JP2003060300A - Surface emitting laser and array thereof - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a surface emission laser and a surface emission laser array, which are formed on a p-type GaAs substrate and can maintain satisfac tory characteristics and high reliability. SOLUTION: A lower mirror layer 14 having a p-type AlGaAs system DBR structure, an active layer 24 having a GaAs/AlGaAs system MQW structure, and an upper mirror layer 28 having an n-type AlGaAs system DBR structure are formed on a p-type GaAs substrate 12 to constitute a vertical resonator. Furthermore, an n-type GaInAs contact layer 30 having a thickness of 5 to 200 nm and an impurity concentration of not less than 10<19> cm<-3> is formed on the upper mirror layer 28, having the n-type AlGaAs system DBR structure, and a non-alloy system Cr/Au upper electrode 38 is formed on the contact layer 30 to provide an ohmic contact, without forming an alloy layer in the contact boundary in between the contact layer 30 and the electrode 38.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a surface-emission laser device including a surface-emission laser device and a plurality of surface-emission laser devices having a common substrate, and more particularly to a surface-emission laser device and a surface-emission laser device using a p-type GaAs substrate. The present invention relates to a light emitting laser array.

[0002]

2. Description of the Related Art A surface emitting laser element which is a semiconductor laser element which emits laser light in a direction perpendicular to the surface of a semiconductor substrate, and more particularly a vertical cavity surface emitting laser which forms a laser resonator perpendicular to the surface of the semiconductor substrate. Element (Vertical Cavity Su
rface Emitting Laser (VCSEL) makes it easy to form monolithic resonators, especially two-dimensional monolithic resonator formation, and extremely low threshold operation.
Capable of dynamic single wavelength operation, capable of narrow emission circular beam with large emission area, suitable for high density two-dimensional array, especially devices formed on p-type substrate In recent years, great attention has been paid to its excellent characteristics such as good compatibility with LSIs (large-scale integrated circuits).

An example of a conventional vertical cavity surface emitting laser device using a p-type substrate as a semiconductor substrate is shown in FIG.
Will be explained. As shown in FIG. 6, in the conventional vertical cavity surface emitting laser device 50, p-Ga is used.
Two types of p-Al having different Al compositions are formed on the As substrate 52.
DBR (Distributed Bragg Reflec) consisting of GaAs layer
tor) structure (hereinafter referred to as “p-AlGaAs-based DBR structure”) lower mirror layer 54, for example, AlAs layer 5
6 is a side edge thereof a current confinement region 60 surrounded by the AlO _X layer 58, the lower clad layer 62 made of AlGaAs, GaAs well layer and an AlGaAs barrier layer and a plurality pairs stacked and becomes MQW (Multi Quantum Well;
Multiple quantum well) structure (hereinafter referred to as “GaAs / AlGaAs
System MQW structure ") active layer 64, AlGaAs
And a DBR structure (hereinafter, referred to as an “n-AlGaAs layer”) composed of two n-AlGaAs layers having different Al compositions.
An upper mirror layer 68 (referred to as “n-AlGaAs-based DBR structure”) is formed in a lattice-matched order.

The laminated body composed of the upper mirror layer 68, the upper clad layer 66, the active layer 64, the lower clad layer 62, and the current confinement region 60 is processed into a cylindrical mesa structure. In addition, the sidewall of the cylindrical mesa structure and the exposed surface of the lower mirror layer 54 are covered with the SiN _x film 7.
It is covered by 0. Then, the peripheral portion of the cylindrical mesa structure is filled with a polyimide layer 72 via the SiN _x film 70, and the entire surface is substantially flattened.

On the back surface of the p-GaAs substrate 52,
A lower electrode 74 made of AuZn alloy is formed.
An upper electrode 76 made of AuGeNi / Au is formed in an annular shape on the circular upper mirror layer 68 which is the uppermost layer of the cylindrical mesa structure. When forming the upper electrode 76, A
After sequentially forming a uGeNi alloy film and an Au film and patterning them into a predetermined shape, in order to reduce the contact resistance with the underlying upper mirror layer 68, annealing treatment is performed at a predetermined temperature, for example, in a nitrogen atmosphere, An alloy layer is formed at the contact interface between the two. That is, the upper electrode 76 is a so-called alloy-based electrode in which an alloy layer of a semiconductor layer and a metal layer is formed at the contact interface with the upper mirror layer 68.

