JP5096271B2 - Semiconductor Mach-Zehnder type optical circuit and manufacturing method thereof, and optical modulator, optical switch, and optical filter provided with the semiconductor Mach-Zehnder type optical circuit - Google Patents

Description

  The present invention relates to a semiconductor Mach-Zehnder type optical circuit used in an optical device for optical communication, a manufacturing method thereof, and an optical modulator, an optical switch, and an optical filter provided with the semiconductor Mach-Zehnder type optical circuit.

As an optical modulator which is an optical device provided with a conventional semiconductor Mach-Zehnder type optical circuit, there are those shown in FIGS.
FIG. 10 is an explanatory view showing the upper surface of a conventional semiconductor Mach-Zehnder type optical modulator, FIG. 11 is an explanatory view showing a cross section taken along the line CC in FIG. 10, and FIG. 12 is a cross section taken along the line DD in FIG. It is explanatory drawing which shows the cross section along.

10 to 12, reference numeral 1 denotes a semiconductor Mach-Zehnder optical modulator, which is an optical modulator using a Mach-Zehnder interference optical circuit 2 (described later).
Reference numeral 3 denotes a semiconductor substrate. A compound semiconductor substrate made of indium (In) and phosphorus (P) and having a thickness of 100 μm is made of silicon (Si), sulfur (S), selenium (Se), telel (Te), etc. The first conductive semiconductor is formed by diffusing N-type impurities as conductive impurities (hereinafter referred to as N-type InP substrate 3).

  Further, on the front surface side of the N-type InP substrate 3, as shown in FIG. 10, two branch branches 5 for branching the light from the input port 4 in two directions are arranged on the input side. A Y-shaped branching section 6 as a branching section and an output-side Y-shaped branching section 6 that combines the lights from the branching branches 5 and outputs them from the output port 7 are arranged with the branching branches 5 facing each other. The optical circuit 2 optically connected between the branch branches 5 by the first arm portion 8a and the second arm portion 8b (referred to as the arm portion 8 when there is no need to distinguish them) is formed. Has been.

Reference numeral 10 denotes an N-type InP layer as a first cladding layer, which is a first conductivity type semiconductor layer made of a compound semiconductor formed by etching the N-type InP substrate 3 into the shape of the optical circuit 2, and is shown in FIG. It functions as an optical coating layer for preventing leakage of light guided to the well layer 12 shown by shading.
The well layer 12 includes an InGaAsP layer having a thickness of 10 nm, which is a compound semiconductor layer made of indium, gallium (Ga), arsenic (As), and phosphorus, and a compound semiconductor layer made of indium and phosphorus on the N-type InP layer 10. MQW (Multi-Quantum Well) formed by laminating an InP layer having a thickness of 10 nm as a core of the optical circuit 2 that guides light input from the input port 4 to the output port 7 Function.

Reference numeral 13 denotes a P-type InP layer as a second cladding layer. A compound semiconductor layer made of indium and phosphorus is formed on the well layer 12 and a second conductive material such as zinc (Zn) opposite to the first conductive type impurity. A second conductivity type semiconductor layer formed by diffusing P-type impurities as type impurities, and functions as an optical covering layer that prevents leakage of light guided to the well layer 12.
The resistivity of the P-type InP layer 13 is normally formed to about 0.5 Ωcm.

Reference numeral 14 denotes a contact layer, which is a high-concentration second conductive semiconductor layer in which a P-type impurity is diffused in a compound semiconductor layer made of indium, gallium, and arsenic at a higher concentration than the P-type InP layer 13. Each P-type InP layer 13 of the first and second arm portions 8 has a function of electrically connecting the first and second electrodes 16a and 16b.
The first and second electrodes 16a and 16b (referred to as the electrode 16 when there is no need to distinguish between them) are conductive on the contact layer 14 such as an alloy made of gold (Au) and zinc (Zn). This is a convex electrode made of a material.

