JP2002323646A - Optical communication system - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an optical communication system by which a laser beam can be highly efficiently coupled with an optical fiber by using a surface emitting type semiconductor laser device chip which can make an operating voltage, an oscillation threshold current, etc., low as a light-emitting light source. SOLUTION: An n-semiconductor distribution Bragg reflection mirror 3 is formed on an n-GaAs substrate 2, and an n-Gax In1-x Py As1-y layer 11 with thickness of λ/4 is deposited on it. Then, a lower undoped part GaAs spacer layer 4, multiple quantum well active layer which consists of an active layer (quantum well active layer) 12 consisting of three-layers, namely Gax In1-x As quantum well layer and a GaAs barrier layer (20 nm) 13, and an upper undoped part GaAs spacer layer 4 are deposited on the layer 11, and a resonator of the thickness for one oscillation wavelength λ in the medium (thickness of λ) is formed.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a semiconductor laser used for optical communication and the like and an optical communication system therefor. The present invention relates to an optical communication system in which a plurality of laser elements are formed using a surface emitting laser to enable large-capacity communication.

[0002]

2. Description of the Related Art A surface emitting semiconductor laser emits laser light in a vertical direction from the surface of a substrate, so that two-dimensional parallel integration is possible, and the spread angle of the output light is relatively narrow (about 10 degrees). Therefore, it is easy to couple with an optical fiber and easy to inspect the element.
For this reason, in particular, development as an element suitable for configuring an optical transmission module (optical interconnection device) of a parallel transmission type has been actively conducted. The immediate application of the optical interconnection device is short-distance optical fiber communication in addition to parallel connection between housings of computers and the like and between boards, but large-scale computer networks and long-distance communication are expected applications in the future. There is a trunk system for distance and large-capacity communication. Generally, a surface emitting semiconductor laser is made of GaAs or Ga.
Although it is common to comprise an active layer made of InAs, an upper semiconductor distributed Bragg reflector arranged above and below the active layer, and an optical resonator composed of a lower semiconductor distributed Bragg reflector on the substrate side. Since the length of the optical resonator is significantly shorter than that of the edge emitting type semiconductor laser,
By setting the reflectivity of the reflecting mirror to an extremely high value (99% or more), it is necessary to easily cause laser oscillation. For this reason, a semiconductor distributed Bragg reflector formed by alternately laminating a low-refractive-index material made of AlAs and a high-refractive-index material made of GaAs at a period of １ ／ wavelength is usually used.

By the way, as described above, a long wavelength band laser having a laser wavelength of 1.1 μm or more used for optical communication, for example, a long wavelength band having a laser wavelength of 1.3 μm or 1.55 μm. In the laser, InP is used for the production substrate and InGaAsP is used for the active layer. However, the lattice constant of InP of the substrate is large, and a reflective mirror material matching the substrate cannot obtain a large refractive index difference. Must be more than pairs. Another problem with the semiconductor laser formed on the InP substrate is that the characteristics greatly change with temperature. For this reason, it is necessary to add a device for keeping the temperature constant, and it is difficult to use the device for general purposes such as consumer use. Light emitting semiconductors have not yet been put to practical use. As an invention made to solve such a problem, Japanese Patent Application Laid-Open No. 9-237942 has been proposed.
The one disclosed in Japanese Patent Application Laid-Open Publication No. H10-202, 1993 is known. According to this, a GaAs substrate is used as a production substrate, and a semiconductor layer made of AlInP that can be lattice-matched with the substrate is used as a low refractive index layer of at least one of the semiconductor distributed Bragg reflectors in the lower upper portion on the substrate side. G is applied to at least one of the lower and upper semiconductor distributed Bragg reflectors in the high refractive index layer.
The purpose of the present invention is to realize a semiconductor Bragg reflector having a high reflectivity with a small number of layers by using a semiconductor layer made of aInNAs so as to obtain a larger refractive index difference than before. GaInNAs is used as a material for the active layer. This is because the bandgap (forbidden band width) can be reduced from 1.4 eV to 0 eV by increasing the N composition, so that it can be used as a material that emits a wavelength longer than 0.85 μm. Because it becomes. In addition, it mentions that a semiconductor layer made of GaInNAs is preferable as a material for a long-wavelength surface emitting semiconductor laser in a 1.3 μm band and a 1.55 μm band because lattice matching with a GaAs substrate is possible.

[0004] However, in the past, only suggesting the possibility of realizing a surface emitting semiconductor laser in a wavelength band longer than 0.85 µm, such a thing has not been actually realized. This is because, although the basic configuration is almost theoretically determined, a more specific configuration for actually obtaining stable laser emission is still unknown. As an example, as described above, Al
A semiconductor distributed Bragg reflector formed by alternately laminating a low-refractive-index material composed of As and a high-refractive-index material composed of GaAs at a period of 1/4 wavelength;
Alternatively, as disclosed in Japanese Patent Application Laid-Open No. 9-237942, in a semiconductor distributed Bragg reflector using a low refractive index layer made of a semiconductor layer made of AlInP that can be lattice-matched with the substrate, a laser element is not used at all. No light was emitted, or even if light was emitted, its luminous efficiency was low, far from a practical level. This is because a material containing Al is chemically very active and crystal defects caused by Al are likely to occur. In order to solve this, Japanese Patent Application Laid-Open Nos. 8-340146 and 7-307 disclose
There is a proposal to constitute a semiconductor distributed Bragg reflector from GaInNP and GaAs that do not contain Al as in the invention disclosed in Japanese Patent Application Publication No. 525. However, GaInNP
The refractive index difference between AlAs and GaAs is about half the refractive index difference between AlAs and GaAs. That is, at present, optical fiber communication is expected in computer networks and the like.
There is no long-wavelength surface emitting semiconductor laser having a wavelength of 1.7 μm and a communication system using the same.

[0005]

SUMMARY OF THE INVENTION In view of the above-mentioned problems, the present invention has a laser oscillation wavelength of 1.
The present invention relates to a long-wavelength surface emitting semiconductor laser having a wavelength of 1 μm to 1.7 μm and an optical communication system thereof.
The purpose is to use a surface-emitting type semiconductor laser device chip that can lower the operating voltage, oscillation threshold current, etc. as a light emitting light source,
An object of the present invention is to propose an optical communication system that enables laser light to be efficiently coupled to an optical fiber.
A second object is to use a long-wavelength surface emitting semiconductor laser element chip having a laser oscillation wavelength of 1.1 μm to 1.7 μm, which can be used stably, as a light source, and to couple laser light to an optical fiber with high efficiency. It is to propose an optical communication system that enables ringing. A third object of the present invention is to provide a high-efficiency coupling when coupling a laser or an optical fiber by a lens or a lens system in such an optical communication system, and to achieve stable coupling without using an optical isolator. It is to propose an optical communication system that enables the above. The fourth
It is an object of the present invention to propose a large-capacity optical communication system capable of efficiently coupling in such an optical communication system and enabling stable coupling without using an optical isolator. A fifth object of the present invention is to propose a large-capacity optical communication system capable of performing high-efficiency and stable coupling without using an optical isolator in such an optical communication system.

[0006]

According to the present invention, there is provided a laser chip and an optical communication system connected to the laser chip, wherein the laser chip has an oscillation wavelength of 1.1 μm. To 1.7 μm, and the main elements of the active layer that generates light are Ga, In, N, and As.
Or a layer of Ga, In, As, and a surface-emitting type semiconductor laser device chip having a resonator structure including reflectors provided above and below the active layer in order to obtain a laser beam. The reflective mirror has a reflection wavelength of 1.1 μm or more, the refractive index of a material layer constituting the reflective mirror periodically changes to a value different from a small value, and a semiconductor distributed Bragg reflection that reflects incident light by light wave interference. with a mirror, the material layer of the refractive index is small is _Al x _{Ga 1-x} as
(0 <x ≦ 1), and the material layer having a large refractive index is Al _{y
Ga 1-y As (0 ≦} y <x ≦ 1) and then, and the the refractive index between the refractive index is small and large material layer has a value between the small and large _Al z _{Ga 1-z} As A surface-emitting type semiconductor laser device chip, which is a reflector provided with a heterospike buffer layer of (0 ≦ y <z <x ≦ 1) having a thickness of 20 nm to 50 nm, is used as a light emitting source. The diameter of a circle inscribed in the light emitting portion of the surface emitting semiconductor laser element chip is d,
Assuming that the core diameter of the optical fiber is F, 0.5 ≦ F / d ≦
2.

In fields where the laser oscillation wavelength is expected to be 1.1 μm to 1.7 μm for optical fiber communication, such as computer networks and trunk systems for long-distance large-capacity communication, the operating voltage, oscillation threshold current and the like are reduced. Although there was no surface emitting semiconductor laser capable of performing stable oscillation with little heat generation from the laser element and an optical communication system using the same, the operation of the present invention was improved by devising a semiconductor distributed Bragg reflector as in the present invention. The voltage, the oscillation threshold current, and the like can be reduced, the laser element generates less heat, stable oscillation can be achieved, and a low-cost practical optical communication system can be realized. In addition, in order to increase the efficiency of coupling between the edge emitting laser of the conventional 1.1 μm band to the 1.7 μm band and the single mode optical fiber with high efficiency, the shape of the light emitting portion of the laser and the coupling lens system are devised. However, the use of the surface emitting laser according to the present invention has realized an optical communication system capable of coupling to a single mode optical fiber with high efficiency in the same band. According to the invention, by devising a semiconductor distributed Bragg reflector, an operating voltage, an oscillation threshold current, and the like can be reduced, a stable oscillation can be performed with less heat generation of a laser element, and a low-cost practical optical communication system Was realized. Further, by using a surface emitting laser, it is possible to realize an optical communication system capable of coupling to a single mode optical fiber with high efficiency in the same band.

