JPH10233558A - Multilayer film structure wherein diamond layer is incorporated, optical device with it and its manufacturing method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a multilayer film structure such as a multilayer film reflection mirror wherein a highly heat-conductive diamond layer is incorporated, an optical device with it and its manufacturing method. SOLUTION: A multilayer film structure has a diamond layer 2 wherein a diamond layer part formed by hetero-epitaxy is at least partially included. It has the diamond layer 2 as a first layer and is formed by forming a thin film 3 of other materials and the diamond layer 2 alternately thereon. A multilayer film structure is formed as a multilayer film reflection mirror, etc., and is used in an optical device such as a surface light emitting type semiconductor laser.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a multilayer structure such as a multilayer reflecting mirror having excellent heat dissipation, an optical device having the multilayer structure such as a vertical cavity surface emitting laser device, and a method of manufacturing the same.

[0002]

2. Description of the Related Art Since the gain region is small, the oscillation threshold value is low, the power consumption is small, and the light emitting surface is relatively wide (10 μm
Since the beam does not spread and the optical coupling with the fiber is easy because it has a diameter of about φ, a vertical cavity surface emitting semiconductor laser (Vertical Cavity Surface) can be obtained.
Emitting Laser (VCSEL) has been actively developed in recent years.

Since a VCSEL injects a current into a minute region, the gain is likely to be suppressed by heat unless the injection efficiency due to the current confinement structure and the quantum efficiency in the active layer are high. Therefore, a wavelength band of 0.8 μm to 1.0 μm
In the region (2), the practical level has been reached (because the thermal characteristics of the GaAs-based material used in this region are good), but sufficient characteristics have not been obtained in other wavelength bands. In particular, in the 1.3 to 1.55 μm band, which is a communication wavelength band, an InP-based material is used. Due to its poor thermal characteristics, a small amount of heat generated in the active region causes suppression of the gain and continuous oscillation at room temperature. It is becoming difficult to manufacture lasers with good yield.

In the case of VCSELs, since the gain region is small, a high reflection mirror of 99% or more is required. In general, a multilayer mirror of Si / SiO ₂ having a thickness of λ / 4 is used. ing. However, since the thermal conductivity of SiO ₂ is poor, it is inconvenient to use it in the communication wavelength band as it is. Therefore, by using a Si / Al ₂ O ₃ pair having relatively good thermal conductivity as the dielectric multilayer mirror near the active layer, continuous oscillation at room temperature can be obtained even in the 1.3 μm band (Uchiyama) Others: IEICE IEICE Technical Report LQ
E95-111 p. 15). The structure is shown in FIG.
In this structure, heat generation in the active layer 131 is efficiently reduced by Si /
It is devised to conduct the heat to the heat sink through the dielectric multilayer mirror 130 of the Al ₂ O ₃ pair. here,
132 is a dielectric multilayer mirror on the light output side, 135 is an electrode on the heat sink side, 136 is a cap layer, 137 is a buried layer, 138 is an etch stop layer, 139 is a substrate, 1
Reference numeral 40 denotes upper and lower cladding layers, and 141 denotes an electrode on the light output side.

The heat sink is also required to have high thermal conductivity, and a diamond crystal is used as the heat sink having the highest thermal conductivity. However, the diamond crystal is expensive and the mounting cost increases. Therefore,
Recently, it has been proposed to provide an inexpensive diamond heat sink by growing a diamond thin film by the CVD method (see Japanese Patent Application Laid-Open No. 8-102511). In this case, a thermistor as a temperature sensor is also integrated, and temperature control can be performed quickly and efficiently.

[0006]

However, the thermal conductivity of the Al ₂ O ₃ film of the dielectric multilayer mirror is 55 W / m · K.
It is higher than about 10 W / m · K of SiO ₂ , but smaller than about 200 W / m · K of Si. Therefore, high-temperature operation at 80 ° C. or higher for ensuring environmental resistance has not yet been achieved. Therefore, in order to enable high-temperature operation by improving the thermal characteristics or heat dissipation, it is necessary to form the multilayer mirror with a material having even higher thermal conductivity.

