Selectively growing high-speed electro-absorption modulated laser chip and preparation method thereof
Through the selective region growth scheme designing the mask on the substrate, the integration of the DFB laser and the electrical absorption modulator is achieved, solving the problems of high cost and interface defects in the prior art, and achieving high-performance and low-cost high-speed electrical absorption modulation lasers.
Patent Information
- Application Number
- CN202510219581.6
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2025-02-26
- Publication Date
- 2025-04-15
AI Technical Summary
When existing electrical absorption modulation lasers (EMLs) integrate DFB lasers and electrical absorption modulators, it is difficult to optimize the laser's output efficiency and extinction ratio separately, and multiple epitaxial growths lead to high costs and interface defects, affecting reliability.
A selective region growth scheme is adopted to design a mask on the substrate to make the growth thickness of different regions different, and the integration of LD and EAM is achieved through one epitaxial growth, avoiding multiple epitaxial growth and docking interfaces.
It reduces production costs, improves material quality and chip reliability, and realizes a high-performance high-speed electrical absorption modulation laser.
Smart Images
Figure CN119834058A_ABST
Abstract
Description
Technical Field
[0001] The invention relates to the technical field of optical communication, in particular to a selectively grown high-speed electro-absorption modulated laser chip and a preparation method thereof. Background Art
[0002] Electro-absorption modulated laser (EML) is an integrated device of electro-absorption modulator (EAM) and DFB laser (LD). It is a high-performance optical communication light source with small volume and low wavelength chirp, which is integrated by electro-absorption modulator working by quantum confined Stark effect (QCSE) and DFB laser which determines wavelength by internal grating coupling. It is a universal ideal light source for information transmission carrier in current high-speed optical fiber transmission network at home and abroad. It has a large number of applications in access network, such as signal light emission source for optical fiber transmission in metropolitan area network and local area network, and light source for electrical-optical signal conversion and remote transmission in phased array radar base station, etc.
[0003] Compared with directly modulated lasers (DMLs), EMLs have better transmission characteristics and effects, especially in high-frequency modulation or long-distance transmission. The current solutions for LD and EAM integration include: identical layer, butt-joint, etc. The identical layer EML laser is grown through a single epitaxial growth, and the LD and EAM structures are grown simultaneously. By adjusting the wavelength detuning of the LD, the absorption of the EAM meets the application requirements. However, the structures of the LD and EAM cannot be optimized separately, and the light output efficiency of the LD and the extinction ratio (ER) of the EAM cannot be taken into account. In addition, the butt-joint growth is used to design the structures of the LD and EAM separately. The LD structure is first grown on the substrate, and then a mask is made to protect the LD area through photolithography. After dry etching and wet etching, the LD structure outside the mask is removed, and then multiple epitaxial growths are performed to grow the EAM structure and other structures. The disadvantage is that multiple epitaxial growths are required, and defects are prone to occur at the growth interface, resulting in performance degradation or reliability problems.
[0004] The present invention adopts a selective area growth scheme, and by designing masks on the substrate, the epitaxial deposition rates in the areas between the masks are different, and structures with different growth thicknesses are obtained. After one epitaxial growth, LD and EAM with different structures can be obtained, and selective growth of different functional layers can be achieved, and multiple functions can be integrated on the same substrate. Multiple epitaxial growths are not required, which effectively reduces the cost; at the same time, there is no docking interface, which can effectively improve the material quality, avoid docking interface defects, and improve the reliability of the chip. Summary of the invention
[0005] The present invention provides a selectively grown high-speed electro-absorption modulated laser chip and a preparation method thereof, which does not require multiple epitaxial growths and effectively reduces costs; at the same time, there is no docking interface, which can effectively improve material quality, avoid docking interface defects, and improve chip reliability.
[0006] The present invention adopts the following technical solutions.
[0007] A selectively grown high-speed electro-absorption modulated laser chip can be used for a high-speed electro-absorption modulated laser produced by a selective growth process, the chip comprising a substrate, and also comprising a buffer layer, an EAM active region and a grating layer whose growth thickness is adjusted according to a preset shape of a mask layer on the substrate during a selective growth process; the active region of the chip is divided into an LD region on one side for generating laser light and an EAM region on the other side for modulating the laser light according to a preset shape of the mask layer on the substrate before the selective growth process; the LD region comprises a grating layer and a grating at the grating layer, the grating layer is sequentially covered with an upper cladding layer, a contact layer and a first metal electrode, an isolation region is provided at the junction of the LD region and the EAM region, and a second metal electrode is provided at the bottom surface of the substrate.
[0008] The EAM region and the LD region are adjacent to the grating layer in the same layer and are filled with InP.
[0009] The EAM region does not have a grating layer.
[0010] The substrate is an InP substrate.
