JP6996183B2 - Semiconductor optical device - Google Patents

Description

The present invention relates to the structure of a semiconductor optical element used as a light source for an optical transmitter or the like. More specifically, the present invention relates to a semiconductor optical element used in 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 speed and capacity of optical fiber transmission have increased significantly. Semiconductor lasers have continued to develop as light source devices that support optical fiber communication. In particular, the realization of a single-mode light source using a distributed feedback (DFB) semiconductor laser is to increase the speed and capacity of optical fiber communication by the time division multiplexing method and the wavelength division multiplexing (WDM) method. Has greatly contributed to.

In recent years, optical communication is applied not only to telecom 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 has been standardized using the configuration of a WDM type multi-wavelength array light source, and the capacity of short-range optical communication is rapidly increasing. Against this background, it is essential to increase the speed and reduce the power consumption of the optical transmitter, and as a high-performance modulation light source that modulates the light from the integrated laser light source with an electric signal and outputs it, a modulator integrated semiconductor. Lasers have advanced.

In particular, the EA-DFB laser, which monolithically integrates a single-mode DFB laser and an electric field absorption (EA) type optical modulator on the same substrate, is compact, has low power consumption, and is capable of high-speed modulation exceeding 40 Gbit / s. Therefore (Non-Patent Document 1), it has been put into practical use as an optical transmitter for a relatively short distance of 100 km or less. As of 2017, the standardization of 400 Gbit Ethernet is being completed, and an EA-DFB laser capable of supporting 50 Gbit / s class PAM (Pulse Amplitude Modulation) is also 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 D. A. B. Miller et al., “Electric field dependence of optical absorption near the band gap of quantum-well structures”, Physical Review, vol. B32, pp. 1043-1060, 1985.

The EA modulator operates by photomodulation due to a change in the light absorption coefficient when an electric field due to a modulated electric signal is applied to a quantum well active layer which is an optical waveguide core through which the modulated light passes.

FIG. 1A shows a cross-sectional view of a board of a general conventional EA modulator. In FIG. 1A, the modulated light is assumed to pass through the quantum well layer (core layer, active layer) 1 in the in-plane direction of the substrate (direction perpendicular to the paper surface or left-right direction in the paper surface).

The quantum well layer 1 is a multi-layer structure in which a barrier layer made of a material having a large bandgap and a well layer made of a material having a small bandgap are alternately and periodically laminated. Above and below this quantum well layer 1 (usually a non-doped intrinsic semiconductor, expressed as i-type), a p-type clad layer (for example, p-InP) 2 and an n-type clad layer (for example, n-InP) 3 A pin semiconductor structure is formed by three layers in which the above are arranged. An electric field is applied in the vertical direction (direction perpendicular to the quantum well layer 1) in the vertical bias together with the modulated electric signal from the modulated signal source 41 by the upper and lower electrodes facing each other across the semiconductor structure. In this way, the light absorption coefficient for the light passing through the quantum well layer 1 is controlled, and the light is modulated.

FIG. 1B is a diagram showing changes in the absorption coefficient (light absorption spectrum) of the EA modulator having the quantum well structure when the applied electric field is zero (solid line) and when a predetermined electric field is applied (dotted line). Is. The light absorption spectrum of the quantum well structure consists of the interband absorption corresponding to the interband transition wavelength (the left section of the "band end" in FIG. 1 (b)) and the exciton absorption peak on the long wavelength side thereof.

When an electric field is applied, the exciton absorption peak of the light absorption spectrum is lowered due to the localization of carriers in the quantum well layer 1, and the effective band gap is further reduced to shift the absorption spectrum by a long wavelength, that is, so-called quantum confinement. A Stark (QCSE) effect is produced. Therefore, by setting the operating wavelength of the laser to a longer wavelength side than the exciton absorption wavelength, the absorption coefficient increases with the application of the electric field, and the intensity modulation operation becomes possible.

FIG. 2 shows a cross-sectional view of a substrate of a general EA-DFB laser along an optical waveguide core layer. The EA-DFB laser element 10 is composed of an electric field absorption modulator region 8 and a laser region 9 along the optical waveguide core layer, and the laser light generated in the laser region 9 is modulated in the electric field absorption modulator region 8 to output light. Will be.

