JP2004186484A - Semiconductor light emitting element, optical transmission module, optical transmission/reception module, and optical communication system - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a semiconductor light emitting element of good temperature characteristics and low threshold value, which uses GaInNAs quantum well active layer of compression strain, by expanding freedom in design to reduce strain of the quantum well active layer. <P>SOLUTION: The semiconductor light emitting element comprises an active layer composed of nitrogen (N) which has a compression strain relative to a GaAs substrate, a quantum well active layer containing other group V element as well, and a barrier layer formed around the former. The barrier layer is a group III-V hybrid semiconductor containing both phosphor (P) and antimony (Sb). <P>COPYRIGHT: (C)2004,JPO&NCIPI

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a semiconductor light emitting device, an optical transmitting module, an optical transmitting and receiving module, and an optical communication system.
[0002]
[Prior art]
In recent years, as seen in the explosive spread of the Internet, the amount of information handled has been dramatically increased, and it is expected that the amount of information will be further accelerated in the future. For this reason, optical fibers are introduced not only into trunk lines but also into subscriber lines such as homes and offices, transmission lines close to users such as LANs (Local Area Network), and wiring between devices and in devices. Therefore, large-capacity information transmission technology becomes extremely important.
[0003]
As such a light source, a 1.3 μm band and a 1.55 μm band semiconductor laser having a small transmission loss of silica fiber and a good matching is required. It is an absolute condition to be a system.
[0004]
In the wavelength band of 1.3 μm band and 1.55 μm band, the material system on the InP substrate is generally used, and the edge emitting laser has a track record. However, this conventional long-wavelength band semiconductor laser has a major drawback that when the ambient temperature changes from room temperature to 80 ° C., the operating current increases three times. Therefore, in order to realize a low-cost system that does not use a cooling element, it is extremely important to develop a long-wavelength band semiconductor laser having good temperature characteristics.
[0005]
Recently, attention has been paid to a material system capable of forming a 1.3 μm band semiconductor laser on a GaAs substrate, and (Ga) InAs quantum dots, GaAsSb, and GaInNAs (for example, see Patent Document 1) have been studied. In particular, GaInNAs have attracted attention as a material capable of extremely reducing the temperature dependence of laser characteristics. Note that the GaInNAs-based material may include another group III-V element such as P, Sb, or Al.
[0006]
GaInNAs is a group III-V mixed crystal semiconductor containing nitrogen (N) and other group V elements. That is, by adding nitrogen (N) to GaInAs having a larger lattice constant than GaAs, the lattice constant of GaInNAs can be lattice-matched to that of GaAs, and the band gap energy is further reduced to 1.3 μm, 1.3 μm. It is a material that can emit light in the 55 μm band.
[0007]
For example, in Non-Patent Document 1, the band lineup of GaInNAs is calculated by Kondo et al. Although the band gap energy of GaInNAs decreases with the addition of nitrogen (N), the energy of both the conduction band and the valence band decreases, and the band discontinuity of the conduction band with respect to GaAs lattice-matched materials such as GaInP, AlGaAs, and GaAs. Is extremely large, and therefore, it is expected that a high characteristic temperature semiconductor laser can be realized. Actually, when the In composition is 10%, the nitrogen composition can form a 1.3 μm band at about 3%, but there is a problem that the threshold current density sharply increases as the nitrogen composition increases. FIG. 1 is a diagram showing the nitrogen composition dependency of the threshold current density experimentally obtained by the inventor. The horizontal axis shows the nitrogen composition ratio (%), and the vertical axis shows the threshold current density. ing. As shown in FIG. 1, the reason why the threshold current density sharply increases with an increase in the nitrogen composition is that the crystallinity of the GaInNAs layer deteriorates with an increase in the nitrogen composition. For this reason, a method of increasing the In composition and decreasing the nitrogen composition has been adopted (for example, see Patent Documents 2 and 3), and a GaInNAs-based material having a large compression strain of about 2% or more with respect to the substrate. A quantum well active layer is used. Thereby, the threshold current density of the semiconductor laser is 1 kA / cm. ² A good laser has been reported that has a low value below, the operating current increases only 1.3 times even when the ambient temperature changes from room temperature to 80 ° C., and the characteristic temperature exceeds 200 K ( For example, see Non-Patent Document 2.) Note that a GaAs layer is used for the barrier layer. When a GaInNAs-based quantum well active layer having a compressive strain is used, GaAs is often used for the barrier layer.
[0008]
However, in the case of having such a large compressive strain, it is necessary to grow a thickness close to a substantial critical film thickness that changes from two-dimensional growth to three-dimensional growth, and a device for this is required. Conventionally, a low-temperature growth method (for example, see Patent Document 2) and a method of adding Sb to obtain a surfactant effect (for example, see Patent Document 3) have been proposed, but in order to suppress the occurrence of crystal defects. There are restrictions on device design, such as restrictions on the number of quantum wells.
[0009]
As a method of improving this, Ga has a lattice constant smaller than that of the substrate. _d In _1-d N _e P _f As _1-ef A strain that reduces (compensates) the distortion of the active layer by using a system material (for example, see Patent Document 4), a GaNPAs or GNAs layer (for example, see Patent Document 5), and a GNAs layer (for example, see Patent Document 3) as a barrier layer. Compensation structures have been proposed.
[0010]
When nitrogen (N) is added to GaAs, the lattice constant decreases. In addition, since the conduction band discontinuity of GaNAs with the GaInNAs-based quantum well active layer is reduced and the quantum level energy is reduced, GaNAs has the effect of increasing the oscillation wavelength. However, for the same reason (the conduction band discontinuity with the GaInNAs-based quantum well layer is reduced), there is a disadvantage that the overflow of electrons increases and the temperature characteristics deteriorate.
[0011]
Further, when P is added to GaAs, the lattice constant decreases, the band gap increases, and the energy of the conduction band increases. Therefore, when GaNPAs is used as the barrier layer, by adjusting the composition of P and N, the energy of the conduction band can be made approximately equal to that of the junction between GaAs and GaInNAs. However, since the addition of P and N both makes the lattice constant smaller than that of GaAs, it is impossible to independently control both the conduction band discontinuity and the strain amount. For this reason, the amount of tensile strain increases, and there arises a problem that a good interface cannot be obtained because the strain difference from the GaInNAs-based quantum well active layer is too large. This causes a problem that the degree of freedom in device design is limited.
