JP5373585B2 - Semiconductor laser and electroabsorption modulator integrated distributed feedback laser - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an element achieving high output even at high temperatures, in regard to a distributed feedback semiconductor laser or Fabry-Perot laser with an oscillation wavelength of 1.290-1.350 &mu;m. <P>SOLUTION: The semiconductor laser includes an active layer 2 having a multi quantum well structure of an InGaAlAs material excellent in high output power at high temperatures on an InP substrate, with its barrier layer optimal values (x value and y value of In<SB>(1-x-y)</SB>Ga<SB>(x)</SB>Al<SB>(y)</SB>As) being in the range of 0.19&lt;x&lt;0.27 and 0.31&lt;y&lt;0.39 simultaneously. <P>COPYRIGHT: (C)2011,JPO&amp;INPIT

Description

  The present invention relates to a semiconductor laser (for example, a distributed feedback laser or a Fabry-Perot laser) and an electroabsorption modulator integrated distributed feedback laser capable of realizing a high output at a high temperature.

A semiconductor laser used for optical communication is generally used while keeping the temperature of the semiconductor laser element constant with a temperature control element (Peltier element). For example, the electroabsorption modulator (EA modulator) integrated distributed feedback laser (DFB laser) (EADFB laser) is widely used at a modulation rate of 10 Gb / s, characterized by its small size and low chirp. However, these are all used in a state in which the temperature is maintained by a Peltier element.

  With the recent increase in data traffic, there is a strong demand for lower power consumption in optical communication systems. While the general power consumption of EADFB lasers is about 0.2 W, the power consumption of Peltier elements requires about 1 to 2 W, depending on the difference between the external temperature and the set temperature.

  For this reason, if an EADFB laser that does not require temperature control (no temperature control operation) and has no characteristic degradation over a wide temperature range can be realized, a significant reduction in power consumption can be realized.

H. Temkin et al., Appl. Phys. Lett., Vol.62, No.19, pp.2402-2404, 1993

In order to realize an EADFB laser with no characteristic degradation over a wide temperature range, it is necessary to prevent the DFB laser part from degrading output over a wide temperature range.
However, the conventional technology uses an InGaAsP-based material on an InP substrate, so the conduction band offset value is small when a quantum well structure is fabricated, and electrons overflow from the well layer at high temperatures, resulting in deterioration of characteristics. was there.

The configuration of the semiconductor laser of the present invention that solves the above problems is as follows.
In a distributed feedback semiconductor laser or Fabry-Perot laser with an oscillation wavelength of 1.290 to 1.350 μm,
The active layer has a multiple quantum well structure of In _(1-xy) Ga _(x) Al _(y) As-based material, and the composition x, y of the barrier layer has the following numbers simultaneously. To do.
0.19 <x <0.27
0.31 <y <0.39
x + y = 0.58

The electroabsorption modulator integrated distributed feedback laser of the present invention is characterized in that the distributed feedback semiconductor laser and the electroabsorption modulator are integrated on the same wafer.

According to the present invention, the active layer has a multiple quantum well structure of an In _(1-xy) Ga _(x) Al _(y) As-based material, and the composition x, y of the barrier layer is 0.19 <x <0.27. , 0.31 <y <0.39, and x + y = 0.58 at the same time, a large conduction band offset value (ΔEc) with excellent characteristics at high temperatures and a small valence band offset value that does not cause nonuniform injection of holes (ΔEv) can be compatible.
Therefore, a distributed feedback semiconductor laser, a Fabry-Perot laser, or an electroabsorption modulator integrated distributed feedback laser capable of high output at high temperatures and having an oscillation wavelength of 1.290 to 1.350 μm is realized. be able to.

The characteristic view which shows the relationship between a barrier layer wavelength and offset. The characteristic view which shows the relationship between a band gap wavelength and a refractive index. The characteristic view which shows the barrier layer composition dependence of the IL characteristic in 20 degreeC. The characteristic view which shows the barrier layer composition dependence of the IL characteristic in 95 degreeC. 1 is a configuration diagram illustrating a distributed feedback semiconductor laser according to Embodiment 1. FIG. FIG. 3 is an explanatory diagram illustrating a creation procedure of the first embodiment. FIG. 6 is a configuration diagram illustrating an electroabsorption modulator integrated distributed feedback laser according to a second embodiment. Explanatory drawing which shows the first half of the preparation procedures of Example 2. FIG. Explanatory drawing which shows the second half of the preparation procedures of Example 2. FIG.