In the EA-DFB laser element 10 of FIG. 2, a modulator core layer (quantum well layer, active layer) 1 and a laser core layer (quantum well) are placed on an n-type clad layer (n-InP clad layer / substrate) 3 as a substrate. A layer (layer, active layer) 4 is formed and is connected to form an optical waveguide that communicates with the layer. A diffraction grating 11 that determines the oscillation wavelength of the laser is formed on the upper portion of the laser core layer 4. A p-type clad layer 2a and 2b having a common two-layer structure, two p-contact layers 7, and two p-electrodes 6 are formed on the upper portions of both core layers. The modulator region 8 and the laser region 9 are electrically separated by a gap region between the left and right contact layers 7, and are independently bias-driven. The n electrodes 5 under the n substrate 3 may be common.

Further, FIG. 3 shows a cross-sectional view of the substrate at two locations when the EA-DFB laser element 10 of FIG. 2 is viewed from the waveguide direction of light. FIG. 3A is a cross-sectional view of a substrate showing a cross-sectional structure in a laser region 9 and FIG. 3B is a cross-sectional structure in a modulator region 8. This structure is an EA-DFB laser structure called a semi-insulating embedded type.

In both FIGS. 3A and 3B, the optical waveguide has high resistance semi-insulating (SI) on both the left and right sides of the pin structure that vertically sandwiches the active layer 1 of the modulator region 8 and the active layer 4 of the laser region 9. It is an embedded waveguide structure embedded in the InP embedded layer 15. Here, the p-type clad layer is laminated on the upper part of the active layers 1 and 4, but the doping concentration of the p-type clad layer is set in order to suppress the electric resistance and efficiently inject holes into the active layer region. High is desirable. On the other hand, from the viewpoint of light propagation loss, it is desirable that the doping concentration of the p-type clad layer is low.

For this reason, the p-type clad layer is provided with a low-concentration doping p-type clad layer 2a directly above the active layers 1 and 4 in which the electric field distribution in the waveguide mode exists, and is high on the low-concentration doping layer. It is common to have a two-layer structure provided with a concentration-doped p-type clad layer 2b. Therefore, in the case of producing a conventional structure, it is necessary to separately form a two-layer structure for the overclad layer in the laser region and the modulator region according to each region, which requires man-hours.

Further, although it is important to suppress the element capacitance for high-speed modulation operation, in a modulator using a vertical electric field, the capacitance is defined by the electrode area because the electrodes are arranged above and below the element. Therefore, the generation of parasitic capacitance under the electrode is unavoidable, which hinders the high-speed modulation operation.

The present invention has been made in view of such a problem, and an object of the present invention is to realize a high-performance electric field absorption modulator integrated laser with a simple manufacturing process.

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

(Structure 1 of the invention)
A semiconductor optical device composed of an electric field absorption modulator region and a laser region formed on a semiconductor substrate.
The active layer in the electric field absorption modulator region and the active layer in the laser region communicating with each other,
The p-type clad layer and the n-type clad layer adjacent to the active layer are arranged on both sides in the direction parallel to the substrate surface of the active layer of the electric field absorption modulator region.
In the laser region and the electric field absorption modulator region , the p-type clad layer arranged on both sides of the active layer in the laser region in the direction parallel to the substrate surface, the n-type clad layer adjacent to the active layer, and the electric field absorption modulator region. It is provided with a transition region disposed between the p-type clad layer and the active layer, in which the doping concentration increases as the distance from the end on the side of the active layer increases.
The width of the transition region in the electric field absorption modulator region is wider than the width of the transition region in the laser region, and the width is a length in a direction parallel to the substrate surface and a direction perpendicular to the optical axis. A semiconductor optical element characterized by.

(Structure 2 of the invention)
The semiconductor optical device according to the configuration 1 of the present invention.
A semiconductor optical device characterized in that a connecting waveguide region that electrically separates and optically couples both regions is provided between the electric field absorption modulator region and the laser region.

(Structure 3 of the invention)
In the semiconductor optical device according to the configuration 2 of the invention,
The width of the active layer in the electric field absorption modulator region is wider than the width of the active layer in the laser region, and the width is a length in a direction parallel to the substrate surface and a direction perpendicular to the optical axis. A semiconductor optical device characterized in that the core layer of the connection waveguide region has a tapered structure.

(Structure 4 of the invention)
The semiconductor optical device according to any one of the configurations 1 to 3 of the present invention.
A semiconductor optical device characterized in that the semiconductor substrate is a two-layer substrate in which a SiO ₂ layer is formed on a silicon substrate.

