JP2006114612A - Optical semiconductor device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an optical semiconductor device which can form a quantum dot of good quality in a desired density and to provide a method of manufacturing it. <P>SOLUTION: In the optical semiconductor device having the quantum dot 20 formed on a base layer 16, trace element 18 with different configuration element and ionic radius of the base layer exists in at least the surface layer part of the base layer. The quantum dot is formed by the local distortion generated in the surface layer part by the existence of a trace element. The surface density of the quantum dot can be controlled by setting suitably the surface density of the trace element made to exist in the surface layer part of the base layer. Moreover, since the trace element made to exist in the surface layer part of the base layer is a minute amount, the quality of the base layer is not spoiled as well. Therefore, the quantum dot can be formed by a desired density without spoiling the quality of the base layer or the quantum dot. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to an optical semiconductor device and a manufacturing method thereof, and more particularly, to an optical semiconductor device capable of forming quantum dots at a desired density and a manufacturing method thereof.

  Conventionally, as a method of forming quantum dots, a method of forming by Stranski-Krastanaw mode (SK mode) is known.

  The SK mode is a mode in which a semiconductor crystal to be epitaxially grown grows two-dimensionally (film growth) at the beginning of the growth, but grows three-dimensionally when the elastic limit of the film is exceeded. By epitaxially growing a film having a lattice constant different from that of the underlying material, quantum dots made of three-dimensional growth islands of several nanometers to several tens of nanometers are self-formed.

  The SK mode is a mode in which quantum dots can be easily formed, and is widely used in the field of optical semiconductor devices and the like.

  In consideration of application of an optical semiconductor device in a wide field, it is desirable to form quantum dots with a desired density.

  The following techniques have been proposed as techniques for controlling the density of quantum dots.

  The first technique is a technique in which a concave portion is formed in advance on the surface of the underlayer using a photolithography technique, and then a quantum dot layer is grown on the underlayer. Since the quantum dots tend to grow in the recesses, the quantum dots can be formed in the recesses.

  The second technique is a technique in which impurities are attached to the surface of the underlayer, and then quantum dots are grown on the underlayer. Since quantum dots tend to be formed with impurities as nuclei, quantum dots can be formed according to the density of impurities to be deposited.

The third technique is a technique in which precipitates are formed in the underlayer by performing heat treatment, and then quantum dots are grown on the underlayer. Since quantum dots tend to be generated above the place where the precipitates are formed, the quantum dots can be formed according to the density of the precipitates.
JP-A-7-302763 Applied Physics Letters, Volume 80, Number 18, (2002), 3277-3279

  However, in the first technique, since the concave portions are formed using the photolithography technique, it is difficult to form the concave portions at an extremely high density. For this reason, quantum dots could not be formed at an extremely high density. In the second technique, since the impurities are taken into the quantum dots, it is not possible to form high-quality quantum dots. In the third technique, it is difficult to form a large number of precipitates at a high density, and it is therefore difficult to form quantum dots at a high density.

  An object of the present invention is to provide an optical semiconductor device capable of forming high-quality quantum dots at a desired density and a method for manufacturing the same.

  The above object is an optical semiconductor device having a quantum dot formed on an underlayer, wherein at least a surface layer portion of the underlayer has a trace element having an ion radius different from that of the constituent element of the underlayer, This is achieved by an optical semiconductor device in which the quantum dots are formed by local strain generated in the surface layer portion due to the presence of the trace element.

  As described above, according to the present invention, since a trace element is present in at least the surface layer portion of the underlayer, a local tensile strain or compressive strain is generated at a location where the trace element is present. Then, nuclei for growing quantum dots are generated according to local tensile strain or compressive strain. Therefore, according to the present invention, the surface density of the quantum dots can be controlled by appropriately setting the surface density of the trace element present in the surface layer portion of the underlayer. In addition, since the trace elements present in the surface layer of the underlayer are very small, the quality of the underlayer is not impaired. Therefore, according to the present invention, quantum dots can be formed at a desired density without deteriorating the quality of the underlayer and the quantum dots.

  As described above, it has been difficult to form high-quality quantum dots at a desired density with the conventional technology.

  As a result of intensive studies, the present inventor has come up with the idea that good quantum dots can be formed at a desired density as follows.

  FIG. 1 is a sectional view showing the principle of the present invention. Fig.1 (a) is a conceptual diagram which shows the case where a quantum dot grows above the location in which a trace element exists. FIG.1 (b) is a conceptual diagram which shows the case where a quantum dot grows so that the upper part of the location where a trace element exists may be avoided.