[0007] Although there is little mention in the conventional example of bonding a diamond heat sink synthesized by a CVD method to an element, there is no gap between the heat sink and the element so as not to lose thermal conductivity. It is necessary to increase productivity.

[0008] In view of such problems, the present invention has the following objects. A first object is to provide a multilayer film structure such as a multilayer reflection mirror including a diamond layer having high thermal conductivity (corresponding to claims 1 to 6).

A second object is to provide a method of manufacturing a multilayer structure such as a multilayer reflection mirror including a diamond layer having high thermal conductivity (corresponding to claims 7 and 8).

A third object is to provide an optical device having a multilayer structure such as a multilayer reflection mirror including a diamond layer having high thermal conductivity (corresponding to claims 9 to 14).

A fourth object is to provide a method for manufacturing an optical device having a multilayer structure such as a multilayer reflection mirror including a diamond layer having high thermal conductivity.
5 to 22).

[0012]

According to the present invention, a diamond synthetic thin film having a very high thermal conductivity of about 2,000 W / m · K is used as a structure, so that it is inexpensive and has excellent thermal characteristics or heat dissipation. An element can be provided.

The synthesis of diamond can be performed, for example, on a Si substrate by microwave plasma CVD. Although polycrystalline, a thin film having a thickness of about 0.1 μm can be formed relatively flat. The film forming method will be briefly described.

When diamond is grown on the Si (100) plane, (a) carbonization of the substrate is performed in a CVD apparatus.
Generally, three steps of (b) bias processing and (c) growth are performed. In (a), the substrate is kept at 850 ° C. in an unbiased state, and CH ₄ 1s is used as a reaction gas.
ccm / H ₂ 200sccm, pressure 30Torr
At 400 r, a microwave of 400 W at 2.45 GHz is supplied.
Next, in (b), the microwave is stopped, and a DC bias voltage of -130 V is applied to the substrate for about 8 minutes without changing the substrate temperature, the reaction gas, and the pressure. As a result, a material close to the lattice constant of diamond is formed on the surface. Next, diamond growth is started in (c) under the same conditions as (a) to obtain a film having a desired thickness.

Next, a film of Si or the like is formed on the diamond. The SiH ₄ gas may be used as a reaction gas and deposited by the CVD method in the same manner. However, the substrate temperature is 1200 ° C. When a diamond / Si multilayer film is used as a reflection mirror, films having a thickness of λ / 4 are alternately formed. The number of layers capable of obtaining a sufficient reflectivity (99% or more) is about 10 pairs, and after this film formation, a diamond thick film (about 100 μm) is used as a final layer. (This is determined from the need to satisfy both the requirement of being thin and the requirement of the support not to be cracked or warped), and the Si substrate is removed by wet etching. Then, the first layer of diamond which was in contact with the substrate surface is very flat. A laser wafer or the like is bonded to the flat diamond surface by direct bonding. This can be performed by annealing (heating) in a hydrogen atmosphere under pressure (the heating temperature is lowered in a hydrogen atmosphere). On the other hand, if the non-flat diamond final layer is bonded to a laser mount base (metal, etc.) with solder or the like, a VCSEL equipped with a multilayer reflective mirror and a heat sink having excellent heat conductivity or heat dissipation can be obtained. Can be made.

Means and operation corresponding to the invention of each claim for achieving the above object (for example, 1 corresponds to claim 1) will be described below. 1) The multilayer film structure is characterized by having a diamond layer at least partially including a diamond layer portion formed by heteroepitaxial growth. The first diamond layer must at least partially have an epitaxially grown portion, but subsequent layers may include an amorphous layer. 2) The multilayer structure is characterized in that the diamond layer is used as a first layer, and a thin film of another material and a diamond layer are alternately grown thereon. 3) The thin film of the other material is a Si thin film. 4)
The thin film of another material and the diamond layer are formed by heteroepitaxial growth. 5) The final layer is a sufficiently thick diamond layer. 6) The film thickness of the final diamond layer is about 100 μm. With these configurations, a multilayer structure such as a multilayer reflection mirror having high thermal conductivity can be realized.