(Structure 5 of the invention)
The semiconductor optical device according to any one of the configurations 1 to 3 of the present invention.
A semiconductor optical device characterized in that the semiconductor substrate is a semi-insulating (SI) InP single-layer substrate.

According to the configuration described in the configuration 1 of the present invention, the width of the intrinsic semiconductor region can be easily and independently controlled in each active layer region of the laser and the modulator. Further, by using the lateral electric field, the element capacity is dominated by the thickness of the p-type clad layer and the n-type clad layer, so that it is not easily affected by the electrode area, and the element capacity per unit length is suppressed. Therefore, it is advantageous for high-speed operation.

Further, in the configuration described in the configuration 2 of the invention, a transition region in which the doping concentration increases as the distance from the core layer edge is provided is provided in the p-type clad region beside the core layer, and the side of the core layer in which the light in the waveguide mode exists is provided. The doping distribution can be adjusted by setting the low doping region and the others to the high doping region.

As described above, according to the present invention, it is possible to realize a semiconductor optical device such as an electric field absorption modulator integrated laser having a simple manufacturing process and high performance.

It is the substrate sectional view (a) of the conventional EA modulator, and the figure (b) which shows the change of the light absorption spectrum by the QCSE effect. It is sectional drawing of the substrate along the optical waveguide core layer of the conventional EA-DFB laser. It is a substrate cross-sectional view (a) of a laser region and a substrate cross-sectional view (b) of a modulator region seen from the waveguide direction of the light of a conventional EA-DFB laser. It is a perspective view of the semiconductor optical element of Example 1 of this invention. It is a top view of the semiconductor region of the semiconductor optical element of Example 1 of this invention. It is a substrate cross-sectional view (a) of the laser region of the semiconductor optical element of Example 1, a substrate cross-sectional view (b) of a modulator region, and a substrate cross-sectional view (c) of a connection waveguide region of this invention. In the quantum well structure of the semiconductor optical device of the first embodiment of the present invention, the change in the absorption spectrum when an electric field is applied in the parallel direction to the substrate (a) and the absorption spectrum when the electric field is applied in the vertical direction to the substrate. It is a figure which shows the change (b). It is the substrate sectional view (a) of the laser region of the semiconductor optical element of Example 2 of this invention, and the substrate sectional view (b) of the modulator region. It is a perspective view of the semiconductor optical element of Example 3 of this invention. It is a substrate cross-sectional view (a) of the laser region of the semiconductor optical element of Example 3, a substrate cross-sectional view (b) of a modulator region, and a substrate cross-sectional view (c) of a connection waveguide region of this invention. It is the substrate sectional view (a) of the laser region of the semiconductor optical element of Example 4 of this invention, and the substrate sectional view (b) of the modulator region. It is a top view of the semiconductor optical element of Example 5 of this invention. It is a figure explaining the method of determining the taper angle in the semiconductor optical element of Example 5 of this invention.

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

FIG. 4 is a perspective view showing the structure of the semiconductor optical device according to the first embodiment of the present invention. FIG. 5 is a top view showing only the semiconductor region of the semiconductor optical device according to the first embodiment of the present invention.

Further, FIG. 6 shows a cross-sectional view (a) of the cross section A-A'of the laser region 9 of FIG. 5, a cross-sectional view (b) of the substrate of the cross-section BB'of the modulator region 8 of FIG. 5, and the modulator. 6 is a cross-sectional view (c) of a substrate of a cross section CC'of a connecting waveguide region 13 connecting a region 8 and a laser region 9.

As shown in FIGS. 4 to 6, in the semiconductor optical device of the first embodiment of the present invention, the substrate is a two-layer substrate in which the SiO ₂ layer 21 is formed on the silicon substrate 20. On this substrate, an embedded core layer having a current injection structure in the lateral direction, that is, parallel to the laminated surface of the quantum well layer which is the core layer (parallel to the substrate surface) and perpendicular to the optical axis is formed. ..

The core layer 23 of the EA modulator region 8 and the core layer 24 of the laser region 9 include a laminated quantum well layer as an active layer and are embedded in the i-InP layer 22 to form a connecting waveguide region 13. It constitutes an optical waveguide that communicates through. For example, the core layer 23 of the EA modulator region 8 and the core layer 24 of the laser region 9 are both formed from a 6-layer InGaAsP quantum well.