[0012]
In this case, if In is added, the lattice constant can be increased. However, Ga _d In _1-d N _e P _f As _1-ef It has been found that it is difficult to control the valence band discontinuity with the GaInNAs-based quantum well active layer when forming a strain compensation layer having a lattice constant smaller than that of GaAs with a system material. Specifically, it has been found that it is difficult to reduce the valence band discontinuity as compared with the junction with the GaAs barrier layer. Therefore, it was found that the degree of freedom in device design was limited.
[0013]
[Patent Document 1]
JP-A-6-37355
[0014]
[Non-patent document 1]
Jpn. J. Appl. Phys. Vol. 35 (1996) pp. 1273-1275
[0015]
[Patent Document 2]
JP 2000-332363 A
[0016]
[Patent Document 3]
JP-A-2002-118329
[0017]
[Non-patent document 2]
Jpn. J. Appl. Pyys. Vol. 39 (2000) pp. 3403-3405
[0018]
[Patent Document 4]
JP-A-10-126004
[0019]
[Patent Document 5]
JP-A-10-145003
[0020]
[Problems to be solved by the invention]
The present invention provides a semiconductor light emitting device using a GaInNAs-based quantum well active layer having a compressive strain, thereby increasing the degree of freedom of design and reducing the strain of the quantum well active layer, and has a good temperature characteristic and a low threshold value. It is an object of the present invention to provide a semiconductor light emitting device, an optical transmitting module, an optical transmitting and receiving module, and an optical communication system.
[0021]
[Means for Solving the Problems]
In order to achieve the above object, according to the first aspect of the present invention, a quantum well active layer simultaneously containing nitrogen (N) having a compressive strain with respect to a GaAs substrate and another group V element is formed around the active layer. In a semiconductor light emitting device having an active layer including a barrier layer, the barrier layer is a III-V mixed crystal semiconductor containing phosphorus (P) and antimony (Sb) simultaneously.
[0022]
According to a second aspect of the present invention, in the semiconductor light emitting device of the first aspect, the barrier layer contains nitrogen (N) at the same time.
[0023]
According to a third aspect of the present invention, in the semiconductor light emitting device of the first aspect, the barrier layer is GaNPAsSb, GaPAsSb, GaInNPAsSb, or GaInPAsSb.
[0024]
According to a fourth aspect of the present invention, there is provided a semiconductor light emitting device having an active layer including a quantum well active layer simultaneously containing Ga, As, and Sb having a compressive strain with respect to a GaAs substrate, and a barrier layer formed therearound. The device is characterized in that the barrier layer is a group III-V mixed crystal semiconductor containing phosphorus (P) and antimony (Sb) simultaneously.
[0025]
According to a fifth aspect of the present invention, in the semiconductor light emitting device of the fourth aspect, the barrier layer is made of GaPAsSb, AlGaPAsSb, GaInPAsSb, or AlGaInPAsSb.
[0026]
According to a sixth aspect of the present invention, in the semiconductor light emitting device according to any one of the first to fifth aspects, the quantum well active layer is a multiple quantum well active layer.
[0027]
According to a seventh aspect of the present invention, in the semiconductor light emitting device according to any one of the first to sixth aspects, the semiconductor light emitting element is a surface emitting semiconductor laser.
[0028]
The invention according to claim 8 is an optical transmission module, wherein the semiconductor light emitting device according to claim 7 is used as a light source.
[0029]
According to a ninth aspect of the present invention, there is provided an optical transceiver module, wherein the semiconductor light emitting device according to the seventh aspect is used as a light source.
[0030]
According to a tenth aspect of the present invention, there is provided an optical communication system in which the semiconductor light emitting device according to the seventh aspect is used as a light source.
[0031]
BEST MODE FOR CARRYING OUT THE INVENTION
Hereinafter, embodiments of the present invention will be described.
[0032]
(1st Embodiment)
The first embodiment of the present invention relates to an active layer comprising a quantum well active layer containing nitrogen (N) having a compressive strain and another group V element simultaneously with respect to a GaAs substrate, and a barrier layer formed around the quantum well active layer. A semiconductor light emitting device having a layer is characterized in that the barrier layer is a group III-V mixed crystal semiconductor containing phosphorus (P) and antimony (Sb) simultaneously.
[0033]
In the case where GaAs is doped with 1% of P, the band gap is increased by about 11.7 meV. That is, the conduction band rises by 7 meV and the valence band falls by 4.7 meV (Ag. Thompson et al., "Pys. Rev. 146 (1966) p601", Su-Huai Wei et al., "Appl. Pys. Lett." Vol.72 (1998) p2011 "). Since the lattice constants of GaAs and GaP are 5.65325 angstroms and 5.4495 angstroms, respectively, the tensile strain is 0.0360% per 1% of P with respect to GaAs.
[0034]
In a material in which N is added to GaAs by 1%, the band gap is reduced by 156 meV, the conduction band is reduced by 175 meV, and the valence band is reduced by 19 meV (Kitatani et al. ^th Semiconductor Laser Symposium "). Further, since the lattice constant of GaN having a zinc blend structure is 4.5 angstroms, the tensile strain is 0.204% per 1% of N with respect to GaAs.
[0035]
In a material in which 1% of In is added to GaAs, the band gap is reduced by about 15 meV. The valence band energy increases when In is added, but the valence band energy is only 60 meV for GaAs and InAs, and most of the decrease in the band gap is due to the lowering of the conduction band (Yu.F. Biryulin et al., Sov. Pys. 17 (1983) p68 ", Su-Huawei et al.," Appl. Pys. Lett. Vol. 72 (1998) p2011 ", etc.). Further, since the lattice constant of InAs is 6.058 Å, the compression strain is 0.0716% per 1% of In with respect to GaAs.
