High-speed electroabsorption modulated laser and method of manufacturing the same

Abstract

The present application relates to the technical field of electro-absorption modulation laser, and provides a manufacturing method of electro-absorption modulation laser.In the butt joint growth manufacturing process, the mixing of As and Ga elements in the multi-quantum well layer at the butt joint of the distributed feedback laser and the electro-absorption modulator is realized by sputtering copper, the Cu element is mixed, the concentration of each element at the butt joint interface is balanced, so that the corrosion speed of the chemical solution is balanced, and the butt joint interface state is more flat; in the grating manufacturing step, the nano-imprint etching grating is adopted, the grating precision is high, and the nano-imprint template can be repeatedly used.The embodiment of the present application improves the wet etching butt joint interface state by inducing the mixing of Cu, As and Ga elements; the grating layer is manufactured by adopting the nano-imprint technology, and the grating precision and manufacturing efficiency are improved.

Description

Technical Field

[0001] This invention relates to the field of electroabsorption modulated laser technology, and more specifically, to a high-speed electroabsorption modulated laser grown by docking and its fabrication method. Technical Background

[0002] Semiconductor lasers have become the most important light source in optical communication systems due to their simple fabrication, small size, long lifespan, and high efficiency. Electro-absorption modulated lasers (EMLs) are integrated devices combining electro-absorption modulators (EAMs) and distributed feedback lasers (DFBs), offering advantages such as small size and low wavelength chirp, making them the preferred light source for high-speed fiber optic communication systems.

[0003] Compared to directly modulated lasers (DMLs), electro-absorption modulated lasers offer superior transmission characteristics and performance, especially for high-frequency modulation or long-distance transmission. Currently, the grating structure schemes used to fabricate high-speed electro-absorption modulated lasers include holographic exposure and electron beam exposure.

[0004] Holographic exposure is simple, efficient, and inexpensive to fabricate, but it can only produce uniform gratings. Electron beam exposure can produce phase-shifting gratings and variable-period gratings, but it is time-consuming, inefficient, and expensive. Furthermore, both methods require dry etching and wet etching to finalize the grating.

[0005] The docking growth technique combines dry etching and wet etching when removing the electroabsorption modulator region. Wet etching has the problem of lateral etching, and the lateral etching depth is related to the concentration of As and Ga elements. This results in an uneven docking growth interface between the distributed feedback laser part and the electroabsorption modulator part, causing a mismatch in the interface docking growth and ultimately affecting the overall performance of the electroabsorption modulated laser.

[0006] Nanoimprinting requires that the imprinting adhesive thickness not be too thick. Excessive thickness not only leaves a significant amount of adhesive residue at the bottom but also makes the imprinting template prone to breakage during the imprinting process. Furthermore, it is impossible to effectively fabricate grating structures with uneven imprinting adhesive thickness. Summary of the Invention

[0007] To overcome the shortcomings of existing technologies, this invention provides a method for fabricating a high-speed electro-absorption modulated laser chip. The method employs docking growth technology to separately grow and design the structures of a distributed feedback laser and an electro-absorption modulator. Through multiple epitaxial growths, the independently grown distributed feedback laser and electro-absorption modulator are obtained, thereby optimizing the luminous efficiency of the distributed feedback laser and the absorption performance of the electro-absorption modulator.

[0008] To achieve the above objectives, the present invention specifically adopts the following technical solution:

[0009] An electro-absorption modulated laser grown by docking includes a distributed feedback laser section and an electro-absorption modulator section, wherein: the distributed feedback laser section includes a substrate, and a lower waveguide layer, a distributed feedback laser multi-quantum well layer, an upper waveguide layer, a buried layer, a capping layer, and an ohmic contact layer sequentially disposed on the substrate, and the lower waveguide layer is bonded to the substrate layer.