The emission wavelength (PL wavelength) of the laser region 9 is 1.55 μm, the emission wavelength (PL wavelength) of the modulator region 8 is 1.46 μm, and the emission wavelength (PL wavelength) of the core layer of the laser region 9 is the modulator. The wavelength is set to be longer than the emission wavelength (PL wavelength) of the core layer of the region 8. The core width of both core layers is 0.8 μm, and the thickness of the slab layer including the core layer is 350 nm.

InP layers, each of which has been subjected to different types of doping for lateral current injection, are embedded as clad layers on both sides of both core layers (active layers) 23 and 24 in the direction parallel to the substrate surface on the substrate. It has been. That is, on the left side of the core layer 24 which is the active layer of the laser region 9 in FIG. 6A, the Si n-type doping layer 25 having a doping concentration of 1 × 10 ¹⁸ cm ^-3 is on the right side of the core layer 24. , A Zn p-type doping layer 26 having a doping concentration of 1 × 10 ¹⁸ cm ^-3 is formed as a clad layer.

On the other hand, in the core layer 23 of the modulator region 8 of FIG. 6B, the n-type doping layer 25 is the same, but the p-side doping layer 26 has the core layer 23 at the end on the side of the core layer 23. It is different from the laser region 9 in that it is formed at a distance of 0.1 μm with respect to the laser region 9 and the i-InP layer 22 is embedded between them.

That is, in the first embodiment of the present invention, the end portion of the p-type clad layer in the modulator region on the core layer side is farther from the core layer than the end portion of the p-type clad layer in the laser region on the core layer side. It is characterized in that it is formed so as to be in a position.

InGaAs contact layers 27 and 28 for current injection are formed above the doping layers (clad layers) 25 and 26 in both regions, respectively, and n-type doping and p-type doping with a doping concentration of 1 × 10 ¹⁹ cm ^-3 , respectively. Is given. Further, electrodes 29 and 30 for current injection are formed on the regions of the contact layers 27 and 28, a SiO ₂ protective film 31 is formed on the surface of the modulator region 8, and surface diffraction is performed on the surface of the laser region 9. The grating 12 is formed. For ease of viewing, the SiO ₂ protective film 31 is not shown in the perspective view of FIG.

As shown in the perspective view of FIG. 4 and the top view of FIG. 5, the semiconductor optical device of the first embodiment of the present invention is composed of a modulator region 8, a laser region 9, and a connecting waveguide region 13. The active layer length of the laser region 9 is 600 μm, the active layer length of the modulator region 8 is 150 μm, and the waveguide length of the connecting waveguide region 13 is 20 μm.

As shown in FIG. 4, a SiN insulating film having a thickness of 20 nm is formed on the upper part of the core layer 24 of the laser region 9, and a λ / 4 shift diffraction grating structure having a Bragg wavelength of 1.55 μm composed of SiN and SiO ₂ is formed. The surface diffraction grating 12 is formed. Further, as shown in FIG. 6C, the connecting waveguide region 13 is configured by a waveguide structure in which a core similar to the core 23 in the modulator region is embedded only by the i-InP layer 22. As shown in FIGS. 4 and 5, the modulator region 8 and the laser region 9 are electrically separated by etching the InP region 22 between the regions, and are optically coupled by the connecting waveguide region 13. Further, each of the n-type semiconductor layer and the p-type semiconductor layer in the modulator region 8 and the laser region 9 is formed only in a portion necessary for each region.

In manufacturing a semiconductor optical device having this waveguide structure, a technique such as wafer bonding can be used to form an InP thin film on a SiO ₂ / Si substrate. Further, a metalorganic vapor phase growth method (MOVPE) is used for crystal growth of InP, InGaAsP, etc., and a general semiconductor laser manufacturing method such as wet etching or dry etching is used for manufacturing a laser waveguide structure and a diffraction grating. be able to.

The doping layers (clad layers) 25 and 26 for current implantation on the left and right of the active layers (core layers) 23 and 24 can be formed by regrowth of the intrinsic semiconductor region, p region, and n region, and are also intrinsic after the formation of the active layer. It is effective to embed InP and re-grow, and then form an impurity semiconductor only in the required region by a method such as ion implantation from the surface or thermal diffusion.

By this method, the n region and the p region of the laser region 9 and the modulator region 8 shown in FIGS. 6 (a) and 6 (b) can be formed at one time, respectively. Further, the surface diffraction grating 12 can be formed by pattern formation and etching by electron beam exposure to the laser surface.

