JP6939411B2 - 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 the structure of a semiconductor optical element such as a modulator integrated laser used in a modulator integrated light source in which a semiconductor laser and an optical modulator are integrated.

Due to the explosive increase in network traffic volume accompanying the spread of the Internet, the speed and capacity of optical fiber transmission have increased remarkably. 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 fedback (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 has been 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 even between 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 absorption (EA) type optical modulator on the same substrate, is compact and 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 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 operates by photomodulation due to a change in the light absorption coefficient when an electric field is applied to the quantum well active layer, which is the core of the optical waveguide through which the modulated light passes.

FIG. 1A shows a cross-sectional view of a substrate in a modulation region of a general conventional EA modulator. In FIG. 1A, it is assumed that the modulated light passes through the quantum well layer (core layer, active layer) 1 in the in-plane direction of the substrate (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. The upper and lower layers of the quantum well layer 1 (usually a non-doped intrinsic semiconductor, expressed as i-type) have a clad layer having different semiconductor polarities, for example, a p-type clad layer (p-InP) 2. , The pin semiconductor structure is formed by three layers in which the n-type clad layer (n-InP) 3 is arranged. An electric field is applied in the vertical direction (direction perpendicular to the quantum well layer 1, vertical direction) by reverse bias together with the modulated electric signal from the modulated signal source 41 by the upper and lower electrodes facing each other across the pin semiconductor structure. This electric field controls the light absorption coefficient for light passing through the quantum well layer 1 and modulates the light.

FIG. 1B is a diagram showing changes in the absorption coefficient (light absorption spectrum) with respect to the wavelength of the EA modulator having the quantum well structure when the 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 interband absorption corresponding to the interband transition wavelength (the section on the left side 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 absorption spectrum is shifted by a long wavelength by further reducing the effective band gap, that is, so-called quantum confinement. The Stark (QCSE) effect occurs. Therefore, in general, the light modulation operation is achieved by setting the operating wavelength of the laser to a longer wavelength side than the exciton absorption wavelength and increasing the light absorption coefficient by applying an electric field.

The EA-DFB laser element 10 is composed of an electric field absorption (EA) modulator region provided along the optical waveguide core layer and a laser region that functions as a DFB laser, and the laser light generated in the laser region absorbs the electric field. It is modulated in the modulator area to become output light.

FIGS. 2 and 3 show a cross-sectional view of a substrate of a waveguide structure of a general conventional EA-DFB laser. FIG. 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 electric field absorption modulator region 8. Is. FIG. 3 is a cross-sectional view of a substrate including an optical axis along the optical waveguide core layer.

In FIGS. 2A and 2B, both sides are embedded on the n-type clad layer (n-InP clad layer / substrate) 3, which is also an n-type substrate, by a semi-insulating InP embedded 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 different compositions. A common p-type clad 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 and 4 are connected by an optical waveguide in the connection waveguide region 13. 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 common p-type clad layer 2, two p-type contact layers 7, and two p-electrodes 6 are formed on the upper portions of both core layers 1 and 4. A common n electrode 5 is provided under the n-type clad layer / substrate 3 and is grounded.

In the EA-DFB laser, electrical separation is required in order to bias drive the electric field absorption modulator and the laser independently. In the example of the conventional structure shown in FIG. 3, the substrate 3 is shared and grounded by the n electrode 5. On the other hand, on the p-electrode side, the p-type clad layer 2 above the connection waveguide region 13 is thinned within a range that does not affect the waveguide mode by etching, and the contact layer 7 is further removed. As a result, the p-electrode 6 is electrically separated into two in the electric field absorption modulator region 8 and the laser region 9.

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

Therefore, for example, if the absolute value of the bias voltage by the modulation signal source (bias voltage source) 41 of the electric field 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 is | V _bEA + V _bLD |, which is the absolute value of the sum, and the potential difference applied to the portion of the connection waveguide region 13 becomes considerably large.