[0010] The modulator section includes a substrate, a buffer layer, an electro-absorption modulator multi-quantum-well layer, an upper cladding layer, a capping layer, an ohmic contact layer, and a P-plane metal electrode. The multi-quantum-well layer of the distributed feedback laser section and the multi-quantum-well layer of the electro-absorption modulator are interconnected, wherein the multi-quantum-well layer of the electro-absorption modulator is thicker than the multi-quantum-well layer of the distributed feedback laser. The centers of the multi-quantum-well layers of the electro-absorption modulator and the distributed feedback laser are aligned. A grating layer is provided in the distributed feedback laser region. The grating layer is located in the upper waveguide layer and is covered by a cladding layer of the same material as the upper waveguide layer. Following this are a buried layer, a capping layer, an ohmic contact layer, and a P-plane metal electrode. There is an isolation region at the electrode junction of the distributed feedback laser section and the electro-absorption modulator section. A metal electrode is provided on the substrate.

[0011] The electroabsorption modulator region does not have a grating layer. The electroabsorption modulator region includes a substrate, and a buffer layer, an electroabsorption modulator multi-quantum well layer, an upper cladding layer, a capping layer, an ohmic contact layer, and a P-side metal electrode arranged sequentially on the substrate. The metal electrode is provided on the substrate, and the buffer layer is bonded to the substrate layer.

[0012] Furthermore, the multi-quantum-well layer includes at least one InGaAsP quantum well potential layer and one barrier layer.

[0013] Furthermore, the number of quantum well potential layers and barrier layers in a multi-quantum well layer is the same.

[0014] Furthermore, the substrate of the distributed feedback laser and the substrate of the electroabsorption modulator are the same substrate.

[0015] A method for fabricating an electroabsorption modulated laser by docking growth involves optimizing the distributed feedback laser (DFP) and electroabsorption modulator (EAB) components using docking growth technology. The DFP structure is grown on a substrate. As and Ga elements are mixed at the docking growth interface using methods such as copper sputtering, ion implantation, or high-temperature annealing. A grating is fabricated using nanoimprint lithography. A mask protecting the DFP region is then created using metal-organic chemical vapor deposition (MOCVD). This mask is removed by dry and wet etching down to the substrate layer, eliminating the DFP structure outside the mask. A second epitaxial growth is then performed to fabricate the EAB. The specific steps are as follows:

[0016] Step 1: The lower waveguide layer, the distributed feedback laser multi-quantum well layer, and the upper waveguide layer are sequentially grown on the substrate using a metal-organic chemical vapor deposition apparatus.

[0017] Step 2: On the chip from Step 1, a SiO2 dielectric layer with a thickness of 100 nm is uniformly grown on the chip using plasma-enhanced chemical vapor deposition. A photoresist layer is then applied to the surface of the dielectric layer. The area to be mixed is defined onto the photoresist using photolithography. Then, the area to be mixed is transferred to the SiO2 dielectric layer using inductively coupled plasma etching. Copper is then sputtered onto the chip using a magnetron sputtering machine for 60 seconds. After sputtering, the chip is removed and placed in acetone to remove the photoresist mask and the attached copper. The chip is then placed in a rapid annealing furnace for annealing at 750 degrees Celsius for 10 seconds. After the chip has naturally cooled to room temperature, it is removed, and the SiO2 layer is removed using HF solution.

[0018] Step 3: On the chip prepared in Step 2, uniformly apply nanoimprint adhesive, use a nanotemplate with a grating pattern for imprinting, transfer the grating structure to the upper waveguide layer by etching, and remove the residual nanoimprint adhesive; grow a wet etching resist layer and a buried layer on the chip surface using a metal-organic chemical vapor deposition device to protect the fabricated grating.

[0019] Step 4: On the chip after Step 3, a SiO2 mask is grown by plasma-enhanced chemical vapor deposition. The mask is then fabricated to protect the distributed feedback laser region through spin coating, exposure, development and etching.

[0020] Step 5: After fabricating the chip with the mask pattern, the upper waveguide layer, the distributed feedback laser multi-quantum well layer, and the lower waveguide layer on the area outside the mask are removed by inductively coupled plasma dry etching process, followed by lateral etching using H2SO4:H2O2:H2O solution; then, the buffer layer, multi-quantum well layer, and upper cladding layer of the electroabsorption modulator region are grown by metal-organic chemical vapor deposition.

