JPH05275811A - Semiconductor optical modulation element - Google Patents

Abstract

PURPOSE:To obtain an optical modulation element which enables actual optical system application using a quantum well structure. CONSTITUTION:In an optical switching element where a multiple quantum well structure 2 of InGaAsP/InP group is formed on an n-type InP substrate 1, a p-type InP layer 3 is formed thereon with a striped pattern and a crossing waveguide 4 is formed by an n-type InP layer so that the p-type InP layer 3 is located at the crossing portion, a tensile distortion is given to the InGaAsP well layer of the multiple quantum well structure 2, realizing optical switching without dependence on polarized plane.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a semiconductor optical modulation device using a quantum well structure.

[0002]

2. Description of the Related Art As a semiconductor optical modulation device, a device using a quantum well structure has been proposed. This utilizes a phenomenon in which the refractive index changes by applying an electric field to the quantum well structure (so-called electric field application effect). By utilizing this phenomenon, it is possible to manufacture an optical switch element or the like that is ultra-compact and can operate at ultra-high speed. However, up to now, the optical switch element using the electric field application effect of the quantum well has not been used in an actual system. One of the reasons is that the characteristics greatly depend on the plane of polarization of incident light. For example, in the InGaAs / InP quantum well structure, the electric field refractive index change in the TE mode is about twice as large as that in the TM mode.

As is well known in the quantum well structure, the degeneracy is partially released to separate the light hole band and the heavy hole band. The change in the refractive index for the TE mode corresponds to the transition between the heavy hole band and the conduction band, and the change in the refractive index for the TM mode corresponds to the transition between the light hole band and the conduction band, but the light hole band and the heavy positive band. Since the energy levels of the pore zones are different, there is a difference in the refractive index change between the TE mode and the TM mode as described above.

[0004]

As described above, the optical switch device using the quantum well structure has a problem that it is difficult to apply it to an actual system because of its large polarization plane dependency. The present invention has been made in view of such circumstances, and an object thereof is to provide an optical modulator using a quantum well structure that enables actual optical system applications.

[0005]

According to the present invention, a multiple quantum well structure is formed on a semiconductor substrate, and a waveguide whose waveguide characteristic is controlled by the electric field refractive index changing effect of this multiple quantum well structure is formed. In the semiconductor light modulation device described above, the multi-quantum well structure has a so-called strained multi-quantum well structure in which well layers and barrier layers are alternately laminated in a state in which the well layers are strained.

[0006]

When the strain is introduced by intentionally making the well layer of the multiple quantum well structure lattice-mismatch with the barrier layer,
The energy levels of the light hole band and the heavy hole band shift according to the strain. For example, in the InGaAs / InP-based multiple quantum well structure, if a slight lattice mismatch is introduced during crystal growth so that extension strain is applied to the InGaAs layer that becomes the well layer, a light positive contribution to the electric field refractive index change in the TE mode is achieved. It is possible to equalize the energy levels of the hole band and the heavy hole band that contribute to the change in the electric field refractive index in the TM mode. By combining such a strained multiple quantum well structure and a waveguide, an optical switch element that does not depend on the polarization plane of incident light can be obtained.

On the other hand, when reverse compressive strain is introduced into the well layer of the same InGaAs / InP system multiple quantum well structure, TE
The difference in electric field refractive index change between the mode and the TM mode can be further increased. By combining the strained multi-quantum well structure having the positive polarization plane dependence with the waveguide as described above, it can be used as a mode filter for extracting specific linearly polarized light from incident light.

[0008]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is a plan view of an optical switch element according to an embodiment of the present invention, and FIG. 2 is a sectional view taken along the line AA '. This optical switching element is a combination of a crossed waveguide and a multi-quantum well structure, and comprises an n-type InP substrate 1, a strained multi-quantum well structure 2 formed on this, and a stripe-shaped structure on this multi-quantum well structure 2. It has a p-type InP layer 3 formed in a pattern, and a cross-type waveguide 4 formed of an n-type InP layer so that the p-type InP layer 3 is located at a crossing portion. The multiple quantum well structure 2 has a non-doped (i
Type). The surface on which the p-type InP layer 3 and the waveguide 4 are patterned is covered with a SiO ₂ film 5. A contact window is opened in this SiO ₂ film 5,
A p-side electrode 6 that contacts the p-type InP layer 3 is formed. An n-side electrode 7 is formed on the back surface of the n-type InP substrate 1.

