JP3748140B2 - Surface emitting semiconductor laser, optical transmission / reception module using the laser, and parallel information processing apparatus using the laser - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a surface emitting semiconductor laser, and more particularly to a surface emitting semiconductor laser suitable for general use such as consumer use.
[0002]
[Prior art]
The surface emitting semiconductor laser emits laser light in the vertical direction from the surface of the substrate, so that it can be two-dimensionally integrated, and the spread angle of the output light is relatively narrow (around 10 degrees), so In addition to being easy to combine, it has the feature of being easy to inspect elements. For this reason, in particular, development has been actively conducted as an element suitable for configuring a parallel transmission type optical transmission module (optical interconnection device). Current applications of optical interconnection devices include short-distance optical fiber communications as well as parallel connections between computers and other cabinets and boards. Future applications are expected to include large-scale computer networks and There is a trunk line system for long distance and large capacity communication.
[0003]
In general, a surface emitting semiconductor laser is constituted by an optical resonator comprising an active layer made of GaAs or GaInAs, an upper reflecting mirror disposed on the upper and lower sides of the active layer, and a lower reflecting mirror on the substrate side. Normally, the length of the optical resonator is significantly shorter than in the case of an edge-emitting semiconductor laser, so that the laser oscillation is caused by setting the reflectivity of the reflector to a very high value (99% or more). It needs to be easy. For this reason, a multilayer film reflector formed by alternately laminating a low-refractive index material made of AlAs and a high-refractive index material made of GaAs at a quarter wavelength period is usually used.
[0004]
Since the reflectance can be increased by increasing the number of stacked layers, the number of stacked layers ranging from 30 to 40 pairs is often adopted. However, with such a large number of stacked layers, it is difficult to manufacture a multilayer reflector and the yield of the device is deteriorated. In addition, there are problems that the series resistance increases and the power consumption increases. As a result of the increase in height, electrical wiring becomes difficult, and integration with other semiconductor elements such as laser driving transistors becomes difficult. Therefore, it is desirable that the number of stacked layers is as small as possible. The reduction in the number of stacked layers can be achieved by increasing the refractive index difference between the low refractive index layer and the high refractive index layer.
[0005]
Therefore, selection of a material that can provide a large refractive index difference is important. However, it is also necessary to select a material that is lattice-matched with the substrate from the viewpoint of suppressing the occurrence of transition. At present, there are few materials that satisfy both sides. For example, among the substrate materials, a GaAs substrate is easy to obtain a high-quality crystal and the temperature characteristics of a semiconductor laser formed on the substrate is stable, and is widely used for general purposes. At present, the materials that lattice match with the GaAs substrate are AlAs as a low refractive index material and GaAs as a high refractive index material to some extent.
[0006]
On the other hand, recently, a proposal has been made to alleviate the problems associated with lattice mismatch by adopting a material that is not lattice-matched and providing a buffer layer between the substrate and the reflecting mirror (see JP-A-6-132605). . In this example, AlInP is adopted for the low refractive index layer, and InGaAsP is adopted for the high refractive index layer. Both are materials that are not lattice matched to the substrate. However, since the thickness of each layer of the refractive index layer is fixed to ¼ of the wavelength and is significantly thicker than the critical film thickness (around 10 nm), the effect of lattice mismatch cannot be avoided and crystal defects are generated. There was an easy problem.
[0007]
Next, the problem of the number of stacked layers is generally particularly serious when the laser wavelength is in the 1.3 μm band or 1.55 μm band. In the case of such a long wavelength band laser, InP is used exclusively for the substrate and InGaAsP is used for the active layer, but the lattice constant of InP of the substrate is large, and a reflecting mirror material matching this has a refractive index difference. Therefore, it was necessary to increase the number of stacked layers to 40 pairs or more. On the other hand, another problem with semiconductor lasers formed on InP substrates is that their characteristics vary greatly 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 use such as consumer use. Due to such problems of the number of stacked layers and temperature characteristics, a practical long-wavelength surface emitting semiconductor has not yet been put into practical use.
[0008]
[Problems to be solved by the invention]
An object of the present invention is to provide a novel surface-emitting semiconductor laser including a reflecting mirror that can solve the above-described problems of the prior art and obtain a high reflectance with a small number of stacked layers. Another object of the present invention is to provide a long-wavelength surface emitting semiconductor laser.
[0009]
[Means for Solving the Problems]
AlInP can be made lattice-matched with the GaAs substrate by reducing the composition ratio of In. As a result of investigating the refractive index of AlInP in such a state by characteristic analysis, the refractive index is lower than that of the conventional material. It turns out that the rate can be obtained. The survey results are shown on the left side of FIG.
[0010]
The present invention has been made on the basis of such research results. The greatest feature of the present invention is that a GaAs substrate is used, and the low refractive index layer of at least one of the reflectors on the lower side on the substrate side is used. This is in that a semiconductor layer made of AlInP capable of lattice matching with the substrate is used. Note that the high refractive index layer is also a semiconductor layer capable of lattice matching with the substrate. As a result, it is possible to obtain a larger refractive index difference than in the prior art. Due to this large refractive index difference, a multilayer film reflecting mirror having a high reflectivity can be realized with a small number of layers. Needless to say, it is possible to avoid the occurrence of dislocations by using the above semiconductor layer that can be lattice-matched with the substrate for the lower reflector, but also when using the same semiconductor layer for the upper reflector, Since the active layer and the clad layer between the substrate and the upper reflecting mirror are related to the lattice matching with the substrate, the effect of avoiding the occurrence of dislocation can be obtained. It should be noted that other elements can be added to AlInP within a range where the refractive index does not change greatly.
[0011]
Next, paying attention to the fact that nitrogen changes the refractive index of III-V group materials, and investigating the refractive index by characteristic analysis, it was found that GaInNAs is a material having a higher refractive index than conventional materials. did. The survey results are shown on the right side of FIG.