[Feature]
The feature of the present invention is not only to set the barrier layer so as to increase the conduction band offset value (ΔEc) but also to increase the conduction band offset value (ΔEc) in order to realize high output at high temperature. Then, in consideration of the fact that the refractive index is lowered and the optical confinement is reduced, the barrier layer composition is set such that an upper limit is set for the conduction band offset value (ΔEc).

[Action]
Calculation results of band gap wavelength, conduction band offset value (ΔEc) and valence band offset value (ΔEv) of the barrier layer when a multi quantum well (MQW) structure is made of InGaAlAs and InGaAsP materials It is shown in FIG. This is the case where the MQW PL wavelength is 1.29 μm and the well layer and barrier layer strains are +1.0% / − 0.6% with respect to the InP substrate. As can be seen from FIG. 1, the InGaAlAs material has a larger conduction band offset value (ΔEc) and a smaller valence band offset value (ΔEv) than the InGaAsP material.

  At high temperatures, the energy distribution of electrons contributing to light emission spreads, so the overflow effect of overflowing electrons from the well layer appears. Since it can be taken large, overflow can be suppressed.

Further, when the valence band offset value (ΔEv) is large, there is a problem that holes contributing to light emission are difficult to be injected into the well layer.
The InGaAsP material has a problem that the valence band offset value (ΔEc) is larger than the conduction band offset value (ΔEc), so that holes are likely to be non-uniformly injected and the conduction band offset value (ΔEc) cannot be increased.

  In the present invention, since an InGaAlAs material is used, it is possible to achieve both a large conduction band offset value (ΔEc) excellent in characteristics at high temperatures and a small valence band offset value (ΔEv) that does not cause nonuniform injection of holes.

FIG. 2 shows the calculation result of the relationship between the band gap wavelength of the barrier layer and its refractive index when the measurement wavelength is 1.30 μm. The barrier layer is calculated with a strain of -0.6% with respect to the InP substrate. It can be seen that the refractive index decreases as the wavelength of the barrier layer becomes shorter.
When considering the optical confinement of the active layer of the semiconductor laser, it is desirable that the refractive index of the barrier layer is large. This is because the higher the refractive index of the barrier layer, the better the optical confinement of the entire active layer, and the lower threshold of laser oscillation can be achieved.

  In consideration of the above-mentioned “relationship between the barrier layer wavelength and offset” and “relationship between the bandgap wavelength of the barrier layer and its refractive index”, it is desirable that the barrier layer has a shorter wavelength for the confinement of electrons. It is desirable that the barrier layer has a longer wavelength. In fact, using an InGaAlAs material, a Fabry-Perot laser having a length of 500 μm was fabricated by fixing the PL wavelength to 1.29 μm and the strain amount of the well layer and the barrier layer to +1.0% / − 0.6%. The barrier layer wavelength was changed to 0.85Q, 0.90Q, 0.95Q, 1.0Q, and 1.1.1Q, and the characteristics were compared at 20 ° C and 95 ° C. The results are shown in FIG. 3 and FIG.

  FIG. 4 shows that the barrier layer wavelength is 0.9Q or more and 1.0Q or less in order to obtain an optical output of 8 mW or more at 95 ° C. According to FIG. 1, the conduction band offset is 220 meV or more and 330 meV or less.

When actually manufacturing a laser, the PL wavelength of the quantum well structure is determined from the oscillation wavelength of the laser to be manufactured. The strain of the well layer and the barrier layer is determined, and the well layer wavelength and the barrier layer wavelength are changed so that the MQW PL does not change. When the PL wavelength is set to 1.28 and 1.30 μm, the conduction band offset value (ΔEc), valence band offset value (ΔEv) and In _(1-xy) Ga _(x) Al _(y) As composition Tables 1 and 2 show. In Tables 1 and 2, the italic characters indicate that the barrier layer wavelength is 0.9Q to 1.0Q.

