JP2006196880A - Optical semiconductor device and method of manufacturing it - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To improve controllability of a composition to a group V element constituting a strain compensation quantum well structure and make it possible to achieve an active layer of high gain. <P>SOLUTION: An optical semiconductor device has a quantum well active layer 4 constituted by alternately laminating a compressive strain quantum well layer 4a and a tension strain barrier layer 4b whose forbidden band width is larger than the compressive strain quantum well layer 4's. Forbidden band widths of the compressive strain quantum well layer 4a and the tension strain barrier layer 4b are constant. Compressive strain is equally applied to each compressive strain quantum well layer 4a. Tensile strain in which a central portion in a thickness direction in each tensile strain barrier layer 4b is large and a portion near the compressive strain quantum well layer 4a is small is applied to each tensile strain barrier layer 4b. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to an optical semiconductor device having a strain compensated quantum well structure composed of a compressive strain quantum well layer and an extension strain barrier layer, and a method for manufacturing the same.

  2. Description of the Related Art In recent years, a surface emitting semiconductor laser device is expected to have many advantages of lower operating current and higher density integration and cost reduction by a two-dimensional array arrangement compared to an edge emitting semiconductor laser device. Development is progressing. In particular, research and development has been promoted for short-distance high-speed optical communication such as Gigabit Ethernet (registered trademark) or optical data link using a gallium arsenide (GaAs) compound semiconductor material having an oscillation wavelength of 850 nm or longer. Has already been commercialized.

The 850 nm band surface emitting semiconductor laser device reported so far uses an aluminum gallium arsenide (AlGaAs) multiple quantum well structure as an active layer (see, for example, Non-Patent Document 1). Here, for example, GaAs is used for the well layer, and Al _0.3 Ga _0.7 As is used for the barrier layer.

  In recent years, it has been composed of a well layer with compressive strain and a barrier layer with tensile strain as a means to realize further improvement of the optical gain in the active layer constituting the semiconductor laser device and lowering the threshold current of the semiconductor laser device. A so-called strain compensation quantum well active layer has been proposed (see, for example, Patent Document 1).

  When compressive strain is imparted to the well layer of the quantum well structure, the degeneration of the valence band is released by the compression effect, and the hole state density is reduced. Since the effective mass of holes becomes small due to the decrease in the density of states and recombination with electrons is likely to occur, the optical gain increases, so that a reduction in threshold current and an increase in light output efficiency can be realized. In addition, by providing the barrier layer with tensile strain, the compressive strain of the well layer is relieved, and it is possible to suppress deterioration of crystallinity such as misfit dislocation. However, since the lattice constant of the AlGaAs-based material hardly changes even when the Al composition is changed, almost no stress strain occurs in the active layer.

Therefore, the distortion compensation quantum well active layer capable of realizing an oscillation wavelength of 850 nm, the constituent elements of the AlGaAs-based compound semiconductor, the well layer by adding indium _{(In) Al x Ga y In} 1-xy As ( where , X and y use 0 <x, y <1, 0 <x + y <1), and phosphorus (P) is added to the barrier layer to add Al _x Ga _1-x As _y P _1-y (where A strain compensation quantum well active layer using 0 <x, y <1) for x and y has been proposed. By using a quantum well active layer having such a stress strain, a surface emitting semiconductor laser device having a low threshold current can be realized.
JP-A-9-162482 IEEE Photon.Technol.Lett., Vol.3, 1991, pp.859-862

However, when an attempt is made to form a layered structure composed of AlGaInAs (well layer) / AlGaAsP (barrier layer) having the conventional strain compensation quantum well structure, for example, metalorganic vapor phase epitaxy widely used for crystal growth of compound semiconductors. (Metal Organic Chemical Vapor Deposition: MOCVD) method uses only arsine (AsH ₃ ) as a group V source gas for the growth of the well layer, and arsine (AsH ₃ ) and phosphine (PH ₃ ) for the growth of the barrier layer. Need to supply. Since switching of these group V source gases requires a certain amount of time, when shifting from the well layer growth step to the barrier layer growth step, or when shifting from the barrier layer growth step to the well layer growth step. Stops the crystal growth. While the crystal growth is interrupted, the group V element arsenic (As) or phosphorus (P) is desorbed from the crystal, and the group V source gas is supplied to the group V element at the interface between the well layer and the barrier layer. There is a problem that it is extremely difficult to switch the composition so that the composition becomes steep.

