JP2022015036A - Semiconductor laser - Google Patents

Abstract

To obtain a single mode with a smaller element size by a waveguide type laser in which an active layer is composed of a GaAs-based compound semiconductor.SOLUTION: A semiconductor laser includes: a lower clad layer 102 formed on a substrate 101; an active layer 103 formed on the lower clad layer 102 on the substrate 101; and a diffraction grating 121 formed on the active layer 103. Moreover, the semiconductor laser includes a p-type semiconductor layer 105 and an n-type semiconductor layer 106 which are arranged across the active layer 103 and formed in contact with the active layer 103 on the substrate 101.SELECTED DRAWING: Figure 1A

Description

The present invention relates to a semiconductor laser used as a light source for an optical transmitter or the like.

The amount of network traffic continues to increase explosively with the spread of the Internet. It is estimated that the power consumption of the data center increases with the amount of information communication, and the power consumption of the data center reaches 2% of the total power consumption. Above all, since more than 70% of data center traffic is consumed by communication in the data center, increasing the capacity and reducing the power consumption of short-distance communication are indispensable issues.

Due to the above background, optical interconnection technology that performs short-distance data communication by light is drawing attention. Currently, in addition to optical fiber connection between data centers, optical interconnection using a Vertical Cavity Surface Emitting Laser (VCSEL) has already been introduced for data communication between racks and boards. A typical short-range optical interconnection in recent years is multimode optical transmission using a VCSEL. The VCSEL is a small laser in which reflection mirrors are formed above and below the active layer.

For example, an active layer having a quantum well structure made of a compound semiconductor such as InGaAs or InGaAlP is formed on a GaAs substrate and operates at a wavelength of 635 to 1100 nm. Since the GaAs substrate can be manufactured using a substrate having a larger diameter than the InP substrate, many elements can be manufactured on one substrate, and it has a feature that it can be mass-produced at low cost. On the other hand, in VCSEL, it is difficult to achieve both high output and stable single-mode oscillation because there is a trade-off between the aperture of light extraction and the single-mode property of the transverse mode, and it is possible to support wavelength multiplexing. It is an issue.

Currently, the range of application of optical interconnection is expected to expand because the communication capacity of electrical wiring is limited, and it is expected that it will be applied to optical wiring for inter-chip and in-chip data communication in the future. .. Realization of these short-distance data communications requires high-density large-scale integration technology. In optical devices for optical fiber communication in the telecom region, a planar lightwave circuit (PLC) using quartz, an integrated light source using an InP substrate, and a modulator integrated light source have been put into practical use. In the InP substrate, a waveguide type single-mode laser including an active layer of the waveguide concept and a distributed Bragg reflector, such as a distributed reflection type (DFB) laser and a distributed Bragg reflection type (DBR) laser, has been commercialized. ..

In recent years, silicon photonics in which optical components are integrated on a silicon substrate has been attracting attention for the purpose of large-scale low-cost production, and hybrid integration with an InP light source is progressing. In order to cope with the future increase in capacity, the application of wavelength division multiplexing technology is expected, and active light such as a single-mode light source is placed on a substrate such as GaAs or silicon that can use a large-diameter substrate. High-density integration technology for devices is important.

However, in realizing a single-mode laser manufactured on a GaAs substrate, there is a problem in forming a diffraction grating for forming a resonator. Conventionally, a ridge type semiconductor laser has been developed as a waveguide type semiconductor laser. In this semiconductor laser (ridge structure laser), an n-type AlGaAs clad layer and an active layer are formed in a slab shape on an n-type GaAs substrate, and a ridge waveguide is formed by the p-type AlGaAs upper clad layer and the p-type GaAs contact layer. It is formed. An n-type electrode and a p-type electrode are formed above and below the active layer. In this semiconductor laser, when viewed from the substrate side, electrodes are arranged so as to sandwich the active layer in the vertical direction, and a current is injected into the active layer in the vertical direction.

