JP2019079993A - Semiconductor optical element - Google Patents

Abstract

To achieve a semiconductor optical element excellent in electrical isolation properties between a laser region and a modulator region.SOLUTION: In a semiconductor optical element (electric field absorption modulator integrated laser) where an electric field absorption modulator region 8 and a laser region 9 are formed on a substrate and connected by a connection waveguide region 13 and a waveguide structure is formed where clad layers 25, 26 having semiconductor polarities different from each other are arranged on both sides of a core layer 23 in a direction parallel to a lamination plane of the core layer and in a direction orthogonal to an optical waveguide direction: arrangement of the semiconductor polarities of the clad layers is opposite to each other between the electric field absorption modulator region and the laser region; and two clad layers having semiconductor polarities different from each other on one side when viewed in an optical waveguide direction are connected by a common electrode; and the common electrode is grounded; and a revere bias power supply is connected to the electric field absorption modulator region and a forward bias power supply is connected to the laser region.SELECTED DRAWING: Figure 6

Description

  The present invention relates to the structure of a semiconductor optical device used as a light source for an optical transmitter or the like. More particularly, the present invention relates to the structure of a semiconductor optical device such as a modulator integrated laser used for a modulator integrated light source in which a semiconductor laser and an optical modulator are integrated.

  Due to the explosive increase in the amount of network traffic accompanying the spread of the Internet, the increase in speed and capacity of optical fiber transmission is remarkable. Semiconductor lasers have continued to evolve as light source devices to support optical fiber communications. In particular, the realization of a single mode light source by distributed feedback (DFB) semiconductor laser is speeding up and increasing the capacity of optical fiber communication by time division multiplexing method and wavelength division multiplexing (WDM) method. Has greatly contributed to

  In recent years, optical communication has been applied not only to telecommunications areas such as core networks and metro networks, but also to short distance data communication between data centers, racks and boards. For example, 100 Gbit Ethernet is standardized using the configuration of a WDM-type multi-wavelength array light source, and the capacity increase of short-distance optical communication is rapidly advancing. In these backgrounds, it is essential to speed up and reduce the power consumption of the optical transmitter, and as a high-performance modulation light source that modulates light from an integrated laser light source with an electric signal and outputs it, a modulator integrated semiconductor Lasers have evolved.

  In particular, an EA-DFB laser monolithically integrating a single mode DFB laser and an electroabsorption (EA) type optical modulator on the same substrate is small in size and consumes low power, and can perform high-speed modulation exceeding 40 Gbit / s. Because of that (non-patent document 1), it is put to practical use as an optical transmitter for relatively short distances of 100 km or less. As of 2017, standardization of 400 Gbit Ethernet is in progress, and an EA-DFB laser capable of supporting 50 Gbit / s class PAM (Pulse Amplitude Modulation) is desired.

W. Kobayashi et al., "Design and Fabrication of 10- / 40-Gb / s, Uncooled Electroabsorption Modulator, Integrated DFB Laser with Butt-Joint Structure," IEEE Journal of Lightwave Technology, vol. 28, no. 1, pp. 164-171, 2010

  The EA-DFB laser is formed by integrating an EA modulator and a single mode DFB laser on the same substrate. The EA modulator performs the light modulation operation by the change of the light absorption coefficient when an electric field by the modulation electric signal is applied to the quantum well active layer which becomes the optical waveguide core through which the light to be modulated passes.

  FIG. 1A shows a cross-sectional view of a substrate of a modulation region of a general conventional EA modulator. In FIG. 1A, light to be modulated passes through the quantum well layer (core layer, active layer) 1 in the in-plane direction of the substrate (perpendicular to the plane of the drawing or to the lateral direction in the plane of the drawing).

  The quantum well layer 1 has a multilayer structure in which a barrier layer made of a material having a large band gap and a well layer made of a material having a small band gap are alternately and periodically laminated. In the upper and lower layers of the quantum well layer 1 (usually an undoped intrinsic semiconductor and expressed as i-type), cladding layers different in semiconductor polarity, for example, p-type cladding layer (p-InP) 2 The pin semiconductor structure is formed of three layers in which an n-type cladding layer (n-InP) 3 is disposed. An electric field is applied in the vertical direction (vertical direction to the quantum well layer 1, vertical direction) by the reverse electric field together with the modulation electric signal from the modulation signal source 41 by the upper and lower electrodes facing each other with the pin semiconductor structure interposed therebetween. The electric field controls the light absorption coefficient for the light passing through the quantum well layer 1 to modulate the light.

