CN107623250B - Short-cavity long-surface emitting laser and manufacturing method thereof - Google Patents
Short-cavity long-surface emitting laser and manufacturing method thereof Download PDFInfo
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- CN107623250B CN107623250B CN201710919392.5A CN201710919392A CN107623250B CN 107623250 B CN107623250 B CN 107623250B CN 201710919392 A CN201710919392 A CN 201710919392A CN 107623250 B CN107623250 B CN 107623250B
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Abstract
The invention relates to the field of photoelectronic devices, and provides a method for manufacturing a short-cavity long-surface emitting laser, which comprises the following steps: s1, selecting a substrate, and growing a buffer layer on the substrate; s2, growing an intermediate layer above the buffer layer; meanwhile, a grating layer is manufactured on the buffer layer, and the grating layer is positioned on two opposite sides of the middle layer; the middle layer comprises a lower waveguide layer, a multi-quantum well layer and an upper waveguide layer which are sequentially grown upwards; the middle layer is in butt joint with a gain region of the laser, and the two grating layers are in butt joint with a passive waveguide growth region respectively; s3, growing a stop layer, a cladding layer and a contact layer above the upper waveguide layer in sequence; s4, manufacturing a ridge waveguide, an isolation region and a contact strip; s5, manufacturing a P-surface electrode and an N-surface electrode, and thinning the substrate; and S6, stripping and de-numbering. The invention integrates a section of passive waveguide area on both sides of the gain area, which solves the problem of difficult process caused by small cavity length.
Description
Technical Field
The invention relates to the field of photoelectronic devices, in particular to a short-cavity long-surface emitting laser and a manufacturing method thereof.
Background
The system upgrading of the optical network does not benefit from the upgrading of the optical device, the performance of the laser as a core component of the optical device limits the performance of the whole system, and the laser capable of realizing the single-channel baud rate of 25Gb/s and even better rate is urgently needed.
At present, two schemes are mainly adopted for high-speed modulated lasers, the first scheme is a distributed feedback laser monolithic integrated electro-absorption modulator (EMLs), the EMLs are not influenced by frequency chirp characteristics, have relatively good extinction ratio and clear eye pattern, and are very suitable for long-distance transmission systems. But the manufacturing process is relatively complex and the power consumption is relatively large. Neophoronics issued 25G EML first in 2009 with an emitted optical power of 6.5dBm and a dynamic Extinction Ratio (ER) of 7.6dB at 35 ℃. Another solution is to directly modulate a semiconductor laser (DML) to directly modulate the driving current of the laser at high speed, and the DML generally has high light output power, low power consumption, low cost, and is suitable for small-sized packaging. The design and optimization for DML is mainly injected from two aspects, firstly to increase the relaxation oscillation frequency fr of the chip itself and secondly to reduce RC by means of manufacturing process optimization and package design optimization. The mode of reducing RC is direct, and the lower part of the electrode can be filled with a material with low dielectric constant in the aspect of manufacturing process, so that the area of the electrode pad is reduced, and the like; the length of gold wire can be reduced in the packaging design. In the fr optimization scheme, the structural design of a multi-slave chip starts, and the general principle is to reduce the threshold current, the cavity length, the number and the thickness of quantum wells, reduce the width of an active region and simultaneously improve the optical field limiting factor and the differential gain.
However, the design of these parameters is often interrelated, for example, decreasing the cavity length can increase fr but decrease the power output, and decreasing the number of quantum wells also makes the optical field restriction factor smaller, so the optimum design of these parameters often needs to be balanced. It can be seen from the scheme design of the current mainstream high-speed DML that, for directly modulating a 3dB bandwidth above 30GHz, reducing the laser gain region to below 200 μm is the main option. Chip fabrication with cavity lengths less than 200 μm is not a small challenge for many post-processing steps, such as thinning and bar cleaving.
Disclosure of Invention
The invention aims to provide a short-cavity long-surface emitting laser and a manufacturing method thereof, which solve the problem of difficult process caused by small cavity length by integrating a section of passive waveguide region at two sides of a gain region respectively.