  As shown in FIG. 1, the surface layer portion of the underlayer 16 contains a trace element 18 having an ionic radius different from that of the main constituent element (not shown) of the underlayer 16.

  Since the ionic radius of the trace element 18 is different from the ionic radius of the main constituent element (not shown) of the underlayer 16, a tensile strain or a compressive strain is locally present at the location where the trace element 18 exists. Arise.

  When the quantum dot layer 19 is formed on the base layer 16 in which such local tensile strain or compressive strain is generated, a nucleus for growing the quantum dots 20 according to the local tensile strain or compressive strain is formed. Will occur. For this reason, the quantum dot 20 grows according to local tensile strain or compressive strain.

  In the case where nuclei are likely to be generated above the location where the trace element 18 exists, the quantum dot 20 grows above the location where the trace element 18 exists (see FIG. 1A).

  In the case where nuclei are likely to be generated so as to avoid the location above the portion where the trace element 18 exists, the quantum dot 20 grows so as to avoid the location above the location where the trace element 18 exists (FIG. 1B). )reference).

  According to the present invention, since the trace element 18 is present in at least the surface layer portion of the underlayer 16, local tensile strain or compression strain is generated at the location where the trace element 18 is present. Then, nuclei for growing the quantum dots 20 are generated according to local tensile strain or compressive strain. Therefore, according to the present invention, the surface density of the quantum dots 20 can be controlled by appropriately setting the surface density of the trace element 18 present in the surface layer portion of the underlayer 16. Moreover, since the amount of the trace element 18 present in the surface layer portion of the underlayer 16 is small, the quality of the underlayer 16 is not impaired. For this reason, according to the present invention, the quantum dots 20 can be formed at a desired density without deteriorating the quality of the underlying layer 16 and the quantum dots 20. Moreover, according to the present invention, the quantum dots 20 can be formed at a high density.

[First Embodiment]
Next, the optical semiconductor device according to the first embodiment of the present invention will be explained with reference to FIGS. FIG. 2 is a cross-sectional view of the optical semiconductor device according to the present embodiment.

As shown in FIG. 2, a buffer layer 12 is formed on the substrate 10. For example, a (311) B n-type InP substrate is used as the substrate 10. The concentration of the n-type dopant impurity introduced into the substrate 10 is, for example, about 1 × 10 ¹⁸ cm ⁻³ . As the buffer layer 12, for example, an n-type InP layer is used. The concentration of the n-type dopant impurity introduced into the buffer layer 12 is, for example, about 1 × 10 ¹⁸ cm ⁻³ .

A lower cladding layer 14 is formed on the buffer layer 12. For example, an n-type InP layer is used as the lower cladding layer 14. The concentration of the n-type dopant impurity introduced into the lower cladding layer 14 is, for example, about 1 × 10 ¹⁷ to 1 × 10 ¹⁸ cm ⁻³ . The thickness of the lower cladding layer 14 is, for example, about 3 μm.

  An active layer 24 is formed on the lower cladding layer 14.

  As shown in FIG. 1, the active layer 24 includes a base layer 16, a quantum dot layer (wetting layer) 19 formed on the base layer 16, and a cap layer 22 formed on the quantum dot layer 19. Have.

The material of the underlying layer 16, for example, _{In X Ga 1-X As Y} P 1-Y layer is used.

  For example, N (nitrogen) can be used as the trace element 18.

  For example, an InAs layer is used as the quantum dot layer 19. The supply amount of the quantum dot layer 19 is, for example, a trimolecular layer (monolayer).

  The thickness of the active layer 24 is about 0.5 μm, for example.

  The quantum dot 20 is formed above the portion where the trace element 18 exists.

  In addition, although the case where the quantum dot 20 was formed above the location where the trace element 18 exists was described here, the quantum dot 20 is formed so as to avoid the location above the location where the trace element 18 exists. Sometimes it is done. In any case, the surface density of the quantum dots 20 can be controlled according to the surface density of the trace element 18. Therefore, the quantum dot 20 may be formed above the location where the trace element 18 exists, or the quantum dot 20 may be formed so as to avoid the location above the location where the trace element 18 exists.

  A cap layer 22 is formed on the quantum dot layer 19. For example, an InGaAsP layer is used as the cap layer 22. The thickness of the cap layer 22 is 20 nm, for example.

  Thus, the active layer 24 is configured.

An upper cladding layer 26 is formed on the active layer 24. As the upper cladding layer 26, for example, a p-type InP layer is used. The concentration of the p-type dopant impurity introduced into the upper cladding layer 26 is, for example, about 1 × 10 ¹⁷ to 1 × 10 ¹⁸ cm ⁻³ . The thickness of the upper cladding layer is, for example, about 3 μm.