[0036]
As described above, Ga obtained by adding N, and / or P, and / or In to GaAs _d In _1-d N _e P _f As _1-ef When a strain compensation layer having a lattice constant smaller than that of GaAs is formed of a system material (see Japanese Patent Application Laid-Open No. H10-126004), the valence band discontinuity with the GaInNAs quantum well active layer is caused by the GaAs barrier layer. It turned out to be larger than that. For example, when tensile strain is caused by adding 1% of P to GaAs, the valence band is reduced by 4.7 meV. To compensate for this with In, it is necessary to add about 8% of In, resulting in compressive strain. I will. Also, if N is added to GaAs and tensile strain is caused by adding 1%, the valence band is reduced by 19 meV, but to compensate for this by In, it is necessary to add In by about 32%, resulting in compressive strain. .
[0037]
The effective mass of holes is larger than the effective mass of electrons, and the uniformity of hole injection depends sensitively on the barrier height. Therefore, when the valence band discontinuity increases, it becomes difficult to uniformly inject holes into each well layer of the multiple quantum well structure, and adversely affects device characteristics such as an increase in threshold current. I will give it. In most cases, a GaAs layer is used around the GaInNAs-based quantum well active layer including the quantum well active layer and the barrier layer. In this case, if the valence band energy of the barrier layer is lower than that of GaAs, the barrier layer becomes a barrier for hole injection into the well layer, causing a problem that holes are hardly injected.
[0038]
On the other hand, a 1.3 μm band semiconductor laser using a GaAsSb quantum well active layer grown on a GaAs substrate has been reported in the document “Technical Report Technical Report, LQE99-133 (2000-02)” by Yamada et al. ing. GaAs and GaAs _0.64 Sb _0.36 It is estimated that the conduction band discontinuity is about 35 meV, the valence band discontinuity is 430 meV, and most of the decrease in the band gap due to the addition of Sb increases the valence band energy (per 1% of Sb). 12 meV). Also, the addition of Sb increases the lattice constant. Therefore, the inventor of the present application has found that the addition of Sb to a material having a tensile strain with respect to GaAs can compensate for the increase in the valence band discontinuity. Since the lattice constant of GaSb is 6.094 Å, the compression strain is 0.0780% per 1% of Sb with respect to GaAs.
[0039]
As a material having a tensile strain with respect to GaAs, it is necessary to add at least one of N and P to GaAs. In a Ga (In) NAsSb tensile strained layer to which N and Sb are added without adding P, the conduction band discontinuity is reduced as in the case of the GaNAs barrier layer, so that the temperature characteristics of the semiconductor laser are deteriorated. Note that when Al is added to Ga (In) NAsSb, the effect of increasing the conduction band energy without substantially changing the lattice constant is obtained. However, a material containing N needs to be grown at a low temperature of 600 ° C. or lower. It is not preferable for the growth of a layer containing Al, and it is desirable not to contain Al and N at the same time.
[0040]
As described above, in a structure using a GaInNAs-based quantum well active layer having a compressive strain, when a material in which at least P and Sb are simultaneously added to GaAs is used as a barrier layer, the conduction band discontinuity is so small that overflow of electrons becomes a problem. It is possible to obtain a strain-compensated quantum well active layer structure that does not cause the valence band discontinuity to be so large as to hinder hole injection.
[0041]
In the semiconductor light emitting device of the first embodiment described above, N can be simultaneously contained in the barrier layer.
[0042]
In the above-mentioned document “Jpn. J. Appl. Is disclosed, and there are sufficient applications that can be used without further increasing the conduction band discontinuity between the GaInNAs-based quantum well active layer and the barrier layer. Conversely, if the conduction band energy of the barrier layer is further increased, the quantum level becomes larger and the wavelength becomes shorter. Therefore, it is necessary to increase the nitrogen composition of the GaInNAs-based quantum well active layer, which causes a problem of crystallinity deterioration. Can occur. Addition of N to the barrier layer is preferable because it mainly lowers the conduction band energy, so that the conduction band discontinuity can be controlled and compensated almost independently.
[0043]
Further, the crystallinity at the interface between the barrier layer and the quantum well active layer is important. When the GaInNAs-based material is grown by the MOCVD method, the supply amount of the N raw material is 0 with respect to the supply amount of the As raw material (“N raw material” / (“N raw material” + “As raw material”)). It is necessary to supply a large amount of the N raw material, and it is difficult to improve the controllability at the time of ON / OFF of the raw material supply, that is, the controllability of the interface. Further, in the case of growing by MBE, since the N source is activated and supplied by RF or the like, it is not easy to rapidly turn ON and OFF the source supply. It is difficult to improve. However, if a structure in which N is also added to the barrier layer is used, there is no need to turn on and off the supply of the raw material at this interface, and it becomes easy to control and obtain a good interface.
[0044]
Further, in the semiconductor light emitting device of the first embodiment described above, the barrier layer can be specifically made of GaNPAsSb, GaPAsSb, GaInNPAsSb, GaInPAsSb, or the like.
[0045]
(Second embodiment)
The second embodiment of the present invention is a semiconductor light emitting device having an active layer including a quantum well active layer simultaneously containing Ga, As, and Sb having a compressive strain with respect to a GaAs substrate and a barrier layer formed around the quantum well active layer. The device is characterized in that the barrier layer is a group III-V mixed crystal semiconductor containing phosphorus (P) and antimony (Sb) simultaneously.
[0046]
The barrier layer containing both P and Sb is effective even when a GaAsSb-based compression-strained quantum well active layer is used. As described above, GaAs (barrier layer) and GaAs _0.64 Sb _0.36 The conduction band discontinuity with the (compressed strained quantum well active layer) is estimated to be about 35 meV, the valence band discontinuity is 430 meV, and most of the decrease in the band gap due to the addition of Sb is the valence band energy. Is increased (12 meV per 1% of Sb). Therefore, when a GaAs barrier layer is used, the overflow of electrons is large and the temperature characteristics are extremely poor. Furthermore, the valence band discontinuity is extremely large, and uneven injection of holes is a problem in the multiple quantum well active layer. Improvement can be achieved by using a p-type modulation doping structure in which the barrier layer is p-type. (Reference: “Technical Report of IEICE, IEICE, LQE99-133 (2000-02)”).