  That is, there is a problem that it is difficult to obtain a high gain active layer having a desired crystal strain because the controllability of the composition with respect to the group V elements constituting the strain compensation quantum well structure is low.

  An object of the present invention is to solve the above-mentioned conventional problems, improve the controllability of the composition for the group V elements constituting the strain compensation quantum well structure, and realize a high-gain active layer.

  In order to achieve the above-described object, the present invention provides an optical semiconductor device in which a tensile strain generated in a barrier layer in a quantum well structure including a well layer and a barrier layer is increased at a central portion in the thickness direction and between the well layer and the well layer. The size is set to be small in the vicinity.

  For example, when a strain-compensated quantum well structure including a well layer made of AlGaInAs and a barrier layer made of AlGaAsP is used as the active layer, the composition of phosphorus (P) that is added to the barrier layer to induce tensile strain is Near the center of the barrier layer and higher at the center of the barrier layer in the thickness direction. Accordingly, while supplying arsenic (As), which is another group V source, between the growth step of the well layer and the growth step of the barrier layer, the supply amount of phosphorus (P) is changed from the start of growth to the supply amount. Can be gradually increased and gradually decreased before the end of growth, so that the well layer growth step and the barrier layer growth step can be performed continuously. This prevents the group V element from being detached from the crystal by interrupting the well layer growth step and the barrier layer growth step, thereby improving the controllability of the composition for the group V element and increasing the gain. An active layer can be realized.

  Specifically, an optical semiconductor device according to the present invention includes an active layer having a quantum well structure in which well layers and barrier layers having a larger forbidden band width (band gap) than the well layers are alternately stacked, The forbidden band widths of the well layer and the barrier layer are constant, and compressive strain is uniformly applied to each well layer, while each barrier layer has a large central portion in the thickness direction of each barrier layer and A small extension strain is applied in the vicinity of the well layer.

  In the optical semiconductor device of the present invention, the forbidden band widths of the well layer and the barrier layer are constant, and compressive strain is uniformly applied to each well layer, while the thickness of each barrier layer is applied to each barrier layer. A strain compensation quantum well structure that achieves both a desired forbidden band width and a desired amount of strain can be obtained because a tensile strain is applied in the central portion in the longitudinal direction and in the vicinity of the well layer is small. .

  In the optical semiconductor device of the present invention, the active layer is made of a III-V compound semiconductor, each well layer has a constant composition of group III elements and group V elements regardless of position, and each barrier layer is made of group III and It is preferable that the composition of the group V element changes in the thickness direction of each barrier layer. In this way, when having an active layer made of a III-V group compound semiconductor, a desired forbidden band width and a desired strain amount can be obtained.

  In the optical semiconductor device of the present invention, it is preferable that the extension strain is distributed symmetrically in the thickness direction in each barrier layer.

  In this case, each well layer is preferably made of AlGaInAs, and each barrier layer is preferably made of AlGaAsP, and the AlGaAsP in each barrier layer is preferably formed by composition modulation.

  In this case, the P composition of AlGaAsP in each barrier layer is preferably high in the central portion in the thickness direction in each barrier layer and low in the vicinity of the well layer.

  In this case, the Ga composition of AlGaAsP in each barrier layer is preferably high in the central portion in the thickness direction in each barrier layer and low in the vicinity of the well layer. In this way, the variation in the forbidden band width due to the composition modulation of the group V elements As and P can be compensated by the composition modulation of the group III elements Al and Ga, so that the forbidden band width of the barrier layer is made constant. Can do.

  In the optical semiconductor device of the present invention, when the active layer is made of a group III-V compound semiconductor, the active layer is preferably formed on a substrate made of GaAs.

  In this case, the optical semiconductor device of the present invention further includes a first reflective layer and a second reflective layer that are each formed of a laminated film made of AlGaAs on the substrate and sandwich the active layer in the thickness direction. Preferably it is.

  In the optical semiconductor device of the present invention, when each well layer is made of AlGaInAs and each barrier layer is made of AlGaAsP, the active layer is at least one of the first reflective layer and the second reflective layer. And an oxide layer formed by oxidizing AlGaAs, and the Al composition of the oxide layer is preferably higher than that of the well layer, the barrier layer, the first reflective layer, and the second reflective layer.