A contact layer 28 is formed on the upper cladding layer 26. As the contact layer 28, for example, a p-type In _0.53 Ga _0.47 As layer is used. The concentration of the p-type dopant impurity introduced into the contact layer 28 is, for example, about 1 × 10 ¹⁹ cm ⁻³ . The contact layer 28 has a thickness of about 0.5 μm, for example.

  The contact layer 28 and the upper part of the cladding layer 26 are formed in a mesa shape as a whole.

  On the contact layer 28, an upper electrode 30 made of metal is formed.

  A lower electrode 32 made of metal is formed below the substrate 10.

  Thus, the optical semiconductor device according to the present embodiment is constituted.

  In the optical semiconductor device according to the present embodiment, the trace element 18 exists in the surface layer portion of the base layer 16 in the active layer 24, and the trace element 18 exists on the base layer 16 according to the presence of the trace element 18 in the surface layer portion of the base layer 16. The main feature is that the quantum dots 20 are formed.

  With the proposed technique, as described above, it is difficult to form quantum dots with high density.

  On the other hand, according to the present embodiment, since the trace element 18 is present in at least the surface layer portion of the underlayer 16, local tensile strain or compression strain is generated at the location where the trace element 18 is present. Then, nuclei for growing the quantum dots 20 are generated according to local tensile strain or compressive strain. Therefore, according to the present embodiment, the surface density of the quantum dots 20 can be controlled by appropriately setting the surface density of the trace element 18 present in the surface layer portion of the underlayer 16. In addition, since the trace element 18 present in the surface layer portion of the underlayer 16 is very small, the quality of the underlayer 16 is not impaired. Therefore, according to the present embodiment, the quantum dots 20 can be formed at a desired density without deteriorating the quality of the underlayer 16 and the quantum dots 20.

(Manufacturing method of optical semiconductor device)
Next, the method for fabricating the optical semiconductor device according to the present embodiment will be explained with reference to FIGS. 3 to 5 are process cross-sectional views illustrating the method for manufacturing the optical semiconductor device according to the present embodiment.

First, as shown in FIG. 3A, a substrate 10 is prepared. As the substrate 10, for example, a (311) B n-type InP substrate is used. The concentration of the n-type dopant impurity introduced into the substrate 10 is, for example, about 1 × 10 ¹⁸ cm ⁻³ .

Next, the buffer layer 12 is formed on the substrate 10 by MOCVD, for example. For example, an n-type InP layer is formed as the buffer layer 12. The concentration of the n-type dopant impurity introduced into the buffer layer 12 is, for example, about 1 × 10 ¹⁸ cm ⁻³ .

Next, the lower cladding layer 14 is formed on the entire surface by, eg, MOCVD. For example, an n-type InP layer is formed as the lower cladding layer 14. The concentration of the n-type dopant impurity introduced into the lower cladding layer 14 is, for example, about 5 × 10 ¹⁷ cm ⁻³ . The thickness of the lower cladding layer 14 is about 3 μm, for example.

  Next, an active layer 24 is formed on the lower cladding layer 14.

  Here, a method of forming the active layer 24 will be described with reference to FIG.

First, as shown in FIG. 4A, an underlayer 16 is formed on the entire surface of the lower cladding layer 14 (see FIG. 3B) by, for example, the MBE method. As the underlayer 16, for example, an In _X Ga _1-X As _{YP 1-Y} layer is formed. The temperature in the film formation chamber when forming the underlayer 16 is, for example, about 550 to 650 ° C.

  At this time, the underlayer 16 is formed so that the trace element 18 exists in at least the surface layer portion of the underlayer 16. Specifically, the base layer 16 is grown using the raw material containing the constituent elements of the base layer 16, and then the base layer is further made using the raw material containing the constituent elements of the base layer 16 and the raw material containing the trace element 18. Growing 16

The surface density of the trace element 18 is, for example, 1 × 10 ¹² cm ⁻² . For example, nitrogen is used as the trace element 18. In order to contain nitrogen in the underlayer 18, for example, radical nitrogen may be used. Thus, the underlayer 16 in which the trace element 18 is present at least in the surface layer portion is formed.