In the first embodiment, in the laser region 9, by arranging the p-type clad layer 26 to the side of the core layer 24, efficient current injection into the quantum well of the core layer 24 is performed. On the other hand, in the modulator region 8, by arranging the InP layer 22 of the intrinsic semiconductor between the core layer 23 and the p-type clad layer 26, the light propagation loss is suppressed and the capacity of the core layer is suppressed. .. Since the laser region 9 and the modulator region 8 are formed separately, the doping region of both regions can be designed individually. Therefore, it is possible to easily form a doping distribution suitable for each region.

Further, in the first embodiment, since the quantum well is used for the core layer 23 of the modulator, a lateral electric field application (a current injection structure parallel to the laminated surface of the quantum well layer, that is, the substrate surface and perpendicular to the optical axis) is applied. ), The modulation efficiency can be increased and the element length can be shortened.

FIG. 7 shows the absorption coefficient spectra of an InGaAsP quantum well structure having a thickness of 10 nm when (a) an electric field is applied in a direction parallel to the substrate and (b) an electric field is applied in a direction perpendicular to the substrate. It is a figure which contrasts and shows the Absorption cohesion). The range of the electric field to be applied was 6 ways from 0 kV / cm to 100 kV / cm.

The change in absorption coefficient (a) when a lateral electric field is applied to the quantum well is mainly caused by shielding exciton absorption by the electric field (Non-Patent Document 2). When the operating wavelength is set to the long wavelength side with respect to the exciton absorption peak wavelength (for example, at an operating wavelength of 1.55 μm), as is clear from FIG. 7, when an electric field is applied in parallel to the substrate (a). However, the amount of absorption change at a low electric field is larger than that when an electric field is applied perpendicularly to the substrate (b). Therefore, it is possible to shorten the length of the optical modulation element, and in addition to reducing the loss, there is an effect of increasing the modulation band by suppressing the parasitic capacitance of the element.

As described above, according to the configuration of the semiconductor optical device according to the first embodiment of the present invention, an EA-DFB laser capable of high-speed modulation can be realized by a simple manufacturing process. In particular, since this structure constitutes an InP slab region as thin as 350 nm on SiO ₂ having a low refractive index, the optical confinement of the core layer is improved and the modulator region can be shortened.

In addition, the modulator region and the laser region are completely separated by etching, and impurities can be formed only in the required region. This ensures good electrical separation. Further, the element capacity is defined not by the electrode area but by the cross-sectional area of the layer, and the element capacity per unit length is suppressed, so that a high-speed response exceeding 50 Gbit / s can be realized.

FIG. 8 describes the configuration of the semiconductor optical device according to the second embodiment of the present invention. 8 (a) is a substrate sectional view of a laser region 9, and FIG. 8 (b) is a cross-sectional view of a substrate of a modulator region 8. Since the structure of the semiconductor optical device of Example 2 is the same as that of Example 1 except for the doping transition region of the p-type clad layer beside the core, a perspective view and a top view are not shown.

In the semiconductor optical device of the second embodiment, as shown in FIG. 8A, the active layer (core layer) 24 of the laser region 9 is not in direct contact with the p-type cladding 26 on the right side, and has a width of 0.2 μm. It is different from Example 1 in that the p-type doping transition region 26a is provided. The p-type doping concentration at the end of the doping transition region 26a on the active layer 24 side is 5 × 10 ¹⁷ cm ^-3 , and increases to 1 × 10 ¹⁸ cm ^-3 as the distance from the active layer 24 increases.

Further, as shown in FIG. 8B, in the active layer (core layer) 23 of the modulator region 8 of the second embodiment, the i-InP layer 22 is replaced with the p-type clad layer 26 on the right side. Therefore, a p-type doping transition region 26b having a width of 0.3 μm, which is wider than the laser region 9, is provided. The p-type doping concentration at the end of the doping transition region 26b on the side of the active layer 23 is 1 × 10 ¹⁷ cm ^-3 , and increases to 1 × 10 ¹⁸ cm ^-3 as the distance from the active layer 23 increases.

That is, in the second embodiment of the present invention, each of the p-type clad layers in both regions has a transition region on the core layer side in which the doping concentration increases as the distance from the end on the core layer side increases. The width of the transition region in the absorption modulator region is wider than the width of the transition region in the laser region.

