JP2005079541A - Semiconductor optical amplifier and its manufacturing method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To obtain a semiconductor optical amplifier realizing a superior element characteristic with a high gain saturation level and a small wave form distortion and having a reliability over a long period of time. <P>SOLUTION: The semiconductor optical amplifier is composed of: a semiconductor substrate 1 having a half insulation; a primary DBR layer 2 and a primary cladding layer 3 which are formed on the semiconductor substrate 1; an activity layer 4 which is formed on the primary cladding layer 3 and has a predetermined width; a primary conductive layer 5 and a secondary conductive layer 6 which are provided respectively so as to contact with both side faces of the activity layer 4 on the primary cladding layer 3; a secondary cladding layer 7 which is provided so as to cover the activity layer 4, the primary conductive layer 5 and the secondary conductive layer 6; a secondary DBR layer 8 which is provided at a position opposite to the activity layer 4 on the secondary cladding layer 7; a primary electrode 9 formed in an etching groove penetrating the secondary cladding layer 7, a bottom face of the etching groove reaching the primary conductive layer 5; and a secondary electrode 10 formed in an etching groove penetrating the secondary cladding layer 7, a bottom face of the etching groove reaching the secondary conductive layer 6. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to a semiconductor optical amplifier used exclusively in an optical communication system and a manufacturing method thereof.

  A semiconductor optical amplifier has a function of optically amplifying input signal light and then outputting it, and is used to compensate attenuation due to scattering, absorption, branching, etc. of an optical signal in a wavelength division multiplexing (WDM) optical fiber communication system. It is done.

  In a semiconductor optical amplifier, waveform distortion caused by relative gain reduction due to gain saturation of the semiconductor optical amplifier that occurs when the optical signal strength is strong, or one wavelength that occurs when optical signals of multiple wavelengths are amplified simultaneously The occurrence of crosstalk in which the amplification factor of the optical signal changes depending on the intensity of the optical signal of the other wavelength has been a big problem in practical use.

  In order to solve such a problem, in the conventional semiconductor optical amplifier disclosed in Patent Document 1 or Non-Patent Document 1, DBR (Distributed Bragg Reflectors) having high reflectivity above and below the active layer with respect to the main surface of the substrate. A reflector is provided, and each DBR layer is formed as a pair of reflectors in the direction perpendicular to the waveguide direction of incident light, and an optical resonator is formed to cause laser oscillation, thereby fixing the gain in the active layer to a constant value. In addition, a constant gain independent of the light intensity of the incident signal light has been realized in a wide wavelength range. In such an element structure, current is injected into the active layer through the lower DBR layer. The element structure is a ridge mesa structure, and the side surface of the active layer is not protected by the semiconductor layer and is exposed to the outside.

US Patent Application Publication No. US2003 / 0095326A1

D. A. Francis et al., “A single-chip linear optical amplifier”, Optical Fiber Communication Conference (OFC) 2001, Post Deadline Paper, PD13

  However, in the conventional semiconductor optical amplifier, since current is passed through the active layer through the DBR layer, heat is generated excessively due to the high resistance of the DBR portion. As a result, the threshold current of laser oscillation by the vertical DBR layer is affected by the heat. There is a problem that the gain saturation level is lowered. In addition, since both sides of the active layer are exposed to the outside due to the ridge mesa structure, there is a large practical problem that the long-term reliability of the semiconductor optical amplifier is impaired by a high operating current.

  The present invention has been made to solve the above-described problems, and prevents current from flowing through the DBR portion to prevent generation of unnecessary heat and protect both side surfaces of the active layer with a semiconductor layer. It is an object of the present invention to provide a semiconductor optical amplifier that achieves excellent device characteristics with a high gain saturation level and low waveform distortion and has long-term reliability, and further to easily provide such a semiconductor optical amplifier. To do.

  A semiconductor optical amplifier according to the present invention includes a semi-insulating semiconductor substrate, a first DBR layer formed on the semiconductor substrate, a first cladding layer formed on the first DBR layer, and the first cladding layer. An active layer having a predetermined width, a first conductive layer and a second conductive layer provided on the first cladding layer so as to be in contact with both side surfaces of the active layer; the active layer; A second cladding layer provided to cover the first conductive layer and the second conductive layer; a second DBR layer provided on the second cladding layer at a position facing the active layer; and the second cladding. A first electrode formed in an etching groove penetrating the layer and having a bottom surface reaching the first conductive layer; and a second electrode formed in an etching groove penetrating the second cladding layer and having the bottom surface reaching the second conductive layer. And so on.