Tables 1 and 2 are calculated values. When actually fabricating a device, there is no precision to the third decimal place of a number such as 0.1436 of the composition. Therefore, to take a composition of 0.9Q-1.0Q,
For PL 1.28, 0.19 <x <0.27, 0.31 <y <0.39
For PL 1.30, 0.19 <x <0.27, 0.31 <y <0.39
It becomes.

Embodiment 1 of the present invention will be described below with reference to the drawings.

(Constitution)
As shown in FIG. 5, the distributed feedback semiconductor laser of the present invention uses an n-type InP substrate 1 as a substrate, an MQW active layer 2 made of InGaAlAs material, an InGaAsP guide layer 3, a diffraction grating 4, and a p-type InP cladding layer 5. , InGaAsP or InGaAs contact layer 6 and dielectric multilayer 9.

In this case, the active layer 2 has a multiple quantum well structure of an In _(1-xy) Ga _(x) Al _(y) As-based material, and the composition x, y of the barrier layer is a number in the following range. Have at the same time.
0.19 <x <0.27
0.31 <y <0.39
x + y = 0.58

Thus, in Example 1, since the active layer 2 using the InGaAlAs material has the above composition, a large conduction band offset value (ΔEc) excellent in characteristics at high temperatures and hole nonuniformity. It is possible to achieve both a small valence band offset value (ΔEv) that does not cause injection.
Therefore, high output can be achieved at high temperatures.

(Production method)
The manufacturing procedure will be described with reference to FIG. 6, the left side shows a front view and the right side shows a cross-sectional view.

First, the substrate 1 is prepared from [Procedure 1].
As in [Procedure 2], the MQW active layer 2 and the InGaAsP guide layer 3 are crystal-grown on the substrate 1 by the MOVPE (metal-organic vapor-phase epitaxy) method.

Thereafter, as in [Procedure 3], the diffraction grating 4 is formed on the guide layer 3 by EB (electron beam) drawing, and the p-type InP cladding layer 5 and the InGaAsP or InGaAs contact layer 6 are crystal-grown.
As in [Procedure 4], a ridge-type waveguide is fabricated by dry etching using a CH ₄ gas.

Then, as in [Procedure 5], a SiO ₂ film 7 is formed as an insulating film as a whole, and only the SiO ₂ film above the InGaAsP or InGaAs contact layer 6 is removed by dry etching with C ₂ F ₆ gas. Then, an Au metal pad 8 is formed thereon using EB vapor deposition.
Thereafter, the element is cut out by cleavage, and the dielectric multilayer film 9 is formed on the end face of the cut out element to complete the element.

  The distributed feedback semiconductor laser of Example 1 had an element length of 400 μm, and an optical output at current injection of 100 mA was 85 (10 mW or more at C).

(Constitution)
An electroabsorption modulator integrated distributed feedback laser according to Embodiment 2 of the present invention includes a semiconductor laser section and an electroabsorption modulator section.
That is, as shown in FIG. 7, the semiconductor laser section uses an n-type InP substrate 1 as the substrate, and the laser section uses an MQW active layer 2, InGaAsP guide layer 3, diffraction grating 4, and p-type InP cladding layer 5 made of InGaAlAs material. , InGaAsP or InGaAs contact layer 6.
The electroabsorption modulator section is composed of an MQW active layer 10 and an InGaAsP guide layer 11 made of InGaAlAs material.
In FIG. 7, 7 is a SiO ₂ film, 8 is a metal pad of Au, and 9 is a dielectric multilayer film.

In this case, the active layer 2 has a multiple quantum well structure of an In _(1-xy) Ga _(x) Al _(y) As-based material, and the composition x, y of the barrier layer is a number in the following range. Have at the same time.
0.19 <x <0.27
0.31 <y <0.39
x + y = 0.58

Thus, in Example 2 , since the active layer 2 using the InGaAlAs material has the above composition, a large conduction band offset value (ΔEc) excellent in characteristics at high temperatures and hole nonuniformity are obtained. It is possible to achieve both a small valence band offset value (ΔEv) that does not cause injection.
Therefore, high output can be achieved at high temperatures.