A region surrounded by the annular upper electrode 76, that is, a circular region where the upper mirror layer 68 is exposed serves as a light output window 78 for outputting laser light to the outside.

[0007]

However, in the above-described conventional vertical cavity surface emitting laser device 50, the upper electrode 76 of the alloy system made of AuGeNi / Au and the upper part of the DBR structure of the n-AlGaAs system are used. Since the alloy layer is formed at the contact interface with the mirror layer 68, the contact resistance can be reduced, but when the surface emitting laser element 50 is energized, the element characteristics are deteriorated and the reliability is lowered. There was a problem that happened. For example 100
Under an energizing condition of 20 ° C. and 20 ° C., the light output sometimes decreased after 1000 hours.

The deterioration of the device characteristics during the energization operation of the surface emitting laser device 50 causes stress due to the formation of an alloy layer at the contact interface between the upper electrode 76 and the upper mirror layer 68. It is considered that this is because the metal atoms of the upper electrode 76 penetrate into the upper mirror layer 68 via the alloy layer at the contact interface. Thus, in the vertical cavity surface emitting laser device formed on the conventional p-GaAs substrate, if an alloy-based electrode is used as the upper electrode provided on the n-AlGaAs upper mirror layer, long-term operation is achieved. There is a problem that element characteristics are sometimes deteriorated.

The present invention has been made in consideration of the above problems, and provides a surface emitting laser element and a surface emitting laser array formed on a p-GaAs substrate, which have good characteristics when energized. An object of the present invention is to provide a surface emitting laser element and a surface emitting laser array capable of maintaining high reliability.

[0010]

The present inventors have found that the conventional p
-It is considered that the deterioration of the device characteristics of the surface emitting laser device formed on the GaAs substrate during the energization operation is caused by the formation of the alloy layer at the contact interface between the upper electrode and the upper mirror layer. By using a non-alloy-based upper electrode in which an alloy layer is not formed at the contact interface with the underlying layer, instead of the upper electrode of, it is possible to solve the above-mentioned problems. embraced.

However, the upper mirror layer of the n-AlGaAs type DBR structure of the surface emitting laser element formed on the p-GaAs substrate (when the contact layer made of n-GaAs is formed on the upper mirror layer). , An upper electrode made of various non-alloy-based substances was formed on the contact layer), and repeated experiments showed that the contact resistance of the non-alloy-based upper electrode with the upper mirror layer or the contact layer was very high. It turned out that it became large and a good ohmic contact could not be obtained.

Therefore, after further studies, it is possible to reduce the contact resistance between the upper electrode and the upper mirror layer and the non-alloy-based upper electrode, and the difference in lattice constant between the upper mirror layer and the upper mirror layer. As a result of conducting experiments on various substances, the inventors have come to find GaInAs by interposing a contact layer made of a substance satisfying the condition that is small. Thus, the following surface emitting laser device and surface emitting laser array according to the present invention were developed.

That is, the surface emitting laser device according to the present invention is
A surface emitting laser device comprising a p-type GaAs substrate, a lower mirror layer, an active layer, and an upper mirror layer, wherein an n-type GaInAs contact layer is formed on the upper mirror layer, and the n-type GaInAs contact layer is formed. A non-alloy-based electrode is formed on the upper surface in ohmic contact (Claim 1).

In the surface emitting laser device according to claim 1,
The non-alloy-based electrode is at least n-type GaInAs
Cr layer, Ti layer, Pt at the part that contacts the contact layer
It is preferable that the electrode has a layer, a Mo layer, or a W layer.
There is (claim 2). In addition, n-type GaInAs contact
The layer has a thickness of 5 nm or more and 200 nm or less.
(Claim 3), and the concentration of the doped impurities is
10¹⁹cm ^-3Above (Claim 4), and the set
Ga is successful_XIn_1-XAs (x> 0.6) (Request
Item 5) is suitable for each.

Further, in the surface emitting laser array according to the present invention, the surface emitting laser element according to any one of claims 1 to 5 is a p-type Ga.
A plurality of As substrates are arranged as a common substrate (claim 6).