Reference numeral 17 denotes an electrode pad, which is formed of a conductive multilayer film in which titanium (Ti), platinum (Pt), and gold are stacked in this order from the electrode 16 side on the protruding portion of the convex electrode 16. Electrically connected.
Reference numeral 18 denotes a protective layer, which is a resin layer made of a polyimide resin that protects the optical circuit 2 formed around and inside the optical circuit 2, and is an optical coating that prevents leakage of light guided to the well layer 12 It functions as a layer and also functions as an insulating layer that electrically insulates between the electrode 16 and each of the semiconductor layers.

A lower electrode 19 is formed on the entire back surface of the N-type InP substrate 3 and is formed of a conductive metal film such as an alloy made of nickel (Ni), germanium (Ge), or gold.
The N-type InP layer 10, the well layer 12, and the P-type InP layer 13 form a ridge-type optical waveguide having a stacked PIN structure, and the electrode 16 and the lower electrode 19 formed on the arm portion 8 are connected to each other. When a potential is applied between them, an electric field is intensively applied to the well layer 12 having a high resistivity, and the refractive index of the well layer 12 that is the I layer of the PIN structure changes due to the electrooptic effect of the PIN structure.

  The thickness of the P-type InP layer 13 constituting the optical waveguide is 2.1 μm, and the light traveling direction (from the input port 4 to the output port) between the two Y-shaped branch portions 6 and the two arm portions 8 is determined. The width E (refer to FIG. 10) of the optical waveguide in the direction orthogonal to the direction of light traveling along the optical waveguide of the optical circuit 2 between 2 and 7 is 2 μm and the height H3 μm (FIG. 11, FIG. 12), the center-to-center distance K (see FIG. 10) between the first arm portion 8a and the second arm portion 8b is 20 μm.

In the semiconductor Mach-Zehnder type optical modulator having such a configuration, when light having a wavelength of 1.56 μm is input to the input port 4, the light is split into two arm portions 8 by 50% each by the Y-shaped branching portion 6 on the input side. Distributed.
At this time, the lower electrode 19 is used as a ground, and one arm portion 8, for example, the first electrode 16a on the first arm portion 8a is set to the ground via the electrode pad 17, and the other second arm portion 8b is provided. When a voltage is applied to the second electrode 16b via the electrode pad 17, an electric field is applied to the well layer 12 of the second arm portion 8b, and the refractive index of the well layer 12 changes to substantially change the optical waveguide. When the optical path length changes, the phase of the light waveform changes, and the light from the first arm portion 8a and the second arm portion 8b is guided to the output Y-shaped branching portion 6 and multiplexed. When the lights from the two arm portions 8 are combined and the two lights are in the same phase, the light of the original intensity is output from the output port 7 and the two lights are in opposite phases (the phase is shifted by 180 degrees). In the case of the above, light having an intensity of “0” is output from the output port 7 and If the supply voltage signal 16, modulated light is output accordingly.

A semiconductor Mach-Zehnder type modulator having the above-described configuration is disclosed in Patent Document 1, for example.
JP 2000-66156 (paragraphs 0009-0010, FIG. 1)

  However, in the above-described conventional technique, the first and second electrodes 16a and 16b formed on the first and second arm portions 8a and 8b are not connected to the first and second arm portions 8a and 8b. Since it is connected by the P-type InP layer 13 on the well layer 12 formed in the Y-shaped branching portion 6 connected to both ends, it is usually 0.5 Ωcm on both sides of the first electrode 16a and the second electrode 16b. A conductive circuit (see FIG. 8) is formed to electrically connect the first electrode 16a and the second electrode 16b through the P-type InP layer 13 formed with a certain resistivity. When different potentials are applied to the electrode 16a and the second electrode 16b, a leakage current flows due to the potential difference, and the planned electric field cannot be applied to the first arm portion 8a and the second arm portion 8b. The refractive index of the well layer 12 is Not change the image as the modulation operation in the semiconductor Mach-Zehnder optical modulator device becomes unstable.

This is one factor that hinders the practical use of semiconductor Mach-Zehnder type optical modulators.
Therefore, if the impurity concentration of the P-type InP layer is lowered to increase the resistivity and the current flowing through the P-type InP layer is reduced, when an electric field is applied to the PIN structure, the well layer that is the I layer is applied to the well layer. It becomes difficult for the electric field to concentrate, and the change in the refractive index is suppressed, thereby reducing the efficiency of the modulation operation.

