JP4829508B2 - Manufacturing method of optical semiconductor device - Google Patents

Description

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

  Quantum dot lasers have the advantage that they can be uncooled (uncooled) even at high temperatures and have lower power consumption than quantum well lasers, and various studies are currently underway.

  FIG. 1 is an enlarged cross-sectional view of the main part of the quantum dot laser.

  In this quantum dot laser, an underlayer 2, an InAs quantum dot 3, and a barrier layer 4 are sequentially formed on a semiconductor substrate 1 made of InP, and electrons are injected from the barrier layer 4 into the InAs quantum dots 3. As a result, laser light is output from the InAs quantum dots 3.

  FIG. 2 is an energy band diagram of this quantum dot laser.

In FIG. 2, the energy gap ΔE _d in the InAs quantum dots 3 is determined only by InAs that is the material of the quantum dots 3. On the other hand, the energy difference ΔE ₁ from the bottom to the top of the valence band and the energy difference ΔE ₂ from the top to the bottom of the conduction band are in addition to the top and bottom of the InAs quantum dots 3 in addition to the InAs constituting the quantum dots 3. It is also determined by the respective materials of the underlying layer 2 and the barrier layer 4 formed in the above.

The “barrier” that is the name of the barrier layer 4 is that the band gap ΔE _b of the barrier layer 4 is wider than that of the quantum dot 3, so that the electrons 9 confined in the quantum dot 3 are outside the quantum dot 3. This is because the barrier layer 4 has a function of blocking leakage.

In such a quantum dot laser, the threshold current value becomes more stable as the electrons 9 are more easily confined in the InAs quantum dots 3, but there is a band offset as an index representing the ease of confinement of the electrons. The band offset is a value defined by ΔE ₂ / (ΔE ₁ + ΔE ₂ ) using ΔE ₁ and ΔE ₂ described above. The larger this value, the deeper the conduction band from the top to the bottom of the InAs quantum dots 3, and the easier it is to confine the electrons 9 in the InAs quantum dots 3.

  Patent Documents 1 and 3 below disclose structures in which each of the underlayer 2 and the barrier layer 4 is formed of an InGaAsP layer or an InP layer.

  However, if an InGaAsP layer or InP layer is formed as the underlayer 2 and the barrier layer 4, the band offset described above is reduced, so that electrons cannot be stably confined in the InAs quantum dots 3 and the laser is oscillated. And the threshold current value at a high temperature becomes unstable.

As a structure for increasing the band offset, Non-Patent Document 2 proposes a structure in which an aluminum-based compound semiconductor, for example, an InAlGaAs layer is used for the base layer 2 and the barrier layer 4.
Weon et al., Appl. Phys. Lett. 78, 1171 (2001) Journal of Crystal Growth 245 (2002) pp31-36 K. Kawaguch et al., Appl. Phy. Lett., 85, 4331 (2004)

  By the way, InAs constituting the quantum dots 3 has a property of easily evaporating and losing its shape when heated at a high temperature. Therefore, as in Patent Document 2, when an InAlGaAs layer serving as the barrier layer 4 is formed on the InAs quantum dots 3, in order to prevent the InAs quantum dots 3 from evaporating and disappearing, for example, a temperature of 500 ° C. or lower. It is necessary to form an InAlGaAs layer.

  However, when the InAlGaAs barrier layer 4 is formed at such a low temperature, impurities such as oxygen remaining in the reactor and the piping are taken into the barrier layer 4 and the film quality of the barrier layer 4 is deteriorated. If the film quality of the barrier layer 4 is deteriorated in this way, a disadvantage such as an increase in operating current of the quantum dot laser occurs, which is not preferable.

An object of the present invention is to provide a method of manufacturing an optical semiconductor device capable of improving the film quality of a barrier layer in which quantum dots are embedded.