[0011] The preset shape of the mask layer is a preset mask pattern, and the mask pattern is two symmetrical trapezoids; the mask layer is a SiO2 mask layer.
[0012] The first metal electrode is a P-side metal electrode.
[0013] The contact layer is an InGaAs contact layer that forms an ohmic contact with the P-surface metal electrode.
[0014] The second metal electrode is an N-face metal electrode.
[0015] The isolation region is provided at the joint portion of the LD region and the EA region, and is used to prevent the current in the LD region and the EA region from being turned on and affecting each other; The grating layer is a holographic grating with a period of 245.61 nm and a duty cycle of 50%.
[0016] A method for preparing a selectively grown high-speed electro-absorption modulated laser chip, the method comprising the following steps: Step 1: Grow a layer of SiO2 mask on the InP substrate by PECVD, and make a specific mask pattern by coating, exposure, development and etching. The mask pattern includes two symmetrical trapezoids. The upper base L1 of the trapezoid is 462.5um long, the lower base L2 is 637.5um long, the height Wm is 87.5um, and the distance Wg between the two trapezoids is 30um; Step 2: grow the buffer layer, EAM active area and grating layer on the wafer that has completed step 1 by MOCVD, and use BOE solution to clean it after the growth is completed, and remove the SiO2 mask grown in step 1 at the same time; Step 3: Make a grating on the wafer of step 2, obtain a photoresist mask by holographic exposure, and then use HCL solution for etching to obtain a holographic grating with a period of 245.61nm and a duty cycle of 50%; after the grating is made, continue to form a photoresist mask in the LD area through coating, photolithography and development, and etch the grating in the EAM area with HCL solution. After all the etching is completed, remove the photoresist; Step 4: After completing step 3, use BOE solution to remove the oxide on the surface of the wafer, and then put it into the MOCVD equipment to grow a highly doped InP layer and an InGaAs contact layer; Step 5: After completing the above steps, the chip is taped out. A layer of SiO2 mask is grown using PECVD. The SIO2 mask pattern is made by coating, exposure, development and etching. The ridge waveguide is then completed by etching with a Br2 solution and an HCL:H3PO4 solution. Then, the docking area of LD and EA is isolated to prevent the current conduction in the LD and EA areas from affecting each other. Then, a P-side electrode layer is made to form an ohmic contact with the InGaAs contact layer. The back of the substrate is ground and thinned, and the final thickness is retained at 110±10um. The N-side electrode layer is plated on the back, and then the wafer is cut into bars. The two ends of the bars are optically coated, and finally the bars are separated into single chips to complete the entire process.
[0017] The present invention adopts a selective area growth scheme, and by designing masks on the substrate, the epitaxial deposition rates in the areas between the masks are different, and structures with different growth thicknesses are obtained. After one epitaxial growth, LD and EAM with different structures can be obtained, and selective growth of different functional layers can be achieved, and multiple functions can be integrated on the same substrate. Multiple epitaxial growths are not required, which effectively reduces the cost; at the same time, there is no docking interface, which can effectively improve the material quality, avoid docking interface defects, and improve the reliability of the chip.
[0018] The present invention obtains LD and EAM of different structures by a selective growth process with a specific setting of a mask pattern, and optimizes the number of epitaxial growth times, so as to prepare a high-performance, low-cost, high-speed electro-absorption modulated laser. BRIEF DESCRIPTION OF THE DRAWINGS
[0019] The present invention is further described in detail below with reference to the accompanying drawings and specific embodiments: Attached Figure 1 A schematic diagram of a chip of a high-speed electro-absorption modulated laser of the present invention; Attached Figure 2 This is a schematic diagram after completing step 2 of the present invention; Attached Figure 3 is a schematic diagram of a mask pattern in step 2 of the present invention; Attached Figure 4 This is a schematic diagram after completing step three of the present invention; Attached Figure 5 This is a schematic diagram after completing step 4 of the present invention; Attached Figure 6 It is a schematic diagram after forming an isolation area in step five of the present invention; In the figure: 1-LD region; 2-EAM region; 3-grating; 4-contact layer; 5-upper cladding layer; 6-first metal electrode; 7-grating layer; 8-EAM active region; 9-buffer layer; 10-substrate; 11-second metal electrode; 12-isolation region. DETAILED DESCRIPTION
[0020] As shown in the figure, a selectively grown high-speed electro-absorption modulated laser chip can be used for a high-speed electro-absorption modulated laser produced by a selective growth process, wherein the chip includes a substrate 10, and also includes a buffer layer 9, an EAM active region 8 and a grating layer whose growth thickness is adjusted according to a preset shape of a mask layer on the substrate during the selective growth process; the active region of the chip is divided into an LD region 1 on one side for generating laser light and an EAM region 2 on the other side for modulating the laser light according to a preset shape of the mask layer on the substrate before the selective growth process; the LD region includes a grating layer 7 and a grating 3 at the grating layer, and the grating layer is sequentially covered with an upper cladding layer 5, a contact layer 4 and a first metal electrode 6, an isolation region 12 is provided at the junction of the LD region and the EAM region, and a second metal electrode 11 is provided at the bottom surface of the substrate.