For example, the forward bias voltage of a general laser is about +1 to + 3V, and the reverse bias voltage of a modulator is about -1 to -4V, so a maximum voltage of 7V is applied to the waveguide in the connection waveguide region 13. .. In addition, since the connection waveguide region 13 is connected by the clad region 2 which has conductivity although it is thinned by etching, a leakage current is generated. In order to suppress this leakage 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 a problem, and an object of the present invention is to realize a high-performance electric field absorption modulator integrated laser having a simple manufacturing process and excellent electrical separation characteristics. It is in.

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

(Structure 1 of the invention)
And the silicon substrate, SiO ₂ layer is formed on the silicon substrate, a substrate having a two-layer structure,
Wherein A electroabsorption modulator region formed on the substrate, wherein the substrate on both sides of the direction of the core layer is perpendicular to the direction and the optical waveguide direction parallel to the stacking surface of the core layer, different cladding layer of semiconductor polar An electric field absorption modulator region having a waveguide structure in which
In the laser region formed on the substrate, clad layers having different semiconductor polarities are arranged on the substrates on both sides of the core layer in the direction parallel to the laminated surface of the core layers and in the direction orthogonal to the optical waveguide direction. A laser region having a waveguide structure arranged opposite to the semiconductor polarity of the clad layer in the electric field absorption modulator region,
A connection waveguide region connecting the electric field absorption modulator region and the laser region, which is formed by an embedded waveguide made of an intrinsic semiconductor, and both sides of the intrinsic semiconductor are _{embedded in SiO 2} layers of the substrate. With a connection waveguide area with
Two clad layers having different semiconductor polarities on one side of the electric field absorption modulator region and the laser region viewed in the optical waveguide direction are connected by a common electrode, the common electrode is grounded, and the electric field absorption modulator is grounded. A semiconductor optical device characterized in that a reverse bias power supply is connected to a region and a forward bias power supply is connected to the laser region.

(Structure 2 of the invention)
The semiconductor optical device according to the configuration 1 of the present invention.
The embedded waveguide made of the intrinsic semiconductor in the connection waveguide region is located in the connection waveguide region from the optical input / output portions on both sides in the optical waveguide direction in contact with the electric field absorption modulator region and the laser region in the connection waveguide region. A semiconductor optical element characterized in that it is formed so as to narrow the embedding width toward the central portion.

(Structure 3 of the invention)
The semiconductor optical device according to the configuration 2 of the present invention.
A semiconductor optical device characterized in that an embedded waveguide of the connecting waveguide region by the intrinsic semiconductor is formed so as not to be embedded by the intrinsic semiconductor in a central portion of the connecting waveguide region.

(Structure 4 of the invention)
The semiconductor optical device according to the configuration 1 of the present invention.
A semiconductor optical device characterized in that the entire connection waveguide region is formed of a thin wire waveguide that is not embedded by an intrinsic semiconductor.

(Structure 5 of the invention)
The semiconductor optical device according to any one of the configurations 1 to 4 of the present invention.
A semiconductor optical device characterized in that the core layers of the electric field absorption modulator region and the laser region have a quantum well structure.

(Structure 6 of the invention)
The semiconductor optical device according to any one of the configurations 1 to 5 of the present invention.
A semiconductor optical device characterized in that the substrate is a semi-insulating (SI) InP substrate.

According to the present invention, the potential difference between the modulator region and the laser region is suppressed, and the electrical separation is improved, so that the leakage current is suppressed and the voltage tolerance is improved. Further, since the connecting waveguide is composed of an intrinsic semiconductor, the electrical resistance is high and the optical loss is suppressed, so that the connecting waveguide can be shortened, so that the device can be miniaturized.

Further, since the structure is such that n layers and p layers are provided on both sides of the core layer of the modulator region and the laser region and a voltage is applied in the lateral direction, the modulator is sandwiched between regions having a low refractive index in the vertical direction. It is possible to adopt a thin film structure and realize high light confinement. In addition, 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 thickness of the p-type clad layer and the n-type clad layer of the thin film. The capacity per unit length can be suppressed compared to the vessel. Further, by using a quantum well structure for the active layer of the modulator region and applying an electric field in the lateral direction (direction parallel to the laminated surface of the quantum well layer) to the quantum well, the modulation efficiency is increased.

