JPH07312460A - Optical semiconductor device - Google Patents

Abstract

(57) [Abstract] [Purpose] An optical semiconductor device having an optical film on the end face, which has a low reflectance for both TE and TM waves and has a high performance of protecting the end face. [Structure] An optical semiconductor device 1 having an end face provided with an optical film.
The optical film is composed of a combination of two layers of dielectric thin films 2 and 3, and the first thin film 2 on the end face side is composed of at least one material selected from AlN and Si ₃ N ₄ and a material of SiN _x . A second thin film 3 formed of a film and formed on the first thin film 2.
Is made of a material of SiO ₂ . The composition concentration of at least one material selected from AlN and Si ₃ N ₄ is large on the element end face side, gradually decreases in the film thickness direction, and S
The composition concentration of iN _x is small on the end face side and gradually increases in the film thickness direction.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a high bandwidth semiconductor optical amplifier or the like for directly amplifying an optical signal used in an optical communication system or the like, which has an end face having a protective performance and an antireflection coating optical film. The present invention relates to an optical semiconductor device having

[0002]

2. Description of the Related Art Conventionally, as shown in FIG. 7, a semiconductor optical amplifier has an upper and lower cladding layers 105 formed on a substrate 100.
A semiconductor laser structure 101 including an active layer 102 sandwiched by 106 is provided, and anti-reflection (AR) coatings 103a and 103b are applied to the cleaved end face of the semiconductor laser structure 101 to provide a high internal gain by injection of a current 104. It has a structure that suppresses laser oscillation.

The quality of the AR coating determines the performance of the semiconductor optical amplifier, and it is necessary to keep the reflectance of the AR coating low in order to suppress the gain increase / decrease (gain ripple) with respect to the input wavelength spectrum. The condition of the single pass gain G and the reflectance R of the AR coating when the gain ripple is 2 dB is given by G · R ≦ 0.1. For example, when the gain is 20 dB, the reflectance is R ≦ 0.1%.

An optical amplifier which reduces the reflectance R and eliminates the gain ripple for the wavelength spectrum is useful for optical amplification of a multi-wavelength multiplexed signal and is called a traveling wave type optical amplifier.

As a means for forming the AR coatings 103a and 103b, a desired refractive index n'on the cleaved end face is usually used.
Is deposited with a thickness of λ / 4n ′ (λ is a light wavelength). The desired refractive index here differs depending on the semiconductor material used and the waveguide structure, but InP / InGaAsP
In a laser of the system, the value of the optimum refractive index is approximately n '.
≈1.81.

By the way, a semiconductor optical amplifier generally has two polarization states of a TE wave and a TM wave, and the gains thereof are different from each other. Single mode optical fibers are usually used for input and output of these semiconductor optical amplifiers.
The polarization state of transmitted light changes with time due to changes in stress due to pressure, temperature, vibration, etc. on the optical fiber. Therefore, the gain of the semiconductor optical amplifier receiving the output light from the optical fiber becomes unstable. Therefore, as a countermeasure, it is necessary to reduce the end face reflectance of the semiconductor optical amplifier for both TE waves and TM waves.

However, when a single layer film is used as the antireflection film, TE has an optimum refractive index (1.81).
A reflectance of about 0.01% can be expected for both waves and TM waves, but even if the refractive index fluctuates only 0.1, the ratio of the respective reflectances of TE wave and TM wave expands to 100 times or more. , It becomes difficult to control the refractive index on the film formation.

Therefore, an antireflection film having a film structure of two or more layers in which a material having a high refractive index and a material having a low refractive index are relatively wide tolerant to fluctuations in the refractive index can be considered.
In the case of the above example, the high refractive index material has a refractive index of 2.20 to 2.
65, low refractive index material achieves low refractive index (0.1% or less) for both TE and TM waves in combination with each refractive index in the range of 1.25 to 1.48 and its film thickness. It becomes possible to do. The specific materials are:
TiO ₂ , CeO ₂ , ZnS, etc. are known as high refractive index materials, and MgF ₂ , CaF ₂ , LiF, etc. are known as low refractive index materials.