According to a second aspect of the present invention, in a laser chip and an optical communication system connected to the laser chip, the laser chip has an oscillation wavelength of 1.1 μm to 1.7 μm, and the active layer for generating light includes a main element. Is Ga, In, N, As
Or a layer made of Ga, In, As, and a surface-emitting type semiconductor laser device chip having a resonator structure including reflectors provided above and below the active layer in order to obtain a laser beam. The reflective mirror has a reflection wavelength of 1.1 μm or more, the refractive index of a material layer constituting the reflective mirror periodically changes to a value different from a small value, and a semiconductor distributed Bragg reflection that reflects incident light by light wave interference. with a mirror, the material layer of the refractive index is small is _Al x _{Ga 1-x} as
(0 <x ≦ 1), and the material layer having a large refractive index is Al _y
Ga _1-y As (0 ≦ y <x ≦ 1), wherein the main composition between the active layer and the reflector is Ga _x
In _{1-x Py} As _1-y (0 <x ≦ 1, 0 <y ≦ 1)
A surface-emitting type semiconductor laser device chip provided with a non-radiative recombination prevention layer composed of a layer is used as a light-emitting source, and the diameter of a circle inscribed in a light emitting portion of the surface-emitting type semiconductor laser device chip is d, Assuming that the core diameter of the optical fiber is F,
It is characterized in that 0.5 ≦ F / d ≦ 2. According to this invention, the same operation and effect as those of the first aspect can be obtained. Claim 3 is that a lens or a lens system is disposed between the surface emitting semiconductor laser element chip and the optical fiber, and
Assuming that the diameter of a circle inscribed in the light emitting portion of the surface emitting semiconductor laser element chip is d, and the core diameter of the optical fiber is F,
F / d ≦ 1 is also an effective means of the present invention. In such an optical communication system, an optical communication system capable of coupling with high efficiency when coupling a laser with a lens or a lens system to an optical fiber and enabling stable coupling without using an optical isolator. Can be realized. According to such technical means,
A lens or a lens system is disposed between the surface emitting semiconductor laser element chip and the optical fiber, and the diameter of a circle inscribed in the light emitting portion of the surface emitting semiconductor laser element chip is d, and the core diameter of the optical fiber is Is F, F / d ≦
By setting to 1, it is possible to realize an optical communication system in which coupling can be performed with high efficiency and stable coupling can be performed without using an optical isolator.

According to a fourth aspect of the present invention, the surface emitting semiconductor laser chip and the optical fibers are arranged in an array. In such an optical communication system, when coupling a laser array and an optical fiber array, coupling can be performed efficiently, and stable coupling can be performed without using an optical isolator. Since it is used, a low-cost optical communication system with a large amount of information can be realized. According to such a technical means, the surface-emitting type semiconductor laser device chip and the optical fibers are arranged in an array,
Coupling can be performed efficiently, stable coupling can be performed without using an optical isolator, and a low-cost optical communication system with a large amount of information can be realized by using a plurality of light emitting elements. According to a fifth aspect of the present invention, the surface emitting semiconductor laser chip, the lens or the lens system, and the optical fibers are arranged in an array. In such an optical communication system, when coupling a laser array and a lens array optical fiber array, coupling can be performed with higher efficiency and stable coupling can be performed without using an optical isolator. Since the light emitting element of the above is used, a low-cost optical communication system having a large amount of information can be realized. According to this technical means, the same operation and effect as those of the fourth aspect can be obtained.

[0010]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, the present invention will be described in detail with reference to an embodiment shown in the drawings. However, the components, types, combinations, shapes, relative arrangements, and the like described in this embodiment are not merely intended to limit the scope of the present invention but are merely illustrative examples unless otherwise specified. . First, the laser oscillation wavelength with a small transmission loss, which is a light emitting element applied to the optical communication system of the present invention, is as follows.
One example of a long-wavelength band surface emitting semiconductor laser of 1 μm to 1.7 μm will be described with reference to FIG. As described above, conventionally, the laser oscillation wavelength to be applied by the present invention is 1.
With respect to the long-wavelength surface emitting semiconductor laser having a wavelength of 1 μm to 1.7 μm, there is only a suggestion of the possibility, and a material for realizing the laser, and a more specific and detailed configuration were unknown. In the present invention, a material such as GaInNAs is used for the active layer, and a more specific configuration is clarified. The details are described below.

In the present invention, n-Ga having a plane orientation of (100) is used.
Oscillation wavelength λ in each medium on As substrate 2
N-Al with a thickness of 1/4 (thickness of λ / 4)_xGa
_1-xAs (x = 1.0) (low refractive index layer to low refractive index
Layer) and n-Al_yGa_1-yAs (y = 0) (high refractive index
N-semiconductor in which 35 layers are alternately stacked with each other
Body distribution Bragg reflector 3 (AlAs / GaAs lower semiconductor)
And a λ / 4 thick layer on it.
Sano n-Ga_xIn_1-xP_yAs_1-y(X = 0.
5, y = 1) Layer 11 was laminated. In this example, n-Ga_x
In_1-xP_yAs_{1 -Y}(X = 0.5, y = 1) layer
A part of the lower reflector, a low refractive index layer (low refractive index layer)
Has become. And undoped lower GaAs
Pacer layer 4 and three layers of Ga_xIn_{1 -X}As quantum well layer
Active layer (quantum well active layer) 12 and GaAs barrier
A multiple quantum well active layer comprising a layer (20 nm) 13;
And an upper doped GaAs spacer layer,
Of the thickness of one oscillation wavelength λ (thickness of λ)
A resonator is formed. In addition, C (carbon)
P-Ga_xIn_1-xP_yAs_1-y(X = 0.
5, y = 1) layer and Zn-doped p-Al_xGa_1-xAs
(X = 0) is set to 1 of the oscillation wavelength λ in each medium.
/ 4 times the thickness of the periodic structure (one cycle) laminated alternately
Layer on which C-doped p-Al_xGa_1-xAs
(X = 0.9) and Zn-doped p-Al_xGa_1-xAs
(X = 0) is set to 1 of the oscillation wavelength λ in each medium.
With a periodic structure (25 periods) alternately stacked with a thickness of / 4 times
Semiconductor Bragg reflector 5 (Al_0.9Ga
_0.1As / GaAs upper semiconductor distributed Bragg reflector)
Is formed. In this example, p-Ga_xIn_1-xP _y
As_1-yThe (x = 0.5, y = 1) layer is also a part of the upper reflecting mirror.
And a low refractive index layer (a layer having a low refractive index).
Here, both the upper and lower mirrors have low refractive index layers.
(Low refractive index layer) / high refractive index layer (high refractive index layer) alternately
In the present invention, there is a refraction
Al with a ratio between small and large_zGa_1-zAs (0 ≦
providing a hetero-spike buffer layer consisting of y <z <x ≦ 1)
ing.

FIG. 2 shows a surface emitting semiconductor device applied to the present invention.
Reflector whose reflection wavelength of body laser is 1.1μm or more
This will be described more specifically. The reflection wavelength applied to the present invention is
In a reflecting mirror of 1.1 μm or more, a low refractive index layer (a low refractive index layer) is used.
Layer) and the high refractive index layer (high refractive index layer)
Hetero spike buffer layer Al with a value between_zGa
_1-zAs (0 ≦ y <z <x ≦ 1) 15 is provided.
Figure 2 shows a part of a semiconductor distributed Bragg reflector.
There is a figure (it is omitted in FIG. 1 because the figure is complicated)
are doing). Conventional semiconductor with laser wavelength 0.85μm band
With respect to the laser, such a heterospike buffer layer 15
It is being considered to establish
The material, its thickness, etc.
It has not been. Also, the laser oscillation wavelength as in the present invention is
1.1 μm to 1.7 μm long wavelength band surface emitting semiconductor laser
Is not considered at all. The reason is this field
(Long wavelength band whose laser oscillation wavelength is 1.1 μm to 1.7 μm
Surface emitting semiconductor lasers) is a new field, and it is still almost
This is because research has not progressed. The inventor is quick
In this field (the laser oscillation wavelength is 1.1 μm to 1.7 μm)
Long wavelength surface emitting semiconductor laser and optical communication using the same
Of the usefulness of shin) and intensive study to realize it
Was done. Such a heterospike buffer layer is formed during formation.
The Al composition is controlled by controlling the gas flow rate.
By changing the material layer continuously or stepwise
Shaped so that the refractive index changes continuously or stepwise
To achieve. More specifically, Al_zGa_1-zAs (0 ≦
y <z <x ≦ 1) Change the value of z of the layer from 0 to 1.0
GaAs to AlGaAs to AlAs
The shape is such that the ratio of Al and Ga gradually changes
To achieve. This is because the gas flow rate is controlled during layer formation as described above.
Created by trawling. Al and G
Formed so that the ratio of a changes continuously as described above
Or even if the ratio changes gradually
It has the same effect.

The reason for providing such a hetero-spike buffer layer is to solve the problem that the electrical resistance of the p-semiconductor distributed Bragg reflector, which is one of the problems of the distributed Bragg reflector, is high. This is due to a hetero-barrier generated at the interface between the two types of semiconductor layers constituting the semiconductor distributed Bragg reflector. By making the Al composition gradually change to the other composition and changing the refractive index, it is possible to suppress the generation of the hetero barrier. Such a hetero spike buffer layer will be described more specifically. FIG. 3 shows an example of a semiconductor distributed Bragg reflector in which a heterospike buffer layer is provided between two types of semiconductor layers constituting the semiconductor distributed Bragg reflector. In the figure, AlGaAs-based semiconductor material as an example of the material of the semiconductor distributed Bragg reflector _(Al z Ga
_1-z As (0 ≦ y <z <x ≦ 1) is shown. The two kinds of semiconductor layers constituting the semiconductor distributed Bragg reflector are AlAs and GaAs, and AlAs and GaAs.
As a hetero-spike buffer layer having an intermediate valence band energy, a composition gradient layer in which the Al composition is changed is provided therebetween. _{That, Al z Ga 1-z As} (0 ≦
(y <z <x ≦ 1) The value of z of the layer is changed from 0 to 1.0, that is, the ratio of Al to Ga is gradually changed such as GaAs to AlGaAs to AlAs. The AlGaAs-based semiconductor material has an increased bandgap energy and a decreased refractive index as the Al composition increases. At this time, in the conduction band, the Al composition was 0.43.
Until the energy increases, the energy begins to decrease, but in the valence band, the valence band energy decreases monotonically in proportion to the increase in the Al composition (total band gap energy increases with respect to the composition). ing.). In addition to this, if an AlGaInP-based material is taken as an example, this material is a quaternary material.
It shows the same tendency as the increase in the Al composition in the GaAs system. The conduction band energy begins to decrease after increasing to an AlInP composition of 0.7. But the valence band energy is
Similarly, it monotonically decreases with an increase in the AlInP composition.

In the example shown in FIG. 3, the composition gradient rate (increase rate of band gap energy) of the region near the GaAs layer (region I in FIG. 3) is shown in FIG.
In the region II), the composition gradient is increased as compared with the composition gradient. For comparison, FIG. 4 shows a structure in which a linear composition gradient layer having a linearly changed Al composition is used as a hetero-spike buffer layer. FIG. 5 shows AlAs.GaAs having a reflection wavelength of 1.3 μm.
4 shows the results of estimating the electrical resistance of a 4-pair p-DBR in which the heterospike buffer layer of FIG. In FIG. 5, the carrier density of each layer of the DBR including the hetero-spike buffer layer is a P-type of 1E18 [cm ⁻³ ], and the vertical axis indicates the differential sheet resistance near zero bias. The abscissa indicates the Al composition gradient in the region I, and indicates the thickness of the different region I (shown in the drawing). The sum of region I and region II is always 2
0 nm, and the thickness of the region II and the composition gradient are determined by the thickness of the region I and the composition gradient. When the linear composition gradient layer is simply provided between the GaAs layer and the AlAs layer, the Al composition gradient is 0.05 [nm ^-1 ].
Hit the point. By increasing the gradient of the Al composition in the region I as shown in FIG. 5, the resistance value is reduced as compared with the conventional case where the composition gradient is simply made linear. Also,
It can be seen that there is an optimum Al composition gradient that is a minimum. For example, when the thickness of the region I is 10 nm (the same thickness as the region II), the Al composition gradient is 0.09 [nm ⁻¹ ].
In this case, the resistance is reduced to about 80% of the conventional value (this tendency does not depend on the applied voltage).