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

FIG. 1 (a) is a cross-sectional view of a substrate of a conventional EA modulator, and FIG. 1 (b) shows a change in the light absorption spectrum due to the QCSE effect. It is a figure of the substrate cross section perpendicular 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 cross-sectional view of the substrate along the 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 substrate cross section perpendicular 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 a connection waveguide region, and FIG. 5 (c) is a cross-sectional view of the substrate in the modulator region. It is a top view explaining the connection with the power source of the semiconductor optical element of Example 1 of this invention. It is explanatory drawing of the change of the absorption coefficient and the quenching characteristic of the modulator region of Example 1 of this invention. 8 (a) is a top view of the semiconductor optical device of the first modification of the first embodiment of the present invention, and 8 (b) and 8 (c) are cross-sectional views of partial substrates at two locations in the connection waveguide region. It is a top view explaining the connection with the power source 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 substrate cross section perpendicular 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 connection waveguide region, and FIG. 11 (c) is a cross-sectional view of the substrate in the 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 overall structure of the semiconductor optical device according to the first embodiment of the present invention. Further, FIG. 5 is a cross-sectional view of the substrate of the semiconductor optical device according to 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 connection waveguide region 13, and FIG. 5 (c) is a cross-sectional view of the substrate in the modulator region 8. FIG. 6 is a top view of the semiconductor region of the semiconductor optical device according to the first embodiment of the present invention, and also shows electrodes for explaining a method of connecting to a drive power source.

As shown in FIGS. 4 and 5, in the semiconductor optical device of the first embodiment of the present invention, the substrate has _{a two-layer structure in which the SiO 2} layer 21 is formed on the silicon substrate 20, and the substrate is on the substrate. An embedded 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 connecting waveguide region 13, and the laser region 9 are all formed from, for example, a 6-layer InGaAsP quantum well. For the modulator region 8 and the connecting waveguide region 13, the same core layer 23 having a photoluminescence wavelength of 1.48 μm in the quantum well can be used. The photoluminescence wavelength of the quantum well in the core layer 24 of the laser region 9 is 1.55 μm. The core width is 0.7 μm, and the thickness of the slab layer including the core layer is 350 nm.

As shown in FIGS. 5A and 5C, on the substrates on both sides of the core layer (quantum well layer) 23, 24, the direction parallel to the laminated surface of the core layer and the direction orthogonal to the optical waveguide direction. In order to apply voltage from both sides, it is embedded by InP clad layers 25, 26 which have been doped with different types (type, semiconductor polarity). At this time, in the arrangement of the InP clad layers 25 and 26 in the laser region 9 and the modulator region 8, the doping polarity (p-type / n-type) of the semiconductor is viewed on both the left and right sides of the substrate with the core layer in the optical waveguide direction. They are arranged interchangeably so that they are reversed.

^{That is, a p-type clad layer 26 having 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. 5 (a), and a Si doping concentration of 1 is on the right side of the core layer 24. × 10 ¹⁸ cm ^-3 n-type clad layer 25 is formed.

^{On the other hand, the n-type clad layer 25 having a Si doping concentration of 1 × 10 18} cm ^-3 is on the left side of the core layer 23 of the modulator region 8 in FIG. 5 (c), and the Zn doping concentration is on the right side of the core layer 23. A 1 × 10 ¹⁸ cm ^-3 p-type clad layer 26 is formed.

The periphery of the core layer 23 of the connection waveguide region 13 in FIG. 5B is embedded as a clad layer by an intrinsic semiconductor (i-InP) layer 22, and both sides thereof _{continue to the SiO 2} layer 21 on the substrate upper layer. _{It is embedded in two} layers of SiO 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 above the clad layers 25 and 26 of the laser region 9 and the modulator region 8, respectively, and the doping concentration is 1 × 10, respectively. ¹⁹ cm- ³ n-type doping and p-type doping are applied. Further, an n electrode 29 or a p electrode 30 and a common electrode 50 are formed on the region of the contact layer, and a SiO ₂ protective film 31 or a surface diffraction grating 12 is formed on the surface between the electrodes. For the sake of clarity, 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. 6, the semiconductor optical element of the first embodiment of the present invention is composed of a modulator region 8, a laser region 9, and a connection waveguide region 13 between both regions. 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 connecting waveguide region 13 is 20 μm.