[0009]

However, in terms of not only the antireflection effect but also the high performance of protecting the end face of the semiconductor laser structure from oxygen and moisture from the ambient atmosphere, the above material group is not always sufficient. It can not be said. For example, when the first thin film in contact with the end face of the semiconductor laser structure is an oxide such as TiO ₂ or CeO ₂ , free oxygen has an effect on the end face, and when the second thin film is a fluoride, it has hygroscopicity. The problem arises.

Therefore, in the present invention, the optical film laminated on the end face of an optical semiconductor element such as a semiconductor optical amplifier is a TE film.
Wave and TM wave both have a low reflectance of 0.1% or less, and are an antireflection film having a two-layer film structure with a large allowable variation in the refractive index on the film formation, and an optical semiconductor element from an ambient atmosphere. It also solves the problem of requiring high durability as a film for protecting the end face.

Therefore, an object of the present invention is to provide an optical semiconductor device having an optical film on the end face, which solves the above problems.

[0012]

According to the present invention, in an optical semiconductor device such as a semiconductor optical amplifier having an end face provided with an optical film (such as an antireflection film), the optical film is composed of a combination of two dielectric thin films. And the first thin film on the end face side of the element is A
1N and at least one material selected from Si ₃ N ₄ and S
It consists film of material iN _x, the composition concentration of at least one material the AlN, selected from Si ₃ N ₄ has a larger device end face side, gradually composition concentration in the thickness direction decreases, and SiN _x The composition concentration of is a film of a gradient composition in which the element end face side is small and the composition concentration gradually increases in the film thickness direction,
The second thin film is characterized by being made of a material of SiO ₂ .

Further, the average refractive index n of the gradient composition film of the first thin film is preferably in the range of 2.50≤n≤2.65.

[0014]

Example 1 First, FIG. 1 is a perspective view showing an example of a semiconductor optical amplifier using the optical film material of the present invention. A ridge type laser 1 is used as a semiconductor laser structure as a basic structure, and a cleavage plane is composed of two layers of optical film materials 2 and 3 including a gradient composition film 2. Next, the structure and manufacturing method of the semiconductor laser device will be described.

In FIG. 2, reference numeral 21 is an n-type InP substrate, 2
2 is an n-type InP buffer layer, 23 is an InGaAsP active layer having a composition of 1.55 μm, 24 is a p-type InP clad layer,
Reference numeral 25 is a p-type InGaAsP cap layer. These epitaxial films are deposited and formed by a metal organic thermal decomposition (MO-CVD) method or the like. Then, after patterning the ridge portion by photolithography, a width of 2 to 3 μm is formed by a reactive ion beam etching (RIBE) method.
and a ridge portion having a depth of 0.3 to 0.4 μm up to the active layer 23. Further, after depositing the Si ₃ N ₄ film 26, a window is opened to allow current injection from the cap portion 25, and electrodes 27 and 28 are formed on the upper and lower surfaces. The laser wafer that has undergone the above process is cleaved into a bar shape or a chip shape, and the cleaved end face is subjected to coating treatment with the above optical film material configuration.

FIG. 3 shows the layer structure of the coating.
2 and 3 are two layers of light including the gradient composition film 2 of this embodiment.
It is an academic film. The first thin film 2 on the end face side of the semiconductor laser is inclined
It is a composition film. AlN, Si constituting the gradient composition film 2₃
N_FourThe compositional concentration of at least one material selected from
The surface side is large, and the composition concentration gradually decreases in the film thickness direction.
It In addition, Si which similarly constitutes the gradient composition film 2 N_xMaterial of
The composition concentration of the material is small on the end surface side of the optical semiconductor element and
The composition concentration is gradually increasing.