[0047]
The addition of P to GaAs increases the conduction band discontinuity, and the addition of Sb to GaAs has the effect of reducing the valence band discontinuity, and furthermore, it is preferable because it compensates for the change of the lattice constant with each other. . This makes it possible to form a junction in which the conduction band discontinuity can be made larger and the valence band band discontinuity can be made smaller than in the case where a GaAs barrier layer is used, thereby reducing electron overflow and improving hole injection efficiency. Can be improved.
[0048]
In the semiconductor light emitting device of the second embodiment described above, the barrier layer can be specifically made of GaPAsSb, AlGaPAsSb, GaInPAsSb, AlGaInPAsSb, or the like.
[0049]
In the first and second semiconductor light emitting devices described above, the quantum well active layer can be, for example, a multiple quantum well active layer.
[0050]
The effective mass of holes is larger than the effective mass of electrons, and the uniformity of hole injection depends sensitively on the barrier height. Therefore, when the valence band discontinuity increases, it becomes difficult to uniformly inject holes into each well layer of the multiple quantum well structure, and adversely affects device characteristics such as an increase in threshold current. I will give it. When P and / or N is added to GaAs to form a material having a smaller lattice constant than GaAs, the valence band discontinuity with the GaInNAs-based quantum well active layer becomes larger than that of the GaAs barrier layer. . The addition of In has the effect of reducing the effect, but the effect is slight. On the other hand, a sufficient effect can be obtained by adding Sb as in the present invention.
[0051]
Also, in the case of a GaAsSb-based quantum well active layer, by adding Sb to the barrier layer, valence band discontinuity can be reduced as compared with the GaAs barrier layer, and hole injection into each well layer becomes uniform.
[0052]
Further, the first and second semiconductor light emitting devices described above can be specifically configured as a surface emitting semiconductor laser.
[0053]
In order to increase the capacity of optical networks and optical wirings at low cost and without concern for distance, as a light source, a 1.3 μm band or 1.55 μm band semiconductor having a small transmission loss of silica fiber and good matching. A semiconductor laser that has good temperature characteristics and does not use a cooling element is required. For this, a VCSEL (Vertical Cavity Surface Emitting Laser: vertical cavity surface emitting semiconductor laser element) is required. Very promising. Surface emitting semiconductor laser devices (surface emitting lasers) are suitable for lower cost, lower power consumption, smaller size, and two-dimensional integration than edge emitting lasers, and can be actually formed on a GaAs substrate. The 85 μm band has already been put to practical use in high-speed LANs such as 1 Gbit / sec Ethernet. Since a GaInNAs-based material or a GaAsSb-based material is used for the active layer, it is possible to cope with these wavelengths.
[0054]
Further, the surface emitting laser requires a large active layer gain because the cavity length is extremely short and the gain region is small as compared with the edge emitting laser. In order to improve the characteristics of the device, it is necessary to increase the gain by increasing the number of quantum well active layers. By providing the strain compensation layer as in the present invention, the number of active layers can be increased, a low threshold current operation, a high output, and a surface emitting laser with good temperature characteristics can be realized. Note that the formation by the MOCVD method is preferable because the resistance of the semiconductor distributed Bragg reflector of the surface emitting laser can be reduced, so that low voltage driving becomes possible.
[0055]
Further, an optical transmission module using the above-described surface emitting laser of the present invention as a light source can be configured.
[0056]
As described above, the surface emitting laser of the present invention has a low resistance, a low driving voltage, a low threshold current operation, and a good temperature characteristic. A cost-effective optical transmission module can be realized.
[0057]
Further, an optical transceiver module using the above-described surface emitting laser of the present invention as a light source can be configured.
[0058]
As described above, the surface emitting laser of the present invention has a low resistance, a low driving voltage, a low threshold current operation, and a good temperature characteristic. It is possible to realize a costly optical transmission / reception module.
[0059]
Further, an optical communication system using the above-described surface emitting laser of the present invention as a light source can be configured.
[0060]
As described above, the surface emitting laser of the present invention has a low resistance, a low driving voltage, a low threshold current operation, and a good temperature characteristic. It is possible to realize an optical communication system such as an optical fiber communication system and an optical interconnection system which is inexpensive.
[0061]
【Example】
Next, embodiments of the present invention will be described in detail with reference to the drawings.
[0062]
(First embodiment)
FIG. 2 is a diagram showing a GaInNAs edge emitting semiconductor laser according to a first embodiment of the present invention. In the example of FIG. 2, a ridge stripe type laser is used. Further, the GaInNAs edge emitting semiconductor laser of FIG. 2 has a SCH-SQW (Separate Definition Heterostructure Single Quantum Well) structure as a layer structure.
[0063]
In the example of FIG. 2, a Se-doped n-GaAs buffer layer, a Se-doped n-AlGaAs lower cladding layer, an undoped GaAs lower light guide layer, an active layer, and an undoped GaAs upper light are formed on an n-GaAs substrate having a (100) plane orientation. A guide layer, a Zn-doped p-AlGaAs upper cladding layer, and a Zn-doped p-GaAs contact layer are sequentially grown.
[0064]
Here, the active layer includes a GaInNAs quantum well active layer (well layer) having a compressive strain, and a GaPAsSb barrier layer (barrier layer) having a tensile strain formed above and below the GaInNAs quantum well active layer. The In composition x of the well layer was 35%, and the nitrogen composition was 0.8%. The thickness of the well layer was 8 nm. The growth was performed by the MOCVD method. The carrier gas is H ₂ Was used. The raw materials include TMG (trimethyl gallium), TMI (trimethyl indium), AsH ₃ (Arsine), PH ₃ (Phosphine), and DMHy (dimethylhydrazine) was used as a nitrogen source. Since DMHy decomposes at a low temperature, it is suitable for low-temperature growth at 600 ° C. or lower. In the first embodiment, the GaInNAs layer was grown at 550 ° C. In particular, when a quantum well layer having a large strain is grown, low temperature growth of, for example, about 500 ° C. to 600 ° C. is preferable. The GaPAsSb barrier layer was also grown at 550 ° C., the same as the GaInNAs layer.