[0016]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of the present invention will be described below with reference to the accompanying drawings. 1 is a schematic perspective sectional view showing a surface emitting laser element according to an embodiment of the present invention, and FIG. 2 is an enlarged schematic sectional view showing an upper electrode portion of the surface emitting laser element of FIG. 3 is a graph showing the relationship between the contact resistance and the impurity concentration of the contact layer of the surface emitting laser device of FIGS. 1 and 2, and FIG. 4 is a schematic sectional view showing a modification of the upper electrode part of FIG. FIG. 5 is a schematic perspective view showing a surface emitting laser array in which a plurality of the surface emitting laser elements of FIG. 1 are arranged in a matrix.

According to this embodiment, as shown in FIG.
In the surface emitting laser device 10, the p-GaAs substrate 1 is used.
On top of the p-AlGaAs system DBR structure (for example, p-
Al _0.2Ga_0.8As layer and p-Al_0.9Ga_0.1As layer
35 pairs of p-Al stacked_0.2Ga_0.8As / Al
_0.9Ga_0.1The lower mirror layer 14 of (As-based DBR structure)
Has been formed. Also, on this lower mirror layer 14, an example
For example, the AlAs layer 16 through which the current flows has its side edge portion made of AlA.
Insulating AlO formed by selective oxidation of s layer_XLayer 1
A current confinement region 20 surrounded by 8 is formed in a ring shape.
Has been done. In addition, this AlO_XRing by layer 18
The current confinement region 20 surrounded by a circle is formed in the lower mirror layer 14.
May be formed in.

On the current confinement region 20, a non-contact
Doped AlGaAs (eg Al _0.3Ga_0.7As)
Via a lower clad layer 22 made of GaAs / AlG
aAs-based MQW structure (eg GaAs well layer and Al
_0.2Ga_0.8G formed by stacking a plurality of pairs of As barrier layers
aAs / Al_0.2Ga_0.8As-based MQW structure) active layer
24 are formed.

Further, on the active layer 24, via the upper cladding layer 26 of non-doped AlGaAs (e.g. _{Al 0.3 Ga 0 .7 As),} n-AlGaAs system DB
R structure (for example, n-Al _0.2 Ga _0.8 As layer and n-Al
N-Al in which 25 pairs of _0.9 Ga _0.1 As layers are laminated
DBR structure of _0.2 Ga _0.8 As / Al _0.9 Ga _0.1 As system)
Of the upper mirror layer 28 is formed. An n-GaInAs contact layer 30 is formed on the upper R mirror layer 28. And this n-GaInAs
The contact layer 30 has an impurity concentration of 10 ¹⁹ cm ⁻³ or more doped with an n-type impurity such as Si or Se,
The thickness is preferably 5 to 200 nm.

The various semiconductor layers sequentially stacked on the p-GaAs substrate 12 are n-GaInAs.
Basically all except the contact layer 30, p-GaAs
It is lattice-matched with the substrate 12. However, this p-GaAs
The n-GaInAs contact layer 30 having a lattice constant different from that of the substrate 12 also has, for example, MOC as in the case of other semiconductor layers.
VD (Metal Organic Chemical Vapor Deposition) equipment and MBE (Molecular Beam E)
It can be formed using a normal crystal growth apparatus such as a pitaxy (molecular beam epitaxial growth) apparatus. Therefore, in the same device, it is possible to continuously grow the underlying n-AlGaAs-based DBR structure upper mirror layer 28 and subsequently form the n-GaInAs contact layer 30 thereon.

Further, the laminated body composed of the n-GaInAs contact layer 30, the upper mirror layer 28, the upper cladding layer 26, the active layer 24, the lower cladding layer 22 and the current confinement region 20 is processed into a cylindrical mesa structure. Has been done. The sidewall of the cylindrical mesa structure and the surface of the lower mirror layer 14 around the sidewall are covered with the SiN _x film 32. Further, the peripheral portion of the cylindrical mesa structure is filled with the polyimide layer 34 via the SiN _x film 32, and the entire surface is substantially flattened.