Material composition and structure of the gradient composition film 2 of this embodiment
Has the following features. (1) Si₃N_FourAnd AlN are non-oxide and are dense
Since it becomes a film, it is half the amount of oxygen and moisture from the environmental atmosphere.
Conductor laser structure has a high ability to protect the end face and therefore the end
Si closer to the surface₃N_FourIt is more reliable to stack with AlN or AlN
Reliability increases. (2) Si N_xIs the stoichiometrically indeterminate composition ratio
However, compositionally stable Si₃N_FourContain more Si
Thereby, the refractive index can be increased. (3) The gradient composition film 2 is a semiconductor laser structure element as described later.
It can be easily laminated by a mechanism such as rotation or movement of the child.

After the gradient composition film 2, a second thin film 3 is laminated. The second thin film 3 is SiO ₂ and is a material that is not hygroscopic and is chemically stable in the low refractive index material group.

Then, the first thin film 2 and the second thin film 3
The first thin film 2 which is a gradient composition film in the combination of
By forming the film so that the average refractive index n of 2.50 ≦ n ≦ 2.65 is satisfied, both the TE wave and TM wave end face reflectances can be made 0.1% or less. The protection performance of the end face of the semiconductor laser structure can also be secured.

Film formation of each material on the end face of the semiconductor laser device
Is a normal vacuum film forming method such as sputtering method or electron beam evaporation method.
The law is applicable. Si N_xThe film is Si₃N_FourTarget of
Place a plurality of Si micro chips on top of the
Si on top₃N_FourPlace multiple micro chips of
Ar gas or Ar + N as tagus _TwoOf mixed gas
Method of controlling composition by the used sputtering method, granular Si and S
i₃N_FourComposition control by electron beam evaporation using a mixture of
Can be obtained.

The AlN film uses AlN as a target.
Ar gas or Ar + N as sputtering gas _TwoA mixture of
Sputtering method using gas, etc., or using AlN as an evaporation source
The film can be formed by a child beam vapor deposition method or the like.

The Si ₃ N ₄ film is formed by sputtering using Si ₃ N ₄ as a target and using Ar gas or a mixed gas of Ar + N ₂ as a sputtering gas, and electron beam evaporation using Si ₃ N ₄ as an evaporation source. You can make a film with.

The mixed film of AlN and _Si 3 _{N 4} is the simultaneous sputtering and using each target of the advance, a method using a target formed by sintering AlN and _Si 3 _{N 4,} AlN target certain sputtering and that composition control in composite target carrying the _Si 3 _{N 4} respectively _Si 3 _{N 4} tip or AlN chip on the target, Al
The film can be formed by an electron beam evaporation method or the like using a mixture of N and Si ₃ N ₄ as an evaporation source.

Next, a method of forming the gradient composition film 2 will be described. FIG. 4 is a diagram schematically showing a film forming method of the gradient composition film 2 and a film forming apparatus using the sputtering method as an example. 61 is Al
A target made of at least one material selected from N and Si ₃ N ₄ , and 62 is a Si ₃ N ₄ target with Si
, A composite target on which a microchip is mounted, 63 is a semiconductor element in which an antireflection film including the gradient composition film 2 is laminated on the end face, 6
Reference numeral 4 is a holder substrate for the semiconductor element 63, 65 is a moving direction of the semiconductor element 63, and 66 is a partition plate.

Multiple targets can be sputtered simultaneously
The optical semiconductor element 63 is transferred using a multi-source simultaneous sputtering device.
Is it closer to the target 61 in a movable or rotatable state?
Then, the film is formed by moving in the direction indicated by arrow 65. The film formation is
The material composition of the target 61 gradually decreases as it moves.
The material of the target 62 (Si N_x) The composition gradually increases
Add

The composition and refractive index of each material of the gradient composition film 2 are determined by the electric power applied to each target 61, 62, the occupied area ratio of each material on the composite target, the sputtering gas pressure, the sputtering gas species, and the substrate-to-substrate ratio. The composition and film forming speed of each material determined by the distance, the moving speed of the optical semiconductor element 63, the partition plate 6
The height can be controlled by the height of 6, the arrangement of the targets 61 and 62, and the like. Then, the average refractive index n of the gradient composition film 2 may be measured in advance, and the film forming conditions may be set so that n is in the range of 2.50 ≦ n ≦ 2.65. In this way, after forming the gradient composition film 2 having a desired refractive index,
Subsequently, the SiO ₂ film 3 is laminated.