In order to achieve the above purpose, the embodiments of the present invention provide the following technical solutions: a method for manufacturing a short cavity long surface emitting laser includes the steps of:
s1, selecting a substrate, and growing a buffer layer on the substrate;
s2, growing an intermediate layer above the buffer layer; meanwhile, a grating layer is manufactured on the buffer layer, and the grating layer is positioned on two opposite sides of the middle layer; the middle layer comprises a lower waveguide layer, a multi-quantum well layer and an upper waveguide layer which are sequentially grown upwards; the middle layer is in butt joint with a gain region of the laser, and the two grating layers are in butt joint with a passive waveguide growth region respectively;
s3, growing a stop layer, a cladding layer and a contact layer above the upper waveguide layer in sequence;
s4, manufacturing a ridge waveguide, an isolation region and a contact strip;
s5, manufacturing a P-surface electrode and an N-surface electrode, and thinning the substrate;
and S6, stripping and de-numbering.
Further, in step S2, the method of electron beam exposure is used to fabricate the grating layer.
Further, in step S2, the method for manufacturing the laser gain region specifically includes: growing SiO on the surface of the epitaxial wafer by adopting a plasma enhanced chemical vapor deposition method2Mask layer, and mask pattern is made by photoetching and etching technology; the manufacturing method of each passive waveguide growth region specifically comprises the following steps: the metal organic chemical vapor deposition method is adopted for manufacturing.
Furthermore, the grating layer is a Bragg grating, the period Lambda of the Bragg grating is determined according to the following formula,
where m is the number of grating stages, λbIs the bragg wavelength.
Further, along the length direction of the cavity, when the laser is reflected at the position with discontinuous refractive index, the wavelength of the Bragg grating has the maximum reflection coefficient.
Further, a first-order grating is manufactured in the two passive waveguide growth areas, namely m is 1, and the first-order grating is the grating layer; and manufacturing a second-order grating in the gain region of the laser, wherein m is 2, and the second-order grating is the middle layer.
Further, under the condition of no current injection, when the effective refractive index of each passive waveguide growth region is equal to that of the laser gain region, the period of the second-order grating is twice that of the first-order grating, and the period of the first-order grating is determined according to the emission wavelength of the device.
Further, in step S4, the ridge waveguide, the isolation region and the contact bar are fabricated by photolithography, reactive ion etching and wet etching.
Further, in step S6, a magnetron sputtering method is used to fabricate a P-side electrode and an N-side electrode.
The embodiment of the invention provides another technical scheme: a short-cavity long-surface emitting laser is manufactured by the method.
Compared with the prior art, the invention has the beneficial effects that: a ridge waveguide structure is adopted, a section of passive waveguide area is respectively integrated in a gain area, a first-order grating with high reflection coefficient is manufactured in the passive waveguide area to be used as optical feedback, a second-order grating is manufactured in the gain area to carry out frequency selection and optical feedback and is used for generating an optical vector vertical to the surface to realize surface emission; under the condition of shorter gain region length, a passive waveguide is integrated, so that the laser is ensured to have higher fr to obtain large high-speed directly-modulated 3dB bandwidth, and meanwhile, the risk caused by the ultra-short cavity length in the process manufacturing is avoided; the manufactured gratings are lateral coupling gratings, so that the conventional grating burying steps are reduced, the chip manufacturing cost is further reduced, the growth defect possibly caused by grating burying can be avoided, and the reliability and consistency of the chip are guaranteed; the DBR reflector is used as a high-reflection film, so that the film coating process is reduced, and the chip manufacturing cost is correspondingly reduced; the manufacturing process of the laser is compatible with the manufacturing process of the conventional edge-emitting laser, and the utilization rate of equipment is improved.
Drawings
Fig. 1 is a flowchart of a method for manufacturing a short cavity long surface emitting laser according to an embodiment of the present invention;
fig. 2 is a schematic structural level diagram of a short cavity long surface emitting laser according to an embodiment of the present invention;
fig. 3 is a schematic structural diagram of a short cavity long surface emitting laser according to an embodiment of the present invention;
in the reference symbols: 1-a substrate; 2-a buffer layer; 3-a lower waveguide layer; 4-a multi-quantum well layer; 5-an upper waveguide layer; 6-a grating layer; 7-a stop layer; 8-coating layer; 9-a contact layer; a-a laser gain region; b-passive waveguide growth area.
