JP2002252405A - Optical communication system - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an optical communication system having high reliability with respect to deterioration of a plane light-emission type semiconductor laser device. SOLUTION: In a lower semiconductor distribution Bragg reflector and an upper semiconductor distribution Bragg reflector, a low refraction index layer and a high refraction index layer, which constitute a structural layer of a long wavelength band plane light-emitting semiconductor laser device, are alternately and periodically laminated. Such a material layer that a refraction index takes a value between two layers is provided between the low refraction index layer and the high refraction index layer. This material layer varies a composition as having a slope from a composition of the high refraction index layer to a composition of the low refraction index layer, whereby the refraction index changes continuously or stepwise. Thus, the generation of a hetero barrier generated on an interface of two types of semiconductor layers which constitute the semiconductor Bragg reflector is prevented, thereby lowering electric resistance of the Bragg reflector. Such the material layer can be formed by controlling a gas flow rate when forming the layers.

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, and more particularly to a so-called surface which emits light in a direction perpendicular to the surface of a semiconductor substrate used for manufacturing the semiconductor laser. The present invention relates to an optical communication system in which a plurality of laser elements are formed using a light 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.
Therefore, 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.

[0003] The immediate application of the optical interconnection device is short-distance optical fiber communication in addition to parallel connection between housings of computers or the like and between boards. There are trunk systems for networks and long-distance large-capacity communications.

Generally, a surface emitting semiconductor laser is made of GaAs.
Or, it is common to comprise an active layer made of GaInAs, and an optical resonator consisting of an upper semiconductor distributed Bragg reflector disposed above and below the active layer and a lower semiconductor distributed Bragg reflector on the substrate side. However, since the length of the optical resonator is significantly shorter than that of the edge emitting semiconductor laser, it is necessary to set the reflectivity of the reflecting mirror to an extremely high value (99% or more) so as to easily cause laser oscillation. There is. 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 with a period of 1/4 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 large difference in the refractive index cannot be obtained with a reflecting mirror material that matches the substrate. Must be more than pairs.

Another problem with semiconductor lasers formed on InP substrates is that the characteristics change significantly 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, one disclosed in Japanese Patent Application Laid-Open No. 9-237942 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 part on the substrate side. A semiconductor layer made of GaInNAs is used as a high refractive index layer of at least one of the lower and upper semiconductor distributed Bragg reflecting mirrors so that a larger refractive index difference is obtained than in the prior art. It is to realize a mirror.

Further, GaInNAs is used as a material for the active layer. This is because the band gap (forbidden band width) is increased from 1.4 eV to 0 eV by increasing the N composition.
0.85 μm
This is because it can be used as a material that emits a longer wavelength. In addition, since lattice matching with the GaAs substrate is possible, the semiconductor layer made of GaInNAs is 1.3 μm.
Reference is also made to the fact that it is preferable as a material for long-wavelength surface emitting semiconductor lasers in the m-band and 1.55 μm band.

[0009] However, the prior art merely suggests the possibility of realizing a surface emitting semiconductor laser in a wavelength band longer than 0.85 µm, and such a device is not actually realized. This is because the basic configuration is almost theoretically determined, but a more specific configuration for realizing stable laser emission is still unknown.

As an example, 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 1/4 wavelength as described above is used. Or a device using a semiconductor layer made of AlInP, which is lattice-matched to the same substrate as the low refractive index layer of the semiconductor distributed Bragg reflector, as disclosed in JP-A-9-237942. The laser element does not emit light at all,
Alternatively, even if light is emitted, the light emission efficiency is low, which is far from a practical level.

This is because the material containing Al is chemically very active, and crystal defects caused by Al are likely to occur. To solve this, Japanese Patent Application Laid-Open No. 8-34001
There is a proposal to form a semiconductor distributed Bragg reflector from GaInNP and GaAs that do not contain Al as in the inventions disclosed in Japanese Patent Application Publication No. 46-46 and Japanese Patent Application Laid-Open No. 7-307525. However, the refractive index difference between GaInNP and GaAs is AlAs
The refractive index difference is about half the refractive index difference between GaAs and GaAs.

That is, at present, optical fiber communication is expected in a computer network or the like. A long-wavelength surface emitting semiconductor laser having a laser wavelength of 1.1 μm to 1.7 μm and a communication system using the same are available. It does not exist and its appearance is longing for.

[0013]

According to the present invention, a laser oscillation wavelength used for such optical communication or the like is 1.1 μm or more.
1. Field of the Invention The present invention relates to a long-wavelength surface emitting semiconductor laser having a wavelength of 1.7 μm and an optical communication system using the same. In addition, by adding a judgment circuit and a switching circuit combining a photodiode and a comparator for monitoring an emission state to the surface emitting semiconductor laser element, the reliability of the surface emitting semiconductor laser element against degradation is improved. An object of the present invention is to propose an optical communication system capable of constructing a high optical communication system.

A second object is to use a long-wavelength surface emitting semiconductor laser device chip having a laser oscillation wavelength of 1.1 μm to 1.7 μm, which can be used stably, as a light emitting light source. By adding a decision circuit and a switching circuit combining a photodiode and a comparator for monitoring the light emitting state of the device, an optical communication system with high reliability against the deterioration of the surface emitting semiconductor laser device can be constructed. An object of the present invention is to propose an optical communication system which enables the optical communication system.