The film forming method by the electron beam evaporation method is
Multiple simultaneous instead of the targets 61 and 62 in FIG.
Simply replace the electron beam evaporation source of
The film may be formed in the same manner as the Ta method. For example, 61 is granular
AlN, Si_ThreeN_FourAt least one material selected from
Material, 62 is granular Si and Si_ThreeN_FourWith a mixture of
It At this time, the composition and the refractive index of the gradient composition film 2 are
Evaporation source (AlN, Si_ThreeN_FourAt least 1 selected from
Seed material and Si N_xIrradiate the composition ratio of materials) and each evaporation source
Of each material determined by the amount of electron beam and the distance between substrates
Growth and film formation speed, optical semiconductor element 63 moving speed, partition plate
It can be controlled by the height of 66, the arrangement of each evaporation source, and the like.

Thus, the end surface of the semiconductor laser has a high refractive index.
Gradient composition film 2 (AlN, Si_ThreeN_FourLess selected from
Both materials and Si N_xAnd gradient composition film) and low refractive index
SiO₂The semiconductor optical amplifier in which the two-layer film of the film 3 is formed is
Both TE and TM waves are reflected by measuring the gain ripple
A rate of 0.1% or less can be realized. As shown in Figure 1,
The body optical amplifier is in a constant current injection state that is slightly smaller than the threshold current.
And a light wave from the outside with a lens or an optical fiber.
4 is input and coupled to the semiconductor optical amplifier.
Therefore, the amplified light wave 5 can be obtained. In this way,
A partial gain of 20 to 30 dB is achieved.

[0029]

Second Embodiment FIG. 5 is a system conceptual diagram when the device of the above example is applied to a wavelength division multiplexing transmission / reception system. In the figure, 10 is the above optical amplifier, 11 is a transmitter, and 1
2 is a receiver, 13 and 14 are multiplexers / demultiplexers, and 15
Is a transmission optical fiber. With such a configuration, for example, signals having wavelengths of 1550 nm and 1540 nm are multiplexed and amplified by the optical amplifier 10 with high gain and low ripple, and
It is possible to exchange signals without crosstalk at a transmission rate of 00 Mbps or higher.

As described above, a high-bandwidth semiconductor optical amplifier for directly amplifying an optical signal used in an optical communication system or the like can be obtained. The gradient composition of the protective film / antireflection film on the input / output end face thereof is obtained. As an example, a two-layer film including the film 2 is used.
The details are described below.

[0031]

[Example 1-3] In the high frequency sputtering apparatus capable of performing two-way simultaneous sputtering as shown in FIG.
25 mmφ AlN, target 62 is the same size Si
A composite target in which 20 to 50 10 mm square Si pieces were placed on ₃ N ₄ was used. Ultimate vacuum is 5 × 10 ^-6
The sputtering power was 200 W to 1 kW, the sputtering gas pressure was 1 to 10 × 10 ⁻³ torr, and the sputtering gas species was Ar.

A substrate holder for the semiconductor laser device 63
One that is installed on the board 64 and the board holder 64 is indicated by the arrow 65
While slowly rotating in the same direction, AlN and Si N_xThe slope of
The composition film 2 was laminated on both end faces of the semiconductor laser.

At this time, the AlN target 61 and Si_Three
N_Four-Supplying power P to the Si composite target 62
5 kinds of gradient composition films including Comparative Example 2 by changing
Were laminated. XPS (soft X-ray photoelectron spectroscopy) was applied to each gradient composition film.
Method) in the film thickness direction. Measuring track of measured elements
The road is Si_2p, Al_2pIs. The measurement result of Example 1
The axis is the distance from the laser end face, and the vertical axis is the chemical bond state.
All Al considering the chemical shifts that occur_2p, S
i_2pConverted from AlN and Si N_xFrom the amount of AlN
The composition ratio is shown in FIG.