7) The above-described method for producing a multilayer film structure requires a single-crystal substrate (a single-crystal substrate in order to make the diamond of the first layer sufficiently flat and at least partially single-crystal or polycrystalline). Materials include Si, GaAs, and Mg.
O, sapphire, etc.), a layer including a diamond layer is formed by heteroepitaxial growth, and thereafter only the substrate is entirely removed by etching. 8) The layer including the diamond layer is formed by a microwave plasma enhanced chemical vapor deposition method. With these manufacturing methods, it is possible to realize a multilayer structure having high thermal conductivity in which the first layer of the multilayer structure such as a multilayer reflection mirror is a flat diamond film without scattering of light.

9) The optical device has the above-mentioned multilayer structure,
It must be provided as at least one end face of an optical device (a filter, an interferometer, etc., in which a multilayer structure is provided on both end faces of a transparent crystal in addition to the VCSEL (the film thickness is appropriately set according to the application)). Features. Since a multilayer film structure having high heat conductivity is provided, an optical device having excellent heat characteristics and heat radiation properties can be realized.

10) The optical device is characterized in that the optical device is configured as a semiconductor laser device by including the multilayer structure formed as a multilayer reflection mirror as at least one end face of a laser resonator. Since a multi-layer reflecting mirror having high thermal conductivity is provided, a semiconductor laser device excellent in thermal characteristics or heat radiation can be realized.

11) The optical device is characterized in that the laser resonator is formed in a direction perpendicular to a semiconductor single crystal substrate obtained by heteroepitaxially growing a laser structure, and functions as a surface emitting laser. A surface emitting laser can be realized by bringing the surface of a laser wafer made of a compound semiconductor into contact with the multilayer reflection mirror.

12) The surface emitting laser according to the present invention is characterized in that the other end face of the laser resonator is a dielectric multilayer mirror formed by alternately forming two types of dielectrics. By performing temperature control using the multilayer film reflection mirror containing diamond as the heat sink side and using a conventional dielectric mirror on the other surface, a surface emitting laser that extracts light from the dielectric mirror side can be realized. By using a conventional dielectric mirror for the reflection end face on the side that does not have a thermal problem, a surface-emitting type laser whose structure and fabrication are simple can be obtained.

13) The optical device is characterized in that a number of the surface emitting lasers are integrated in parallel on the same surface of the multilayer reflection mirror to constitute a surface emitting array semiconductor laser device. An array type surface emitting laser that can oscillate stably can be realized. By attaching an array type surface emitting laser to one multilayer film reflection mirror, a multi-source laser excellent in thermal characteristics can be easily realized at low cost.

14) The optical device is characterized in that the diamond layer, which is the first layer of the multilayer structure, is doped, and current can be directly injected from the diamond layer by an electrode formed on the diamond layer. By omitting a semiconductor layer for electrode contact, such as a surface emitting laser, and reducing light absorption and the like, a low threshold semiconductor laser or the like can be realized. If the first diamond layer having a multilayer structure such as the multilayer reflection mirror is doped by ion implantation or the like and bonded by an appropriate method, current can be injected through the diamond layer.

15) The method of manufacturing an optical device described above is characterized in that a multilayer structure including a diamond layer is heteroepitaxially grown on a single crystal substrate. A semiconductor laser device or the like including diamond having high thermal conductivity as a multilayer film structure such as a multilayer reflection mirror can be realized.

16) In the above-described method for manufacturing an optical device, the single crystal substrate is made of Si, and the multilayer film structure has a diamond thin film and a Si thin film on the substrate surface. (Having good conductivity). 1 of a multilayer structure such as the multilayer reflection mirror
For example, a semiconductor laser having a diamond / Si multilayer film can be realized.