In this way, a vertical resonator composed of the active layer 24 sandwiched between the upper mirror layer 28 and the lower mirror layer 14 is formed on the p-GaAs substrate 12. In addition, AuZn is formed on the back surface of the p-GaAs substrate 12.
A lower electrode 36 made of an alloy is formed. Further, as shown in FIGS. 1 and 2, on the circular n-GaInAs contact layer 30 forming the uppermost layer of the cylindrical mesa structure, for example, a Cr layer 38a having a thickness of 100 nm and an Au layer having a thickness of 300 nm, for example. A Cr / Au upper electrode 38 formed by stacking layers 38b in order from the bottom is formed in an annular ohmic contact. That is, DB of n-AlGaAs system
The present embodiment is characterized in that the Cr / Au upper electrode 38 is formed on the upper mirror layer 28 of the R structure in ohmic contact with the n-GaInAs contact layer 30 interposed therebetween. An alloy layer is not formed at the contact interface between the Cr layer 38a of the Cr / Au upper electrode 38 and the n-GaInAs contact layer 30. That is, the Cr / Au upper electrode 38 is a non-alloy-based electrode for the n-GaInAs contact layer 30.

The n-GaInAs contact layer 30 is also used.
The outer extension of the upper annular Cr / Au upper electrode 38 reaches up to the polyimide layer 34. Then, a region surrounded by the annular Cr / Au upper electrode 38, that is, n-Ga
The circular region where the InAs contact layer 30 is exposed serves as a light output window 40 that emits laser light to the outside.

In the surface emitting laser device 10 according to the above embodiment, the reason why the impurity concentration of the n-GaInAs contact layer 30 is set to 10 ¹⁹ cm ^-3 or more is Cr.
This is because it is preferable that the impurity concentration is 10 ¹⁹ cm ⁻³ or more in order to sufficiently improve the ohmic connection with the / Au upper electrode 38. For example, the impurity concentration of the n-GaInAs contact layer 30 and the Cr / Au upper electrode 38
As is clear from the graph of FIG. 3 showing the relationship with the contact resistance of Cr / Au, by setting the impurity concentration of the n-GaInAs contact layer 30 to 10 ¹⁹ cm ⁻³ or more.
The contact resistance with the upper electrode 38 can be lowered to a level of 10 ⁻⁶ Ω · cm ² or less, which is not a problem in practical use.

The reason why the thickness of the n-GaInAs contact layer 30 is set to 5 to 200 nm is Cr /
This is to ensure good ohmic contact with the Au upper electrode 38 and to suppress the compressive strain that the upper mirror layer 28 of the underlying n-AlGaAs DBR structure having a different lattice constant has. That is, when the thickness of the n-GaInAs contact layer 30 becomes less than 5 nm, the n-GaInAs contact layer 30 is interposed between the Cr / Au upper electrode 38 and the upper mirror layer 28 of the n-AlGaAs-based DBR structure. However, the function of achieving good ohmic contact with the Cr / Au upper electrode 38 may not be fully exhibited. On the other hand, when the thickness of the n-GaInAs contact layer 30 exceeds 200 nm, the underlying n-Al
The strain generated between the GaAs-based DBR structure and the upper mirror layer 28 becomes so large that it cannot be ignored, and for example, there is a risk that dislocations, which cause characteristic deterioration, may occur.

Further, the n-GaInAs contact layer 30 serves as an absorber for light in the 850 nm band, but if the thickness is within the above range of 10 to 200 nm, it is sufficiently large light for practical use. Output is obtained. However, in actuality, in order to match the phase with the oscillating laser light, n-Ga
It is necessary to set the thickness of the InAs contact layer 30 to xλ / 4n (where x is an odd number, λ is an oscillation wavelength, and n is a refractive index). According to the trial experiments of the present inventors, it was confirmed that in the surface-emission laser device 10 having the above-described structure, an optical output of 5 mW can be easily obtained although it varies depending on the reflectance of the n-upper mirror layer 28. .

However, the surface emitting laser element 10 has a long wavelength band 1200 to 1600 nm (1.2 to 1.6 μm) as compared with the case where the oscillation wavelength is in the short wavelength band 850 nm and 980 nm.
In the case of m), the light output is small. Therefore, in the case of oscillating laser light in a long wavelength band, n-GaIn
It is preferable to further limit the thickness of the As contact layer 30 to 100 nm or less. As a result, it is possible to suppress the deterioration of the optical output when the oscillation wavelength is in the long wavelength band.