  FIG. 1 (b) is a graph showing the change in absorption coefficient (light absorption spectrum) with respect to the wavelength of the EA modulator of the quantum well structure in the case of an electric field zero (solid line) and when a predetermined electric field is applied (dotted line). It is. The light absorption spectrum of the quantum well structure comprises inter-band absorption corresponding to the inter-band transition wavelength (a section to the left of the "band edge" in FIG. 1B) and an exciton absorption peak on the long wavelength side.

  When an electric field is applied, localization of carriers in the quantum well layer 1 lowers the exciton absorption peak of the light absorption spectrum, and further reduces the effective band gap to shift the absorption spectrum to a longer wavelength, so-called quantum confinement Stark (QCSE) effects occur. Therefore, in general, the light modulation operation is achieved by increasing the light absorption coefficient by setting the operating wavelength of the laser to a longer wavelength side than the exciton absorption wavelength and applying an electric field.

  The EA-DFB laser device 10 includes an electroabsorption (EA) modulator region provided along the optical waveguide core layer and a laser region functioning as a DFB laser, and laser light generated in the laser region is electroabsorption The light is modulated in the modulator area to become output light.

  2 and 3 show substrate cross-sectional views of the waveguide structure of a typical conventional EA-DFB laser. 2A is a cross-sectional view of the substrate perpendicular to the optical waveguide core layer (optical axis) in the laser region 9, and FIG. 2B is a cross-sectional view of the substrate perpendicular to the optical waveguide core layer in the electroabsorption modulator region 8. It is. FIG. 3 is a cross-sectional view of the substrate including the optical axis along the optical waveguide core layer.

  In FIGS. 2A and 2B, both sides of the n-type cladding layer (n-InP cladding layer / substrate) 3 which is also an n-type substrate are embedded with a semi-insulating InP buried layer 15 The core layer (quantum well layer, active layer) 1 or the laser core layer (quantum well layer, active layer) 4 of the modulator is separately formed with another composition. A common p-type cladding layer 2, two p-type contact layers 7 and two p-electrodes 6 are formed on both core layers 1 and 4.

  As shown in FIG. 3, both core layers 1, 4 are coupled by the optical waveguides of the connection waveguide region 13. Above the laser core layer 4 is formed a diffraction grating 11 that determines the oscillation wavelength of the laser. A common p-type cladding layer 2, two p-type contact layers 7, and two p-electrodes 6 are formed on top of both core layers 1 and 4. Under the n-type cladding layer / substrate 3, a common n electrode 5 is provided and grounded.

  In the EA-DFB laser, electrical isolation is required to independently bias drive the electroabsorption modulator and the laser. In the example of the conventional structure shown in FIG. 3, the substrate 3 is made common and grounded at the n electrode 5. On the other hand, on the p-electrode side, the p-type cladding layer 2 above the connection waveguide region 13 is thinned in a range where the waveguide mode is not affected by etching, and the contact layer 7 is further removed. Thus, the p electrode 6 is electrically separated into two at the electroabsorption modulator area 8 and the laser area 9.

  With such a structure, as described in FIG. 1, in the electro-absorption modulator area 8, it is necessary to drive in the reverse bias state, that is, the potential of the p electrode 6 lower than that of the n electrode 5. On the other hand, in the laser area 9, it is necessary to drive in a forward bias state, that is, the potential of the p electrode 6 is higher than that of the n electrode 5 for current injection operation.

Therefore, assuming that the absolute value of the bias voltage by the modulation signal source (bias voltage source) 41 of the electro-absorption modulator is V _bEA and the absolute value of the bias voltage in the laser region is V _bLD , the electrical polarities of both are opposite. The voltage difference on the p-electrode side becomes an absolute value of the sum of | V _bEA + V _bLD |, and the potential difference applied to the portion of the connection waveguide region 13 becomes considerably large.

  For example, since the forward bias voltage of a general laser is about +1 to +3 V and the reverse bias voltage of the modulator is about -1 to -4 V, a voltage of up to 7 V is applied to the waveguide of the connection waveguide region 13 . In addition, since the connection waveguide region 13 is connected by the conductive cladding region 2 which is thinned by etching, a leak current is generated. In order to suppress this leak current, it is necessary to make the waveguide length of the connection waveguide region 13 sufficiently long, and the length of the element becomes long. For example, in Non-Patent Document 1, the waveguide length of the connection waveguide region 13 is set to 50 μm.

  The present invention has been made in view of such problems, and an object of the present invention is to realize a high-performance electro-absorption modulator integrated laser having a simple manufacturing process and excellent electrical isolation characteristics. It is in.

  The present invention is characterized by having the following configuration in order to achieve such an object.

