JP4283079B2 - Semiconductor optoelectronic waveguide - Google Patents

Description

  The present invention relates to a semiconductor optoelectronic waveguide, and more particularly to a semiconductor optoelectronic waveguide having an electrical isolation region structure of an optoelectronic waveguide using a nin type heterostructure and used for an ultrafast optical modulator in a long wavelength band. Is.

In recent years, large-capacity optical communication systems have transmitted optical signals modulated at a high speed of Gbit / s or higher. However, the longer the distance, the more likely the influence of the dispersion effect of the optical fiber occurs. It is necessary to use an optical signal with a small amount or controlled wavelength chirping. For this purpose, an optical signal is generated not by direct modulation of the laser diode but by a configuration in which a laser diode that is normally operated in direct current and an external modulator are combined. A conventional typical external modulator used for long-distance transmission is an LN modulator composed of a LiNbO ₃ (LN) waveguide.

  The principle of operation of this type of optical modulator is that the optical waveguide is coupled with an electrical waveguide (photoelectron waveguide) to apply a refractive index change based on the electro-optic effect, and the input electrical signal is transmitted via the refractive index change. It is possible to function as an optical switch having a higher function by combining a light intensity modulator with an optical phase modulator or a Mach-Zehnder interferometer, or by combining a number of waveguides. .

However, since LNbO ₃ is a dielectric material, the LN modulator requires advanced manufacturing techniques for stabilizing the material surface and processing the waveguide. Further, it is necessary to use special photolithography having a relatively long waveguide length and different from that of a normal semiconductor process. Further, the size of the package for mounting the LN modulator must be increased. For this reason, the manufacturing cost of the LN modulator module is high, and the size of the optical transmitter is relatively large.

  There is also a semiconductor optical modulator using the same operating principle as the LN modulator. Using a GaAs optical modulator or hetero pn junction with a Schottky electrode in semi-insulating GaAs and using it as a photoelectron waveguide, a voltage is effectively applied to the core portion of the waveguide along with light confinement. InP / InGaAsP optical modulator and the like. However, these semiconductor optical modulators have a problem that the former has a long waveguide length and a large electric loss, and the latter has a problem that the light absorption of the p-cladding layer is large and the waveguide cannot be made long. There is a problem that cannot be lowered. Recently, as a structure for avoiding these problems, a structure in which the clad layers on both sides of the InP / InGaAsP optical modulator are n-type (so-called nin-type structure) has been proposed.

  FIG. 4 is a configuration diagram of a conventional semiconductor optical modulator having a nin-type structure. In FIG. 4, reference numeral 41 denotes an n-type third semiconductor clad layer, 42 denotes a p-type fifth semiconductor clad layer, and 43 denotes a first semiconductor clad layer. 1 is a semiconductor core layer having an electro-optic effect, 45 is a second semiconductor cladding layer, 46 is an n-type fourth semiconductor cladding layer, 47 and 48 are n-electrodes, and 49 is a concave etching. The electric isolation area | region formed by is shown. Although an electrical isolation structure in which a semi-insulating semiconductor is regrown on the concave etched portion has been reported (see, for example, Patent Document 1), the structure becomes more complicated. Absent.

  On the n-type third semiconductor clad layer 41, a p-type fifth semiconductor clad layer 42 and a first semiconductor clad layer 43 are sequentially laminated, and the first semiconductor clad layer 43 and the second semiconductor clad layer 43 are stacked. A semiconductor core layer 44 having an electro-optic effect is provided so as to be sandwiched between the semiconductor clad layer 45. Further, an n-type fourth semiconductor cladding layer 46 having an electrical isolation region 49 formed by concave etching is laminated on the second semiconductor cladding layer 45. An electrode 48 is provided on the fourth semiconductor clad layer 46, and electrodes 47 are provided on both sides of the convex portion of the third semiconductor clad layer 41.

  In the waveguide structure shown in FIG. 4, since the electrical isolation region 49 is provided by etching a part of the n-type InP cladding layer 46 into a concave shape, the light propagation mode changes at the portion where the thickness of the cladding layer changes. As a result, light scattering loss occurred. In the conventional waveguide structure, the etching of the fourth semiconductor clad layer 46 is relatively deep, and its controllability is a problem.