  Since the semiconductor optical amplifier according to the present invention employs a so-called lateral current injection structure, current does not flow through each DBR layer, so that unnecessary heat generation in each DBR layer can be almost completely prevented. Since the laser oscillation threshold current due to the layer is not affected by heat, problems such as an increase in the threshold current due to heat can be avoided, and a decrease in gain saturation level can be effectively prevented, so that a semiconductor optical amplifier having excellent device characteristics can be obtained.

  In the semiconductor optical amplifier according to the present invention, the first conductive layer and the second conductive layer are provided so as to be in contact with both side surfaces of the active layer, and the active layer itself is not exposed to the outside. Therefore, the conventional ridge mesa structure is applied. This is superior in terms of long-term reliability compared to an element structure in which both side surfaces of the active layer are exposed to the outside, such as a semiconductor optical amplifier.

Embodiment 1 FIG.
FIG. 1 is a cross-sectional view (a) and a front view (b) taken along line AA in the cross-sectional view (a) of the semiconductor optical amplifier according to the first embodiment of the present invention. In the figure, 1 is a semi-insulating InP substrate (semi-insulating semiconductor substrate), 2 is a first DBR layer, 3 is a first cladding layer, 4 is an active layer, and 5 is an n-type conductive layer (first conductive layer). , 6 is a p-type conductive layer (second conductive layer), 7 is a second cladding layer, 8 is a second DBR layer, 9 is a first electrode, 10 is a second electrode, and 11 and 12 are a first electrode and a second electrode. Gold wires connected to each.

  The configuration of the semiconductor optical amplifier according to the first embodiment will be described below. On a semi-insulating indium phosphide (InP) substrate 1, a high-resistance first DBR layer 2 made of a semiconductor multilayer film by epitaxial crystal growth, a first cladding layer 3 made of a high-resistance InP crystal, and little polarization dependency An active layer 4 composed of indium gallium arsenide phosphide (InGaAsP) crystal in a tensile strain bulk is sequentially formed. The active layer 4 is undoped and has a predetermined width W optimum for optical waveguide. The width W of the active layer 4 is preferably in the range of 1 to 2 μm. The active layer 4 may have a multiple quantum well structure.

  An n-type conductive layer (first conductive layer) 5 and a p-type conductive layer (second conductive layer) 6 are provided on the first cladding layer 3 so as to be in contact with both side surfaces of the active layer 4. The band gap energy of the semiconductor crystal constituting each conductive layer 5, 6 is set to be larger than the band gap energy of the semiconductor crystal constituting the active layer 4. This is for effectively confining light and carriers in the active layer 4. As a semiconductor crystal material for each of the conductive layers 5 and 6, indium phosphide (InP) is suitable.

  A second cladding layer 7 is formed by epitaxial crystal growth so as to cover active layer 4, n-type conductive layer 5, and p-type conductive layer 6. The second cladding layer 7 is made of a high resistance InP crystal.

  A high-resistance second DBR layer 8 made of a semiconductor multilayer film is provided on the second cladding layer 7 at a position facing the lower active layer 4.

  The second cladding layer 7 is provided with an etching groove whose bottom surface reaches the n-type conductive layer 5 and an etching groove that reaches the p-type conductive layer 6, and each of the etching grooves is made of metal and is electrically connected to the n-type conductive layer 5. The first electrode 9 and the second electrode 10 electrically connected to the p-type conductive layer 6 are respectively provided. The electrodes 9 and 10 are provided with gold wires 11 and 12 for electrical connection with an external power source or the like.

  Next, the operation of the semiconductor optical amplifier according to the first embodiment will be described. When a voltage is applied so that the first electrode 9 is negative and the second electrode 10 is positive, the current flows through the second electrode 10, the p-type conductive layer 6, the active layer 4, the n-type conductive layer 5, and the first electrode 9. It flows in order. Incidentally, such a current injection method is called lateral current injection because a current flows in the active layer 4 in a direction parallel to the main surface of the InP substrate 1. Light emission recombination occurs in the active layer 4 due to the carriers injected into the active layer 4, but the generated light is an optical resonator having the first DBR layer 2 and the second DBR layer 8 as a pair of reflecting mirrors, that is, the semiconductor substrate 1. When light is amplified by an optical resonator in the vertical direction with respect to the main surface and the injection current to the active layer 4 exceeds a predetermined threshold current, laser oscillation occurs between the DBR layers 2 and 8 in the vertical direction.