[0021] Step 6: After completing step 5, use HF solution to remove the SiO2 mask from the surface of the laser part, and then grow the cover layer and ohmic contact layer by metal-organic chemical vapor deposition. The P-side electrode layer is fabricated on the ohmic contact layer, and the N-side electrode layer is fabricated on the substrate.

[0022] Furthermore, in step six, when fabricating the P-surface electrode layer, there is an isolation region at the junction of the distributed feedback laser and the electroabsorption modulator electrodes.

[0023] In summary, the invention has the following beneficial effects:

[0024] This invention employs docking growth technology to separately grow and design the structures of a distributed feedback laser (DFP) and an electro-absorption modulator (EAB), thereby optimizing the luminous efficiency of the DFP and the absorption performance of the EAB. First, the DFP structure is grown on a substrate. Then, by methods such as sputtering metallic copper or ion implantation, the quantum wells at the docking point between the DFP and EAB are mixed with As and Ga elements. This invention uses metallic copper sputtering to balance the elemental concentrations at the docking point, thus equalizing the corrosion rate of the chemical solution and resulting in a smoother docking interface. During the epitaxial growth of the EAB portion, material buildup at the docking point is reduced, optimizing the docking effect of the multi-quantum-well layers of the DFP and EAB, and improving the efficiency of the EAB. A grating structure is fabricated on the upper waveguide layer using nanoimprint lithography, avoiding damage to the underlying grating layer caused by over-etching and eliminating lateral corrosion issues. The fabricated grating has consistent depth and structure. The nanoimprint template can be reused, reducing production costs and facilitating mass production. Attached Figure Description

[0025] Figure 1 This is a schematic diagram of a high-speed electro-absorption modulated laser according to an embodiment of the present invention;

[0026] Figure 2 This is a schematic diagram showing the preparation method of the present invention after step one is completed;

[0027] Figure 3 This is a schematic diagram of the double mask used for sputtering metallic copper in step two of the preparation method of the present invention;

[0028] Figure 4 This is a schematic diagram of the sputtering of metallic copper using a magnetron sputtering machine in step two of the preparation method of the present invention;

[0029] Figure 5 This is a schematic diagram illustrating the effect of sputtered metallic copper on elemental mixing in the multi-quantum well layer during step two of the preparation method of this invention.

[0030] Figure 6 This is a schematic diagram showing the preparation method of the present invention after step two is completed;

[0031] Figure 7 This is a schematic diagram of the spin-coating nanoimprint adhesive in step three of the preparation method of the present invention;

[0032] Figure 8 This is a schematic diagram of the nanoimprint grating fabrication in step three of the preparation method of the present invention;

[0033] Figure 9 This is a schematic diagram of the removal of residual nanoimprint adhesive in step three of the preparation method of the present invention;

[0034] Figure 10 This is a schematic diagram of the growth of the wet corrosion resistant layer and the buried layer by MOCVD metal-organic chemical vapor deposition in step three of the preparation method of the present invention;

[0035] Figure 11 This is a schematic diagram showing the preparation method of the present invention after step four is completed;

[0036] Figure 12 This is a schematic diagram showing the results of dry etching and wet etching in step five of the preparation method of the present invention;

[0037] Figure 13 This is a schematic diagram showing the preparation method of the present invention after step five is completed;

[0038] Figure 14 This is a schematic diagram showing the preparation method of the present invention after step six is ​​completed.

[0039] The reference numerals in the figure are as follows: 100-substrate, 110-lower waveguide layer, 120-distributed feedback laser multi-quantum well layer, 130-upper waveguide layer, 200-SiO2 dielectric layer, 210-photoresist, 220-sputtered copper, 300-nanometer imprinting adhesive, 400-wet etching resistant layer, 410-buried layer, 420-SiO2 mask, 500-electro-absorption modulator buffer layer, 510-electro-absorption modulator multi-quantum well layer, 520-electro-absorption modulator upper cladding, 530-capping layer, 600-substrate electrode, 610-distributed feedback laser electrode, 620-electro-absorption modulator electrode. Detailed Implementation

[0040] The present invention will now be described in further detail with reference to the accompanying drawings.

[0041] It should be noted that, for ease of description, the descriptions of direction in the following text are consistent with the directions in the accompanying drawings, but do not limit the structure of the present invention.