JP 2003-177368 A

  However, in the typical structure of this nin-type InP / InGaAsP optical modulator, the electrical separation between the waveguide portion (modulation portion) for modulation and the connection waveguide portion outside thereof is performed by partially separating the upper n-cladding layer 46. Since this is done by removing a part of the groove, the concave portion 49 is generated in the waveguide. This has a problem that an optical loss due to a change in the propagation mode of light occurs from the connection waveguide to the electrical isolation region portion and from the electrical isolation region portion to the main waveguide portion. Furthermore, since it is necessary to leave a high-resistance cladding layer having a certain thickness or more immediately below the electrical isolation region portion (concave portion), the high-resistance cladding layer is thinned so that an electric field is effectively applied to the semiconductor core layer 44. There is also a problem that it cannot be applied (modulation efficiency is poor).

  The present invention has been made in view of such problems, and an object of the present invention is to provide an electrical separation unit formed between the modulation unit connection conductor of the nin-type InP / InGaAsP optical modulator waveguide. An object of the present invention is to provide a semiconductor optoelectronic waveguide that solves the problems of optical loss and modulation efficiency caused by the structure and realizes a structure that further reduces the driving voltage of the modulator.

  The present invention has been made to achieve such an object, and the invention according to claim 1 includes a semiconductor core layer having an electro-optic effect, and a semiconductor core layer sandwiched between the upper and lower sides of the semiconductor core layer. A first semiconductor clad layer having a larger band gap than the first layer, a third semiconductor clad layer disposed under the first semiconductor clad layer and including an n-type dopant, and the second semiconductor A semiconductor optoelectronic waveguide comprising a semiconductor heterostructure stack including at least a fourth semiconductor cladding layer disposed on the cladding layer, wherein the first and third semiconductor cladding layers are disposed on the substrate side. A fifth semiconductor layer containing a p-type dopant and having a larger band gap than the semiconductor core layer is inserted between the first semiconductor clad layer and the third semiconductor clad layer; An n-type main region is formed in a part of the fourth semiconductor clad layer, and other regions maintain high resistance, and the n-type main region of the fourth semiconductor clad layer and the third semiconductor clad Each of the layers is provided with an independent electrode, and a voltage is applied to the semiconductor core layer.

  According to a second aspect of the present invention, in the first aspect of the present invention, the donor concentration of the n-type main region of the fourth semiconductor cladding layer is distributed in the vertical cross section of the waveguide, and the center of the waveguide It is characterized in that the donor concentration of the part is a convex shape protruding to the semiconductor core layer side.

  According to a third aspect of the present invention, in the first or second aspect of the present invention, the n-type main region of the fourth semiconductor clad layer is opposite to the high-resistance region of the fourth semiconductor clad layer. Further, two n-type regions and an n electrode are formed on the side, and the n electrode is connected to the n electrode of the third semiconductor clad layer.

  As described above, according to the present invention, the optical loss and the modulation efficiency caused by the structure of the electrical separation portion formed between the modulation portion connecting conductor of the nin-type InP / InGaAsP optical modulator waveguide are reduced. It is possible to provide a semiconductor optoelectronic waveguide which solves the problem of being bad and realizes a structure for further reducing the driving voltage of the modulator.

  In addition, compared with the conventional electrical isolation region due to the formation of recesses, it does not significantly affect the propagation of the optical mode, solves the problem of optical loss, and stably controls the light modulation unit and the electrical isolation region. It is possible to provide a semiconductor optoelectronic waveguide having:

  In addition, an electric field can be effectively applied to the core portion without changing the electric signal propagation speed and impedance of the waveguide, thereby reducing the operating voltage required for modulation.

  In addition, it is effective in stably realizing the characteristics of optical modulators using nin-type heterostructures with low drive voltage characteristics, and optical modulation is achieved through reduction of input optical power and electrical input signal power. This can contribute to lower power consumption and cost of the module.

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

  FIG. 1 is a configuration diagram for explaining a first embodiment of a semiconductor optoelectronic waveguide according to the present invention, in which reference numeral 11 denotes an n-type third semiconductor cladding layer, and 12 denotes a p-type fifth semiconductor cladding. 13 is a first semiconductor clad layer, 14 is a semiconductor core layer having an electro-optic effect, 15 is a second semiconductor clad layer, 16 is a fourth semiconductor clad layer, and 17 is a fourth semiconductor clad layer 16. N-type portions (light modulation waveguide portions) 18 and 19 indicate n electrodes.

  A p-type fifth semiconductor cladding layer 12 and a first semiconductor cladding layer 13 are sequentially stacked on the n-type third semiconductor cladding layer 11, and the first semiconductor cladding layer 13 and the second semiconductor cladding layer 13 are stacked. A semiconductor core layer 14 having an electro-optic effect is provided so as to be sandwiched between the semiconductor cladding layers 15. Further, a fourth semiconductor clad layer 16 having an n-type portion (light modulation waveguide portion) 17 is laminated on the second semiconductor clad layer 15. An electrode 19 is provided on the fourth semiconductor clad layer 16, and electrodes 18 are provided on both sides of the convex portion of the third semiconductor clad layer 11.