According to one aspect of the present invention, a step of forming an underlayer made of In _x Al _y Ga _1-xy As (0 <x, y <1) on a semiconductor substrate, and at a first substrate temperature, Forming a quantum dot made of a mixed crystal containing at least In, As (arsenic), and a group III element on the underlayer; and at a second substrate temperature, the In _p Ga _{1 -p} As _q P _1-q ( 0 <p, q <1 ) forming the first barrier layer, and at a third substrate temperature higher than the second substrate temperature, the first barrier layer And forming a second barrier layer made of In _r Al _s Ga _1-rs As ( 0 <r, s <1 ), and the first substrate temperature and the second substrate temperature. Is 450 ° C. or higher and 500 ° C. or lower, and the third substrate temperature is 600 ° C. or higher.

  According to the present invention, the first barrier layer is formed on the quantum dots at a second substrate temperature of, for example, 450 ° C. or more and 500 ° C. or less, so that the quantum dots evaporate due to the high substrate temperature, The shape is prevented from collapsing.

  Further, after the quantum dots are embedded in the first barrier layer, a second barrier layer made of InAlGaAs is formed on the first barrier layer at a third substrate temperature higher than the second substrate temperature. When the InAlGaAs layer is formed at a low temperature, impurities such as oxygen are easily taken into the film. However, in the present invention, the second barrier layer is formed at a third substrate temperature higher than the second substrate temperature. Incorporation of impurities into the second barrier layer is suppressed, and the film quality of the second barrier layer is improved.

  In addition, since the second barrier layer is made of InAlGaAs, the energy difference between the conduction bands of the quantum dots and the second barrier layer is increased. Therefore, it is easy to prevent the electrons from escaping from the quantum dots by the second barrier layer, so that the electrons are easily confined in the quantum dots. As a result, the threshold current can be lowered when the laser structure is used, and the output of the optical signal can be increased when the optical amplifier structure is used.

  According to the present invention, since the first barrier layer is formed at a temperature of 450 ° C. or more and 500 ° C. or less when forming the quantum dots, the quantum dots evaporate depending on the substrate temperature when forming the first barrier layer. The shape can be prevented from collapsing. In addition, since the first barrier layer is made of InGaAsP, even if the first barrier layer is formed at a low temperature in this way, impurities are not easily taken into the film of the first barrier layer, and the film quality of the first barrier layer is high. Deterioration can be prevented.

  Furthermore, since the second barrier layer is formed at a higher substrate temperature than when the first barrier layer is formed, the film quality of the second barrier layer can be improved. Since the second barrier layer is made of InAlGaAs, the energy difference between the conduction bands of the quantum dots and the second barrier layer is increased, and electrons are easily trapped in the quantum dots.

  Next, embodiments of the present invention will be described in detail with reference to the accompanying drawings.

(1) 1st Embodiment FIGS. 3-6 is sectional drawing in the middle of manufacture of the quantum dot laser which concerns on 1st Embodiment of this invention.

  First, steps required until a sectional structure shown in FIG.

First, an n-type InP substrate (semiconductor substrate) 10 having a surface orientation (100) is placed in a reactor (not shown), and the substrate temperature is stabilized at 630 ° C. Then, trimethylindium (TMI), phosphine (PH ₃ ), and silane (SiH ₄ ) are supplied into the reactor, and silicon is used as an n-type impurity by MOCVD (Metal Organic Chemical Vapor Deposition) method. An InP layer doped at a concentration of ¹⁷ cm ⁻³ is formed on the n-type InP substrate 10 to a thickness of about 1.0 μm, and this is used as the lower cladding layer 12.

  Next, as shown in FIG. 3B, the same reactive gas as that of the lower cladding layer 12 is supplied into the reactor, and the InAlGaAs having a composition wavelength of 1.10 μm is formed by MOCVD under the condition that the substrate temperature is 630 ° C. The layer is formed to a thickness of about 50 nm, and this is used as the underlayer 13.

The composition ratio of In, Al, Ga, and As constituting the underlayer 13 is not particularly limited, and an In _x Al _y Ga _1-xy As layer in which both x and y are 0 or more and 1 or less is used as the underlayer 13. It may be formed as

  By the way, in the next step shown in FIG. 3C, InAs quantum dots 14 are formed on the underlayer 13, but In (indium) constituting the InAs quantum dots 14 has a high vapor pressure and evaporates even at a low temperature. Therefore, if the substrate temperature is maintained at 630 ° C., which is the formation temperature of the underlayer 13, it becomes difficult to form the quantum dots 14 on the underlayer 13.