[0042] To obtain a higher power and higher speed electro-absorption modulated laser, it is necessary to optimize the structure and docking interface of the distributed feedback laser and the electro-absorption modulator, respectively. This embodiment provides a method for fabricating an electro-absorption modulated laser by docking growth, and the detailed technical solution is as follows:

[0043] like Figure 1As shown, this invention discloses a docked-grown electro-absorption modulated laser, comprising a distributed feedback laser portion and an electro-absorption modulator portion. The distributed feedback laser portion includes a substrate, and on the substrate, a lower waveguide layer, a distributed feedback laser multi-quantum well layer, an upper waveguide layer, a buried layer, a capping layer, and an ohmic contact layer are sequentially disposed. The lower waveguide layer is bonded to the substrate. The modulator portion includes a substrate, a buffer layer, an electro-absorption modulator multi-quantum well layer, an upper cladding layer, a capping layer, an ohmic contact layer, and a p-plane metal electrode. The multi-quantum well layer of the distributed feedback laser portion and the multi-quantum well layer of the electro-absorption modulator are docked to each other. The electro-absorption modulator multi-quantum well layer is thicker than the distributed feedback laser multi-quantum well layer, and the centers of the distributed feedback laser and the electro-absorption modulator multi-quantum well layer are aligned. A grating layer is provided in the upper waveguide layer region of the distributed feedback laser, and the grating layer is covered by a cladding layer. The cladding layer is made of the same material as the upper waveguide layer. There is an isolation region at the electrode junction of the distributed feedback laser portion and the electro-absorption modulator portion. A metal electrode is provided on the substrate. There is no grating layer in the electroabsorption modulator region.

[0044] The grating layer is covered with a buried layer and a capping layer, followed by an ohmic contact layer and a P-side metal electrode. An isolation region is set at the junction of the distributed feedback laser and the electroabsorption modulator, and an N-side metal electrode is set at the bottom of the substrate.

[0045] like Figure 2-7 As shown, this invention also discloses a method for fabricating an electro-absorption modulated laser by docking growth. Using docking growth technology, the distributed feedback laser portion and the electro-absorption modulator portion are optimized respectively. The structure of the distributed feedback laser is grown on a substrate. As and Ga elements are mixed at the docking growth interface by sputtering metallic copper, ion implantation, or high-temperature annealing. A grating is fabricated using nanoimprint lithography. Then, a mask protecting the distributed feedback laser region is fabricated by metal-organic chemical vapor deposition. After dry and wet etching down to the substrate layer, the distributed feedback laser structure outside the mask is removed. A second epitaxial growth is then performed to fabricate the electro-absorption modulator portion. The specific steps are as follows:

[0046] Step 1: The lower waveguide layer, the distributed feedback laser multi-quantum well layer, and the upper waveguide layer are sequentially grown on the substrate using a metal-organic chemical vapor deposition apparatus.

[0047] Step 2: On the chip from Step 1, a SiO2 dielectric layer with a thickness of 100 nm is uniformly grown by plasma-enhanced chemical vapor deposition. A photoresist layer is then coated on the surface of the dielectric layer. The area to be mixed is defined onto the photoresist using photolithography. Then, the area to be mixed is transferred to the SiO2 dielectric layer using inductively coupled plasma etching. Copper is sputtered onto the chip using a magnetron sputtering machine for 60 seconds. After sputtering, the chip is removed and placed in acetone to remove the photoresist mask and the attached copper. The chip is then placed in a rapid annealing furnace for annealing at 750 degrees Celsius for 10 seconds. After the chip cools naturally to room temperature, it is removed and the SiO2 layer is removed using HF solution.

[0048] Step 3: On the chip prepared in Step 2, uniformly apply nanoimprint adhesive, use a nanotemplate with a grating pattern for imprinting, transfer the grating structure to the upper waveguide layer by etching, and remove the residual nanoimprint adhesive; grow a wet etching resist layer and a buried layer on the chip surface using a metal-organic chemical vapor deposition device to protect the fabricated grating.

[0049] Step 4: On the chip after Step 3, a SiO2 mask is grown by plasma-enhanced chemical vapor deposition. The mask is then fabricated to protect the distributed feedback laser region through spin coating, exposure, development and etching.