[0012]
Another feature of the present invention is based on such research results, and is that a semiconductor layer made of GaInNAs is used for the high refractive index layer of at least one of the lower upper mirrors. As a result, it is possible to obtain a larger refractive index difference than in the prior art. Due to this large refractive index difference, a multilayer film reflecting mirror having a high reflectivity can be realized with a small number of layers. It is possible to add other elements to GaInNAs within a range where the refractive index does not change greatly.
[0013]
From the above results, it goes without saying that when the AlInP semiconductor layer is adopted as the low refractive index layer of the reflecting mirror, it is possible to obtain a larger refractive index difference by adopting the GaInNAs semiconductor layer as the high refractive index layer. It is.
[0014]
Furthermore, GaInNAs can reduce the series resistance of the P-type semiconductor multilayer reflector by increasing its N (nitrogen) composition (in a surface-emitting laser, the resistance of a P-type semiconductor with a large effective mass is a problem). Becomes). Series resistance decreases with decreasing band discontinuity in the valence band. When the N composition is increased, the energy at the top of the valence band is decreased, so that the valence band discontinuity at the heterointerface between the high refractive index layer and the low refractive index layer is reduced. Specifically, the AlAs / GaAs semiconductor multilayer reflector has a band discontinuity of about 600 meV in the AlAs / GaAs semiconductor multilayer reflector, but the AlInP / GaInNAs semiconductor multilayer reflector has a predetermined N composition ratio. Band discontinuity in the valence band can be lowered to about 400 meV. Since the series resistance is determined by an exponential function of the magnitude of the band discontinuity in the valence band, the series resistance at one heterointerface is reduced to about 1/5. Therefore, in the p-type semiconductor multilayer film reflecting mirror, the series resistance is greatly reduced in combination with the reduction in the number of stacked layers.
[0015]
Next, when GaInNAs is used as the material of the active layer, the band gap (forbidden band width) decreases from 1.4 eV to 0 eV as the N composition is increased, and thus emits a wavelength longer than 0.85 μm. It is possible to use it as a material. In addition, since lattice matching with the GaAs substrate is possible, it is preferable as a material for long-wavelength surface emitting semiconductor lasers in the 1.3 μm band and the 1.55 μm band. However, proposals have already been made to use the GaInNAs in combination with a GaAs substrate for an edge-emitting semiconductor laser (see Japanese Patent Laid-Open Nos. 7-154023, 7-162097, and 8-195522). However, the proposal does not mention the surface-emitting type.
[0016]
On the other hand, Japanese Patent Application Laid-Open No. 7-297476 discloses a surface emitting semiconductor laser having an InGaN active layer. This publication discloses a semiconductor laser having a Bragg reflector formed by alternately laminating GaN and InAlN. However, each semiconductor crystal of InGaN, GaN, and InAlN disclosed in this publication has a hexagonal wurtzite structure as shown in FIG. Therefore, based on the technique disclosed in this publication, a semiconductor laser having an active layer made of a III-V group compound semiconductor layer having a cubic zinc blende structure and containing N as a constituent element is realized. It is impossible. The reason is that the crystal structures of each other are essentially different.
[0017]
The inventor of the present invention paid attention to the fact that a surface emitting semiconductor laser employing an active layer made of a GaAs substrate and GaInNAs can be realized by using a semiconductor multilayer film lattice-matched to the GaAs substrate as a reflecting mirror. Yet another feature of the present invention is based on such findings. That is, another semiconductor laser of the present invention is a reflector comprising a GaAs substrate, a low-refractive index semiconductor layer lattice-matched to the same substrate, and a high-refractive index semiconductor layer lattice-matched to the same substrate. And an active layer made of GaInNAs, and the reflecting mirror is disposed in at least one of the upper and lower portions. As a result, since any of the low refractive index layer, the high refractive index layer and the active layer can be used in a lattice-matched state with the GaAs substrate, a stable and practical long-wavelength surface emitting semiconductor that does not cause crystal defects. A laser can be realized.
[0018]
[Problems to be solved by the invention]
  The present inventionExamples ofThe purpose ofImprovementAnd providing a novel surface emitting semiconductor laser including a reflecting mirror capable of obtaining a high reflectivity with a small number of layers,OrAn object of the present invention is to provide a practical long-wavelength surface emitting semiconductor laser.
[0019]
In addition, when using GaInNAs for the multilayer reflector of such a long-wavelength surface emitting semiconductor laser, in order to prevent the laser light from being absorbed by the multilayer reflector, the composite composition is adjusted and the multilayer reflector is used. It is desirable to set the band gap of the mirror GaInNAs to be larger than the band gap of the active layer.
[0020]
Further, since GaInNAs of the active layer can be fabricated on a GaAs substrate, it can be combined with a semiconductor such as AlInP, AlGaInP, GaInP, GaInPAs, or AlGaAs having a large band gap. Such a combination can strengthen electron confinement and reduce leakage current at room temperature. Such a combination can be implemented by using such a semiconductor having a large band gap for a semiconductor multilayer reflector or a cladding layer, and room temperature operation of a surface emitting semiconductor laser using GaInNAs as an active layer can be realized.
[0021]
The semiconductor multilayer mirror and the active layer described above can be stably crystal-grown on the substrate, and any one of actinic epitaxy, molecular beam epitaxy, or metal organic vapor phase epitaxy can be used. Can also be produced.
[0022]
In addition, since the surface emitting semiconductor laser is configured with a small number of stacked layers, the height can be reduced. Therefore, it is easy to integrate on the same substrate crystal as other semiconductor elements, and a highly integrated optical transmission module can be realized.
[0023]
The multilayer reflector made of semiconductor has been described above. However, the lower upper reflector can be composed of a semiconductor multilayer reflector, and one of them can be a dielectric multilayer reflector. . For example, when the lower reflecting mirror is composed of a semiconductor multilayer film reflecting mirror, the upper reflecting mirror can be a dielectric multilayer film reflecting mirror.