  Next, as shown in FIG. 4B, a quantum dot layer 19 is formed on the entire surface by, eg, MBE. For example, an InAs layer is formed as the quantum dot layer 19. The thickness of the quantum dot layer 19 is, for example, about 3 molecular layers. The temperature in the film formation chamber when forming the quantum dot layer 19 is set to 450 to 550 ° C., for example. Thus, quantum dots 20 are formed above the locations where the trace elements 18 are present. Here, the case where the quantum dot 20 is formed above the location where the trace element 18 exists is described as an example, but the quantum dot 20 is avoided so as to avoid the location above the location where the trace element 18 exists. May be formed.

  Next, the cap layer 20 is formed on the entire surface by, eg, MBE. For example, an InGaAsP layer is formed as the cap layer 20. The thickness of the cap layer 20 is 30 nm, for example.

  Thus, the active layer 24 is formed. The thickness of the active layer 24 is, for example, about 0.5 μm.

  Although the case where the active layer 24 is formed by the MBE method has been described as an example here, the method of forming the active layer 24 is not limited to the MBE method. For example, the active layer 24 may be formed by MOCVD.

  The film formation conditions when the active layer 24 is formed by the MOCVD method may be as follows, for example.

  The temperature in the film formation chamber when the underlayer 16 is formed is, for example, 550 to 700 ° C. The temperature in the film formation chamber when forming the quantum dot layer 19 is set to 450 to 550 ° C., for example. For example, dimethylhydrazine may be used as a raw material for including nitrogen in the underlayer 16.

  As described above, the active layer 24 may be formed by MOCVD.

Next, as shown in FIG. 5, the upper cladding layer 26 is formed on the entire surface by, eg, MOCVD. For example, a p-type InP layer is formed as the upper clad layer 26. The concentration of the p-type dopant impurity introduced into the upper cladding layer 26 is, for example, about 1 × 10 ¹⁸ cm ⁻³ . The thickness of the upper cladding layer 26 is about 3 μm, for example.

Next, the contact layer 28 is formed on the entire surface by, eg, MOCVD. For example, a p-type In _0.53 Ga _0.47 As layer is formed as the contact layer 28. The concentration of the p-type dopant impurity introduced into the contact layer 28 is, for example, about 1 × 10 ¹⁹ cm ⁻³ . The thickness of the contact layer 28 is, for example, about 0.5 μm.

  Next, the upper portions of the contact layer 28 and the cladding layer 26 are patterned into a mesa shape as a whole.

  Next, the upper electrode 30 made of metal is formed on the contact layer 28 by, eg, sputtering.

  Further, the lower electrode 32 made of metal is formed on the lower surface side of the substrate 10 by, for example, sputtering.

  Thus, the optical semiconductor device according to the present embodiment is manufactured.

(Modification (Part 1))
Next, a modification (No. 1) of the optical semiconductor device according to the present embodiment will be explained with reference to FIG. FIG. 6 is a conceptual diagram showing an optical semiconductor device according to this modification. FIG. 6A shows a case where quantum dots are formed above a portion where a trace element is present. FIG. 6B shows a case where the quantum dots are formed so as to avoid the upper portion where the trace element exists.

  The optical semiconductor device according to this modification is mainly characterized in that the trace element 18 exists only in one atomic layer of the surface layer portion of the underlayer 16.

  As shown in FIG. 6, the trace element 18 exists only in one atomic layer of the surface layer portion of the underlayer 16.

  In order to make the trace element 18 exist only in one atomic layer of the surface layer portion of the underlayer 16, a delta doping technique may be used. That is, the base layer 16 is grown using the raw material for forming the base layer 16, and then the supply of the raw material for forming the base layer 16 is stopped, and only the raw material for the trace element 18 is supplied. .

  As described above, if the trace element 18 is present in at least one atomic layer of the surface layer portion of the underlayer 16, local tensile strain or compression strain is generated due to the presence of the trace element 18 as described above. For this reason, similarly to the above, it is possible to generate nuclei for growing the quantum dots 20 in accordance with local tensile strain or compressive strain. Accordingly, the quantum dots 20 can be formed with a desired surface density also by this modification.

  Here, the trace element 18 is present in one atomic layer of the surface of the underlayer 16, but the trace element 18 is present in at least one of the range of 1 to 5 atomic layers from the surface of the underlayer 16. It may be. If the trace element 18 is present in the range of 1 to 5 atomic layers from the surface of the underlayer 16, the quantum dots 20 are grown according to the local tensile strain or compression strain caused by the presence of the trace element 18. Is possible.

(Modification (Part 2))
Next, a modification (No. 2) of the optical semiconductor device according to the present embodiment will be explained with reference to FIG. FIG. 7 is a conceptual diagram showing an optical semiconductor device according to this modification. FIG. 7A shows a case where quantum dots are formed above a portion where a trace element is present. FIG. 7B shows a case where the quantum dots are formed so as to avoid the upper portion where the trace element is present.