Such a doping transition region is obtained by providing a distance between the active layer core and the boundary of the clad layer, forming a true InP layer there, and then applying diffusion or ion implantation.

In the second embodiment, in the laser region 9, the doping transition region 26a is provided and the p-doping layer is arranged to the side of the core layer, so that efficient current injection into the quantum well is performed, and the doping amount is increased. Since it is lowered, it is effective in reducing the loss. On the other hand, in the modulator region 8, a wider doping transition region 26b can be provided to suppress light propagation loss, and holes can be extracted at high speed by an electric field.

In these doping transition regions, for example, after the formation of the active layer, intrinsic InP is embedded and re-grown, and then p-type impurities such as Zn are placed in the vertical direction by using a technique such as ion implantation or thermal diffusion from the surface. It can be formed by spreading it laterally. In diffusion and ion implantation, it is a physically general behavior that the substance penetrates in the vertical direction and then spreads in the horizontal direction after entering the substance to be implanted, so that such formation is possible.

9 and 10 show the configuration of the semiconductor optical device according to the third embodiment of the present invention. FIG. 9 is a perspective view showing the structure of the semiconductor optical device according to the third embodiment of the present invention. 10 (a) to 10 (c) are a cross-sectional view of the substrate 9 of the laser region 9 of the third embodiment of the present invention and a cross-sectional view of the substrate 10 of the modulator region 8 (a), similarly to FIG. 6 of the first embodiment. b), and is a cross-sectional view 10 (c) of the substrate of the connection waveguide region 13 connecting the modulator region 8 and the laser region 9.

In Example 3 of the present invention of FIGS. 9 and 10, the same parts as those of Example 1 of FIGS. 4 to 6 are indicated by the same reference numerals. In Example 3, unlike Example 1, the substrate is a semi-insulating (SI) InP single-layer substrate 40, on which an embedded core layer having a lateral current injection structure is formed. For example, the core layer 23 of the EA modulator region 8 and the core layer 24 of the laser region 9 are both formed from a 20-layer InGaAsP quantum well.

The emission wavelength (PL wavelength) of the laser region 9 is 1.55 μm, and the emission wavelength (PL wavelength) of the modulator region 8 is 1.46 μm. The core width of both core layers is 0.8 μm, and the thickness of the embedded layer is 400 nm.

InP layers, each of which has been subjected to different types of doping for lateral current injection, are embedded as clad layers on both sides of both core layers (active layers) 23 and 24 in the direction parallel to the substrate surface on the substrate. It has been. That is, on the left side of the core layer 24 which is the active layer of the laser region 9 in FIG. 10 (a), the Si n-type doping layer 25 having a doping concentration of 1 × 10 ¹⁸ cm ^-3 is on the right side of the core layer 24. , A Zn p-type doping layer 26 having a doping concentration of 1 × 10 ¹⁸ cm ^-3 is formed as a clad layer.

On the other hand, in the core layer 23 of the modulator region 8 of FIG. 10B, the n-type doping layer 25 is the same, but the p-side doping layer 26 has the core layer 23 at the end on the side of the core layer 23. It is different from the laser region 9 in that it is formed at a distance of 0.1 μm with respect to the laser region 9 and the i-InP layer 22 is embedded between them.

That is, in the third embodiment of the present invention, the end portion of the p-type clad layer in the modulator region on the core layer side is farther from the core layer than the end portion of the p-type clad layer in the laser region on the core layer side. It is characterized in that it is formed so as to be in a position.

InGaAs contact layers 27 and 28 for current injection are formed above the doping layers (clad layers) 25 and 26 in both regions, respectively, and n-type doping and p-type doping with a doping concentration of 1 × 10 ¹⁹ cm ^-3 , respectively. Is given. Further, electrodes 29 and 30 for current injection are formed on the regions of the contact layers 27 and 28, a SiO ₂ protective film 31 is formed on the surface of the modulator region 8, and surface diffraction is performed on the surface of the laser region 9. The grating 12 is formed. For ease of viewing, the SiO ₂ protective film 31 is not shown in the perspective view of FIG.

As shown in the perspective view of FIG. 9, the semiconductor optical device of the third embodiment of the present invention is composed of a modulator region 8, a laser region 9, and a connecting waveguide region 13. The active layer length of the laser region 9 is 600 μm, the active layer length of the modulator region 8 is 150 μm, and the waveguide length of the waveguide region 13 is 20 μm.