Next, the reason will be described. FIG.
FIG. 3 is a band diagram of a thermal equilibrium state of a DBR hetero interface made of AlAs / GaAs. As shown in the figure, heterospikes caused by band discontinuity mainly appear remarkably on the AlAs layer side having a large band gap, and almost no notch is generated on the GaAs layer side. The notch generated on the GaAs layer side does not originally cause a high resistance, so that the AlA
It is important to lower the resistance efficiently that spikes generated on the s layer side are efficiently flattened with a limited thickness of the hetero spike buffer layer. In the structure of FIG.
This corresponds to the fact that the composition is rapidly increased on the aAs side and the composition gradient on the AlAs side where spikes occur is gradually changed. This makes it possible to reduce the occurrence of spikes as compared with the case where the change in the composition of the hetero-spike buffer layer is simply linear. Increases.). FIG. 7 is a schematic diagram of a band diagram in the thermal equilibrium state of FIG. Compared to the conventional simple composition gradient layer, A
The composition gradient on the lAs side can be reduced. From the above, it can be understood that the electric resistance can be reduced as compared with the related art by increasing the composition gradient rate of the region I.

[0016] Next hetero spike buffer layer _{Al z Ga 1-z As (} 0 ≦ such a refractive index takes a value between the small and large
The result of study on the optimum thickness of y <z <x ≦ 1) will be described. FIG. 8 shows A having a reflection center wavelength at 1.3 μm.
It is the result of calculating the differential electric resistivity near zero bias for the 4-pair DBR of 1As / GaAs by changing the thickness of the hetero-spike buffer layer. Doping density of the DBR layer 1E18 cm ^- and ^3, the doping density of each layer containing a hetero spike buffer layer are uniform. The value indicated by the broken line is the resistivity obtained from the bulk resistance of each semiconductor layer, and shows the resistivity of the DBR obtained when there is no influence from the hetero interface. FIG.
In a DBR without a hetero-spike buffer layer (hetero-spike buffer layer thickness is 0), the resistivity is as high as 1 Ωcm ² , and as a practical problem, the device is passed through a DBR having 20 pairs or more stacked. It is difficult to energize itself, and a very high voltage is required to further energize. Therefore, it is difficult to actually oscillate the surface emitting laser device having such a DBR. However, 5
When the hetero-spike buffer layer of nm is provided, the resistivity can be reduced by about two orders of magnitude as compared with the case where the hetero-spike buffer layer is not provided. Can be obtained. Further, since the voltage required for energization is also reduced, various problems relating to reliability, such as destruction and failure of the element, are greatly improved. Furthermore, the resistivity sharply decreases as the thickness of the heterospike buffer layer is increased, and particularly when the thickness is 20 nm or more, the resistivity becomes a substantially constant value.

FIG. 8 shows a hetero-spike buffer layer and each layer.
p-type doping density 1E18cm ^-3As a uniform de
It shows the structure in the case of a loop. In addition,
This doping concentration is the standard value normally used for DBR.
Value. In the DBR structure of FIG. 8, the decrease in resistivity is saturated.
The thickness of the heterospike buffer layer that begins to
The resistivity at this time is approximately 2.5 times the bulk resistivity.
The degree has been reduced to very low values. In other words, terrorism
The lower limit of the thickness of the spike buffer layer is 20 nm, and more
The operating voltage of the device should be the lowest value if the thickness is
And heat generation of the element can be minimized. Therefore
The temperature at which oscillation can be maintained and the resulting light output increase
You. However, on the contrary, the optical characteristics of DBR
The reflectivity increases as the thickness of the heterospike buffer layer increases.
There is a problem of lowering. FIG. 9 shows the heterospike moderation.
How the reflectivity of the DBR decreases with changes in the thickness of the impact layer
This is shown in detail. Compare with the straight line shown in the figure
The thickness of the hetero-spike buffer layer suddenly increases from 50 nm or more.
It can be seen that the rate of change of the reflectivity becomes extremely large. Elemental
The oscillation threshold current starts to increase correspondingly sharply. Obedience
Therefore, the upper limit of the thickness of the hetero spike buffer layer is 50 nm.
It is appropriate to do. As described above, 20 nm or more, 50 n
m in a DBR provided with a heterospike buffer layer
It is possible to effectively reduce the resistance due to the effect of the terrorist interface.
Yes, and a high reflectance can be obtained at the same time. this
In a surface emitting laser device using
Therefore, it is possible to easily obtain oscillation with a low threshold current.
You. The laser oscillation wavelength as in the present invention is 1.1 μm-1.
20 nm in the case of a long wavelength band surface emitting semiconductor laser of 7 μm
The thickness is preferably about 50 nm.
And the current hardly flows, causing the element to generate heat or drive
There is a problem that energy is high. When it is thick again
The resistance becomes small, and heat generation of the element and drive energy are reduced.
This is an advantage, but the problem is that the reflectance cannot be obtained this time.
Yes, as described above, the optimum range (20 nm to 50 nm)
Thickness).

As described above, the provision of such a hetero-spike buffer layer for a conventional semiconductor laser having a laser wavelength in the 0.85 μm band has been studied. 1 μm to 1.7 μm
In the case of a long-wavelength band surface emitting semiconductor laser, it is more effective. Because, for example, the equivalent reflectance (for example, 99.5)
% Or more) is required to be 1.1 or more than the 0.85 μm band.
In the case of the μm band to 1.7 μm band, such a material layer is formed by about 2 μm.
Because the resistance can be reduced, the operating voltage, oscillation threshold current, etc. can be reduced. This is advantageous. In other words, providing such a hetero-spike buffer layer on a semiconductor distributed Bragg reflector is particularly effective for a long-wavelength surface emitting semiconductor laser having a laser oscillation wavelength of 1.1 μm to 1.7 μm as in the present invention. It can be called a device. In addition, as an example of a more detailed examination result for obtaining an effective reflectance, for example, in a 1.3 μm band surface emitting laser element, Al
_{x Ga 1-x As (x} = 1.0) ( low refractive index layer-refractive index small layer) and _{Al y Ga 1-y As (} y = 0) ( high refractive index layer-refractive index large layer) in case where the 20-period stacking, the reflectance of the semiconductor distributed Bragg reflector is 99.7% or less _{Al z Ga 1-z as (} 0 ≦ y <z <x ≦ 1)
The thickness of the layer is 30 nm. The reflectivity is 99.5%.
The above wavelength band is 53 nm, and the reflectance is 99.
If it is designed to be 5% or more, it is only necessary to control the film thickness by ± 2%. Therefore, 10n equivalent and thinner
When a prototype of m, 20 nm, and 30 nm was manufactured as a prototype, a 1.3 μm band surface emitting laser that could keep the reflectivity to a practically negligible level and reduced the resistance of the semiconductor distributed Bragg reflector was reduced. The device was realized and laser oscillation was successful. Other configurations of the prototyped laser element are as described below.

In the multilayer mirror, there is a band having a high reflectance including a design wavelength (assuming that the film thickness can be completely controlled). It is referred to as a high-reflectance band (including a region where the reflectivity is equal to or more than a required value for a target wavelength). This is a region where the reflectance at the design wavelength is the highest, and decreases only slightly as the wavelength is further away. It drops off sharply from some area. Originally, it is necessary to completely control the film thickness of the multilayer mirror at the atomic layer level so that the reflectance is higher than the required reflectance for the target wavelength. But actually ± 1
Since a film thickness error of about% occurs, the target wavelength deviates from the wavelength having the highest reflectance. For example, if the target wavelength is 1.3
In the case of μm, when the film thickness control is shifted by 1%, the wavelength having the highest reflectance is shifted by 13 nm. Therefore, it is desirable that the high reflectance band (here, the region where the reflectance is equal to or more than a required value with respect to a target wavelength) is wide. As described above, in the long-wavelength surface emitting semiconductor laser having a laser oscillation wavelength of 1.1 μm to 1.7 μm as in the present invention, the reflectivity is improved by devising and optimizing the configuration of such a semiconductor distributed Bragg reflector. The resistance value can be reduced while maintaining high, so that the operating voltage, oscillation threshold current, etc. can be reduced,
Prevention of heat generation of the laser element, stable oscillation, and low energy driving are possible. Returning to FIG. 1 again, the uppermost pA
_{l x Ga 1-x As (} x = 0) layer also has the role of a contact layer (p- contact layer) for taking electrode and a contact. Here, the In composition x of the quantum well active layer was 39% (Ga _0.61 In _0.39 As). The thickness of the quantum well active layer was 7 nm. The quantum well active layer had a compressive strain of about 2.8% with respect to the GaAs substrate. In addition, the entire surface emitting semiconductor laser was grown by MOCVD. In this case, no lattice relaxation was observed. Materials for forming each layer of the semiconductor laser include TMA (trimethylaluminum), TMG
(Trimethyl gallium), TMI (trimethyl indium), AsH ₃ (arsine), PH ₃ (phosphine)
Was used. H ₂ was used as a carrier gas. FIG.
In the case where the strain is large as in the active layer (quantum well active layer) of the device shown in FIG. Here, the GaInAs layer (quantum well active layer) is grown at 550 ° C. The MOCVD method used here has a high degree of supersaturation and is suitable for crystal growth of a high strain active layer. Also MB
It is excellent in mass productivity because the supply flow rate and supply time of the raw material gas need only be controlled without requiring a high vacuum as in the E method.