  In this case, in the optical semiconductor device of the present invention, the active layer, the first reflective layer, and the second reflective layer are formed in a columnar shape, and the first electrode formed above and below the columnar active layer. And a second electrode, and emitted light from the active layer generated by the current injected from the first electrode or the second electrode is extracted to the outside through the first reflective layer or the second reflective layer. It is preferable.

  In this case, the optical semiconductor device of the present invention further includes a dielectric film formed around the active layer, the first reflective layer, and the second reflective layer formed in a columnar shape and having a dielectric constant smaller than 4. It is preferable. In this way, since the parasitic capacitance of the dielectric film that embeds the active layer formed in a columnar shape can be reduced, high-speed operation of the optical semiconductor device becomes easier.

  In this case, the dielectric film is preferably made of benzocyclobutene (BCB).

  An optical semiconductor device according to the present invention is directed to a method for manufacturing an optical semiconductor device made of a III-V group compound semiconductor, and includes a step (a) of forming a well layer on a substrate, and the well layer on the well layer. A quantum well in which a well layer and a barrier layer are alternately stacked by repeating a step (b) of forming a barrier layer having a larger forbidden band width and a step (a) and a step (b) a plurality of times. A step (c) for forming an active layer having a structure, wherein in the step (a), the well layer is formed with a constant composition of the group III element and the group V element, and in the step (b), the barrier layer is formed By forming the composition of the group III element and the group V element in the thickness direction, compressive strain is uniformly applied to each well layer, while the thickness in each barrier layer is applied to each barrier layer. A tensile strain is applied in the central part of the direction and small in the vicinity of the well layer. It is characterized by that.

  According to the method for manufacturing an optical semiconductor device of the present invention, in the well layer forming step (a), the well layer is formed with a constant composition of each of the group III element and the group V element, and in the barrier layer forming step (b), the barrier layer is formed. The layers are formed by changing the composition of each of the group III element and the group V element in the thickness direction, so that compressive strain is uniformly applied to each well layer, while each barrier layer has a structure in each barrier layer. A tensile strain is applied in the central portion in the thickness direction and small in the vicinity of the well layer. Therefore, the optical semiconductor device of the present invention can be realized.

  In the method of manufacturing an optical semiconductor device of the present invention, in step (a), each well layer is formed of AlGaInAs, in step (b), each barrier layer is formed of AlGaAsP, and the P composition in the AlGaAsP of each barrier layer is It is preferable that the central portion in the thickness direction of each barrier layer is high and the vicinity of the well layer is low.

  In the method for manufacturing an optical semiconductor device of the present invention, in step (b), the Ga composition in the AlGaAsP of each barrier layer is such that the central portion in the thickness direction of each barrier layer is high and the vicinity of the well layer is low. preferable.

  In the method for manufacturing an optical semiconductor device of the present invention, it is preferable that the step (a) and the step (b) are performed continuously. This makes it possible to reliably control the composition of the group V element at the interface between the well layer and the barrier layer as designed, so that an active layer having a strain compensated quantum well structure with excellent crystallinity can be obtained. it can.

  In the method for manufacturing an optical semiconductor device of the present invention, it is preferable to use a metal organic chemical vapor deposition method for the step (a) and the step (b).

  In the method of manufacturing an optical semiconductor device of the present invention, when each well layer is formed of AlGaInAs and each barrier layer is formed of AlGaAsP, arsine is used as the As raw material in step (a), and As is used in step (b). It is preferable to use arsine as the raw material and phosphine as the P raw material.

  According to the optical semiconductor device and the manufacturing method thereof according to the present invention, the controllability of the semiconductor composition at the interface between the well layer and the barrier layer of the active layer having the strain compensated quantum well structure is improved, so that a high gain active layer is realized. it can.

(One embodiment)
An embodiment of the present invention will be described with reference to the drawings.

  FIG. 1 schematically shows a cross-sectional configuration of a surface emitting semiconductor laser device having an active layer having a strain compensation quantum well structure, which is an optical semiconductor device according to an embodiment of the present invention.