[0024]
Note that “lattice matching” in the present invention is to suppress the generation of lattice mismatch dislocations, and if this is realized, there may be a slight amount of lattice mismatch. For example, the lattice mismatch degree may be about ± 0.5%.
[0025]
DETAILED DESCRIPTION OF THE INVENTION
In a surface emitting semiconductor laser using a GaAs substrate and an AlInP semiconductor layer lattice-matched with the substrate in the low refractive index layer of the lower reflecting mirror on the substrate side, a GaAs semiconductor layer is used as the high refractive index layer of the reflecting mirror, and active The layer was a GaInAs / GaAs strained quantum well active layer. The above surface emitting semiconductor lasers were integrated in a 4 × 4 two-dimensional array element to form an optical transmission module.
[0026]
Next, in a surface emitting semiconductor laser using a GaInNAs semiconductor layer as a high refractive index layer of a lower reflecting mirror on the substrate side, a GaAs substrate is used as the substrate, and an AlInP semiconductor layer lattice-matched with the substrate is used as the low refractive index layer. It was. The active layer was a GaInAs / GaInPAs stress compensated quantum well active layer. On the substrate, MES-FET type transistors (Metal Semiconductor-Field Effect Transistors) for driving the surface emitting semiconductor laser were simultaneously integrated.
[0027]
Further, in a surface emitting semiconductor laser using a GaAs substrate and using GaInNAs as an active layer, the active layer is a GaInNAs unstrained active layer that lattice matches with the substrate, and a low refractive index GaInP semiconductor layer that lattice matches with the substrate and the substrate. A reflecting mirror in which lattice-matched high refractive index GaInNAs semiconductor layers are alternately stacked is disposed between the active layer and the substrate. The surface emitting semiconductor laser described above emitted light at room temperature and obtained an emission wavelength of 1.3 μm.
[0028]
Hereinafter, the present invention will be described in more detail with reference to some embodiments shown in the drawings.
[0029]
【Example】
<Example 1>
FIG. 2 shows a polyimide embedded surface emitting semiconductor laser having an emission wavelength of 0.98 μm. In the figure, 1 is an n-GaAs substrate (n impurity concentration = 1 × 10¹⁸cm^-3) 2 is an n-type semiconductor multilayer mirror (n impurity concentration = 1 × 10¹⁸cm^-3) 3 is a GaAs spacer layer, 4 is a GaInAs / GaAs strained quantum well active layer, 5 is a GaAs spacer layer, 6 is a p-GaInP cladding layer lattice-matched to the GaAs substrate (p impurity concentration = 1 × 10)¹⁸cm^-3), 7 is a p-GaAs contact layer (p impurity concentration = 1 × 10¹⁹cm^-3).
[0030]
The active layer 4 has three layers of 7 nm thick Ga_0.85In_0.15A strained quantum well layer having a band gap of 1.27 eV (wavelength; 0.98 μm) was used by separating the As well layer with a 10 nm thick GaAs barrier layer.
[0031]
The semiconductor multilayer mirror 2 is formed by alternately stacking a GaAs layer having a high refractive index having a quarter wavelength thickness in a semiconductor and an AlInP layer having a low refractive index having a quarter wavelength thickness in the semiconductor. For the AlInP layer, the proportion of Al group III elements was set to 50% so as to achieve lattice matching with the substrate 1. In order to make the reflectivity 99% or more, the number of reflecting mirror layers was 12 pairs.
[0032]
Using actinic epitaxy equipment, 1 × 10^-FiveEach of the semiconductor layers 2 to 7 was continuously crystal-grown in a high vacuum of Torr. In addition, a molecular beam epitaxy apparatus or a metal organic vapor phase apparatus can be used for crystal growth. Group III aluminum (Al), gallium (Ga) and indium (In) raw materials are organometallic alane, triethylgallium and trimethylindium, respectively, and group V phosphorus (P) and arsenic (As) raw materials. Phosphine and arsine were used, respectively. Silicon (Si) and beryllium (Be) were used as raw materials for n-type impurities and p-type impurities, respectively. The temperature for crystal growth was set to 500 ° C.
[0033]
Next, circular SiO 2 with a diameter of 10 μm is obtained by a chemical vapor deposition process and a photoresist process.₂A film (not shown in FIG. 2 for removal in a later step) is formed, and this is used as a mask to wet-etch the middle of the n-type semiconductor multilayer mirror 2 to form a mesa shape. Then, SiO₂With the chemical vapor deposition process while leaving the mask, the SiO₂A protective layer 8 was formed, and subsequently polyimide was applied and cured to form a polyimide film 9.
[0034]
Next, by reactive ion beam etching, SiO₂The polyimide film 9 is etched until the mask is exposed, and the SiO on the top of the mesa₂The mask was removed to obtain a flat surface. Thereafter, a ring-shaped p-side electrode 10 was formed by a lift-off method, a dielectric multilayer film reflecting mirror 11 was further formed by a sputtering method, and an n-side electrode 12 was formed. The dielectric multilayer mirror 11 includes a high refractive index amorphous Si layer having a quarter wavelength thickness in the dielectric and a low refractive index SiO having a quarter wavelength thickness in the dielectric.₂It was produced by alternately laminating layers. In order to make the reflectance 99% or more, the number of stacked layers was set to 4 pairs.
[0035]
When current was injected into the fabricated main surface emitting semiconductor laser, laser light was emitted from the dielectric multilayer film reflecting mirror side, and the oscillation wavelength was 0.98 μm at room temperature. Since this surface emitting semiconductor laser does not use a deliquescent material, it has a long element lifetime of 100,000 hours or more.
[0036]
In the present embodiment, an amorphous Si layer and an SiO2 are applied to a dielectric multilayer reflector of a surface emitting semiconductor laser.₂Although a dielectric multilayer reflector is used as long as the high refractive index layer and the low refractive index layer are alternately laminated, SiN and SiO are used.₂, Amorphous Si and SiN_xOr TiO₂And SiO₂Other material systems such as can be used.