In this example, the portion outside the current path was irradiated with protons (H ⁺ ) to form an insulating layer (high-resistance portion), thereby forming a current narrowing portion. In this example, a p-side electrode is formed on the p-contact layer which is the uppermost layer of the upper reflector and is a part of the upper reflector, excluding the light emitting portion, and an n-side electrode is formed on the back surface of the substrate. Was formed. In this example, the active region (in this embodiment, a resonator composed of the upper and lower spacer layers and the multiple quantum well active layer) sandwiched between the upper and lower reflectors and into which carriers are injected and recombined, has an active region. material containing al (percentage of group III 1% or more) without using a further layer closest to the active layer of the low refractive index layer of the lower and upper reflector _{Ga x in 1-x P y} As
_1-y (0 <x ≦ 1, 0 <y ≦ 1) as a non-radiative recombination preventing layer. That is, by appropriately selecting the value of x or y, GaInP, GaInPAs, or GaPAs is used as the non-radiative recombination preventing layer. Note that this layer, there is a case where a material other than Al is added small amount, the main _{material, Ga x In 1-x P} y As
_1-y (0 <x ≦ 1, 0 <y ≦ 1). Carriers are confined between the low-refractive index layers of the upper and lower reflectors, which are the wide gaps closest to the active layer, so that only the active region is an Al-free layer (1% of the group III).
%), The low refractive index layer (wide gap layer) of the reflector in contact with the active region has a structure including Al, so that when carriers are injected and recombined, non-emission light is regenerated at this interface. Coupling occurs and the luminous efficiency decreases. Therefore, it is desirable that the active region be formed of a layer containing no Al.
Also this main composition _{Ga x In 1-x P y} As 1-y
The non-radiative recombination preventing layer composed of (0 <x ≦ 1, 0 <y ≦ 1) has a lattice constant smaller than that of the GaAs substrate and has tensile strain. In the epitaxial growth, the growth is performed by reflecting the information of the base, and if there is a defect on the surface of the substrate, it goes up to the growth layer. However, it is known that the presence of a strained layer is effective in preventing such defects from climbing. When the defects reach the active layer, the luminous efficiency is reduced. In the case of an active layer having a strain, there arises a problem that the critical thickness is reduced and a layer having a required thickness cannot be grown. Especially when the amount of compressive strain of the active layer is as large as 2% or more,
In the case where the strained layer is grown to be thicker than the critical thickness, there is a particular problem that even if non-equilibrium growth such as low-temperature growth is performed, growth cannot be performed due to the presence of defects. The presence of a strained layer suppresses such a defect from climbing up, so that the luminous efficiency can be improved, and a layer having a compressive strain of 2% or more of the active layer can be grown.
It is possible to grow the thickness of the strained layer larger than the critical thickness.

This Ga_xIn_1-xP_yAs_1-y(0
<X ≦ 1, 0 <y ≦ 1) layer is in contact with the active region and is active
It also has the role of confining carriers in the region,
_xIn_1-xP_yAs_1-y(0 <x ≦ 1, 0 <y ≦
1) The band gap energy of the layer decreases as the lattice constant decreases.
It can take large amounts of lugi. For example, Ga_xIn_1-xP
In the case of (y = 1), x increases and approaches GaP.
Increase the lattice constant and the band gap.
You. The band gap Eg is Eg (Γ) =
1.351 + 0.643x + 0.786x², Indirect transition
And Eg (X) = 2.24 + 0.02x
You. Therefore, the active region and Ga_xIn_1-xP_yAs _1-y
(0 <x ≦ 1, 0 <y ≦ 1) layer has a large hetero barrier.
As a result, carrier confinement is improved and threshold current is reduced.
This has the effect of reducing the temperature and improving the temperature characteristics. Furthermore, this Ga_x
In_1-xP_yAs_1-y(0 <x ≦ 1, 0 <y ≦ 1)
The non-radiative recombination prevention layer composed of a layer has a lattice constant of Ga.
Larger than the As substrate, having a compressive strain, and
When the lattice constant of the active layer is Ga_xIn_1-xP_yAs_1
-Y(0 <x ≦ 1, 0 <y ≦ 1) Larger compressive strain than layer
have. In addition, this Ga_xIn_1-xP_yAs
_1-y(0 <x ≦ 1, 0 <y ≦ 1) The direction of strain in the layer is active
Substantial compressive strain perceived by the active layer because it is in the same direction as the layer
Work in the direction of reducing The larger the distortion, the more the influence of external factors
The active layer has a compressive strain of 2% or more, for example.
Is particularly effective when the thickness is large or when the thickness exceeds the critical thickness.
You. For example, a surface emitting laser with an oscillation wavelength of 1.3 μm band
It is preferably formed on a GaAs substrate.
In many cases, a conductor multilayer reflector is used, and the total thickness is
Before growing the active layer, 50 to 80 semiconductor layers of 5 to 8 μm are formed.
Need to be grown (while edge-emitting lasers,
The total thickness before growing the active layer is about 2 μm and about 3 layers.
It is only necessary to grow a semiconductor layer). In this case, high quality
Various causes (even once occurred
Defects basically creep up in the crystal growth direction,
Surface defects on the GaAs substrate
What is the defect density of the surface just before the active layer growth compared to the depression density?
Even if it increases. Insertion of strained layer before active layer growth
In addition, when the effective compressive strain perceived by the active layer is reduced,
To reduce the effect of defects on the surface just before the growth of the conductive layer
become. In this example, in the active area and the mirror and the active area
Since the interface with Al does not contain Al, the carrier injection
Non-light emission due to crystal defects caused by Al when entering
There was no recombination and non-radiative recombination was reduced.

As mentioned above, the interface between the reflector and the active area
In which Al does not contain, that is, non-radiative recombination prevention
The provision of a stop layer can be applied to both upper and lower reflectors.
Although preferred, it is effective to apply it to one of the mirrors.
You. In this example, both the upper and lower reflectors are semiconductor distribution black.
Mirror, but one of the mirrors is a semiconductor distributed Bragg
It is also possible to use a reflecting mirror and the other reflecting mirror as a dielectric mirror
No. In the above-described example, the most active layer of the low refractive index layer of the reflecting mirror is used.
Only the layer close to_xIn_1-xP_yAs_1-y(0 <
x ≦ 1, 0 <y ≦ 1)
Has a plurality of layers of Ga _xIn_1-xP_yAs_1-y(0 <x
≦ 1, 0 <y ≦ 1) may be used as the non-radiative recombination preventing layer.
No. Further, in this example, the distance between the GaAs substrate and the active layer is
Applying this idea to the lower reflector, there is a problem when growing the active layer
The crawling of crystal defects caused by Al onto the active layer
The adverse effect of the active layer is suppressed and the active layer is crystallized with high quality.
Can be lengthened. Due to these, luminous efficiency is high,
A surface emitting semiconductor laser with sufficient reliability for practical use can be obtained.
Was. In addition, the low refractive index layer of the semiconductor distributed Bragg reflector is
Not all but at least the part closest to the active area
Ga not containing l_xIn_1-xP_yAs _1-y(0 <x
≦ 1, 0 <y ≦ 1)
The above effect can be obtained without particularly increasing the number.
coming. The surface-emitting type semiconductor laser fabricated in this manner
The oscillation wavelength of the laser was about 1.2 μm. On GaAs substrate
GaInAs has a longer wavelength due to an increase in the In composition, but strain
Longer wavelength up to 1.1 μm with conventional increase
Was considered to be the limit (see "IEEE Photonics.Techn.
ol. Lett. Vol. 9 (1997) pp. 1319-1321 "). But
However, as the inventor made this time, low temperature of 600 ° C or less
High strain GaIn by growth method with high non-equilibrium such as growth
Coherent growth of As quantum well active layer thicker than before
Wavelength can reach up to 1.2 μm
Was. This wavelength is transparent to the Si semiconductor substrate.
You. Therefore, when an electronic device and an optical device are integrated on a Si substrate,
Optical transmission through Si substrate
You. As is clear from the above description, the high In composition is large.
By using compressive strained GaInAs for the active layer, G
Forming long-wavelength surface-emitting semiconductor laser on aAs substrate
I knew I could do it.

As described above, such a surface emitting semiconductor laser can be grown by MOCVD, but other growth methods such as MBE can also be used.
In addition, a triple quantum well structure (TQ
Although the example of W) is shown, a structure (SQW, MQW) using a quantum well of another number of wells or the like can be used. The structure of the laser may be another structure. Although the length of the resonator is set to the thickness of λ, it can be set to an integral multiple of λ / 2.
Desirably, it is an integral multiple of λ. G is used as a semiconductor substrate.
Although an example using aAs has been described, the above concept can be applied even when another semiconductor substrate such as InP is used. The period of the reflecting mirror may be another period. In this example, an example in which the main element is a layer composed of Ga, In, and As, that is, Ga _x In _1-x As (GaInAs active layer) is shown as an active layer. Is
What is necessary is just to make it the layer (GaInNAs active layer) which adds N and the main element consists of Ga, In, N, and As. Actually Ga
By changing the composition of the InNAs active layer, 1.3 μm
Laser oscillation could be performed in each of the m band and the 1.55 μm band. By examining the composition, a surface emitting laser having a longer wavelength, for example, in the 1.7 μm band can be obtained. Further, even if GaAsSb is used for the active layer, a 1.3 μm band surface emitting laser can be realized on a GaAs substrate. As described above, a semiconductor laser having a wavelength of 1.1 μm to 1.7 μm has not conventionally been available with a suitable material.
By using aInAs, GaInNAs, and GaAsSb, and providing a non-radiative recombination preventing layer, a high-performance surface emitting laser in a long wavelength region of the 1.1 μm to 1.7 μm band where stable oscillation has been difficult in the past. Can be realized.

Next, the present invention is applied to the optical transmitting / receiving system of the present invention.
Other long-wavelength surface-emitting semiconductor lasers
The configuration will be described with reference to FIG. Again, figure
N-GaAs substrate having a plane orientation of (100) as in the case of 1.
21 is used. Oscillation wave in each medium
N-Al with a thickness 1/4 times the length λ (thickness of λ / 4)_xG
a_1-xAs (x = 0.9) and n-Al_xGa_1-xA
n-semiconductor distribution in which s (x = 0) is alternately stacked for 35 periods
Bragg reflector 24 (Al _0.9Ga_0.1As / Ga
As lower reflector), and a λ / 4-thick n is formed thereon.
-Ga_xIn_1-xP_yAs_1-y(X = 0.5, y =
1) Layers were laminated. In this example, n-Ga_xIn_1-xP
_yAs_1-yThe (x = 0.5, y = 1) layer is also the lower reflector
It is a part and is a low refractive index layer. And on top of that,
Undoped lower GaAs spacer layer 23 and three Ga layers
_xIn_1-xN_yAs_1-yActive layer 3 which is a quantum well layer
3 (quantum well active layer) and GaAs barrier layer 34 (15n
m) of the multi-quantum well active layer (3 in this example)
Quantum well (TQW)) and undoped upper GaAs
An oscillation wavelength in the medium is formed by laminating the
A resonator having a thickness of one wavelength (thickness of λ) is formed.
You. In addition, a p-semiconductor distributed Bragg reflector
(Upper reflector) 24 is formed. The upper reflector is
The AlAs layer 27 serving as the selectively oxidized layer is formed as a GaInP layer.
Low refractive index layer having a thickness of 3λ / 4 sandwiched between AlGaAs layers
(C-doped p-Ga having a thickness of (λ / 4-15 nm)_xI
n_1-xP_yAs_1-y(X = 0.5, y = 1) layer, C
Doped p-Al_zGa_1-zAs (z = 1) selective oxidation
Layer (thickness 30 nm), thickness (2λ / 4-15 nm)
C-doped p-Al_xGa_1-xAs layer (x = 0.9)
GaAs layer (one period) having a thickness of λ / 4, and C-doped
P-Al_xGa_{1 -X}As layer (x = 0.9) and pA
l_xGa_1-xAs (x = 0) layer in each medium
Period alternately stacked with a thickness of 1/4 of the oscillation wavelength
Structure (22 periods)
Reflector (Al_0.9Ga_0.1As / GaAs upper part
Reflecting mirror). Note that in this example as well, FIG.
Although illustration is omitted because it is complicated, semiconductor components
The structure of the cloth Bragg reflector has a low refraction as shown in Fig. 2.
Index layer (low refractive index layer) and high refractive index layer (high refractive index layer)
In the meantime, Al whose refractive index takes a value between small and large_zGa_1-z
Heterospike relaxation consisting of As (0 ≦ y <z <x ≦ 1)
An opposing layer is provided. And the topmost p-Al
_xGa_1-xThe As (x = 0) layer connects the electrode and the contact.
Contact layer (p-contact layer)
They also have a role.