[0015]

According to the present invention, in order to achieve the above object, first, 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 μm. 0.7 μm, and the light-generating active layer is a layer whose main element is Ga, In, N, As or a layer consisting of Ga, In, As. What is claimed is: 1. A surface-emitting type semiconductor laser device chip having a resonator structure including a reflecting mirror provided at a lower portion, wherein the reflecting mirror periodically changes the refractive index of a material layer constituting the reflecting mirror to be small / large and is incident. A semiconductor distributed Bragg reflector for reflecting light by light wave interference, and the material layer having a small refractive index is made of Al _x Ga _{1 -x} As.
(0 <x ≦ 1) and then, the material layer of the refractive index is large is Al _y
A reflecting mirror having Ga _1-y As (0 ≦ y <x ≦ 1),
And a material layer Al _z Ga _{1 -z} As (0 ≦ y <z) in which the refractive index takes a value between small and large between the material layers with small and large refractive indexes.
<X ≦ 1) is used as a light emitting light source, and the optical communication system includes 2N surface emitting semiconductor lasers, N optical fibers, and the surface emitting semiconductor laser. The semiconductor laser device includes a determination circuit for monitoring the light emission state of the semiconductor laser device and a switching circuit.

Secondly, 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 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 reflector is a semiconductor distributed Bragg reflector in which the refractive index of the material constituting the reflector changes periodically as small / large and reflects incident light by light wave interference. Al _x Ga _1-x
As (0 <x ≦ 1), the material having a large refractive index is Al
a reflecting mirror with _y Ga _1-y As (0 ≦ y <x ≦ 1),
GaInP or Ga between the active layer and the reflector.
A surface-emitting type semiconductor laser device chip provided with a non-light-emitting recombination prevention layer made of InPAs is used as a light-emitting source, and the optical communication system comprises 2N surface-emitting type semiconductor lasers and N optical fibers. The switching device includes a determination circuit for monitoring a light emitting state of the surface emitting semiconductor laser device and a switching circuit.

[0017]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS First, an example of a long-wavelength surface emitting semiconductor laser having a small laser oscillation wavelength of 1.1 to 1.7 .mu.m, which is a light emitting element applied to the optical communication system of the present invention, having a small transmission loss. This will be described with reference to FIG. As described above, a long-wavelength surface emitting semiconductor laser having a laser oscillation wavelength of 1.1 μm to 1.7 μm to which the present invention is conventionally applied only suggests the possibility. The material, as well as the more specific and detailed composition, 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.
On the As substrate, n-Al _x Ga _{1 -x} A with a thickness (thickness of λ / 4) of 発 振 of the oscillation wavelength λ in each medium.
s (x = 1.0) (low refractive index layer to low refractive index layer) and n−
An n-semiconductor distributed Bragg reflector (AlAs / GaAs lower semiconductor distributed Bragg reflector) in which 35 cycles of Al _y Ga _1-y As (y = 0) (high refractive index layer to high refractive index layer) are alternately stacked. And n-Ga _x In _1-x P _{y having} a thickness of λ / 4 is formed thereon.
As _1-y (x = 0.5, y = 1) layers were laminated. In this example _{n-Ga x In 1-x} P y As 1-y (x = 0.5, y =
1) The layer is also a part of the lower reflecting mirror and is a low refractive index layer (a layer having a small refractive index).

An undoped lower GaAs spacer layer, an active layer (quantum well active layer), which is a three-layer Ga _x In _1-x As quantum well layer, and a GaAs barrier layer (20 n
m) and an undoped upper G layer
The aAs spacer layer is laminated to form a resonator having a thickness of one oscillation wavelength λ (thickness of λ) in the medium.

In addition, C (carbon) doped p-
Ga _x In _{1-x Py} As _1-y (x = 0.5, y = 1) layer and Z
A periodic structure (one cycle) in which n-doped p-Al _x Ga _1-x As (x = 0) is alternately stacked with a thickness of １ ／ times the oscillation wavelength λ in each medium is stacked. C-doped p-Al _x Ga _{1 -x} As (x = 0.9) and Zn-doped p
A semiconductor distributed Bragg reflector (a periodic structure (25 periods) in which -Al _x Ga _{1 -x} As (x = 0) is alternately stacked with a thickness of １ ／ times the oscillation wavelength λ in each medium; Al _0.9 Ga _0.1 As / GaAs upper semiconductor distributed Bragg reflector)
Is formed. In this example _{p-Ga x In 1-x} P y As
_{The 1-y} (x = 0.5, y = 1) layer is also a part of the upper reflecting mirror and is a low refractive index layer (a layer having a small refractive index).

Here, both the upper and lower reflectors are formed by alternately laminating a low refractive index layer (a layer having a low refractive index) / a high refractive index layer (a layer having a high refractive index). Between these, the material layer Al _z G whose refractive index takes a value between small and large
a _1-z As (0 ≦ y <z <x ≦ 1) is provided.

