does not constitute a part of the diffraction grating. That is, a diffraction grating is constituted by GaAs layers periodically provided at intervals and an AlGaAs layer formed between these GaAs layers.

However, when the compositional nonuniformity occurs in the AlGaAs layer that embeds the GaAs layer, and the AlGaAs layer above the GaAs layer and the AlGaAs layer above the GaAs layer have different compositions, these portions also This constitutes a part of the diffraction grating.
The Al composition of the AlGaAs layer is increased and the refractive index is lowered above the GaAs layers periodically provided at intervals, and the Al composition of the AlGaAs layer is decreased between the GaAs layers and the GaAs layers. The refractive index increases.

Therefore, when an AlGaAs layer is provided in the first region, a GaAs layer is provided in the second region, and a diffraction grating having alternating first regions and second regions having a higher refractive index than the first region is configured. In addition, an AlGaAs layer having a lower refractive index than the AlGaAs layer in the first region is included in the second region where the refractive index is desired to be increased.
As a result, the refractive index difference between the first region and the second region constituting the diffraction grating becomes small, and the coupling constant becomes small.

  As described above, when the AlGaAs layer is grown at a low temperature of about 650 ° C. or less, the refractive index difference is reduced in the regions having different refractive indexes constituting the diffraction grating, and the coupling constant is reduced. For this reason, when the diffraction grating is formed by embedding the GaAs layer with the AlGaAs layer, it is necessary to increase the growth temperature to about 700 ° C. or higher in order to suppress nonuniform composition of the AlGaAs layer.

  As described above, when the growth temperature is set to a low temperature of about 650 ° C. or less in order to suppress mass transport of the GaAs layer, nonuniform composition of the AlGaAs layer occurs and the coupling constant decreases. On the other hand, if the growth temperature is set to a high temperature of about 700 ° C. or higher in order to suppress the compositional non-uniformity of the AlGaAs layer, mass transport of the GaAs layer occurs and it becomes difficult to control the coupling constant.

  Therefore, by suppressing the mass transport of the GaAs layer and suppressing the compositional nonuniformity of the AlGaAs layer and ensuring the refractive index difference of the diffraction grating having alternating regions having different refractive indexes, it has a large coupling constant. I want to realize a diffraction grating with good controllability.

  The semiconductor device includes a diffraction grating having alternatingly first regions and second regions having a higher refractive index than the first region, the first region includes a first AlGaAs layer, and the second region includes GaAs. And a second AlGaAs layer provided on the GaAs layer and having a lower refractive index than the first AlGaAs layer, and a third AlGaAs layer provided on the second AlGaAs layer and having a higher refractive index than the second AlGaAs layer. And

  The manufacturing method of the semiconductor device includes a step of forming a diffraction grating having first regions and second regions having a higher refractive index than the first region, and the diffraction grating formation step is spaced apart from each other. The method includes a step of forming a periodically provided GaAs layer and a step of forming an AlGaAs layer that embeds the GaAs layer, and the AlGaAs layer forming step is performed to cover the GaAs layer at a temperature that can suppress mass transport. It is necessary to include a step of forming an AlGaAs layer and a step of forming an upper AlGaAs layer on the lower AlGaAs layer at a temperature capable of suppressing nonuniform composition.

  Therefore, according to the semiconductor device and the manufacturing method thereof, the refractive index difference of the diffraction grating having alternating regions having different refractive indexes while suppressing the mass transport of the GaAs layer and suppressing the nonuniform composition of the AlGaAs layer. By securing the above, there is an advantage that a diffraction grating having a large coupling constant can be realized with good controllability.

It is a typical sectional view showing the composition of the diffraction grating with which the semiconductor device concerning a 1st embodiment is equipped. 1 is a schematic perspective view showing a configuration of a semiconductor device according to a first embodiment. It is typical sectional drawing which shows the structure of the diffraction grating of a comparative example. (A)-(C) are typical sectional drawings for demonstrating the formation method of the diffraction grating with which the semiconductor device concerning 1st Embodiment is equipped. (A)-(E) are typical sectional drawings for demonstrating the manufacturing method of the semiconductor device concerning 1st Embodiment, Comprising: It is sectional drawing seen from the [-110] direction. It is typical sectional drawing for demonstrating the manufacturing method of the semiconductor device concerning 1st Embodiment, Comprising: It is sectional drawing seen from the [-110] direction. (A), (B) is typical sectional drawing for demonstrating the manufacturing method of the semiconductor device concerning 1st Embodiment, Comprising: It is sectional drawing seen from the [110] direction. It is typical sectional drawing for demonstrating the manufacturing method of the semiconductor device concerning 1st Embodiment, Comprising: It is sectional drawing seen from the [110] direction. It is a typical perspective view which shows the structure of the semiconductor device concerning 2nd Embodiment. (A), (B) is typical sectional drawing for demonstrating the manufacturing method of the semiconductor device concerning 2nd Embodiment, Comprising: It is sectional drawing seen from the [-110] direction.

Hereinafter, a semiconductor device and a manufacturing method thereof according to an embodiment of the present invention will be described with reference to the drawings.
[First Embodiment]
First, the semiconductor device and the manufacturing method thereof according to the first embodiment will be described with reference to FIGS.

  The semiconductor device according to this embodiment includes a semiconductor laser such as a DFB laser or a DBR laser. Therefore, in the present semiconductor device, as shown in FIG. 1, a GaAs layer 6A periodically provided at intervals is buried with AlGaAs layers 6B, 6C, and 6D, and the first region 6Y and the first region 6Y A diffraction grating 6X having alternating second regions 6Z having a refractive index higher than that of the first region 6Y is provided. Note that the semiconductor device is also referred to as an optical semiconductor element.

Hereinafter, the first region 6Y and the second region 6Z having a higher refractive index than the first region 6Y are formed by embedding the concavo-convex structure formed on the surface of the GaAs layer 5 with the AlGaAs layers 6B, 6C, and 6D. A description will be given by taking a DFB laser including diffraction gratings 6X alternately provided as an example.
As shown in FIG. 2, the DFB laser has an n-GaAs substrate 1, an n-GaAs buffer layer 2, an n-AlGaAs lower cladding layer 3, an active layer 4, a p-GaAs layer 5, and a p-GaAs / p. A semiconductor laminated structure in which an AlGaAs diffraction grating layer 6, a p-AlGaAs upper cladding layer 7 and a p-GaAs contact layer 8 are laminated. For this reason, the diffraction grating 6X is provided in the semiconductor multilayer structure (laser element).

Here, the n-AlGaAs lower cladding layer 3 has, for example, an Al composition of about 0.30.
The p-AlGaAs upper cladding layer 7 has an Al composition of about 0.35, for example. The material of the upper cladding layer 7 is not limited to AlGaAs, and for example, InGaP may be used. For example, InGaP having an In composition of 0.48, which is a lattice matching composition, may be used.

