CN112490848B - Distributed feedback laser and preparation method thereof - Google Patents
Distributed feedback laser and preparation method thereof Download PDFInfo
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Classifications
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- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01S—DEVICES USING THE PROCESS OF LIGHT AMPLIFICATION BY STIMULATED EMISSION OF RADIATION [LASER] TO AMPLIFY OR GENERATE LIGHT; DEVICES USING STIMULATED EMISSION OF ELECTROMAGNETIC RADIATION IN WAVE RANGES OTHER THAN OPTICAL
- H01S5/00—Semiconductor lasers
- H01S5/10—Construction or shape of the optical resonator, e.g. extended or external cavity, coupled cavities, bent-guide, varying width, thickness or composition of the active region
- H01S5/12—Construction or shape of the optical resonator, e.g. extended or external cavity, coupled cavities, bent-guide, varying width, thickness or composition of the active region the resonator having a periodic structure, e.g. in distributed feedback [DFB] lasers
-
- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01S—DEVICES USING THE PROCESS OF LIGHT AMPLIFICATION BY STIMULATED EMISSION OF RADIATION [LASER] TO AMPLIFY OR GENERATE LIGHT; DEVICES USING STIMULATED EMISSION OF ELECTROMAGNETIC RADIATION IN WAVE RANGES OTHER THAN OPTICAL
- H01S5/00—Semiconductor lasers
- H01S5/20—Structure or shape of the semiconductor body to guide the optical wave ; Confining structures perpendicular to the optical axis, e.g. index or gain guiding, stripe geometry, broad area lasers, gain tailoring, transverse or lateral reflectors, special cladding structures, MQW barrier reflection layers
- H01S5/22—Structure or shape of the semiconductor body to guide the optical wave ; Confining structures perpendicular to the optical axis, e.g. index or gain guiding, stripe geometry, broad area lasers, gain tailoring, transverse or lateral reflectors, special cladding structures, MQW barrier reflection layers having a ridge or stripe structure
-
- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01S—DEVICES USING THE PROCESS OF LIGHT AMPLIFICATION BY STIMULATED EMISSION OF RADIATION [LASER] TO AMPLIFY OR GENERATE LIGHT; DEVICES USING STIMULATED EMISSION OF ELECTROMAGNETIC RADIATION IN WAVE RANGES OTHER THAN OPTICAL
- H01S5/00—Semiconductor lasers
- H01S5/30—Structure or shape of the active region; Materials used for the active region
- H01S5/3013—AIIIBV compounds
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- Condensed Matter Physics & Semiconductors (AREA)
- General Physics & Mathematics (AREA)
- Electromagnetism (AREA)
- Optics & Photonics (AREA)
- Geometry (AREA)
- Semiconductor Lasers (AREA)
Abstract
The invention discloses a distributed feedback laser and a preparation method thereof, wherein the distributed feedback laser comprises: the laser epitaxial structure comprises a substrate and a plurality of epitaxial layers positioned on one side of the substrate, wherein each epitaxial layer comprises a middle epitaxial layer, and an upper light field limiting layer and an upper contact layer which are sequentially positioned on one side of the middle epitaxial layer far away from the substrate; the material of the epitaxial layer comprises Al x1Iny1Ga1‑x1‑y1 N, wherein x1 is more than or equal to 0 and less than or equal to 1, y1 is more than or equal to 0 and less than or equal to 1, and (x1+y1) is more than or equal to 0 and less than or equal to 1; a first type ohmic contact metal layer on a side of the upper contact layer away from the substrate; wherein the upper light field limiting layer, the upper contact layer and the first type ohmic contact metal layer form a ridge structure; the ridge structure extends along the m direction, and in the ridge structure, the side surfaces of the upper contact layer and part of the upper light field limiting layer are m surfaces; and a second type ohmic contact metal layer positioned on one side of the substrate away from the epitaxial layer. The invention solves the technical problems of non-radiative recombination and electric leakage of dry etching ridge side walls and unstable lasing wavelength.
Description
Technical Field
The embodiment of the invention relates to the technical field of lasers, in particular to a distributed feedback laser and a preparation method thereof.
Background
The III nitride semiconductor is called a third-generation semiconductor material, and has the advantages of large forbidden bandwidth, high luminous efficiency and the like; the light-emitting wavelength ranges from deep ultraviolet to near infrared, and can be used for manufacturing semiconductor light-emitting devices, such as light-emitting diodes, lasers and the like. The DFB laser based on the III nitride semiconductor has very narrow output spectrum and good single-mode characteristic, has very important application prospect in the fields of atomic clocks, laser radars, sensing mapping and the like, is focused, and becomes a research hotspot in academic circles and industry at home and abroad.