FIG. 2 shows a material layer AlzGa1- having a refractive index between a small and a large value between a low refractive index layer (a layer with a small refractive index) and a high refractive index layer (a layer with a large refractive index). zAs (0 ≦ y <z <
FIG. 1 shows a part of a semiconductor distributed Bragg reflector provided with x ≦ 1 (in FIG. 1, illustration is omitted because the figure becomes complicated).

Conventionally, it has been studied to provide such a material layer for a semiconductor laser having a laser wavelength of 0.85 μm band. However, it is still in the stage of study, and the material or its thickness is not described in detail. Not considered. Further, the laser oscillation wavelength as in the present invention is 1.1 μm to 1.7 μm.
No consideration has been given to a long-wavelength surface emitting semiconductor laser having a wavelength of m. The reason for this is that this field (a long-wavelength surface emitting semiconductor laser having a laser oscillation wavelength of 1.1 μm to 1.7 μm) is a new field, and little research has yet been made.

The present inventor has quickly noticed the usefulness of this field (a long-wavelength surface emitting semiconductor laser having a laser oscillation wavelength of 1.1 μm to 1.7 μm and optical communication using the same).
In order to realize it, we studied diligently. Such a material layer controls the gas flow rate during formation, etc.
The Al layer is formed so that the Al composition is changed continuously or stepwise so that the refractive index of the material layer is changed continuously or stepwise. More specifically, Al _z Ga _1-z
The value of z of the As (0 ≦ y <z <x ≦ 1) layer is changed from 0 to 1.0.
GaAs to AlGaAs to A
It is formed such that the ratio of Al and Ga gradually changes to 1As. This is created by controlling the gas flow during layer formation as described above. Further, it may be formed so that the ratio of Al and Ga changes continuously as described above, or the same effect can be obtained even if the ratio changes stepwise.

The reason for providing such a material 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 the hetero barrier generated at the interface between the two types of semiconductor layers constituting the semiconductor distributed Bragg reflector. However, as in the present invention, the interface between the low refractive index layer and the high refractive index layer is changed from one composition to the other. It is possible to suppress the generation of the hetero barrier by changing the Al composition gradually to the composition and changing the refractive index.

The material layer AlzGa1-zAs having such a refractive index between a small value and a large value (0 ≦ y <z <x ≦
1) The laser oscillation wavelength as in the present invention is 1.1 μm or more.
In the case of a long-wavelength surface emitting semiconductor laser of 1.7 μm, 5n
The thickness is preferably from m to 50 nm. If the thickness is smaller than this, there is a problem that the resistance becomes large and current does not easily flow, and the element generates heat and the driving energy becomes high. If the thickness is large, the resistance becomes small, which is advantageous in terms of heat generation of the element and driving energy. However, there is a problem that the reflectance cannot be obtained, and the optimum range (thickness of 5 nm to 50 nm) as described above. You need to choose

As described above, it has been considered to provide such a material layer for a conventional semiconductor laser having a laser wavelength in the 0.85 μm band. In the case of a long-wavelength surface emitting semiconductor laser having a wavelength of 1.7 μm, it is more effective. This is because, for example, in order to obtain the same reflectance (for example, 99.5% or more), the band from 1.1 μm to 1.0 μm is more than 0.85 μm.
In the case of the 7 μm band, such a material layer can be approximately doubled, so that the resistance value of the semiconductor distributed Bragg reflector can be reduced, the operating voltage, the oscillation threshold current, and the like are reduced, and the laser device This is advantageous in terms of preventing heat generation, stable oscillation, and low energy driving. In other words, providing such a material layer on the semiconductor distributed Bragg reflector is particularly effective in the case of 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. I can say.

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 device, Al _x Ga _{1 -x} As (x = 1.0)
(Low refractive index layer to low refractive index layer) and Al _y Ga _1-y As (y
= 0) (in the case of a high refractive index layer-refractive index large layer) 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 wavelength band in which the reflectivity is 99.5% or more is 53 nm. When the reflectivity is designed to be 99.5% or more, it is only necessary to control the film thickness by ± 2%. Therefore, 10 nm, 20 nm, 3
When a prototype of 0 nm was fabricated, a 1.3 μm band surface emitting laser device which could keep the reflectivity to a practically acceptable level and reduced the resistance value of the semiconductor distributed Bragg reflector was realized. Laser oscillation succeeded. Other configurations of the prototyped laser element are as described below.

In the multilayer mirror, there is a band having a high reflectance including the 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 the region where the reflectance at the design wavelength is the highest and decreases very little as the wavelength increases. 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.

However, a film thickness error of about ± 1% actually occurs, so that the target wavelength deviates from the wavelength having the highest reflectance. For example, when the target wavelength is 1.3 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 band of the high reflectance (here, the region where the reflectance is equal to or more than a required value with respect to a target wavelength) is wide. However, thickening the intermediate layer tends to narrow this band.

As described above, in 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, the configuration of such a semiconductor distributed Bragg reflector is devised and optimized. Since the resistance value can be reduced while maintaining a high reflectance, the operating voltage, the oscillation threshold current, and the like can be reduced, so that heat generation of the laser element, stable oscillation, and low-energy driving can be achieved.