In this structure, the element size becomes large because the current spreads from the lower part of the ridge to both sides of the active layer (in the plane direction of the substrate) when the current is injected. Further, it is difficult to embed the GaAs diffraction grating formed on the active layer with the clad layer of AlGaAs. Therefore, there is a report example in which the active layer is composed of quantum dots and a DFB laser using InGaP as the upper clad material is produced (Non-Patent Document 1). With this technique, a coupling coefficient of 50 cm ^-1 is obtained, but the reflectance is insufficient to realize a VCSEL-class low power consumption drive.

Further, the laser formed on the GaAs substrate is difficult to apply to the 1.3 μm band or the 1.55 μm band due to material limitations. In order to realize the 1.3 μm operation, the active layer has a GaInNAs quantum well structure or an InAs quantum dot structure. In particular, the InAs quantum dot structure is characterized by having high luminous efficiency and excellent temperature characteristics due to the confinement of three-dimensional carriers accompanying the quantization of the energy of the active layer.

In addition, since each dot of each quantum dot structure emits light and stimulated emission independently, it is not easily affected by defects generated during crystal growth. For this reason, in the InAs quantum dot structure, GaAs is grown not only on a GaAs substrate but also on a silicon substrate, and a quantum dot laser manufactured on the GaAs is being studied.

K. Takada et al., "Temperature-stable 10.3-Gb / s Operation of 1.3-μm Quantum-dot DFB Lasers with GaInP / GaAs Gratings", Conference on Optical Fiber Communication incudes post deadline papers, JWA28, 2009.

However, since the InAs dots have a high lattice strain, it is difficult to make the active layer multi-layered when applied to a laser having the above-mentioned structure. Further, the laser having the above-mentioned structure cannot sufficiently confine light to the active layer.

As described above, a waveguide type laser in which the active layer is composed of a GaAs-based compound semiconductor has problems that it is difficult to make a single mode, the element size is larger than that of a VCSEL, and the power consumption is high. was there.

The present invention has been made to solve the above problems, and is a waveguide type laser in which the active layer is composed of a GaAs-based compound semiconductor, and a single mode can be obtained with a smaller element size. The purpose is to be able to.

The semiconductor laser according to the present invention has an active layer formed on a substrate including GaAs, a lower clad layer formed under the active layer on the side of the substrate, and a lower clad layer having a refractive index lower than that of GaAs, and an active layer. A p-type semiconductor layer and an n-type semiconductor layer formed by contacting a diffraction lattice formed on a layer and an active layer on a substrate so as to sandwich the active layer and containing a Ga-containing compound semiconductor. And an n-type electrode connected to the n-type semiconductor layer and a p-type electrode connected to the p-type semiconductor layer.

As described above, according to the present invention, the active layer is arranged on the lower clad layer having a refractive index lower than that of GaAs, and the p-type semiconductor layer and the n-type semiconductor layer are arranged on the substrate with the active layer interposed therebetween. Therefore, a waveguide type laser in which the active layer is composed of a GaAs-based compound semiconductor can obtain a single mode with a smaller element size.

FIG. 1A is a cross-sectional view showing the configuration of a semiconductor laser according to the first embodiment of the present invention. FIG. 1B is a perspective view showing the configuration of a semiconductor laser according to the first embodiment of the present invention. FIG. 1C is a cross-sectional view showing the configuration of another semiconductor laser according to the first embodiment of the present invention. FIG. 2A is a cross-sectional view showing a partial configuration of a semiconductor laser according to the first embodiment of the present invention. FIG. 2B is a cross-sectional view showing a partial configuration of another semiconductor laser according to the first embodiment of the present invention. FIG. 3 is an explanatory diagram showing the energies of the bottom of the conduction band and the apex of the valence band of Al _x Ga _1-x As and InGaP. FIG. 4 is a band diagram for explaining the barrier between InGaP and AlGaAs. FIG. 5A is a cross-sectional view showing the configuration of the semiconductor laser according to the second embodiment of the present invention. FIG. 5B is a cross-sectional view showing the configuration of another semiconductor laser according to the second embodiment of the present invention. FIG. 6A is a characteristic diagram showing the waveguide width dependence of the optical confinement coefficient of the active layer. FIG. 6B is a characteristic diagram showing the relationship between the depth of the groove recess and the coupling coefficient of the diffraction grating.