[0065]
Then, a portion other than the stripe region having a width of 3 μm was removed halfway through the p-AlGaAs layer by photolithography and etching technology to form a ridge structure. Then, on this ridge structure, a p-side electrode was formed via an insulating film from which a portion serving as a current injection portion was removed. An n-side electrode was formed on the back surface of the substrate.
[0066]
In the first embodiment, a GaPAsSb barrier layer is formed between a GaAs light guide layer and a GaInNAs quantum well active layer. When the barrier layer is GaPAs, a valence band discontinuity is formed between GaAs and GaPAs, but the valence band discontinuity is reduced by adding an appropriate amount of Sb, and hole injection is performed. There are no obstacles. On the other hand, the addition of P increases the conduction band discontinuity, and the electrons that easily overflow due to the small effective mass are effectively confined in the quantum well. As a result, although the single quantum well structure was used, the temperature characteristics were extremely improved. Further, a distortion compensation structure is provided, and the reliability of the element is improved by the effect of reducing distortion.
[0067]
In the above-described example, the example of the growth by the MOCVD method is shown, but another growth method such as the MBE method can be used. Also, DMHy was used as a nitrogen source, but activated nitrogen and NH ₃ Other nitrogen compounds can also be used. Although the single quantum well structure (SQW) has been described as an example of the stacked structure, a multiple quantum well structure can be used. Further, the composition thickness and the like of each layer can be set as needed. In addition, a wide-gap AlGaInP-based material can be used for the cladding layer as in the case of the AlGaAs-based material. Further, the structure of the laser may be another structure.
[0068]
(Second embodiment)
FIG. 3 is a diagram showing a GaInNAs surface emitting semiconductor laser device according to a second embodiment of the present invention.
[0069]
The surface-emitting type semiconductor laser device according to the second embodiment has a thickness of 1/4 times the oscillation wavelength in each medium on an n-GaAs substrate having a plane orientation (100) of 3 inches. n-Al _x Ga _1-x An n-semiconductor distributed Bragg reflector (lower semiconductor distributed Bragg reflector: also simply referred to as a lower reflector) having a periodic structure in which As (x = 0.9) and n-GaAs are alternately stacked for 35 periods is formed. . Then, an undoped lower GaAs spacer layer, a multiple quantum well active layer composed of four GaInNAs well layers and five GaNPAsSb barrier layers (barrier layers), and an undoped upper GaAs spacer layer are formed thereon. A p-semiconductor distributed Bragg reflector (upper semiconductor distributed Bragg reflector: also simply referred to as an upper reflector) is formed thereon.
[0070]
The top reflector is C-doped p-Al _x Ga _1-x It has a periodic structure (for example, 25 periods) in which As (x = 0.9) and p-GaAs are alternately stacked with a thickness of 1/4 times the oscillation wavelength in each medium. A selective oxidation layer made of AlAs is provided at a position close to the active layer in the upper reflecting mirror, for example, with a thickness of 30 nm. The GaAs layer at the top of the upper reflector also functions as a contact layer for making contact with the electrode.
[0071]
In the second embodiment, the In composition x of the well layer in the active layer was 37%, and the nitrogen composition was 0.5%. The well layer had a thickness of 7 nm and had a compressive strain (high strain) of about 2.5% with respect to the GaAs substrate. The GaNPAsSb barrier layer has a thickness of 20 nm, has a tensile strain of 0.2% with respect to the GaAs substrate, and has substantially the same conduction band and valence band as those when GaAs is used as the barrier layer. Was adjusted to a suitable composition. Specifically, the P composition of the GaNPAsSb barrier layer was 21%, the N composition was 0.8%, and the Sb composition was 9.2%. Conceptually, it can be explained as follows. That is, when P is added to GaAs, a tensile strain occurs in a form in which the conduction band and valence band discontinuity with the GaInNAs quantum well become large. When N is further added to this GaPAs, tensile strain is further increased mainly in a form in which conduction band discontinuity is reduced. When Sb is further added to the GaNPAs, the amount of tensile strain is reduced in such a manner that the valence band discontinuity is reduced. Thus, the GaAs substrate can be designed so as to have a tensile strain and to have the same conduction band and valence band as those in the case where GaAs is used as the barrier layer. Therefore, it is possible to form a strain compensation structure that does not reduce the conduction band discontinuity so that the overflow of electrons becomes a problem, and does not increase the valence band discontinuity so as to cause a failure in hole injection.
[0072]
The growth was performed by MOCVD. The carrier gas is H ₂ Was used. The raw materials of the GaInNAs active layer include TMG (trimethyl gallium), TMI (trimethyl indium), AsH ₃ (Arsine), and DMHy (dimethylhydrazine) was used as a nitrogen source. Since DMHy decomposes at low temperatures, it is suitable for low-temperature growth at a temperature of 600 ° C. or less, and is a preferable raw material particularly when growing a large-quantity well layer that requires low-temperature growth. In the case where the strain is large as in the active layer of the GaInNAs surface emitting semiconductor laser device of the second embodiment, low temperature growth in which non-equilibrium is obtained is preferable. In this second example, the GaInNAs layer was grown at 540 ° C.
[0073]
In the second embodiment, a mesa of a predetermined size is formed by exposing at least the side surface of the p-AlAs selectively oxidized layer, and the AlAs that has appeared on the side surface is oxidized from the side surface with water vapor to form an Al layer. _x O _y A current narrowing portion was formed. Then, the etched portion is buried and flattened with polyimide, the polyimide on the upper reflector having the p-contact portion and the light-emitting portion is removed, and a p-side electrode is formed in a portion other than the light-emitting portion on the p-contact layer, Further, an n-side electrode was formed on the back surface of the substrate.
[0074]
The oscillation wavelength of the manufactured surface-emitting type semiconductor laser device was about 1.3 μm. Since GaInNAs was used for the active layer, a long-wavelength surface emitting semiconductor laser device could be formed on a GaAs substrate. In addition, since the strain compensation structure is employed, the number of wells can be increased without generating crystal defects even when an active layer having a large compressive strain is used. Was controlled to the same degree as when the GaAs barrier layer was used, so that the temperature characteristics were good and the device was operated up to a high temperature.