Returning again to FIG. 1, the uppermost p-Al _x G
The a _1-x As (x = 0) layer also has a role as a contact layer (p-contact layer) for making contact with the electrode. Here, the In composition x of the quantum well active layer is 3
9% (Ga0.61In0.39As). The thickness of the quantum well active layer was 7 nm. The quantum well active layer is made of GaAs.
It had a compression strain of about 2.8% with respect to the substrate.

The whole surface emitting semiconductor laser was grown by MOCVD. In this case, no lattice relaxation was observed. The materials constituting each layer of the semiconductor laser include TMA (trimethylaluminum), TMG (trimethylgallium), TMI (trimethylindium),
AsH ₃ (arsine) and PH ₃ (phosphine) were used. H ₂ was used as a carrier gas. 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. In addition, high vacuum is not required as in the MBE method, and the supply flow rate and supply time of the source gas may be controlled.

In this example, the portion outside the current path was irradiated with protons (H ⁺ ) to form an insulating layer (high resistance portion) to form 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, an active region (in this embodiment, a resonator composed of upper and lower spacer layers and a multiple quantum well active layer) sandwiched between upper and lower reflectors and into which carriers are injected and recombined, is used as an active region. In the material containing Al (II
The ratio of the low refractive index layer of the lower and upper reflectors closest to the active layer is G.
It is set to _{a x In 1-x P y} As 1-y (0 <x <1,0 <y ≦ 1) non-radiative recombination preventing layer. Since the carriers are confined between the low-refractive index layers of the upper and lower reflectors, which are closest to the active layer and have a wide gap, only the active region is constituted by a layer containing no Al (the percentage of group III is 1% or less). However, if the low-refractive index layer (wide gap layer) of the reflector in contact with the active region has a structure including Al, when carriers are injected and recombined, non-radiative recombination occurs at this interface, and the luminous efficiency is reduced. Will drop. Therefore, it is desirable that the active region be formed of a layer containing no Al.

The Ga _x In _{1-x Py} As _1-y (0 <x
The non-radiative recombination preventing layer composed of <1, 0 <y ≦ 1)
Its lattice constant is smaller than that of a 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 above 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. In particular, when the amount of compressive strain of the active layer is large, for example, 2% or more, or when the thickness of the strained layer is larger than the critical thickness, even if non-equilibrium growth such as low-temperature growth is performed, growth cannot be performed due to the presence of defects. This is particularly problematic. If a strained layer is present, such a defect can be prevented from climbing up, so that the luminous efficiency can be improved, a layer having a compressive strain of 2% or more of the active layer can be grown, or the thickness of the strained layer can be reduced to a critical film. It becomes possible to grow thicker than thick.

This Ga _x In _{1-x Py} As _1-y (0 <x <
1,0 <y ≦ 1) layer also has the role of carrier confinement in which the active region in contact with the active region but, Ga _x an In
_{The 1-x Py} As _1-y (0 <x <1, 0 <y ≦ 1) layer can have a larger band gap energy as the lattice constant decreases.

For example, in the case of Ga _x In _{1 -x} P (when y = 1), the lattice constant increases and the band gap increases as x increases and approaches x GaP. The band gap Eg is Eg (Γ) = 1.351 + 0.643x + 0.78 by direct transition.
6x ² , and Eg (X) = 2.24 + 0.02x in the indirect transition. Therefore, the active region and Ga _x In _{1-x Py} As _1-y (0
<X <1, 0 <y ≦ 1) The hetero barrier in the layer is large, so that the carrier confinement is good, the threshold current is reduced,
This has the effect of improving temperature characteristics.

Further, the Ga _x In _{1-x Py} As _1-y (0 <
x <1, 0 <y ≦ 1) The non-radiative recombination preventing layer has a larger lattice constant than the GaAs substrate, has a compressive strain, and has a lattice constant of the active layer of Ga _x.
It has a larger compressive strain than the In _{1-x Py} As _1-y (0 <x <1, 0 <y ≦ 1) layer.

The Ga _x In _{1-x Py} As _1-y (0 <x
<1, 0 <y ≦ 1) Since the direction of strain of the layer is the same as that of the active layer, it acts in the direction of reducing the substantial amount of compressive strain felt by the active layer. The larger the strain is, the more easily affected by external factors. Therefore, it is particularly effective when the amount of compressive strain of the active layer is as large as 2% or more, or when it exceeds the critical film thickness.

For example, a surface emitting laser having an oscillation wavelength in the 1.3 μm band is preferably formed on a GaAs substrate, and a semiconductor multilayer mirror is often used for the resonator, and the total thickness is 5 to 8 μm. It is necessary to grow 50 to 80 semiconductor layers before growing the active layer. (On the other hand, in the case of an edge-emitting laser, the total thickness before growing the active layer is about 2 μm, and it is only necessary to grow about three semiconductor layers.) In this case, even if a high-quality GaAs substrate is used, various methods are used. Due to the cause (defects once generated basically creep up in the crystal growth direction and defects are generated at the hetero interface).
The defect density on the surface immediately before the active layer growth is inevitably higher than the defect density on the s substrate surface. If the insertion of a strained layer or the substantial amount of compressive strain felt by the active layer is reduced before the growth of the active layer, the influence of defects on the surface immediately before the growth of the active layer can be reduced.