[0050] Step 5: After fabricating the chip with the mask pattern, the upper waveguide layer, the distributed feedback laser multi-quantum well layer, and the lower waveguide layer on the area outside the mask are removed by inductively coupled plasma dry etching process, followed by lateral etching using H2SO4:H2O2:H2O solution; then, the buffer layer, multi-quantum well layer, and upper cladding layer of the electroabsorption modulator region are grown by metal-organic chemical vapor deposition.

[0051] Step 6: After completing step 5, use HF solution to remove the SiO2 mask from the surface of the laser part, and then grow the cover layer and ohmic contact layer by metal-organic chemical vapor deposition. The P-side electrode layer is fabricated on the ohmic contact layer, and the N-side electrode layer is fabricated on the substrate.

[0052] In the process of fabricating an electroabsorption modulated laser using docking growth technology, the present invention addresses the issue of selective chemical solution (H2SO4:H2O2:H2O) etching the passive region, where the etchant affects In... (1-x) Ga x As y P (1-y)Quaternary compounds exhibit significant lateral corrosion, with varying corrosion rates depending on the component. Higher Ga and As content leads to faster selective corrosion. In the high-speed electro-absorption modulated laser fabrication process of this invention, As and Ga elements are first mixed within the multi-quantum well layer at the LD and EAM docking point using methods such as sputtering metallic copper or ion implantation. This invention employs sputtering metallic copper to achieve As and Ga mixing, while also incorporating Cu to balance the element concentrations at the docking interface, thus equalizing the corrosion rate of the chemical solution and resulting in a smoother docking interface. Secondly, current methods for fabricating electro-absorption modulated laser gratings mostly utilize holographic exposure and electron beam exposure, combined with dry etching and wet etching. Reactive ion etching can damage the underlying grating layer due to over-etching, while non-selective wet etching suffers from lateral corrosion issues, leading to inconsistent etching depths. This invention avoids these problems by using nanoimprint etching of the grating during chip fabrication, resulting in high-precision gratings, and the nanoimprint template can be reused. Following the sequence of fabricating the waveguide grating first and then growing the modulator structure, the waveguide grating structure is first fabricated using nanoimprint lithography, and the grating is protected by an MOCVD growth mask. The modulator portion is then grown. This fabrication sequence allows the grating to be formed in a single step, resulting in high quality, high precision, and no breakage issues. This embodiment of the invention improves the interface states of wet etching by inducing the mixing of Cu, As, and Ga elements; and improves grating precision and fabrication efficiency by employing nanoimprint lithography to fabricate the grating layer.

[0053] The above description is merely a preferred embodiment of the present invention. The scope of protection of the present invention is not limited to the above embodiments. All technical solutions falling within the scope of the present invention's concept are within the scope of protection of the present invention. It should be noted that for those skilled in the art, any improvements and modifications made without departing from the principles of the present invention should also be considered within the scope of protection of the present invention.