  Further, as will be described later, the p-GaAs / p-AlGaAs diffraction grating layer 6 has a concavo-convex structure formed on the surface of the p-GaAs layer 5 having a two-layer structure at least above the convex portion 6A. It is formed by embedding with layers 6B, 6C, 6D. That is, the p-GaAs / p-AlGaAs diffraction grating layer 6 has p-AlGaAs layers 6B and 6C having a two-layer structure on the p-GaAs layer 5 having a concavo-convex structure formed on the surface at least above the convex portion 6A. , 6D are laminated.

Specifically, as shown in FIG. 1, a p-AlGaAs layer (p-Al _0.15 Ga ₀ having an Al composition of 0.15) is formed on the concave portion of the concavo-convex structure formed on the surface of the p-GaAs layer 5. _.85 As layer) 6D is formed. Further, a p-AlGaAs layer (p-Al _0.35 Ga _0.65 As layer) 6B having an Al composition of 0.35 is formed on the projection 6A having a concavo-convex structure formed on the surface of the p-GaAs layer 5; A p-AlGaAs layer (p-Al _0.27 Ga _0.73 As layer) 6C having an Al composition of 0.27 is laminated to form p-AlGaAs layers 6B and 6C having a two-layer structure. That is, the first region 6Y including the p-Al _0.15 Ga _0.85 As layer 6D on the p-GaAs layer 5, the convex portion 6A of the p-GaAs layer 5, p-Al _0.35 Ga _0. A p-GaAs / p-AlGaAs diffraction grating layer 6 including diffraction gratings 6X alternately having ₆₅ As layers 6B and second regions 6Z including p-Al _0.27 Ga _0.73 As layers 6C is provided.

As described above, the present DFB laser includes the first region 6Y including the p-Al _0.15 Ga _0.85 As layer 6D, the p-GaAs layer (convex portion) 6A, and the p-GaAs layer (convex portion) 6A. P-Al _0.35 Ga _0.65 As layer 6B provided on the p-Al _0.35 Ga _0.65 As layer 6B and p-Al _0.27 Ga _0.73 As layer provided on the p-Al _0.35 Ga _0.65 As layer 6B The diffraction grating 6X which has the 2nd area | region 6Z provided with 6C alternately is provided.

The p-Al _0.15 Ga _0.85 As layer 6D is referred to as a first AlGaAs layer, the p-Al _0.35 Ga _0.65 As layer 6B is referred to as a second AlGaAs layer or a lower AlGaAs layer, and p-Al ₀ the _.27 Ga _0.73 as layer 6C of the 3AlGaAs layer or upper AlGaAs layer.
Here, the p-Al _0.15 Ga _0.85 As layer 6D has a refractive index of about 3.38. The p-GaAs layer (convex portion) 6A has a refractive index of about 3.50. The p-Al _0.35 Ga _0.65 As layer 6B has a refractive index of about 3.30. The p-Al _0.27 Ga _0.73 As layer 6C has a refractive index of about 3.34. Thus, the lower AlGaAs layer 6B (p-Al _0.35 Ga _0.65 As layer) in the second region 6Z is the AlGaAs layer 6D (p-Al _0.15 Ga _0.85 As layer in the first region 6Y. ) Has a higher Al composition and a lower refractive index. Further, the upper AlGaAs layer 6C (p-Al _0.27 Ga _0.73 As layer) in the second region 6Z has an Al composition higher than that of the lower AlGaAs layer 6B (p-Al _0.35 Ga _0.65 As layer). Low and high refractive index. That is, the second region 6Z is provided on the GaAs layer (convex portion) 6A and the GaAs layer (convex portion) 6A, and on the second AlGaAs layer 6B and the second AlGaAs layer 6B having a refractive index lower than that of the first AlGaAs layer 6D. And a third AlGaAs layer 6C having a higher refractive index than the second AlGaAs layer 6B.

In this case, since the first region 6Y is composed of the p-Al _0.15 Ga _0.85 As layer 6D, the refractive index of the first region 6Y is the refraction of the p-Al _0.15 Ga _0.85 As layer 6D. The rate is about 3.38.
The second region 6Z is composed of a p-GaAs layer (convex portion) 6A, a p-Al _0.35 Ga _0.65 As layer 6B, and a p-Al _0.27 Ga _0.73 As layer 6C. The refractive index of the two regions 6Z is the average refractive index of the refractive indexes of the layers 6A to 6C. That is, the refractive index of the second region 6Z is such that the p-GaAs layer (convex portion) 6A having a thickness of about 30 nm, the p-Al _0.35 Ga _0.65 As layer 6B having a thickness of about 5 nm, and the thickness of about 35 nm. In consideration of the ratio of the thickness of each layer 6A to 6C to the total thickness (about 70 nm) of the p-Al _0.27 Ga _0.73 As layer 6C, it can be obtained by the following formula, and about 3.41 is there.
(3.50 × 30/70) + (3.30 × 5/70) + (3.34 × 35/70)
As described above, the DFB laser includes the diffraction grating 6X having first regions 6Y having a refractive index of about 3.38 and second regions 6Z having a higher refractive index of about 3.41. . In this case, the refractive index difference between the first region 6Y and the second region 6Z is about 0.03.

  Here, when the duty ratio of the diffraction grating 6X is about 50%, the coupling constant κ can be obtained by the following equation (1).

Here, n ₁ and n ₂ are the refractive indexes of the second region 6Z and the first region 6Y of the diffraction grating 6X (n ₁ > n ₂ ). Γ grating is a ratio of light intensity in the diffraction grating region, that is, a light confinement coefficient. Λ is the wavelength of the guided light. N _eq is the equivalent refractive index of the guided light.
For example, λ = about 1064 nm, n _eq = about 3.33, Γ grating = about 0.04, the refractive index n ₁ of the second region 6Z described above is about 3.41, and the refractive index n ₂ of the first region 6Y = Substituting approximately 3.38 results in a coupling constant κ of approximately 23.

Here, for example, the configuration of the comparative example as shown in FIG. 3, that is, the p-Al _0.27 Ga _0.73 As layer 6C is not provided, and the p-Al _0.35 Ga _0.65 As layer 6B is not provided. Regarding the configuration in which the thickness is increased, the difference in refractive index between the first region 6Y and the second region 6Z and the coupling constant are determined.
In such a comparative example, the refractive index of the first region 6Y is the refractive index of the p-Al _0.15 Ga _0.85 As layer 6D, which is about 3.38. In addition, since the second region 6Z includes a p-GaAs layer (convex portion) 6A and a p-Al _0.35 Ga _0.65 As layer 6B, the refractive index of the second region 6Z is the refraction of each layer 6A, 6B. The average refractive index of the index. That is, the refractive index of the second region 6Z is the total thickness of the p-GaAs layer (convex portion) 6A having a thickness of about 30 nm and the p-Al _0.35 Ga _0.65 As layer 6B having a thickness of about 40 nm ( In consideration of the ratio of the thickness of each layer 6A, 6B to about 70 nm), it can be obtained by the following equation, which is about 3.39.
(3.50 × 30/70) + (3.30 × 40/70)
In this manner, the diffraction grating 6X has first regions 6Y having a refractive index of about 3.38 and second regions 6Z having a higher refractive index of about 3.39. In this case, the difference in refractive index between the first region 6Y and the second region 6Z is about 0.01.