In this example, since Al is not contained in the active region and at the interface between the reflector and the active region, non-radiative recombination caused by crystal defects caused by Al during carrier injection is eliminated. And non-radiative recombination was reduced.

As described above, it is preferable to apply a structure in which Al is not contained at the interface between the reflector and the active region, that is, to provide a non-radiative recombination preventing layer for both the upper and lower reflectors. It is effective even when applied to a reflector. In this example, both the upper and lower reflecting mirrors are semiconductor distributed Bragg reflecting mirrors, but one reflecting mirror may be a semiconductor distributed Bragg reflecting mirror and the other reflecting mirror may be a dielectric reflecting mirror.

Further, in the above-described example, the uppermost layer of the low refractive index layer of the reflecting mirror is used.
Only the layer close to the active layer is Ga_xIn_{1 -x}P_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.

Further, in this example, this idea is applied to the lower reflector between the GaAs substrate and the active layer, and a crystal defect caused by Al, which is a problem during the growth of the active layer, rises into the active layer. The adverse effect is suppressed, and the active layer can be crystal-grown with high quality. As a result, a surface-emitting type semiconductor laser having high luminous efficiency and sufficient reliability for practical use was obtained. In addition, not all of the low refractive index layers of the semiconductor distributed Bragg reflector but at least a portion closest to the active region is Ga _x In _{1 -x Py} As _{1 -y} (0 <x <
Since only 1,0 <y ≦ 1) layers are provided, the above-described effect can be obtained without particularly increasing the number of stacked reflectors.

The oscillation wavelength of the surface emitting semiconductor laser manufactured as described above was about 1.2 μm. GaInAs on a GaAs substrate has a longer wavelength due to an increase in the In composition, but with an increase in the amount of strain. Conventionally, up to 1.1 μm has been considered to be the limit of a longer wavelength (see the document “IEEE Photo”).
onics. Technol. Lett. Vol. 9
(1997) p. 1319-1321 ").

However, as manufactured by the inventor of the present invention, a high strain GaInAs quantum well active layer can be grown coherently thicker than before by a non-equilibrium growth method such as low-temperature growth at 600 ° C. or less. Reached 1.2 μm. This wavelength is transparent to the Si semiconductor substrate. Therefore, light transmission through the Si substrate becomes possible in a circuit chip in which an electronic element and an optical element are integrated on the Si substrate.

As is clear from the above description, it was found that a surface emitting semiconductor laser in a long wavelength band can be formed on a GaAs substrate by using GaInAs having a large In composition and a high compression strain for the active layer. 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. Although the triple quantum well structure (TQW) has been described as an example of the stacked structure of the active layer, a structure (SQW, MQW) using a quantum well of another number of wells may 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. Also, an example in which GaAs is used as the semiconductor substrate has been described.
The above concept can be applied even when another semiconductor substrate such as P is used. The period of the reflecting mirror may be another period.

In this example, as the active layer, a layer whose main element is Ga, In, or As, that is, Ga _x In _{1 -x}
Although an example of As (GaInAs active layer) has been described, in order to perform laser oscillation of a longer wavelength, a layer (GaInNAs active layer) in which N is added and the main element is Ga, In, N, and As is used. Good.

By actually changing the composition of the GaInNAs active layer, it was possible to perform laser oscillation in each of the 1.3 μm band and the 1.55 μm band. By studying the composition, a longer wavelength, for example, 1.7
A surface emitting laser in the μm band is also possible.

Also, when GaAsSb is used for the active layer,
A 1.3 μm band surface emitting laser can be realized on an aAs 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, another configuration of a long wavelength band surface emitting semiconductor laser which is a light emitting element applied to the optical transmitting / receiving system of the present invention will be described with reference to FIG. Also in this case, FIG.
As in the case of (1), an n-GaAs substrate having a plane orientation of (100) is used. N-Al _x Ga _{1 -x} A in a thickness of １ ／ of the oscillation wavelength λ (thickness of λ / 4) in each medium.
An n-semiconductor distributed Bragg reflector (Al _0.9 Ga _0.1 As / GaAs lower reflector) in which s (x = 0.9) and n-Al _x Ga _1-x As (x = 0) are alternately stacked for 35 periods. _{formed, n-Ga x in 1-} x P thickness on the lambda / 4 Part _{y As 1-y (x =} 0.
5, y = 1) layers were laminated. In this example, n-Ga _x In
_{The 1-x Py} As _1-y (x = 0.5, y = 1) layer is also a part of the lower reflector and is a low refractive index layer.

On top of that, undoped lower GaAs
A multi-quantum well active layer (a quantum well active layer) composed of a spacer layer, an active layer (quantum well active layer) which is a three-layer Ga _x In _1-x N _y As _1-y quantum well layer, and a GaAs barrier layer (15 nm). In the example, triple quantum well (TQW)) and undoped upper Ga
An As spacer layer is laminated to form a resonator having a thickness (λ thickness) of one oscillation wavelength in the medium.