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

As shown in FIG. 6, the modulator region 8 and the laser region 9 are separated by etching the InP layer of the connecting waveguide region 13 between the two regions. Further, the n-type clad layer 25 and the p-type clad 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 clad layer 26 side in the EA modulator region 8 and the electrode on the n-type clad layer 25 side in the laser region 9 are electrically connected and integrally common. It is formed as an electrode 50 and is grounded.

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

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

FIG. 7 shows the quenching characteristics of the modulator region 8 of this device. FIG. 7A shows a change in the absorption coefficient spectrum when an electric field of various intensities is applied in a direction parallel to the substrate for an InGaAsP quantum well structure having a thickness of 10 nm and a bandgap wavelength of 1.45 μm. The range of electric field strength was 0 kV / cm to 100 kV / cm. Exciton absorption is suppressed by applying an electric field and the absorption spectrum is widened. In addition, band edge absorption is changed by the two-dimensional Franz-Keldish effect, and the absorption coefficient increases on the long wavelength side with respect to the exciton absorption peak.

FIG. 7B shows the quenching characteristics of the modulator region 8 of the present device at a plurality of laser oscillation wavelengths. Since the oscillation wavelength of the laser is set to 1.55 μm, a quenching 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 present element. Both the p-side electrode of the modulator region 8 and the n-side electrode of the laser region 9 are formed as an integral common electrode 50 and are grounded.

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

At this time, in the present invention, since the semiconductor polarities (p-type / n-type) of the clad layers on both sides of the core layers 23 and 24 are oppositely arranged in the modulator region 8 and the laser region 9, the voltages of the two bias power supplies The polarities are 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 in the modulator region 8 and the p electrode 30 in the laser region 9 is | V _bEA −V _bLD | and the absolute value of the difference. That is, since the potential difference is represented by the difference in the absolute value of the voltage, the electric field applied to the connecting 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 by the intrinsic semiconductor (i-InP) layer 22, a pin structure is formed between the modulator and the laser. Therefore, the effect of suppressing the leakage current is high as compared with the conventional structure of FIG. 3 in which the connection waveguide region is connected by the conductive impurity semiconductor.

In particular, when the absolute value of the bias voltage of the modulator 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 p-clad 26 is reverse biased, and current leakage can be suppressed almost completely.

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 larger than that, in this embodiment, since the connection waveguide region 13 is composed of the intrinsic semiconductor 22, the resistance is high and the current leakage can be suppressed.

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

As described above, according to the configuration of the present invention, it is possible to realize an EA-DFB laser having good electrical separation between the laser region and the modulator region.

(Modification 1 of Example 1)
FIG. 8 shows a modification 1 of the first embodiment. In the first embodiment of FIGS. 4 to 6, the connecting waveguide region 13 is composed of an embedded waveguide made of an intrinsic semiconductor 22, but the waveguide width of the connecting waveguide region 13 may be narrowed in order to increase the resistance. It is valid.

8 (a) is a top view of the semiconductor portion of the modified example 1 of the first embodiment, and FIGS. 8 (b) and 8 (c) are cross-sectional views of the substrates in AA'and BB' of FIG. 8 (a). It is a figure which shows the outline.

For example, as shown in FIGS. 8A and 8B, the optical input / output portions on both sides in the optical waveguide direction in contact with the modulator region 8 and the laser region 9 of the connection waveguide region 13 are formed by an intrinsic semiconductor (i-InP). As the embedded waveguide structure by 22 (FIG. 8B), the embedding width of the i-InP layer 22 is narrowed toward the central portion of the connecting waveguide region 13, or the i-InP layer 22 is embedded in the central portion. By eliminating and using only the core layer 23 (FIG. 8 (c)), 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 of the modification 1 of the first embodiment, as shown in the BB'cross-sectional view of FIG. 8C, the embedded i-InP layers 22 on both the left and right sides of the waveguide core layer 23. A thin wire waveguide structure in which is completely removed may be used. Further, all the connection waveguide regions 13 including the optical input / output portion can be formed into a thin wire waveguide structure without the embedded i-InP layer 22. In this configuration, the photocoupling efficiency is slightly inferior, but the effect of electrical separation is higher.