  The optical semiconductor device according to this modification is mainly characterized in that the base layer 16 and the quantum dot layer 19 are alternately stacked.

  As shown in FIG. 7, the underlayer 16 and the quantum dot layer 19 are alternately stacked.

  Trace elements 18 exist in the surface layer portion of each base layer 16. In the place where the trace element 18 exists, the tensile strain or the compressive strain is locally generated as described above.

  The quantum dots 20 are formed according to local tensile strain or compression strain.

  Thus, the underlayer 16 and the quantum dot layer 19 may be alternately stacked. Even when the underlayer 16 and the quantum dot layer 19 are alternately stacked, the quantum dots 20 can be formed with a desired surface density in the same manner as described above.

(Modification (Part 3))
Next, a modification (No. 3) of the optical semiconductor device according to the present embodiment will be explained with reference to FIG. FIG. 8 is a conceptual diagram showing an optical semiconductor device according to this modification.

  The optical semiconductor device according to this modification is mainly characterized in that a plurality of types of trace elements 18 a and 18 b exist in the surface layer portion of the underlayer 16.

  As shown in FIG. 8, a plurality of types of trace elements 18 a and 18 b exist in the surface layer portion of the base layer 16.

  For example, a trace element 18a having a relatively large ion radius is used. In contrast, as the trace element 18b, an element having a relatively small ion radius is used.

  According to this modification, local tensile strain and compressive strain can be further increased by the combination of the trace element 18a and the trace element 18b. Therefore, the quantum dots 20 can be grown more reliably in response to local tensile strain and compression strain.

(Modification (Part 4))
Next, a modification (No. 4) of the optical semiconductor device according to the present embodiment will be explained with reference to FIG. FIG. 9 is a cross-sectional view showing an optical semiconductor device according to this modification.

  The optical semiconductor device according to the present modification is mainly characterized in that the lower cladding layer 14, the active layer 24, and the upper cladding layer 26 are formed in a mesa shape as a whole, and buried layers 34 are formed on both sides of the mesa shape. There are features.

  As shown in FIG. 9, the lower cladding layer 14, the active layer 24, and the upper cladding layer 26 are formed in a mesa shape as a whole.

  A buried layer 34 composed of a p-type InP layer 34a and an n-type InP layer 34b is formed on both sides of the mesa shape. The buried layer 34 functions as a current confinement layer, for example.

  As described above, the lower cladding layer 14, the active layer 24, and the upper cladding layer 26 may be formed in a mesa shape as a whole, and the buried layers 34 may be formed on both sides of the mesa shape.

[Second Embodiment]
An optical semiconductor device according to the second embodiment of the present invention will be described with reference to FIGS. FIG. 10 is a cross-sectional view of the optical semiconductor device according to the present embodiment. The same components as those of the optical semiconductor device and the manufacturing method thereof according to the first embodiment shown in FIGS. 1 to 9 are denoted by the same reference numerals, and description thereof will be omitted or simplified.

(Optical semiconductor device)
First, the optical semiconductor device according to the present embodiment will be explained with reference to FIG. FIG. 10 mainly shows the active layer of the optical semiconductor device according to the present embodiment. The components other than the active layer can be the same as that of the optical semiconductor device according to the first embodiment, for example.

  The optical semiconductor device according to the present embodiment is mainly characterized in that the quantum dots 20 are formed only in a part of the surface layer portion of the underlayer 16.

  As shown in FIG. 10, the trace element 18 exists only in a part of the surface layer portion of the base layer 16.

  Similar to the above, a compressive strain or a tensile strain is locally generated at a location where the trace element 18 exists. The quantum dots 20 are formed according to local compressive strain or tensile strain.

  As described above, the trace element 18 may exist only in a part of the surface layer portion of the base layer 16.

  According to this modification, since the trace element 18 exists only in a partial region of the surface layer portion on the underlayer 16, the quantum dots 20 can be formed only in a partial region of the surface layer portion of the underlayer 16. it can.

(Manufacturing method of optical semiconductor device)
Next, the method for fabricating the optical semiconductor device according to the present embodiment will be explained with reference to FIGS. 11 and 12 are process cross-sectional views illustrating the method for manufacturing the optical semiconductor device according to the present embodiment.

  First, the process up to the step of forming the base layer 16 is the same as the above-described method for manufacturing an optical semiconductor device, and thus the description thereof is omitted (see FIG. 11A).