Here, the In composition x of the quantum well active layer is 37
%, And the N (nitrogen) composition was 0.5%. Also the quantum well activity
The thickness of the conductive layer was 7 nm. In addition, this surface-emitting type semiconductor laser
The laser was grown by MOCVD. Semiconductor laser
The raw material for each layer is TMA (trimethylaluminum).
), TMG (trimethylgallium), TMI (g)
Limethylindium), AsH₃(Arsine), PH₃
(Phosphine), and DMHy
Methylhydrazine) was used. DMHy decomposes at low temperature
Therefore, it is suitable for low-temperature growth below 600 ° C.
A highly strained quantum well layer that requires low temperature growth
Preferred in the case. The carrier gas is H₂Was used.
In this example, a GaInNAs layer (quantum well active layer) is used.
Grew at 540 ° C. MOCVD has a high degree of supersaturation
Suitable for crystal growth of materials containing N and other V-groups at the same time
You. Also, high vacuum is not required unlike the MBE method,
Control the supply flow rate and supply time of
Is also excellent. Furthermore, in this example, a mesa
Part is p-Ga_xIn_1-xP_yAs _1-y(X = 0.
5, y = 1) p-Al until the layer is reached_zGa_1-zA
s (z = 1) is formed by exposing the side surface of the selective oxidation layer,
Al that appeared on the side_zGa_1-zAs (z = 1) layer is steamed
Oxidized from the side with air_xO_yForming a current narrowing layer
ing.

Finally, a mesa etch with polyimide (insulating film)
The part removed by polishing is embedded and flattened, and the upper reflector
Remove polyimide on top and emit light on p-contact layer
A p-side electrode is formed except for the portion, and n-side electrode is formed on the back surface of the GaAs substrate.
Side electrodes were formed. In this example, the selective oxidation layer
The lower part has Ga as part of the upper reflector._xIn _1-xP_yA
s_1-y(0 <x ≦ 1, 0 <y ≦ 1)
You. For example, in the case of wet etching,
If a chant is used, GaIn can be used for an AlGaAs system.
PAs based can be used as etch stop layer
Therefore, Ga_xIn_1-xP_yAs_1-y(0 <x ≦ 1,
0 <y ≦ 1) Insertion of the layer allows selective oxidation.
The height of the mesa etching can be strictly controlled. others
Therefore, uniformity and reproducibility can be improved, and cost can be reduced.
In addition, the surface emitting semiconductor laser (element) of this example is reduced to one dimension.
Or two-dimensional integration, controllability during device fabrication
Improves the characteristics of each element in the array.
The effect is that the uniformity and reproducibility of
You. In this example, G serving as an etching stop layer is also used.
a_xIn_1-xP_yAs_{1 -Y}(0 <x ≦ 1, 0 <y ≦
1) The layer is provided on the upper reflector side, but is provided on the lower reflector side
May be. In this example, too,
In addition, the active region where carriers are injected and recombine (this embodiment)
Then, the upper and lower spacer layers and the multiple quantum well active layer
Including the Al in the active region.
Low refractive index layers of lower and upper reflectors without using materials
The layer closest to the active layer of_xIn_1-xP_yAs
_1-yNon-radiative recombination prevention (0 <x ≦ 1, 0 <y ≦ 1)
And layers. That is, in this example, the
The interface between the mirror and the active region should not contain Al
Therefore, at the time of carrier injection, crystal defects caused by Al
Can reduce non-radiative recombination due to entrapment
You. It should be noted that the interface between the reflector and the active region does not contain Al.
It is preferable to apply the configuration to the upper and lower reflectors as in this example.
It is effective even if applied to only one of the reflectors
There is. In this example, both the upper and lower reflecting mirrors have a semiconductor distribution block.
Rag reflector was used, but one reflector was
And the other reflector as a dielectric reflector
good. Further, also in this example, between the GaAs substrate and the active layer.
The same idea as in the example of FIG. 1 was applied to the lower reflector of
Therefore, a crystal caused by Al, which is a problem when growing the active layer,
Negative effects due to crawling of defects into active layer are suppressed
As a result, the active layer can be grown with high quality crystals. What
In addition, such a non-radiative recombination preventing layer is provided in FIG. 1 and FIG.
In either configuration, a semiconductor distributed Bragg reflector
The thickness of the oscillating wave in the medium.
The thickness is set to １ ／ of the length λ (thickness of λ / 4). Ah
Alternatively, a plurality of layers may be provided.

Although an example in which the non-radiative recombination preventing layer is provided on a part of the semiconductor Bragg reflector has been described above, the non-radiative recombination preventing layer may be provided in the resonator. For example,
The resonator section is composed of an active layer composed of a GaInNAs quantum well layer and a GaAs barrier layer, and GaAs is a first barrier layer.
A structure in which a non-radiative recombination preventing layer made of nPAs, GaAsP, and GaInP is used as the second barrier layer is exemplified. The thickness of the resonator section can be one wavelength. Since the band gap of the non-radiative recombination prevention layer is larger than that of the GaAs first barrier layer, the active region into which carriers are injected substantially extends to the GaAs barrier layer. Also, the remaining Al raw material,
In the case where a step of removing an Al reactant, an Al compound, or Al is provided, the step may be provided in the middle of the non-radiative recombination preventing layer, or a GaAs layer may be provided between the non-radiative recombination preventing layer and the layer containing Al. And can be performed in the middle of the layer. As is clear from the above description, a surface-emitting type semiconductor laser having high luminous efficiency and sufficient reliability for practical use was obtained with such a configuration. Also, not all of the low refractive index layers of the semiconductor distributed Bragg reflector, but at least the portion closest to the active region is Ga _x In containing no Al.
_{1-x Py} As _1-y (0 <x ≦ 1, 0 <y ≦ 1) is used as the non-radiative recombination preventing layer, so that the above-described effect can be obtained without particularly increasing the number of stacked reflectors. I was able to. In addition, even with such a configuration, since the polyimide can be easily embedded, the wiring (the p-side electrode in this example) is hardly disconnected, and a device having high reliability can be obtained.

The oscillation wavelength of the surface emitting semiconductor laser manufactured as described above was about 1.3 μm. In this example, a layer composed mainly of Ga, In, N, and As was used as the active layer (GaInNAs active layer), so that a long-wavelength surface emitting semiconductor laser could be formed on a GaAs substrate. A
Since the current was narrowed by selective oxidation of the layer to be selectively oxidized containing l and As as main components, the threshold current was low. According to the current narrowing structure using the current narrowing layer made of the Al oxide film in which the selective oxidation layer is selectively oxidized, the current spreading can be suppressed by forming the current narrowing layer close to the active layer, so that the current narrowing can be prevented from being exposed to the atmosphere. Carriers can be efficiently confined in the region. Further, by oxidizing to form an Al oxide film, the refractive index is reduced, light can be efficiently confined in a minute region in which carriers are confined by the effect of a convex lens, the efficiency is extremely improved, and the threshold current can be reduced. . In addition, because the current narrowing structure can be easily formed,
Manufacturing costs can be reduced. As is clear from the above description, even in the configuration as shown in FIG. 10, as in the case of FIG.
A surface emitting semiconductor laser in the 1.3 μm band can be realized, and a low-power and low-cost device can be obtained. FIG.
The surface-emitting type semiconductor laser of 0 is similar to the MOC of FIG.
Although growth can be performed by the VD method, other growth methods such as the MBE method can also be used. In addition, D
Although MHy was used, activated nitrogen and other nitrogen compounds such as NH ₃ can also be used. Further, an example of a triple quantum well structure (TQW) is shown as a stacked structure of the active layer, but a structure (SQW, DQW, M
QW) can also be used. The structure of the laser may be another structure. In the surface-emitting type semiconductor laser shown in FIG. 10, the composition of the GaInNAs active layer is changed so that the 1.55 μm band, and further, the longer wavelength 1.7 μm.
An m-band surface emitting semiconductor laser is also possible. GaInN
The As active layer may contain other III-V elements such as Tl, Sb, and P. The active layer is made of GaAsS.
Even if b is used, a 1.3 μm band surface emitting semiconductor laser can be realized on a GaAs substrate. In the present invention, as the active layer, a layer (Ga) whose main element is Ga, In, or As
InAs active layer) or the main element added with N is G
Although a description has been given using a layer made of a, In, N, and As (an active layer of GaInNAs), other than GaNAs, Ga,
PN, GaNPAs, GaInNP, GaNAsSb,
GaInNAsSb or the like can also be suitably used. Particularly in the case of an active layer containing nitrogen as in these examples, the non-radiative recombination preventing layer of the present invention is particularly effective. This will be described below.

FIG. 11 shows a room-temperature photoluminescence spectrum of an active layer having a GaInNAs / GaAs double quantum well structure including a GaInNAs quantum well layer and a GaAs barrier layer manufactured by our MOCVD apparatus. FIG. 12 shows a sample structure. 20 on GaAs substrate
1, a lower cladding layer 202, an intermediate layer 203, an active layer 204 containing nitrogen, an intermediate layer 203, and an upper cladding layer 205.
Are sequentially laminated. In FIG. 11, A is AlGa
A sample in which a double quantum well structure is formed on an As clad layer with a GaAs intermediate layer interposed therebetween, and a sample B in which a double quantum well structure is continuously formed with a GaAs intermediate layer interposed on a GaInP clad layer. It is. As shown in FIG. 11, the photoluminescence intensity of Sample A is lower than that of Sample B by less than half. Therefore, when an active layer containing nitrogen such as GaInNAs is continuously formed on a semiconductor layer containing Al as a constituent element such as AlGaAs using one MOCVD apparatus, the emission intensity of the active layer is deteriorated. A problem arose. Therefore, the threshold current density of the GaInNAs-based laser formed on the AlGaAs cladding layer is 2 times smaller than that formed on the GaInP cladding layer.
More than twice as high. The elucidation of this cause was examined. FIG. 13 shows the nitrogen and oxygen concentrations when an element having a cladding layer of AlGaAs, an intermediate layer of GaAs, and an active layer of a GaInNAs / GaAs double quantum well structure was formed using a single epitaxial growth apparatus (MOCVD). FIG. 5 is a diagram showing a distribution in a depth direction. The measurement was performed by SIMS. Table 1 shows the measurement conditions.