(Production method)
The manufacturing procedure will be described with reference to FIGS. 8A and 8B. 8A, the left side shows the front view, the right side shows the II cross section, the right side shows the front view, and the center shows the II cross section. The figure shows the II-II cross section on the right side.

First, as shown in FIG. 8A, the substrate 1 is prepared from [Procedure 1].
As in [Procedure 2], the MQW active layer 2 and the InGaAsP guide layer 3 are crystal-grown on the substrate 1 by the MOVPE (metal-organic vapor-phase epitaxy) method.

  After that, the diffraction grating 4 is formed on the guide layer 3 by EB (electron beam) drawing as in [Procedure 3], and the MQW active layer 2, the guide layer 3, and the diffraction grating other than the LD part as in [Procedure 4]. 4 is removed by wet etching.

Thereafter, as in [Procedure 5], the MOVPE method is used to grow crystals of the semiconductor layer 10 and the InGaAsP guide layer 11 which are InGaAlAs active layers of the electroabsorption modulator.
Note that the diffraction grating 4 may be formed in the order of this procedure, or after the semiconductor layer 10 and the guide layer 11 are first crystal-grown.

  Thereafter, as in [Procedure 6], the p-type InP cladding layer 5 and the InGaAsP or InGaAs contact layer 6 are crystal-grown.

Next, as in [Procedure 7] shown in FIG. 8B, the ridge-type waveguides of the LD part and the modulator part are simultaneously produced by dry etching using a CH4 gas.
Thereafter, as in [Procedure 8], the electrode separation 12 of the LD portion and the modulator portion is fabricated by removing a part of the InGaAsP or InGaAs contact layer 6 by wet etching.

Thereafter, as in [Procedure 9], an SiO ₂ film 7 is formed as an insulating film as a whole, and an organic film 13 is formed thereon to embed the waveguide measuring section.
After that, as in [Procedure 10], only the SiO ₂ film 7 and the organic film 13 on the contact layer 6 are removed by dry etching with C ₂ F ₆ -based gas and O ₂ -based gas. The pad 8 is formed using the EB vapor deposition method.
Thereafter, the element is cut out by cleavage, and the dielectric multilayer film 9 is formed on the end face of the cut out element to complete the element.

  The electroabsorption modulator integrated distributed feedback semiconductor laser of Example 2 has an LD section length of 400 μm and a modulator section length of 200 μm, and an optical output at an LD section current injection of 100 mA is 85 (10 mW or more at C).

  The present invention can be applied not only to the distributed feedback laser shown in the first embodiment and the electroabsorption modulator integrated distributed feedback laser shown in the second embodiment, but also to a Fabry-Perot laser.

In other words, in a Fabry-Perot laser with an oscillation wavelength of 1.290 to 1.350 μm, the active layer employs a multiple quantum well structure of In _(1-xy) Ga _(x) Al _(y) As material, and the composition of the barrier layer It can be configured that x and y have numbers in the following ranges at the same time.
0.19 <x <0.27
0.31 <y <0.39
x + y = 0.58
By doing so, even in a Fabry-Perot laser having an oscillation wavelength of 1.290 to 1.350 μm, a high output can be realized at a high temperature.

1 n-type InP substrate 2 MQW active layer of InGaAlAs material 3 InGaAsP guide layer 4 diffraction grating 5 p-type InP clad layer 6 InGaAsP or InGaAs contact layer 7 SiO ₂ film 8 Au metal pad 9 dielectric multilayer film 10 InGaAlAs material activity Semiconductor layer 11 InGaAsP guide layer 12 Electrode separation 13 Organic film

Claims (2)

In a distributed feedback semiconductor laser or Fabry-Perot laser with an oscillation wavelength of 1.290 to 1.350 μm,
The active layer has a multiple quantum well structure of In _(1-xy) Ga _(x) Al _(y) As-based material, and the composition x, y of the barrier layer has the following numbers simultaneously. Semiconductor laser.
0.19 <x <0.27
0.31 <y <0.39
x + y = 0.58 2. An electroabsorption modulator integrated distributed feedback laser, wherein the distributed feedback semiconductor laser according to claim 1 and the electroabsorption modulator are integrated on the same wafer.

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