  That is, the semiconductor optoelectronic waveguide of the present invention includes the semiconductor core layer 14 having an electro-optic effect, and the first and second semiconductors sandwiching the upper and lower sides of the semiconductor core layer 14 and having a band gap larger than that of the semiconductor core layer 14. Cladding layers 13 and 15, a first semiconductor clad layer 13 disposed below the first semiconductor clad layer 13, and a third semiconductor clad layer 11 including an n-type dopant and a second semiconductor clad layer 15 disposed on the second semiconductor clad layer 15. 4 of a semiconductor heterostructure including at least four semiconductor clad layers 16.

  First and third semiconductor clad layers 13 and 11 are disposed on the substrate (not shown) side, and a p-type dopant is included between the first semiconductor clad layer 13 and the third semiconductor clad layer 11. In addition, the fifth semiconductor layer 12 having a larger band gap than the semiconductor core layer 14 is inserted, an n-type main region is formed in a part of the fourth semiconductor cladding layer 16, and the other region has a high resistance. In addition, the n-type main region of the fourth semiconductor clad layer 16 and the third semiconductor clad layer 11 are provided with independent electrodes, respectively, so that a voltage is applied to the semiconductor core layer 14.

  As described above, from the substrate side (not shown), the third InPn-type clad layer 11, the fifth InP clad layer 12 containing the p-type dopant, and the first InGaAlAs clad layer 13 usually having a low doping concentration. And a semiconductor core layer 14 whose structure is determined so that the electro-optic effect works effectively at the operating light wavelength and the light absorption does not become a problem. If it exists, it has a multiple quantum well structure in which the Ga / Al composition layer of InGaAlAs is changed into a quantum well layer and a barrier layer, respectively.

  Furthermore, a low doping concentration second InGaAlAs cladding layer 15 and a fourth high resistance InP cladding layer 16 are disposed on the semiconductor core layer 14. A voltage is applied to the electrode 18 with the electrode 19 as a positive polarity. In the applied voltage range used in the operating state, the fifth InP cladding layer 12 to the second InP cladding layer 15 are all depleted, and the n-type InP cladding layer 16 is only partially depleted. Since the fifth InP clad layer 12 is p-type, it acts as a potential barrier against electrons, so that it is possible to apply a voltage to the core layer with little leakage current. In this n-type InP region, for example, after the layers from the third semiconductor clad layer 11 to the fourth semiconductor clad layer 16 are grown, the portion corresponding to the reference numeral 17 is removed by etching, and the n-type InP is regrown, or It can be formed by introducing Si donor into a part of the fourth semiconductor clad layer 16 by ion implantation.

  In order for this device to function as an optoelectronic waveguide, an electric signal is input to the electrode 18 in a state where light is propagated in a direction perpendicular to the cross section of the mesa structure shown in FIG. 1, and the third InPn clad layer 11 and A voltage is applied between the second InP cladding layers 15 and the optical phase is modulated based on the electro-optic effect. Normally, when an optoelectronic waveguide is used as an optical modulator, a light modulation waveguide portion to which a voltage is applied from the electrode 19 and a connection waveguide are arranged on the light input / output side of the light modulation waveguide portion, It is necessary to electrically separate them.

  In the structure of the first embodiment, the portion indicated by reference numeral 17 is selectively an n-type region, and the fourth semiconductor cladding layer 16 has a high resistance, so that the light propagation mode is affected. The electric input can be applied to the light modulation waveguide portion without giving. That is, in the conventional waveguide structure shown in FIG. 4, since the electrical isolation region 49 is provided by etching a part of the n-type InP cladding layer 46 into a concave shape, the light propagation occurs at the portion where the thickness of the cladding layer changes. A mode change occurred, resulting in a light scattering loss. On the other hand, in the structure of the first embodiment, since the shape of the waveguide is maintained, no light scattering loss accompanying such a change in the light propagation mode occurs. In the conventional structure, the etching of the fourth semiconductor clad layer 46 is relatively deep, and its controllability is a problem. However, in the structure of the first embodiment, the position of the lower surface of the n-type region can be freely set. Therefore, a high electric field can be induced in the semiconductor core layer. As a result, the structure of the first embodiment improves the problem of the conventional optoelectronic waveguide caused by the formation of the electrical isolation region, and increases the output of the optical converter by reducing the optical loss, thereby improving the optical modulation efficiency. Can be raised.