[Table 1]

In FIG. 13, GaInNAs / GaAs
Two nitrogen peaks are found in the active layer corresponding to the s2 quantum well structure. Then, an oxygen peak is detected in the active layer. However, the oxygen concentration in the intermediate layer containing neither N nor Al is about one digit lower than the oxygen concentration in the active layer. On the other hand, the cladding layer is made of GaInP.
, The intermediate layer is GaAs, and the active layer is GaInNAs.
When the depth direction distribution of the oxygen concentration was measured for the device configured as the / GaAs double quantum well structure, the oxygen concentration in the active layer was at the background level. That is, when a semiconductor light emitting device having a semiconductor layer containing Al between a substrate and an active layer containing nitrogen is continuously grown by a single epitaxial growth apparatus using a nitrogen compound raw material and an organic metal Al raw material, Our experiments revealed that oxygen was incorporated into the active layer containing nitrogen. Oxygen incorporated in the active layer forms a non-radiative recombination level, which lowers the luminous efficiency of the active layer. It has been newly found that the oxygen incorporated in the active layer causes a reduction in the luminous efficiency of the semiconductor light emitting element in which the semiconductor layer containing Al is provided between the substrate and the active layer containing nitrogen. The origin of this oxygen is considered to be a substance containing oxygen remaining in the apparatus or a substance containing oxygen contained as an impurity in the nitrogen compound raw material.

Next, the cause of the incorporation of oxygen was examined. FIG. 14 is a diagram illustrating the distribution of Al concentration in the depth direction of the same sample as in FIG. 13. The measurement was performed by SIMS. Table 2 shows the measurement conditions.

[Table 2] FIG. 14 shows that Al was detected in the active layer into which the Al material was not originally introduced. However, in the intermediate layer (GaAs layer) adjacent to the semiconductor layer containing Al (cladding layer), the Al concentration is about one digit lower than that of the active layer. This indicates that Al in the active layer is not diffused, replaced or mixed in from the semiconductor layer (cladding layer) containing Al. On the other hand, like GaInP, Al
When an active layer containing nitrogen was grown on a semiconductor layer containing no, Al was not detected in the active layer. Therefore,
The Al detected in the active layer is the Al source remaining in the growth chamber or in the gas supply line, or an Al reactant, or an Al compound, or Al reacts with the nitrogen compound source or impurities (such as moisture) in the nitrogen compound source. It is bonded and taken into the active layer. That is, when a semiconductor light emitting device having a semiconductor layer containing Al between a substrate and an active layer containing nitrogen is continuously crystal-grown by a single epitaxial growth apparatus using a nitrogen compound raw material and an organic metal Al raw material. It was newly found that Al was naturally taken into the active layer containing nitrogen. Compared with the depth distribution of nitrogen and oxygen concentrations in the same device shown in FIG. 14, the two oxygen peak profiles in the double quantum well active layer do not correspond to the nitrogen concentration peak profiles. Corresponding to the Al concentration profile. From this, the oxygen impurities in the GaInNAs well layer are:
It became clear that rather than being taken in with the nitrogen source, they were taken in together with Al taken in the well layer. That is, when the Al raw material or Al reactant remaining in the growth chamber or the Al compound or Al comes into contact with the nitrogen compound raw material, the moisture contained in the Al and the nitrogen compound raw material or the water remaining in the gas line or the reaction chamber. Al and oxygen are taken into the active layer by bonding with a substance containing oxygen such as. Our experiments have clarified for the first time that oxygen taken into the active layer has reduced the luminous efficiency of the active layer. Therefore, in order to improve this, at least the nitrogen source material or the Al source material or the Al reactant remaining at the place where the impurities contained in the nitrogen compound source contact the growth chamber.
It was found that it was necessary to provide a step for removing the l-compound or Al.

If this step is provided after the growth of the semiconductor layer containing Al and before the start of the growth of the active layer containing nitrogen, when a nitrogen compound raw material is supplied to the growth chamber for growing the active layer containing nitrogen, Residual Al raw material or Al reactant,
Alternatively, an Al compound or Al reacts with a nitrogen compound raw material or an impurity contained in the nitrogen compound raw material and a substance containing oxygen remaining in the device to reduce the concentration of Al and oxygen impurities taken into the active layer. We were able to. Further, it is preferable to remove the non-radiative recombination preventing layer after the growth thereof, since the adverse effect on non-radiative recombination in the active layer can be suppressed when carriers are injected into the active layer by current injection. For example, by reducing the Al concentration in the active layer containing nitrogen to 1 × 10 ¹⁹ cm ⁻³ or less,
Room temperature continuous oscillation became possible. Further, by reducing the Al concentration in the nitrogen-containing active layer to 2 × 10 ¹⁸ cm ⁻³ or less, light emission characteristics equivalent to those formed on a semiconductor layer containing no Al were obtained. Al source or Al reactant or Al remaining in the growth chamber where the nitrogen compound source or impurities contained in the nitrogen compound source touch.
The step of removing the compound or Al includes, for example, providing a step of purging with a carrier gas. Here, the time of the purge step is set after the growth of the Al-containing semiconductor layer is completed and the supply of the Al raw material to the growth chamber is stopped.
It refers to an interval until a nitrogen compound raw material is supplied to a growth chamber to start growth of a semiconductor layer containing nitrogen. As a method of the purging, there is a method of interrupting the growth in an intermediate layer containing neither Al nor nitrogen and purging with a carrier gas. In the case where the growth is interrupted and the purge is performed, the place where the growth is interrupted can be provided between the growth of the Al-containing semiconductor layer and the middle of the non-radiative recombination preventing layer.

FIG. 15 shows an example of a sectional structural view of a semiconductor light emitting device for explaining that a step of purging with a carrier gas in the present invention is provided. 15, a first semiconductor layer 202 containing Al as a constituent element, a first lower intermediate layer 601, a second lower intermediate layer 602, an active layer 204 containing nitrogen, and an upper intermediate layer 20 are formed on a substrate 201.
Third, the second semiconductor layer 205 is sequentially stacked. For crystal growth, an epitaxial growth apparatus using an organic metal Al raw material and an organic nitrogen raw material is used. A growth interruption step is provided between after the growth of the first lower intermediate layer and the start of the growth of the second lower intermediate layer. During the growth interruption, the Al source material, the Al reactant, or the Al compound, or the Al remaining in the growth chamber where the nitrogen compound source material or the impurities contained in the nitrogen compound source material touch is purged with hydrogen as a carrier gas. Has been removed. FIG.
6 is a first lower intermediate layer 601 and a second lower intermediate layer 60
2 shows a measurement result of the distribution of the Al concentration in the depth direction in a semiconductor light emitting device in which the growth was interrupted between 2 and the purge time was set to 60 minutes. As shown in FIG. 16, the Al concentration in the active layer is 3 ×
It could be reduced to 10 ¹⁷ cm ⁻³ or less. This value is about the same as the Al concentration in the intermediate layer. FIG.
FIG. 7 shows the result of measuring the distribution of the nitrogen and oxygen concentrations in the depth direction for the same device. As shown in FIG. 17, the oxygen concentration in the active layer was reduced to a background level of 1 × 10 ¹⁷ cm ⁻³ . The reason why a peak appears in the oxygen concentration in the lower intermediate layer is that oxygen segregates at the growth interruption interface. Therefore, in the case of purging after interrupting the growth, it is preferable that the place where the growth is interrupted be provided after the growth of the Al-containing semiconductor layer until the end of the growth of the non-radiative recombination preventing layer. The non-radiative recombination prevention layer can increase the bandgap energy compared to the quantum well active layer and the barrier layer. This is because adverse effects due to the above can be suppressed. When an active layer containing nitrogen is used as described above, providing a non-radiative recombination preventing layer is particularly effective.

In this semiconductor light emitting device, the growth is interrupted between the first lower intermediate layer and the second lower intermediate layer, and the purge time is set to 6 hours.
By providing for 0 minutes, Al and O in the active layer containing nitrogen are removed.
, Etc. could be reduced. This allows
The luminous efficiency of the active layer containing nitrogen could be improved.
In the step of purging the growth chamber with a carrier gas, by purging the susceptor while heating it,
The Al raw materials and reaction products adsorbed on the susceptor or around the susceptor can be degassed and removed efficiently. However, when the substrates are heated simultaneously, it is necessary to keep supplying a group V source gas such as AsH ₃ or PH ₃ to the growth chamber even during the interruption of the growth, in order to prevent the semiconductor layer on the outermost surface from being thermally decomposed. is there. Further, when purging the growth chamber with a carrier gas, the substrate can be transferred from the growth chamber to another chamber. By transporting the substrate from the growth chamber to another chamber, there is no need to supply a group V source gas such as AsH ₃ or PH ₃ to the growth chamber when purging while heating the susceptor. Therefore, the thermal decomposition of the reaction product containing Al deposited around the susceptor or the susceptor can be further promoted. Thereby, the Al concentration in the growth chamber can be efficiently reduced. Also,
There is a method of purging while growing the intermediate layer. Since the non-radiative recombination preventing layer is provided between the AlGaAs-based reflecting mirror containing Al and the active layer containing nitrogen,
Since the distance between the layer containing Al and the active layer containing nitrogen becomes longer, there is an advantage that the purge time can be lengthened even when purging is performed while growing. In this case, it is better to slow down the growth rate and lengthen the time. In addition, Al containing Al
There is also a method in which a GaAs-based reflecting mirror and an active layer containing nitrogen are formed by different apparatuses. Even in this case, if the regrowth interface is provided below the non-radiative recombination preventing layer, the concentration of impurities such as Al and O in the active layer containing nitrogen can be reduced. In the case of using a crystal growth method that does not use an organometallic Al material and a nitrogen compound material as in a normal MBE method, a semiconductor light emitting device in which a semiconductor layer containing Al is provided between a substrate and an active layer containing nitrogen. No report has been made on the decrease in luminous efficiency of the device. On the other hand, in the MOCVD method, it has been reported that the luminous efficiency of a GaInNAs active layer formed on a semiconductor layer containing Al decreases. Electron.Lett., 2000, 36 (2
1), pp1776-1777, A in the same MOCVD growth chamber
It has been reported that even when an intermediate layer made of GaAs is provided on an lGaAs cladding layer, the photoluminescence intensity is significantly deteriorated when a GaInNAs quantum well layer is continuously grown. In the above report, an AlGaAs cladding layer and a GaInNAs active layer are grown in different MOCVD growth chambers in order to improve the photoluminescence intensity. Therefore, like the MOCVD method,
In the case of the crystal growth method using the organic metal Al raw material and the nitrogen compound raw material, this is a problem that occurs at least.