[0021] The EAM region and the LD region are adjacent to the grating layer in the same layer and are filled with InP.
[0022] The EAM region does not have a grating layer.
[0023] The substrate is an InP substrate.
[0024] The preset shape of the mask layer is a preset mask pattern, and the mask pattern is two symmetrical trapezoids; the mask layer is a SiO2 mask layer.
[0025] The first metal electrode is a P-side metal electrode.
[0026] The contact layer is an InGaAs contact layer that forms an ohmic contact with the P-surface metal electrode.
[0027] The second metal electrode is an N-face metal electrode.
[0028] The isolation region is provided at the joint portion of the LD region and the EA region, and is used to prevent the current in the LD region and the EA region from being turned on and affecting each other; The grating layer is a holographic grating with a period of 245.61 nm and a duty cycle of 50%.
[0029] A method for preparing a selectively grown high-speed electro-absorption modulated laser chip, the method comprising the following steps: Step 1: Grow a layer of SiO2 mask on the InP substrate by PECVD, and make a specific mask pattern by coating, exposure, development and etching. The mask pattern includes two symmetrical trapezoids. The upper base L1 of the trapezoid is 462.5um long, the lower base L2 is 637.5um long, the height Wm is 87.5um, and the distance Wg between the two trapezoids is 30um; Step 2: grow the buffer layer, EAM active area and grating layer on the wafer that has completed step 1 by MOCVD, and use BOE solution to clean it after the growth is completed, and remove the SiO2 mask grown in step 1 at the same time; Step 3: Make a grating on the wafer of step 2, obtain a photoresist mask by holographic exposure, and then use HCL solution for etching to obtain a holographic grating with a period of 245.61nm and a duty cycle of 50%; after the grating is made, continue to form a photoresist mask in the LD area through coating, photolithography and development, and etch the grating in the EAM area with HCL solution. After all the etching is completed, remove the photoresist; Step 4: After completing step 3, use BOE solution to remove the oxide on the surface of the wafer, and then put it into the MOCVD equipment to grow a highly doped InP layer and an InGaAs contact layer; Step 5: After completing the above steps, the chip is taped out. A layer of SiO2 mask is grown using PECVD. The SIO2 mask pattern is made by coating, exposure, development and etching. The ridge waveguide is then completed by etching with a Br2 solution and an HCL:H3PO4 solution. Then, the docking area of LD and EA is isolated to prevent the current conduction in the LD and EA areas from affecting each other. Then, a P-side electrode layer is made to form an ohmic contact with the InGaAs contact layer. The back of the substrate is ground and thinned, and the final thickness is retained at 110±10um. The N-side electrode layer is plated on the back, and then the wafer is cut into bars. The two ends of the bars are optically coated, and finally the bars are separated into single chips to complete the entire process.
[0030] Example: In order to obtain a high-performance, low-cost high-speed electro-absorption modulated laser, it is necessary to obtain LDs and EAMs with different structures and optimize the number of epitaxial growth. Therefore, in this example, a selectively grown high-speed electro-absorption modulated laser and its preparation method are used. The detailed technical scheme is as follows: In this example, the selectively grown high-speed electro-absorption modulated laser includes a substrate, a mask layer on the substrate, a buffer layer, an active region of LD and EAM, a grating layer in the LD region, and an InP-filled region without a grating layer in the EAM region. The grating layer is covered with an upper cladding layer, followed by a contact layer and a P-side metal electrode. There is an isolation region at the junction of LD and EAM, and there is an N-side metal electrode at the bottom of the substrate.
[0031] The preparation method comprises the following steps: Step 1: Grow a layer of SiO2 mask on the InP substrate by PECVD, and make a specific mask pattern by coating, exposure, development and etching. The mask pattern has two symmetrical trapezoids, with an upper base L1 length of 462.5um, a lower base L2 length of 637.5um, a height Wm of 87.5um, and a spacing Wg of 30um between the two trapezoids.