The strained multiple quantum well structure 2 has a thickness of 3 nm to 1
0 nm of In _x Ga _1-x As _y P _1-y (0 <x <1,0 ≦
y ≦ 1) The well layers 21 and the InP barrier layers 22 having a thickness of 15 nm to 30 nm are alternately laminated for 30 to 40 cycles. FIG. 2 shows an enlarged view of the laminated structure.
The In _x Ga _1-x As _y P _1-y well layer 21 has a band gap energy of 1.03 to 0.75 eV, and In
The band gap energy of the P barrier layer 22 is 1.3 eV.
Is. The In _x Ga _1-x As _y P _1-y well layer 21 will be simply referred to as an InGaAsP well layer 21 in the following description.

The composition ratio of the InGaAsP well layer 21 of the multiple quantum well structure 2 is set so that its lattice constant deviates from the lattice constant of the InP barrier layer 22 by −0.5 to −2%. As a result, the InGaAsP well layer 21 is in a state where tensile strain is applied.

3 (a) to 3 (e) show the manufacturing process of the optical switch element of this embodiment with respect to the cross section of FIG.
On the n-type InP substrate 1, for example, using the MBE method,
A multiple quantum well structure 2 in which GaAsP well layers and InP barrier layers are alternately laminated is epitaxially grown, and then a p-type InP layer 3 is epitaxially grown thereon ((a)). At this time, as described above, tensile strain is introduced into the InGaAs well layer by selecting the composition. Next, the p-type InP layer 3 is selectively etched using, for example, a SiO ₂ mask to leave it in a stripe pattern ((b)).

Next, an n-type InP layer 40 used as a waveguide is grown around the p-type InP layer 3 so that the surface becomes flat ((c)). The growth process of the n-type InP layer 40 is performed, for example, in a state where the mask such as SiO ₂ used in the selective etching is formed on the surface of the p-type InP layer 3,
Selective epitaxial growth may be performed on the exposed multiple quantum well structure 2. Then, the n-type InP layer 40 is selectively etched to form the crossed waveguide 4 having the pattern shown in FIG.
((D)). Finally, the surface is covered with a SiO ₂ film 5, a contact hole is formed on the p-type InP layer 3 to form a p-side electrode 6, and an n-side electrode 7 is formed on the back surface of the substrate ((e)).
).

In the element of this embodiment, by applying a predetermined bias voltage between the p-side electrode 6 and the n-side electrode 7,
Optical switching is performed by changing the electric field refractive index in the multiple quantum well structure 2. In the case of this embodiment, tensile strain is applied to the InGaAsP well layer of the multiple quantum well structure 2, and as a result, TE is increased in this multiple quantum well structure 2.
The energy levels of the heavy hole band affecting the electric field refractive index change of the mode and the light hole band affecting the electric field refractive index change of the TM mode are the same. This allows optical switching that does not depend on the polarization plane of the incident light.

Next, an embodiment in which the present invention is applied to a mode filter will be described. The basic structure of the element is the same as that of the above-mentioned embodiment, so that the drawing is omitted. In the case of mode filter,
A compressive strain is introduced into the InGaAsP well layer 21 of the multiple quantum well structure 2 contrary to the above embodiment. This is InGaAs
Select the composition ratio of the P well layer 21 and set its lattice constant to InP.
It is possible by shifting in the positive direction as compared with that.

By doing so, the energy levels of the heavy hole band and the light hole band of the multiple quantum well structure are more separated than in the case of no strain. As a result, the difference between the TE mode electric field refractive index change and the TM mode electric field refractive index change becomes larger. Therefore, with a predetermined electric field applied, for example, specific linearly polarized light is extracted from incident natural light from a certain terminal, or two orthogonal linearly polarized light components (TE mode wave and TM mode wave) are separated from circularly polarized light. You can take it out.