[0037]
The above surface emitting semiconductor lasers were integrated in a 4 × 4 two-dimensional array array. An optical transmission module (optical connection device) was configured by combining the array element, a chip in which circuits for driving each laser were integrated, and an optical fiber bundle (16 bundles). This is shown in FIG. In FIG. 3, 51 is a laser array element, 52 is an IC (integrated circuit) chip in which a drive circuit 53 is integrated, 54 is an optical fiber bundle, and 55 is an optical connector. Each surface emitting semiconductor laser transmits a signal of 200 Mb / sec. Therefore, the entire module transmits a signal of 200 Mb / sec × 16 = 3.2 Gb / sec.
[0038]
A parallel information processing apparatus was constructed by connecting computers using eight of the optical transmission modules. FIG. 4 shows the configuration of the apparatus. In the figure, 61 is an optical transmission module, 62 is an optical reception module comprising a two-dimensional photodiode array, 63 is an optical fiber array, 64 is a computer, 65 is a transmission board of computer 64, and 66 is a reception board of computer 64. Indicates. A large capacity signal of 3.2 Gb / sec × 8 = 25.6 Gb / sec is transmitted between the two computers.
[0039]
Note that the surface emitting semiconductor laser of this example can be used as a single element without being integrated.
[0040]
<Example 2>
FIG. 5 shows a cylindrical surface emitting semiconductor laser having an emission wavelength of 0.98 μm, in which driving MES-FET transistors are integrated on the same substrate. A semiconductor laser is shown on the left side of the figure, and a transistor is shown on the right side. In the figure, 20 is a semi-insulating GaAs substrate, 21 is an n-GaAs buffer layer (n impurity concentration = 1 × 10¹⁷cm^-3On the left side of the figure, 22 is an n-type semiconductor multilayer mirror (n impurity concentration = 1 × 10).¹⁸cm^-3), 23 is Ga_0.82In_0.18P_0.37As_0.63 The spacer layer, 24 is a GaInAs / GaInPAs stress compensation type quantum well active layer, 25 is a GaInPAs spacer layer, and 26 is a p-type semiconductor multilayer mirror (p impurity concentration = 1 × 10).¹⁹cm^-3). The buffer layer 21 was formed up to the transistor part in addition to the semiconductor laser part.
[0041]
The active layer 24 includes 5 layers of 7 nm thick Ga having compressive strain._0.85In_0.15As well 6nm thick Ga with well strain_0.88In_0.12P_0.29As_0.71 A stress compensated quantum well active layer having a band gap of 1.27 eV (wavelength: 0.98 μm) effectively separated by a barrier layer was used. The semiconductor multilayer reflectors 22 and 26 are made of Ga having a ¼ wavelength thickness in a semiconductor._0.95In_0.05N_0.01As_0.99 Al of 1/4 wavelength thickness in layers and semiconductors_0.5In_0.5P layers were alternately stacked. In both layers, the composition ratio was set so as to achieve lattice matching with the substrate 20 and the buffer layer 21. The proportion of Al in the group III element of the AlInP layer was set to 50%. In order to make the reflectivity 99% or more, the number of laminated mirror layers was 11 pairs.
[0042]
Each of the semiconductor layers 21 to 26 is formed by using a molecular beam epitaxy apparatus.^-FourCrystals were grown continuously in a high vacuum of Torr. In addition, for the crystal growth, it is possible to use a chemical beam epitaxy apparatus or a metal organic vapor phase epitaxy apparatus. Respective metals were used as the raw materials for Al, Ga and In, phosphine and arsine were used as the raw materials for P and As, respectively, and nitrogen molecules activated by high-frequency plasma were used as the raw materials for N. In addition, the activation of the nitrogen molecules can be performed using ECR plasma (Electron Cyclotron Resonance). Si and CBr are used as raw materials for n-type impurities and p-type impurities, respectively._FourWas used. The temperature for crystal growth was set to 500 ° C.
[0043]
Next, the surface of the buffer layer 21 was etched by reactive ion beam etching to leave a cylindrical light emitting region having a diameter of 5 μm as shown in FIG. Thereafter, SiO is performed by a chemical vapor deposition process.₂A protective layer 27 was formed, a p-side electrode 28 and an n-side electrode 29 were formed, and a surface emitting semiconductor laser was manufactured.
[0044]
Next, fabrication of the transistor portion on the right side of FIG. 5 will be described. First, the outer portion of the transistor was etched until it reached the semi-insulating substrate 20 to separate the elements. Then, the source electrode 30, the gate electrode 31, and the drain electrode 32 were formed, and the MES-FET type transistor was completed.
[0045]
Finally, electrical wiring 33 was performed by depositing aluminum. The wiring 33 connects the source electrode 30 of the transistor and the p-side electrode 28 of the surface emitting semiconductor laser.
[0046]
In the surface emitting semiconductor laser according to the present invention, the number of multilayer reflectors stacked is one-fifth that of a conventional element, so that the height of the element is also a fraction of that of a conventional element. As a result, the wiring 33 can be formed with a uniform thickness, and disconnection at the side surface of the surface emitting semiconductor laser, which has been a problem with conventional devices, can be avoided. As a result, the device yield can be greatly improved.
[0047]
Wiring for the n-side electrode 29 of the surface emitting semiconductor laser and the gate electrode 31 and drain electrode 32 of the transistor can be easily formed by conventional wiring techniques. These wirings are shown in a simplified manner in FIG.