As shown in FIG. 9, a SiN insulating film having a thickness of 20 nm is formed on the upper part of the core layer 24 of the laser region 9, and a λ / 4 shift diffraction grating structure having a Bragg wavelength of 1.55 μm composed of SiN and SiO ₂ is formed on the surface. The diffraction grating 12 is formed. Further, as shown in FIG. 10C, the connecting waveguide region 13 is configured by a waveguide structure in which a core similar to the modulator core 23 is embedded only in the i-InP layer 22. As shown in FIG. 9, the modulator region 8 and the laser region 9 are electrically separated by etching the InP region between the regions, and are optically coupled by the connecting waveguide region 13. Further, each of the n-type semiconductor layer and the p-type semiconductor layer in the modulator region 8 and the laser region 9 is formed only in a portion necessary for each region. Similar to Examples 1 and 2, this configuration can also be manufactured by using a general method for manufacturing a semiconductor device.

In the structure of the third embodiment, since the laser is configured on the InP substrate 40, the effect of heat dissipation is high. Further, since the light mode extends to the low-loss semi-insulating InP region, the loss is low, which is advantageous for increasing the light output of the laser.

FIG. 11 describes another embodiment according to the fourth embodiment of the present invention. 11 (a) is a substrate sectional view of a laser region 9, and FIG. 11 (b) is a cross-sectional view of a substrate of a modulator region 8. The structure of the semiconductor optical device of Example 4 is the same as that of Example 3 of FIG. 10 except for the doping transition region of the p-type clad layer beside the core.

In the semiconductor optical device of the fourth embodiment, as shown in FIG. 11A, the active layer (core layer) 24 of the laser region 9 is not in direct contact with the p-type cladding 26 side on the right side, and has a width of 0. It differs from Example 3 in that a transition region 26a of p-doping of .2 μm is provided. The doping concentration at the end of the p-doping transition region 26a on the active layer 24 side is 5 × 10 ¹⁷ cm ^-3 , and increases to 1 × 10 ¹⁸ cm ^-3 as the distance from the active layer 24 increases.

Further, as shown in FIG. 11B, in the active layer 23 of the modulator region 8 of the fourth embodiment, the width is wider than that of the p-type clad 26 on the right side instead of the i-InP layer 22. A wide 0.3 μm p-type doping transition region 26b is provided. The doping concentration at the end of the doping transition region 26b on the active layer 23 side is 1 × 10 ¹⁷ cm ^-3 , and increases to 1 × 10 ¹⁸ cm ^-3 as the distance from the active layer 23 increases.

That is, in the fourth embodiment of the present invention, each of the p-type clad layers in both regions has a transition region on the core layer side in which the doping concentration increases as the distance from the end on the core layer side increases. The width of the transition region in the absorption modulator region is wider than the width of the transition region in the laser region.

In the fourth embodiment as well, in the laser region 9, the doping transition region is provided and the p-doping layer is arranged to the side of the core layer, so that efficient current injection into the quantum well is performed. In addition, since the doping amount is reduced, it is effective in reducing the loss. On the other hand, in the modulator region 8, a wider doping transition region can be provided to suppress light propagation loss, and holes can be extracted at high speed by an electric field.

In the doping transition region, for example, after the formation of the active layer, the true InP is embedded and regrown, and then the p-type impurities such as Zn are implanted vertically and laterally by using a technique such as ion implantation or thermal diffusion from the surface. It can be formed by diffusing into.

In Examples 1 to 4, the core width on the laser region side and the core width on the modulator region side are described as the same width, but the core widths in both regions do not necessarily have to be the same. When the core layer structure is different, in order to adjust the optical confinement coefficient, for example, the core width on the modulator region side is made larger than that on the laser region side to increase the optical confinement coefficient and at the same time under lateral voltage. It can be expected that the capacitance will be reduced to achieve a high-speed response.

On the other hand, by narrowing the core width on the laser region side, the waveguide structure utilizes the improvement of transverse carrier injection efficiency, stable single transverse mode oscillation, and low loss optical mode spread to the lower InP substrate. You can expect the effect of increasing the output. It is advantageous to fabricate the device with an appropriate core width in the laser region and the modulator region, respectively.