[0075]
In addition, the threshold current was low because the current was narrowed by selective oxidation of the selectively oxidized layer containing Al and As as main components. 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. Furthermore, by oxidizing to form an Al oxide film, the refractive index is reduced, and light can be efficiently confined in a small region in which carriers are confined by the effect of the convex lens, and the efficiency is extremely improved, and the threshold current is reduced. Is done. In addition, since the current narrowing structure can be easily formed, the manufacturing cost can be reduced.
[0076]
Although the MBE method has been mainly used for manufacturing a semiconductor layer containing nitrogen such as GaInNAs and another group V, the supply amount of the raw material cannot be increased because the growth is performed in a high vacuum in principle. That is, there is a demerit that increasing the raw material supply amount places a burden on the exhaust system. Although an exhaust pump of a high vacuum exhaust system is required, the throughput is poor because the exhaust system is burdensome for removing residual materials and the like in the MBE chamber and is liable to break down.
[0077]
A surface-emitting type semiconductor laser device is configured such that an active region including at least one active layer for generating laser light is sandwiched between semiconductor multilayer film reflecting mirrors. While the thickness of the crystal growth layer of an edge-emitting laser is about 3 μm, for example, a surface-emitting semiconductor laser device in a 1.3 μm wavelength band requires a thickness of more than 10 μm as the thickness of the crystal growth layer. However, the MBE method requires a high vacuum, so that the supply amount of the raw material cannot be increased, the growth rate is about 1 μm / hour, and the supply amount of the raw material is changed in order to grow the thickness of 10 μm. It takes at least 10 hours even if no growth interruption time is provided.
[0078]
The thickness of the active region is usually very small (10% or less) as compared with the whole, and most of the layers constitute the multilayer mirror. The semiconductor multilayer mirror has a low refractive index layer and a high refractive index layer alternately stacked at a thickness (thickness of λ / 4) of １ ／ times the oscillation wavelength in each medium (for example, 20 to 40). 40 pairs). In a surface-emitting type semiconductor laser device on a GaAs substrate, an AlGaAs-based material is used to change the Al composition to form a low refractive index layer (large Al composition) and a high refractive index layer (small Al composition). However, in practice, especially on the p side, the resistance increases due to the hetero barrier of each layer. Therefore, an intermediate layer having an Al composition between them is inserted between the low refractive index layer and the high refractive index layer to form a multilayer film. The resistance of the reflector has been reduced.
[0079]
As described above, in the surface-emitting type semiconductor laser device, a semiconductor layer having a composition of more than 100 layers must be grown, and an intermediate layer between the low refractive index layer and the high refractive index layer of the multilayer mirror is required. It is an element that requires instantaneous control of the raw material supply amount, such as providing a layer. However, in the MBE method, the raw material supply amount is controlled by changing the temperature of the raw material cell, and the composition cannot be flexibly controlled. Therefore, it is difficult to reduce the resistance of the semiconductor multilayer mirror grown by the MBE method, and the operating voltage is high.
[0080]
On the other hand, the MOCVD method only needs to control the flow rate of the source gas, can control the composition instantaneously, does not require a high vacuum unlike the MBE method, and can increase the growth rate to, for example, 3 μm / hour or more. This is a growth method that is extremely suitable for mass production because the throughput can be increased.
[0081]
In the second embodiment, GaNPAsSb is used as the barrier layer. However, any one of GaPAsSb, GaInNPAsSb, and GaInPAsSb having a smaller lattice constant than GaAs can be used. Although GaInNAs is used as the quantum well active layer, GaInNAsSb, GaInNPAs, and GaInNPAsSb having a larger lattice constant than GaAs can also be used. Although the wavelength is shorter than the 1.3 μm band, GaAs is conventionally used as the barrier layer in the case where the In composition is increased to, for example, 1.1 μm or more even in the case of GaInAs containing no N. Therefore, a similar effect can be obtained by the present invention.
[0082]
As described above, according to the second embodiment, a low-cost, low-power, low-cost, 1.3 μm-band surface emitting semiconductor laser device can be realized.
[0083]
(Third embodiment)
FIG. 4 is a diagram showing a 1.3 μm band GaAsSb surface emitting semiconductor laser device according to a third embodiment of the present invention.
[0084]
The third embodiment is different from the second embodiment in that GaAsSb (Sb composition: 36%) is used as a quantum well active layer and GaPAsSb (P composition: 39%, Sb composition: 18%) is used as a barrier layer (barrier layer). This is the point used. The number of wells was 2. The barrier layer is substantially lattice-matched to the GaAs substrate. In the third embodiment, the conduction band discontinuity is increased by 255 meV and the valence band discontinuity is decreased by 33 meV as compared with the case where the GaAs barrier layer is used. As a result, the temperature characteristics were improved, and the threshold current was further reduced. In the third embodiment, GaAsSb is used as the quantum well active layer, but it may contain In, Al, and P slightly.
[0085]
(Fourth embodiment)
FIG. 5 is a diagram (top view) showing a surface emitting laser array according to a fourth embodiment of the present invention.
[0086]
The surface emitting laser array according to the fourth embodiment includes ten elements of the surface emitting laser according to the second embodiment arranged one-dimensionally. This may be integrated in two dimensions. However, the surface emitting laser array of the fourth embodiment has the conductivity types p and n opposite to those of the second embodiment. That is, in the surface emitting laser array of the fourth embodiment, the n-side individual electrode is formed on the upper surface, and the p-side common electrode is formed on the back surface of the substrate. This is because a bipolar transistor drive circuit capable of high-speed operation can be used as the anode common, so that more data can be transmitted simultaneously by a plurality of elements. This enables parallel transmission of transmitting more data at the same time.
[0087]
(Fifth embodiment)
FIG. 6 is a diagram showing an optical transmission module according to a fifth embodiment of the present invention. The optical transmission module according to the fifth embodiment combines the surface emitting laser array chip of the fourth embodiment with a silica fiber. It has become something. In the fifth embodiment, laser light from a surface emitting laser array chip is input to an optical fiber and transmitted. Here, a single mode fiber is used as the optical fiber. In order to transmit more data at the same time, parallel transmission using a laser array in which a plurality of semiconductor lasers are integrated has been attempted. In the fifth embodiment, since a single-mode high-output surface-emitting laser is used, high-speed parallel transmission is possible, and more data can be transmitted simultaneously than in the past.
