JPH07312459A - Optical semiconductor element - Google Patents

Abstract

PURPOSE:To improve the endurance performance by a method wherein two layer optical film materials including a gradient composition films comprising a specific material are laminated on the end of an optical semiconductor element such as a semiconductor laser structure, etc., for avoiding the end oxidation due to moisture or oxygen. CONSTITUTION:At least one kind of material selected from AlN, Si3N4 comprising a gradient composition films 2 on the semiconductor laser end side as a non-oxide becomes a high protective film protecting the semiconductor end from the oxygen or moisture contained in environmental atmosphere. Besides, Al2O3 likewise comprising these films 2 in the heat expansion coefficient value of close to that of GaAs is to be a material suffering no deterioration at all in a semiconductor element due to thermal stress. In such a constitution, both materials can be mixed with each other further gradient composition so that the mean refractive index of the gradient composition films 2 may exceed 1.90 as well as the second layer films 3 may be made Al2O3 in the low refractive index, thereby enabling the end reflecting power not to exceed 0.1%.

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, 1 formed on a substrate 100.
Semiconductor laser structure 1 including an active layer 102 sandwiched between 06
01, and by applying antireflection (AR) coatings 103a and 103b to the cleaved end face,
The structure is such that laser oscillation can be suppressed even when a high internal gain is given by injection of 04.

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 GR <or ≈0.1. For example, when the gain is 20 dB, the reflectance is R <or ≈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 dielectric film having a desired refractive index is usually deposited on the cleaved end face in a thickness of λ / 4 (λ is a light wavelength). The desired refractive index here differs depending on the semiconductor material used and the waveguide structure, but in the laser of GaAs / AlGaAs system, the optimum refractive index value is approximately n≈1.85.
Is.

Further, the GaAs / AlGaAs semiconductor laser device has an interface level at its end face,
The temperature rises due to the absorption of the laser light, and the oxygen in the atmosphere promotes the oxidation of the end faces, resulting in the destruction of the device. Therefore, it is necessary to stack a film having a protective property on the end face of the device. On the other hand, if the thermal expansion coefficients of GaAs and the protective film material are too different, thermal stress causes dislocation in the active layer of the semiconductor device. However, the element may deteriorate.

Conventionally, Al ₂ O ₃ having a thermal expansion coefficient substantially equal to that of GaAs has been used as the protective film. Further, AlN and Si ₃ N ₄ are also used in optical discs and the like as a protective film for preventing oxidation. Further, there is an example in which an antireflection coating is disclosed by controlling the refractive index by mixing a material having a high refractive index and a material having a low refractive index. In addition, there is also an example in which a multi-layer structure including two or more layers is used.

[0008]

However, in the Al ₂ O ₃ single layer of the above conventional example, the refractive index of Al ₂ O ₃ is small (1.63 to 1.66), so that R is 0.1% or less. It is impossible to do this. Further, since AlN and Si ₃ N ₄ have large refractive indexes (2.0 to 2.2), R cannot be 0.1% or less in each single layer. Further, there is a problem that a lattice defect occurs in the semiconductor laser active layer due to the difference in thermal expansion coefficient from GaAs.

In the case of a mixed layer of a material having a high refractive index and a material having a low refractive index, when an oxide is used in the combination, the end surface is affected by free oxygen, and when a non-oxide is used, the protective performance is improved. Besides, the problem of thermal expansion coefficient with GaAs must be solved. Furthermore, in order to reduce R to 0.1% or less, in a GaAs / AlGaAs laser,
Since the value of the optimum refractive index is about 1.85, the refractive index n of the mixed layer must be within the range of 1.80 ≦ n ≦ 1.90.

In the case of a multilayer film structure, it is necessary to consider the refractive index, protective performance, thermal expansion coefficient, etc. of the material used for each layer. For example, in the case of a two-layer film using Al ₂ O ₃ for the first thin film and AlN or Si ₃ N ₄ for the second thin film on the device end face side, R can be designed to be low by controlling the film thickness, and the durability is comparatively low. Good performance, but still not enough. This is the influence of free oxygen from the Al ₂ O ₃ in contact with the element is not nil, and Al ₂ O ₃ has a problem in adhesion to the GaAs, the thickness in the multilayer is increased, the laser device This is due to reasons such as peeling from the end faces.