(Structure 1 of the Invention)
A semiconductor optical device having an electroabsorption modulator region and a laser region formed on a substrate, the semiconductor optical device comprising:
The electroabsorption modulator region and the laser region are connected by a connecting waveguide region,
In the waveguide structure of the electroabsorption modulator area and the laser area, cladding layers different in semiconductor polarity are formed on the substrate on both sides of the core layer in the direction parallel to the laminated surface of the core layer and orthogonal to the light waveguide direction. Each is formed of a waveguide structure arranged
In the electro-absorption modulator region and the laser region, the arrangement of the semiconductor polarity of the cladding layer is reversed,
The two cladding layers different in semiconductor polarity are connected by a common electrode on one side of the electroabsorption modulator region and the laser region viewed in the light waveguide direction,
A semiconductor optical device, wherein the common electrode is grounded, a reverse bias power source is connected to the electro-absorption modulator region, and a forward bias power source is connected to the laser region.

(Structure 2 of the Invention)
A semiconductor optical device according to Configuration 1 of the invention,
A semiconductor optical device characterized in that the connection waveguide region is formed of an intrinsic semiconductor buried waveguide.

(Composition 3 of the Invention)
A semiconductor optical device according to Configuration 2 of the invention,
The buried waveguide of the intrinsic semiconductor in the connection waveguide region is formed from the light input / output portion on both sides of the electro-absorption modulator region in the connection waveguide region and the light waveguide direction in contact with the laser region. A semiconductor optical device characterized in that the embedded width is narrowed toward the central portion.

(Structure 4 of the Invention)
The semiconductor optical device according to Configuration 3 of the invention,
A semiconductor optical device, wherein a buried waveguide of the intrinsic semiconductor in the connection waveguide region is formed so as not to be buried by the intrinsic semiconductor in a central portion of the connection waveguide region.

(Structure 5 of the Invention)
A semiconductor optical device according to Configuration 1 of the invention,
A semiconductor optical device characterized in that the whole of the connection waveguide region is formed of a thin wire waveguide which is not embedded with an intrinsic semiconductor.

(Structure 6 of the Invention)
A semiconductor optical device according to any one of the first to fifth aspects of the invention,
A semiconductor optical device characterized in that a core layer of the electroabsorption modulator region and the laser region has a quantum well structure.

(Structure 7 of the Invention)
The semiconductor optical device according to any one of the first to sixth aspects of the invention,
A semiconductor optical device characterized in that the substrate is a substrate in which a SiO ₂ layer is formed on a silicon substrate.

(Structure 8 of the Invention)
The semiconductor optical device according to any one of the first to sixth aspects of the invention,
A semiconductor optical device characterized in that the substrate is a semi-insulating (SI) InP substrate.

  According to the present invention, since the potential difference between the modulator region and the laser region is suppressed and the electrical separation is improved, the leakage current is suppressed and the voltage resistance is improved. In addition, since the connection waveguide is made of an intrinsic semiconductor and the electrical resistance is high and the optical loss is suppressed, the connection waveguide can be shortened, so that the element can be miniaturized.

  In addition, n-layer and p-layer are provided on both sides of the core region of the modulator area and the laser area, and voltage is applied in the lateral direction, so the modulator is sandwiched by areas with low refractive index in the vertical direction. It is possible to adopt a thin film structure, and high light confinement can be realized. In addition, since the electrodes do not face each other, the element capacitance is not easily affected by the electrode area, and the element capacitance is defined by the thicknesses of the thin film p-type cladding layer and the n-type cladding layer. The capacity per unit length can be reduced compared to the Furthermore, the modulation efficiency is increased by using a quantum well structure in the active layer of the modulator region and applying an electric field to the quantum well in the lateral direction (direction parallel to the stacking plane of the quantum well layer).

  As described above, it is possible to realize an EA-DFB laser that is compact and has excellent electrical isolation characteristics.

FIG. 1A is a cross-sectional view of a substrate of a conventional EA modulator, and FIG. 1B is a diagram showing a change in light absorption spectrum due to the QCSE effect. It is a figure of the substrate cross section perpendicular | vertical to the waveguide direction of the conventional EA-DFB laser. FIG. 2A is a cross-sectional view of the substrate in the laser region, and FIG. 2B is a cross-sectional view of the substrate in the modulator region. It is a substrate sectional view which met a waveguide direction of the conventional EA-DFB laser. It is a perspective view which shows the whole structure of the semiconductor optical element of Example 1 of this invention. It is a figure of the board | substrate cross section perpendicular | vertical to the waveguide direction of the semiconductor optical element of Example 1 of this invention. 5 (a) is a cross-sectional view of the substrate in the laser region, FIG. 5 (b) is in the connection waveguide region, and FIG. 5 (c) is in the modulator region. It is a top view explaining the connection with the power supply of the semiconductor optical element of Example 1 of this invention. It is explanatory drawing of a change of the absorption coefficient, and the extinction characteristic of the modulator area | region of Example 1 of this invention. FIG. 8A is a top view of a semiconductor optical device according to a first modification of the first embodiment of the present invention, and FIG. 8B is a partial substrate cross-sectional view at two locations in the connection waveguide region. It is a top view explaining the connection with the power supply of the semiconductor optical element of the modification 2 of Example 1 of this invention. It is a perspective view which shows the whole structure of the semiconductor optical element of Example 2 of this invention. It is a figure of the board | substrate cross section perpendicular | vertical to the waveguide direction of the semiconductor optical element of Example 2 of this invention. 11 (a) is a cross-sectional view of the substrate in the laser region, FIG. 11 (b) is a substrate in the connection waveguide region, and FIG. 11 (c) is a modulator region.

Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.

Example 1
FIG. 4 is a perspective view showing the entire structure of the semiconductor optical device according to the first embodiment of the present invention. FIG. 5 is a cross-sectional view of the substrate of the semiconductor optical device of the first embodiment of the present invention, which is perpendicular to the waveguide direction. 5 (a) is a cross-sectional view of the substrate in the laser region 9, FIG. 5 (b) is a substrate in the connection waveguide region 13, and FIG. FIG. 6 is a top view of the semiconductor region of the semiconductor optical device according to the first embodiment of the present invention, in which electrodes are also shown in order to explain a method of connection to a drive power source.

As shown in FIGS. 4 and 5, in the semiconductor optical device according to the first embodiment of the present invention, the substrate has a two-layer structure in which an SiO ₂ layer 21 is formed on a silicon substrate 20. A buried core layer having a lateral current injection structure and a voltage application structure parallel to the substrate surface is formed.

  The core layers 23 and 24 of the EA modulator region 8, the connection waveguide region 13 and the laser region 9 are all formed of, for example, six-layer InGaAsP quantum wells. The modulator region 8 and the connection waveguide region 13 can use the same core layer 23 of the quantum well photoluminescence wavelength 1.48 μm. The photoluminescence wavelength of the quantum well of the core layer 24 of the laser region 9 is 1.55 μm. The core width is 0.7 μm in all cases, and the thickness of the slab layer including the core layer is 350 nm.

  As shown in FIGS. 5A and 5C, on the substrate on both sides of the core layers (quantum well layers) 23 and 24, a direction parallel to the lamination surface of the core layers and a direction orthogonal to the light guiding direction In order to apply a voltage from both sides, it is embedded by InP cladding layers 25 and 26 which are doped with different types (type, semiconductor polarity). At this time, in the arrangement of the InP cladding layers 25 and 26 in the laser area 9 and the modulator area 8, the doping polarity (p-type / n-type) of the semiconductor is opposite to the left and right sides of the substrate across the core layer as viewed in the light guiding direction. It is arranged in reverse, so that it is reversed.

That is, the p-type cladding layer 26 with a Zn doping concentration of 1 × 10 ¹⁸ cm ^-3 is provided on the left side of the core layer 24 in the laser region 9 of FIG. An n-type cladding layer 25 of × 10 ¹⁸ cm ^-3 is formed.

On the other hand, on the left side of the core layer 23 of the modulator region 8 in FIG. 5C, the n-type cladding layer 25 having a Si doping concentration of 1 × 10 ¹⁸ cm ⁻³ is provided. A 1 × 10 ¹⁸ cm ^-3 p-type cladding layer 26 is formed.

The periphery of the core layer 23 of the connection waveguide region 13 in FIG. 5B is embedded with an intrinsic semiconductor (i-InP) layer 22 as a cladding layer, and both sides thereof follow the SiO ₂ layer 21 in the upper layer of the substrate. It is embedded with a SiO ₂ layer, and supports the common electrode 50 on the right side.

As shown in FIGS. 5A and 5C, InGaAs contact layers 27 and 28 are formed on the cladding layers 25 and 26 of the laser region 9 and the modulator region 8, respectively, and each has a doping concentration of 1 × 10 ¹⁹ cm ^-3 n-type doping and p-type doping are applied. Furthermore, an n electrode 29 or a p electrode 30 and a common electrode 50 are formed on the region of the contact layer, and an SiO ₂ protective film 31 or a surface diffraction grating 12 is formed on the surface between the electrodes. The SiO ₂ protective film 31 is not shown in the perspective view of FIG. 4 for ease of viewing.