  Therefore, after the base layer 13 is formed, the substrate temperature (first substrate temperature) is lowered to a temperature of 450 ° C. to 500 ° C., more preferably about 480 ° C., which is a temperature at which the InAs quantum dots are difficult to evaporate. .

  Thereafter, when trimethylindium and arsine are supplied into the reactor, an InAs wetting layer having a thickness of about 1 to 1.5 ML (Mono Layer) is formed on the InAlGaAs underlayer 13, and then the InAs InAs quantum dots 14 are formed on the InAs wetting layer so as to alleviate the strain caused by the difference in lattice constant between InAlGaAs and InAlGaAs. Such a formation mode of the InAs quantum dots 14 is called an S-K (Stranski-Krastanov) mode. The quantum dot 14 is an active region of the laser, is composed of a mixed crystal of In and As, and typically has a thickness of about 2 ML.

  Note that group III elements (Al, Ga) may diffuse from the InAlGaAs layer constituting the underlayer 13 into the quantum dots 14. In that case, the quantum dot 14 is not composed of InAs alone, but is a mixed crystal containing the above group III elements.

  Next, steps required until a sectional structure shown in FIG.

First, in order to prevent the InAs quantum dots 14 from evaporating due to the high substrate temperature, the substrate temperature is lowered to a second substrate temperature of 450 ° C. or more and 500 ° C. or less, more preferably 480 ° C. in the reactor. . Then, a mixed gas of trimethylindium, triethylgallium, arsine, and phosphine is supplied into the reactor, and growth of the first barrier layer 15 made of InGaAsP is started. Then, when the InGaAsP first barrier layer 15 is grown to a thickness such that the top of the quantum dots 14 is completely embedded, for example, about 10 nm, the supply of gas other than phosphine is stopped, and the first barrier layer Finish 15 growth. The composition wavelength of the first barrier layer 15 is not particularly limited as long as it is wider than that of the quantum dots 14, and is set to about 1.10 μm in this embodiment. Further, the composition ratio of In, Ga, As, and P constituting the first barrier layer is not particularly limited, and an In _p Ga _1-p As _q P _1-q layer in which both p and q are 0 or more and 1 or less. May be used as the first barrier layer 15.

  In the state where the InAs quantum dots 14 are completely buried by the InGaAsP first barrier layer 15 in this way, there is no possibility that the InAs quantum dots 14 will evaporate even if the substrate temperature is increased. Therefore, in a state where phosphine as a supply source of P element is supplied into the reactor, the temperature of formation of the InGaAsP first barrier layer 15 is 480 ° C. or higher, for example, 600 ° C. or higher, more preferably 630 ° C. to 640 ° C. Increase the substrate temperature. Thereafter, the supply of phosphine is stopped, and instead, a mixed gas of trimethylindium, trimethylaluminum, triethylgallium, and arsine is supplied to the reactor.

Then, on the first barrier layer 15 under the condition that the substrate temperature (third substrate temperature) is 600 ° C. or higher, more preferably 630 ° C. or higher and 640 ° C. or lower, by MOCVD using these mixed gases. Then, an InAlGaAs layer having a composition wavelength of about 1.10 μm is formed to a thickness of about 50 nm, and this is used as the second barrier layer 16. However, the composition ratio of In, Al, Ga, and As constituting the second barrier layer 16 is not particularly limited, and the In _r Al _s Ga _1-rs As layer in which both r and s are 0 or more and 1 or less is used. Two barrier layers 12 may be formed.

  As described above, the second barrier layer 16 is formed at a higher substrate temperature than when the InAs quantum dots 14 are formed. By increasing the substrate temperature in this way, impurities such as oxygen remaining in the reactor and the pipes are formed. Becomes difficult to be taken into the second barrier layer 16. As a result, defects due to impurities are less likely to enter the second barrier layer 16 and the quantum dots 14 below the second barrier layer 16, improving the film quality of the second barrier layer 16 and reducing the operating current of the finally obtained quantum dot laser. It is possible to prevent a decrease or the like.