Therefore, the object of the present invention is to provide Al ₂ O ₃ , A
An object of the present invention is to provide an optical semiconductor element having an optical film on the end face, which solves the above-mentioned problems while using 1N, Si ₃ N _4, etc.

[0012]

In the present invention, Ga
Provided is an element that realizes high durability and a reflectance of 0.1% or less as an end face protective film / optical film of an As / AlGaAs semiconductor laser device.

That is, in the semiconductor optical amplifier of the present invention, in the semiconductor optical amplifier having a semiconductor laser structure in which an antireflection optical film is applied to the input / output end face, the optical film is composed of a combination of two dielectric thin films. a first thin film of the semiconductor laser structure end face side, AlN, and at least one material selected from Si ₃ N _4, made from the membrane of a material of the Al ₂ O _3, the AlN, the Si ₃ N ₄ The composition concentration of at least one material selected is large on the end face side of the semiconductor laser structure,
The composition concentration gradually decreases in the film thickness direction, and the composition concentration of Al ₂ O ₃ is small on the end face side of the semiconductor laser structure, the composition concentration gradually increases in the film thickness direction, and the average refractive index is larger than 1.90. It is a graded composition film, and the second thin film is made of a material of Al ₂ O ₃ .

Further, in the optical semiconductor element of the present invention, in the optical semiconductor element having an end face provided with an optical film, the optical film is 2
The first thin film on the end face side of the optical semiconductor element is made of a combination of at least one material selected from aluminum nitride and silicon nitride and a material of aluminum oxide. The composition concentration of at least one material selected from aluminum and silicon nitride is large on the end face side of the optical semiconductor element, gradually decreases in the film thickness direction, and the composition concentration of aluminum oxide is
The optical semiconductor element is characterized in that the end face side is small, the composition concentration gradually increases in the film thickness direction, and the second thin film is made of a material of aluminum oxide.

[0015]

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, 21 is an n-type GaAs substrate,
22 is an n-type Al _x Ga _1-x As clad layer (Al mixed crystal ratio x = 0.3), 23 is a GaAs active layer, and 24 is p-type A
1 _x Ga _1-x As (x = 0.3) cladding layer, and 25 is a p ⁺ cap layer. These epitaxial films are deposited and formed by a molecular beam epitaxy (MBE) method or a metal organic thermal decomposition (MO-CVD) method. Then, after patterning the ridge portion by photolithography, a ridge portion having a width of 2 to 3 μm and a depth of 0.3 to 0.4 μm is formed by a reactive ion beam etching (RIBE) method. Further, after depositing the SiN _x film 26,
A window is opened to allow current injection from the cap portion 25, an Au film is deposited on the upper and lower surfaces and alloyed to form ohmic electrodes 27 and 28.

The laser wafer which 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 constitution.

In FIG. 3 showing the layer structure of the coating, reference numerals 2 and 3 denote two-layer optical films including the gradient composition film 2 of this embodiment. At least one material selected from AlN and Si ₃ N ₄ forming the gradient composition film 2 on the semiconductor laser end face side is a non-oxide, and has a property of protecting the semiconductor end face from oxygen and moisture from the ambient atmosphere. It becomes a high protective film. Also,
Similarly, Al ₂ O ₃ forming the gradient composition film 2 has a coefficient of thermal expansion (5.60 × 10 ⁻⁶ deg ⁻¹ ) of GaAs (5.7).
It is a material close to 3 × 10 ⁻⁶ deg ⁻¹ ) and does not cause deterioration of the semiconductor element due to thermal stress.