[0088]
Further, when the surface emitting semiconductor laser device according to the present invention is used in an optical communication system, a low-cost and highly reliable optical transmission module can be realized, and a low-cost and high-reliability optical communication system using the same can be realized. realizable. Further, the surface emitting semiconductor laser device using GaInNAs has a good temperature characteristic and a low threshold value, so that a system which generates little heat and can be used without cooling to a high temperature can be realized.
[0089]
In the fifth embodiment, the surface emitting semiconductor laser device and the optical fiber are in one-to-one correspondence, but a plurality of surface emitting semiconductor laser devices having different oscillation wavelengths are arranged in a one-dimensional or two-dimensional array. Then, by performing wavelength multiplex transmission, it is possible to further increase the transmission speed.
[0090]
(Sixth embodiment)
FIG. 7 is a diagram showing an optical transceiver module according to a sixth embodiment of the present invention. The optical transceiver module according to the sixth embodiment includes a surface-emitting type semiconductor laser device according to the second embodiment, It is a combination of a diode and an optical fiber.
[0091]
When the surface emitting semiconductor laser device according to the present invention is used in an optical communication system, the surface emitting semiconductor laser device is inexpensive. Therefore, as shown in FIG. 7, the surface emitting semiconductor laser device for transmission (1.3 μm) is used. A low-cost and highly reliable optical communication system can be realized by combining a band GaInNAs surface emitting semiconductor laser device), a receiving photodiode, and an optical fiber. In addition, the surface emitting semiconductor laser device using GaInNAs according to the present invention has good temperature characteristics, low operating voltage, and low threshold value. A system that can be used at lower cost can be realized.
[0092]
Further, when a fluorine-doped POF (plastic fiber), which has low loss in a long wavelength band such as 1.3 μm, and a surface emitting semiconductor laser using GaInNAs as an active layer are combined, the cost of the fiber is reduced, Since the diameter is large and coupling with the fiber is easy and the mounting cost can be reduced, an extremely low-cost module can be realized.
[0093]
The optical communication system using the surface emitting semiconductor laser device of the present invention can be used not only for long-distance communication using an optical fiber, but also for transmission between devices such as a computer such as a LAN (Local Area Network). Can be used for short-distance communication as optical interconnection such as data transmission between boards, between LSIs in a board, between elements in an LSI, and the like.
[0094]
In recent years, processing performance of LSIs and the like has been improved, but the transmission speed of a portion connecting these components will become a bottleneck in the future. When the signal connection in the system is changed from the conventional electrical connection to the optical interconnect (for example, between the boards of the computer system, between the LSIs in the board, between the elements in the LSI, etc., the optical transmission module or the optical transmission / reception module according to the present invention is used). ), An ultra-high-speed computer system is possible.
[0095]
Further, when a plurality of computer systems and the like are connected using the optical transmission module and the optical transmission / reception module according to the present invention, an ultra-high-speed network system can be constructed. In particular, a surface-emitting type semiconductor laser device is significantly lower in power consumption than an edge-emitting type laser and can be easily formed into a two-dimensional array, so that it is suitable for a parallel transmission type optical communication system.
[0096]
As described above, according to the GaInNAs-based material or the GaAsSb-based material, which is a semiconductor layer containing nitrogen, Al (Ga) As / has a proven track record in a 0.85 μm band surface emitting semiconductor laser device using a GaAs substrate. A (Al) GaAs-based semiconductor multilayer film distributed Bragg reflector or a structure in which the current is narrowed by selective oxidation of AlAs can be applied. By adopting the present invention, a long-wavelength such as a 1.3 μm band having a practical level of high performance can be obtained. A band-emission semiconductor laser device can be realized, and if these devices are used, a low-cost optical communication system such as an optical fiber communication system and an optical interconnection system that does not require a cooling device can be realized.
[0097]
【The invention's effect】
As described above, according to the first to third aspects of the present invention, a quantum well active layer simultaneously containing nitrogen (N) having a compressive strain with respect to a GaAs substrate and another group V element is provided. In a semiconductor light emitting device having an active layer composed of a barrier layer formed therearound, the barrier layer is a group III-V mixed crystal semiconductor containing phosphorus (P) and antimony (Sb) at the same time (that is, compressed). In a structure using a strained GaInNAs-based quantum well active layer, a material in which at least P and Sb are simultaneously added to GaAs is used as a barrier layer), so that conduction band discontinuity is reduced so that electron overflow becomes a problem. And a strain-compensated quantum well active layer structure can be obtained which does not cause valence band discontinuity to be so large as to hinder hole injection. Yoshido is improved, the temperature characteristics operates to good high temperature, and it is possible to provide a highly reliable semiconductor light-emitting device.
[0098]
In particular, according to the second aspect of the present invention, in the semiconductor light emitting device according to the first aspect, the barrier layer also contains nitrogen (N) at the same time, and the addition of nitrogen (N) mainly reduces the conduction band energy. The lowering is preferable because the conduction band discontinuity can be controlled almost independently of P and Sb, and it is possible to compensate for the increase in the conduction band energy due to the addition of P to increase the quantum level and shorten the wavelength. Therefore, it is possible to provide a highly reliable semiconductor light emitting device with improved design flexibility, good temperature characteristics, operation at high temperatures, and high reliability. Further, it is difficult to control the switching of the N source material by the MOCVD method or the MBE method. However, if the barrier layer has a structure in which N is added, there is no need to turn on and off the supply of the N material at this interface. It becomes easy to control and obtain a suitable interface.