Up to this point, the embodiment of the combination of the crossed waveguide and the multiple quantum well structure has been described, but the present invention can also be applied to the case where a directional coupling type optical waveguide is used. Such an embodiment will now be described.

FIG. 4 is a plan view of an optical switch element of such an embodiment, and FIG. 5 is a sectional view taken along line AA 'of FIG.
This optical switch element comprises an n-type InP substrate 11, a strained multiple quantum well structure 12 formed on the substrate 11, a nodoop (i-type) InP layer 13a on the multiple quantum well structure 12,
It has a directional coupling type optical waveguide composed of p-type InP layers 14a and 14b formed in a parallel stripe pattern adjacent to each other via 13b. Multiple quantum well structure 1
2 is i-type. P-type InP layer 1 forming an optical waveguide
The surface on which 4a and 14b are patterned is SiO ₂
It is covered by the membrane 15. A contact window is opened in the SiO ₂ film 15 so that the p-type InP layers 14a and 14b are formed.
A p-side electrode 16 is formed to be in contact with each. An n-side electrode 17 is formed on the back surface of the n-type InP substrate 11.

The strained multiple quantum well structure 12 has a thickness of 3 nm to 10 nm of In _x Ga _1-x As _y P as in the previous embodiment.
_1-y (0 <x <1, 0 ≦ y ≦ 1) well layer 21 and thickness 1
The InP barrier layers 22 having a thickness of 5 nm to 30 nm are alternately arranged to have a thickness of 30 to 40
It is formed by periodic lamination. FIG. 5 shows an enlarged view of the laminated structure. The In _x Ga _1-x As _y P _1-y well layer 21 has a band gap energy of 1.03 to
0.75 eV, and the InP barrier layer 22 has a bandgap energy of 1.3 eV. In _x Ga _1-x As
_{The y} P _1-y well layer 21 will be simply referred to as InGa in the following description.
It will be referred to as an AsP well layer 21.

As in the previous embodiment, the multiple quantum well structure 1
No. 2 InGaAsP well layer 21 has an In lattice constant of In
The composition ratio is set so as to deviate from the lattice constant of the P barrier layer 22 by −0.5 to −2%. In this way, InG
A tensile strain is applied to the aAsP well layer 21.

FIGS. 6 (a) to 6 (c) show the manufacturing process of the optical switch element of this embodiment with respect to the cross section of FIG.
On the n-type InP substrate 11, for example, by using the MBE method, I
A multiple quantum well structure 12 in which nGaAsP well layers and InP barrier layers are alternately stacked is epitaxially grown, and then an i-type InP layer 13 and a p-type InP layer 14 are sequentially epitaxially grown thereon ((a)). At this time, as described above, tensile strain is introduced into the InGaAs well layer by selecting the composition. Next, p-type In
The P layers 14 and 13 are selectively etched using the SiO ₂ mask 18 to leave two stripe-shaped patterns 14a, 14b and 13a, 13b adjacent in parallel ((b)). This constitutes a directional coupling type optical waveguide.

Next, the SiO used for the selective etching.
₂ After removing the mask 18, the entire surface on which the directional coupling type optical waveguide is patterned is covered with the SiO ₂ film 16 again, and contact holes are formed on the p-type InP layers 14a and 14b to form the p-side electrode 16. To do. N-side electrode 1 on the backside of the substrate
7 is formed ((c)).

Also in the device of this embodiment, the p-side electrode 16 and the n-side
By applying a predetermined bias voltage between the side electrodes 17, optical switching is performed by a change in electric field refractive index in the multiple quantum well structure 12. And in the case of this embodiment,
As a result of the tensile strain being applied to the InGaAsP well layer of the multiple quantum well structure 12, this multiple quantum well structure 1
In No. 2, the energy levels of the heavy hole band affecting the electric field refractive index change of the TE mode and the light hole band affecting the TM mode electric field refractive index change are the same. This allows
Optical switching that does not depend on the plane of polarization of incident light can be performed.