  FIGS. 2A to 2C are configuration diagrams for explaining a second embodiment of the semiconductor optoelectronic waveguide according to the present invention, FIG. 2A is a cross-sectional view, and FIG. 2B is a light propagation mode. FIG. 2C is a diagram showing another example of the second embodiment.

  In the figure, reference numeral 21 denotes an n-type third semiconductor cladding layer, 22 denotes a p-type fifth semiconductor cladding layer, 23 denotes a first semiconductor cladding layer, 24 denotes a semiconductor core layer having an electro-optic effect, and 25 denotes a first semiconductor cladding layer. 2 is a fourth semiconductor cladding layer, 27 and 27a are n-type portions (light modulation waveguide portions) of the fourth semiconductor cladding layer, 27b is a low dielectric constant insulator layer, and 28 and 29 are An n-electrode is shown. The laminated structure other than the light modulation waveguide portions 27, 27a, 27b is the same as that of the first embodiment shown in FIG.

  In the first embodiment described above, the lower surface position of the n-type InP cladding layer of the light modulation waveguide portion 17 is flat. However, in the second embodiment, the upper n-type InP cladding layer that is the light modulation waveguide portion is arranged. The light modulation waveguide portion 27 has a convex shape in which the donor concentration protrudes toward the semiconductor core layer at the center of the waveguide in the vertical cross section of the waveguide. The convex n-type InP region is formed, for example, by growing a layer from the third semiconductor clad layer 21 to the fourth semiconductor clad layer 26 and then removing a portion corresponding to the light modulation waveguide portion 27 by etching. It can be formed by regrowth of InP or by selectively introducing Si donor into a part of the fourth semiconductor clad layer 26 by ion implantation.

  As shown in FIG. 2B, when the donor concentration distribution of the n-type InP cladding layer is convex toward the semiconductor core layer, the electric field intensity distribution of the semiconductor core layer is obtained at the center of the waveguide. Higher and lower at the periphery. Since the electric field intensity distribution in the photoelectric propagation mode is also high at the center of the waveguide, light modulation can be performed more effectively than in the case of the electric field intensity distribution of the flat core layer. That is, if the comparison is made under the condition that the waveguide capacity per unit length is constant (characteristic impedance and electric signal propagation speed is constant), it is better to take a distribution where the capacitance is larger at the center of the waveguide and smaller at the periphery. The integrated value of (light intensity × electric field intensity) per unit waveguide length can be increased. Eventually, the light modulation effect becomes more efficient, and the drive voltage can be lowered with the same waveguide length, and the waveguide length can be shortened with the same drive voltage.

The structure shown in FIG. 2C is a modification of the structure shown in FIG. 2A, in which the light modulation waveguide portion 27a of the upper n-type InP cladding layer is left only in the portion near the center of the waveguide. is there. By inserting a material 27b such as SiO ₂ having a low dielectric constant into a portion where there is no n layer directly under the electrode 29, the capacitance of that portion can be lowered. Eventually, the capacity of the central portion of the semiconductor core layer can be increased by the amount that the capacity of the portion adjacent to the n region decreases, and an electric field can be further applied to the semiconductor core layer.

  FIG. 3 is a block diagram for explaining Example 3 of the semiconductor optoelectronic waveguide according to the present invention, in which reference numeral 31 denotes an n-type third semiconductor cladding layer, and 32 denotes a p-type fifth semiconductor cladding. 33, a first semiconductor clad layer, 34 a semiconductor core layer having an electro-optic effect, 35 a second semiconductor clad layer, 36 a fourth semiconductor clad layer, and 37a an n of the fourth semiconductor clad layer. Shaped portion (light modulation waveguide portion), 37b is a connecting waveguide portion of the fourth semiconductor cladding layer, 38 and 39 are n electrodes, 40a is an electrode formed in the connecting waveguide portion of the fourth semiconductor cladding layer, Reference numeral 40b denotes a wiring in which the connecting waveguide portion of the fourth semiconductor clad layer has the same potential as that of the third clad layer. The laminated structure other than the waveguide portions 37a and 37b, the electrode 40a, and the wiring 40b is the same as that of the first embodiment shown in FIG.

  An n-electrode 39 is formed on a portion of the fourth semiconductor clad layer 36 that opposes the light modulation waveguide portion 27a across the electric isolation region, and this is used as a connection waveguide 37b. And the same potential. When the resistance of the electrical isolation region is not sufficiently high, the potential that the potential outside the electrical isolation region rises and a bias voltage is applied to the main waveguide portion can be eliminated. Here, the conductivity type of the connection waveguide may be p, n, or a depletion layer. This is because in either case, the current does not flow due to the forward bias between the modulation waveguide portion.