The average refractive index n of the graded composition film 2 is 1.9 by mixing both materials and making them a graded composition.
And the second layer film 3 is made of Al ₂ having a low refractive index.
By using O ₃ , the end face reflectance can be set to 0.1% or less. Further, Al ₂ O the impact on the end face of the free oxygen from _3, the composition concentration of the end face, AlN, Si ₃ at least selected from N ₄ increases the composition concentration of one material Al ₂
By reducing the composition concentration of O _3, the composition can be prevented and the average thermal expansion coefficient of the graded composition film 2 can be set to a value close to GaAs (5 to 7 × 10 ⁻⁶ deg ⁻¹ ). Further, there is no problem with the adhesion to the device end face because the Al ₂ O ₃ concentration on the end face side is low.

Inclined set of each material to the end face of the semiconductor laser device
The stacking of the film formation 2 is performed by a sputtering method, an electron beam evaporation method, or the like.
The usual vacuum film forming method can be applied. In the case of AlN, AlN
The target is Ar and the sputtering gas is Ar or Ar.
+ N _TwoOf AlN and the sputtering method using mixed gas of
The film can be formed by the electron beam evaporation method used as the source. Si_ThreeN_Four
Similarly, in the case of_ThreeN_FourTarget, Ar
Or Ar + N_TwoSputtering using as a sputtering gas
Law, Si₃N_FourElectron beam evaporation method using
Wear.

[0021] Mixtures 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 and Si ₃ The film can be formed by an electron beam evaporation method using a mixture of N _{4 as} an evaporation source.

As Al ₂ O ₃ , a sputtering method using Al ₂ O ₃ as a target and Ar or Ar + O ₂ as a sputtering gas, an Al target as Ar + O ₂ as a sputtering gas, or Al ₂ O ₃ is used. The electron beam evaporation method used is simple.

FIG. 4 is a diagram schematically showing a film forming method and a film forming apparatus for the gradient composition film 2 by the sputtering method according to the embodiment of the present invention. 61 is a target made of at least one material selected from AlN and Si ₃ N ₄ , and 62 is Al ₂ O.
₃ is a target, 63 is a semiconductor element in which an antireflection film including the gradient composition film 2 is laminated on the end face, 64 is a holder substrate of the semiconductor element 63, 65 is a moving direction of the semiconductor element 63, and 66 is a partition plate.

Using a binary simultaneous sputtering apparatus capable of simultaneously sputtering two targets, the semiconductor element 63 can be moved or rotated, and the semiconductor element 63 can be moved from the side closer to the target 61.
The film is formed by moving in the direction indicated by arrow 65. In the film formation, the material composition of the target 61 gradually decreases as it moves,
The material (Al ₂ O ₃ ) composition of the target 62 gradually increases.

The composition of each material of the gradient composition film 2 is determined by the power supplied to the targets 61 and 62, the sputtering gas pressure, the sputtering gas species, the distance between the substrates, and the like, and the semiconductor element 63. Can be controlled by the moving speed, the height of the partition plate 66, the arrangement of the targets 61 and 62, and the like. Then, the average refractive index n of the gradient composition film 2 is measured in advance, and when n is larger than 1.90, when the second layer 3 following the gradient composition film 2 is formed of Al ₂ O ₃ , it is reflected. The rate R can be made 0.1% or less.

For example, the average refractive index n of the gradient composition film 2 of the first layer is 2.2, and the average refractive index n of the second layer 3 is Al ₂ O ₃ (refractive index 1.6.
3 to 1.66), in order to satisfy R of 0.1% or less, the thickness of the first layer is preferably 480 to 620Å and the thickness of the second layer is preferably 750 to 950Å. . When n of the first layer is 2.0, the thickness of the first layer is 600 to 8
The film thickness of 00Å and the second layer is preferably in the range of 500 to 800Å. When n of the first layer is 1.95, the thickness of the first layer is 650 to 950Å and the thickness of the second layer is 250 to 7
A range of 50Å is desirable. When n of the first layer is 1.91, the thickness of the first layer is preferably 680 to 1100Å, and the thickness of the second layer is preferably 100 to 620Å.