As a result, the end surface side of the semiconductor laser is AlN
Has a high composition concentration and gradually decreases in the film thickness direction (S
i N_xIt can be seen that the compositional concentration of is the reverse tendency). In addition, comparison
In Example 3, the semiconductor laser device is mounted on the partition plate 66.
Install it in one position and do not rotate the substrate holder 64
Laminated with AlN and Si N_xThe mixed film of was laminated. this
The results of analysis of the mixed film in the film thickness direction by XPS
The dotted line in FIG. This result shows that the composition of both is
It showed a nearly constant value.

Next, the semiconductor laser device having the gradient composition film and the mixed film laminated on both end faces is transferred to another sputtering apparatus having a 125 mmφ SiO ₂ target installed, and the gradient composition film and the mixed film are successively placed. SiO ₂ films were laminated on both end faces.

With respect to the semiconductor laser device having the two-layer film laminated on both end faces, the reflectances R _TE and R _TM of TE waves and TM waves were measured. The durability performance was evaluated by the change of the injection current value into the semiconductor laser when the output of the semiconductor laser was set to 30 mW and the semiconductor laser was allowed to stand in an environment of 80 ° C. for 6000 hours. When the injection current value has dropped to almost 0 and when the injection current value is more than twice the initial value, it is considered as an element failure. , △
Mark: The number of failures was expressed as more than 5% of all products.

As described above, the first layer of the gradient composition film 2 laminated on the end face of the semiconductor laser device, the average refractive index n of the mixed film,
Thickness d _1, and the thickness d ₂ of the second layer of SiO ₂ film 3, shown in Table 1 combined reflectivity R, the durability test results.

[0038]

[Table 1] As a result, when the refractive index of the gradient composition film of the first layer is high, the Si content is relatively high, and the durability performance tends to be inferior to the others. On the other hand, when the refractive index is low, the reflectance is not so low and the antireflection effect is small. Further, in the case of the mixed film, the end face of the laser is in contact with the layer containing Si, so that the durability performance is slightly inferior.

Therefore, the first layer has an average refractive index of 2.50.
~ 2.65 AlN and Si N_xGradient composition film, second layer and
Then SiO₂A semi-conductor in which a two-layer antireflection film composed of
A semiconductor optical amplifier having a body laser has an end face reflectance of T
Both E wave and TM wave can achieve less than 0.1% and is durable
It was found that the performance was also good.

[0040]

[Example 4-6] AlN targets in Examples 1 to 3
Instead of Si_ThreeN_FourSimilar except using target
In the procedure, Si_ThreeN_FourAnd Si N_xLaminated gradient composition film 2
Then SiO₂Results for a two-layer membrane with membrane 3 subsequently laminated
Are shown in Table 2 as Examples 4-6. Comparative Example 4 is a comparative example.
In the same manner as 3_ThreeN_FourAnd Si N_xThe mixed film of the first
Layer, then SiO₂Results for a two-layer film in which the films are subsequently laminated
Are also shown in Table 2.

[0041]

[Table 2]As a result, the average refractive index of the first layer is 2.50 to 2.6.
5 Si_ThreeN_FourAnd Si N_xGradient composition film of_Three
N_FourThe composition concentration of is large on the semiconductor laser end face side,
The composition concentration gradually decreases, and N_xThe composition concentration of
The surface side is small and the composition concentration gradually increases in the film thickness direction.
SiO 2 as the second layer in the film₂2-layer film with laminated anti-reflection
The film has a semiconductor laser end face reflectance for both TE wave and TM wave.
In addition, 0.1% or less can be achieved, and the durability performance is good.
I found out that

[0042]

[Example 7-9] Si in Examples 4 to 6_ThreeN_FourTarget
Composite target with AlN target chip attached on top
The same procedure was used except that the get was used._ThreeN_Four-Al
N (result of analysis, composition ratio 52:48) and Si N_xThe slope of
Composition film 2 is laminated, then SiO₂Membrane 3 was subsequently laminated
The results of the two-layer film are shown in Table 3 as Examples 7-9.