Further, a p-semiconductor distributed Bragg
A reflecting mirror (upper reflecting mirror) is formed. Top reflector
Is a method in which an AlAs layer to be a 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 3
0 nm) and a C-doped p having a thickness of (2λ / 4-15 nm)
-Al_xGa_1-xAs layer (x = 0.9)) and the thickness is λ /
4 GaAs layer (one period) and C-doped p-Al_xG
a_1-xAs layer (x = 0.9) and p-Al_xGa_1-xAs
The (x = 0) layer has an oscillation wavelength of 1 in each medium.
With a periodic structure (22 periods) alternately stacked with a thickness of / 4 times
Consisting of a semiconductor distributed Bragg reflector (Al_0.9G
a_0.1As / GaAs upper reflector).

Also in this example, although not shown because it is complicated in FIG. 3, the structure of the semiconductor distributed Bragg reflector has a low refractive index layer (low refractive index layer) as shown in FIG. Layer) and a high refractive index layer (high refractive index layer), a material layer Al _z Ga _1-z having a refractive index between low and high
As (0 ≦ y <z <x ≦ 1) is provided. And the uppermost p-Al _x Ga _{1 -x} As (x = 0) layer is
It also serves as a contact layer (p-contact layer) for making contact with the electrode.

Here, the In composition x of the quantum well active layer is 37
%, And the N (nitrogen) composition was 0.5%. The thickness of the quantum well active layer was 7 nm. The surface emitting semiconductor laser was grown by MOCVD. Materials for forming each layer of the semiconductor laser include TMA (trimethylaluminum), TMG (trimethylgallium), TMI (trimethylindium), AsH ₃ (arsine), PH
₃ (phosphine), and DMHy
(Dimethylhydrazine) was used. Since DMHy decomposes at low temperature, it is suitable for low-temperature growth at a temperature of 600 ° C. or lower, and is particularly preferable when growing a quantum well layer having a large strain that requires low-temperature growth. Note that H ₂ was used as a carrier gas.

In this example, the GaInNAs layer (quantum well active layer) was grown at 540 ° C. The MOCVD method has a high degree of supersaturation and is suitable for crystal growth of a material containing N and another V group simultaneously. In addition, high vacuum is not required as in the MBE method, and the supply flow rate and supply time of the source gas may be controlled.

[0062] Further in this example, the predetermined size mesa portion of the _{p-Ga x In 1-x} P y As 1-y (x = 0.5, y =
Until reaching 1) _{layer, p-Al z Ga 1-} z As (z = 1)
The selective oxidation layer is formed by exposing the side surface, and the Al _x Ga _{1 -z} As (z = 1) layer on the side surface is oxidized from the side surface with water vapor to form an Al _x O _y current narrowing layer. .

Finally, the portion removed by mesa etching with polyimide (insulating film) is buried and flattened, the polyimide on the upper reflecting mirror is removed, and the p-side electrode is formed on the p-contact layer except for the light emitting portion. And n on the back surface of the GaAs substrate.
Side electrodes were formed.

In this example, the lower part of the selectively oxidized layer
Ga as part of the top reflector_xIn_{1 -x}P_yAs_1-y(0 <
x <1, 0 <y ≦ 1) layers are inserted. For example
In the case of etching, a sulfuric acid-based etchant is used.
For example, the GaInPAs system is an etch to the AlGaAs system.
Ga can be used as a stopping layer._xIn
_1-xP_yAs_1-y(0 <x <1, 0 <y ≦ 1) layer inserted
The high mesa etching for selective oxidation.
Can be strictly controlled. Therefore, uniformity and reproducibility are improved.
Cost can be reduced.

When the surface emitting semiconductor laser (element) of this example is integrated one-dimensionally or two-dimensionally, the controllability at the time of element production is improved, and the uniformity of the element characteristics of each element in the array is improved. In addition, there is an effect that reproducibility becomes extremely good. In this example, Ga _x In _{1-x Py} As _1-y (0 <x <1, 0 <
Although the y ≦ 1) layer is provided on the upper reflecting mirror side, it may be provided on the lower reflecting mirror side.

Also in this example, in an active region (in this embodiment, a resonator composed of upper and lower spacer layers and a multiple quantum well active layer) sandwiched between upper and lower reflectors and into which carriers are injected and recombined, No material containing Al is used in the active region, and the lower refractive index layers of the lower and upper mirrors, which are closest to the active layer, are formed of Ga _x In _{1-x Py} As _1-y (0
<X <1, 0 <y ≦ 1). That is, in this example, Al is not included in the active region and at the interface between the reflecting mirror and the active region, so that non-radiative recombination caused by crystal defects caused by Al during carrier injection is reduced. Can be done.

It is preferable to apply a structure in which Al is not contained at the interface between the reflecting mirror and the active region to the upper and lower reflecting mirrors as in this example, but it is effective to apply it to only one of the reflecting mirrors. . In this example, both the upper and lower reflecting mirrors are semiconductor distributed Bragg reflecting mirrors, but one reflecting mirror may be a semiconductor distributed Bragg reflecting mirror and the other reflecting mirror may be a dielectric reflecting mirror.