Thus, the semiconductor optical amplifier having the graded composition film 2 formed on the end face of the semiconductor laser can achieve a reflectance of 0.1% or less by measuring the gain ripple. As shown in FIG. 1, the semiconductor optical amplifier is set to a constant current injection state that is slightly smaller than the threshold current, the optical wave 4 is input from the outside by a lens or an optical fiber, and is coupled to the semiconductor optical amplifier to obtain an amplified optical wave 5. be able to. In this way, the internal gain of 20 to 30 dB is achieved.

[0028]

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 this configuration, the wavelength of 8
The signals of 30 nm and 840 nm are multiplexed, amplified by the optical amplifier 10 with high gain and low ripple, and 100 Mbps.
It is possible to exchange signals without crosstalk at the above transmission rates.

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.

[0030]

[Example 1-3] In the high frequency sputtering apparatus capable of performing two-way simultaneous sputtering as shown in FIG.
25 mmφ Si ₃ N ₄ and the target 62 used Al ₂ O ₃ of the same size. The ultimate vacuum is 5 × 10 ⁻⁶ to
rr or less, the sputtering power was 100 W to 1 kW, the sputtering gas pressure was 1 to 10 × 10 ⁻³ torr, and the sputtering gas species was Ar.

The semiconductor laser device 63 is placed on the substrate holder 64, and Si ₃ N ₄ and Al ₂ O ₃ are slowly rotated while the substrate holder 64 is rotated in the direction shown by the arrow 65.
The gradient composition film 2 was laminated on the end face of the semiconductor laser. Next, the semiconductor laser device 63 is arranged so as to be on the target 62, and the shutter on the target 61 is closed, or the input power to the target 61 is set to 0 and only Al ₂ O ₃ is continuously laminated. Then, a two-layer antireflection film was formed.

Further, the Si ₃ N ₄ target 61 and the Al ₂
By changing the input sputtering power P to the O ₃ target 62, three types of gradient composition films were laminated. Each gradient composition film 2
Average refractive index n, film thickness d ₁ , film thickness d _{2 of} Al ₂ O ₃ film 3,
The reflectance R is shown in Table 1. Further, the first gradient composition film 2 of the two-layer film was analyzed in the film thickness direction by XPS (soft X-ray photoelectron spectroscopy). The measured trajectories of the measured elements are Si _2p , A
l _2p . The measurement result of Example 1 is the distance from the laser end face on the horizontal axis, and Si ₃ N converted from Si _2p and Al _2p on the vertical axis.
₄ , the composition ratio of Si ₃ N ₄ from the amount of Al ₂ O ₃ is shown in FIG.

The durability performance is 20 m when the output of the semiconductor laser is
It was evaluated by the change of the injection current value to the semiconductor laser when it was set to W and left to stand in an environment of 70 ° C. for 5000 hours. When the injection current value is reduced to almost 0 and when the injection current value is required to be more than twice the initial value, it is regarded as an element failure,
Depending on the number of failures, ◎: Number of failures, 5% or less of all products,
◯: Number of failures, 10% or less of all products, Δ: Number of failures, more than 10% of all products.

As Comparative Example 1, the semiconductor laser device was installed above the partition plate 66, and the mixed film of Si ₃ N ₄ and Al ₂ O ₃ laminated without rotating the substrate holder was used as the first layer. Next, an Al ₂ O ₃ film was successively laminated 2
The results of the layer film are also shown in Table 1. XP of the first layer of Comparative Example 1
The measurement result of S is also shown in FIG.

[0035]

[Table 1] As a result of the above, the gradient composition film 2 of Si ₃ N ₄ and Al ₂ O ₃
Is the first layer, and the Al ₂ O ₃ film is the second layer 3. The antireflection film can achieve end face reflectance of 0.1% or less, and has the durability performance of the mixed film of Comparative Example 1 as the first layer. It was found that the antireflection film having the structure is improved.