Even in this configuration, both sides of the core layer 23 of the connection waveguide region 13 other than the portion embedded in the i-InP layer 22 are embedded in the _{same SiO 2 layer as the SiO 2} layer 21 on the substrate upper layer. , Supports the common electrode 50.

(Modification 2 of Example 1)
FIG. 9 shows a modification 2 of the first embodiment. In Example 1 of FIG. 6, the p electrode of the modulator region 8 and the n electrode of the laser region 9 are shared and grounded as an integrated common electrode 50, but in the second modification of Example 1 of FIG. , The semiconductor polarity (type, doping) and the polarity of the bias voltage in both regions 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 shared and integrated. It is grounded as a common electrode 50.

Then, the p electrode 30 on the modulator region 8 side has a (negative) reverse bias power supply (modulation signal source) 41, and the n electrode 29 on the laser region 9 side has a (negative) forward bias power supply (laser drive current source). 42 is connected.

Also in the case of the modification 2 of the first embodiment of FIG. 9, the potential difference between the p electrode 30 in the modulator region 8 and the n electrode 29 in the laser region 9 is | V _bEA −V _bLD |, which is compared with the conventional structure. , The electric field applied to the connecting waveguide can be suppressed.

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

In the second embodiment of the present invention of FIG. 10, unlike the first embodiment of FIG. 4, the substrate is a single-layer semi-insulating (SI) InP substrate 40, which is placed on the substrate in the horizontal direction parallel to the substrate surface. An embedded 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 connecting waveguide region 13, and the laser region 9 are all formed from, for example, a 20-layer InGaAsP quantum well. For the modulator region 8 and the connecting waveguide region 13, the same core layer 23 having a photoluminescence wavelength of 1.48 μm in the quantum well can be used. The photoluminescence wavelength of the quantum well in the core layer 24 of the laser region 9 is 1.55 μm. The core width is 0.8 μm, and the thickness of the embedded layer is 400 nm.

As shown in FIGS. 11A and 11C, the substrates on both sides of the core layers (quantum well layers) 23 and 24 of the modulator region 8 and the laser region 9 are parallel to the laminated surface of the core layers. It is embedded from InP clad layers 25 and 26 that have been doped with different types (types, semiconductor polarities) in order to apply voltage from both sides in the direction and in the direction orthogonal to the optical waveguide direction. At this time, in the laser region 9 and the modulator region 8, the arrangement of the InP clad layers 25 and 26 is such that the doping polarity (p-type / n-type) of the semiconductor is located on the left and right sides of the substrate with the core layer in the optical waveguide direction. They are arranged interchangeably so that they are reversed.

^{That is, the p-type clad layer 26 having 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. 11 (a), and the Si doping concentration 1 is on the right side of the core layer 24. × 10 ¹⁸ cm ^-3 n-type clad layer 25 is formed.

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

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 clad layer, and both sides thereof are SiO _{following the SiO 2} layer 21 on the substrate upper layer. _{It is embedded in two} layers and supports the common electrode 50 on the right side.

In the second embodiment as well, the embedding width of the connection waveguide region 13 may be narrowed or the embedding may be eliminated at the central portion, as in the modified example 1 (FIG. 8) of the first embodiment. Further, all the optical connection waveguide regions 13 including the optical input / output portion can be embedded to form a thin wire waveguide structure without the i-InP layer 22.

As shown in FIGS. 11A and 11C, InGaAs contact layers 27 and 28 are formed above the clad layers 25 and 26 of the laser region 9 and the modulator region 8, respectively, and the doping concentration is 1 × 10 ^{19 respectively.} cm- ³ n-type doping and p-type doping are applied. Further, electrodes 29 and 30 for current injection and a common electrode 50 are formed on the regions of the contact layers 27 and 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 the sake of clarity, 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 is composed of a modulator region 8, a laser region 9, and a connection waveguide region 13 between both 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 connecting waveguide region 13 is 20 μm.