In the MBE method, crystal growth is performed under ultra-low pressure (in a high vacuum), whereas in the MOCVD method, several tens of To
Since the pressure in the reaction chamber is higher than that of the MBE method from rr to about atmospheric pressure, the mean free path is extremely short, and the supplied raw material and carrier gas come into contact with and react with others in a gas line, a reaction chamber, or the like. It is thought to be. Therefore, in the case of a growth method in which the pressure in the reaction chamber or gas line is high, such as the MOCVD method, it is more preferable to prevent non-radiative recombination after the growth of the semiconductor layer containing Al and before the growth of the active layer containing nitrogen. Until the end of the layer growth, an Al source or an Al reactant, or an Al compound remaining in a place where the nitrogen compound source or an impurity contained in the nitrogen compound source touches in the growth chamber.
Alternatively, when a step of removing Al is provided, the effect of preventing oxygen from being taken into the active layer containing nitrogen is high.
For example, there is a method in which a gas line or a growth chamber is evacuated after growing a semiconductor layer containing Al and before growing an active layer containing nitrogen. In this case, the effect is high if heating is performed. There is also a method of removing the semiconductor layer containing Al by flowing an etching gas after growing the semiconductor layer before growing the active layer containing nitrogen. An example of a gas that can react with and remove an Al-based residue is an organic-based compound gas. As described above, when a DMHy gas, which is one of the organic compound gases, is supplied using a DMHy cylinder during the growth of the active layer containing nitrogen, it is apparent that the gas reacts with the Al-based residue. Therefore, when the organic compound gas is supplied using the organic compound gas cylinder after the growth of the semiconductor layer containing Al and before the growth of the active layer containing nitrogen, a jig for holding the reaction chamber side wall, the heating zone, and the substrate is used. And the like, can be removed by reacting with the Al-based residue remaining in the active layer, etc., so that the incorporation of oxygen into the active layer can be suppressed. Furthermore, it is preferable to use the same gas as the nitrogen material of the active layer containing nitrogen, since it is not necessary to add a special gas line. This step may be performed by interrupting the growth, and includes GaNAs, GaInNAs, Ga
A layer containing nitrogen such as an InNP layer may be formed by crystal growth as a dummy layer separately from the active layer. It is preferable to perform the Al removal step by crystal growth as compared with the case where the growth is interrupted, because there is no time loss. When GaInAs is used for the active layer, up to 1.1 μm has conventionally been considered to be the limit of increasing the wavelength.
The aInAs quantum well active layer can be grown thicker than before, and the wavelength can reach up to 1.2 μm. As described above, a semiconductor laser having a wavelength of 1.1 μm to 1.7 μm has not conventionally been available with a suitable material.
By using nAs, GaInNAs, and GaAsSb, and by providing a non-radiative recombination prevention layer, a high-performance surface emitting laser can be realized in a long wavelength region of a wavelength of 1.1 μm to 1.7 μm where stable oscillation has conventionally been difficult. It is now possible to apply it to optical communication systems.

FIG. 18 shows an example in which such a long-wavelength band surface emitting semiconductor laser device is formed as a number of chips on an n-GaAs wafer 40 having a plane orientation of (100), and a laser device chip. In the laser element chip shown here, 1 to n laser elements 41 are formed, and the number n and the arrangement method are determined according to the application. FIG. 19 shows an example of an optical communication system using a long-wavelength band surface emitting semiconductor laser, which comprises a surface emitting laser 51 and an optical fiber 51W. In FIG. 19, the surface emitting laser and the optical fiber are directly coupled. However, a coupling using a lens or a lens system may be used. The diameter of the light emitting portion 51W of the surface emitting laser 51 is d, and the core diameter of the optical fiber 12 is F. If the light emitting portion is polygonal, the diameter of the inscribed circle is d. The laser light from the surface emitting laser diverges as shown by a dotted line (51B) in FIG. However, it is smaller than the spread angle of the edge emitting laser. When the surface emitting laser and the optical fiber are brought close to each other as shown in FIG. Can be the highest. The surface emitting laser used in the embodiment has a wavelength of 1.
The band is from 1 μm to 1.7 μm. Particularly, when the 1.3 μm band or the 1.55 μm band is used, the internal loss in the quartz fiber is small, so that it is suitable for long-distance transmission. Surface emitting laser 51
The light emitting portion 51W has a diameter d (when the light emitting portion is polygonal, the diameter of an inscribed circle is d), and the optical fiber 5
Assuming that the core diameter of No. 2 is F, the coupling efficiency can be increased by setting the ratio of F and d to F / d ≦ 2 (Equation 1).

Next, an embodiment on the assumption that the laser and the optical fiber are directly coupled will be described with reference to FIG. Conventionally, coupling directly to an optical fiber with an edge emitting laser in the 1.3 μm band or the like has a disadvantage that the coupling efficiency is low and that the laser oscillation state fluctuates due to the influence of the return light from the optical fiber. However, in the present invention, since the surface emitting laser is used, the beam shape can be circular, and the divergence angle is not anisotropic. For this reason, the coupling efficiency is higher than that of the end face type laser. Further, since the surface emitting laser is provided with a reflection film having a very high reflectance, it is hardly affected by return light. This allows direct coupling. Therefore, in the related art, the optical isolator is used so that the return light does not return to the laser, but the optical isolator can be omitted by using the surface emitting laser.
If the diameter of the light emitting portion of the surface emitting laser is d (the diameter of an inscribed circle is d when the light emitting portion is polygonal) and the core diameter of the optical fiber is F, 0.5 ≦ F / If d ≦ 2 (Equation 2), the coupling efficiency can be increased. The reasons for this range are described in detail below.

Table 3 shows the results of an investigation by the authors on the coupling loss between the surface emitting laser and the single mode optical fiber. Table 3 shows the case of direct coupling. When the light emitting portion of the surface emitting laser becomes larger than the core diameter, the coupling efficiency decreases, but d ≦ 2F (that is, 0.5 ≦ 2F).
If ≦ F / d), the coupling loss can be suppressed within 3 to 5 dB. Further, when the size of the light emitting portion is smaller than the core diameter, the NA (divergence angle of the laser beam determined by the diameter and wavelength of the circle inscribed in the light emitting portion) can be coupled to the single mode optical fiber in a single mode. The coupling can be performed with high efficiency when the aperture ratio is equal to or less. For example, core diameter 10
In μm, the refractive index of the core is 1.4469, the refractive index of the cladding is 1.4435, and if the laser wavelength is 1.3 μm, the NA that can be coupled in a single mode is 0.0995. The diameter of the light emitting portion corresponding to this NA is about 6.5 μm
It is. However, the coupling loss can be suppressed to 3 to 5 dB even at 6.5 μm or less, for example, at about 5 μm. It is sufficient that d ≧ 0.5F (that is, F / d ≦ 2). As described above, when the surface emitting laser is directly coupled to the optical fiber, the coupling loss can be relatively reduced by setting the range of 0.5 ≦ F / d ≦ 2 (Equation 2), and the efficiency can be reduced. Can be well coupled. In this embodiment, the single mode optical fiber is used. However, even if the single mode optical fiber is coupled to a single mode optical fiber via a multimode optical fiber or a tapered light guide path, the same applies if the relationship of Equation 2 is maintained. The effect of is obtained.

[Table 3]

Next, as another example, FIG. 20 shows an optical communication system using a surface emitting laser, a coupling lens, and an optical fiber. A coupling lens 53 is arranged between the surface emitting laser 51 and the single mode optical fiber 52. The coupling lens may be a single lens or a lens system combining a plurality of lenses. In order to form a single lens, it is preferable to dispose the lens 53 near the emission part of the surface emitting laser. By selecting the lens power (or focal length) of the coupling lens, the diameter d of the light emitting portion (when the light emitting portion is polygonal, the diameter of the inscribed circle is set to d) or more than the core diameter of the optical fiber. However, the coupling loss can be reduced. For example, when the core diameter is 10 μm and the diameter of the light emitting portion is 20 μm, the beam diameter is set to 1 by a lens.
/ 2. The focal length of the lens is f, the laser wavelength is λ (= 1.3 μm), and the radius of the light emitting portion is ω ₀ (=
10 μm) and the refractive index n (= 1), It is sufficient to find f that satisfies At this time, the focal length f is about 1
It becomes 40 μm. When a coupling lens is used, if the diameter of the light emitting portion is d (the diameter of an inscribed circle is d if the light emitting portion is polygonal) and the core diameter of the optical fiber is F, d ≧ F, That is, if F / d ≦ 1 (Equation 3), coupling to the optical fiber can be efficiently performed.

[Table 4]

In FIG. 20, the coupling lens is constituted by one lens, but a lens system constituted by a plurality of lenses may be constituted. For example, FIG. 21 shows an embodiment in which two lenses are used for coupling. First lens 54 and second lens
The laser light is coupled to the optical fiber by the lens 53. The first lens 54 converges the divergent light from the light emitting portion 51W of the surface emitting laser 51 toward the second lens 53, and forms a beam waist on the second lens surface.
The second lens has the same function as the lens 53 of FIG.
If one lens cannot be placed in the vicinity of the laser light emitting part, or if the divergence angle of the laser beam is large and the coupling efficiency to the optical fiber is low, coupling the lens with multiple lenses will Efficiency can be increased.
In this embodiment, the single mode optical fiber is used.
Even when coupling to a multimode optical fiber or a single mode optical fiber via a tapered light guide path, the same effect can be obtained if the relationship of Expression 3 is maintained. When a conventional edge-emitting laser is used, the laser oscillation state may be changed by return light from the coupling lens,
To avoid this, an optical isolator was required. However, when a surface-emitting laser is used, since a reflection film having a light reflectance is used, it is hardly affected by return light, so that an optical isolator is unnecessary.