  The present invention has been made to solve the above-described problems, and an object of the present invention is to provide means for preventing a leakage current generated between two electrodes of a semiconductor Mach-Zehnder type optical circuit.

  In order to solve the above-mentioned problem, the present invention is formed by two branch portions that branch an optical waveguide in two directions, and first and second arm portions that connect between the branched optical waveguides. An optical circuit, and the optical waveguide includes a first clad layer made of a first conductivity type semiconductor, a well layer formed on the first clad layer, and the first clad layer formed on the well layer. A second clad layer made of a second conductivity type semiconductor opposite to the one conductivity type is laminated and electrically connected to the second clad layer of the first and second arm portions. In the semiconductor Mach-Zehnder type optical circuit in which the first and second electrodes are formed, the first and second arm portions in the regions on both sides of the first and second electrodes are connected to both ends thereof, respectively. Formed from the first electrode to the second At least a portion except immediately below each of the second cladding layer electrodes leading to the electrodes, characterized in that the formation of the third cladding layer of a first conductivity type semiconductor.

  Thus, according to the present invention, a potential barrier by a PN junction can be formed in the second cladding layer on the well layer that forms the conductive circuit between the first electrode and the second electrode. Even if a potential difference is generated between the first electrode and the second electrode, an effect is obtained that the occurrence of a leakage current can be prevented by the formed potential barrier.

  Embodiments of a semiconductor Mach-Zehnder optical circuit according to the present invention and a method for manufacturing the same will be described below with reference to the drawings.

FIG. 1 is an explanatory view showing the upper surface of the semiconductor Mach-Zehnder type optical modulator of the embodiment, FIG. 2 is an explanatory view showing a cross section along the AA cross section line of FIG. 1, and FIG. FIG. 4 and FIG. 5 are explanatory views showing a method of manufacturing the semiconductor Mach-Zehnder type optical modulator of the embodiment.
The parts similar to those in FIGS. 10 to 12 are given the same reference numerals, and the description thereof is omitted.

4 and 5 are cross-sectional views showing the same cross section as FIG. 2 on the left side and the same cross section as FIG. 3 on the right side.
In FIGS. 1 and 3, reference numeral 21 denotes an N-type InP layer as a third cladding layer. A P-type InP layer 13 constituting an optical waveguide of two Y-shaped branch portions 6 on the input side and the output side is changed to a P-type. Is a first conductive type semiconductor layer formed by inverting the N type of the opposite conductivity type, and functions as an optical covering layer that prevents leakage of light guided to the well layer 12.

Also, the N-type InP layer 21 is formed so that the equivalent refractive index to the P-type InP layer 13 constituting the optical waveguide of the arm portion 8 is equal by adjusting the impurity concentration to be implanted.
As shown in FIG. 3, the contact layer 14 on the N-type InP layer 21 in the branch 5 of the Y-shaped branch 6 of this embodiment is removed.
The configuration of the second arm portion 8b below the second electrode 16b shown in FIG. 2 is the same as the configuration of the first arm portion 8a below the first electrode 16a. The configuration is the same.

  The P-type InP layer 13 and the N-type InP layer 21 constituting the optical waveguide of the present embodiment are formed to have a thickness of 1.6 μm, and the two Y-shaped branch portions 6 and 2 in the direction perpendicular to the light traveling direction are formed. The width E (see FIG. 1) of the optical waveguide with the two arm portions 8 is 2 μm, the height H is 2.6 μm (see FIGS. 2 and 3), and the first arm portion 8a and the second arm portion 8b The center-to-center distance K (see FIG. 1) is 20 μm, and the length of the light traveling direction is 800 μm.

Further, the carrier concentration of the P-type InP layer 13 of this example is 5 × 10 ¹⁷ / cm ³ and the resistivity is 0.06 Ωcm.
4 and 5, reference numeral 25 denotes a resist mask as a mask member. A positive or negative resist applied by spin coating or the like to the front surface side of the N-type InP substrate 3 by photolithography is applied to an ultraviolet ray. Is a mask pattern formed by the exposure and development processes according to the above, and functions as a mask in the etching process and ion implantation process of this embodiment.