  The signal light that has entered the active layer 4 from one end face of the semiconductor optical amplifier in this state is amplified as the light is guided through the active layer 4 and then emitted from the other end face to the outside as output light. Is done. Since the gain in the active layer 4 is fixed to a constant value over a wide wavelength range by the laser oscillation between the DBR layers 2 and 8 in the vertical direction, light that does not depend on the light intensity of the incident signal light in a wide wavelength range. Amplification can be realized.

  Since the semiconductor optical amplifier according to the first embodiment employs a so-called lateral current injection structure as described above, it has an element structure in which no current flows in the DBR layer, unlike the conventional semiconductor optical amplifier. That is, the first DBR layer 2 and the second DBR layer 8 are not current paths. Therefore, it is possible to almost completely prevent the generation of unnecessary heat that has conventionally been caused by flowing a current through a DBR layer having a high resistance value, so that the threshold current value of laser oscillation between the respective DBR layers 2 and 8 in the vertical direction is the heat value. As a result, a problem such as an increase in threshold current due to heat is avoided, and as a result, a decrease in gain saturation level can be prevented, so that a semiconductor optical amplifier excellent in device characteristics with small waveform distortion can be obtained. In addition, since each DBR layer is not a current path as described above, it is not necessary to perform impurity doping for the purpose of reducing the resistance. Therefore, the impurity dopant in each DBR layer as generated in the conventional element structure is used. Since the resulting light absorption can be effectively suppressed, the threshold current for laser oscillation can be further reduced.

  In the semiconductor optical amplifier of the first embodiment, the n-type conductive layer 5 and the p-type conductive layer 6 are provided so as to be in contact with both side surfaces of the active layer 4, and the active layer 4 itself is not exposed to the outside. Compared with an element structure in which the side surface is exposed to the outside, such as a semiconductor optical amplifier using the ridge mesa structure, a semiconductor optical amplifier excellent in long-term reliability can be easily obtained.

  In the above description, the first DBR layer 2 and the second DBR layer 8 are composed of semiconductor layers, but either one or both of the DBR layers are composed of a material other than a semiconductor, for example, a dielectric multilayer film. Also good. In a so-called long wave band semiconductor multilayer DBR reflector having a wavelength of 1.3 to 1.55 μm, the difference in refractive index between a high refractive index material (for example, InGaAsP) and a low refractive index material (for example, InP) is small. In order to obtain a high refractive index material, a large number of pairs of a high refractive index material and a low refractive index material must be formed, and the formation of such a semiconductor DBR layer requires a very long crystal growth time. By configuring the DBR layers 2 and 8 with dielectric multilayer films, there is an advantage that the crystal growth time can be greatly shortened and the reflecting mirror can be optimized independently of the active layer 4.

  In the above description, the active layer 4 is undoped, but may be lightly doped. If the active layer 4 is a high-purity undoped crystal layer, the active layer 4 itself acts as a high resistance when current is injected in the lateral direction, and unnecessary heat may be generated. Therefore, it is extremely advantageous in terms of device characteristics to reduce the DC resistance value of the active layer portion by light doping in a range where the light emission quality of the active layer 4 does not deteriorate. The light doping of the active layer 4 is performed at the same time as the epitaxial crystal growth of the active layer 4 or is annealed during or after the crystal growth of the n-type and p-type conductive layers 5 and 6 to enter the undoped active layer 4. This can be realized by a method of promoting thermal diffusion of dopant (drive-in diffusion).

Embodiment 2. FIG.
FIG. 2 is a sectional view of a semiconductor optical amplifier according to the second embodiment of the present invention. In the figure, reference numeral 15 denotes a buffer layer. The semiconductor optical amplifier according to the second embodiment is different from the semiconductor optical amplifier according to the first embodiment in that the active layer 4 and the conductive layers 5 and 6 are interposed between the active layer 4 and the n-type conductive layer 5 and the p-type conductive layer 6. The buffer layer 15 having an intermediate band gap energy is provided. The introduction of the buffer layer 15 can reduce the influence of notches caused by band discontinuity at the heterointerface between the active layer 4 and the conductive layers 5 and 6 in the band diagram. Since the direct current resistance of the layer 4 can be lowered, the heat generation in the active layer 4 during element operation is suppressed, so that a semiconductor optical amplifier having excellent element characteristics and long-term reliability can be obtained.