Further, the coupling constant κ can be obtained by the above formula (1). For example, λ = about 1064 nm, n _eq = about 3.33, Γ grating = about 0.04, and the refractive index of the second region 6Z described above. Substituting n ₁ = about 3.39 and the refractive index n ₂ of the first region 6Y = about 3.38, the coupling constant κ is about 8.
As described above, by adopting the configuration of the above-described embodiment, the difference in refractive index between the first region 6Y and the second region 6Z can be increased as compared with the comparative example, thereby the coupling constant κ. Can be increased. As a result, laser characteristics such as an oscillation threshold can be improved.

By the way, in the present DFB laser, as shown in FIG. 2, the p-GaAs contact layer 8 and the p-AlGaAs upper clad layer 7 are processed into a ridge shape. That is, the DFB laser includes a ridge structure 12 including a p-GaAs contact layer 8 and a p-AlGaAs upper cladding layer 7.
In the present DFB laser, the surface is covered with the SiO ₂ passivation film 9 having an opening above the ridge structure 12.

In the present DFB laser, a p-side electrode 10 is provided on the ridge structure 12 and the SiO ₂ passivation film 9, and an n-side electrode 11 is provided on the back surface of the n-GaAs substrate 1.
Next, a method for manufacturing the semiconductor device according to the present embodiment will be described with reference to FIG.

  That is, in the method for manufacturing the semiconductor device, as shown in FIGS. 4A to 4C, the first regions 6Y and the second regions 6Z having a higher refractive index than the first regions 6Y are alternately formed. Forming a diffraction grating 6X. As shown in FIG. 4A, this diffraction grating forming step includes a step of forming GaAs layers (here, convex portions) 6A provided periodically and spaced apart from each other, and FIG. 4C, forming AlGaAs layers 6B to 6D for embedding the GaAs layer (convex portion) 6A. Among these, as shown in FIG. 4B, the AlGaAs layer forming step is performed at a temperature lower than about 650 ° C. so as to cover the GaAs layer (convex portion) 6A at a temperature at which mass transport can be suppressed. The step of forming the AlGaAs layer 6L (6B, 6D) and the upper portion of the upper AlGaAs layer 6L on the lower AlGaAs layer 6L at a temperature at which compositional non-uniformity can be suppressed, that is, at a temperature of about 700 ° C. Forming an AlGaAs layer 6U (6C, 6D).

Hereinafter, a DFB laser including a diffraction grating 6X formed by embedding a concavo-convex structure formed on the surface of a GaAs layer 5 with AlGaAs layers 6B to 6D in a semiconductor multilayer structure formed on a GaAs substrate 1 will be described as an example. Will be described in detail with reference to FIGS.
Here, the case of using a metal organic chemical vapor deposition (MOCVD) method as an example of the crystal growth method will be described as an example. However, the present invention is not limited to this. For example, molecular beam epitaxy ( Molecular Beam Epitaxy (MBE) method or the like may be used.

First, as shown in FIG. 5A, an n-GaAs buffer layer 2, an n-AlGaAs lower cladding layer 3, an active layer 4, and a p-GaAs layer are formed on an n-GaAs substrate 1 by using, for example, the MOCVD method. 20 is formed.
Here, the n-GaAs buffer layer 2 has a thickness of, for example, about 0.3 μm. The n-AlGaAs lower cladding layer 3 has a thickness of about 2 μm, for example, and an Al composition of about 0.30, for example. The active layer 4 is, for example, an InGaAs / GaAs multiple quantum well (MQW) active layer. The p-GaAs layer 20 has a thickness of about 50 nm, for example.

Next, as shown in FIGS. 5B to 5E, a p-GaAs / p-AlGaAs diffraction grating layer 6 is formed. In addition, this process is a process of forming the diffraction grating 6X which has the 1st area | region 6Y and the 2nd area | region 6Z whose refractive index is higher than the 1st area | region 6Y by turns.
Here, first, as shown in FIG. 5B and FIG. 5C, an uneven structure is formed on the surface of the p-GaAs layer 20.

That is, as shown in FIG. 5B, after forming a SiO ₂ film on the entire surface and applying a photoresist, the resist pattern 21 is used by, for example, an electron beam (EB) exposure method or an interference exposure method. Then, the SiO ₂ stripe pattern 22 is formed.
Next, after the photo pattern 21 is removed, the p-GaAs layer 20 is etched to a desired depth by using the SiO ₂ stripe pattern 22 as an etching mask, and as shown in FIG. An uneven structure is formed on the surface of 20. Thereafter, the SiO ₂ stripe pattern 22 is removed.

  In this case, for example, an uneven structure is formed on the surface of the p-GaAs layer 20 by etching from the surface side of the p-GaAs layer 20 to a depth of about 30 nm using an ammonia-based etchant. In this way, the p-GaAs layer 5 having a thickness of about 20 nm and the convex portion (p-GaAs layer) 6A provided on the p-GaAs layer 5 are formed. In this case, the protrusions 6 </ b> A formed on the surface of the p-GaAs layer 5 are periodically provided at intervals. For this reason, this step is a step of forming GaAs layers (in this case, convex portions) 6A that are periodically provided at intervals. Further, the convex portion 6A formed on the surface of the p-GaAs layer 5 constitutes a diffraction grating 6X as will be described later. For this reason, the diffraction grating forming step includes this step.

Next, as shown in FIGS. 5D and 5E, p-AlGaAs layers 6L and 6U are grown (regrown) on the p-GaAs layers 5 and 6A by using, for example, the MOCVD method. That is, the concavo-convex structure formed on the surface of the p-GaAs layer 5 is buried with the p-AlGaAs layers 6B to 6D having a two-layer structure at least above the convex portion 6A.
This step is a step of forming AlGaAs layers 6B to 6D for embedding GaAs layers (here, convex portions) 6A provided periodically and spaced from each other. Further, the buried AlGaAs layers 6B to 6D constitute a diffraction grating 6X as described later. For this reason, the diffraction grating forming step includes this step.

  Here, first, at a temperature at which mass transport can be suppressed, that is, at a temperature at which changes in the shape and thickness of the GaAs layer due to mass transport, that is, changes in the shape and depth of the diffraction grating can be suppressed, FIG. As shown in (D), a p-AlGaAs layer 6L as a lower AlGaAs layer is formed so as to cover the p-GaAs layers 5 and 6A. That is, the p-AlGaAs layer 6L as the lower AlGaAs layer is formed so as to cover the p-GaAs layers 5 and 6A at a temperature of about 650 ° C. or less. The p-AlGaAs layer 6L as the lower AlGaAs layer functions as a protective layer for suppressing changes in the shape and thickness of the GaAs layer due to mass transport, that is, changes in the shape and depth of the diffraction grating. Also referred to as an AlGaAs protective layer or an AlGaAs coating layer. The temperature at which mass transport can be suppressed is a temperature at which thermal deformation of the GaAs layer, that is, thermal deformation of the diffraction grating can be suppressed.