Claims

1. A method for fabricating an electroabsorption modulated laser by docking growth, characterized in that, The docking-grown electroabsorption modulated laser includes a distributed feedback laser part and an electroabsorption modulator part, wherein: the distributed feedback laser part includes a substrate, and a lower waveguide layer, a distributed feedback laser multi-quantum well layer, an upper waveguide layer, a buried layer, a capping layer, and an ohmic contact layer sequentially disposed on the substrate, and the lower waveguide layer is bonded to the substrate layer. The electro-absorption modulator portion includes a substrate, and on the substrate, a buffer layer, an electro-absorption modulator multi-quantum well layer, an upper cladding layer, a capping layer, an ohmic contact layer, and a p-plane metal electrode, sequentially disposed on the substrate. The multi-quantum well layer of the distributed feedback laser portion and the multi-quantum well layer of the electro-absorption modulator are interconnected, wherein the multi-quantum well layer of the electro-absorption modulator is thicker than the multi-quantum well layer of the distributed feedback laser, and the centers of the multi-quantum well layers of the electro-absorption modulator and the distributed feedback laser are aligned. The distributed feedback laser section has a grating layer located in the upper waveguide layer. The grating layer is covered by a cladding layer made of the same material as the upper waveguide layer. Then there is a buried layer, a capping layer, an ohmic contact layer, and a P-plane metal electrode. There is an isolation region at the electrode junction between the distributed feedback laser section and the electroabsorption modulator section. An N-plane metal electrode is provided on the substrate. The electroabsorption modulator section does not have a grating layer, but has an N-plane metal electrode on the substrate, and a buffer layer is bonded to the substrate layer. The fabrication method utilizes docking growth technology to optimize both the distributed feedback laser (DFP) and electro-absorption modulator (EAB) components. The DFP structure is grown on a substrate. As and Ga elements are mixed at the docking growth interface using copper sputtering. A grating is fabricated using nanoimprint lithography. A mask protecting the DFP component is then created using metal-organic chemical vapor deposition (MOCVD). Dry and wet etching processes are employed until the substrate layer is reached, removing the DFP structure outside the mask. A second epitaxial growth is then performed to fabricate the EAB. The specific steps are as follows: Step 1: The lower waveguide layer, the distributed feedback laser multi-quantum well layer, and the upper waveguide layer are sequentially grown on the substrate using a metal-organic chemical vapor deposition apparatus. Step 2: On the chip from Step 1, a SiO2 dielectric layer with a thickness of 100 nm is uniformly grown on the chip using plasma-enhanced chemical vapor deposition. A photoresist layer is then applied to the surface of the dielectric layer. The area to be mixed is defined onto the photoresist using photolithography. Then, the area to be mixed is transferred to the SiO2 dielectric layer using inductively coupled plasma etching. Copper is then sputtered onto the chip using a magnetron sputtering machine for 60 seconds. After sputtering, the chip is removed and placed in acetone to remove the photoresist mask and the attached copper. The chip is then placed in a rapid annealing furnace for annealing at 750 degrees Celsius for 10 seconds. After the chip has naturally cooled to room temperature, it is removed, and the SiO2 layer is removed using HF solution. Step 3: On the chip prepared in Step 2, uniformly apply nanoimprint adhesive, use a nanotemplate with a grating pattern for imprinting, transfer the grating structure to the upper waveguide layer by etching, and remove the residual nanoimprint adhesive; grow a wet etching resist layer and a buried layer on the chip surface using a metal-organic chemical vapor deposition device to protect the fabricated grating. Step 4: On the chip after Step 3, a SiO2 mask is grown by plasma-enhanced chemical vapor deposition. The mask is then fabricated to protect the distributed feedback laser section by spin coating, exposure, development and etching. Step 5: After fabricating the chip with the mask pattern, the upper waveguide layer, the distributed feedback laser multi-quantum well layer, and the lower waveguide layer on the area outside the mask are removed by inductively coupled plasma dry etching process, followed by lateral etching using H2SO4:H2O2:H2O solution; then, the buffer layer, multi-quantum well layer, and upper cladding layer of the electroabsorption modulator are grown by metal-organic chemical vapor deposition. Step 6: After completing Step 5, use HF solution to remove the SiO2 mask from the surface of the laser part, and then grow a capping layer and an ohmic contact layer by metal-organic chemical vapor deposition. The P-side electrode layer is fabricated on the ohmic contact layer, and the N-side electrode layer is fabricated on the substrate.

2. The method for fabricating an electroabsorption modulated laser by docking growth according to claim 1, characterized in that, The multi-quantum-well layer includes at least one InGaAsP quantum well potential layer and one barrier layer.

3. The method for fabricating an electroabsorption modulated laser by docking growth according to claim 2, characterized in that, The number of quantum well potential layers and barrier layers in the multi-quantum well layer is the same.

4. The method for fabricating an electroabsorption modulated laser by docking growth according to any one of claims 1 to 3, characterized in that, The substrate of the distributed feedback laser and the substrate of the electroabsorption modulator are the same substrate.

5. The method for fabricating an electroabsorption modulated laser by docking growth according to claim 1, characterized in that: In step six, when fabricating the P-surface electrode layer, there is an isolation region at the junction of the distributed feedback laser and the electroabsorption modulator electrodes.

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