Detailed Description
The technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the drawings in the embodiments of the present invention, and it is obvious that the described embodiments are only a part of the embodiments of the present invention, and not all of the embodiments. All other embodiments, which can be derived by a person skilled in the art from the embodiments given herein without making any creative effort, shall fall within the protection scope of the present invention.
Referring to fig. 1, fig. 2 and fig. 3, a method for manufacturing a short cavity long surface emitting laser according to an embodiment of the present invention includes the following steps: s1, selecting a substrate 1, and growing a buffer layer 2 on the substrate 1; s2, growing an intermediate layer over the buffer layer 2; meanwhile, a grating layer 6 is manufactured on the buffer layer 2, and the grating layer 6 is positioned on two opposite sides of the intermediate layer; the middle layer comprises a lower waveguide layer 3, a multi-quantum well layer 4 and an upper waveguide layer 5 which are sequentially grown upwards; the middle layer is butted to form a laser gain area, and the two grating layers 6 are respectively butted to a passive waveguide growth area B; s3, sequentially growing a stop layer 7, a cladding layer and a contact layer above the upper waveguide layer 5; s4, manufacturing a ridge waveguide, an isolation region and a contact strip; s5, manufacturing a P-surface electrode and an N-surface electrode, and thinning the substrate 1; and S6, stripping and de-numbering.
In this embodiment, a buffer layer 2, a lattice-matched lower waveguide layer 3, a multiple quantum well layer 4, a lattice-matched upper waveguide layer 5, and a lattice-matched grating layer 6 are sequentially grown on a substrate 1 by a metal organic chemical vapor deposition method, wherein the substrate 1 and the buffer layer 2 are both made of N-type indium phosphide, the lower waveguide layer 3, the upper waveguide layer 5, and the grating layer 6 are all made of indium gallium arsenic phosphide, the buffer layer 2 is 1 μm thick, the lower waveguide layer 3 is 100nm thick, the multiple quantum well layer 4 is 115nm thick, and includes 7 quantum wells and 8 barrier layers, each well and each barrier is 5nm and 10nm thick, the upper waveguide layer 5 is 90nm thick, and the grating layer 6 is 305nm thick. Two grating layers 6 are arranged on two sides of the middle layer, the laser is divided into three parts which respectively correspond to an area A and an area B in the graph 2, the area A is a laser gain area, the two areas B are both passive waveguide growth areas, and the two passive waveguide areas are integrated on the gain area. The problem of difficult process caused by the small cavity length can be solved.
In step S2, the grating layer 6 is formed by electron beam exposure. The resulting grating layer 6 is a laterally coupled grating. The manufacturing cost of the chip can be reduced, and the reliability of the chip can be improved.
As an optimized solution of the embodiment of the present invention, in step S2, the method for manufacturing the laser gain region specifically includes: growing SiO on the surface of the epitaxial wafer by adopting a plasma enhanced chemical vapor deposition method2Mask layer, and mask pattern is made by photoetching and etching technology; the manufacturing method of each passive waveguide growth region specifically comprises the following steps: the metal organic chemical vapor deposition method is adopted for manufacturing. Prepared SiO2The mask pattern was in the form of periodic stripes of 100 μm in length and 25 μm in width, and the pattern period was 250 μm in the stripe length direction and stripe width direction. Next, portions of the upper waveguide layer 5, the multiple quantum well layer 4, and the lower waveguide layer 3 outside the mask pattern are removed by reactive ion etching and chemical etching, and then concentrated sulfuric acid: hydrogen peroxide: and etching by using the selective etching solution with the volume ratio of the deionized water of 3:1:1 to remove the other part of the lower waveguide layer 3, wherein the etching is stopped on the buffer layer 2. And finally, manufacturing a core layer of the passive waveguide by adopting a metal organic chemical vapor deposition method, wherein the material of the core layer is P-type indium gallium arsenic phosphorus, and the thickness of the core layer is 305 nm.