Hereinafter, the semiconductor laser according to the embodiment of the present invention will be described.

[Embodiment 1]
First, the semiconductor laser according to the first embodiment of the present invention will be described with reference to FIGS. 1A and 1B. FIG. 1A shows a cross section perpendicular to the waveguide direction.

This semiconductor laser has a lower clad layer 102 formed on the substrate 101, an active layer 103 formed on the lower clad layer 102 on the substrate 101, and a diffraction grating formed on the active layer 103. It is equipped with 121. Further, this semiconductor laser includes a p-type semiconductor layer 105 and an n-type semiconductor layer 106 which are arranged on the substrate 101 with the active layer 103 interposed therebetween and formed in contact with the active layer 103. The active layer 103 is sandwiched between the lower guide layer 104a and the upper guide layer 104b in the vertical direction when viewed from the substrate 101. Further, the laminated structure of the lower guide layer 104a, the active layer 103, and the upper guide layer 104b is sandwiched (embedded) in the p-type semiconductor layer 105 and the n-type semiconductor layer 106.

Further, the p-type electrode 109 is electrically connected to the p-type semiconductor layer 105, and the n-type electrode 110 is electrically connected to the n-type semiconductor layer 106. In the first embodiment, the p-type electrode 109 is connected to the p-type semiconductor layer 105 via the contact layer 107, and the n-type electrode 110 is connected to the n-type semiconductor layer 106 via the contact layer 108. .. With this configuration, a current is injected into the active layer 103 in a direction parallel to the plane of the substrate 101.

Further, the active layer 103 extends in the light emission direction with a predetermined length, and in the resonator region 122 in the extending direction, a diffraction grating 121 having a Bragg wavelength of 1.3 μm is formed on the active layer 103. ing. Here, the diffraction grating 121 is formed on the upper surface of the upper guide layer 104b. Although not shown, a non-reflective film or a non-reflective film / high-reflective film is formed on the laser output end faces at both ends of the resonator region 122 to form a distributed feedback type laser. Although not shown, a protective film made of SiO ₂ is formed on the surface of the device. For example, a layer of SiO ₂ is formed in contact with the upper guide layer 104b on which the diffraction grating 121 is formed.

The substrate 101 is made of semi-insulating GaAs. The lower clad layer 102 is made of a material having a refractive index lower than that of GaAs. The lower clad layer 102 is made of, for example, AlGaAs, and can have a thickness of about 1.5 μm. Further, the lower clad layer 102 can also be composed of AlAs. Further, the lower clad layer 102 can be made of Al ₂ O ₃ . It is important that the lower clad layer 102 has a thickness that can suppress the exudation of light to the substrate 101, and can be 1 μm or more.

The active layer 103 is configured to include GaAs. The active layer 103 can be composed of, for example, a quantum dot layer. The lower guide layer 104a and the upper guide layer 104b are made of GaAs.

Here, when the active layer 103 is composed of a quantum dot layer, as shown in FIG. 2A, on the buffer layer 131 made of GaAs, the wet layer 132 formed on the buffer layer 131, and the wet layer 132. The formed plurality of quantum dots 133 and the strain control layer 134 formed by covering the plurality of quantum dots 133 are used as one set of dot layers, and the dot layers are laminated in three layers. The uppermost layer is terminated by the buffer layer 131. The overall shape of the active layer 103 can be 0.5 μm wide and 375 nm thick in cross-sectional view.

The buffer layer 131 is made of GaAs and has a thickness of 50 nm. The wet layer 132 is composed of InAs. The strain control layer 134 is made of InGaAs and has a thickness of 8 nm. The quantum dot 133 is composed of InAs. Further, the quantum dots 133 are formed in a hemispherical shape, and have a diameter of 30 nm and a height of 4 nm. Further, as shown in FIG. 2B, a wet layer 135 composed of InAs can be formed between vertically adjacent dot layers.