A method for manufacturing the semiconductor Mach-Zehnder optical modulator of this embodiment will be described below in accordance with the process indicated by P in FIGS.
An N-type InP substrate 3 having a thickness of P1 (FIG. 4) and a thickness of 100 μm is prepared, and a well layer 12 is epitaxially grown on the front surface by a metal organic chemical vapor deposition method (MDCVD method). A P-type InP layer 13 is epitaxially grown by MDCVD method to which a P-type impurity (zinc in this embodiment) is added, and a contact layer 14 is epitaxially grown on the P-type InP layer 13 by MDCVD method. A well layer 12, a P-type InP layer 13, and a contact layer 14 are stacked in this order.

P2 (FIG. 4), a resist mask 25 is formed on the contact layer 14 by photolithography to cover the formation region of the optical circuit 2 including the two Y-shaped branch portions 6 and the first and second arm portions 8a and 8b. Then, using this as a mask, the contact layer 14, the P-type InP layer 13, the well layer 12, and the N layer are anisotropically etched by reactive ion etching using a mixed gas of chlorine (Cl ₂ ) and argon (Ar). The surface layer of the type InP substrate 3 is removed by etching, and the optical waveguide of the optical circuit 2 including the N type InP layer 10, the well layer 12, and the P type InP layer 13 and the contact layer 14 are formed on the N type InP substrate 31. The optical circuit 2 is formed.

P3 (FIG. 4), the resist mask 25 formed in the process P2 is removed, a polyimide resin is applied to the entire surface of the N-type InP substrate 31 by spin coating, and this is thermally cured to surround and inside the optical circuit 2. Then, a protective layer 18 is formed, and this is planarized to expose the contact layer 14.
Then, a gold-zinc alloy is deposited on the protective layer 18 and the contact layer 14 by sputtering to form a conductive material layer, and the first and first layers are formed on the protective layer 18 and the contact layer 14 by photolithography. A resist mask 25 (not shown) is formed to cover the formation regions of the two electrodes 16a and 16b, and the conductive material layer is etched by anisotropic etching using the resist mask 25 as a mask to form the first and second convex shapes. Two electrodes 16a and 16b are formed.

  After removal of the resist mask 25, titanium, platinum, and gold are sequentially deposited on the protective layer 18 and the electrode 16 by sputtering to form a multilayer film, and the first and second convex shapes are formed by photolithography. A resist mask 25 (not shown) that covers the formation region of each electrode pad 17 on the protruding portions of the second electrodes 16a and 16b is formed, and using this as a mask, the multilayer film is etched by anisotropic etching, An electrode pad 17 is formed on the protruding portions of the convex first and second electrodes 16a and 16b, and the resist mask 25 is removed.

P4 (FIG. 4), a resist mask 25 exposing the contact layer 14 of the two Y-shaped branch portions 6 on the input side and the output side is formed on the protective layer 18 and the contact layer 14 by photolithography, Using this as a mask, the contact layer 14 is etched away by anisotropic etching, and the P-type InP layer 13 under the contact layer 14 is exposed.
P5 (FIG. 5), N-type impurity (silicon in this embodiment) ions are then applied to the exposed P-type InP layer 13 by ion implantation, leaving the resist mask 25 formed in step P4 as it is. An N type in which a dose amount of 5 × 10 ¹⁴ ions / cm ² and an acceleration energy of 1.1 MeV are implanted and activated by heat treatment at 500 ° C. for 60 seconds by a lamp annealing method, and the P type InP layer 13 is inverted to the N type. An InP layer 21 is formed.

The silicon ions implanted at this time have an impurity concentration of 5 × 10 ¹⁷ atoms / cm ³ or more up to a depth of about 1.6 μm corresponding to the thickness of the P-type InP layer 13 after activation, as shown in FIG. An N-type InP layer 21 that reaches the well layer 12 is formed.
The resist mask 25 formed in P6 (FIG. 5) and process P4 is removed, and a lower electrode 19 is formed by depositing a nickel-germanium-gold alloy on the back surface of the N-type InP substrate 3 by sputtering.