17) The method of manufacturing an optical device described above, wherein a diamond thin film and a Si thin film are alternately heteroepitaxially grown on the (100) plane of the single crystal substrate (which is easily available). .

(18) In the above-mentioned method for fabricating an optical device, the first layer of the multilayer structure is a diamond layer which emerges from a single crystal substrate which is removed by selective etching after epitaxial growth. It is possible to realize a semiconductor laser or the like in which the first layer of a multilayer structure such as a multilayer reflection mirror is a flat diamond film without scattering light. If the substrate is etched after epitaxial growth to expose the first growth layer, diamond, the surface in contact with the substrate is flat, allowing light to enter and exit from the flat surface without light scattering. It can be a multilayer film structure.

19) In the above-described method for manufacturing an optical device, the multilayer structure may be such that a layer containing diamond is formed by a microwave plasma enhanced chemical vapor deposition method, and a sufficiently thick film made of diamond is formed as a final layer. Is formed by etching and removing only the substrate after growing the substrate. 20) The thickness of the final diamond layer is about 100 μm. Diamond and other single crystal materials are alternately grown by a microwave plasma enhanced chemical vapor deposition method, a diamond thick film is formed as a final layer, and the substrate is completely removed to obtain a desired multilayer film structure.

21), 22) In the above-mentioned method for manufacturing an optical device, the first layer of the multilayer structure and the main structure of the optical device (such as a surface emitting laser) are directly subjected to pressure bonding and heat treatment to form crystals. Are joined. The structure can be directly bonded by superposing the flat crystal faces of a surface emitting laser or the like in an appropriate crystal axis direction, and then applying pressure and heat.

[0030]

BEST MODE FOR CARRYING OUT THE INVENTION

First Embodiment In a first embodiment of the present invention, a diamond / Si multilayer film is formed on a Si substrate, and the diamond / Si multilayer film and a laser structure laminated on an InP substrate are bonded by a bonding technique. Then, the structure as shown in FIG. 1 is obtained by performing processing to form a laser structure. FIG. 1A shows the V
FIG. 4 is a cross-sectional view of the CSEL, and FIG. The manufacturing method will be described below.

First, a method of manufacturing a multilayer mirror (FIG. 2) will be described. The diamond layer 2 is grown on the (100) plane of the Si substrate 1 by the microwave CVD apparatus in the three steps described above. Each step is as described above. Next, a Si layer 3 is formed on the diamond layer 2.
Similarly, H ₄ gas may be used as a reaction gas and deposited by a CVD method. However, the substrate temperature is 1200 ° C. In the present embodiment, a diamond layer (refractive index n = 2.4) 135 nm / Si layer (n = 3.
5) Ten pairs are alternately laminated with a thickness of 930 nm, and the uppermost layer is a diamond thick film (about 100 μm) 4. Although the laminated diamond / Si multilayer film did not become completely flat, after the Si substrate 1 was removed by etching, the surface of the first layer of diamond 2 on the substrate side was very flat.

Next, the laser wafer (FIG. 3) is MOCVD
N-InP (100) substrate 20 is formed by nI
nGaAsP (energy band gap wavelength λg =
1.15 μm) 0.3 μm of contact layer 21 and n−I
The nP cladding layer 22 is 1.0 μm, undoped-I
The nGaAsP (λg = 1.3 μm) active layer 23 has a thickness of 0.7
μm, 1.0 μm of p-InP cladding layer 24, p-I
The nGaAsP contact layer 25 is grown to 0.3 μm.

Next, the Si substrate 1 of the multilayer mirror is KOH
Then, the growth surface of the laser wafer, that is, the p-InGaAsP contact layer 25 and the mirror side of the diamond layer 2 (the surface in contact with the Si substrate 1) are joined. This bonding is performed by treating both surfaces with hydrofluoric acid (adding F to the surface to make it difficult to oxidize), and then applying a load and holding at about 600 ° C. for 30 minutes in a hydrogen atmosphere. After the bonding, the InP substrate 20 is removed by etching with HCl.