The p-type semiconductor layer 105 and the n-type semiconductor layer 106 can be composed of a compound semiconductor having a refractive index lower than that of the active layer 103. By doing so, sufficient light confinement to the active layer 103 can be realized. The p-type semiconductor layer 105 can be composed of, for example, InGaP which is doped with Zn having a doping concentration of 1 × 10 ¹⁸ cm ^-3 to form a p-type. Further, the n-type semiconductor layer 106 can be composed of, for example, InGaP which is doped with Si having a doping concentration of 1 × 10 ¹⁸ cm ^-3 to form an n-type.

The contact layer 107 can be made of, for example, a p-type GaAs doped with Zn having a doping concentration of 1 × 10 ¹⁹ cm ^-3 . Further, the contact layer 108 can be made of GaAs which is doped with Si having a doping concentration of 1 × 10 ¹⁹ cm ^-3 to form an n-type.

Here, the fabrication of the above-mentioned semiconductor laser will be briefly described. First, each semiconductor layer can be formed by a crystal growth technique such as a metalorganic vapor phase growth method (MOVPE) or a molecular beam epitaxy method (MBE). Further, for the structure of the waveguide and the formation of the diffraction grating 121, a known lithography technique and a general method for manufacturing a semiconductor laser such as wet etching or dry etching can be used.

Further, as is well known, in the heteroepitaxial growth of InAs on the GaAs layer, the quantum dot 133 has a three-dimensional island shape after the two-dimensional planar structure (wet layer 132) is formed. The structure is self-forming. In this heteroepitaxial growth, lattice mismatch causes strain to accumulate in the growing layer. An island is formed in the process of alleviating this distortion. The size of this island is several tens of nm, which indicates the properties of quantum dots.

The p-type semiconductor layer 105 and the n-type semiconductor layer 106 can be formed by embedding and re-growing the n-type doping InGaP and the p-type doping InGaP, respectively. Further, after the active layer 103 is formed, the intrinsic InGaP can be embedded and re-grown, and then impurities are introduced by ion implantation or thermal diffusion to bring each of them into a conductive type.

As shown in FIG. 1C, a semiconductor layer 111 made of InGaP and having a thickness of about 10 nm can be formed on the lower clad layer 102. The semiconductor layer 111 can suppress the oxidation of the lower clad layer 102 during embedding regrowth for forming the p-type semiconductor layer 105 and the n-type semiconductor layer 106. Further, a semiconductor layer 112 made of InGaP and having a thickness of about 10 nm can be formed on the upper guide layer 104b. The semiconductor layer 112 can suppress damage to the upper guide layer 104b during the etching process for forming the contact layer 107 and the contact layer 108. Even when the semiconductor layer 111 and the semiconductor layer 112 are formed, it is possible to obtain the same characteristics as when the semiconductor layer 111 and the semiconductor layer 112 are not formed, both electrically and optically.

Next, the configuration and effect of the semiconductor laser according to the first embodiment will be described in detail. First, the refractive index of GaAs at a wavelength of 1.3 μm is 3.45. The refractive index of InGaP at a wavelength of 1.3 μm is 3.19. Therefore, it is sandwiched between the p-type semiconductor layer 105 and the n-type semiconductor layer 106 composed of InGaP. In the active layer 103 made of GaAs, light can be strongly confined in the lateral direction.

Further, the refractive index of SiO ₂ constituting the protective film arranged on the upper part of the element is 1.47. Further, the refractive index of the lower clad layer 102 when composed of AlGaAs is lower than that of GaAs, and the refractive index of the lower clad layer 102 particularly when composed of AlAs is 2.93. Therefore, in this semiconductor laser, high light confinement can be realized even in the vertical direction when viewed from the substrate 101. When the lower clad layer 102 is composed of AlAs, the difference in refractive index between the active layer 103 and the lower clad layer 102 is maximized, and a laser structure with the highest light confinement in the active layer 103 can be realized.