Next, an embodiment comprising a surface emitting laser array and an optical fiber array will be described with reference to FIG. The surface emitting laser 51 may have an array of light emitting portions as shown in FIG. 22 or an array of surface emitting elements themselves. Further, a plurality of laser element chips may be arranged in an array. In FIG. 22, since the corresponding light emitting portion 51W and the optical fiber 52 are directly coupled, the aforementioned FIG.
As described in FIG. 9, when the relationship between the diameter d of the circle inscribed in the light emitting portion and the core diameter F of the optical fiber is set to be within the range of Expression 2, the coupling loss can be made relatively small, and the coupling can be efficiently performed. it can. Since these are arranged in an array, an optical communication system having high light use efficiency and a large amount of information can be constructed. FIG. 23 is a view for explaining an embodiment comprising a surface emitting laser array, a coupling lens array and an optical fiber array. The surface emitting laser 51 may have an array of light emitting portions as shown in FIG. 23, or an array of surface emitting elements themselves. In FIG. 23, the relationship between the corresponding light emitting portion 51W, one lens element of the lens array, and the optical fiber 52 is the same as that described in FIG.
That is, if the relationship between the diameter d of the light emitting portion (when the light emitting portion is polygonal, the diameter of the inscribed circle is d) and the core diameter F of the optical fiber is expressed by Equation 3, coupling can be efficiently performed. . Since these are arranged in an array, an optical communication system having high light use efficiency and a large amount of information can be constructed. Although one lens array 55 is used in this embodiment, a plurality of lens arrays may be used. When constructing an optical communication system in an array, an optical isolator array was necessary to avoid the influence of return light in the conventional edge-emitting laser array, but in the present invention, the influence of return light is used because a surface-emitting laser is used. It is not necessary to use an optical isolator array because it is hardly affected by the optical isolator. Therefore, it is a low-cost optical communication system.

[0042]

As described above, according to the first and second aspects of the present invention, by devising the semiconductor distributed Bragg reflector, the operating voltage, the oscillation threshold current and the like can be reduced, and the heat generation of the laser element is reduced and the laser element is stabilized. Oscillation was achieved and a low-cost practical optical communication system was realized. Further, if a surface emitting laser is used, an optical communication system capable of coupling to a single mode optical fiber with high efficiency in the same band can be realized. In a third aspect, a lens or a lens system is disposed between the surface emitting semiconductor laser chip and the optical fiber, and the diameter of a circle inscribed in the light emitting portion of the surface emitting semiconductor laser chip is d. Assuming that the core diameter of the optical fiber is F, by setting F / d ≦ 1,
It is possible to realize an optical communication system capable of performing coupling with high efficiency and performing stable coupling without using an optical isolator. According to claims 4 and 5, the surface emitting type semiconductor laser device chip and the optical fibers are arranged in an array, so that coupling can be efficiently performed,
In addition, stable coupling can be performed without using an optical isolator, and a low-cost optical communication system with a large amount of information can be realized because a plurality of light emitting elements are used.

[Brief description of the drawings]

FIG. 1 is a sectional view of an element part of a long-wavelength band surface emitting semiconductor laser according to an embodiment of the present invention.

FIG. 2 is a partial cross-sectional view of a configuration of a semiconductor distributed Bragg reflector of a long wavelength band surface emitting semiconductor laser according to an embodiment of the present invention.

FIG. 3 is a diagram showing an example in which the composition gradient of the hetero-spike buffer layer of the semiconductor distributed Bragg reflector applied to the present invention is larger near the GaAs layer than the AlAs layer.

FIG. 4 is a diagram showing an example in which the Al composition of the hetero-spike buffer layer is changed linearly.

FIG. 5 is a diagram showing a result of estimating a differential sheet resistance of the hetero-spike buffer layer of FIG. 3;

FIG. 6 is a band diagram showing a thermal equilibrium state of a DBR heterointerface of a semiconductor distributed Bragg reflector made of AlAs / GaAs.

FIG. 7 is a band diagram of the hetero-spike buffer layer of FIG. 3 in a thermal equilibrium state.

FIG. 8: AlAs / GaAs (p = 1E18 cm ⁻³ )
It is a figure which shows the resistivity of 4 pairs.

FIG. 9 is a graph showing the rate of change of the reflectance of an AlAs / GaAs semiconductor distributed Bragg reflector.

FIG. 10 is a sectional view of an element portion of another configuration of a long-wavelength band surface emitting semiconductor laser according to an embodiment of the present invention.

FIG. 11 shows GaInNAs / according to an embodiment of the present invention.
FIG. 3 is a room-temperature photoluminescence spectrum diagram of an active layer having a GaAs double quantum well structure.

FIG. 12 is a structural diagram of a sample.

FIG. 13 is a diagram showing a depth direction distribution of nitrogen and oxygen concentrations.

FIG. 14 is a diagram showing the distribution of the Al concentration in the depth direction.

FIG. 15 is an explanatory structural view in the case where growth is interrupted by carrier gas purge.

FIG. 16 is a diagram showing the distribution of the Al concentration in the depth direction in a case where a growth interruption step is provided and purged with hydrogen.

FIG. 17 is a diagram showing a depth direction distribution of nitrogen and oxygen concentrations when a growth interruption step is provided and purged with hydrogen.

FIG. 18 is a plan view showing a wafer substrate and a laser element chip on which a long wavelength band surface emitting semiconductor laser element according to one embodiment of the present invention is formed.

FIG. 19 is a diagram of an optical communication system in which a long wavelength band surface emitting semiconductor laser device according to an embodiment of the present invention is directly coupled with an optical fiber.

FIG. 20 is a diagram of an optical communication system using a long wavelength band surface emitting semiconductor laser device, a coupling lens, and an optical fiber according to an embodiment of the present invention.

FIG. 21 is a diagram of an optical communication system using a long-wavelength band surface emitting semiconductor laser device, a two-piece coupling lens, and an optical fiber according to an embodiment of the present invention.

FIG. 22 is a diagram of an optical communication system using a long-wavelength band surface emitting semiconductor laser device and an optical fiber array according to an embodiment of the present invention.

FIG. 23 is a diagram of an optical communication system using a long wavelength band surface emitting semiconductor laser device, a lens array, and an optical fiber array according to an embodiment of the present invention.

[Explanation of symbols]

1 n-side electrode, 2 n-GaAs substrate, 3 lower distributed Bragg reflector, 4 GaAs spacer layer, 5 upper distributed Bragg reflector, 6 p-contact layer,
12 TQW active layer, 13 GaAs barrier layer

 ──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Teruyuki Furuta 1-3-6 Nakamagome, Ota-ku, Tokyo Inside Ricoh Company (72) Inventor Ken Kanai 1-3-6 Nakamagome, Ota-ku, Tokyo Share Inside Ricoh Company (72) Inventor Atsuyuki Watada 1-3-6 Nakamagome, Ota-ku, Tokyo Stock Company Ricoh Company (72) Inventor Shunichi Sato 1-3-6 Nakamagome, Ota-ku, Tokyo Stock Company Ricoh ( 72) Inventor Yukie Suzuki 1-3-6 Nakamagome, Ota-ku, Tokyo Ricoh Co., Ltd. (72) Inventor Satoru Sugahara 1-3-6 Nakamagome, Ota-ku, Tokyo Ricoh Co., Ltd. (72) Inventor Shinji Sato 1-3-6 Nakamagome, Ota-ku, Tokyo Inside Ricoh Company (72) Inventor Shuichi Hikichi 1-3-6 Nakamagome, Ota-ku, Tokyo Stock Company Inside Ricoh (72) Inventor Takuro Sekiya 1-3-6 Nakamagome, Ota-ku, Tokyo Inside Ricoh Company (72) Inventor Naoto Shakuya 1-3-6 Nakamagome, Ota-ku, Tokyo Inside Ricoh Company ( 72) Inventor Takashi Takahashi 1-3-6 Nakamagome, Ota-ku, Tokyo F-term in Ricoh Co., Ltd. (reference) 2H037 AA01 BA03 CA13 DA03 DA04 DA05 5F073 AA07 AA08 AA51 AA53 AA65 AA74 AA89 AB05 AB17 AB27 AB28 BA02 BA09 CA07 CA17 CB02 CB19 DA05 DA23 DA27 DA35 EA02 EA23 EA27 EA29

Claims (5)

[Claims] In a laser chip and an optical communication system connected to the laser chip, the laser chip has an oscillation wavelength of 1.1 μm to 1.7 μm, and a main element of an active layer for generating light is Ga, In. , N, As
Or a surface emitting semiconductor laser device chip having a resonator structure including a reflecting mirror provided on an upper portion and a lower portion of the active layer in order to obtain a laser beam as a layer made of Ga, In, and As, The reflecting mirror has a reflection wavelength of 1.1 μm
As described above, the refractive index of the material layer constituting the reflecting mirror is a semiconductor distributed Bragg reflecting mirror that periodically changes to a value different from a small value and reflects incident light by light wave interference, and the material layer having the small refractive index is used. Is Al _x Ga _1-x As (0 <x ≦ 1)
And then, the material layer of the refractive index is large is _Al y _{Ga 1-} y As
(0 ≦ y <x ≦ 1), and Al _z Ga having a value between the small and large refractive index between the material layers having the small and large refractive index.
A surface-emitting type semiconductor laser device chip which is a reflector having a hetero-spike buffer layer made of _1-z As (0 ≦ y <z <x ≦ 1) with a thickness of 20 nm to 50 nm is used as an emission light source. Where d is the diameter of a circle inscribed in the light emitting portion of the surface-emitting type semiconductor laser element chip and F is the core diameter of the optical fiber, and 0.5 ≦ F / d ≦ 2. Optical communication system. 2. A laser chip connected to the laser chip.
In an optical communication system, the laser chip
The wavelength is 1.1 μm to 1.7 μm, and the light generating activity
The main layer is made of Ga, In, N, As
Layer or a layer made of Ga, In, As
Provided at the top and bottom of the active layer to obtain light
Surface-emitting type semiconductor laser having a resonator structure including a reflector
The element chip, wherein the reflection mirror has a reflection wavelength of 1.1.
When the refractive index of the material layer constituting the reflecting mirror is larger than μm,
Periodically changes to different values, and the incident light is reflected by light wave interference.
A semiconductor distributed Bragg reflecting mirror,
The material layer with a small refractive index is Al _xGa_1-xAs (0 <x ≦
1) and the material layer having a large refractive index is Al_yGa_{1 -Y}
A reflecting mirror having As (0 ≦ y <x ≦ 1),
The main composition between the layer and the reflector is Ga_xIn_1-xP
_yAs_1-y(0 <x ≦ 1, 0 <y ≦ 1)
Surface-emitting type semiconductor laser device provided with emission recombination prevention layer
The light emitting source is a semiconductor chip, and the surface emitting type semiconductor
The diameter of the circle inscribed in the light emitting part of the laser diode chip
d, where F is the core diameter of the optical fiber, 0.5 ≦ F /
An optical communication system, wherein d ≦ 2. 3. A lens or lens system is arranged between the surface emitting semiconductor laser device chip and an optical fiber,
Further, when a diameter of a circle inscribed in the light emitting portion of the surface emitting type semiconductor laser element chip is d and a core diameter of the optical fiber is F, F / d ≦ 1 is satisfied. 3. The optical communication system according to claim 1. 4. The optical communication system according to claim 1, wherein said surface-emitting type semiconductor laser device chip and optical fibers are arranged in an array. 5. The optical communication system according to claim 3, wherein said surface-emitting type semiconductor laser device chip, a lens or a lens system, and optical fibers are arranged in an array.