[0048]
Next, the operation of this integrated circuit will be described. When the voltage Vd is applied to the drain electrode 32, a current flows from the drain electrode 32 to the source electrode 30 when the transistor is in a conductive state. As a result, a current is injected into the surface emitting semiconductor laser through the wiring 33, and the surface emitting semiconductor laser oscillates. A laser beam having an oscillation wavelength of 0.98 μm was emitted from the substrate side at room temperature. The conduction / non-conduction of the transistor is controlled by the voltage Vg applied to the gate electrode 31, and the current injected into the laser is controlled. The magnitude of the current is set by a resistor R connected to the n-side electrode 29 of the surface emitting semiconductor laser.
[0049]
The surface-emitting semiconductor laser that was implemented did not use a deliquescent material and therefore had a long device life of 10,000 hours or more. In addition, the number of stacked semiconductor multilayer mirrors could be reduced to a fraction of that of conventional elements. Furthermore, since GaInNAs is used for the p-type reflector, the series resistance of the semiconductor multilayer reflector can be reduced and the power consumption of the semiconductor laser can be reduced. By integrating the semiconductor laser and the transistor into a two-dimensional array, a small optical transmission module can be configured. The module could be used as a light source for an encoding logic operation system, which is one of parallel optical information processing.
[0050]
In this embodiment, the surface emitting semiconductor laser and the MES-FET type transistor are integrated, but needless to say, it can be integrated with other semiconductor elements including resistors and capacitors. On the other hand, the surface emitting semiconductor laser shown in this embodiment can be used as a single element.
[0051]
The relationship between the number of layers and the reflectivity of the AlInP / GaInNAs-based multilayer mirror employed in this example was examined. FIG. 6 shows the result of comparison with a conventional GaInP / GaAs multilayer reflector. When there is no loss at the multilayer mirror, the solid line indicates the loss is 40 cm.^-1This case is indicated by a broken line. First, a case where there is no loss will be described. In the GaAs / GaAs multilayer mirror, 32 pairs of layers are required to obtain the target reflectivity of 99.5%. On the other hand, the AlInP / GaInNAs multilayer reflector of the present invention achieves 13 pairs, and the number of stacked layers can be reduced to about 1/3. This number of layers exceeds 16 pairs of conventional chemically unstable AlAs / GaAs multilayer reflectors.
[0052]
Then, the loss is 40cm^-1The case will be described. The AlInP / GaInNAs multi-layer film reflecting mirror has a reflectance of 99.5% with 15 pairs. However, in the conventional GaInP / GaAs multilayer reflector, the reflectance is saturated at 99.3% and does not reach 99.5% no matter how many layers are stacked. In an actual multilayer mirror, the loss is 40 cm.^-1It can be seen that the AlInP / GaInNAs-based multilayer mirror is very effective in reducing the number of layers and ensuring a high reflectance.
[0053]
The above result is the case where AlInP and GaInNAs are lattice-matched to the GaAs substrate, but the same effect can be obtained even when the strained layer is formed in a range where no lattice mismatch dislocation occurs. Further, it is possible to perform stress compensation so that crystal defects do not occur in the strained layer, and in this case, the same effect of reducing the number of stacked layers can be obtained.
[0054]
<Example 3>
FIG. 7 shows a surface emitting semiconductor laser having a wavelength band of 1.3 μm. In the figure, 1 is an n-GaAs substrate (n impurity concentration = 1 × 10¹⁸cm^-3), 42 is an n-type semiconductor multilayer mirror (n impurity concentration = 1 × 10¹⁸cm^-3), 43 is a GaAs spacer layer, 44 is Ga_0.8In_0.2N_0.04As_0.96 Unstrained active layer, 45 is GaAs spacer layer, 46 is p-Al_0.3Ga_0.7As cladding layer (p impurity concentration = 1 × 10¹⁸cm^-347 is a p-GaAs contact layer (p impurity concentration = 1 × 10¹⁹cm^-3).
[0055]
As the active layer 44, a non-doped GaInNAs layer having a lattice gap of 0.95 eV with respect to a wavelength of 1.3 μm and a lattice match with the GaAs substrate 1 was used. The semiconductor multilayer mirror 42 is a high refractive index Ga having a quarter wavelength thickness in a semiconductor._0.9In_0.1N_0.01As_0.99 Low refractive index Ga with 1/4 wavelength thickness in layers and semiconductors_0.5In_0.5P layers were alternately stacked. In both layers, the composition ratio was set so as to achieve lattice matching with the substrate 1. In order to make the reflectivity 99% or more, the number of laminated mirrors 42 is 27.
[0056]
Each of the semiconductor layers 42 to 47 is continuously formed by using a metal organic vapor phase epitaxy apparatus.^-1Crystals were grown in a low vacuum of Torr. In addition, it is possible to use a chemical beam epitaxy apparatus or a molecular beam epitaxy apparatus for crystal growth. Trimethylgallium and trimethylindium were used as raw materials for Ga and In, phosphine and arsine were used as raw materials for P and As, respectively, and tributylamine was used as a raw material for N. Disilane and dimethyl zinc were used as raw materials for n-type impurities and p-type impurities, respectively. The temperature of crystal growth was set to 600 ° C.
[0057]
Next, circular SiO 2 with a diameter of 10 μm is obtained by a chemical vapor deposition process and a photoresist process.₂A film is formed, and this is used as a mask to wet-etch halfway through the n-type semiconductor multilayer reflector 42 to form a mesa shape. Then, SiO₂With the chemical vapor deposition process while leaving the mask, the SiO₂The protective layer 8 is formed, and polyimide is applied and cured. Next, by reactive ion beam etching, SiO₂The polyimide layer 9 was formed by etching the polyimide until the mask was exposed. Next, the top of the mesa₂The mask was removed to obtain a flat surface.
[0058]
Thereafter, a ring-shaped p-side electrode 10 was formed by a lift-off method. Further, the dielectric multilayer film reflecting mirror 11 was formed by the sputtering method, and the n-side electrode 12 was formed. The dielectric multilayer mirror 11 includes a high refractive index amorphous Si layer having a quarter wavelength thickness in the dielectric and a low refractive index SiO having a quarter wavelength thickness in the dielectric.₂Layers were alternately stacked. The number of layers was 5 pairs.