In this way, the semiconductor Mach-Zehnder type optical modulator of this embodiment shown in FIGS. 1 to 3 is formed.
In the semiconductor Mach-Zehnder type optical modulator of this embodiment, when light having a wavelength of 1.56 μm is input to the input port 4, the light is distributed to the two arm portions 8 by 50% by the Y-shaped branching portion 6 on the input side. Is done.

  At this time, the lower electrode 19 is grounded, one arm part 8, for example, the first electrode 16a on the first arm part 8a is grounded, and the second electrode 16b on the other second arm part 8b is grounded. When a voltage signal is applied, an electric field corresponding to the voltage signal is applied to the well layer 12 constituting the optical waveguide of the second arm portion 8b, and the refractive index of the well layer 12 changes according to the voltage signal, thereby When a change occurs in the phase of the waveform and light from the first arm portion 8a and the second arm portion 8b is guided to the Y-shaped branching portion 6 on the output side and combined, the two arm portions 8 The lights are combined, and the light modulated according to the phase shift is output from the output port 7.

  In this case, as shown in FIG. 7, the P-type InP layer 13 on the well layer 12 constituting the optical waveguide of the optical circuit 2 of the present embodiment extends from the first electrode 16a to the second electrode 16b. An N-type InP layer 21 having a conductivity type opposite to that of the P-type InP layer 13 is formed on the well layer 12 of the Y-shaped branch portion 6 forming the conductive circuit (see FIG. 8). Even if a potential barrier corresponding to the band gap of the PN junction is formed in the P-type InP layer 13 that forms the conductive circuit, and a potential difference occurs between the first electrode 16a and the second electrode 16b, the PN In addition to preventing leakage current from being generated by the potential barrier caused by the junction, leakage current is generated even if the resistivity of the P-type InP layer 13 under the electrode 16 is set to 0.06 Ωcm lower than the conventional resistivity of 0.5 Ωcm. No, electrode 16 and lower electrode When a voltage is applied to the well layer 12, an electric field can be more concentratedly applied to the well layer 12, and the efficiency of the modulation operation in the semiconductor Mach-Zehnder optical modulator can be improved.

In this case, the well layer 12 which is an I layer having a PIN structure is formed with a high resistivity and therefore does not form a current path. The N-type InP substrate 3 sandwiches the well layer 12 between the electrode 16 and the well layer 12. Therefore, there is no current path, and since the contact layer 14 on the N-type InP layer 21 is removed, there is no current path.
In addition, the N-type InP layer 21 on the well layer 12 constituting the optical waveguide of the Y-branch portion 6 on each of the input side and the output side in this embodiment is on the well layer 12 constituting the optical waveguide of the arm portion 8. The P-type InP layer 13 is formed so as to have an equivalent refractive index, so that no light is reflected at the interface between the N-type InP layer 21 and the P-type InP layer 13 and is guided to the optical waveguide. Loss of light that is lost can be prevented.

  Furthermore, in the manufacturing method of this example, the N-type impurity is implanted into the P-type InP layer 13 on the well layer 12 using the resist mask 25 formed for etching the contact layer 14 in step P4 as it is. Since the N-type InP layer 21 is formed by inverting the conductivity type, an increase in steps for improving the efficiency of the modulation operation of the semiconductor Mach-Zehnder optical modulator can be minimized.

  In the present embodiment, it has been described that the N-type InP layer 21 is formed on all the well layers 12 of the two Y-shaped branch portions 6 disposed at both ends of the two arm portions 8. An N-type InP layer 21 may be formed on a part of each well layer 12 of the branch portion 6, and the arms on both sides of the electrode 16 excluding the region below the electrode 16 formed on the arm portion 8. The N-type InP layer 21 may be formed on a part of the well layer 12 of the portion 8. In short, as shown in FIG. 8, the first and second arms in the regions on both sides of the first and second electrodes 16a and 16b except for the region immediately below the first and second electrodes 16a and 16b. Two conductors indicated by thick solid lines with arrows in FIG. 8 from the first electrode 16a to the second electrode 16b, which are formed by the portions 8a and 8b and the Y-shaped branching portion 6 that connects the both ends thereof. An N-type InP layer 21 made of an N-type semiconductor reaching the well layer 12 may be formed on part or all of the P-type InP layer 13 constituting the circuit.