Embodiment 3 FIG.
FIG. 3 is a cross-sectional view (a) and a front view (b) taken along line BB in the cross-sectional view (a) of the semiconductor optical amplifier according to the third embodiment of the present invention. The semiconductor optical amplifier according to the third embodiment has the same structure as that of the semiconductor optical amplifier according to the first and second embodiments, but a semiconductor layer in which the first DBR layer 2 is grown on a different substrate, for example, AlGaAs on a gallium arsenide (GaAs) substrate. / GaAs multilayer film, and bonded using a substrate bonding technique that has been remarkably developed in recent years (FIG. 3). That is, the upper and lower wafers are separately formed and bonded together with the line CC in FIG.

  By adopting such a method, the choice of the material constituting the first DBR layer 2 is increased. Therefore, it has been difficult to obtain a high-reflectivity reflector with conventional InGaAsP / InP-based materials. Since it is possible to easily reduce the threshold current of laser oscillation by the optical resonator in the vertical direction, heat generation in the active layer 4 during element operation is suppressed, and as a result, good element characteristics are obtained. As a result, a semiconductor optical amplifier excellent in long-term reliability can be obtained.

Embodiment 4 FIG.
FIG. 4 is a top view of a semiconductor optical amplifier according to Embodiment 4 of the present invention. In the figure, 9a and 9b are first electrodes divided into two in the optical waveguide direction, and 10a and 10b are second electrodes similarly divided into two in the optical waveguide direction. In the semiconductor optical amplifier according to the fourth embodiment, the first and second electrodes 9 and 10 in the semiconductor optical amplifier according to the first embodiment are configured by two or more divided electrodes that are electrically separated in the optical waveguide direction. It is characterized in that it is. Although it is difficult to electrically completely separate the first electrodes 9a and 9b or the second electrodes 10a and 10b, the separation resistance between the electrodes is increased to a sufficiently high level for practical use.

  While the signal light is guided through the active layer 4 inside the semiconductor optical amplifier, the stimulated emission light is superimposed and optically amplified. Since the stimulated emission light component increases near the exit end face as compared to near the entrance end face, more carriers are consumed near the exit end face at the same current injection density, and gain saturation is likely to occur. Therefore, by configuring each of the first and second electrodes as a plurality of divided electrodes so that a larger amount of current can be injected into the divided electrode farther from the incident side, it is possible to effectively prevent the gain saturation level from being lowered. . As a result, the optical signal can be amplified with a constant gain up to a high output level, and the device characteristics can be improved.

Embodiment 5 FIG.
FIG. 5 is a cross-sectional view (a) and a front view (b) taken along line DD in the cross-sectional view (a) of the semiconductor optical amplifier according to the fifth embodiment of the present invention. In the figure, 21 is a first conductivity type semiconductor substrate (InP substrate) that also serves as a cladding layer, 22 is an active layer, 23 is a second conductivity type cladding layer (InP cladding layer), 24 is a current blocking layer, and 25 is The DBR layer, 26 indicates a first electrode, and 27 indicates a second electrode.

  In the semiconductor optical amplifier according to the fifth embodiment, as shown in FIG. 5, a rectangular cross section is formed on both side surfaces of the ridge mesa on the semiconductor substrate 21, extending substantially parallel to the ridge mesa and orthogonal to the optical waveguide direction. Low and low refractive index such as periodically arranged semiconductor layers (refractive index 3.2) and air (refractive index 1) or benzocyclobutene (BCB, Benzocyclobutene, refractive index 1.546, not shown) The DBR layer 25 is composed of a pair of conductive polymer materials. An example in which such a DBR layer 25 is used for an end face high reflection mirror of a semiconductor laser is described in J. Org. Wiedmann et al., Jpn. Appl. Phys. Vol. 40 (2001.12) pp6845-6851, Part 1, No. 40. 12.