  Through the steps so far, a stacked body 17 composed of the InAs quantum dots 14, the InGaAsP first barrier layer 15, and the InAlGaAs second barrier layer 16 is obtained on the InAlGaAs underlayer 13.

  Next, as shown in FIG. 4B, the stacked body 17 described above is further formed in two layers to obtain a structure in which three InAs quantum dots 14 are formed above the substrate 10. The number of stacked InAs quantum dots 14 is not limited to three, and the InAs quantum dots 14 having an arbitrary number of layers may be formed.

Subsequently, as shown in FIG. 5A, a mixed gas of trimethylindium, phosphine, and diethylzinc (DEZn) is supplied into the reactor so that Zn is approximately about on the uppermost InAlGaAs second barrier layer 16. A p-type InP layer doped at a concentration of 5.0 × 10 ¹⁷ cm ⁻³ is formed to a thickness of about 300 nm, and this is used as the lower layer 18 a of the upper cladding layer.

Next, after a silicon oxide (SiO ₂ ) layer is formed to a thickness of about 200 nm by a CVD method, the silicon oxide layer is patterned by photolithography to form a striped mask 20 extending in the axial direction of the resonator. . The width of the mask 20 is, for example, about 1.5 μm.

  Subsequently, as shown in FIG. 5B, the lower layer 18a, the stacked body 17, the base layer 13, and the lower cladding layer 12 are sequentially etched by plasma etching using a chlorine-based gas as an etching gas. The etching is stopped at a thickness in the middle of the lower cladding layer 12. Thereby, in each layer described above, the portion covered with the mask 20 becomes the mesa 22 having a height of about 1.5 μm. The planar shape of the mesa 22 is a stripe shape like the mask 20.

  Next, steps required until a sectional structure shown in FIG.

  First, with the mask 20 formed, a p-type InP layer is formed as a buried layer 24 on both sides of the mesa 22 by MOCVD, and the side surface of the mesa 22 is completely covered with the buried layer 24. Although the reaction gas used in this MOCVD method is not particularly limited, in this embodiment, trimethylindium and phosphine are used as sources of In and P, respectively, and diethylzinc is used as a dopant gas for doping into p-type. (DEZn) is used.

Then, while continuing supply of trimethylindium and phosphine among these gases, the dopant gas is changed to monosilane (SiH ₄ ), thereby forming an n-type InP layer as a current blocking layer 25 on the buried layer 24. It is formed to a thickness of about 500 nm.

  In the MOCVD method for forming the buried layer 24 and the current blocking layer 25 described above, no film is grown on the mask 20 made of silicon oxide. The mask 20 is removed by wet etching using an HF solution as an etchant after the growth of the layers 24 and 25 is completed.

  Next, steps required until a sectional structure shown in FIG.

First, by MOCVD using the same reaction gas as the lower layer 18a of the upper cladding layer, Zn is approximately 1.0 × 10 ¹⁸ cm ^{−3 on} the upper surface of the lower layer 18a and the current blocking layer 25, respectively. A p-type InP layer doped at a concentration is formed to a thickness of about 2000 nm, and this is used as the upper layer 18 b of the upper cladding layer 18.

  Further, a p-type InGaAs layer is formed as a contact layer 26 on the upper layer 18b to a thickness of about 500 nm by the MOCVD method. For example, a mixed gas of trimethylindium, triethylgallium, and phosphine is used as a reaction gas for forming the contact layer 26. As a dopant gas for doping into p-type, for example, diethyl zinc (DEZn) is used. Is used.

  Next, a metal laminated film formed by laminating a gold layer, a zinc layer, and a gold layer in this order on the upper surface of the contact layer 26 is formed to a thickness of about 300 nm by an evaporation method to form a p-side electrode layer 28. A metal laminated film in which a gold layer, a germanium layer, and a gold layer are laminated in this order on the back surface of the n-type InP substrate 10 is formed by vapor deposition, and this is used as an n-side electrode layer 29.

  FIG. 7 is a cross-sectional view after finishing the subsequent steps, and is a cross-sectional view along the axial direction of the laser resonator.