If the wavelength of the laser light output from the surface emitting laser element 10 is 1.3 μm or more, n
The composition of -GaInAs contact layer 30 Ga _X In _1-X
It is preferable to set As (x> 0.6). This is because in the case of this composition, the n-GaInAs contact layer 30 becomes transparent to light having a wavelength of 1.3 μm or more, and the loss of emitted light can be suppressed.

Further, the lower mirror layer 14 of the DBR structure of p-AlGaAs system, the MQW of GaAs / AlGaAs system.
A vertical resonator composed of an active layer 24 having a structure and an upper mirror layer 28 having an n-AlGaAs-based DBR structure is a p-Ga.
The case where the vertical cavity is formed on the As substrate 12 has been described, but the vertical cavity may have any structure as long as it is a surface emitting laser element formed on the p-GaAs substrate. The present invention can be applied to surface-emitting laser elements of any resonator structure that oscillates laser light in the wavelength band of 1600 nm.

Further, instead of the Cr / Au upper electrode 38 as the non-alloy-based electrode, for example, as shown in FIG.
For example, a Ti layer 42a having a thickness of 100 nm, for example, a thickness of 20
0 nm Pt layer 42b and, for example, 300 nm thick A
Ti / Pt / A in which u layers 42c are stacked in order from the bottom
The u upper electrode 42 may be formed. In this case, Ti /
Pt / Au upper electrode 42 Ti layer 42a and n-GaIn
While a good ohmic connection with the As contact layer 30 can be obtained, a non-alloy-based electrode in which an alloy layer is not formed at the contact interface thereof has the same effect as the Cr / Au upper electrode 38.

Further, the upper electrode of the surface emitting laser element 10 is not limited to the multilayer structure in which a plurality of metal layers such as the Cr / Au upper electrode 38 and the Ti / Pt / Au upper electrode 42 are laminated, and for example, other The electrode may have a multi-layer structure with the metal layer. Next, a surface emitting laser array in which a plurality of surface emitting laser elements 10 of FIG. 1 are arranged will be described with reference to FIG.

The surface emitting laser array 44 according to the present embodiment.
Is an application of the surface-emission laser device 10 of FIG. 1 to a laser array. As shown in FIG.
The substrate 12 is used as a common substrate, and the surface-emission laser device 10 of FIG. 1 is arranged thereon in a 3 × 3 matrix.
Further, the nine surface emitting laser elements 10 arranged two-dimensionally are insulated and separated from each other by the polyimide layer 34. Instead of using the polyimide layer 34, the two-dimensionally arranged surface emitting laser elements 10 may be insulated and separated by a mesa post structure.

In the surface-emission laser array 44 thus two-dimensionally integrated in parallel, the surface-emission laser device 10 has a high density.
It can be easily manufactured by taking advantage of the characteristic that it is suitable for forming a three-dimensional array. In the surface-emission laser array 44 according to the above-described embodiment, the case where the surface-emission laser devices 10 are arranged in a 3 × 3 matrix is illustrated, but the number of the matrix, the arrangement pattern, and the like are variously modified. It goes without saying that is possible. Further, it is not limited to a two-dimensional array, and it is possible to form a one-dimensional array in which a plurality of surface emitting laser elements 10 are linearly arranged. Further, the driving method of each surface emitting laser element 10 may be any of an independent driving type, a matrix driving type and a simultaneous driving type.

[0034]

As is apparent from the above description, according to the surface emitting laser element and the surface emitting laser array of the present invention, the following effects can be obtained. That is, according to the surface emitting laser element of claim 1 or 2, the n-type GaInAs contact layer provided on the n-type upper mirror layer and the non-alloy-based electrode, for example, a portion of the n-type GaInAs contact layer that is in contact with Cr is Cr. A non-alloy-based electrode having a layer, a Ti layer, a Pt layer, a Mo layer, or a W layer is in ohmic contact without forming an alloy layer at its contact interface, so that the alloy layer is formed at the contact interface. Stress may occur,
It is possible to prevent metal atoms of the electrode from penetrating into the upper mirror layer through this metal layer, and prevent deterioration of characteristics during long-term operation. In other words, good ohmic contact characteristics of the upper electrode as well as good element characteristics and high reliability during operation of the surface emitting laser element can be realized.