  Next, at a temperature at which compositional nonuniformity can be suppressed, that is, at a temperature at which nonuniform composition of the AlGaAs layer can be suppressed, as shown in FIG. 5E, on the p-AlGaAs layer 6L as the lower AlGaAs layer, A p-AlGaAs layer 6U is formed as an upper AlGaAs layer. That is, the p-AlGaAs layer 6U as the upper AlGaAs layer is formed on the p-AlGaAs layer 6L as the lower AlGaAs layer at a temperature of about 700 ° C. or higher.

  More specifically, first, a source supply ratio of Al and Ga (Al supply composition) for forming an AlGaAs layer having an Al composition of, for example, about 0.25 at a growth temperature of, for example, 640 ° C. using, for example, the MOCVD method. As shown in FIG. 5D, for example, a p-AlGaAs layer 6L having a thickness of about 5 nm is formed as the lower AlGaAs layer. Note that the Al supply composition of about 0.25 is a raw material supply ratio of Al and Ga that forms an AlGaAs layer with an Al composition of about 0.25 when an AlGaAs layer is formed on a flat surface without unevenness. .

In this case, since the growth temperature is low at about 640 ° C., changes in the shape and thickness of the GaAs layer due to mass transport, that is, changes in the shape and depth of the diffraction grating can be suppressed. Further, since the growth temperature is low at about 640 ° C., the p-AlGaAs layer 6L as the lower AlGaAs layer has a non-uniform composition. That is, in the p-AlGaAs layer 6L as the lower AlGaAs layer, a portion formed in the recess is a p-Al _0.15 Ga _0.85 As layer, and this portion is a p-Al _0.15 Ga _0.85 As layer. A portion formed on the convex portion 6A as a part of 6D becomes a p-Al _0.35 Ga _0.65 As layer, and this portion becomes a p-Al _0.35 Ga _0.65 As layer 6B. As described above, the p-AlGaAs layer (p-Al _0.15 Ga _0.85 As layer) 6D having an Al composition of about 0.15 is formed on the concave portion of the concavo-convex structure formed on the surface of the p-GaAs layer 5. A part is formed, and an AlGaAs layer (p-Al _0.35 Ga _0.65 As layer) 6B having an Al composition of about 0.35 is formed on the convex portion 6A.

Subsequently, for example, the temperature is raised from about 640 ° C. to about 700 ° C. while supplying AsH ₃ , for example.
In this case, the p-AlGaAs layer 6B formed on the concavo-convex convex portion 6A formed on the surface of the p-GaAs layer 5 is a p-Al _0.35 Ga _0.65 As layer and has an Al composition. Made of material that is high and difficult to mass transport. For this reason, changes in the shape and depth of the diffraction grating due to the mass transport can be suppressed. That is, by utilizing the compositional non-uniformity generated by growing the p-AlGaAs layer at a low temperature of about 640 ° C., the p-GaAs layer 5 has a high Al composition and is difficult to mass transport on the convex portion 6A. By forming the AlGaAs layer 6B, the shape and depth of the diffraction grating can be maintained even when the temperature is raised to a high temperature of about 700 ° C., and the coupling constant can be easily controlled. In this way, AlGaAs is hard to be mass transported so as to cover the GaAs layer (here, the convex portion) 6A at a temperature (about 640 ° C. here) that can suppress a change in the shape and thickness of the GaAs layer due to mass transport. By forming the layer 6B and maintaining the shape and depth of the diffraction grating even after the temperature rises, the controllability of the coupling constant is improved.

  After the temperature is raised in this manner, the raw material supply ratio (Al supply composition) for forming an AlGaAs layer having an Al composition of about 0.25, for example, at a growth temperature of about 700 ° C., for example, using MOCVD, for example. As shown in FIG. 5E, for example, a p-AlGaAs layer 6U having a thickness of about 40 nm is formed as the upper AlGaAs layer. That is, the concavo-convex structure formed on the surface of the p-GaAs layer 5 and the p-AlGaAs layer as the upper AlGaAs layer so as to embed the p-AlGaAs layer 6L as the lower AlGaAs layer covering the surface of the concavo-convex structure. Layer 6U is formed. Thereby, the concavo-convex structure formed on the surface of the p-GaAs layer 5 is planarized.

  Here, the Al and Ga source supply ratio for forming the lower AlGaAs layer 6L is the same as the Al and Ga source supply ratio for forming the upper AlGaAs layer 6U. That is, the raw material supply ratio of Al and Ga when forming the lower AlGaAs layer 6L at a temperature of about 650 ° C. or lower, and the raw material supply ratio of Al and Ga when forming the upper AlGaAs layer 6U at a temperature of about 700 ° C. or higher. Is the same.

In this case, since the growth temperature is high at about 700 ° C., the p-AlGaAs layer 6U as the upper AlGaAs layer has a suppressed compositional nonuniformity. That is, in the p-AlGaAs layer 6U as the upper AlGaAs layer, the concave portion and the portion formed above the concave portion are p-Al _0.15 Ga _0.85 As layers, and this portion is p-Al _0.15 Ga _0. The remaining portion of the ₈₅ As layer 6D, the portion formed above the convex portion 6A is a p-Al _0.27 Ga _0.73 As layer, and this portion is the p-Al _0.27 Ga _0.73 As layer. 6C. Thus, on a part of the p-Al _0.15 Ga _0.85 As layer 6D in the concave portion of the concavo-convex structure formed on the surface of the p-GaAs layer 5, the p-type having an Al composition of about 0.15 The remaining part of the AlGaAs layer (p-Al _0.15 Ga _0.85 As layer) 6D is formed, and on the p-Al _0.35 Ga _0.65 As layer 6B formed on the convex portion 6A, Al An AlGaAs layer (p-Al _0.27 Ga _0.73 As layer) 6C having a composition of about 0.27 is formed.

In this way, by increasing the growth temperature to 700 ° C. or higher, the surface migration of Ga atoms is promoted, the incorporation of Ga atoms in the (311) A plane, which is the main growth surface of the recesses, is suppressed, and the projections 6A By reducing the difference from the incorporation of Ga atoms in the (001) plane, which is the main growth plane, the compositional nonuniformity of the AlGaAs layer can be suppressed.
The p-AlGaAs layer 6U as the upper AlGaAs layer may be grown until it is uniform with an Al composition of about 0.25. In this case, the p-AlGaAs layer in a region uniform with an Al composition of about 0.25 does not constitute a diffraction grating. Therefore, the semiconductor multilayer structure constituting the DFB laser has a p-AlGaAs layer (p-Al _0.25 Ga ₀ ...) Between the p-GaAs / p-AlGaAs diffraction grating layer 6 and the p-AlGaAs upper cladding layer 7 _{. 75} As layer).

As described above, the p-Al _0.15 Ga _0.85 As layer 6D is formed on the concave portion of the concavo-convex structure formed on the surface of the p-GaAs layer 5, and the p-Al layer is formed on the convex portion 6A. A p-AlGaAs layer having a two-layer structure in which a _0.35 Ga _0.65 As layer 6B and a p-Al _0.27 Ga _0.73 As layer 6C are laminated is formed. That is, the first region 6Y including the p-Al _0.15 Ga _0.85 As layer 6D on the p-GaAs layer 5, the p-GaAs layer (convex portion) 6A, and the p-Al _0.35 Ga _0. A p-GaAs / p-AlGaAs diffraction grating layer 6 including diffraction gratings 6X having ₆₅ As layers 6B and second regions 6Z including p-Al _0.27 Ga _0.73 As layers 6C alternately is formed.