  The semiconductor optical amplifier according to the fifth embodiment is different from the semiconductor optical amplifier according to the first embodiment in that a DBR layer 25 extending in parallel with the ridge mesa, that is, extending in parallel with the optical waveguide direction is formed. Different. Both side surfaces of the ridge mesa are covered with a current blocking layer 24 made of a semiconductor material such as InP crystal whose band gap energy is larger than that of the active layer 22. After the formation of the ridge mesa, the semiconductor layer 24a embedded and grown by selective crystal growth is removed by predetermined partial etching using a lithography technique and a dry etching technique, and a plurality of semiconductor layers are formed in a direction substantially parallel to the optical waveguide direction and perpendicular to the optical waveguide direction. Are formed in a predetermined cycle, and the DBR layer 25 is formed by filling the grooves between the semiconductor layers with air or with the above-described polymer material or the like. Since the DBR layer 25 has a large difference in refractive index between the semiconductor layer / air and the polymer material, a high reflectance of 95% or more can be obtained with a pair of three cycles or more. The active layer 22 is subjected to vertical current injection, that is, so-called vertical current injection. The active layer 22 given gain by current injection is positioned inside the optical resonator surrounded by the DBR reflector 25 having high reflectivity in the lateral direction, that is, in the direction orthogonal to the optical waveguide direction. As a result, laser oscillation occurs in the lateral direction, and once such laser oscillation occurs, the gain in the active layer 22 is fixed to a constant value, and saturation of the gain level is prevented.

  In the semiconductor optical amplifier of the fifth embodiment, no current is injected into the DBR layer in spite of employing the so-called vertical current injection structure as described above. That is, as in the semiconductor optical amplifier of the first embodiment, the DBR is not injected. Since it has an element structure in which no current flows through the layer, it is possible to almost completely prevent the generation of unnecessary heat generated by flowing current through a DBR layer having a relatively high resistance value. Since the oscillation threshold current value is not affected by heat, problems such as an increase in threshold current due to heat can be avoided, and as a result, a decrease in gain saturation level can be prevented. For example, a semiconductor optical amplifier having excellent device characteristics such as low waveform distortion Is obtained.

  In the semiconductor optical amplifier of the fifth embodiment, since the current blocking layer is provided so as to be in contact with both side surfaces of the active layer and the active layer itself is not exposed to the outside, the semiconductor optical amplifier using the conventional ridge mesa structure is used. A semiconductor optical amplifier excellent in long-term reliability can be easily obtained as compared with the element structure in which the side surface is exposed to the outside.

Embodiment 6 FIG.
FIG. 6 is a front view of an element structure in which an electroabsorption optical modulator is integrated on the incident side with respect to the semiconductor optical amplifier according to the fifth embodiment of the present invention. In the figure, 28 and 29 are gold wires, 32 is a light amplification region, and 33 is a light modulation region. The light amplification region 32 and the light modulation region 33 are electrically separated from each other, and are independently driven by separate electrodes 26, 27 and 30, 31. The signal light generated by the light modulation region 33 is optically amplified by the light amplification region 32.

  In the semiconductor optical modulator of the sixth embodiment, since the wavelength dependence of the gain level of the optical amplification region is extremely small and gain saturation hardly occurs as described above, optical amplification with almost no signal distortion can be performed even at high frequencies. The input signal level in the optical modulation region is stably amplified, modulation with a high S / N ratio is possible, and a semiconductor optical modulator having excellent device characteristics can be obtained.

Embodiment 7 FIG.
FIG. 7 is a schematic diagram showing a series of manufacturing methods of the semiconductor optical amplifier according to the first embodiment of the present invention. A method for manufacturing the semiconductor optical amplifier according to the present embodiment will be described below.

  First, by epitaxial crystal growth, a high-resistance first DBR layer 2 made of a semiconductor multilayer film, a first cladding layer 3 made of a high-resistance InP crystal, and a tension with less polarization dependence are formed on a semi-insulating InP substrate 1. The active layer 4 composed of strained bulk InGaAsP crystal is sequentially formed (FIG. 7A). As the epitaxial crystal growth method, for example, a vapor phase crystal growth method such as MOCVD method or MBE method is suitable.

  After the epitaxial crystal growth, the active layer 4 is processed into a stripe shape having a predetermined width W that is optimal for optical waveguide by lithography and wet or dry etching techniques (FIG. 7B). The width W of the active layer 4 is preferably in the range of 1 to 2 μm.

  The first conductive layer 5 is formed on the first cladding layer 3 so as to be in contact with one side surface of the active layer 4 by selective crystal growth (FIG. 7C). At this time, since an insulating film is formed on the active layer 4 to form a selective growth mask, crystal growth is not performed on the active layer 4. A second conductive layer 6 is formed by a similar method (FIG. 7D).