  As shown in the perspective view of FIG. 4 and the top view of FIG. 6, the semiconductor optical device according to the first embodiment of the present invention comprises a modulator area 8 and a laser area 9 and a connection waveguide area 13 between both areas. There is. The active layer length of the laser region 9 is 600 μm, the active layer length of the modulator region 8 is 200 μm, and the length of the connection waveguide region 13 is 20 μm.

As shown in the perspective view of FIG. 4, a 10 nm thick SiN insulating film is formed on the core layer 24 of the laser region 9, and a λ / 4 shift grating made of SiN and SiO ₂ and having a Bragg wavelength of 1.55 μm. The structure forms a surface diffraction grating 12.

  As shown in FIG. 6, the modulator area 8 and the laser area 9 are separated by etching the InP layer of the connecting waveguide area 13 between the two areas. Also, the n-type cladding layer 25 and the p-type cladding layer 26 in the modulator region 8 and the laser region 9 are formed only in necessary portions of the respective regions.

  Further, as shown in FIGS. 4 and 6, the electrode on the p-type cladding layer 26 side of the EA modulator region 8 and the electrode on the n-type cladding layer 25 side of the laser region 9 are electrically connected together It is formed as an electrode 50 and is grounded.

In order to form an InP thin film on a SiO ₂ / Si substrate (21/20) in manufacturing an element having this waveguide structure, a technique such as wafer bonding can be used. In addition, metal organic chemical vapor deposition (MOVPE) can be used for crystal growth of InP, InGaAsP, etc., and general semiconductor lasers such as wet etching or dry etching can be used for producing a laser waveguide structure and a diffraction grating. A manufacturing method can be used.

  The cladding layers 25 and 26 for current injection on the left and right of the active layers (core layers) 23 and 24 can be formed by embedding intrinsic InP and regrowth, and thereafter forming an impurity semiconductor by a method such as ion implantation or thermal diffusion. By this method, the doping region can be formed only in the necessary region without repeating the regrowth. Alternatively, n-type doped InP and p-type doped InP may be formed by buried regrowth, respectively. The surface diffraction grating 12 can be formed by performing pattern formation and etching by electron beam exposure on the laser surface after formation of the active layer.

  FIG. 7 shows the extinction characteristic of the modulator region 8 of this element. FIG. 7A shows a change in absorption coefficient spectrum when an electric field of various strengths is applied in a direction parallel to the substrate for an InGaAsP quantum well structure having a thickness of 10 nm and a band gap wavelength of 1.45 μm. The range of the electric field strength was 0 kV / cm to 100 kV / cm. Excitation absorption is suppressed by the application of an electric field, and the absorption spectrum is broadened. In addition, band edge absorption changes due to the two-dimensional Franz-Keldysh effect, and the absorption coefficient increases on the long wavelength side with respect to the exciton absorption peak.

  FIG. 7 (b) shows the extinction characteristics of the modulator region 8 of this element at a plurality of laser oscillation wavelengths. Since the oscillation wavelength of the laser is set to 1.55 μm, an extinction characteristic of 10 dB can be realized with a drive voltage of 1 V or less having a voltage amplitude of about 0.8 V.

  The top view of the first embodiment of FIG. 6 also shows the connection configuration of the power supply for driving the device. The p-side electrode of the modulator region 8 and the n-side electrode of the laser region 9 are both formed as an integral common electrode 50 and grounded.

  Also, a modulator bias voltage source (modulation signal source) 41 is connected to the n electrode 29 of the modulator area 8, and a laser drive current source 42 is connected to the p electrode 30 of the laser area 9. Reverse bias, forward bias is applied to the laser area 9.

  At this time, in the present invention, the semiconductor polarity (p-type / n-type) of the cladding layers on both sides of the core layers 23 and 24 is reversely arranged in the modulator area 8 and the laser area 9, The polarity is the same.

That is, assuming that the absolute value of the bias voltage on the modulator side is V _bEA and the absolute value of the bias voltage in the laser region is V _bLD , the potential difference between the n electrode 29 of the modulator region 8 and the p electrode 30 of the laser region 9 is | It becomes an absolute value of a difference with _VbEA - _VbLD . That is, since the potential difference is expressed by the difference of the absolute value of the voltage, the electric field applied to the connection waveguide can be suppressed as compared with the conventional structure.

  Further, in FIG. 6, since the core layer 23 of the connection waveguide region 13 is embedded with the intrinsic semiconductor (i-InP) layer 22, a pin structure is formed between the modulator and the laser. Therefore, compared to the conventional structure of FIG. 3 in which the connection waveguide region is connected by the conductive impurity semiconductor, the effect of suppressing the leakage current is high.

In particular, when the absolute value of the modulator bias voltage is higher than the bias voltage of the laser, that is, V _bEA > V _bLD , the n-clad 25 on the modulator side and the laser side of the portion above the core layers 23 and 24 in FIG. The reverse bias is applied between the p-claddings 26 and the current leak can be almost completely suppressed.