As an optimized solution of the embodiment of the present invention, in step S3, a hydrofluoric acid solution is used to remove SiO2And a mask pattern, wherein a stop layer 7, a coating layer 8 and a contact layer are sequentially grown by using a metal organic chemical vapor deposition method, the stop layer 7 and the contact layer are made of P-type indium gallium arsenic phosphorus, the thicknesses of the stop layer 7 and the contact layer are respectively 10nm and 100nm, and the coating layer 8 is made of P-type indium phosphide.
As an optimized solution of the embodiment of the present invention, in step S4, a ridge waveguide, an isolation region, and a contact strip are sequentially fabricated by using photolithography and etching techniques. The ridge waveguide is made by photoetching and etching technology, a through strip with the width of 2 mu m is provided with a groove with the width of 16 mu m and the depth of about 2 mu m on each side, the period in the strip width direction is 250 mu m, and the isolation region is a high-resistance region formed by etching or ion implantation. The contact strip is formed by first depositing SiO with a thickness of 350nm on the ridge waveguide2And removing the SiO2 on the ridge waveguide mesa by adopting photoetching and etching technologies to form an electric injection window.
As an optimized scheme of the embodiment of the present invention, the grating layer 6 is a bragg grating, and the period Λ thereof is determined according to the following formula:
where m is the number of grating stages, λbIs the bragg wavelength. The Bragg grating is used as a high-reflection film of the traditional transmitting laser, so that the film coating process is reduced, and the manufacturing cost of the chip is correspondingly reduced. Preferably, a first order grating, i.e., m 1, is formed in the two passive waveguide growth regions B, and a second order grating, i.e., m 2, is formed in the laser gain region a. The first order grating corresponds to the grating layer 6 and the second order grating corresponds to the intermediate layer. The first-order grating and the second-order grating both adopt lateral coupling gratings, so that the conventional grating burying steps are reduced, the chip manufacturing cost is further reduced, the growth defect possibly introduced by grating burying can be avoided, and the reliability and the consistency of the chip are guaranteed. And along the length direction of the cavity, when the laser is reflected at the position with discontinuous refractive index, the wavelength of the Bragg grating has the maximum reflection coefficient.
Further optimizing the scheme, under the condition of no current injection, when the effective refractive index of each passive waveguide growth region is equal to that of the laser gain region, the period of the second-order grating is about twice that of the first-order grating, the period of the first-order grating is determined according to the emission wavelength of the device, and the depth of the first-order grating is 1.5 mu m. The first order grating of each of the passive waveguide growth regions can be used as a high emission film for conventional lasers and the residual transmitted light can be used for backlight monitoring.
In step S5, the P-side electrode is a Ti/Pt/Au layer with a thickness of 40nm/100nm/250nm formed by magnetron sputtering, and the N-side electrode is a Pt/Au layer with a thickness of 40nm/100nm formed by magnetron sputtering. The thinning is to thin the wafer with a thickness of about 350 μm to about 110 μm by using a polishing technique.
The embodiment of the invention provides a short-cavity long-surface emitting laser which is manufactured by the method. The laser comprises three parts, as shown in fig. 2, the middle part is a laser gain region, two ends of the laser gain region are respectively integrated with a section of passive waveguide, gratings are manufactured on the passive waveguides to be used as DBR reflectors, meanwhile, electricity is applied to carry out wavelength fine tuning, and a second-order grating is manufactured on the gain region of the middle part to be used for frequency selection and generating surface emission light.
Although embodiments of the present invention have been shown and described, it will be appreciated by those skilled in the art that changes, modifications, substitutions and alterations can be made in these embodiments without departing from the principles and spirit of the invention, the scope of which is defined in the appended claims and their equivalents.