[0043]

[Table 3]As a result, the average refractive index of the first layer is 2.50 to 2.6.
5 Si_ThreeN_FourAnd a mixture of AlN and Si N_xInclined set
Film formation (Si_ThreeN_FourThe composition concentration of the mixture of AlN and AlN is semiconductor
The end face of the body laser is large, and the composition concentration gradually increases in the film thickness direction.
Decreased, Si N_xThe composition concentration of is smaller on the end face side and in the film thickness direction
Film whose composition concentration gradually increases), and S as the second layer
iO₂Is a two-layer anti-reflection film with
Surface reflectance of less than 0.1% for both TE and TM waves
It was found that it was possible and the durability performance was also good.

[0044]

As described above, according to the present invention,
At the end face of an optical semiconductor element such as a semiconductor optical amplifier having a semiconductor laser structure, the first thin film on the end face side is made of AlN or Si.
_It is composed of a film of at least one material selected from ₃ N ₄ and a material of SiN _x , and the composition concentration of the at least one material selected from AlN and Si ₃ N ₄ is large on the end face side of the semiconductor laser structure. The composition concentration gradually decreases in the film thickness direction,
Further, the composition concentration of SiN _x is a gradient composition film in which the element end face side is small and the composition concentration gradually increases in the film thickness direction, and the second thin film formed on the first thin film is made of a SiO ₂ material. By laminating two layers of optical film materials consisting of
The TE and TM waves can be made to have a low reflectance without being influenced by the polarization state of the transmitted light, and the film has a high performance of protecting the end face of the element.

[Brief description of drawings]

FIG. 1 is a perspective view of a semiconductor optical amplifier using an optical film material of the present invention.

FIG. 2 is a sectional view of a semiconductor laser device using the optical film material of the present invention.

FIG. 3 is a longitudinal sectional view of a semiconductor laser device using the optical film material of the present invention.

FIG. 4 is a simplified diagram of a film forming apparatus for laminating the optical film material of the present invention.

FIG. 5 is a block diagram of an example of performing wavelength division multiplexing transmission by an optical communication system.

FIG. 6 is a view showing an example of composition distribution of a graded composition film of the present invention measured by XSP.

FIG. 7 is a diagram showing a conventional example.

[Explanation of symbols]

 1, 10 Ridge-type semiconductor optical amplifier 2 Gradient composition film of the first layer 3 Film of the second layer 4 Input light 5 Amplified light wave 11 Transmitter 12 Receiver 13 Combiner 14 Demultiplexer 15 Transmission optical fiber 21 Substrate 22, 24 Clad layer 23 Active layer 25 Cap layer 26 Insulating layer 27, 28 Electrode 61, 62 Target 63 Semiconductor element 64 Holder substrate 65 Moving direction of semiconductor element 66 Partition plate

Claims (2)

[Claims] 1. In an optical semiconductor device having an optical film on its end face, the optical film is composed of a combination of two dielectric thin films, and the first thin film on the end face side of the device is AlN, Si ₃ N ₄
Consists film of at least one material and SiN _x material selected from, the composition concentration of at least one material selected the AlN, the Si ₃ N ₄ has a larger device end face side, and gradually in the thickness direction The composition concentration is decreased, and the composition concentration of SiN _x is a film of a graded composition in which the element end face side is small and the composition concentration is gradually increased in the film thickness direction.
An optical semiconductor device comprising an iO ₂ material. 2. The optical semiconductor device according to claim 1, wherein the average refractive index n of the gradient composition film of the first thin film is in the range of 2.50 ≦ n ≦ 2.65.