In the process shown in FIG. 7, the low reflectance film 30 is formed on the emission end face of the laser light 39, and the high reflectance film 31 is formed on the end face opposite to the emission end face. The low reflectance film 30 and the high reflectance film 31 constitute a resonator, and the light generated by the InAs quantum dots 14 is repeatedly reflected by the films 30 and 31, thereby causing the InAs quantum dots 14 to be reflected. In this case, a new stimulated emission of laser light is performed. The low reflectivity film 30 and the high reflectivity film 31 are not particularly limited as long as they are dielectric films, and any film forming method such as an evaporation method or a CVD method can be employed.
Thus, the basic structure of the quantum dot laser according to this embodiment is completed.

  FIG. 8 is a diagram showing the state of the energy band in the quantum dot 14 and its surroundings.

In the present embodiment, an InAlGaAs layer is formed as a semiconductor layer constituting the base layer 13 instead of the InP layer and the InGaAsP layer disclosed in Patent Documents 1 and 3. The energy difference ΔE ₃ between the conduction bands of the underlying layer 13 and the InAs quantum dots 14 composed of the InAlGaAs layer is compared with the case where the underlying layer 13 is composed of InP layers and InGaAsP layers in Patent Documents 1 and 3. Since it becomes large, the electrons 40 in the conduction band are easily confined in the InAs quantum dots 14, and the electrons 40 are difficult to escape from the quantum dots 14 even at a high temperature, and the threshold current of the quantum dot laser 14 at a high temperature is stabilized.

  Furthermore, in this embodiment, as shown in FIG. 4A, an InGaAsP layer is formed as a first barrier layer 15 at a temperature of 450 ° C. or more and 500 ° C. or less, and the InAs quantum dots 14 are formed by the first barrier layer 15. Was completely embedded. By forming the first barrier layer 15 at a low temperature in this way, it is possible to prevent the InAs quantum dots 14 from evaporating or losing their shape due to the high substrate temperature.

  Furthermore, even if the InGaAsP layer constituting the first barrier layer 15 is formed at a temperature of 450 ° C. or higher and 500 ° C. or lower, impurities such as oxygen are not easily taken into the film. Therefore, compared to the conventional example in which quantum dots are embedded in an AlGaInAs layer that easily mixes oxygen when formed at a low temperature, in this embodiment, the first barrier layer 15 and the InAs quantum dots 14 are generated due to the incorporated impurities. This reduces the number of defects and the like, improves the film quality of the first barrier layer 15, and suppresses the increase in operating current of the quantum dot laser.

By the way, as shown in FIG. 8, the energy difference ΔE ₄ between the conduction bands of the InGaAsP first barrier layer 15 and the InAs quantum dots 14 is the conduction band of the AlGaInAs second barrier layer 16 and the InAs quantum dots 14, respectively. small compared to the energy difference Delta] E _5. Therefore, without forming the second barrier layer 16 AlGaInAs, when the barrier layer an InGaAsP first barrier layer 15 alone, the electron 40 trapped in the InAs quantum dots 14, the ride over a small energy difference Delta] E ₄ It becomes easy to escape to the 1 barrier layer 15 side.

Therefore, in this embodiment, the AlGaInAs second barrier layer 16 is formed on the InGaAsP first barrier layer 15 so that the energy difference ΔE ₅ with the conduction band of the InAs quantum dots 14 is increased. This makes it difficult for the electrons 40 trapped in the quantum dots 14 to escape to the upper side of the second barrier layer 16 due to the large energy difference ΔE ₅ described above, and try to stay in the quantum dots 14. This prevents the threshold current from becoming unstable due to the escape of the electrons 40 from the quantum dots 14 and provides a high-quality quantum dot laser with stable oscillation intensity even at high temperatures.

However, if the InGaAsP first barrier layer 15 is formed too thick, the number of electrons that move to the first barrier layer 15 having a small energy difference ΔE ₄ among the electrons in the quantum dots 14 increases. The number of electrons in 14 may be reduced. If this is a concern, the thickness of the InGaAsP first barrier layer 15 is kept to the minimum necessary thickness for embedding the quantum dots 14, that is, the same thickness as the quantum dots 14, and the first barrier layer 15 It is preferable to reduce the number of electrons that move to the second barrier layer 16 and to reduce the number of electrons that escape above the second barrier layer 16.