Next, an embodiment in which the present invention is applied to a mode filter by combining the directional coupling type optical waveguide and the multiple quantum well structure will be described. The basic structure of the element is similar to that of the embodiment shown in FIG. In the case of the mode filter, compressive strain is introduced into the InGaAsP well layer 21 of the multiple quantum well structure 12 contrary to the above-mentioned embodiment. This can be done by selecting the composition ratio of the InGaAsP well layer 21 and shifting its lattice constant in the positive direction as compared with that of InP.

By doing so, the energy levels of the heavy hole band and the light hole band of the multiple quantum well structure are more separated than in the case of no strain. As a result, the difference between the TE mode electric field refractive index change and the TM mode electric field refractive index change becomes larger. Therefore, with a predetermined electric field applied, for example, specific linearly polarized light is extracted from incident natural light from a certain terminal, or two orthogonal linearly polarized light components (TE mode wave and TM mode wave) are separated from circularly polarized light. You can take it out.

Although the embodiment of the InGaAsP / InP system has been described above, the present invention is not limited to this, and other semiconductor material systems such as AlGaAs / GaA are used.
It is possible to obtain a similar light modulator using the s system.

[0026]

As described above, according to the present invention, by using the strained multiple quantum well structure, it is possible to obtain an optical switching or mode filter that does not depend on the polarization plane of incident light.

[Brief description of drawings]

FIG. 1 is a plan view showing an optical switch element according to an embodiment of the present invention.

FIG. 2 is a sectional view taken along the line AA ′ in FIG.

FIG. 3 is a cross-sectional view showing the manufacturing process of the embodiment.

FIG. 4 is a diagram showing an optical switch element according to another embodiment of the present invention.

5 is a cross-sectional view taken along the line AA ′ of FIG.

FIG. 6 is a cross-sectional view showing the manufacturing process of the embodiment.

[Explanation of symbols]

1 ... n-type InP substrate, 2 ... i-type InGaAsP / InP
Strained multiple quantum well structure, 3 ... p-type InP layer, 4 ... n-type I
nP waveguide, 5 ... SiO ₂ film, 6 ... P-side electrode, 7 ... N-side electrode. 11 ... n-type InP substrate, 12 ... i-type InGaAs
P / InP strained multiple quantum well structure, 13 (3a, 3b)
... i-type InP layer, 14 (4a, 4b) ... p-type InP layer,
15 ... SiO ₂ film, 16 ... P-side electrode, 17 ... N-side electrode.

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[Procedure amendment]

[Submission date] June 1, 1992

[Procedure Amendment 1]

[Document name to be amended] Statement

[Correction target item name] 0010

[Correction method] Change

[Correction content]

The InGaAsP well layer 21 of the multiple quantum well structure 2 has a composition ratio x, y such that its lattice constant deviates from the lattice constant of the InP barrier layer 22 by −0.5 to −2%.
Is set to x = 0.46 to 0.24 and y = 1 . As a result, the InGaAsP well layer 21 is in a state where tensile strain is applied. By the way, the above group
Strain degree of well layer in the range and bandgage in bulk state
Cap Eg and the corresponding wavelength λg are shown together.
If it does, it will be as follows. Well _{layer: In x Ga 1-x As} y P 1-y, y = 1 x skewness bulk Eg bulk wavelength λg 0.46 -0.5% 0.83eV 1.50μm 0.38 -1.0 % 0 .92eV 1.35μm 0.32 -1.5% 0.99eV 1.25μm 0.24 -2.0% 1.09eV 1.14μm

Claims (1)

[Claims] 1. A semiconductor substrate, a multi-quantum well structure in which well layers and barrier layers are alternately laminated on the semiconductor substrate in a state in which the well layers are strained, and a multiple quantum well structure formed on the semiconductor substrate. Further, a semiconductor optical modulation element comprising: a waveguide whose waveguide characteristic is controlled by an electric field refractive index change effect of the quantum well structure.