[0032] Step 2: Grow the buffer layer, EAM active area and grating layer on the wafer that has completed step 1 by MOCVD, and use BOE solution to clean it after the growth is completed, and remove the SiO2 mask grown in step 1 at the same time; Step 3: Make a grating on the wafer of step 2, obtain a photoresist mask by holographic exposure, and then use HCL solution for etching until a holographic grating with a period of 245.61nm and a duty cycle of 50% is obtained; after the grating is made, continue to form a photoresist mask in the LD area through coating, photolithography and development, and etch the grating in the EAM area with HCL solution. After all the etching is completed, remove the photoresist; Step 4: After completing step 3, use BOE to remove the surface oxide, and then put it into the MOCVD equipment to grow a highly doped InP layer and an InGaAs contact layer; Step 5: After completing the above steps, the chip is taped out. A layer of SiO2 mask is grown using PECVD, and the SIO2 mask pattern is made through coating, exposure, development and etching. The ridge waveguide is then completed by etching with a Br2 solution and an HCL:H3PO4 solution. Isolation is then performed in the docking area between LD and EA to prevent the current conduction in the LD and EA areas from affecting each other. A P-side electrode layer is then made to form an ohmic contact with the InGaAs contact layer, and the back of the substrate is ground and thinned to retain a final thickness of 110±10um. An N-side electrode layer is plated on the back, and the wafer is then cut into bars. Optical coating is performed on both ends of the bars, and finally the bars are separated into single chips to complete the entire process.
Claims
1. A selectively grown high-speed electro-absorption modulated laser chip, characterized in that: The chip includes a substrate, and also includes a buffer layer, an EAM active area and a grating layer whose growth thickness is adjusted according to the preset shape of the mask layer on the substrate during the selective growth process; the active area of the chip is divided into an LD area on one side for generating laser and an EAM area on the other side for modulating the laser according to the preset shape of the mask layer on the substrate before the selective growth process; the LD area includes a grating layer and a grating at the grating layer, the grating layer is sequentially covered with an upper cladding layer, a contact layer and a first metal electrode, an isolation area is provided at the junction of the LD area and the EAM area, and a second metal electrode is provided at the bottom surface of the substrate.
2. The selectively grown high-speed electro-absorption modulated laser chip according to claim 1, characterized in that: The EAM region and the LD region are adjacent to the grating layer in the same layer and are filled with InP.
3. The selectively grown high-speed electro-absorption modulated laser chip according to claim 2, characterized in that: The EAM region does not have a grating layer.
4. The selectively grown high-speed electro-absorption modulated laser chip according to claim 1, characterized in that: The substrate is an InP substrate.
5. The selectively grown high-speed electro-absorption modulated laser chip according to claim 1, characterized in that: The preset shape of the mask layer is a preset mask pattern, and the mask pattern is two symmetrical trapezoids; the mask layer is a SiO2 mask layer.
6. The selectively grown high-speed electro-absorption modulated laser chip according to claim 1, characterized in that: The first metal electrode is a P-side metal electrode.
7. The selectively grown high-speed electro-absorption modulated laser chip according to claim 6, characterized in that: The contact layer is an InGaAs contact layer that forms an ohmic contact with the P-surface metal electrode.
8. The selectively grown high-speed electro-absorption modulated laser chip according to claim 1, characterized in that: The second metal electrode is an N-face metal electrode.
9. The selectively grown high-speed electro-absorption modulated laser chip according to claim 1, characterized in that: The isolation region is provided at the joint portion of the LD region and the EA region, and is used to prevent the current in the LD region and the EA region from being turned on and affecting each other; The grating layer is a holographic grating.
10. A method for preparing a selectively grown high-speed electro-absorption modulated laser chip, characterized in that: The method comprises the following steps: Step 1: grow a layer of SiO2 mask on the InP substrate by PECVD, and make a specific mask pattern by coating, exposure, development and etching. The mask pattern includes two symmetrical trapezoids; Step 2: grow the buffer layer, EAM active area and grating layer on the wafer that has completed step 1 by MOCVD, and use BOE solution to clean it after the growth is completed, and remove the SiO2 mask grown in step 1 at the same time; Step 3: Make a grating on the wafer of step 2, obtain a photoresist mask by holographic exposure, and then use HCL solution to etch to obtain a holographic grating; after the grating is made, continue to form a photoresist mask in the LD area by coating, photolithography and development, and etch the grating in the EAM area by HCL solution, and remove the photoresist after all etching is completed; Step 4: After completing step 3, use BOE solution to remove the oxide on the surface of the wafer, and then put it into the MOCVD equipment to grow a highly doped InP layer and an InGaAs contact layer; Step 5: After completing the above steps, the chip is taped out. A layer of SiO2 mask is grown using PECVD. The SIO2 mask pattern is made by coating, exposure, development and etching. The ridge waveguide is then completed by etching with a Br2 solution and an HCL:H3PO4 solution. Then, the docking area of LD and EA is isolated to prevent the current conduction in the LD and EA areas from affecting each other. Then, a P-side electrode layer is made to form an ohmic contact with the InGaAs contact layer, and the back of the substrate is ground and thinned. An N-side electrode layer is plated on the back side.