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

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

As shown in FIGS. 10 and 11, the modulator region 8 and the laser region 9 are separated by etching the InP region between the two regions. Further, the n-type clad layer and the p-type clad 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, the electrode on the p-type clad layer 26 side in the modulator region 8 and the electrode on the n-type clad layer 25 side in the laser region 9 are integrally common electrodes that are electrically connected. It is formed as 50.

The configuration of the second embodiment can also be manufactured by a general method for manufacturing a semiconductor element as in the first embodiment.

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 leakage current can be suppressed and the EA-DFB laser having high voltage tolerance can be realized. In particular, the structure of the second embodiment has a high heat dissipation effect because the laser is configured on the InP substrate. 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.

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

Further, although the core layer 24 of the laser is InGaAsP-based, other compound semiconductor materials such as InGaAlAs-based can also be applied. Further, in this embodiment, the core layer of the laser region, the modulator region, and the connection region has a quantum well structure, but any region or all regions may have a bulk structure. Further, although the diffraction grating 12 is _{composed of SiN and SiO 2} , it may be composed of other insulating films such as SiON and SiOx, or may be formed by etching the surface of InP. Further, a diffraction grating 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 having excellent electrical separation characteristics by a simple manufacturing method, and it can be widely used in an optical transmitter for an optical communication system. can.

1 Quantum well layer (core layer, active layer)
2 p-type clad layer (p-InP)
3 n-type clad layer (n-InP) / substrate 4 Laser core layer (quantum well layer, active layer)
5, 6 n electrodes, p electrodes 7 p-type contact layer 8 electric field absorption (EA) 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 Intrinsic semiconductor (i-InP) layer 23, 24 Core layer (quantum well layer, active layer)
25, 26 n-type clad layer, p-type clad 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 (6)

And the silicon substrate, SiO ₂ layer is formed on the silicon substrate, a substrate having a two-layer structure,
Wherein A electroabsorption modulator region formed on the substrate, wherein the substrate on both sides of the direction of the core layer is perpendicular to the direction and the optical waveguide direction parallel to the stacking surface of the core layer, different cladding layer of semiconductor polar An electric field absorption modulator region having a waveguide structure in which
In the laser region formed on the substrate, clad layers having different semiconductor polarities are arranged on the substrates on both sides of the core layer in the direction parallel to the laminated surface of the core layers and in the direction orthogonal to the optical waveguide direction. A laser region having a waveguide structure arranged opposite to the semiconductor polarity of the clad layer in the electric field absorption modulator region,
A connection waveguide region connecting the electric field absorption modulator region and the laser region, which is formed by an embedded waveguide made of an intrinsic semiconductor, and both sides of the intrinsic semiconductor are _{embedded in SiO 2} layers of the substrate. With a connection waveguide area with
Two clad layers having different semiconductor polarities on one side of the electric field absorption modulator region and the laser region viewed in the optical waveguide direction are connected by a common electrode, the common electrode is grounded, and the electric field absorption modulator is grounded. A semiconductor optical device characterized in that a reverse bias power supply is connected to a region and a forward bias power supply is connected to the laser region. The semiconductor optical device according to claim 1.
The embedded waveguide made of the intrinsic semiconductor in the connection waveguide region is located in the connection waveguide region from the optical input / output portions on both sides in the optical waveguide direction in contact with the electric field absorption modulator region and the laser region in the connection waveguide region. A semiconductor optical element characterized in that it is formed so as to narrow the embedding width toward the central portion. The semiconductor optical device according to claim 2.
A semiconductor optical device characterized in that an embedded waveguide of the connecting waveguide region by the intrinsic semiconductor is formed so as not to be embedded by the intrinsic semiconductor in a central portion of the connecting waveguide region. The semiconductor optical device according to claim 1.
A semiconductor optical device characterized in that the entire connection waveguide region is formed of a thin wire waveguide that is not embedded by an intrinsic semiconductor. The semiconductor optical device according to any one of claims 1 to 4.
A semiconductor optical device characterized in that the core layers of the electric field absorption modulator region and the laser region have a quantum well structure. The semiconductor optical device according to any one of claims 1 to 5.
A semiconductor optical device characterized in that the substrate is a semi-insulating (SI) InP substrate.

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