When the upper AlGaAs layer 6U in which the compositional nonuniformity is suppressed as described above is laminated on the lower AlGaAs layer 6L, the Al composition formed on the convex portion 6A of the concavo-convex structure formed on the surface of the p-GaAs layer 5 The p-Al _0.27 Ga _0.73 As layer 6C having a low Al composition is formed on the p-Al _0.35 Ga _0.65 As layer 6B having a high Al. Here, the refractive index of the AlGaAs layer decreases as the Al composition increases. For this reason, p-Al _0.35 having a low refractive index formed to suppress mass transport in the second region 6Z of the diffraction grating 6X that is provided with a GaAs layer (in this case, a convex portion) 6A and that wants to increase the refractive index. A p-Al _0.27 Ga _0.73 As layer 6C having a high refractive index is formed on the Ga _0.65 As layer 6B. Accordingly, by providing the p-Al _0.35 Ga _0.65 As layer 6B to suppress mass transport, the refractive index of the second region 6Z of the diffraction grating 6X is lowered, and the first region 6Y is compared with the first region 6Y. Although the difference in refractive index is reduced and the coupling constant is reduced, the p-Al _0.27 Ga _0.73 As layer 6C is provided to refract the first region 6Y and the second region 6Z of the diffraction grating 6X. It is possible to increase the rate difference and increase the coupling constant.

In the present embodiment, the p-GaAs / p-AlGaAs diffraction grating layer 6 formed as described above includes the first region 6Y having a refractive index of about 3.38 and a refractive index of about 3 higher than that of the first region 6Y. .41 of the second regions 6Z are provided, and the difference in refractive index between the first region 6Y and the second region 6Z is about 0.03. The coupling constant κ is about 23.
On the other hand, in the case of the above-described comparative example (see FIG. 3), the diffraction grating 6X is formed as follows. That is, the growth temperature is set to about 650 ° C. or lower (for example, about 640 ° C.) to suppress mass transport, and the Al / Ga raw material supply ratio (Al supply composition) for forming an AlGaAs layer having an Al composition of about 0.25, for example. About 0.25), one p-AlGaAs layer is grown on the p-GaAs layer 5, and the uneven structure formed on the surface of the p-GaAs layer 5 is buried with one p-AlGaAs layer. The diffraction grating 6X is formed. In this case, since the growth temperature is low at about 650 ° C. or lower (eg, about 640 ° C.), the p-AlGaAs layer has a non-uniform composition. That is, a p-AlGaAs layer (p-Al _0.15 Ga _0.85 As layer) 6D having an Al composition of about 0.15 is formed on the concave portion of the concavo-convex structure formed on the surface of the p-GaAs layer 5. Thus, an AlGaAs layer (p-Al _0.35 Ga _0.65 As layer) 6B having an Al composition of about 0.35 is formed on the convex portion 6A. This phenomenon is due to the fact that Ga atoms undergoing surface migration are preferentially taken into the (311) A plane, which is the main growth surface of the recess, so that the Al composition is lowered on the recess and the Al composition is raised on the projection 6A. Due to that. This comparative example includes a diffraction grating 6X having first regions 6Y having a refractive index of about 3.38 and second regions 6Z having a higher refractive index of about 3.39. The difference in refractive index between the first region 6Y and the second region 6Z is about 0.01. The coupling constant κ is about 8.

Thus, by adopting the manufacturing method of the above-described embodiment, the refractive index difference between the first region 6Y and the second region 6Z can be increased with respect to this comparative example (see FIG. 3). Thereby, the coupling constant κ can be increased. As a result, laser characteristics such as an oscillation threshold can be improved.
Next, as shown in FIG. 6, a p-AlGaAs upper cladding layer 7 and a p-GaAs contact layer 8 are formed on the p-GaAs / p-AlGaAs diffraction grating layer 6 by using, for example, the MOCVD method.

Here, the p-AlGaAs upper cladding layer 7 has a thickness of about 1 μm, for example, and an Al composition of about 0.35, for example. The p-GaAs contact layer 8 has a thickness of about 0.3 μm, for example.
In this way, a semiconductor multilayer structure that constitutes the DFB laser is formed.
Next, as shown in FIG. 7A, an SiO ₂ film 23 having an opening in a region where a groove is to be formed is formed. Thereafter, using the SiO ₂ film 23 as an etching mask, the p-GaAs contact layer 8 and the p-AlGaAs upper cladding layer 7 are subjected to, for example, dry etching or wet etching to form a ridge structure 12 as shown in FIG. Form.

Next, as shown in FIG. 8, the SiO ₂ film 23 is removed, and an SiO ₂ passivation film 9 having an opening above the ridge structure 12 is formed so as to cover the surface.
Thereafter, a p-side electrode 10 (upper electrode) in contact with the p-GaAs contact layer 8 is formed on the ridge structure 12 and the SiO ₂ passivation film 9, and an n-side electrode (lower electrode) is formed on the back surface of the n-GaAs substrate 1. 11 is formed.

In this manner, the semiconductor device according to the present embodiment (here, the DFB laser) can be manufactured.
Therefore, according to the semiconductor device and the manufacturing method thereof according to the present embodiment, the diffraction grating having alternately different regions having different refractive indexes while suppressing the compositional nonuniformity of the AlGaAs layer while suppressing the mass transport of the GaAs layer. By securing the difference in refractive index, it is possible to realize a diffraction grating having a large coupling constant with good controllability.
[Second Embodiment]
Next, a semiconductor device and a manufacturing method thereof according to the second embodiment will be described with reference to FIGS.

In the present embodiment, the two-layer structure having a different composition in the concave portion of the concavo-convex structure formed on the surface of the GaAs layer 5 as shown in FIG. 9 as compared to the one in the first embodiment (see FIG. 2). The difference is that the AlGaAs layers 6D and 6E are provided. That is, the difference is that the first region 6Y of the diffraction grating 6X includes AlGaAs layers 6D and 6E having a two-layer structure having different compositions.
Also, the Al composition of the AlGaAs layer 6C as the upper AlGaAs layer is different among the two-layered AlGaAs layers 6B and 6C formed on the convex portion 6A of the concavo-convex structure formed on the surface of the GaAs layer 5.