In addition, even if V _bEA <V _bLD , almost no current flows if the potential difference is within the diffusion potential. Even if the potential difference is more than that, in the present embodiment, since the connection waveguide region 13 is formed of the intrinsic semiconductor 22, the resistance is high, and current leakage can be suppressed.

  In addition, since all the regions are formed of buried waveguides, high optical coupling between the waveguides can be realized. Another feature is that the optical loss is low because the connection waveguide region 13 is made of an intrinsic semiconductor.

  Thus, according to the configuration of the present invention, an EA-DFB laser having good electrical separation of the laser area and the modulator area can be realized.

(Modification 1 of Embodiment 1)
A first modification of the first embodiment is shown in FIG. In the first embodiment shown in FIGS. 4 to 6, the connection waveguide region 13 is constituted by a buried waveguide made of the intrinsic semiconductor 22. However, in order to further increase the resistance, the waveguide width of the connection waveguide region 13 may be narrowed. It is valid.

  8 (a) is a top view of a semiconductor portion of the first modification of the first embodiment, and FIGS. 8 (b) and 8 (c) are cross-sectional views of the substrate taken along the lines AA 'and BB' of FIG. 8 (a). It is a figure showing an outline.

  For example, as shown in FIGS. 8A and 8B, light input / output portions on both sides of the optical waveguide direction in contact with the modulator region 8 and the laser region 9 of the connection waveguide region 13 are intrinsic semiconductors (i-InP) In the embedded waveguide structure 22 (FIG. 8B), the embedded width of the i-InP layer 22 is narrowed toward the central portion of the connection waveguide region 13, or the embedded portion of the i-InP layer 22 is By eliminating only the core layer 23 (FIG. 8C), the separation resistance between the modulator region 8 and the laser region 9 can be increased without deteriorating the optical coupling.

  In the central portion of the connection waveguide region 13 according to the first modification of the first embodiment, the buried i-InP layers 22 on both the left and right sides of the waveguide core layer 23 as shown in the cross-sectional view of FIG. It may be a thin wire waveguide structure in which is completely removed. In addition, all the connection waveguide regions 13 including the light input / output portion can be formed as a thin line waveguide structure without the embedded i-InP layer 22. In this configuration, the light coupling efficiency is somewhat lower, but the electrical isolation effect is higher.

Also in this configuration, both sides of the core region 23 of the connection waveguide region 13 except the portion embedded with the i-InP layer 22 are embedded with the same SiO ₂ layer as the SiO ₂ layer 21 in the upper layer of the substrate. , Common electrode 50 is supported.

(Modified Example 2 of Example 1)
The modification 2 of Example 1 is shown in FIG. The first embodiment of FIG. 6 shows a configuration in which the p electrode of the modulator region 8 and the n electrode of the laser region 9 are made common and grounded as an integral common electrode 50. However, in the second modification of the first embodiment of FIG. The semiconductor polarity (type, doping) in both regions and the polarity of the bias voltage are reversed from those in Example 1 of FIG. 6, and the n electrode on the modulator region 8 side and the p electrode on the laser region 9 side are made common. The common electrode 50 is grounded.

  Then, a (negative) reverse bias power supply (modulation signal source) 41 for the p electrode 30 on the modulator area 8 side and a (negative) forward bias power supply (laser drive current source) for the laser area 9 side 42 are connected.

Also in the case of the second modification of the first embodiment of FIG. 9, the potential difference between the p electrode 30 of the modulator region 8 and the n electrode 29 of the laser region 9 is | V _bEA −V _bLD | The electric field applied to the connection waveguide can be suppressed.

(Example 2)
FIG. 10 is a perspective view showing the entire structure of a semiconductor optical device according to a second embodiment of the present invention. 11 is a cross-sectional view of the substrate of the laser region 9 perpendicular to the waveguide direction seen in the optical axis direction of the semiconductor optical device of the second embodiment of the present invention, as in FIG. 5 of the first embodiment. FIG. 11B is a substrate cross-sectional view 11 (b) of the connection waveguide region 13 and a substrate cross-sectional view 11 (c) of the modulator region 8;

  In the second embodiment of the present invention shown in FIG. 10, unlike the first embodiment shown in FIG. 4, the substrate is a single layer semi-insulating (SI) InP substrate 40 on which the lateral direction is parallel to the substrate surface. A buried core layer having a current injection structure and a voltage application structure is formed.