  Next, a photoresist film 36 is formed on the entire surface of the base layer 16 by, eg, spin coating. Thereafter, the photoresist film 36 is patterned using a photolithography technique. As a result, an opening 38 reaching the base layer 16 is formed in the photoresist film 36 (see FIG. 11B).

Next, as shown in FIG. 11C, the trace element 18 is implanted by the ion implantation method, for example, using the photoresist film 36 as a mask. For example, boron is used as the trace element 18. The surface density of the trace element 18 is, for example, about 1 × 10 ¹⁴ cm ⁻² . A tensile strain or a compressive strain is locally generated at a place where the trace element 18 is introduced.

  Next, as shown in FIG. 12A, the photoresist film 36 is removed.

  Next, as shown in FIG. 12B, the quantum dot layer 19 is formed by, for example, the MBE method. Then, the quantum dots 20 are formed according to local tensile strain or compression strain.

  Next, as shown in FIG. 12C, the cap layer 22 is formed.

  Thus, the active layer 24 is formed.

  The subsequent manufacturing method of the optical semiconductor device is the same as the manufacturing method of the optical semiconductor device described above with reference to FIG.

[Modified Embodiment]
The present invention is not limited to the above embodiment, and various modifications can be made.

For example, in the above-described embodiment, the In _X Ga _1-X As _{YP 1-Y} layer is formed as the base layer 16, but the base layer 16 is limited to the In _X Ga _1-X As _{YP 1-Y} layer. It is not a thing. For example, an In _X Ga _1-X As layer or a GaAs layer may be used as the base layer 16.

  In the above embodiment, the case where N (nitrogen) is used as the trace element 18 has been described as an example. However, the trace element 18 is not limited to N, and the main element and the ionic radius constituting the base layer 16 are not limited. Different elements can be used as appropriate.

  For example, when an InGaAs layer is used as the underlayer 16, for example, B, Al, N, P, or Sb can be used as the trace element 18. B and Al are group III elements similar to In and Ga, and N, P and Sb are group V elements similar to As. For this reason, when such a trace element 18 is used, the trace element 18 is electrically inactive in the underlayer 16.

  When an InGaAs layer is used as the underlayer 16, for example, Si, Zn, Se, or S may be used as the trace element 18. Si is a group IV element, Zn is a group II element, and Se and S are group VI elements. For this reason, when such a trace element 18 is used, the trace element 18 becomes electrically active in the underlayer 16. That is, when such a trace element 18 is used, the trace element 18 becomes an n-type or p-type impurity in the underlayer 16.

  When a GaAs layer is used as the underlayer 16, for example, B, In, Al, N, P, or Sb can be used as the trace element 18. B, In, and Al are group III elements as described above, and N, P, and Sb are group V elements as described above. For this reason, when such a trace element 18 is used, the trace element 18 is electrically inactive in the underlayer 16.

  When a GaAs layer is used as the underlayer 16, Si, Zn, Se, S, or the like may be used as the trace element 18. Si is a group IV element as described above, Zn is a group II element as described above, and Se and S are group VI elements as described above. For this reason, when such a trace element 18 is used, the trace element 18 becomes electrically active in the underlayer 16.

  Further, when an InGaAsP layer is used as the underlayer 16, for example, B, Al, N, or Sb can be used as the trace element 18. B and Al are group III elements as described above, and N and Sb are group V elements as described above. For this reason, when such a trace element 18 is used, the trace element 18 is electrically inactive in the underlayer 16.

  Further, when an InGaAsP layer is used as the underlayer 16, Si, Zn, Se, or S may be used as the trace element 18. Si is a group IV element as described above, Zn is a group II element as described above, and Se and S are group VI elements as described above. For this reason, when such a trace element 18 is used, the trace element 18 becomes electrically active in the underlayer 16.

Moreover, in the said embodiment, although the surface density of the trace element 18 contained in the surface layer part of the base layer 16 was 1 * 10 ^{< 12} > cm ^<-2> , the surface density of the trace element 18 contained in the surface layer part of the base layer 16 is It is not limited to 1 × 10 ¹² cm ⁻² . What is necessary is just to set suitably the surface density of the trace element 18 contained in the surface layer part of the base layer 16 so that the quantum dot 20 can be grown with a desired density. What is necessary is just to set the surface density of the trace element 18 made to exist in the surface layer part of the base layer 16 in the range of 1 * 10 ^{< 8} > ^-1 * 10 ^{< 14} > cm ^<-2 >, for example. In this case, it is considered that the quantum dots 20 can be formed with a surface density of, for example, 1 × 10 ⁸ to 1 × 10 ¹² .