In this case, it is preferable that the resist mask 25 formed in the step P4 is a resist mask 25 in which a part or all of the contact layer 14 of the conductive circuit is exposed.
In this way, even if a potential barrier is formed between each of the two conductive circuits by the N-type InP layer 21 due to the PN junction and a potential difference is generated between the first electrode 16a and the second electrode 16b. The leakage current generated between these electrodes 16 can be prevented.

  As described above, the present embodiment includes the optical circuit 2 in which the two branch portions having branch branches that branch the optical waveguide in two directions are connected by the optical waveguides of the first and second arm portions. In the semiconductor Mach-Zehnder type optical circuit, the first and second arm portions in the regions on both sides of the first and second electrodes formed on the first and second arm portions are connected to both ends thereof, respectively. By forming the N-type InP layer on at least a part of the P-type InP layer formed from the first electrode to the second electrode on the well layer constituting the optical waveguide with the character branching portion, the first A potential barrier by a PN junction can be formed in a P-type InP layer on a well layer that forms a conductive circuit between the first electrode and the second electrode, and the first electrode and the second electrode Even if there is a potential difference between them, the potential barrier formed Thus, it is possible to prevent the occurrence of leakage current.

In the above embodiment, the branching portion of the optical circuit 2 of the optical modulator has been described as a Y-shaped branching portion. However, the multimode interference coupling unit 30 shown in FIG. 9 is used as the branching portion. May be.
The multimode interference type coupling unit 30 causes the light input from the input port 4 to interfere with each other inside the multimode interference type coupling unit 30, and an exit to the arm unit 8 is formed on a waveform peak formed thereby. And has a function of branching the optical waveguide in two directions, and a function of combining the light from the two arm portions 8 by the reverse action and outputting the light from the output port 7.

  In this case, when the N-type InP layer 21 of this embodiment is formed, as shown in FIG. 9, the first and second electrodes 16a excluding the regions under the first and second electrodes 16a and 16b are used. , 16b, the first and second arm portions 8a, 8b, and the multi-mode interference type coupling portion 30 that connects both ends of the first and second arm portions 8a, 8b, respectively. An N-type InP layer 21 made of an N-type semiconductor reaching the well layer 12 is formed on a part or all of the P-type InP layer 13 constituting the two conductive circuits indicated by thick solid lines with arrows in FIG. 9 reaching the electrode 16b. What is necessary is just to form.

  In the above embodiments, the optical device including the semiconductor Mach-Zehnder type optical circuit is described as an optical modulator. However, the optical device including the semiconductor Mach-Zehnder type optical circuit is not limited to the above, and is input from the input port. An optical switch that outputs the light of a specific wavelength from the input light by combining an optical switch that outputs the output light from the output port by turning on and off the semiconductor Mach-Zehnder optical circuit. Etc.

Further, in the above embodiment, the semiconductor forming each part is described as a compound semiconductor, but a silicon semiconductor may be used.
Furthermore, in the above embodiment, the first conductivity type is N type and the second conductivity type is P type. However, the first conductivity type may be P type and the second conductivity type may be N type. The same effects as described above can be obtained.