Another difference is that the raw material supply ratio of Al and Ga for forming the lower AlGaAs layer 6L is different from the raw material supply ratio of Al and Ga for forming the upper AlGaAs layer 6U.
Specifically, a p-AlGaAs layer (p-Al _0.15 Ga _0.85 As layer) 6D having an Al composition of 0.15 is formed on the concave portion of the concavo-convex structure formed on the surface of the p-GaAs layer 5. A p-AlGaAs layer (p-Al _0.20 Ga _0.80 As layer) 6E having an Al composition of 0.20 is laminated to form p-AlGaAs layers 6D and 6E having a two-layer structure. Further, on the convex portion 6A of the concavo-convex structure formed on the surface of the p-GaAs layer 5, a p-AlGaAs layer (p-Al _0.35 Ga _0.65 As layer) 6B having an Al composition of 0.35, Al A p-AlGaAs layer (p-Al _0.32 Ga _0.68 As layer) 6C having a composition of 0.32 is laminated to form p-AlGaAs layers 6B and 6C having a two-layer structure.

In other words, on the p-GaAs layer _5, a first region 6Y comprising a p-Al _{0.15 Ga 0.85} As layer 6D and _{p-Al 0.20 Ga 0.80} As layer 6E, p-GaAs layer ( Convex portion) p- including diffraction grating 6X having 6A, p-Al _0.35 Ga _0.65 As layer 6B and p-Al _0.32 Ga _0.68 As layer 6C provided alternately with second regions 6Z. A GaAs / p-AlGaAs diffraction grating layer 6 is provided.

As described above, the present DFB laser has the p-Al _0.15 Ga _0.85 As layer 6D and the p-Al _0.20 Ga layer provided on the p-Al _0.15 Ga _0.85 As layer 6D. First region 6Y including _0.80 As layer 6E, p-GaAs layer (convex portion) 6A, and p-Al _0.35 Ga _0.65 As layer provided on p-GaAs layer (convex portion) 6A 6B and a diffraction grating 6X having alternating second regions 6Z each having a p-Al _0.32 Ga _0.68 As layer 6C provided on the p-Al _0.35 Ga _0.65 As layer 6B. Prepare.

The p-Al _0.15 Ga _0.85 As layer 6D is referred to as a first AlGaAs layer or a lower AlGaAs layer, and the p-Al _0.35 Ga _0.65 As layer 6B is referred to as a second AlGaAs layer or a lower AlGaAs layer. The p-Al _0.32 Ga _0.68 As layer 6C is referred to as a third AlGaAs layer or an upper AlGaAs layer, and the p-Al _0.20 Ga _0.80 As layer 6E is referred to as a fourth AlGaAs layer or an upper AlGaAs layer. In this modification, the first region 6Y includes a fourth AlGaAs layer 6E on the first AlGaAs layer 6D.

Here, the p-Al _0.15 Ga _0.85 As layer 6D has a refractive index of about 3.38. The p-Al _0.20 Ga _0.80 As layer 6E has a refractive index of about 3.36. The p-GaAs layer (convex portion) 6A has a refractive index of about 3.50. The p-Al _0.35 Ga _0.65 As layer 6B has a refractive index of about 3.30. The p-Al _0.32 Ga _0.68 As layer 6C has a refractive index of about 3.31.

Thus, the lower AlGaAs layer 6B (p-Al _0.35 Ga _0.65 As layer) in the second region 6Z is the lower AlGaAs layer 6D (p-Al _0.15 Ga _0.85 As in the first region 6Y). Layer) and the upper AlGaAs layer 6E (p-Al _0.20 Ga _0.80 As layer), the Al composition is higher and the refractive index is lower. Further, the upper AlGaAs layer 6C (p-Al _0.32 Ga _0.68 As layer) in the second region 6Z has an Al composition higher than that of the lower AlGaAs layer 6B (p-Al _0.35 Ga _0.65 As layer). Low and high refractive index. That is, the second region 6Z is provided on the GaAs layer (convex portion) 6A and the GaAs layer (convex portion) 6A, and on the second AlGaAs layer 6B and the second AlGaAs layer 6B having a refractive index lower than that of the first AlGaAs layer 6D. And a third AlGaAs layer 6C having a higher refractive index than the second AlGaAs layer 6B.

Also, the upper AlGaAs layer 6E (p-Al _0.20 Ga _0.80 As layer) in the first region 6Y, the upper AlGaAs layer 6C (p-Al _0.32 Ga _0.68 As layer) in the second region 6Z, and The refractive index difference (absolute value) is about 0.05. Further, the lower AlGaAs layer 6D (p-Al _0.15 Ga _0.85 As layer) in the first region 6Y and the lower AlGaAs layer 6B (p-Al _0.35 Ga _0.65 As layer) in the second region 6Z The refractive index difference (absolute value) is about 0.08. That is, the refractive index difference between the third AlGaAs layer 6C and the fourth AlGaAs layer 6E is smaller than the refractive index difference between the first AlGaAs layer 6D and the second AlGaAs layer 6B. In other words, the refractive index difference between the first AlGaAs layer 6D and the second AlGaAs layer 6B is larger than the refractive index difference between the third AlGaAs layer 6C and the fourth AlGaAs layer 6E. The fourth AlGaAs layer 6E has a lower refractive index than the first AlGaAs layer 6D.

In this case, since the first region 6Y is composed of the p-Al _0.15 Ga _0.85 As layer 6D and the p-Al _0.20 Ga _0.80 As layer 6E, the refractive index of the first region 6Y is determined by each layer. The average refractive index is 6D and 6E. That is, the refractive index of the first region 6Y is the total thickness of the p-Al _0.15 Ga _0.85 As layer having a thickness of about 10 nm and the p-Al _0.20 Ga _0.80 As layer having a thickness of about 60 nm. In consideration of the ratio of the thickness of each layer 6D, 6E to the thickness (about 70 nm), it can be obtained by the following equation, which is about 3.36.
(3.38 × 10/70) + (3.36 × 60/70)
The second region 6Z includes a p-GaAs layer (convex portion) 6A, a p-Al _0.35 Ga _0.65 As layer 6B, and a p-Al _0.32 Ga _0.68 As layer 6C. The refractive index of the two regions 6Z is the average refractive index of the refractive indexes of the layers 6A to 6C. That is, the refractive index of the second region 6Z is such that the p-GaAs layer (convex portion) 6A having a thickness of about 30 nm, the p-Al _0.35 Ga _0.65 As layer 6B having a thickness of about 5 nm, and the thickness of about 35 nm. In consideration of the ratio of the thickness of each layer 6A to 6C to the total thickness (about 70 nm) of the p-Al _0.32 Ga _0.68 As layer 6C, it can be obtained by the following formula, and about 3.40 is there.
(3.50 × 30/70) + (3.30 × 5/70) + (3.31 × 35/70)
As described above, the DFB laser according to this modified example has a diffraction grating having first regions 6Y having a refractive index of about 3.36 and second regions 6Z having a higher refractive index of about 3.40. 6X is provided. In this case, the refractive index difference between the first region 6Y and the second region 6Z is about 0.04.

Further, the coupling constant κ can be obtained by the above formula (1). For example, λ = about 1064 nm, n _eq = about 3.33, Γ grating = about 0.04, and the refractive index of the second region 6Z described above. Substituting n ₁ = about 3.40 and the refractive index n ₂ of the first region 6Y = about 3.36, the coupling constant κ is about 30.
Thus, by adopting the configuration of the present embodiment, the refractive index difference between the first region 6Y and the second region 6Z can be increased compared to the above-described comparative example (see FIG. 3). Thus, the coupling constant κ can be increased. As a result, laser characteristics such as an oscillation threshold can be improved.