[0036]

[Illustrative 4-6] except for using an AlN target instead the _Si 3 _{N 4} target in examples 1-3, in a similar procedure, AlN and _Al 2 graded composition layer 2 of the _{O 3} stacked next _Al 2 O Example 4 shows the result of a two-layer film in which _three films 3 are successively laminated.
Are shown in Table 2 as ~ 6. In Comparative Example 2, as in Comparative Example 1, a mixed film of AlN and Al ₂ O ₃ was used as the first layer, and then A
Table 2 also shows the results of the two-layer film in which the l ₂ O ₃ film was successively laminated.

[0037]

[Table 2] As a result, the antireflection film having the gradient composition film 2 of AlN and Al ₂ O ₃ as the first layer and the Al ₂ O ₃ film 3 as the second layer is
It was found that the end face reflectance of 0.1% or less can be achieved, and the durability performance is also improved as compared with the antireflection film having the mixed film of Comparative Example 2 as the first layer.

[0038]

[Illustrative 7-9] Instead the _Si 3 _{N 4} target in Examples _{1~3, Si 3 N 4: AlN} = 50: except that a 50 mixed sintered body target _Si 3 _N 4 -AlN of
The results of the two-layer film in which the gradient composition film 2 of Si ₃ N ₄ -AlN and Al ₂ O ₃ was laminated by the same procedure and then the Al ₂ O ₃ film 3 was subsequently laminated are shown as Examples 7 to 9. 3 shows. Comparative Example 3 is similar to Comparative Example 1, and Si ₃ N ₄ , AlN and A
Table 3 also shows the results of a two-layer film in which the mixed film of l ₂ O ₃ was used as the first layer, and then the Al ₂ O ₃ film was subsequently laminated.

[0039]

[Table 3] As a result, the mixed material of Si ₃ N ₄ and AlN and Al ₂
The antireflection film having the gradient composition film 2 with O ₃ as the first layer and the Al ₂ O ₃ film 3 as the second layer can achieve end face reflectance of 0.1% or less, and has durability performance of Comparative Example 3 as well. It was found that the mixed film was improved compared to the antireflection film having the first layer.

[0040]

As described above, according to the present invention,
By stacking two layers of optical film material including a gradient composition film made of a specific material on the end surface of an optical semiconductor element such as a semiconductor laser structure, end surface oxidation due to moisture or oxygen can be suppressed. Furthermore, by suppressing deterioration of the element such as a semiconductor laser due to the difference in thermal expansion coefficient between the element and the two-layer film, durability performance is improved, and the film thickness and refractive index of the two-layer film including the gradient composition film are improved. It is possible to reduce the end face reflectance to 0.1% or less by properly selecting.

[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 shows an example of composition distribution of the 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. A semiconductor optical amplifier having a semiconductor laser structure having an input / output end face provided with an antireflection optical film, wherein the optical film is composed of a combination of two dielectric thin films, and the semiconductor laser structure end face side is provided. The first thin film is AlN, Si
_It is composed of a film of at least one material selected from ₃ N ₄ and Al ₂ O ₃ , and the composition concentration of at least one material selected from AlN and Si ₃ N ₄ is such that the end face side of the semiconductor laser structure is Large, composition concentration gradually decreases in the film thickness direction,
In addition, the composition concentration of Al ₂ O ₃ is small on the end face side of the semiconductor laser structure, the composition concentration gradually increases in the film thickness direction, and the average refractive index is a graded composition film larger than 1.90. A semiconductor optical amplifier comprising a material of ₂ O ₃ . 2. An optical semiconductor element having an end face provided with an optical film, wherein the optical film comprises a combination of two layers of dielectric thin films, and the first thin film on the end face side of the optical semiconductor device is aluminum nitride or nitride. It is composed of a film of at least one material selected from silicon and a material of aluminum oxide. The composition concentration of at least one material selected from aluminum nitride and silicon nitride is large on the end face side of the optical semiconductor element and in the film thickness direction. The composition concentration gradually decreases, and the composition concentration of aluminum oxide is small on the end face side of the optical semiconductor element,
An optical semiconductor element, wherein the composition concentration gradually increases in the film thickness direction, and the second thin film is made of a material of aluminum oxide.