Explanatory drawing which shows the upper surface of the semiconductor Mach-Zehnder type optical modulator of an Example Explanatory drawing which shows the cross section along the AA cross section line of FIG. Explanatory drawing which shows the cross section along the BB cross section line of FIG. Manufacturing method of semiconductor Mach-Zehnder type optical modulator of embodiment Manufacturing method of semiconductor Mach-Zehnder type optical modulator of embodiment The graph which shows the simulation result of the implantation depth distribution of the silicon ion to the InP layer of an Example Explanatory drawing which shows the effect | action of the conductive circuit of an Example Explanatory drawing which shows the other formation state of the N-type InP layer of an Example Explanatory drawing which shows the other aspect of the semiconductor Mach-Zehnder type optical modulator of an Example Explanatory drawing showing the top surface of a conventional semiconductor Mach-Zehnder optical modulator Explanatory drawing which shows the cross section along CC sectional line of FIG. Explanatory drawing which shows the cross section along the DD cross section line of FIG.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Semiconductor Mach-Zehnder type optical modulator 2 Optical circuit 3 N-type InP substrate (semiconductor substrate)
4 Input Port 5 Branch Branch 6 Y-shaped Branch Port 7 Output Port 8 Arm Portion 8a First Arm Portion 8b Second Arm Portion 10, 21 N-type InP Layer 12 Well Layer 13 P-type InP Layer 14 Contact Layer 16 Electrode 16a 1st electrode 16b 2nd electrode 17 Electrode pad 25 Resist mask 30 Multimode interference type coupling | bond part

Claims (8)

An optical circuit formed by two branch portions that branch the optical waveguide in two directions, and first and second arm portions that connect between the branched optical waveguides;
The optical waveguide includes a first clad layer made of a first conductivity type semiconductor, a well layer formed on the first clad layer, and the first conductivity type formed on the well layer. First and second layers formed by laminating a second clad layer made of an inverted second conductivity type semiconductor and electrically connected to the second clad layer of the first and second arm portions. In the semiconductor Mach-Zehnder type optical circuit in which the electrodes are formed,
A first electrode to a second electrode formed by the first and second arm portions in the regions on both sides of the first and second electrodes and the branch portions connecting the both ends thereof, respectively. A semiconductor Mach-Zehnder type optical circuit, wherein a third clad layer made of a first conductivity type semiconductor is formed on at least a part of the second clad layer that extends to each of the second clad layer except directly under the electrode. In claim 1,
A semiconductor Mach-Zehnder type optical circuit, wherein the branch portion is formed of a Y-shaped branch portion. In claim 1,
A semiconductor Mach-Zehnder optical circuit, wherein the branching section is a multimode interference coupling section. In any one of Claims 1 to 3,
A semiconductor Mach-Zehnder optical circuit, wherein the second and third cladding layers are formed of a compound semiconductor. Manufacture of a semiconductor Mach-Zehnder type optical circuit comprising an optical circuit formed by two branch parts for branching an optical waveguide in two directions and first and second arm parts connecting between the branched optical waveguides In the method
Preparing a semiconductor substrate made of a first conductivity type semiconductor;
Forming a well layer on the semiconductor substrate;
Forming a second clad layer made of a second conductivity type semiconductor opposite to the first conductivity type on the well layer;
Forming a contact layer made of a second conductivity type semiconductor having a higher concentration than the second cladding layer on the second cladding layer;
Etching the contact layer, the second cladding layer, the well layer, and the surface layer of the semiconductor substrate in a region excluding the optical circuit formation region, and a first cladding layer made of a first conductivity type semiconductor; and Forming an optical circuit comprising an optical waveguide in which the well layer and the second cladding layer are laminated, and the contact layer;
Forming first and second electrodes on the contact layers of the first and second arm portions;
A first electrode to a second electrode formed by the first and second arm portions in the regions on both sides of the first and second electrodes and the branch portions connecting the both ends thereof, respectively. Removing at least part of the contact layer on each second cladding layer leading to the second cladding layer,
Injecting a first conductivity type impurity into the exposed second clad layer, inverting the conductivity type of the second clad layer, and forming a third clad layer made of the first conductivity type semiconductor. And a method of manufacturing a semiconductor Mach-Zehnder type optical circuit.   An optical modulator comprising the semiconductor Mach-Zehnder optical circuit according to any one of claims 1 to 4.   An optical switch comprising the semiconductor Mach-Zehnder optical circuit according to any one of claims 1 to 4.   An optical filter comprising a combination of a plurality of semiconductor Mach-Zehnder optical circuits according to any one of claims 1 to 4.

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