  The core layers 23 and 24 of the EA modulator region 8, the connection waveguide region 13 and the laser region 9 are both formed of, for example, a 20-layer InGaAsP quantum well. The modulator region 8 and the connection waveguide region 13 can use the same core layer 23 of the quantum well photoluminescence wavelength 1.48 μm. The photoluminescence wavelength of the quantum well of the core layer 24 of the laser region 9 is 1.55 μm. The core width is 0.8 μm in all cases, and the thickness of the buried layer is 400 nm.

  As shown in FIGS. 11 (a) and 11 (c), on the substrate on both sides of the core layer (quantum well layer) 23 and 24 of the modulator region 8 and the laser region 9, parallel to the lamination surface of the core layer In order to apply a voltage from both sides in the direction and the direction orthogonal to the light guiding direction, the layers are buried from the InP cladding layers 25 and 26 to which doping of different types (type, semiconductor polarity) is applied. At this time, in the laser region 9 and the modulator region 8, the arrangement of the InP cladding layers 25 and 26 is such that the doping polarity (p-type / n-type) of the semiconductor is opposite to the left and right of the substrate It is arranged in reverse, so that it is reversed.

That is, the p-type cladding layer 26 with a Zn doping concentration of 1 × 10 ¹⁸ cm ⁻³ is on the left side of the core layer 24 in the laser region 9 of FIG. An n-type cladding layer 25 of × 10 ¹⁸ cm ^-3 is formed.

On the other hand, on the left side of the core layer 23 of the modulator region 8 in FIG. 11C, the n-type cladding layer 25 having a Si doping concentration of 1 × 10 ¹⁸ cm ⁻³ is provided. A 1 × 10 ¹⁸ cm ^-3 p-type cladding layer 26 is formed.

Incidentally, the periphery of the core layer 23 of the connection waveguide region 13 in FIG. 11B is embedded with an intrinsic semiconductor (i-InP) 22 as a cladding layer, and both sides thereof are SiO ₂ following the SiO ₂ layer 21 in the upper layer of the substrate. It is embedded in _two layers and supports the common electrode 50 on the right side.

  Also in the second embodiment, as in the first modification (FIG. 8) of the first embodiment, the embedding width of the connection waveguide region 13 may be narrowed, or the embedding may be eliminated in the central portion. Furthermore, all the optical connection waveguide regions 13 can be made into a thin wire waveguide structure without the embedded i-InP layer 22 including the light input / output part.

As shown in FIGS. 11A and 11C, InGaAs contact layers 27 and 28 are formed on the cladding layers 25 and 26 of the laser region 9 and the modulator region 8, respectively, and each has a doping concentration of 1 × 10 ^19. An n-type doping of cm ^-3 and a p-type doping are performed. Furthermore, electrodes 29, 30 for current injection and a common electrode 50 are formed on the regions of the contact layers 27, 28, and a SiO ₂ protective film 31 or a surface diffraction grating 12 is formed on the surface between the electrodes. There is. For ease of viewing, the SiO ₂ protective film 31 is not shown in the perspective view of FIG.

  Similar to FIG. 4 of the first embodiment, the semiconductor optical device of the second embodiment of FIG. 10 includes the modulator region 8, the laser region 9, and the connection waveguide region 13 between the two regions. The active layer length of the laser region 9 is 600 μm, the active layer length of the modulator region 8 is 200 μm, and the length of the connection waveguide region 13 is 20 μm.

As shown in the perspective view of FIG. 10, a 100 nm thick SiN insulating film is formed on the core layer 24 of the laser region 9, and a λ / 4 shift grating made of SiN and SiO ₂ and having a Bragg wavelength of 1.55 μm. The structure forms a surface diffraction grating 12.

  Further, as shown in the cross-sectional view of FIG. 11B, the connection waveguide region 13 is configured of a buried waveguide in which the core layer 23 is buried with an intrinsic semiconductor (i-InP) 22.

  As shown in FIGS. 10 and 11, the modulator area 8 and the laser area 9 are separated by etching the InP area between the two areas. In addition, the n-type cladding layer and the p-type cladding layer of the modulator region 8 and the laser region 9 are formed only in necessary portions of the respective regions.

  Further, as shown in FIGS. 10 and 11, an electrode on the p-type cladding layer 26 side of the modulator region 8 and an electrode on the n-type cladding layer 25 side of the laser region 9 are integrally connected common electrodes. It is formed as 50.

  The configuration of the present embodiment 2 can also be produced by a general method for producing a semiconductor device in the same manner as the embodiment 1.

  Also in the second embodiment, by connecting the drive voltage sources (current sources) 41 and 42 as in FIG. 6 of the first embodiment, the leak current can be suppressed, and an EA-DFB laser with high voltage resistance can be realized. In particular, the structure of the second embodiment has a high heat dissipation effect because the laser is formed on the InP substrate. In addition, since the light mode is extended to the low loss semi-insulating InP region, the loss is low, which is advantageous for increasing the light output of the laser.