Thereafter, a cylindrical light emitting region of 15 μmφ is formed, and the active layer is formed by utilizing the fact that the sulfuric acid + hydrogen peroxide based etchant etches only ternary and quaternary mixed crystals and does not attack InP at all. The diameter of only 23 is reduced to 10 μm. On the other hand, the p-InGaAsP cap layer 25 on the junction side
Has a diameter of 30 μm and a polyimide 10 around the light emitting region.
To form a shape having a bridging part b having a width of 7 μm in a cylindrical part a having a diameter of 25 μm (see FIG. 1B). Thereafter, an insulating film 13 is formed at an appropriate place,
The electrodes 11 and 12 on the side are formed as shown in FIG. And
The electrode 12 and the contact layer 21 at the center of the light emitting region are removed, and the Si / SiO ₂ multilayer mirror 14 is formed into a cylindrical shape of 10 μmΦ at the center of the light emitting region by lift-off.
Light is extracted from the mirror 14 side. Reference numeral 15 denotes a laser mount table bonded to the diamond thick film 4.

The VCSEL thus manufactured has a sufficient current confinement structure and heat dissipation, oscillates at a threshold value of about 2 mA at room temperature continuous operation, and has a maximum oscillation temperature of 80 ° C.

Second Embodiment In the first embodiment, a cap layer 25 of InGaAsP is provided on the laser substrate in order to make electrode contact. Since the cap layer 25 slightly absorbs light, the presence of the cap layer 25 causes a resonator loss and raises the threshold value. Therefore, the first layer 2 of the diamond layer 2
FIG. 4 shows a second embodiment in which the InGaAsP cap layer is eliminated by doping p with ion doping or the like into a (a method of adding elements such as Zn and Be during the growth of the first layer 2a). Have been. The final growth layer of the laser wafer is the p-InP layer 24. Since the p-InP layer 24 and the p-diamond layer 2a are joined to establish electrical continuity, a metal is directly deposited on the diamond layer 2a to form the p-electrode 12. In this structure, the threshold value can be further reduced since the resonator loss is reduced. Other points are the same as the first embodiment.

In the above embodiment, an example of one VCSEL has been described. However, arraying in the plane direction, which is a feature of the VCSEL, is also possible. For example, on a multilayer film structure of the present invention having a large area, a large number of laser structures arranged on a substrate are turned upside down and bonded, and the same processing as above can be performed to produce an array type surface emitting laser. . In this case, due to the high thermal conductivity of diamond, there is little thermal effect on adjacent elements when arrayed, and an array VCSEL with stable oscillation characteristics can be realized.

In the above embodiment, InGaAsP / I
Although an example of the 1.3 μm band of nP has been described, by changing the thickness of the multilayer structure such as the multilayer reflection mirror of the present invention, 1.
It can be applied to the 55 μm band and the like. In addition, different crystal systems,
For example, InGaAs / GaAs (0.8 to 1 μm) or AlGaN / InGaN / GaN (0.4 to 0.5 μm)
m) and the like.

[Brief description of the drawings]

FIG. 1 is a sectional view (a) and a plan view (b) of a surface emitting laser device with a diamond multilayer mirror according to the present invention.

FIG. 2 is a sectional view illustrating a diamond multilayer mirror.

FIG. 3 is a cross-sectional view illustrating a structure of a laser wafer.

FIG. 4 is a sectional view of a mirror-equipped surface emitting laser device having a p-type diamond layer according to a second embodiment of the present invention.

FIG. 5 is a sectional view showing a conventional example of a surface emitting laser.