As shown in FIG. 1, the surface emitting semiconductor laser device according to this embodiment includes a substrate 1 made of GaAs having n-type conductivity, and sequentially formed on the substrate 1 and made of n-type AlGaAs. the first reflector layer 2, a quantum well active layer 4 composed of the first spacer layer 3, AlGaInAs / AlGaAsP of undoped Al _0.6 Ga _0.4 As, a second spacer layer 5 made of undoped Al _0.6 Ga _0.4 As, the current confinement The layer 6 includes a second reflecting mirror layer 7 made of p-type AlGaAs and a contact layer 8 made of p-type GaAs. Here, each spacer layer 3 and 5 functions as a light guide layer.

The first reflecting mirror layer 2 and the second reflecting mirror layer 7 each have a laminated structure of Al _0.12 Ga _0.88 As which is a high refractive index layer and Al _0.9 Ga _0.1 As which is a low refractive index layer. The thickness of each of the high refractive index layer and the low refractive index layer is λ / 4n (where λ is the oscillation wavelength and n is the refractive index). Assuming one set of the high refractive index layer and the low refractive index layer, 34.5 sets of the first reflecting mirror layer 2 are stacked, and 22.5 sets of the second reflecting mirror layer 7 are stacked. It is configured. Here, 0.5 set means a configuration in which either one of the high refractive index layer and the low refractive index layer is not provided in the uppermost layer or the lowermost layer of each of the reflector layers 2 and 7.

The current confinement layer 6 includes a current aperture region 6a made of p-type Al _0.98 Ga _0.02 As and a current confinement region 6b formed by oxidizing the peripheral portion of the current aperture region 6a. Here, although the current confinement layer 6 is provided between the second spacer layer 5 and the second reflector layer 7, the current confinement layer 6 is provided between the first reflector layer 2 and the first spacer layer 3 and the second spacer. What is necessary is just to provide in at least one between the layer 5 and the 2nd reflective mirror layer 7. FIG.

The upper part of the first reflector layer 2, the first spacer layer 3, the quantum well active layer 4, the second spacer layer 5, the current confinement layer 6, the second reflector layer 7 and the contact layer 8 are formed in a post (post) shape. The periphery of the column-shaped portion is buried with a buried layer 9 made of benzocyclobutene (BCB) with a protective film 12 made of silicon oxide (SiO ₂ ) interposed therebetween.

  An n-side electrode 10 made of an alloy or a laminated film of gold (Au), germanium (Ge), and nickel (Ni) is formed on the surface of the substrate 1 opposite to the first reflecting mirror layer 2. On the buried layer 9, an opening made of an alloy or laminated film of titanium (Ti), platinum (Pt), and gold (Au), the inner edge of which is in contact with the peripheral edge of the planar circular contact layer 8. A p-side electrode 11 having a portion 11a and a protective film 12 interposed is formed.

  A method for manufacturing the surface emitting semiconductor laser device configured as described above will be described below.

First, by MOCVD, a first reflector layer 2 made of n-type AlGaAs, a first spacer layer 3 made of undoped Al _0.6 Ga _0.4 As, and AlGaInAs / AlGaAsP are formed on a substrate 1 made of n-type GaAs. A quantum well active layer 4, a second spacer layer 5 made of undoped Al _0.6 Ga _0.4 As, a current confinement forming layer made of p-type Al _0.98 Ga _0.02 As, a second reflector layer 7 made of p-type AlGaAs, and A contact layer 8 made of p-type GaAs is sequentially epitaxially grown. Here, as a group III source, for example, trimethylgallium (TMG), trimethylaluminum (TMA), and trimethylindium (TMI) are used as Ga, Al, and In. As the group V source, for example, arsine (AsH ₃ ) is used for As, and phosphine (PH ₃ ) is used for P, for example.

Next, by selectively etching the epitaxially grown semiconductor layer until it reaches the first reflecting mirror layer 2 by lithography and dry etching with chlorine (Cl ₂ ) gas as a main component, a columnar operating region is obtained. Form.

Next, the columnar operation region is steam-oxidized by the steam oxidation method, and the current confinement region 6b is selectively formed in the peripheral portion of the current confinement formation layer, whereby the current aperture region is formed in the central portion of the current confinement formation layer. 6a is formed. Here, the composition of the current confinement forming layer is Al _0.98 Ga _0.02 As, and the property that the region where the Al composition is high is more easily steam oxidized than the region where the Al composition is low is utilized.

  Next, a buried layer 9 is formed by spin-coating a BCB having a low dielectric constant so as to embed the periphery of the columnar operation region on the substrate 1 and then curing. Thereafter, the n-side electrode 10 is formed on the back surface of the substrate 1 by sputtering or vacuum deposition, and the p-side electrode 11 is formed on the buried layer 9 including the peripheral portion of the contact layer 8. In this embodiment, the reliability of the semiconductor laser device is improved by covering the bottom, side and top surfaces of the buried layer 9 made of BCB with, for example, a protective film 12 made of silicon oxide having higher hardness and stability than BCB. I am letting.

  The buried layer 9 is preferably made of a dielectric having a dielectric constant (relative dielectric constant) of 4 or less. That is, for example, by using silicon oxide having a dielectric constant of about 3.9, polyimide having a dielectric constant of about 3.3, and BCB having a dielectric constant of about 2.5, the parasitic capacitance of the buried layer 9 can be reduced. The high frequency characteristics of the semiconductor laser device can be improved.

  Hereinafter, a method for manufacturing the quantum well active layer 4 according to the present embodiment and its features will be described with reference to the drawings.

FIG. 2 schematically shows an enlarged cross-sectional structure of the quantum well active layer 4 shown in FIG. As shown in FIG. 2, the quantum well active layer 4 is composed of, for example, a compressive strain quantum well layer 4a made of Al _0.14 Ga _0.73 In _0.13 As having three layers and a thickness of about 6 nm, and four layers. There about 8nm of _{Al 0.1 Ga 0.9 as 0.75 P 0.25} ( provided that the composition of the central portion in the thickness direction) is constructed by laminating the extension strain barrier layer 4b made alternately.

  In the present embodiment, a compressive strain quantum well layer 4a made of AlGaInAs having a compressive strain amount of about + 1.0% with respect to the substrate 1 made of n-type GaAs is used. On the other hand, the composition of the constituent elements is controlled in the extension strain barrier layer 4b so that the extension strain amount is distributed in the barrier layer 4b, and the extension strain amount is about -1.0% at the maximum. AlGaAsP is used.

That is, in the strain compensated quantum well structure according to the present embodiment, the compression strain quantum well layer 4a is made of Al _0.14 Ga _0.73 In _0.13 As whose composition is not modulated, while the extension strain barrier layer 4b is made from the compression strain quantum well layer 4a. Of arsenic (As) and arsenic (As) or phosphorus (P) from the extension strain barrier layer 4b, and further, phosphorus from the extension strain barrier layer 4b to the compression strain well layer 4a is prevented. In order to prevent the diffusion of (P), the composition of the group V element and the group III element is modulated.

  FIG. 3 shows the composition distribution of group V elements in the quantum well active layer 4, and FIG. 4 shows the composition distribution of group III elements in the quantum well active layer 4. 3 and 4, reference numeral 4a indicates the composition distribution of phosphorus (P) and arsenic (As), which are group V elements of the compressive strain quantum well layer 4a, and reference numeral 4b indicates a group V element of the extension strain barrier layer 4b. Each composition distribution of phosphorous (P) and arsenic (As) is shown.

  As shown in FIG. 3, while supplying arsenic (As) between the growth step of the compressive strain well layer 4a and the growth step of the extension strain barrier layer 4b, the supply amount of phosphorus (P) is changed immediately after the start of growth. The supply is gradually increased and gradually decreased before the end of growth. Therefore, the growth process of the compressive strain well layer 4a and the growth process of the extension strain barrier layer 4b can be performed without interruption. As a result, it is possible to prevent detachment of As or P from the crystal by interrupting the growth process of the compressive strain well layer 4a and the growth process of the extension strain barrier layer 4b. The controllability of the composition is improved, and the high-gain quantum well active layer 4 can be realized.

  FIG. 5 shows a forbidden band width having a constant value in each compression strain quantum well layer 4a and each extension strain barrier layer 4b, and a forbidden band width having a constant value of about 1.8 eV in the extension strain barrier layer 4b. As can be seen, the distortion amount changes in a range of about 0% to -1%. In FIG. 5, the positive value of the distortion amount indicates the compressive strain, and the negative value indicates the expansion strain.