Since the other details of the configuration are the same as those of the first embodiment described above, the description thereof is omitted here.
Next, a method for manufacturing the semiconductor device according to the present embodiment will be described with reference to FIG.
Here, the p-GaAs / p-AlGaAs diffraction grating layer 6 of the present embodiment described above is formed on the p-GaAs layers 5 and 6A in the specific example of the semiconductor device manufacturing method of the first embodiment described above. A step of growing the AlGaAs layers 6L and 6U, that is, a step of embedding the concavo-convex structure formed on the surface of the p-GaAs layer 5 with p-AlGaAs layers 6B to 6D having a two-layer structure at least above the convex portion 6A [FIG. 5 (D) and FIG. 5 (E)] can be formed by changing as follows.

That is, first, as in the case of the first embodiment described above, a raw material supply ratio (Al supply composition) for forming an AlGaAs layer having an Al composition of about 0.25 at a growth temperature of, for example, 640 ° C. As shown in FIG. 10A, for example, a p-AlGaAs layer 6L having a thickness of about 5 nm is formed as the lower AlGaAs layer.
In this case, since the growth temperature is low at about 640 ° C., changes in the shape and thickness of the GaAs layer due to mass transport can be suppressed. Further, the p-AlGaAs layer 6L as the lower AlGaAs layer has a non-uniform composition. That is, in the p-AlGaAs layer 6L as the lower AlGaAs layer, a portion formed in the recess is a p-Al _0.15 Ga _0.85 As layer, and this portion is a p-Al _0.15 Ga _0.85 As layer. The portion formed on the convex portion 6A becomes a p-Al _0.35 Ga _0.65 As layer, and this portion becomes the p-Al _0.35 Ga _0.65 As layer 6B. Thus, on the concave portions of the concavo-convex structure formed on the surface of the p-GaAs layer 5, p-AlGaAs layer of the Al composition of about _{0.15 (p-Al 0.15 Ga 0.85} As layer) 6D is As a result, an AlGaAs layer (p-Al _0.35 Ga _0.65 As layer) 6B having an Al composition of about 0.35 is formed on the convex portion 6A.

Subsequently, as in the case of the first embodiment described above, the temperature is raised from about 640 ° C. to about 700 ° C., for example.
In this case, the p-AlGaAs layer 6B formed on the concavo-convex convex portion 6A formed on the surface of the p-GaAs layer 5 is a p-Al _0.35 Ga _0.65 As layer and has an Al composition. Made of material that is high and difficult to mass transport. For this reason, changes in the shape and depth of the diffraction grating due to the mass transport can be suppressed.

  After the temperature is raised in this way, the raw material supply ratio (Al supply composition) for forming an AlGaAs layer having an Al composition of about 0.30, for example, at a growth temperature of about 700 ° C., for example, using MOCVD, for example. As shown in FIG. 10B, a p-AlGaAs layer 6U having a thickness of about 40 nm, for example, is formed as an upper AlGaAs layer. That is, the concavo-convex structure formed on the surface of the p-GaAs layer 5 and the p-AlGaAs layer as the upper AlGaAs layer so as to embed the p-AlGaAs layer 6L as the lower AlGaAs layer covering the surface of the concavo-convex structure. Layer 6U is formed. Thereby, the concavo-convex structure formed on the surface of the p-GaAs layer 5 is planarized.

  Here, the Al and Ga raw material supply ratio for forming the lower AlGaAs layer 6L is different from the Al and Ga raw material supply ratio for forming the upper AlGaAs layer 6U. That is, the raw material supply ratio of Al and Ga when forming the lower AlGaAs layer 6L at a temperature of about 650 ° C. or lower, and the raw material supply ratio of Al and Ga when forming the upper AlGaAs layer 6U at a temperature of about 700 ° C. or higher. Is different.

In this case, since the growth temperature is high at about 700 ° C., the p-AlGaAs layer 6U as the upper AlGaAs layer has a suppressed compositional nonuniformity. That is, in the p-AlGaAs layer 6U as the upper AlGaAs layer, the recessed portion and the portion formed above the recessed portion become a p-Al _0.20 Ga _0.80 As layer, and this portion is p-Al _0.20 Ga _{0. 80} As layer 6E becomes a p-Al _0.32 Ga _0.68 As layer, and a portion formed above the convex portion 6A becomes a p-Al _0.32 Ga _0.68 As layer 6C. Thus, on the p-Al _0.15 Ga _0.85 As layer 6D in the concave portion of the concavo-convex structure formed on the surface of the p-GaAs layer 5, the p-AlGaAs layer (p -Al _0.20 Ga _0.80 As layer) and an AlGaAs layer having an Al composition of about 0.32 on the p-Al _0.35 Ga _0.65 As layer 6B formed on the protrusion 6A. (P-Al _0.32 Ga _0.68 As layer) 6C is formed.

In this way, by increasing the growth temperature to 700 ° C. or higher, the surface migration of Ga atoms is promoted, the incorporation of Ga atoms in the (311) A plane, which is the main growth surface of the recesses, is suppressed, and the projections 6A By reducing the difference from the incorporation of Ga atoms in the (001) plane, which is the main growth plane, the compositional nonuniformity of the AlGaAs layer can be suppressed.
In this manner, the p-Al _0.15 Ga _0.85 As layer 6D and the p-Al _0.20 Ga _0.80 As layer 6E are formed on the concave portion of the concave-convex structure formed on the surface of the p-GaAs layer 5. A p-AlGaAs layer having a two-layer structure is formed, and a p-Al _0.35 Ga _0.65 As layer 6B and a p-Al _0.32 Ga _0.68 As layer 6C are formed on the convex portion 6A. A laminated p-AlGaAs layer having a two-layer structure is formed. In other words, on the p-GaAs layer _5, a first region 6Y comprising a p-Al _{0.15 Ga 0.85} As layer 6D and _{p-Al 0.20 Ga 0.80} As layer 6E, p-GaAs layer ( Convex portion) p- including diffraction grating 6X having 6A, p-Al _0.35 Ga _0.65 As layer 6B and p-Al _0.32 Ga _0.68 As layer 6C provided alternately with second regions 6Z. A GaAs / p-AlGaAs diffraction grating layer 6 is formed.

When the upper AlGaAs layer 6U in which the compositional nonuniformity is suppressed as described above is laminated on the lower AlGaAs layer 6L, the Al composition formed on the convex portion 6A of the concavo-convex structure formed on the surface of the p-GaAs layer 5 The p-Al _0.32 Ga _0.68 As layer 6C having a low Al composition is formed on the p-Al _0.35 Ga _0.65 As layer 6B having a high Al. Here, the refractive index of the AlGaAs layer decreases as the Al composition increases. For this reason, p-Al _0.35 having a low refractive index formed to suppress mass transport in the second region 6Z of the diffraction grating 6X that is provided with a GaAs layer (in this case, a convex portion) 6A and that wants to increase the refractive index. A p-Al _0.32 Ga _0.68 As layer 6C having a high refractive index is formed on the Ga _0.65 As layer 6B. Accordingly, by providing the p-Al _0.35 Ga _0.65 As layer 6B to suppress mass transport, the refractive index of the second region 6Z of the diffraction grating 6X is lowered, and the first region 6Y is compared with the first region 6Y. Although the difference in refractive index is reduced and the coupling constant is reduced, the p-Al _0.32 Ga _0.68 As layer 6C is provided to refract the first region 6Y and the second region 6Z of the diffraction grating 6X. It is possible to increase the rate difference and increase the coupling constant.