Furthermore, you may set the surface density of the trace element 18 made to exist in the surface layer part 16 of the base layer 16 in the range of 1 * 10 ^{< 11} > ^-1 * 10 ^{< 14} > cm ^<-2 >. In this case, it is considered that the quantum dots 20 can be formed with a surface density of 1 × 10 ¹¹ to 1 × 10 ¹² cm ⁻² , for example. That is, the quantum dots 20 can be formed with high density.

Furthermore, you may set suitably in the range of the surface density of the trace element 18 which exists in the surface layer part 16 of the base layer 16, and 1 * 10 < ¹² > ^-1 * 10 ^{< 14} > cm ^<-2 >. In this case, it is considered that the quantum dots 20 can be formed with a surface density of, for example, about 1 × 10 ¹² cm ⁻² . That is, the quantum dots 20 can be formed with higher density.

  In the above embodiment, the InAs layer is formed as the quantum dot layer 19, but the quantum dot layer 19 is not limited to the InAs layer. A material having a lattice constant different from that of the base layer 16 may be appropriately used.

  Further, in the first embodiment, the case where the base layer 16 is formed so that the trace element 18 exists in at least the surface layer portion of the base layer 16 has been described as an example. However, the trace element exists in the surface layer portion of the base layer 16. The method is not limited to this. For example, after forming the base layer 16, the trace element 18 may be introduced into at least the surface layer portion of the base layer 16 by ion implantation. Further, after forming the underlayer 16, the trace element 18 may be introduced into at least the surface layer portion of the underlayer 16 by a thermal diffusion method. That is, the trace element 18 may be diffused into at least the surface layer portion of the underlayer 16 in a high-temperature atmosphere containing the trace element 18.

  The overall configuration of the optical semiconductor device to which the present invention can be applied is not limited to the above-described optical semiconductor device. The principle of the present invention can be applied to optical semiconductor devices having any structure.

  The principle of the present invention can be applied to any optical semiconductor device such as a semiconductor optical amplifier, an optical switch, a wavelength conversion element, and a quantum dot laser.

(Appendix 1) An optical semiconductor device having quantum dots formed on an underlayer,
There is a trace element having an ionic radius different from that of the constituent element of the underlayer in at least the surface layer portion of the underlayer,
The quantum dot is formed by local strain generated in the surface layer portion due to the presence of the trace element.

(Appendix 2) In the optical semiconductor device described in Appendix 1,
The local strain is a tensile strain. An optical semiconductor device, wherein:

(Appendix 3) In the optical semiconductor device according to Appendix 1,
The optical semiconductor device, wherein the local strain is a compressive strain.

(Supplementary note 4) In the optical semiconductor device according to any one of supplementary notes 1 to 3,
The trace element is present at a surface density of 1 × 10 ⁸ to 1 × 10 ¹⁴ cm ⁻² ,
The said quantum dot is formed with the surface density of 1 * 10 ^{< 8} > ^-1 * 10 ^{< 12} > cm ^<-2 >. The optical semiconductor device characterized by the above-mentioned.

(Appendix 5) In the optical semiconductor device described in Appendix 4,
The trace element is present at a surface density of 1 × 10 ¹¹ to 1 × 10 ¹⁴ cm ⁻² ,
The said quantum dot is formed with the surface density of 1 * 10 ^{< 11} > ^-1 * 10 ^{< 12} > cm ^<-2 >. The optical semiconductor device characterized by the above-mentioned.

(Supplementary note 6) In the optical semiconductor device according to any one of supplementary notes 1 to 5,
The said trace element exists in the range of 1-5 atomic layers from the surface of the said base layer. The optical semiconductor device characterized by the above-mentioned.

(Supplementary note 7) In the optical semiconductor device according to any one of supplementary notes 1 to 6,
The underlayer is made of InGaAs, GaAs or InGaAsP.

(Supplementary note 8) In the optical semiconductor device according to any one of supplementary notes 1 to 7,
The said trace element consists of Si, Zn, Se, S, B, Al, N, P, Sb, or In. The optical semiconductor device characterized by the above-mentioned.

(Supplementary note 9) In the optical semiconductor device according to any one of supplementary notes 1 to 8,
The said quantum dot consists of InAs. The optical semiconductor device characterized by the above-mentioned.

(Supplementary Note 10) In the optical semiconductor device according to any one of Supplementary Notes 1 to 9,
In the surface layer portion of the underlayer, there are other trace elements having different ionic radii from the constituent elements of the underlayer and the trace elements, and
The optical semiconductor device, wherein the quantum dots are formed according to local strain generated in the surface layer portion due to the presence of the trace element and the other trace element.