  In the present embodiment, the amount of stretch strain is adjusted so that the forbidden band width of the stretch strain barrier layer 4b shows a constant value. As shown in FIGS. 3 and 4, this adjustment is performed by appropriately modulating the compositions of the group III elements (Al, Ga) and the group V elements (As, P) constituting the stretch strain barrier layer 4b. ing. 3 to 5, the base point of the distance on the horizontal axis of each graph is the upper surface of the first spacer 3.

  FIG. 6 shows the relationship between the lattice constant and the forbidden band width of the compression strain well layer 4a and the compositionally modulated extension strain barrier layer 4b in the quantum well active layer 4 of this embodiment. In FIG. 6, a non-strained well layer and a non-strained barrier layer are also shown for comparison. As shown in FIG. 6, although the lattice constant and the forbidden band width do not change in the compressive strain well layer 4a, the lattice constant is constant so that the forbidden band width is constant at 1.8 eV in the extension strain barrier layer 4b. It can be seen that the composition is controlled by modulating the composition.

  As described above, according to the present embodiment, the growth process of the compression strain well layer 4a and the growth process of the extension strain barrier layer 4b in the so-called strain compensation multiple quantum well structure are not interrupted. Desorption of arsenic (As) from 4a can be prevented. Further, in the growth process of the extension strain barrier layer 4b, the composition of the group V element (As, P) and the group III element (Al, Ga) is gradually changed to desorb arsenic (As) from the well layer. Can be prevented.

  In addition, in the continuous growth process, the composition of the group V elements (As, P) and the group III elements (Al, Ga) is gradually changed when shifting from the extension strain barrier layer 4b to the compression strain well layer 4a. Therefore, that is, since the supply amount of phosphorus (P) is gradually reduced, diffusion of phosphorus (P) into the compressive strain well layer 4a can be suppressed.

  Therefore, the semiconductor laser device according to the present invention can realize a high gain because the composition of the compressive strain well layer 4a can be uniformly formed while generating the strain in the strain barrier layer 4b. Thereby, the threshold current can be reduced and the light emission efficiency can be improved.

  In the present embodiment, the compression strain well layer 4a in the quantum well active layer 4 has three layers and the extension strain barrier layer 4b has four layers. However, the present invention is not limited to this configuration.

  Further, although the surface emitting semiconductor laser device has been described as an example of the optical semiconductor device, the present invention is not limited to the surface emitting semiconductor laser device. That is, the present invention can be applied to an optical semiconductor device having an active layer having a strain compensation quantum well structure.

  The optical semiconductor device and the manufacturing method thereof according to the present invention can realize a high gain active layer by improving the controllability of the semiconductor composition at the interface between the well layer and the barrier layer of the active layer having the strain compensation quantum well structure. For example, it is useful for a vertical cavity surface emitting laser device for optical communication whose oscillation wavelength is around 850 nm.

It is sectional drawing which shows the optical semiconductor device which concerns on one Embodiment of this invention. It is an expanded sectional view showing a quantum well active layer in an optical semiconductor device concerning one embodiment of the present invention. It is a graph which shows the composition distribution of the V group element in the quantum well active layer of the optical semiconductor device which concerns on one Embodiment of this invention. It is a graph which shows the composition distribution of the group III element in the quantum well active layer of the optical semiconductor device which concerns on one Embodiment of this invention. It is a graph which shows the amount of distortion of the forbidden band width and thickness direction in the quantum well active layer of the optical semiconductor device which concerns on one Embodiment of this invention. It is a graph which shows each lattice constant and forbidden band width of a compression strain well layer and a compositionally modulated extension strain barrier layer in quantum well activity of an optical semiconductor device concerning one embodiment of the present invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Substrate 2 1st reflector layer 3 1st spacer layer 4 Quantum well active layer 4a Compression strain quantum well layer 4b Elongation strain barrier layer 5 Second spacer layer 6 Current confinement layer 6a Current aperture region 6b Current confinement region 7 Second reflection Mirror layer 8 contact layer 9 buried layer 10 n-side electrode 11 p-side electrode 11a opening 12 protective film

Claims (18)