Further, by forming the lower clad layer 102 from Al ₂ O ₃ having a thickness of 1 μm, further miniaturization of the laser and low power consumption drive can be realized. Since the refractive index of Al ₂ O ₃ at a wavelength of 1.3 μm is 1.75, it is possible to realize higher light confinement in the active layer 103 as compared with the case where the lower clad layer 102 is made of AlGaAs. Further, since Al ₂ O ₃ is an insulator, current leakage through the lower clad layer 102 can be completely suppressed. Further, the thermal conductivity of Al ₂ O ₃ is 32 W / m · k, which is comparable to the thermal conductivity of GaAs at 44 W / m · K, and is effective for high output operation of the laser.

For example, by growing AlGaAs having an AlAs or Al composition of 85% or more on a GaAs substrate and oxidizing the layer of AlAs or AlGaAs, a lower clad layer made of Al ₂ O ₃ can be formed. Further, after forming the lower clad layer in this way, the laser structure including the active layer 103 is bonded by a method such as wafer bonding, so that each of the above-mentioned layers is placed on the lower clad layer made of Al ₂ O ₃ . Can be formed.

Further, an AlGaAs layer having an AlAs or Al composition of 85% or more is formed on the GaAs substrate, a GaAs layer is grown on the layer, and then the AlAs or AlGaAs layer is oxidized by high temperature treatment or the like to form Al. It is also possible to form a lower clad layer consisting of ₂ O ₃ . After that, each layer such as an active layer can be grown on the GaAs layer, and embedded growth by InGaP can be carried out. By adopting the latter manufacturing method, the device can be manufactured by crystal growth on the GaAs substrate. Since the temperature required for the oxidation treatment is 400 to 500 ° C., it is possible to obtain the effect of suppressing deterioration of the emission intensity of the dot layer constituting the active layer and shortening of the emission wavelength.

As described above, the semiconductor laser according to the embodiment can realize high light confinement in the active layer 103 as compared with the conventional ridge structure laser, and can realize miniaturization of the laser and low current drive. Further, since the quantum dots 133 have strong compressive strain, it has been difficult to form the dot layers in multiple layers in the past. However, as described above, since high light confinement to the active layer 103 is realized, sufficient light confinement can be realized with a small number of dot layers.

Next, the electrical characteristics will be described. FIG. 3 shows the Al composition dependence of the valence band vertices of AlGaAs and InGaP and the energy at the bottom of the conduction band (Γ point, X point). When comparing GaAs constituting the active layer 103, AlGaAs constituting the lower clad layer 102, and InGaP constituting the p-type semiconductor layer 105 and the n-type semiconductor layer 106, both AlGaAs and InGaP are conduction bands rather than GaAs. The bottom is high and the peak of the valence band is high. Therefore, sufficient carrier confinement in the active layer 103 can be realized.

On the other hand, when InGaP and AlGaAs are compared, by making the Al composition higher than 0.6, the bottom of the conduction band of AlGaAs is higher than that of InGaP, and the bottom of the conduction band is higher than the apex of the valence band. At this time, as shown in FIG. 4, since a barrier is formed from the InGaP side to the AlGaAs side, the p-type semiconductor layer 105 to the n-type semiconductor layer 106 and the lower clad layer 102 wrapping around the lower side of the active layer 103. Current leakage is suppressed. Therefore, setting the Al composition of AlGaAs constituting the lower clad layer 102 to 0.6 or more is effective in suppressing light confinement and current leakage.

Further, the semiconductor laser according to the embodiment has a great advantage in terms of fabrication. As described above, after forming the diffraction grating 121 on the upper guide layer 104b, the step of embedding the diffraction grating 121 with a semiconductor is unnecessary, and the formation of the diffraction grating 121 becomes easy. Further, the diffraction grating 121 can be a Bragg reflector having a high reflectance due to the high refractive index difference between the upper guide layer 104b and the protective film made of SiO ₂ or the air layer. Therefore, it is possible to make a small resonator. In addition, since the effect of light confinement is high, the thickness of the active layer 103 can be reduced to 1 μm or less, so that embedded growth for forming the p-type semiconductor layer 105 and the n-type semiconductor layer 106 becomes easy. There is also an effect.