(Additional remark 11) It is the manufacturing method of the optical semiconductor device which has the process of forming a base layer on a board | substrate, and the process of growing a quantum dot on the said base layer,
In the step of forming the base layer, the base layer is grown using a raw material containing the constituent element of the base layer; the raw material containing the constituent element of the base layer and ions with respect to the constituent element of the base layer The base layer is further grown using another raw material containing trace elements having different radii. A method for manufacturing an optical semiconductor device, comprising:

(Additional remark 12) It is a manufacturing method of the optical semiconductor device which has the process of forming a foundation layer on a substrate, and the process of growing a quantum dot on the foundation layer,
In the step of forming the base layer, the base layer is grown using a raw material containing a constituent element of the base layer; another raw material containing a trace element having an ionic radius different from that of the constituent element of the base layer is used. Then, the trace element is introduced into a surface layer portion of the underlayer. A method for manufacturing an optical semiconductor device, comprising:

(Additional remark 13) The process of forming a base layer on a board | substrate,
Introducing a trace element having an ionic radius different from that of the constituent element of the underlayer into at least a surface layer portion of the underlayer;
And a step of growing quantum dots on the underlayer.

It is sectional drawing which shows the principle of this invention. It is sectional drawing which shows the optical semiconductor device by 1st Embodiment of this invention. It is process sectional drawing (the 1) which shows the manufacturing method of the optical semiconductor device by 1st Embodiment of this invention. It is process sectional drawing (the 2) which shows the manufacturing method of the optical semiconductor device by 1st Embodiment of this invention. It is process sectional drawing (the 3) which shows the manufacturing method of the optical semiconductor device by 1st Embodiment of this invention. It is a conceptual diagram which shows the optical semiconductor device by the modification (the 1) of 1st Embodiment of this invention. It is a conceptual diagram which shows the optical semiconductor device by the modification (the 2) of 1st Embodiment of this invention. It is a conceptual diagram which shows the optical semiconductor device by the modification (the 3) of 1st Embodiment of this invention. It is sectional drawing which shows the optical semiconductor device by the modification (the 4) of 1st Embodiment of this invention. It is sectional drawing which shows the optical semiconductor device by 2nd Embodiment of this invention. It is process sectional drawing (the 1) which shows the manufacturing method of the optical semiconductor device by 2nd Embodiment of this invention. It is process sectional drawing (the 2) which shows the manufacturing method of the optical semiconductor device by 2nd Embodiment of this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 ... Substrate 12 ... Buffer layer 14 ... Lower clad layer 16 ... Underlayer 18, 18a, 18b ... Trace element 19 ... Quantum dot layer 20 ... Quantum dot 22 ... Cap layer 24 ... Active layer 26 ... Upper clad layer 28 ... Contact layer 30 ... Upper electrode 32 ... Lower electrode 34 ... Buried layer 34a ... InP layer 34b ... InP layer 36 ... Photoresist film 38 ... Opening

Claims (5)

An optical semiconductor device having quantum dots formed on an underlayer,
There is a trace element having an ionic radius different from that of the constituent element of the underlayer in at least the surface layer portion of the underlayer,
The quantum dot is formed by local strain generated in the surface layer portion due to the presence of the trace element. The optical semiconductor device according to claim 1,
The trace element is present at a surface density of 1 × 10 ⁸ to 1 × 10 ¹⁴ cm ⁻² ,
The said quantum dot is formed with the surface density of 1 * 10 ^{< 8} > ^-1 * 10 ^{< 12} > cm ^<-2 >. The optical semiconductor device characterized by the above-mentioned. The optical semiconductor device according to claim 2,
The trace element is present at a surface density of 1 × 10 ¹¹ to 1 × 10 ¹⁴ cm ⁻² ,
The said quantum dot is formed with the surface density of 1 * 10 ^{< 11} > ^-1 * 10 ^{< 12} > cm ^<-2 >. The optical semiconductor device characterized by the above-mentioned. The optical semiconductor device according to any one of claims 1 to 3,
The said trace element exists in the range of 1-5 atomic layers from the surface of the said base layer. The optical semiconductor device characterized by the above-mentioned. The optical semiconductor device according to any one of claims 1 to 4,
In the surface layer portion of the underlayer, there are other trace elements having different ionic radii from the constituent elements of the underlayer and the trace elements, and
The optical semiconductor device, wherein the quantum dots are formed according to local strain generated in the surface layer portion due to the presence of the trace element and the other trace element.

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