An active layer having a quantum well structure in which well layers and barrier layers having a larger forbidden band width than the well layers are alternately stacked;
Each forbidden band width of the well layer and the barrier layer is constant,
While compressive strain is uniformly applied to each well layer, tensile strain is applied to each barrier layer in a large central portion in the thickness direction in each barrier layer and small in the vicinity of the well layer. An optical semiconductor device. The active layer is made of a III-V compound semiconductor,
In each of the well layers, the composition of the group III element and the group V element is constant regardless of the position,
2. The optical semiconductor device according to claim 1, wherein each of the barrier layers has a composition of a group III element and a group V element changed in a thickness direction of the barrier layers.   3. The optical semiconductor device according to claim 1, wherein in each of the barrier layers, the tensile strain is distributed symmetrically in the thickness direction.   3. The well layers are formed of AlGaInAs, the barrier layers are formed of AlGaAsP, and the AlGaAsP in the barrier layers is formed by composition modulation. Or the optical semiconductor device of 3.   5. The optical semiconductor device according to claim 4, wherein the P composition of AlGaAsP in each barrier layer is high in a central portion in the thickness direction in each barrier layer and low in the vicinity of the well layer.   6. The optical semiconductor device according to claim 4, wherein the Ga composition of AlGaAsP in each of the barrier layers is high in a central portion in the thickness direction of each of the barrier layers and low in the vicinity of the well layer. .   The optical semiconductor device according to claim 2, wherein the active layer is formed on a substrate made of GaAs.   8. The apparatus according to claim 7, further comprising a first reflective layer and a second reflective layer, each of which is formed of a laminated film made of AlGaAs on the substrate and sandwiches the active layer in the thickness direction. The optical semiconductor device described. An oxide layer formed between at least one of the active layer and the first reflective layer and the second reflective layer, and formed by oxidizing AlGaAs;
9. The optical semiconductor device according to claim 8, wherein an Al composition of the oxide layer is higher than that of the well layer, the barrier layer, the first reflective layer, and the second reflective layer. The active layer, the first reflective layer, and the second reflective layer are formed in a columnar shape,
Further comprising a first electrode and a second electrode formed above and below the columnar active layer,
The emitted light from the active layer generated by the current injected from the first electrode or the second electrode is extracted outside through the first reflective layer or the second reflective layer. The optical semiconductor device according to claim 8 or 9.   The dielectric film having a dielectric constant smaller than 4 is further provided around the active layer, the first reflective layer, and the second reflective layer formed in the columnar shape. An optical semiconductor device according to 1.   12. The optical semiconductor device according to claim 11, wherein the dielectric film is made of benzocyclobutene (BCB). A method of manufacturing an optical semiconductor device made of a III-V compound semiconductor,
Forming a well layer on the substrate (a);
Forming a barrier layer having a larger forbidden band width than the well layer on the well layer;
Step (c) of forming an active layer having a quantum well structure in which the well layers and the barrier layers are alternately stacked by repeating the step (a) and the step (b) a plurality of times. Prepared,
In the step (a), the well layer is formed with a constant composition of each of the group III element and the V group element. In the step (b), the barrier layer is formed with a thickness of each of the group III element and the group V element. By forming the well layer in the vertical direction, compressive strain is uniformly applied to each well layer, while each barrier layer has a large central portion in the thickness direction in each barrier layer and the well layer. A method of manufacturing an optical semiconductor device, wherein a small extension strain is applied to a portion in the vicinity. In the step (a), each well layer is formed of AlGaInAs,
In the step (b), each of the barrier layers is formed of AlGaAsP, and the P composition in the AlGaAsP of each of the barrier layers is high in the central portion in the thickness direction of each of the barrier layers and in the vicinity of the well layer. 14. The method of manufacturing an optical semiconductor device according to claim 13, wherein the method is low.   14. The Ga composition in AlGaAsP of each barrier layer in the step (b) is characterized in that the central portion in the thickness direction of each barrier layer is high and the vicinity of the well layer is low. 14. A method for manufacturing an optical semiconductor device according to 14.   The method of manufacturing an optical semiconductor device according to claim 13, wherein the step (a) and the step (b) are performed continuously.   17. The method of manufacturing an optical semiconductor device according to claim 13, wherein a metal organic chemical vapor deposition method is used for the step (a) and the step (b). In the step (a), arsine is used as the As raw material,
The method of manufacturing an optical semiconductor device according to any one of claims 14 to 17, wherein in the step (b), arsine is used as the As raw material and phosphine is used as the P raw material.

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