FIG. 12 is a top view of the semiconductor optical device according to the fifth embodiment of the present invention when such a structure is used. When the width of the core layer 23 on the modulator region 8 side is larger than the width of the core layer 24 on the laser region 9 side, the connecting waveguide region 13 connecting the core layers of both regions (region without doping, separation region). By making the core layer of) a gentle taper structure, it is possible to change the core width without changing the manufacturing process only by changing the photomask at the time of device design.

At this time, as shown in FIG. 13, the angle θ of the taper of the core layer of the connecting waveguide region 13 is WE A for the core width on the modulator side, _WLD for the core width on the _laser side, and the length of the separation region. When set to l, the range is expressed by the following equation (1), and it is designed to be about 0.0001 rad to 0.001 rad.

As described above, according to the present invention, a compact and high-speed EA-DFB laser can be realized by a simple manufacturing method.

The laser structure of the semiconductor optical device according to the present invention is not limited to this embodiment. In the examples, the quantum well layer was used as the active layer, but a bulk active layer may be used. The operating wavelength was set to 1.55 μm, but up to 1.3 μm can be realized within the range of design changes.

Although the core layer of the laser is InGaAsP-based, it can also be applied to other compound semiconductor materials such as InGaAlAs-based. Further, although the diffraction grating is composed of SiN and SiO ₂ , it may be composed of another insulating film such as SiON or SiOx, or may be formed by etching the surface of InP. It is also self-evident that diffraction gratings can be formed above and below the core layer of the laser.

It is also clear that the configuration of Example 5 can be combined and applied to the configurations of Examples 1 to 4.

INDUSTRIAL APPLICABILITY According to the present invention, an electric field absorption modulator integrated laser having a simple manufacturing process and high performance can be realized, and can be used as an optical transmitter for an optical communication system.

1 Quantum well layer (core layer, active layer)
2,2a, 2b p-type clad layer (p-InP)
3 n-type clad layer (n-InP) / substrate 41 Modulation signal source 4 Laser core layer (quantum well layer, active layer)
5 n electrode 6 p electrode 7 p contact layer 8 electric field absorption modulator region 9 laser region 10 EA-DFB laser element 11 diffraction grating 12 surface diffraction grating 13 connection waveguide region 15 semi-insulating InP embedded layer 20 silicon substrate 21 SiO ₂ layer 22 i-InP layer 23, 24 core layer (quantum well layer, active layer)
25 n-type clad layer (n-type doping layer)
26 p-type clad layer (p-type doping layer)
26a, 26b Doping transition region 27, 28 Contact layer 29, 30 Electrode 31 SiO ₂ Protective film 40 Semi-insulating (SI) InP single-layer substrate

Claims (5)

A semiconductor optical device composed of an electric field absorption modulator region and a laser region formed on a semiconductor substrate.
The active layer in the electric field absorption modulator region and the active layer in the laser region communicating with each other,
The p-type clad layer and the n-type clad layer adjacent to the active layer are arranged on both sides in the direction parallel to the substrate surface of the active layer of the electric field absorption modulator region.
In the laser region and the electric field absorption modulator region , the p-type clad layer arranged on both sides of the active layer in the laser region in the direction parallel to the substrate surface, the n-type clad layer adjacent to the active layer, and the electric field absorption modulator region. It is provided with a transition region disposed between the p-type clad layer and the active layer, in which the doping concentration increases as the distance from the end on the side of the active layer increases.
The width of the transition region in the electric field absorption modulator region is wider than the width of the transition region in the laser region, and the width is a length in a direction parallel to the substrate surface and a direction perpendicular to the optical axis. A semiconductor optical element characterized by. The semiconductor optical device according to claim 1.
A semiconductor optical device characterized in that a connecting waveguide region that electrically separates and optically couples both regions is provided between the electric field absorption modulator region and the laser region. In the semiconductor optical device according to claim 2,
The width of the active layer in the electric field absorption modulator region is wider than the width of the active layer in the laser region, and the width is a length in a direction parallel to the substrate surface and a direction perpendicular to the optical axis. A semiconductor optical device characterized in that the core layer of the connection waveguide region has a tapered structure. The semiconductor optical device according to any one of claims 1 to 3.
A semiconductor optical device characterized in that the semiconductor substrate is a two-layer substrate in which a SiO ₂ layer is formed on a silicon substrate. The semiconductor optical device according to any one of claims 1 to 3.
A semiconductor optical device characterized in that the semiconductor substrate is a semi-insulating (SI) InP single-layer substrate.

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