Further, when the upper AlGaAs layer 6U in which compositional nonuniformity is suppressed as described above is laminated on the lower AlGaAs layer 6L, the Al composition formed on the concave portion of the concavo-convex structure formed on the surface of the p-GaAs layer 5 The p-Al _0.20 Ga _0.80 As layer 6E having a high Al composition is formed on the low p-Al _0.15 Ga _0.85 As layer 6D. Therefore, on the p-Al _0.15 Ga _0.85 As layer 6D formed in the first region 6Y of the diffraction grating 6X whose refractive index is desired to be lowered, the p-Al _0.20 having a lower refractive index than this. A Ga _0.80 As layer 6E is formed. As a result, the refractive index of the first region 6Y of the diffraction grating 6X is lowered, the difference in refractive index between the first region 6Y and the second region 6Z of the diffraction grating 6X can be increased, and the coupling constant can be increased.

In the present embodiment, the p-GaAs / p-AlGaAs diffraction grating layer 6 formed as described above includes the first region 6Y having a refractive index of about 3.36 and a refractive index of about 3 higher than this. The diffraction grating 6X alternately having .40 second regions 6Z is provided, and the difference in refractive index between the first region 6Y and the second region 6Z is about 0.04. The coupling constant κ is about 30.
Thus, by adopting the manufacturing method of the above-described embodiment, the refractive index difference between the first region 6Y and the second region 6Z can be increased compared to the above-described comparative example (see FIG. 3). Thereby, the coupling constant κ can be increased. As a result, laser characteristics such as an oscillation threshold can be improved.

The details of the other manufacturing methods are the same as those in the case of the first embodiment described above, and the description thereof is omitted here.
Therefore, according to the semiconductor device and the manufacturing method thereof according to the present embodiment, as in the case of the first embodiment described above, the compositional nonuniformity of the AlGaAs layer is suppressed while suppressing the mass transport of the GaAs layer. By securing a difference in refractive index between diffraction gratings having alternately different regions having different refractive indexes, there is an advantage that a diffraction grating having a large coupling constant can be realized with good controllability.
[Others]
In addition, this invention is not limited to the structure described in each embodiment mentioned above, A various deformation | transformation is possible in the range which does not deviate from the meaning of this invention.

  For example, in each of the above-described embodiments, a DFB laser including a diffraction grating in which a concavo-convex structure formed on the surface of a GaAs layer is embedded with an AlGaAs layer is described as an example. However, the present invention is not limited to this. Any semiconductor device may be used as long as the semiconductor device includes a diffraction grating in which GaAs layers periodically provided at intervals are embedded with an AlGaAs layer. For example, a DFB laser including a diffraction grating in which a GaAs layer divided into fine lines is embedded with an AlGaAs layer may be used. For example, another semiconductor laser such as a DBR laser may be used.

  In addition, the configuration of the DFB laser of each of the above-described embodiments is merely an example, and may be configured by other materials and structures. For example, a substrate having p-type conductivity may be used. In this case, the conductivity of each layer formed on the substrate is reversed. Further, other substrates such as semi-insulating material may be used. Further, for example, a bulk active layer or a quantum dot active layer may be used as the active layer. Further, for example, a buried structure such as a pn buried structure or a semi-insulating buried structure may be used. A diffraction grating layer may be provided below the active layer.

1 n-GaAs substrate 2 n-GaAs buffer layer 3 n-AlGaAs lower cladding layer 4 active layer 5 p-GaAs layer 6 p-GaAs / p-AlGaAs diffraction grating layer 6A p-GaAs layer (convex portion)
6B p-AlGaAs layer (second AlGaAs layer)
6C p-AlGaAs layer (third AlGaAs layer)
6D p-AlGaAs layer (first AlGaAs layer)
6E p-AlGaAs layer (fourth AlGaAs layer)
6X diffraction grating 6Y first region 6Z second region 6L lower AlGaAs layer (p-AlGaAs layer)
6U Upper AlGaAs layer (p-AlGaAs layer)
7 p-AlGaAs upper cladding layer 8 p-GaAs contact layer 9 SiO ₂ passivation film 10 p-side electrode 11 n-side electrode 12 ridge structure 20 p-GaAs layer 21 resist pattern 22 SiO ₂ stripe pattern 23 SiO ₂ film

Claims (7)

A diffraction grating having alternatingly first regions and second regions having a higher refractive index than the first regions,
The first region comprises a first AlGaAs layer;
The second region is provided on the GaAs layer, the second GaAs layer having a refractive index lower than that of the first AlGaAs layer, and provided on the second AlGaAs layer, and having a refractive index higher than that of the second AlGaAs layer. And a high third AlGaAs layer. The first region includes a fourth AlGaAs layer on the first AlGaAs layer,
2. The semiconductor device according to claim 1, wherein a difference in refractive index between the third AlGaAs layer and the fourth AlGaAs layer is smaller than a difference in refractive index between the first AlGaAs layer and the second AlGaAs layer.   The semiconductor device according to claim 1, wherein the fourth AlGaAs layer has a refractive index lower than that of the first AlGaAs layer. Forming a diffraction grating having alternatingly first regions and second regions having a higher refractive index than the first regions,
The diffraction grating forming step includes a step of forming GaAs layers periodically provided at intervals, and a step of forming an AlGaAs layer for embedding the GaAs layer,
The AlGaAs layer forming step includes a step of forming a lower AlGaAs layer so as to cover the GaAs layer at a temperature capable of suppressing mass transport, and an upper AlGaAs layer on the lower AlGaAs layer at a temperature capable of suppressing compositional non-uniformity. Forming a semiconductor device. A method for manufacturing a semiconductor device, comprising: The temperature capable of suppressing the mass transport is a temperature of 650 ° C. or less,
The method for manufacturing a semiconductor device according to claim 4, wherein the temperature at which the compositional nonuniformity can be suppressed is a temperature of 700 ° C. or higher.   An Al and Ga source supply ratio for forming the lower AlGaAs layer in the lower AlGaAs layer forming step, and an Al and Ga source supply ratio for forming the upper AlGaAs layer in the upper AlGaAs layer forming step. 6. The method of manufacturing a semiconductor device according to claim 4, wherein the semiconductor device is the same.   An Al and Ga source supply ratio for forming the lower AlGaAs layer in the lower AlGaAs layer forming step, and an Al and Ga source supply ratio for forming the upper AlGaAs layer in the upper AlGaAs layer forming step. The method of manufacturing a semiconductor device according to claim 4, wherein the semiconductor device is different.

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