[0059]
This surface-emitting semiconductor laser stably oscillates at a wavelength of 1.3 μm at room temperature, and has a long device life of 100,000 hours or more because no deliquescent material is used.
[0060]
Next, the composition ratio of GaInNAs in the active layer 44 was changed to another predetermined value to fabricate a surface emitting semiconductor laser having an oscillation wavelength of 1.55 μm. Both wavelengths of 1.3 μm and 1.55 μm coincide with the wavelength band used in optical fiber communication. Both semiconductor lasers can be integrated and configured as an array element, or can be used as a single element. A single element was used for the light source of an optical fiber communication system.
[0061]
In this embodiment, the oscillation wavelengths are 1.3 .mu.m and 1.55 .mu.m. However, it is possible to further increase the wavelength by further changing the composition ratio of GaInNAs. As described above, it is theoretically possible to set the band gap to 0 eV, so that the wavelength can be made as long as possible. However, the wavelength is in the infrared range in terms of the feasibility of the reflecting mirror.
[0062]
<Example 4>
FIG. 8 and FIG. 9 show an optical transceiver module (optical connection device) in which the surface emitting semiconductor laser of the present invention is mounted on a mounting substrate by flip chip bonding and the surface type photodetector is mounted on the same substrate by flip chip bonding. FIG. 8 is a cross-sectional view showing how the surface emitting semiconductor laser is mounted on the substrate, and FIG. 9 is a structural diagram of the optical transceiver module.
[0063]
In FIG. 8, 81 is a surface emitting semiconductor laser, 82 is a mounting substrate, 83 is a solder bump, 84 is one electrode of the semiconductor laser 81, and 85 is the other electrode of the semiconductor laser 81. Although the element shown in FIG. 2 is adopted as the semiconductor laser 81, the element shown in FIG. 7 can be used.
[0064]
Although the surface-type photodetector is not shown in a mounting form, it can be shown as a structure in which the semiconductor laser 81 in FIG. 8 is replaced with a surface-type photodetector. As the surface photodetector, an InGaAs material was used when the light wavelength was in the 1.3 μm band. Good photoelectric conversion efficiency can be obtained with this material. In the case where the light wavelength is in the visible light band, it is advantageous from the viewpoints of both production cost and photoelectric conversion efficiency to employ the Si material.
[0065]
By the flip chip bonding shown in FIG. 8, in the optical transceiver module, high-speed driving, simplification of the mounting process, and ease of alignment can be obtained. In flip chip bonding, as shown in FIG. 8, electrodes 84 and 85 for supplying current to the semiconductor laser 81 are formed on the upper surface of the same element. The laser beam is emitted from the back surface of the element substrate opposite to the element surface. Similarly, in the case of a photodetector, laser light is incident from the back surface of the element substrate opposite to the element surface.
[0066]
A broadband circuit and wiring are mounted on the substrate 82 on which the elements (semiconductor laser 81 and photodetector) are mounted, and the bandwidth is equal to or higher than the drive frequency of the optical transceiver module. Solder bumps were placed on the bonding pads of such a broadband substrate 82. Mounting was performed by turning the element upside down and bringing the bonding pad of the element and solder bumps into contact with each other in a state where the substrate 82 was heated to a temperature equal to or higher than the solder melting temperature.
[0067]
This flip-chip bonding can reduce inductance compared to generally employed wire bonding, and is advantageous for high-speed driving of elements. Further, the mounting process on the substrate 82 is simple, and the positional deviation can be reduced, so that highly accurate alignment can be easily realized.
[0068]
Although one element is shown in FIG. 8, it is possible to integrate a plurality of elements on an element substrate, provide an electrode for each element, and mount the integrated elements on the substrate 82 at the same time.
[0069]
9, 92 is an optical fiber coupled to the semiconductor laser 81 and the photodetector, 93 is a fiber ferrule that houses the optical fiber 92, 90 is a fiber ferrule guide that guides the fiber ferrule 93, and 94 is a fiber. A guard shelf for fixing the ferrule 93 with high accuracy, 91 is an incoming / outgoing light signal, 95 is an outgoing light signal, 96 is an incident light signal, 97 is a surface emitting laser array in which semiconductor lasers 81 are integrated in an array, and 98 is A surface type photo detector array in which photo detectors are integrated in an array, 99 is a driving IC for driving the surface emitting laser array 97 and the photo detector array 98, 913 is a mother board on which six mounting substrates 82 are mounted, and 911 is a mounting substrate. Mounting board for connecting 82 to motherboard 913 2 side of the signal pin array 912 shows a motherboard 913 side of the signal pin socket for receiving a signal pin array 911.
[0070]
An electrical signal from the motherboard 913 is converted into an optical signal in the transmission / reception module, and conversely, the optical signal is converted into an electrical signal. The electrical signal is transmitted through the optical fiber in the form of an optical signal. The surface emitting semiconductor laser 97 and the photodetector are monolithically integrated into a one-dimensional array shape. In addition, not only a one-dimensional array but a two-dimensional array can be used. These arrays 97 and 98 are mounted on a mounting substrate 82 by flip chip bonding shown in FIG. Then, an integrated circuit containing a drive circuit for driving the arrays 97 and 98 was mounted on the mounting substrate 82. By such mounting, the wiring length is remarkably shortened, and it is possible to suppress the deterioration of the band due to the wiring.
[0071]
As the optical fiber used for each element of the arrays 97 and 98, a ribbon type optical fiber 92 is employed. By arranging the end face of the optical fiber and the elements of the arrays 97 and 98 close to each other, they were optically coupled without using an optical element such as a lens. When the core diameter of the optical fiber is 50 μm and the light input / output diameter of the element is equal to 50 μm, a high optical coupling efficiency exceeding 50% is realized by setting the distance between them to 10 μm or less. Can do. Further, the alignment margin at this time is about ± 5 μm, which can be easily realized, if a power fluctuation of 50% is allowed.