Further, according to the surface emitting laser element of the present invention, the impurity concentration of the n-type GaInAs contact layer is 10 ¹⁹ cm ⁻³ or more, so that a good ohmic contact with the non-alloy-based electrode is obtained. The contact characteristics can be secured. According to the surface emitting laser device of the fourth aspect, the thickness of the n-type GaInAs contact layer is 5 nm.
Since the thickness is 200 nm or less, good ohmic contact with the non-alloy-based electrode can be secured, and compressive strain possessed by the n-type upper mirror layer can be suppressed to maintain good light output characteristics. You can In addition, n-type GaI
Even for light in the 850 nm band in which the nAs contact layer serves as an absorber, a sufficiently large light output can be obtained in practical use.

Further, according to the surface emitting laser element of the fifth aspect, since the composition thereof is Ga _X In _{1 -X} As (x> 0.6), it is transparent to light having a wavelength of 1.3 μm or more. Therefore, it is possible to prevent a decrease in light output. According to the surface emitting laser array of claim 6, the surface emitting laser array according to claim 1 is provided.
Since a plurality of surface-emission laser devices according to 5 are arranged, good characteristics and high reliability can be realized during operation of the surface-emission laser array. Therefore, when this surface-emitting laser array is optically coupled to an optical fiber array and used in the fields of parallel optical information processing, optical interconnection, etc., it is possible to contribute to the realization of its excellent characteristics and high reliability.

[Brief description of drawings]

FIG. 1 is a schematic perspective sectional view showing a surface emitting laser element according to an embodiment of the present invention.

2 is a schematic cross-sectional view showing an enlarged upper electrode portion of the surface-emission laser device of FIG.

FIG. 3 is a graph showing the relationship between the impurity concentration of the contact layer and the contact resistance of the surface-emission laser device of FIGS. 1 and 2.

FIG. 4 is a schematic cross-sectional view showing a modified example of the upper electrode portion of FIG.

5 is a schematic view showing a surface emitting laser array in which the surface emitting laser elements of FIG. 1 are two-dimensionally arranged.

FIG. 6 is a schematic perspective sectional view showing a conventional surface emitting laser element.

[Explanation of symbols]

10 surface emitting laser element 12 p-GaAs substrate 14 lower mirror layer 16 AlAs layer 18 AlO _X layer 20 current confinement region 22 lower cladding layer 24 active layer 26 upper cladding layer 28 upper mirror layer 30 n-GaInAs contact layer 32 SiN _X film 34 polyimide layer 36 lower electrode 38a Cr layer 38b Au layer 38 Cr / Au upper electrode 40 light output window 42a Ti layer 42b Pt layer 42c Au layer 42 Ti / Pt / Au upper electrode 44 surface emitting laser array

   ─────────────────────────────────────────────────── ─── Continued front page    (72) Inventor Noriyuki Yokouchi             2-6-1, Marunouchi, Chiyoda-ku, Tokyo             Kawa Electric Industry Co., Ltd. F-term (reference) 5F073 AA74 AB02 AB17 CA04 CB02                       CB22 DA05 EA28

Claims (6)

[Claims] 1. A surface emitting laser device comprising a p-type GaAs substrate, a p-type lower mirror layer, an active layer, and an n-type upper mirror layer stacked on each other, wherein n is formed on the n-type upper mirror layer. A surface emitting laser element, wherein a GaInAs contact layer is formed, and a non-alloy-based electrode is formed in ohmic contact on the n-type GaInAs contact layer. 2. The non-alloy-based electrode is at least the n-type.
A Cr layer at a portion in contact with the GaInAs contact layer,
The surface emitting laser element according to claim 1, which is an electrode having a Ti layer, a Pt layer, a Mo layer, or a W layer. 3. The surface emitting laser element according to claim 1, wherein the impurity concentration of the n-type GaInAs contact layer is 10 ¹⁹ cm ⁻³ or more. 4. The surface emitting laser element according to claim 1, wherein the n-type GaInAs contact layer has a thickness of 5 nm or more and 200 nm or less. 5. The surface emitting laser element according to claim 1, wherein the composition of the n-type GaInAs contact layer is Ga _X In _{1 -X} As (x> 0.6). 6. A surface emitting laser array comprising a plurality of the surface emitting laser elements according to claim 1, wherein the p-type GaAs substrate is a common substrate.