[Explanation of symbols]

REFERENCE SIGNS LIST 1 Si substrate 2 diamond thin film 2 a p-type diamond layer 3 Si thin film 4 diamond thick film 10 polyimide buried layer 11, 12 electrode 13 insulating film 14, 132 Si / SiO ₂ multilayer film mirror 15 laser mount base 20 InP substrate 21, 25 InGaAsP Contact layers 22, 24 InP clad layer 23 InGaAsP active layer 130 Si / Al ₂ O ₃

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁶ Identification code FI G02B 5/08 G02B 5/08 A

Claims (22)

[Claims] 1. A multilayer structure having a diamond layer at least partially including a diamond layer portion formed by heteroepitaxial growth. 2. The multilayer structure according to claim 1, wherein said diamond layer is provided as a first layer, and a thin film of another material and a diamond layer are alternately grown thereon. 3. The multilayer structure according to claim 2, wherein the thin film of the other material is a Si thin film. 4. The multilayer film structure according to claim 2, wherein the thin film of another material and the diamond layer are formed by heteroepitaxial growth. 5. The multilayer structure according to claim 1, wherein the final layer is a sufficiently thick diamond layer. 6. The film thickness of the final diamond layer is 1
6. The multilayer structure according to claim 5, wherein the thickness is about 00 [mu] m. 7. The method for producing a multilayer film structure according to claim 1, wherein a layer including a diamond layer is formed on the single crystal substrate by heteroepitaxial growth, and thereafter, only the substrate is removed. A method for manufacturing a multilayer film structure, characterized in that all are removed by etching. 8. The method according to claim 7, wherein the layer including the diamond layer is formed by a microwave plasma enhanced chemical vapor deposition method. 9. An optical device comprising the multilayer structure according to claim 1 as at least one end face of the optical device. 10. The optical device according to claim 9, wherein said multilayer film structure formed as a multilayer film reflection mirror is provided as at least one end face of a laser resonator to constitute a semiconductor laser device. . 11. The optical device according to claim 10, wherein said laser resonator is formed in a direction perpendicular to a semiconductor single crystal substrate obtained by heteroepitaxially growing a laser structure, and functions as a surface emitting laser. 12. The surface emitting laser according to claim 11, wherein the other end face of the laser resonator is a dielectric multilayer mirror formed by alternately depositing two types of dielectrics. Optical device. 13. A surface-emitting array semiconductor laser device in which a plurality of surface-emitting lasers are integrated in parallel on the same surface of the multilayer structure formed as a multilayer reflection mirror. Claim 11 or 12
An optical device as described. 14. The diamond layer as the first layer of the multilayer structure is doped, and current can be directly injected from the diamond layer by an electrode formed on the diamond layer. The optical device according to any one of the above. 15. The method of manufacturing an optical device according to claim 9, wherein a multilayer structure including a diamond layer is heteroepitaxially grown on a single crystal substrate. Method. 16. The light according to claim 15, wherein said single crystal substrate is Si, and said multilayer film structure is formed by alternately heteroepitaxially growing a diamond thin film and a Si thin film on said substrate surface. Device fabrication method. 17. The method according to claim 16, wherein a diamond thin film and a Si thin film are alternately heteroepitaxially grown on the (100) plane of the single crystal substrate. 18. The light according to claim 15, 16 or 17, wherein the first layer of the multilayer structure is a diamond layer which appears after the single crystal substrate is removed by selective etching after epitaxial growth. Device fabrication method. 19. The multilayer structure according to claim 1, wherein a layer containing diamond is formed by a microwave plasma enhanced chemical vapor deposition method, and a sufficient thickness of diamond is grown as a final layer. The method for manufacturing an optical device according to claim 15, wherein the optical device is formed by removing all by etching. 20. A diamond layer comprising:
20. A thickness of about 00 μm.
A method for producing the optical device described in the above. 21. The crystal according to claim 15, wherein the first layer of the multilayer structure and the main body structure of the optical device are directly bonded to each other by applying pressure and heat. Method for manufacturing an optical device. 22. The first layer of the multilayer film structure formed as a multilayer film reflection mirror and the surface emitting laser which is the main structure of the optical device are directly bonded to each other by pressing and heating. The method for manufacturing an optical device according to claim 21, wherein: