A method and structure for fabricating an electroabsorption modulated semiconductor laser

Abstract

This invention discloses a method and structure for fabricating an electro-absorption modulated semiconductor laser. The method includes: sequentially growing a first grating layer, a spacer layer, and an active material layer on a substrate surface; selectively removing the active material layer in the modulator region; growing a waveguide layer in the modulator region; fabricating a first control grating in the laser region and a second control grating in the modulator region; growing a modulator material layer and a second grating layer on the overall surface; selectively removing the modulator material layer in the laser region; and finally growing a cladding material and a contact layer material on the overall surface of the device to complete the laser fabrication. This invention, by fabricating a grating in the modulator region, diffracts the light incident on the modulator to propagate in a direction perpendicular to the substrate surface, giving the laser surface emission characteristics, facilitating chip testing and characterization; and by forming two mirrors through the first and second grating layers, light is reflected back and forth between the mirrors, achieving high absorption efficiency with a relatively small modulator area.

Description

Technical Field

[0001] This invention relates to the field of semiconductor optoelectronic integrated device technology, and in particular to a method and structure for fabricating an electroabsorption modulated semiconductor laser. Background Technology

[0002] Electro-absorption modulated semiconductor lasers (EMLs) have broad application prospects in optical fiber communication, especially in high-speed data transmission and high-capacity communication networks. EMLs integrate a single-longitudinal-mode laser and an electro-absorption modulator, offering advantages such as small size, low power consumption, high modulation rate, and long-distance high-speed signal transmission, making them an important component in optical fiber communication systems. With the continuous growth of communication demands, the performance requirements for EMLs are also increasing, particularly in improving modulation efficiency, reducing chip size, and enhancing production efficiency. Therefore, researching new manufacturing methods is of paramount importance.

[0003] In existing technologies, EML chips are typically edge-emitting structures, with their emission direction parallel to the substrate surface. While this structure achieves good laser emission performance, it presents significant challenges in testing and screening. Testing the chip requires disassembly, a cumbersome and time-consuming process that reduces production efficiency and increases costs. Furthermore, to improve modulation efficiency, existing waveguide-type electro-absorption modulators usually require considerable length, leading to increased capacitance and limiting the modulation bandwidth, resulting in poor performance in high-speed modulation and high-bandwidth applications. Summary of the Invention

[0004] In view of this, the present invention provides a method and structure for fabricating an electroabsorption modulated semiconductor laser, which solves the technical problems in the prior art where the side-emitting EML chip requires a cumbersome cleavage process for testing and screening, and the waveguide modulator is too long, resulting in increased capacitance and limiting the improvement of modulation bandwidth.

[0005] To achieve the above-mentioned technical objectives, the present invention adopts the following technical solution:

[0006] In a first aspect, the present invention provides a method for fabricating an electroabsorption modulated semiconductor laser, comprising:

[0007] The substrate is divided into a laser region and a modulator region, and a first grating layer, a spacer layer and an active material layer are grown sequentially on the substrate surface.

[0008] Selectively remove the active material layer in the modulator region;

[0009] A waveguide layer is grown on the surface of the modulator region;

[0010] A first control grating is fabricated in the active material layer within the laser region, and a second control grating is fabricated in the waveguide layer within the modulator region. The first control grating is used to enable the laser to operate in a single longitudinal mode at a preset wavelength by utilizing distributed feedback. The second control grating is used to diffract the incident light into a direction perpendicular to the substrate surface for transmission.

[0011] A modulator material layer and a second grating layer are sequentially grown on the surfaces of the laser region and the modulator region.

[0012] The modulator material layer and the second grating layer in the laser region are selectively removed; the remaining second grating layer and the first grating layer form a mirror, causing light to reflect back and forth between the mirrors;

[0013] The cladding material and contact layer material are grown sequentially on the surface of the entire device to complete the fabrication of the laser.

[0014] Furthermore, the bandgap wavelength of the waveguide layer is smaller than that of the active material layer.

[0015] Furthermore, both the first grating layer and the second grating layer are DBR grating structures, which are composed of multiple pairs of materials with alternating high and low refractive indices.

[0016] Furthermore, the first grating layer and the second grating layer have different reflectivities of light.

[0017] Furthermore, the second control grating is a high-order grating used to diffract light incident from the laser on the waveguide layer in a direction parallel to the substrate surface for transmission in a direction perpendicular to the substrate surface.

[0018] Furthermore, the method for selectively removing the modulator material layer and the second grating layer in the laser region is a dry etching or wet etching technique.

[0019] Furthermore, the modulator material layer is either a bulk material or a multi-quantum-well material.

[0020] Furthermore, the waveguide layer is made of InGaAsP material.

[0021] Furthermore, the substrate is made of one of InP, GaAs, GaN, or Si materials.

[0022] Furthermore, the cladding layer is made of InP material and the contact layer is made of InGaAs material.

[0023] On the other hand, the present invention also provides a structure for an electrically absorbed modulated semiconductor laser, wherein the laser is fabricated using the manufacturing method described in the above technical solution, and the laser is divided into a laser region and a modulator region along its length.

[0024] The laser region of the laser, from bottom to top, includes: a substrate, a first grating layer, a spacer layer, an active material layer, a cladding layer, and a contact layer; the modulator region of the laser, from bottom to top, includes: a substrate, a first grating layer, a spacer layer, a waveguide layer, a modulator material layer, a second grating layer, a cladding layer, and a contact layer.

[0025] The active material layer contains a first control grating, and the waveguide layer contains a second control grating.

[0026] Compared with existing technologies, the fabrication method and structure of the electro-absorption modulated semiconductor laser proposed in this invention have the following advantages:

[0027] (1) This method diffracts the light incident on the modulator into a direction perpendicular to the substrate surface by fabricating a second control grating in the modulator region, which facilitates the testing and characterization of the chip. Since the direction of light propagation is fixed and perpendicular to the substrate surface, the output light of the laser is more stable, the testing and screening process is simpler, the requirements for testing equipment are reduced, and the testing efficiency of the production line is improved.

[0028] (2) After the upper and lower mirrors composed of the first grating layer and the second grating layer reflect the light multiple times, the modulator material absorbs the light multiple times, which can achieve higher modulation efficiency with a smaller modulator size. The smaller modulator size is beneficial to reducing the modulator capacitance, thus improving the modulator bandwidth.

[0029] (3) Through the distributed feedback effect of the first control grating, the laser can operate in single longitudinal mode at the designed emission wavelength. At the same time, by adjusting the reflectivity of the first grating layer and the second grating layer, the direction of light output can be flexibly controlled, which provides greater flexibility in complex applications such as multi-channel and wavelength division multiplexing (WDM). It can accurately control the light output direction of each channel and optimize system performance.

[0030] In summary, this invention enables the laser output light to be perpendicular to the substrate surface, which simplifies the device testing and screening process. By utilizing the relative change in the reflectivity of the grating, the direction of the output light can be flexibly adjusted. This invention not only improves the modulation efficiency, bandwidth, and photoelectric conversion efficiency of the laser, but also enhances the device's integration, reliability, and ease of manufacturing. Attached Figure Description

[0031] Figure 1 A schematic flowchart illustrating the fabrication method of the electroabsorption modulated semiconductor laser provided by the present invention;

[0032] Figure 2 A cross-sectional schematic diagram of the laser after its fabrication, provided for the present invention;

[0033] In the figure, 10-substrate, 20-first grating layer, 30-spacer layer, 40-active material layer, 41-first control grating, 50-waveguide layer, 51-second control grating, 60-modulator material layer, 70-second grating layer, 80-cladding, 90-contact layer. Detailed Implementation

[0034] Preferred embodiments of the present invention will now be described in detail with reference to the accompanying drawings, which form part of this application and are used together with the embodiments of the present invention to illustrate the principles of the present invention, but are not intended to limit the scope of the present invention.

[0035] Example 1

[0036] Please see Figure 1 , Figure 1 This embodiment illustrates a flowchart of a method for fabricating an electroabsorption modulated semiconductor laser, which includes:

[0037] Step S101: Divide the substrate into a laser region and a modulator region, and grow a grating layer, a spacer layer and an active material layer on the substrate in sequence;

[0038] Step S102: Selectively remove the active material layer in the modulator region;

[0039] Step S103: Growing a waveguide layer on the surface of the modulator region;

[0040] Step S104: A first control grating is fabricated in the active material layer in the laser region, and a second control grating is fabricated in the waveguide layer in the modulator region; the first control grating is used to enable the laser to achieve single-longitudinal-mode operation at a preset wavelength by utilizing distributed feedback; the second control grating is used to diffract the incident light to a direction perpendicular to the substrate surface for transmission.

[0041] Step S105: Sequentially grow a modulator material layer and a second grating layer on the surfaces of the laser region and the modulator region;

[0042] Step S106: Selectively remove the modulator material layer and the second grating layer in the laser region; the remaining second grating layer and the first grating layer form a mirror, causing light to reflect back and forth between the mirrors;

[0043] Step S107: Cladding material and contact layer material are grown sequentially on the overall surface of the device to complete the fabrication of the laser.

[0044] The laser fabrication method provided in this embodiment firstly involves fabricating a second control grating in the modulator region to diffract the light incident on the modulator into a direction perpendicular to the substrate surface, facilitating chip testing and characterization. Secondly, the light in the modulator is reflected back and forth between two mirrors formed by the first and second grating layers, achieving high absorption efficiency with a relatively small modulator area, and simultaneously obtaining high bandwidth and high modulation efficiency characteristics.

[0045] In a preferred embodiment, the bandgap wavelength of the waveguide layer is smaller than the bandgap wavelength of the active material layer.

[0046] Designing the waveguide layer to have a bandgap wavelength smaller than that of the active material layer can reduce optical absorption loss.

[0047] In a preferred embodiment, both the first grating layer and the second grating layer are DBR grating structures, which are composed of multiple pairs of materials with alternating high and low refractive indices.

[0048] The DBR grating structure is a periodic refractive index structure layer that selectively reflects specific wavelengths. Its main function is to act as a wavelength-selective reflector, enabling single-mode output and wavelength tuning of the laser. Through the combined action of the first and second grating layers, light perpendicularly incident on the grating is reflected multiple times, improving absorption efficiency.

[0049] In one specific embodiment, the first grating layer and the second grating layer have different reflectivities of light.

[0050] The first and second grating layers can have the same structure, but their reflectivity is different. Based on the difference in the relative reflectivity of the first and second grating layers, the direction of the output light can be flexibly adjusted.

[0051] In a preferred embodiment, the second control grating is a high-order grating, used to diffract light incident from the laser on the waveguide layer in a direction parallel to the substrate surface to a direction perpendicular to the substrate surface for transmission. High-order gratings provide a stronger diffraction effect, enabling the effective guidance and output of light of specific wavelengths. This improves frequency selectivity and ensures the quality and stability of the optical signal, which is particularly important in high-speed data transmission and high-bandwidth applications.

[0052] Furthermore, the first control grating is a first-order grating or a second-order grating, which enables the laser to operate in a single longitudinal mode at the designed emission wavelength through distributed feedback. The single longitudinal mode output not only ensures the stability of the laser, but also makes the wavelength of the output light more accurate, avoiding the spectral width expansion caused by multimode output.

[0053] As a preferred embodiment, the method for selectively removing the modulator material layer and the second grating layer in the laser region is a dry etching or wet etching technique.

[0054] Both dry etching and wet etching techniques can efficiently and accurately remove material from the laser region, and have high processing flexibility, precision and production efficiency, meeting the high-quality processing requirements of this laser.

[0055] In a preferred embodiment, the modulator material layer is either a bulk material or a multi-quantum-well material.

[0056] In a preferred embodiment, the waveguide layer is made of InGaAsP material.

[0057] In a preferred embodiment, the substrate is made of one of InP, GaAs, GaN or Si.

[0058] In a preferred embodiment, the cladding layer is made of InP material and the contact layer is made of InGaAs material.

[0059] In traditional edge-emitting designs, light is emitted parallel to the substrate surface. This means the chip needs to be cleaved to allow light to be emitted perpendicularly for testing. However, the cleaving process is not only cumbersome but also increases the difficulty and time required for testing. The method of this invention achieves a surface-emitting design, allowing light to be emitted perpendicularly directly, thereby greatly simplifying the testing and screening process and improving production efficiency. Furthermore, in the modulator, light reflects back and forth between the upper and lower mirrors, achieving high absorption efficiency with a smaller modulator area, and simultaneously obtaining high bandwidth and high modulation efficiency characteristics.

[0060] The following is combined Figure 2 The above steps will be demonstrated and explained in detail.

[0061] As a specific example, such as Figure 2 As shown, taking the InP-based material system as an example, the steps of this fabrication method include:

[0062] (1) Divide the InP substrate 10 into a laser region L and a modulator region M, and grow a first grating layer 20, a spacer layer 30 and an active layer material layer 40 on the substrate 10 in sequence.

[0063] The first grating layer 20 is a DBR grating structure, which is composed of multiple pairs of materials with high and low refractive indices grown alternately. In practice, it can be formed by alternating stacking of InP and InGaAsP materials. Such a structure has a reflective effect on light that is vertically incident on the grating. The active material layer 40 includes quantum well material or bulk material, and waveguide material located on the upper and lower sides of the quantum well material or bulk material.

[0064] (2) Selectively remove the active material layer 40 of the modulator region M.

[0065] (3) An InGaAsP waveguide layer 50 is grown in the modulator region. The bandgap wavelength of the waveguide layer 50 is smaller than that of the active material 40 to reduce light absorption loss.

[0066] (4) A first control grating 41 is fabricated in the active material layer 40 in the laser region L, and a second control grating 51 is fabricated in the waveguide layer 50 in the modulator region M.

[0067] The first control grating 41 is a first-order grating or a second-order grating, which enables the laser to operate in a single longitudinal mode at the designed emission wavelength through distributed feedback. The second control grating 51 is a second-order or higher grating, which is used to diffract the light incident from the laser on the waveguide layer 50 in a direction parallel to the surface of the substrate 10 to a direction perpendicular to the surface of the substrate 10 for transmission.

[0068] (5) A modulator material layer 60 and a second grating layer 70 are grown on the materials of the laser region L and the modulator region M; wherein, the modulator material layer 60 is a quantum well material or a bulk material, and the intensity modulation of light is achieved by utilizing the electro-absorption modulation effect. The second grating layer 70 is a DBR grating structure, which has the same structure as the first grating layer 20, but the reflectivity of light may be different from that of grating 20.

[0069] (6) Selectively remove the modulator material layer 60 and the second grating layer 70 in the laser region L;

[0070] (7) Grow InP cladding material 80 and InGaAs contact layer material 90 on the overall surface of the device to complete the fabrication of the laser.

[0071] The device operates as follows: Light emitted from laser region L, parallel to the plane of substrate 10, couples into waveguide layer 50 and, under the action of second control grating 51, its transmission direction changes to be perpendicular to the plane of substrate 10. During multiple reflections between the upper and lower mirrors, it is repeatedly absorbed by modulator material layer 60, thus achieving high modulation efficiency with a small modulator size. A smaller modulator size also helps reduce the modulator capacitance, thereby increasing the modulator bandwidth. Simultaneously, under the action of second control grating 51, the output light of the device is perpendicular to the surface of substrate 10, simplifying device testing and screening. The direction of the device's output light can be flexibly adjusted based on the relative reflectivity of the second grating layer 70 and the first grating layer 20. Specifically, when the reflectivity of the second grating layer 70 is greater than that of the first grating layer 20, the light is output from the substrate direction; conversely, the light is output from the chip surface.

[0072] It should be noted that this laser can also be fabricated based on substrate materials such as GaAs, GaN, and Si.

[0073] Example 2

[0074] This invention also provides a structure for an electrically absorbed modulated semiconductor laser, which is fabricated using the method described in Embodiment 1. Figure 2 As shown, the laser is divided into a laser region L and a modulator region M along its length.

[0075] The laser region L of the laser, from bottom to top, includes: a substrate 10, a first grating layer 20, a spacer layer 30, an active material layer 40, a cladding layer 80, and a contact layer 90; the modulator region M of the laser, from bottom to top, includes: a substrate 10, a first grating layer 20, a spacer layer 30, a waveguide layer 50, a modulator material layer 60, a second grating layer 70, a cladding layer 80, and a contact layer 90.

[0076] The active material layer 40 contains a first control grating 41, and the waveguide layer 50 contains a second control grating 51.

[0077] The laser structure provided in this embodiment utilizes the second control grating 51 to couple the light emitted from the laser region L, which is parallel to the plane of the substrate 10, into the waveguide region 50. This changes the light transmission direction to be perpendicular to the plane of the substrate 10, resulting in output light perpendicular to the surface of the substrate 10. This eliminates the need for a cumbersome cleaving process, simplifying device testing and selection. Simultaneously, during the multiple reflections between the upper and lower mirrors of the first grating layer 20 and the second grating layer 70, the output light is repeatedly absorbed by the modulator material layer 60, achieving high modulation efficiency with a small modulator size. A smaller modulator size also helps reduce the modulator capacitance, thereby increasing the modulator bandwidth.

[0078] Therefore, the laser structure provided in this embodiment can exhibit surface emission characteristics. By fabricating a grating in the modulator region, the light incident on the modulator is diffracted to propagate in a direction perpendicular to the substrate surface, facilitating chip testing and characterization without requiring cleaving operations for chip testing and screening. In the modulator, the light reflects back and forth between the upper and lower mirrors, achieving high absorption efficiency with a relatively small modulator area. This not only improves bandwidth, modulation efficiency, and signal quality but also further saves space and energy, making it suitable for high-speed, high-precision optical communication and integrated optical applications.

[0079] The above description is only a preferred embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any changes or substitutions that can be easily conceived by those skilled in the art within the scope of the technology disclosed in the present invention should be included within the scope of protection of the present invention.

Claims

1. A method for fabricating an electroabsorption modulated semiconductor laser, characterized in that, include: The substrate is divided into a laser region and a modulator region, and a first grating layer, a spacer layer and an active material layer are grown sequentially on the substrate surface. Selectively remove the active material layer in the modulator region; A waveguide layer is grown on the surface of the modulator region; A first control grating is fabricated in the active material layer within the laser region, and a second control grating is fabricated in the waveguide layer within the modulator region. The first control grating is used to enable the laser to operate in a single longitudinal mode at a preset wavelength by utilizing distributed feedback. The second control grating is used to diffract the incident light into a direction perpendicular to the substrate surface for transmission. A modulator material layer and a second grating layer are sequentially grown on the surfaces of the laser region and the modulator region. The modulator material layer and the second grating layer in the laser region are selectively removed; the remaining second grating layer and the first grating layer form a mirror, causing light to reflect back and forth between the mirrors; Cladding material and contact layer material are grown sequentially on the surface of the device to complete the fabrication of the laser; both the first grating layer and the second grating layer are DBR grating structures, and both the first grating layer and the second grating layer include multiple pairs of materials with alternating high and low refractive indices.

2. The method for fabricating an electro-absorption modulated semiconductor laser according to claim 1, characterized in that, The bandgap wavelength of the waveguide layer is smaller than that of the active material layer.

3. The method for fabricating an electroabsorption modulated semiconductor laser according to claim 1, characterized in that, The first grating layer and the second grating layer have different reflectivities of light.

4. The method for fabricating an electroabsorption modulated semiconductor laser according to claim 1, characterized in that, The method for selectively removing the modulator material layer and the second grating layer in the laser region is a dry etching or wet etching technique.

5. The method for fabricating an electro-absorption modulated semiconductor laser according to claim 1, characterized in that, The modulator material layer is made of either a bulk material or a multi-quantum-well material.

6. The method for fabricating an electroabsorption modulated semiconductor laser according to claim 1, characterized in that, The waveguide layer is made of InGaAsP material.

7. The method for fabricating an electroabsorption modulated semiconductor laser according to claim 1, characterized in that, The substrate is made of one of the following materials: InP, GaAs, GaN, or Si.

8. The method for fabricating an electroabsorption modulated semiconductor laser according to claim 1, characterized in that, The cladding is made of InP material and the contact layer is made of InGaAs material.

9. A structure for an electroabsorption modulated semiconductor laser, characterized in that, The laser is manufactured using the method described in any one of claims 1-7, and the laser is divided into a laser region and a modulator region along its length. The laser region of the laser, from bottom to top, includes: a substrate, a first grating layer, a spacer layer, an active material layer, a cladding layer, and a contact layer; the modulator region of the laser, from bottom to top, includes: a substrate, a first grating layer, a spacer layer, a waveguide layer, a modulator material layer, a second grating layer, a cladding layer, and a contact layer; both the first grating layer and the second grating layer are DBR grating structures, and both the first grating layer and the second grating layer include multiple pairs of materials with alternating high and low refractive indices; The active material layer contains a first control grating, and the waveguide layer contains a second control grating.

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