  Further, the second cladding layer 7 and the second DBR layer 8 are sequentially epitaxially grown so as to cover the active layer 4, the n-type conductive layer 5 and the p-type conductive layer 6. After the epitaxial crystal growth, the second DBR layer 8 is processed into stripes by lithography and wet or dry etching techniques so that the width is slightly wider than the width W of the active layer 4 (FIG. 7E).

  In the second cladding layer 7, two etching grooves whose bottom surfaces reach the n-type conductive layer 5 and the p-type conductive layer 6, respectively, are formed by lithography and wet or dry etching. The inner surface of the etching groove is covered with a metal film, or the etching groove itself is filled with a metal to form the first electrode 9 and the second electrode 10, and the gold wires 11, 12 are formed on the upper surfaces of the electrodes 9, 10. The main part of the element structure is completed by crimping (FIG. 7F).

  According to the semiconductor optical amplifier manufacturing method of the seventh embodiment, a semiconductor optical amplifier having excellent element characteristics and reliability can be easily manufactured.

Embodiment 8 FIG.
FIG. 8 is a schematic diagram showing a method for manufacturing a semiconductor optical amplifier according to the fifth embodiment of the present invention.
A method for manufacturing the semiconductor optical amplifier according to the present embodiment will be described below.

  First, an active layer 22 and a second conductivity type second cladding layer 23 are sequentially formed on the first conductivity type semiconductor substrate 21 which also serves as the first cladding layer by epitaxial crystal growth (FIG. 8A). . As the epitaxial crystal growth method, for example, a vapor phase crystal growth method such as MOCVD method or MBE method is suitable.

  After such crystal growth, a predetermined width W optimum for optical waveguide is applied to a part of the first conductivity type semiconductor substrate 21, the active layer 22, and the second conductivity type second cladding layer 23 by lithography and dry etching techniques. It is processed into a ridge mesa shape (FIG. 8B). The width W of the active layer 22 is preferably in the range of 1 to 2 μm.

  A crystal layer 24a corresponding to the current blocking layer 24 is formed by selective crystal growth so as to embed a ridge mesa shape on the first conductivity type semiconductor substrate 21 (FIG. 8C). At this time, since an insulating film is formed on the ridge mesa to form a selective growth mask (not shown), crystal growth is not performed on the ridge mesa.

  Next, after forming the first electrode 26 on the back surface side of the semiconductor substrate 21 and the second electrode 27 so as to cover the ridge mesa by a metal film forming method such as EB vapor deposition or sputtering, lithography technology and dry etching are performed. It is processed into a predetermined pattern by technology.

  Of the crystal layer 24a corresponding to the current blocking layer and the DBR layer 25, the current block is formed so as to cover both side surfaces of the ridge mesa by removing by dry etching leaving a certain layer thickness from the portion in contact with both side surfaces of the ridge mesa. The layer 24 is formed (FIG. 8D). A DBR layer 25 is also formed simultaneously with the dry etching.

  The main part of the element structure is completed by crimping the gold wire 28 on the upper surface of the second electrode 27 (FIG. 8F).

  According to the semiconductor optical amplifier manufacturing method of the eighth embodiment, a semiconductor optical amplifier having excellent element characteristics and reliability can be easily manufactured.

2A is a cross-sectional view of the semiconductor optical amplifier according to the first embodiment, and FIG. FIG. 6 is a cross-sectional view of a semiconductor optical amplifier according to a second embodiment. FIG. 6 is a cross-sectional view (a) and a front view (b) of a semiconductor optical amplifier according to a third embodiment. FIG. 6 is a top view of a semiconductor optical amplifier according to a fourth embodiment. FIG. 10A is a sectional view of a semiconductor optical amplifier according to a fifth embodiment, and FIG. FIG. 10 is a front view of a semiconductor optical modulator according to a sixth embodiment. FIG. 10 is a schematic diagram showing a method for manufacturing a semiconductor optical amplifier according to a seventh embodiment. FIG. 10 is a schematic diagram showing a method for manufacturing a semiconductor optical amplifier according to an eighth embodiment.

Explanation of symbols

  1 semi-insulating InP substrate (semiconductor substrate), 2 first DBR layer, 3 first cladding layer, 4 active layer, 5 n-type conductive layer (first conductive layer), 6 p-type conductive layer (second conductive layer) 7 Second cladding layer, 8 Second DBR layer, 9 First electrode, 9a, 9b First electrode divided into two in the optical waveguide direction, 10 Second electrode, 10a, 10b Divided into two in the optical waveguide direction Second wires 11, 12, gold wires connected to the first electrode and the second electrode, 15 buffer layer, 21 semiconductor substrate of the first conductivity type, 22 active layer, 23 clad layer of the second conductivity type, 24 current blocking layer, 25 DBR layer, 26 first electrode, 27 second electrode, 28, 29 gold wire, 32 light amplification region, 33 light modulation region.