[0072]
When the mother board 913 is incorporated into a device that accommodates the mother board 913, it is desirable that the ribbon optical fiber 92 and the mother board 913 are in a parallel positional relationship. Therefore, the mounting substrate 82 is arranged perpendicularly to the mother board 913 so that each element of the arrays 97 and 98 is arranged perpendicularly to the end face of the optical fiber. The mounting board 82 and the motherboard 913 are electrically connected by a signal pin array 911 and a signal pin socket 912.
[0073]
The ribbon-type optical fiber 92 has a positional relationship with each element of the arrays 97 and 98 by a guide mechanism including a fiber ferrule 93 and a fiber ferrule guide 90.
[0074]
In addition, in order to block each element of the arrays 97 and 98 from the outside air, the upper surface of each element was covered with a film of acrylic material having a thickness of 7 μm. Not only this material but also other thin film substances having a thickness and a refractive index that do not disturb the optical coupling state between the end face of the optical fiber and the element can be used.
[0075]
With the configuration of the optical transmission / reception module described above, it was possible to reduce the number of components and increase the accuracy of alignment between the optical fiber and the element. As a result, it was possible to improve convenience as a module, economics of module mounting, and alignment margin.
[0076]
  The present inventionExamples ofSince a semiconductor material having a large refractive index difference is used for the reflecting mirror, a desired reflectance can be obtained with a small number of layers. Further, since a material having no deliquescence is adopted as the material, a long-life surface emitting semiconductor laser can be realized. Since the number of stacked layers is small, the height of the laser can be reduced and integration with other semiconductor elements is facilitated. Therefore, a highly integrated optical transmission module and optical transmission / reception module can be realized. According to another embodiment of the present invention, since a material having Ga, In, N and As is used for the active layer of the surface emitting semiconductor laser, laser beams having wavelengths of 1.3 μm and 1.55 μm are used at room temperature. It can oscillate stably.
(Appendix)
1. An active layer that generates light on the top of the crystal substrate, and a resonator that sandwiches the upper and lower portions of the active layer between the upper reflecting mirror and the lower reflecting mirror on the substrate side in order to obtain laser light from the light generated from the active layer. In a surface emitting semiconductor laser that emits laser light perpendicular to the crystal substrate surface, the crystal substrate is a GaAs substrate, and at least one of the reflecting mirrors is
A low refractive index semiconductor layer lattice-matched to the GaAs substrate and a high-refractive index semiconductor layer lattice-matched to the GaAs substrate are alternately included, and the low refractive index semiconductor layer includes: A surface emitting semiconductor laser characterized in that a main element is made of a material of aluminum, indium and phosphorus.
2. An active layer that generates light on the top of the crystal substrate, and a resonator that sandwiches the upper and lower portions of the active layer between the upper reflecting mirror and the lower reflecting mirror on the substrate side in order to obtain laser light from the light generated from the active layer. A surface-emitting semiconductor laser that emits laser light perpendicular to the crystal substrate surface, wherein at least one of the reflecting mirrors is a semiconductor multilayer in which low-refractive index semiconductor layers and high-refractive index semiconductor layers are alternately stacked A surface-emitting semiconductor laser comprising a film, wherein the high-refractive-index semiconductor layer is made of a material of which main elements are gallium, indium, nitrogen and arsenic.
3. The high refractive index semiconductor layer is characterized in that the main elements are made of materials of gallium, indium, nitrogen and arsenic. A surface emitting semiconductor laser according to claim 1.
4). The semiconductor multilayer film is mixed with an impurity imparting p-type conductivity. Or 3. A surface emitting semiconductor laser according to claim 1.
5. 2. The reflecting mirror having the semiconductor multilayer film, wherein the number of laminated low refractive index semiconductor layers and high refractive index semiconductor layers is 30 pairs or less. A surface emitting semiconductor laser according to claim 1.
6). An active layer that generates light on the top of the crystal substrate, and a resonator that sandwiches the upper and lower portions of the active layer between the upper reflecting mirror and the lower reflecting mirror on the substrate side in order to obtain laser light from the light generated from the active layer. A surface emitting semiconductor laser that emits laser light perpendicular to the crystal substrate surface, wherein the crystal substrate is a GaAs substrate, and at least one of the reflecting mirrors includes a low-refractive index semiconductor layer lattice-matched to the GaAs substrate; The semiconductor device is composed of a semiconductor multilayer film in which high-refractive index semiconductor layers lattice-matched to the GaAs substrate are alternately stacked, and the active layer is composed of materials of gallium, indium, nitrogen and arsenic as main elements. Surface emitting semiconductor laser.
7. The wavelength of the laser beam is longer than 0.85 μm and is in the infrared wavelength range.
The above-mentioned 6. A surface emitting semiconductor laser according to claim 1.
8). 6. The wavelength of the laser beam is in a 1.3 μm band or a 1.55 μm band. A surface emitting semiconductor laser according to claim 1.
9. The semiconductor portion including the active layer and the semiconductor multilayer film of the reflecting mirror is integrated on the same crystal substrate as the other semiconductor elements. -Said 8. The surface emitting semiconductor laser according to any one of the above.
10. The semiconductor part including the active layer and the semiconductor multilayer film of the reflecting mirror is manufactured by any one of actinic epitaxy, molecular beam epitaxy, or metal organic vapor phase epitaxy. -Said 9. The manufacturing method of the surface emitting semiconductor laser as described in any one of these.
11. 1 above. -Said 9. An optical transmission module comprising the surface-emitting semiconductor laser according to claim 1 as a light source.
12 1 above. -Said 9. A parallel information processing apparatus comprising the surface-emitting semiconductor laser according to claim 1 as a light source.
13. 1 above. -Said 9. An optical fiber communication system comprising the surface-emitting semiconductor laser according to claim 1 as a light source.