Further, also in this example, the same idea as in the case of the example of FIG. 1 is applied to the lower reflector between the GaAs substrate and the active layer, so that crystal defects caused by Al which are problematic at the time of growing the active layer. Of the active layer is suppressed, and crystal growth of the active layer with high quality can be achieved.

It should be noted that such a non-radiative recombination preventing layer is
1 and 3, a part of the semiconductor distributed Bragg reflector is formed, and its thickness is 、 of the oscillation wavelength λ in the medium (thickness of λ / 4). ). Alternatively, a plurality of layers may be provided.

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 only as a non-radiative recombination prevention layer, so that the above-described effect can be obtained without particularly increasing the number of stacked reflectors. I was able to.

Even with such a configuration, since the polyimide can be easily buried, the wiring (p-side electrode in this example) is not easily disconnected, and a device having high reliability can be obtained. The oscillation wavelength of the surface emitting semiconductor laser manufactured in this manner was about 1.3 μm.

In this example, the main elements are Ga, In,
A layer composed of N and As was used as an active layer (GaInNAs
As a result, a long-wavelength surface emitting semiconductor laser could be formed on the GaAs substrate. Further, the current was narrowed by selective oxidation of the selectively oxidized layer containing Al and As as main components, so that the threshold current was low.

According to the current narrowing structure using the current narrowing layer made of the Al oxide film obtained by selectively oxidizing the selectively oxidized layer,
By forming the current narrowing layer close to the active layer, the spread of current can be suppressed, and carriers can be efficiently confined in a minute region that is not exposed to the atmosphere. Further oxidized to Al
By forming an oxide film, the refractive index is reduced, and light can be efficiently confined in a minute region in which carriers are confined by the effect of the convex lens, and the efficiency is extremely improved, and the threshold current can be reduced. In addition, since the current narrowing structure can be easily formed, the manufacturing cost can be reduced.

As is apparent from the above description, a 1.3 μm band surface emitting semiconductor laser can be realized in the configuration as shown in FIG. 3, as in the case of FIG. Is obtained. The surface emitting semiconductor laser of FIG. 3 can be grown by MOCVD as in the case of FIG. 1, but other growth methods such as MBE can be used. Although DMHy is used as a nitrogen source, activated nitrogen and other nitrogen compounds such as NH ₃ can be used.

Further, the triple quantum well structure (TQW) has been described as an example of the stacked structure of the active layer. However, a structure using other quantum wells (SQW, DQW, MQW) or the like can be used. The structure of the laser may be another structure.

In the surface-emitting type semiconductor laser shown in FIG. 3, by changing the composition of the GaInNAs active layer, 1.
A surface emitting semiconductor laser in the 55 μm band, and even in the longer wavelength 1.7 μm band, is also possible. The GaInNAs active layer may contain other III-V elements such as Tl, Sb, and P. Also, even if GaAsSb is used for the active layer, a 1.3 μm band surface emitting semiconductor laser can be realized on a GaAs substrate.

When GaInAs is used for the active layer,
Conventionally, up to 1.1 μm has been considered to be the limit of increasing the wavelength.
The quantum well active layer can be grown thicker than before, and the wavelength can reach up to 1.2 μm. in this way,
Conventionally, there is no suitable material for the semiconductor laser having a wavelength of 1.1 μm to 1.7 μm, but GaInAs, G
By using aInNAs and GaAsSb and providing a non-radiative recombination prevention layer, a high-performance surface-emitting laser can be realized in the long wavelength region of the 1.1 μm to 1.7 μm wavelength band where stable oscillation has conventionally been difficult. As a result, application to optical communication systems has become possible.

FIG. 4 shows an example in which such a long wavelength band surface emitting semiconductor laser device is formed as a large number of chips on an n-GaAs wafer having a plane orientation of (100), and a laser device chip. In the laser element chip shown here, 1 to n laser elements are formed, and the number n and the arrangement method are determined according to the application.

When a signal is input to the optical transmission device, the switching circuit emits light when a signal is input to the multi-surface emitting semiconductor laser device, and the optical fiber is irradiated with laser light. A decision circuit for monitoring light emission from the surface-emitting type semiconductor laser device is incorporated in the same package, and operates when the intensity of the laser beam becomes smaller than a certain threshold value.
The determination circuit is obtained by adding a function of a comparison circuit to the photodiode, and operates when the intensity of the laser beam from the surface emitting semiconductor laser element becomes smaller than a certain threshold value.

When the surface-emitting type semiconductor laser device is deteriorated, the intensity of the emitted laser beam becomes smaller than a certain threshold value, the judgment circuit is activated, and the switching circuit is activated by the output of the judgment circuit. The surface-emitting type semiconductor laser device is driven. This makes it possible to construct an optical communication system with high reliability against the deterioration of the surface emitting semiconductor laser device.

[0081]

According to the present invention, the operating voltage, the oscillation threshold current and the like are determined in the field of the laser oscillation wavelength of 1.1 μm to 1.7 μm, which is expected to be used for optical fiber communication, such as a computer network and a trunk line of a long distance and large capacity communication. Although there was no surface-emitting type semiconductor laser and a communication system using the same, which can reduce the heat generation of the laser element and produce stable oscillation with little heat generation, the operation of the present invention is improved by devising a semiconductor distributed Bragg reflector as in the present invention. Voltage, oscillation threshold current, etc. can be reduced, and stable oscillation can be achieved with less heat generation of the laser element.
Moreover, a low-cost and practical optical communication system was realized.