Claims (9)

A semi-insulating semiconductor substrate;
A first DBR layer formed on the semiconductor substrate;
A first cladding layer formed on the first DBR layer;
An active layer formed on the first cladding layer and having a predetermined width;
A first conductive layer and a second conductive layer respectively provided on the first cladding layer so as to be in contact with both side surfaces of the active layer;
A second cladding layer provided to cover the active layer, the first conductive layer, and the second conductive layer;
A second DBR layer provided on the second cladding layer at a position facing the active layer;
A first electrode formed in an etching groove penetrating the second cladding layer and having a bottom surface reaching the first conductive layer;
A second electrode formed in an etching groove that penetrates the second cladding layer and has a bottom surface reaching the second conductive layer;
A semiconductor optical amplifier comprising: 2. The semiconductor optical amplifier according to claim 1, wherein one or both of the first DBR layer and the second DBR layer are formed of a multilayer film made of a dielectric. 2. The semiconductor optical amplifier according to claim 1, wherein the active layer is lightly doped. A crystal having a band gap energy between the active layer and the first and second conductive layers that is larger than a band gap energy of a crystal constituting the active layer and smaller than a band gap energy of a crystal constituting each of the conductive layers; 2. The semiconductor optical amplifier according to claim 1, further comprising a buffer layer configured. 2. The semiconductor optical amplifier according to claim 1, wherein at least the semiconductor substrate and the first DBR layer are bonded to the first cladding layer by a substrate bonding technique. 2. The semiconductor optical amplifier according to claim 1, wherein one or both of the first electrode and the second electrode is composed of two or more divided electrodes that are electrically separated in the optical waveguide direction. . A first conductivity type semiconductor substrate;
A ridge mesa comprising a part of the semiconductor substrate and an active layer formed on the semiconductor substrate and a clad layer of a second conductivity type and having a predetermined width;
A high-resistance current blocking layer provided so as to be in contact with both side surfaces of the ridge mesa;
A DBR layer comprising a plurality of semiconductor layers extending in a direction substantially parallel to the ridge mesa on the semiconductor substrate and periodically arranged in a direction perpendicular to the optical waveguide direction;
A first electrode provided on a surface of the semiconductor substrate opposite to the surface on which the active layer is formed;
A second electrode provided on the second conductivity type cladding layer;
A semiconductor optical amplifier comprising: Sequentially epitaxially growing a first DBR layer, a first cladding layer and an active layer on a semi-insulating semiconductor substrate;
Etching the active layer to a predetermined width;
Selectively crystal-growing the first conductive layer and the second conductive layer on the first cladding layer so as to be in contact with both side surfaces of the active layer;
Epitaxially growing a second cladding layer and a second DBR layer so as to cover the active layer, the first conductive layer, and the second conductive layer;
Forming an etching groove penetrating the second cladding layer and having bottom faces reaching the first conductive layer and the second conductive layer, respectively;
A step of forming a first electrode electrically connected to the first conductive layer and a second electrode electrically connected to the second conductive layer by covering or burying a metal in each etching groove. When,
A method of manufacturing a semiconductor optical amplifier comprising: A step of sequentially epitaxially growing an active layer and a second conductivity type cladding layer on a first conductivity type semiconductor substrate;
Etching a part of the semiconductor substrate, the active layer and the second conductivity type cladding layer to a predetermined width to form a ridge mesa;
Selectively crystal-growing a high-resistance semiconductor layer so as to embed the ridge mesa;
Forming a first electrode on a surface of the semiconductor substrate opposite to the surface on which the active layer is formed;
Forming a second electrode on the second conductivity type cladding layer;
A high-resistance current blocking layer provided so as to be in contact with both side surfaces of the ridge mesa and on the semiconductor substrate, extend in a direction substantially parallel to the ridge mesa and periodically arranged in a direction perpendicular to the optical waveguide direction. Forming a DBR layer composed of a plurality of semiconductor layers by a lithography technique and a dry etching technique;
A method of manufacturing a semiconductor optical amplifier comprising:

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