Claims (8)
1. A method for manufacturing a short cavity long surface emitting laser, comprising the steps of:
s1, selecting a substrate, and growing a buffer layer above the substrate;
s2, growing an intermediate layer above the buffer layer; meanwhile, a grating layer is manufactured on the buffer layer,
the two grating layers are positioned on two opposite sides of the intermediate layer, the intermediate layer and the two grating layers are positioned on the same layer, and the thicknesses of the intermediate layer and the two grating layers are the same; the middle layer comprises a lower waveguide layer, a multi-quantum well layer and an upper waveguide layer which are sequentially grown upwards; the middle layer is positioned in a laser gain area, the two grating layers are respectively positioned in a passive waveguide growth area, and the lower waveguide layer, the upper waveguide layer and the grating layers are all made of indium gallium arsenic phosphorus;
s3, growing a stop layer, a cladding layer and a contact layer above the upper waveguide layer and above the two grating layers in sequence;
s4, manufacturing a ridge waveguide, an isolation region and a contact strip;
s5, manufacturing a P-surface electrode and an N-surface electrode, and thinning the substrate;
s6, stripping and splitting;
the manufacturing method further includes:
the method comprises the steps of manufacturing a first-order grating on a ridge waveguide located in a passive waveguide growth area, manufacturing a second-order grating on the ridge waveguide located in a laser gain area, wherein the grating layer, the first-order grating and the second-order grating are lateral coupling gratings, and the grating layer is a Bragg grating.
2. A method of manufacturing a short cavity long surface emitting laser according to claim 1, wherein: in step S2, the grating layer is formed by electron beam exposure.
3. A method of manufacturing a short cavity long surface emitting laser according to claim 1, wherein: in step S2, the method for manufacturing the laser gain region specifically includes: growing SiO on the surface of the epitaxial wafer by adopting a plasma enhanced chemical vapor deposition method2Mask layer, and mask pattern is made by photoetching and etching technology; the manufacturing method of each passive waveguide growth region specifically comprises the following steps: the metal organic chemical vapor deposition method is adopted for manufacturing.
4. A method of manufacturing a short cavity long surface emitting laser according to claim 1, wherein: and along the length direction of the cavity, when the laser is reflected at the position with discontinuous refractive index, the wavelength of the Bragg grating has the maximum reflection coefficient.
5. A method of manufacturing a short cavity long surface emitting laser according to claim 1, wherein: under the condition of no current injection, when the effective refractive index of each passive waveguide growth region is equal to that of the laser gain region, the period of the second-order grating is twice that of the first-order grating, and the period of the first-order grating is determined according to the emission wavelength of the device.
6. A method of manufacturing a short cavity long surface emitting laser according to claim 1, wherein: in step S4, the ridge waveguide, the isolation region and the contact bar are fabricated by photolithography, reactive ion etching and wet etching.
7. A method of manufacturing a short cavity long surface emitting laser according to claim 1, wherein: in step S6, a P-side electrode and an N-side electrode are formed by a magnetron sputtering method.
8. A short cavity long facet emitting laser characterized by: the laser is manufactured by the method of any one of claims 1 to 7.
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| CN108923254B (en) * | 2018-07-06 | 2020-06-26 | 扬州乾照光电有限公司 | VCSEL chip with single-cavity structure, manufacturing method thereof and laser device |
| CN112366235A (en) * | 2019-07-25 | 2021-02-12 | 上海新微技术研发中心有限公司 | Waveguide type germanium-based photoelectric detector and preparation method thereof |
| CN111370995B (en) * | 2020-03-12 | 2021-05-18 | 中国科学院半导体研究所 | Surface grating semiconductor laser and manufacturing method thereof |
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| US20100327257A1 (en) * | 2008-03-18 | 2010-12-30 | Fujitsu Limited | Optical semiconductor device and method for manufacturing the same |
| CN106129809A (en) * | 2016-08-25 | 2016-11-16 | 武汉华工正源光子技术有限公司 | Electroabsorption modulator and side-coupled grating laser method for integrating monolithic and device |
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|---|---|---|---|---|
| CN1774845A (en) * | 2004-03-23 | 2006-05-17 | 日本电信电话株式会社 | DBR-type variable-wavelength light source |
| US20100327257A1 (en) * | 2008-03-18 | 2010-12-30 | Fujitsu Limited | Optical semiconductor device and method for manufacturing the same |
| US20090296753A1 (en) * | 2008-05-29 | 2009-12-03 | Sumitomo Electric Industries, Ltd. | Semiconductor laser and optical integrated semiconductor device |
| CN101841129A (en) * | 2010-05-24 | 2010-09-22 | 中国科学院长春光学精密机械与物理研究所 | Monolithic phase-locked surface-emitting distributed feedback semiconductor laser array |
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