(2) Second Embodiment Although the quantum dot laser is manufactured in the first embodiment described above, a quantum dot optical amplifier is manufactured in this embodiment. However, since the manufacturing process is the same as that of the quantum dot laser described in the first embodiment, the description thereof is omitted.

  FIG. 9 is a cross-sectional view along the axial direction of the resonator of this quantum dot optical amplifier. In FIG. 9, the elements described in the first embodiment are denoted by the same reference numerals as in the first embodiment.

  In this quantum dot optical amplifier, the low reflectivity film 30 and the high reflectivity film 31 in the quantum dot laser explained in FIG. 7 are changed to the first and second non-reflective films 35 and 36 having a smaller reflectivity than these. It is obtained by replacing. Then, the input light 51 from the first antireflection film 35 causes stimulated emission in the quantum dots 14 functioning as the active region, whereby the incident light is amplified, and the amplified light is transmitted from the second antireflection film 36 to the outside. Are emitted as output light 52.

  In such a quantum dot optical amplifier, as in the first embodiment, even if an InGaAsP layer (first barrier layer) is formed at a substrate temperature of 450 ° C. or higher and 500 ° C. or lower, the amount of impurities incorporated into the film is small. As a result, an increase in operating current due to impurities can be prevented, and a quantum dot optical amplifier with low power consumption can be provided.

Further, since the AlGaInAs second barrier layer 16 is formed on the InGaAsP first barrier layer 15, the energy difference ΔE between the respective conduction bands of the InAs quantum dots 14 and the AlGaInAs second barrier layer 16 is formed as shown in FIG. ₅ becomes larger. As a result, since electrons are easily confined in the InAs quantum dots 14, stimulated emission of photons is effectively performed in the InAs quantum dots 14, and a high-output quantum dot optical amplifier can be realized.

  The features of the present invention are added below.

(Appendix 1) a semiconductor substrate;
An underlayer formed on the semiconductor substrate;
A quantum dot formed on the underlayer and made of a mixed crystal containing at least As (arsenic) and a group III element;
A first barrier layer made of In _p Ga _1-p As _q P _1-q (0 ≦ p, q ≦ 1) formed on the quantum dots;
A second barrier layer formed on the first barrier layer and made of In _r Al _s Ga _1-rs As (0 ≦ r, s ≦ 1);
An optical semiconductor device comprising:

  (Additional remark 2) The said 1st barrier layer was formed in the thickness which covers the top of the said quantum dot, The optical semiconductor device of Additional remark 1 characterized by the above-mentioned.

  (Supplementary note 3) The optical semiconductor device according to supplementary note 2, wherein the thickness of the first barrier layer is the same as the thickness of the quantum dots.

(Supplementary Note 4) The underlying layer optical semiconductor device according to any one of _{In x Al y Ga 1-xy} As (0 ≦ x, y ≦ 1) Appendix 1 to Appendix 3, characterized in that consists of.

(Additional remark 5) While a lower clad layer is formed between the semiconductor substrate and the foundation layer,
The laminate of the underlayer, the quantum dots, and the second barrier layer has a mesa shape, and a buried layer formed on both sides of the laminate, and a current block formed on the buried layer The optical semiconductor device according to any one of appendices 1 to 4, further comprising: a layer; and an upper cladding layer formed on each of the current blocking layer and the stacked body.

  (Supplementary note 6) The optical semiconductor device according to any one of supplementary notes 1 to 5, wherein the quantum dot functions as an active region of any one of a semiconductor laser and a semiconductor optical amplifier.

(Appendix 7) A step of forming a base layer on a semiconductor substrate;
Forming a quantum dot made of a mixed crystal containing at least As (arsenic) and a group III element on the underlayer at a first substrate temperature;
Forming a first barrier layer made of In _p Ga _1-p As _q P _1-q (0 ≦ p, q ≦ 1) on the quantum dots at a second substrate temperature;
A second barrier layer made of In _r Al _s Ga _1-rs As (0 ≦ r, s ≦ 1) is formed on the first barrier layer at a third substrate temperature higher than the second substrate temperature. And a process of
A method for manufacturing an optical semiconductor device, comprising:

  (Additional remark 8) The said 1st substrate temperature and said 2nd substrate temperature are 450 degreeC or more and 500 degrees C or less, The manufacturing method of the optical semiconductor device of Additional remark 7 characterized by the above-mentioned.