[0099]
According to the fourth and fifth aspects of the present invention, the quantum well active layer simultaneously contains Ga, As, and Sb having a compressive strain with respect to the GaAs substrate, and the barrier layer formed around the quantum well active layer. In a semiconductor light emitting device having an active layer, the barrier layer is a group III-V mixed crystal semiconductor containing phosphorus (P) and antimony (Sb) simultaneously, and the barrier layer containing P and Sb is GaAsSb-based compressive strain. It is effective even when a quantum well active layer is used. The addition of P to GaAs has the effect of increasing the conduction band discontinuity, and the addition of Sb has the effect of reducing the valence band discontinuity, and furthermore, it is preferable because it compensates for the mutual change in the lattice constant. As a result, compared to the case of using a GaAs barrier layer, a junction capable of increasing the conduction band discontinuity and reducing the valence band discontinuity becomes possible, reducing the overflow of electrons, and improving the hole injection efficiency. Since the temperature can be improved, a semiconductor light emitting element having good temperature characteristics and a small threshold current can be provided.
[0100]
According to a sixth aspect of the present invention, in the semiconductor light emitting device according to any one of the first to fifth aspects, the quantum well active layer is a multiple quantum well active layer. The effective mass of holes is larger than the effective mass of electrons, and the uniformity of hole injection depends sensitively on the barrier height. Therefore, when the valence band discontinuity becomes large, it becomes particularly difficult to uniformly inject holes into each well layer of the multiple quantum well structure, which adversely affects device characteristics such as an increase in threshold current. Would. When P and / or N is added to GaAs to form a material having a smaller lattice constant than GaAs, the valence band discontinuity with the GaInNAs-based quantum well active layer becomes larger than that of the GaAs barrier layer. . The addition of In has the effect of reducing the valence band discontinuity with the GaInNAs-based quantum well active layer, but the effect is slight. A sufficient effect can be obtained by adding Sb to the barrier layer as in the present invention. Also, in the case of a GaAsSb-based quantum well active layer, by adding Sb to the barrier layer, valence band discontinuity can be reduced as compared with the GaAs barrier layer, and hole injection into each well layer becomes uniform. The threshold decreases.
[0101]
According to a seventh aspect of the present invention, in the semiconductor light emitting device according to any one of the first to sixth aspects, the semiconductor light emitting device is a surface emitting semiconductor laser, and the surface emitting semiconductor laser is Compared to edge emitting semiconductor lasers, it is suitable for lower cost, lower power consumption, smaller size, and two-dimensional integration. Here, since the GaInNAs-based material or the GaAsSb-based material is used for the active layer, it is possible to cope with 1.3 μm band and 1.55 μm band wavelengths in which the transmission loss of the silica fiber is small and the matching is good. Also, the surface emitting semiconductor laser requires a large active layer gain because the cavity length is extremely short and the gain region is small as compared with the edge emitting laser. In order to improve the characteristics of the device, it is necessary to increase the gain by increasing the number of quantum well active layers. Since the strain compensation layer that controls the band discontinuity of the conduction band and the valence band is provided as in the present invention, it is possible to multiplex well layers, operate with a low threshold current, and have a high output, A surface emitting semiconductor laser having good temperature characteristics can be realized. Note that the formation by the MOCVD method is preferable because the resistance of the semiconductor distributed Bragg reflector of the surface emitting semiconductor laser can be reduced, so that low voltage driving is possible. As a result, it is possible to increase the capacity of the optical network and the optical wiring at low cost without worrying about the distance.
[0102]
According to the eighth aspect of the present invention, since the optical transmission module uses the surface emitting semiconductor laser device according to the seventh aspect as a light source, a low-cost optical transmission module that does not require a cooling element can be realized. Can be.
[0103]
According to the ninth aspect of the present invention, an optical transceiver module using the surface emitting semiconductor laser device according to the seventh aspect as a light source can realize a low-cost optical transceiver module that does not require a cooling element. Can be.
[0104]
According to the tenth aspect of the present invention, there is provided an optical communication system using the surface-emitting type semiconductor laser device according to the seventh aspect as a light source. An optical communication system such as a system can be realized.
[Brief description of the drawings]
FIG. 1 is a diagram showing the nitrogen composition dependency of a threshold current density experimentally obtained by the inventor of the present application.
FIG. 2 is a diagram showing a semiconductor light emitting device of a first embodiment.
FIG. 3 is a diagram showing a semiconductor light emitting device of a second embodiment.
FIG. 4 is a diagram showing a semiconductor light emitting device of a third embodiment.
FIG. 5 is a diagram illustrating a surface emitting laser array according to a fourth embodiment.
FIG. 6 is a diagram illustrating an optical transmission module according to a fifth embodiment.
FIG. 7 is a diagram illustrating an optical transceiver module according to a sixth embodiment.

Claims (10)

A semiconductor light emitting device having an active layer including a quantum well active layer simultaneously containing nitrogen (N) having a compressive strain with respect to a GaAs substrate and another group V element and a barrier layer formed therearound. A semiconductor light emitting device, wherein the layer is a group III-V mixed crystal semiconductor containing phosphorus (P) and antimony (Sb) simultaneously. 2. The semiconductor light emitting device according to claim 1, wherein said barrier layer also contains nitrogen (N). 2. The semiconductor light emitting device according to claim 1, wherein said barrier layer is GaNPAsSb, GaPAsSb, GaInNPAsSb, or GaInPAsSb. In a semiconductor light emitting device having an active layer including a quantum well active layer simultaneously containing Ga, As, and Sb having a compressive strain with respect to a GaAs substrate and a barrier layer formed around the active layer, the barrier layer is formed of phosphorus ( A semiconductor light emitting device comprising a group III-V mixed crystal semiconductor containing both P) and antimony (Sb). 5. The semiconductor light emitting device according to claim 4, wherein said barrier layer is GaPAsSb, AlGaPAsSb, GaInPAsSb, or AlGaInPAsSb. 6. The semiconductor light emitting device according to claim 1, wherein the quantum well active layer is a multiple quantum well active layer. 7. The semiconductor light emitting device according to claim 1, wherein the semiconductor light emitting device is a surface emitting semiconductor laser. An optical transmission module, wherein the semiconductor light emitting device according to claim 7 is used as a light source. An optical transceiver module, wherein the semiconductor light emitting device according to claim 7 is used as a light source. An optical communication system, wherein the semiconductor light emitting device according to claim 7 is used as a light source.

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