14 1 above. -Said 9. An optical transceiver module comprising the surface-emitting semiconductor laser according to any one of the above as a light source.
[Brief description of the drawings]
FIG. 1 is a curve diagram for explaining refractive index characteristics of a low refractive index material and a high refractive index material.
FIG. 2 is a cross-sectional view for explaining a first embodiment of a surface emitting semiconductor laser according to the present invention.
FIG. 3 is an arrangement configuration diagram for explaining an example of an optical transmission module according to the present invention.
4 is an arrangement configuration diagram for explaining an example of a parallel information processing apparatus using the optical transmission module of FIG. 3;
FIG. 5 is a cross-sectional view for explaining a second embodiment of the surface emitting semiconductor laser according to the present invention.
FIG. 6 is a curve diagram for explaining the relationship between the number of laminated multilayer mirrors and the reflectance.
FIG. 7 is a cross-sectional view for explaining a third embodiment of the surface emitting semiconductor laser according to the present invention.
FIG. 8 is an element mounting sectional view for explaining a fourth embodiment of the present invention.
FIG. 9 is a structural diagram of an optical transceiver module for explaining a fourth embodiment of the present invention.
[Explanation of symbols]
1 ... n-GaAs substrate
2 ... n-type AlInP / GaAs semiconductor multilayer reflector
4 ... GaInAs / GaAs strained quantum well active layer
9 ... Polyimide protective layer
10, 28 ... p-side electrode
11 ... Dielectric multilayer reflector
12, 29 ... n-side electrode
20 ... Semi-insulating GaAs substrate
21 ... n-GaAs buffer layer
22 ... n-type AlInP / GaInNAs semiconductor multilayer mirror
24 ... GaInAs / GaInPAs Stress compensated quantum well active layer
26 ... p-type AlInP / GaInNAs semiconductor multilayer mirror
30 ... Source electrode
31 ... Gate electrode
33 ... Drain electrode
33 ... Al wiring
42 ... n-type GaInP / GaInNAs semiconductor multilayer mirror
44 ... GaInNAs unstrained active layer
50, 81... Surface emitting semiconductor laser
51. Laser array element
61: Optical transmission module
82 ... Mounting board
83 ... Solder bump
84: One electrode of semiconductor laser
85 ... The other electrode of the semiconductor laser
54, 92 ... optical fiber
91 ... I / O light signal
95: Output light signal
96: Incident light signal
97 ... Surface emitting laser array
98 ... Surface type photo detector array
913 ... Motherboard

Claims (11)

  An active layer that generates light on the top of the crystal substrate, and a resonator that sandwiches the upper and lower portions of the active layer between the upper reflecting mirror and the lower reflecting mirror on the substrate side in order to obtain laser light from the light generated from the active layer. A surface-emitting semiconductor laser that emits laser light perpendicular to the crystal substrate surface, wherein the crystal substrate is a GaAs substrate, and at least one of the reflecting mirrors includes a low-refractive index semiconductor layer lattice-matched to the GaAs substrate; The semiconductor device is configured to include a semiconductor multilayer film formed by alternately laminating high refractive index semiconductor layers lattice-matched to the GaAs substrate, and the low refractive index semiconductor layer is made of a material whose main elements are aluminum, indium and phosphorus, The high-refractive-index semiconductor layer is a surface emitting semiconductor laser characterized in that main elements are made of materials of gallium, indium, nitrogen and arsenic.   An active layer that generates light on the top of the crystal substrate, and a resonator that sandwiches the upper and lower portions of the active layer between the upper reflecting mirror and the lower reflecting mirror on the substrate side in order to obtain laser light from the light generated from the active layer. A surface-emitting semiconductor laser that emits laser light perpendicular to the crystal substrate surface, wherein at least one of the reflecting mirrors is a semiconductor multilayer in which low-refractive index semiconductor layers and high-refractive index semiconductor layers are alternately stacked A surface-emitting semiconductor laser comprising a film, wherein the high-refractive-index semiconductor layer is made of a material of which main elements are gallium, indium, nitrogen and arsenic.   The surface emitting semiconductor laser according to claim 2, wherein the semiconductor multilayer film is mixed with an impurity imparting p-type conductivity.   3. The surface emitting semiconductor laser according to claim 2, wherein the reflecting mirror including the semiconductor multilayer film has 30 or less pairs of low refractive index semiconductor layers and high refractive index semiconductor layers.   An active layer that generates light on the top of the crystal substrate, and a resonator that sandwiches the upper and lower portions of the active layer between the upper reflecting mirror and the lower reflecting mirror on the substrate side in order to obtain laser light from the light generated from the active layer. In a surface emitting semiconductor laser that emits laser light perpendicular to the crystal substrate surface, the crystal substrate is a GaAs substrate, and at least one reflecting mirror includes a low-refractive index semiconductor layer that lattice-matches to the GaAs substrate, The active layer is composed of a material composed of gallium, indium, nitrogen, and arsenic, and the active layer is formed of a semiconductor multilayer film in which high refractive index semiconductor layers lattice-matched to the GaAs substrate are alternately stacked. Surface emitting semiconductor laser.   6. The surface emitting semiconductor laser according to claim 5, wherein the wavelength of the laser beam is longer than 0.85 [mu] m and is in the infrared wavelength range.   The surface emitting semiconductor laser according to claim 5, wherein the wavelength of the laser light is in a 1.3 μm band or a 1.55 μm band. An optical transmission module comprising the surface-emitting semiconductor laser according to any one of claims 1 to 7 as a light source. Parallel processing apparatus comprising the surface emitting semiconductor laser according as the light source to any one of claims 1 to 7. An optical fiber communication system comprising the surface emitting semiconductor laser according to any one of claims 1 to 7 as a light source. Optical transceiver module comprising the surface-emitting semiconductor laser according as the light source to any one of claims 1 to 7.

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