  (Additional remark 9) The said 3rd substrate temperature is 600 degreeC or more, The manufacturing method of the optical semiconductor device of Additional remark 7 or Additional remark 8 characterized by the above-mentioned.

  (Additional remark 10) Additional remark 7 thru | or additional remark characterized by forming at least one of the said foundation | substrate layer, the said quantum dot, the said 1st barrier layer, and the said 2nd barrier layer by MOCVD (Metal Organic Chemical Vapor Deposition) method. 10. A method for manufacturing an optical semiconductor device according to any one of items 9 to 9.

  (Supplementary note 11) The optical semiconductor device according to any one of supplementary notes 7 to 10, wherein in the step of forming the first barrier layer, the first barrier layer is formed to have the same thickness as the quantum dots. Manufacturing method.

(Supplementary note 12) The optical semiconductor device according to any one of Supplementary notes 7 to 11, wherein an In _x Al _y Ga _1-xy As (0 ≦ x, y ≦ 1) layer is formed as the base layer. Manufacturing method.

FIG. 1 is an enlarged cross-sectional view of a main part of a conventional quantum dot laser. FIG. 2 is an energy band diagram of the quantum dot laser shown in FIG. 3A to 3C are cross-sectional views (part 1) in the middle of manufacturing the quantum dot laser according to the first embodiment of the present invention. 4A and 4B are cross-sectional views (part 2) in the middle of manufacturing the quantum dot laser according to the first embodiment of the present invention. FIGS. 5A and 5B are cross-sectional views (part 3) in the middle of manufacturing the quantum dot laser according to the first embodiment of the present invention. FIGS. 6A and 6B are cross-sectional views (part 4) in the middle of manufacturing the quantum dot laser according to the first embodiment of the present invention. FIG. 7 is a cross-sectional view along the axial direction of the resonator of the quantum dot laser according to the first embodiment of the present invention. FIG. 8 is a diagram showing an energy band of the quantum dot laser according to the first embodiment of the present invention. FIG. 9 is a cross-sectional view along the axial direction of the resonator of the quantum dot optical amplifier according to the second embodiment of the present invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Semiconductor substrate, 2 ... Underlayer, 3 ... InAs quantum dot, 4 ... Barrier layer, 10 ... InP substrate, 12 ... Lower clad layer, 13 ... Underlayer, 14 ... Quantum dot, 15 ... 1st barrier layer, 16 2nd barrier layer, 17 ... laminate, 18 ... upper cladding layer, 18a ... lower layer of upper cladding layer, 18b ... upper layer of upper cladding layer, 20 ... mask, 22 ... mesa, 24 ... buried layer, 25 ... current blocking layer, 26 ... contact layer, 28 ... p-side electrode layer, 29 ... n-side electrode layer, 30 ... low reflectivity film, 31 ... high reflectivity film, 35 ... first non-reflective film, 36 ... second Non-reflective film, 39 ... laser light, 40 ... electron, 51 ... incident light, 52 ... output light.

Claims (1)

On the semiconductor substrate _{In x Al y Ga 1-xy} As a step of forming a base layer made of (0 <x, y <1 ),
Forming a quantum dot made of a mixed crystal containing at least In, As (arsenic), and a group III element on the underlayer at a first substrate temperature;
Forming a first barrier layer made of In _p Ga _1-p As _q P _1-q ( 0 <p, q <1 ) on the quantum dots at a second substrate temperature;
Formed at higher than said second substrate temperature third substrate temperature, the first barrier _{layer, In r Al s Ga 1-} rs As the second barrier layer made of (0 <r, s <1 ) And a process of
Have
The method for manufacturing an optical semiconductor device, wherein the first substrate temperature and the second substrate temperature are 450 ° C. or higher and 500 ° C. or lower, and the third substrate temperature is 600 ° C. or higher.

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