  As described above, according to the present invention, it is possible to realize an EA-DFB laser excellent in the electrical separation between the laser area and the modulator area. The structure of the semiconductor optical device according to the present invention is not limited to the form of each embodiment. Although the operating wavelength is 1.55 μm, other wavelengths such as 1.3 μm band can be realized within the design change range. For example, the configuration of an InGaAsP-based laser on an InP substrate can be realized in the operating wavelength range of 1 μm to 2 μm.

Although the core layer 24 of the laser is InGaAsP, other compound semiconductor materials such as InGaAlAs may be applied. Further, in the present embodiment, the core region of the laser region, the modulator region, and the connection region is a quantum well structure, but any region or all regions may be a bulk structure. Although the diffraction grating 12 is made of SiN and SiO ₂ , it may be made of another insulating film such as SiON or SiOx, or may be formed by etching the surface of InP. Alternatively, diffraction gratings can be formed directly above and below the core layer 24 of the laser.

  As described above, according to the present invention, it is possible to realize an EA-DFB laser excellent in electrical separation characteristics by a simple manufacturing method, and can be widely used for an optical transmitter for an optical communication system. it can.

1 Quantum well layer (core layer, active layer)
2 p-type cladding layer (p-InP)
3 n-type cladding layer (n-InP) / substrate 4 laser core layer (quantum well layer, active layer)
5, 6 n electrode, p electrode 7 p type contact layer 8 field absorption (EA) modulator area 9 laser area 10 EA-DFB laser element 11 diffraction grating 12 surface diffraction grating 13 connection waveguide area 15 semi-insulating InP buried layer 20 silicon substrate 21 SiO ₂ layer 22 intrinsic semiconductor (i-InP) layer 23, 24 core layer (quantum well layer, active layer)
25, 26 n-type cladding layer, p-type cladding layer 27, 28 (n-type / p-type) contact layer 29, 30 n electrode, p electrode 31 SiO ₂ protective film 40 semi-insulating (SI) InP single layer substrate 41 modulation Signal source (bias voltage source)
42 laser drive current source 50 common electrode

Claims (8)

A semiconductor optical device having an electroabsorption modulator region and a laser region formed on a substrate, the semiconductor optical device comprising:
The electroabsorption modulator region and the laser region are connected by a connecting waveguide region,
In the waveguide structure of the electroabsorption modulator area and the laser area, cladding layers different in semiconductor polarity are formed on the substrate on both sides of the core layer in the direction parallel to the laminated surface of the core layer and orthogonal to the light waveguide direction. Each is formed of a waveguide structure arranged
In the electro-absorption modulator region and the laser region, the arrangement of the semiconductor polarity of the cladding layer is reversed,
The two cladding layers different in semiconductor polarity are connected by a common electrode on one side of the electroabsorption modulator region and the laser region viewed in the light waveguide direction,
A semiconductor optical device, wherein the common electrode is grounded, a reverse bias power source is connected to the electro-absorption modulator region, and a forward bias power source is connected to the laser region. The semiconductor optical device according to claim 1, wherein
A semiconductor optical device characterized in that the connection waveguide region is formed of an intrinsic semiconductor buried waveguide. The semiconductor optical device according to claim 2, wherein
The buried waveguide of the intrinsic semiconductor in the connection waveguide region is formed from the light input / output portion on both sides of the electro-absorption modulator region in the connection waveguide region and the light waveguide direction in contact with the laser region. A semiconductor optical device characterized in that the embedded width is narrowed toward the central portion. A semiconductor optical device according to claim 3, wherein
A semiconductor optical device, wherein a buried waveguide of the intrinsic semiconductor in the connection waveguide region is formed so as not to be buried by the intrinsic semiconductor in a central portion of the connection waveguide region. The semiconductor optical device according to claim 1, wherein
A semiconductor optical device characterized in that the whole of the connection waveguide region is formed of a thin wire waveguide which is not embedded with an intrinsic semiconductor. The semiconductor optical device according to any one of claims 1 to 5, wherein
A semiconductor optical device characterized in that a core layer of the electroabsorption modulator region and the laser region has a quantum well structure. A semiconductor optical device according to any one of claims 1 to 6, wherein
A semiconductor optical device characterized in that the substrate is a substrate in which a SiO ₂ layer is formed on a silicon substrate. A semiconductor optical device according to any one of claims 1 to 6, wherein
A semiconductor optical device characterized in that the substrate is a semi-insulating (SI) InP substrate.

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