As described above, according to the first embodiment, a low power drive single mode semiconductor laser operating at a wavelength of 1.3 μm can be formed on a large-diameter GaAs substrate.

[Embodiment 2]
Next, the semiconductor laser according to the second embodiment of the present invention will be described with reference to FIG. 5A. This semiconductor laser has a lower clad layer 102, an active layer 103, a p-type semiconductor layer 105, and an n-type semiconductor layer on a substrate 201 made of Si via a buffer layer 202 made of AlGaAs, GaAs, or GaP. 106 is provided.

Further, the active layer 103 is sandwiched between the lower guide layer 104a and the upper guide layer 104b in the vertical direction when viewed from the substrate 201. Further, the laminated structure of the lower guide layer 104a, the active layer 103, and the upper guide layer 104b is sandwiched (embedded) in the p-type semiconductor layer 105 and the n-type semiconductor layer 106. Further, a diffraction grating 121 is formed on the upper surface of the upper guide layer 104b.

Other than the substrate 201 and the buffer layer 202, such as the lower clad layer 102, the active layer 103, the p-type semiconductor layer 105, the n-type semiconductor layer 106, the lower guide layer 104a, the upper guide layer 104b, and the diffraction grating 121, the above-described embodiment It is the same as 1.

It is also possible to insert a dislocation filter layer having a GaAs / InGaAs or GaAs / InAlAs superlattice structure between the buffer layer 202 and the lower clad layer 102 to suppress dislocation propagation to the active layer 103.

The second embodiment is characterized in that the buffer layer 202 and the same laser structure as in the first embodiment described above are formed on the substrate 201 made of silicon. In the second embodiment, a substrate 201 made of Si, which is a dissimilar material for a GaAs-based compound semiconductor, is used, and dislocations accompanying growth are controlled from the buffer layer 202 to form a lower clad layer 102, an active layer 103, and the like. The layers of each GaAs semiconductor can be grown together. As in the first embodiment, the lower clad layer 102 can be made of AlGaAs, AlAs, Al ₂ O ₃ , and the like.

Further, as shown in FIG. 5B, a semiconductor layer 111 made of InGaP and having a thickness of about 10 nm can be formed on the lower clad layer 102. Further, a semiconductor layer 112 made of InGaP and having a thickness of about 10 nm can be formed on the upper guide layer 104b. These configurations are also the same as those in the first embodiment.

Next, the characteristic control of the active layer 103 of the semiconductor laser described above will be described. In a general semiconductor laser manufactured by using a GaAs substrate, it is necessary to form an AlGaAs layer above and below the active layer as a clad layer for light confinement. In this conventional structure, since the growth temperature of AlGaAs is high, there is a problem that the characteristics of the active layer change when AlGaAs is formed after the active layer is formed. In particular, it is known that in an active layer composed of InAs self-formed quantum dots, when exposed to a high temperature after forming the active layer, the structure and plasticity of the quantum dots change and the emission wavelength becomes shorter. .. For example, the growth temperature of AlGaAs of MOVPE is 650 ° C. or higher, and the growth of the AlGaAs layer after forming the active layer shortens the wavelength, making it difficult to realize a laser having a wavelength of 1.3 μm.

However, the structure of the present invention does not require AlGaAs growth of the thick film after the formation of the active layer, and only InGaP regrowth at a growth temperature of about 550 ° C. Therefore, it is possible to suppress changes in the characteristics of the active layer. Further, even when compared with the ridge structure laser in which the clad is composed of InGaP, the thickness of the InGaP clad of the ridge structure laser is 1.5 μm or more, whereas in the embodiment, the p-type semiconductor layer 105 and n Since the thickness of the type semiconductor layer 106 is 1/3 or less of the above-mentioned thickness, the influence of heat can be suppressed.