  In the above-described embodiments, the embodiments using InP and InAlGaAs as materials are described. However, the embodiments are similarly applied to an optoelectronic waveguide structure using other III-V group compound semiconductors including AlGaAs and InGaAsP. it can. It is needless to say that the optoelectronic waveguide of the present invention can be integrated with a semiconductor laser in the same manner as the technique of integrating with an electroabsorption optical modulator and a semiconductor laser. .

  The present invention relates to a semiconductor optoelectronic waveguide having an electrical isolation region structure of an optoelectronic waveguide using a nin type heterostructure, and used for an ultrahigh speed optical modulator in a long wavelength band, and relates to a nin type InP / InGaAsP optical modulator. To solve the problems of optical loss and poor modulation efficiency caused by the structure of the electrical separation part formed between the modulation part connection waveguide part of the waveguide and to realize a structure that further reduces the drive voltage of the modulator A semiconductor optoelectronic waveguide can be provided.

It is a block diagram for demonstrating Example 1 of the semiconductor optoelectronic waveguide which concerns on this invention. BRIEF DESCRIPTION OF THE DRAWINGS It is a block diagram for demonstrating Example 2 of the semiconductor optoelectronic waveguide based on this invention, (a) is sectional drawing, (b) is the electric field strength of the core part of an optical propagation mode, and the electric field intensity of the core part of an electric signal Distribution diagram (c) is a diagram showing another example of the second embodiment. It is a block diagram for demonstrating Example 3 of the semiconductor optoelectronic waveguide concerning this invention. It is a block diagram of the semiconductor optical modulator which has the conventional nin-type structure.

Explanation of symbols

11, 21, 31 n-type third semiconductor clad layer 12, 22, 32 p-type fifth semiconductor clad layer 13, 23, 33 First semiconductor clad layer 14, 24, 34 Semiconductor having electro-optic effect Core layer 15, 25, 35 Second semiconductor clad layer 16, 26, 36 Fourth semiconductor clad layer 17, 27, 27a, 37a n-type portion (light modulation waveguide portion) of fourth semiconductor clad layer
18, 19, 28, 29, 38, 39 n-electrode 27b low dielectric constant insulator layer 37b connection waveguide portion 40a of fourth semiconductor cladding layer electrode 40b formed on connection waveguide portion of fourth semiconductor cladding layer Wiring for connecting the waveguide portion of the fourth semiconductor clad layer to the same potential as the third clad layer 41 n-type third semiconductor clad layer 42 p-type fifth semiconductor clad layer 43 first semiconductor clad layer 44 Semiconductor core layer having electro-optic effect 45 Second semiconductor clad layer 46 n-type fourth semiconductor clad layer 47, 48 n electrode 49 Electrical isolation region formed by concave etching

Claims (3)

A semiconductor core layer having an electro-optic effect, first and second semiconductor clad layers sandwiching the upper and lower sides of the semiconductor core layer and having a larger band gap than the semiconductor core layer, and under the first semiconductor clad layer And a semiconductor heterostructure stack including at least a third semiconductor clad layer containing an n-type dopant and a fourth semiconductor clad layer arranged on the second semiconductor clad layer. A semiconductor optoelectronic waveguide comprising:
The first and third semiconductor clad layers are disposed on the substrate side, the p-type dopant is included between the first semiconductor clad layer and the third semiconductor clad layer, and the band gap is larger than that of the semiconductor core layer. A large fifth semiconductor layer is inserted,
An n-type main region is formed in a part of the fourth semiconductor clad layer, the other region maintains a high resistance, and the n-type main region of the fourth semiconductor clad layer and the third semiconductor A semiconductor optoelectronic waveguide characterized in that an independent electrode is provided on each of the cladding layers, and a voltage is applied to the semiconductor core layer.   The donor concentration of the n-type main region of the fourth semiconductor clad layer is distributed in a vertical cross section of the waveguide, and the donor concentration at the center of the waveguide is a convex shape protruding to the semiconductor core layer side. The semiconductor optoelectronic waveguide according to claim 1.   Two n-type regions and an n-electrode are further formed on the opposite side of the n-type main region of the fourth semiconductor clad layer across the high-resistance region of the fourth semiconductor clad layer. The semiconductor optoelectronic waveguide according to claim 1, wherein the semiconductor optoelectronic waveguide is connected to the n electrode of a third semiconductor clad layer.

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