Further, since there has been no practical optical communication system in the field where the laser oscillation wavelength is in the 1.1 μm band to 1.7 μm band, the surface emitting type semiconductor laser device used for this has been compared. There was no study on how to construct a highly reliable optical communication system using semiconductor laser elements that are easily deteriorated. However, as in the present invention, a switching circuit and a decision circuit are built in a module package. Thus, a more reliable optical communication system can be constructed.

In the field of laser oscillation wavelengths of 1.1 μm to 1.7 μm where optical fiber communication is expected, such as computer networks and trunk lines for long-distance large-capacity communication, long-wavelength surface light emission can be used stably. Although a semiconductor laser and a communication system using the same did not exist, as in the present invention, stable oscillation can be achieved by using a surface emitting semiconductor laser element chip provided with a non-radiative recombination prevention layer, A practical optical communication system using this as a light source was realized.

Further, since there is no practical optical communication system in the field where the laser oscillation wavelength is in the range of 1.1 μm to 1.7 μm, the surface emitting type semiconductor laser device used for this has been compared. There was no study on how to construct a highly reliable optical communication system using semiconductor laser elements that are easily deteriorated. However, as in the present invention, a switching circuit and a decision circuit are built in a module package. Thus, a more reliable optical communication system can be constructed.

[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 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. 4 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. 5 is a configuration diagram of an optical communication system including a plurality of long wavelength band surface emitting semiconductor lasers, a switching circuit, and a determination circuit according to an embodiment of the present invention.

FIG. 6 is a structural diagram of an optical communication system including a plurality of long wavelength band surface emitting semiconductor lasers, a switching circuit, a determination circuit, and an optical fiber according to an embodiment of the present invention.

 ────────────────────────────────────────────────── ─── Continuing on the front page (72) Inventor Atsuyuki Watada 1-3-6 Nakamagome, Ota-ku, Tokyo Inside Ricoh Company (72) Inventor Shunichi Sato 1-3-6 Nakamagome, Ota-ku, Tokyo Share Inside Ricoh Company (72) Inventor Yukie Suzuki 1-3-6 Nakamagome, Ota-ku, Tokyo Stock Company Ricoh Company (72) Inventor Satoru Sugahara 1-3-6 Nakamagome, Ota-ku, Tokyo Stock Company Ricoh Company ( 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 Inside Ricoh Company (72) Inventor Takuro Sekiya 1-3-6 Nakamagome, Ota-ku, Tokyo Inside Ricoh Co., Ltd. (72) Inventor Ken Kanai 1-3-6 Nakamagome, Ota-ku, Tokyo Co., Ltd. In Ricoh (72) Inventor Masayoshi Kato 1-3-6 Nakamagome, Ota-ku, Tokyo F-term in Ricoh Company (reference) 5F073 AA08 AA13 AA21 AA62 AA74 AB02 AB17 AB27 AB28 BA02 CA07 CA17 CB02 DA05 DA22 DA23 EA29 FA02 GA12 GA38

Claims (2)

[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 forms an active layer for generating light by using Ga, In as a main element. , N, As
Alternatively, 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 is a semiconductor distributed Bragg reflecting mirror in which the refractive index of a material layer constituting the reflecting mirror periodically changes between small and large and reflects incident light by light wave interference, and the material layer having a small refractive index 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
A reflecting mirror having As (0 ≦ y <x ≦ 1), and a material layer Al _z Ga _{1 in which the} refractive index takes a value between small and large between the material layers having small and large refractive indexes. _-z As (0 ≦ y <z <x ≦
The surface emitting semiconductor laser device chip provided with 1) is used as a light emitting light source, and the optical communication system comprises 2N surface emitting semiconductor lasers, N optical fibers, and the surface emitting semiconductor laser device. An optical communication system comprising: a determination circuit for monitoring a light emission state of the light emitting device; and a switching circuit. 2. 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 has an active layer for generating light, wherein the main element is Ga, A surface emitting type having a layer structure of In, N, and As or a layer of Ga, In, and As and having a resonator structure including reflectors provided above and below the active layer to obtain a laser beam. A semiconductor laser device chip, wherein the reflecting mirror is a semiconductor distributed Bragg reflecting mirror that periodically changes the refractive index of a material forming the reflecting mirror to small / large and reflects incident light by light wave interference; Is smaller than that of Al _x Ga _{1 -x} As (0 <
x ≦ 1), and the material having a large refractive index is Al _y Ga _1-y A
s (0 ≦ y <x ≦ 1), wherein GaInP or GaInPAs is provided between the active layer and the reflector.
A surface-emitting type semiconductor laser device chip provided with a non-light-emitting recombination prevention layer comprising a light-emitting source, wherein the optical communication system has 2N surface-emitting type semiconductor lasers, N optical fibers, and An optical communication system comprising: a determination circuit for monitoring a light emitting state of a surface emitting semiconductor laser device; and a switching circuit.