Next, the effect of the semiconductor laser according to the above-described embodiment will be described with reference to FIGS. 6A and 6B. FIG. 6A shows the waveguide width dependence of the optical confinement coefficient of the active layer. As shown in FIG. 6A, according to the embodiment in which the lower clad layer is composed of AlAs or Al ₂ O ₃ , a significant improvement in the light confinement coefficient can be obtained as compared with the conventional case. As a result, the threshold gain of the semiconductor laser is reduced, and low current drive can be realized.

FIG. 6B shows the relationship between the depth of the groove recess and the coupling coefficient of the diffraction grating. In the conventional structure, even if the depth of the groove recess of the diffraction grating is 50 nm, the coupling coefficient remains at 150 cm ^-1 , and in addition, it is difficult to embed these diffraction gratings with AlGaAs or InGaP. On the other hand, according to the embodiment in which the lower clad layer is made of Al As or Al ₂ O ₃ , a coupling coefficient exceeding 500 cm ^-1 is obtained when the depth of the groove recess is 50 nm. Further, according to the embodiment, the fabrication is extremely easy because the embedded growth on the diffraction grating is not required. As described above, according to the present invention, a small resonator is realized, and high effects of miniaturization and low power drive can be obtained.

The present invention is not limited to the configuration shown in the above-described embodiment, and any material capable of growing on a GaAs substrate such as InGaAs, GaInNAs, InGaAsP, and InAlGaAs can be used as the material constituting the active layer. can. Further, as the structure of the active layer, a layer made of hemispherical InAs quantum dots is used, but other dot shapes that can be produced by self-formation may be used. In addition, a quantum well active layer structure is also applicable, and the ability to realize a single-mode quantum well laser on a GaAs substrate is also a major feature in comparison with the prior art. Further, although described above as a laser, if the same waveguide structure and active layer structure are used, it can be operated as a small-sized, low-current-driven semiconductor optical amplifier having high saturation resistance.

As described above, according to the present invention, the active layer is arranged on the lower clad layer having a refractive index lower than that of GaAs, and the p-type semiconductor layer and the n-type semiconductor layer are formed by sandwiching the active layer on the substrate. Since the arrangement is made, a waveguide type laser in which the active layer is composed of a GaAs-based compound semiconductor can obtain a single mode with a smaller element size.

It should be noted that the present invention is not limited to the embodiments described above, and many modifications and combinations can be carried out by a person having ordinary knowledge in the art within the technical idea of the present invention. That is clear.

101 ... substrate, 102 ... lower clad layer, 103 ... active layer, 104a ... lower guide layer, 104b ... upper guide layer, 105 ... p-type semiconductor layer, 106 ... n-type semiconductor layer, 107 ... contact layer, 108 ... contact layer , 109 ... p-type electrode, 110 ... n-type electrode, 121 ... diffraction grating, 122 ... resonator region.

Claims (6)

An active layer composed of GaAs formed on the substrate, and
A lower clad layer formed under the active layer on the side of the substrate and having a refractive index lower than that of GaAs.
The diffraction grating formed on the active layer and
A p-type semiconductor layer and an n-type semiconductor layer formed on the substrate with the active layer interposed therebetween and in contact with the active layer and composed of a compound semiconductor containing Ga.
The n-type electrode connected to the n-type semiconductor layer and
A semiconductor laser including a p-type electrode connected to the p-type semiconductor layer. In the semiconductor laser according to claim 1,
A semiconductor laser characterized in that the p-type semiconductor layer and the n-type semiconductor layer are composed of a compound semiconductor having a refractive index lower than that of the active layer. In the semiconductor laser according to claim 2,
A semiconductor laser characterized in that the p-type semiconductor layer and the n-type semiconductor layer are composed of InGaP. The semiconductor laser according to any one of claims 1 to 3.
The active layer is a semiconductor laser characterized in that it is composed of a quantum dot layer. The semiconductor laser according to any one of claims 1 to 4.
A semiconductor laser characterized in that the lower clad layer is composed of any of AlGaAs, AlAs, and Al ₂ O ₃ . The semiconductor laser according to any one of claims 1 to 5.
The substrate is a semiconductor laser characterized in that it is composed of GaAs or Si.

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