Early group III nitride semiconductor DFB lasers generally adopt mask gratings, namely, gratings are manufactured in the DFB lasers, so that multiple epitaxial growth is needed, the preparation process is complex, the cost is high, contamination such as carbon, oxygen and silicon is easy to occur at a secondary epitaxial growth interface, and the performance and reliability of the device are seriously affected. Therefore, the conventional DFB laser mainly adopts a surface grating, i.e., a ridge sidewall grating structure, and as shown in fig. 1, the grating structure with alternately arranged effective refractive index is formed by controlling the ridge stripe width. In order to ensure the flatness of the cavity surface of the DFB laser, the ridge shape of the laser is generally arranged along the m-plane direction, that is, the cavity surface of the laser is m-plane, so that the side wall of the ridge shape is the a-plane. For the conventional (0001) plane III nitride semiconductor material, the chemical stability is good, the material is acid-base resistant and is not easy to corrode, so that the ridge shape of the DFB laser needs to be formed by dry etching. The dry etching not only can lead to interface roughness to cause light scattering and the like, but also can introduce surface states and defects such as dangling bonds and the like, and the surface states and the defects not only become non-radiative recombination centers and influence the internal quantum efficiency of the laser; and also becomes a leakage channel, which affects the reliability and stability of the device. In the prior art, high-temperature wet etching is performed by strong alkali to remove dry etching damage of the side wall. The strong alkali high-temperature wet method corrosion not only can corrode dislocation pits on the a-face of the III-nitride semiconductor to form a leakage channel, but also can corrode the a-face of the III-nitride semiconductor into a saw-tooth shape, so that the light scattering loss of the DFB laser is greatly increased, and the wet corrosion technology is not adopted.
In addition, since the group III nitride semiconductor DFB laser has a short operating wavelength and a small effective refractive index, the grating period thereof is short, and it is difficult to prepare a low-order grating using conventional photolithography techniques, and thus, a high-order grating is often used. The high-order grating contains a plurality of lasing modes, so that the modes are unstable when the DFB laser works, mode jump is easy to occur, and the mode stability and the application scene of the III-nitride semiconductor DFB laser are seriously affected.
Disclosure of Invention
In view of the above, the embodiments of the present invention provide a distributed feedback laser and a method for manufacturing the same, so as to solve the technical problems in the prior art that the surface states and defects such as optical dispersion and the like caused by rough interfaces due to ridge-shaped side walls of a DFB laser manufactured by dry etching, and suspension bonds and the like are introduced, so that non-radiative recombination and electric leakage are caused to affect the reliability and stability of a device, and the lasing wavelength is unstable under a higher-order grating structure.
In a first aspect, an embodiment of the present invention provides a distributed feedback laser, including:
The laser epitaxial structure comprises a substrate and a plurality of epitaxial layers positioned on one side of the substrate, wherein the epitaxial layers comprise a middle epitaxial layer, an upper light field limiting layer and an upper contact layer which are sequentially positioned on one side of the middle epitaxial layer far away from the substrate; the material of the epitaxial layer comprises Al x1Iny1Ga1-x1-y1 N, wherein x1 is more than or equal to 0 and less than or equal to 1, y1 is more than or equal to 0 and less than or equal to 1, and (x1+y1) is more than or equal to 0 and less than or equal to 1;
A first type ohmic contact metal layer located on a side of the upper contact layer away from the substrate; wherein the upper light field limiting layer, the upper contact layer and the first type ohmic contact metal layer form a ridge structure; the ridge structure extends along the m direction; in the ridge structure, the side surfaces of the upper contact layer and part of the upper light field limiting layer are m surfaces; the m direction is parallel to the plane of the substrate;
And the second type ohmic contact metal layer is positioned on one side of the substrate away from the epitaxial layer.
Optionally, the ridge structure includes a plurality of sub-ridge structures sequentially connected along an m direction, where the m direction is parallel to a plane where the substrate is located;
the sub-ridge structure comprises a first sub-ridge structure, a second sub-ridge structure and a third sub-ridge structure which are sequentially connected along the m direction;
The extension width of the first sub-ridge structure is larger than that of the second sub-ridge structure and the third sub-ridge structure along the direction a; and along the m direction, the extension width of the second sub-ridge structure in the a direction is gradually reduced, and the extension width of the third sub-ridge structure in the a direction is gradually increased.
Optionally, along the a direction, the width D of the ridge structure satisfies 0 < D less than or equal to 200 mu m;
Along the a direction, the extension width of the first sub-ridge structure is D1, the extension width of the second sub-ridge structure is D2, and the extension width of the third sub-ridge structure is D3, wherein D1-D2 is more than 0 and less than or equal to 100 mu m, and D1-D3 is more than 0 and less than or equal to 100 mu m.
Optionally, the distributed feedback laser further comprises a connection electrode;
The connection electrode covers the upper light field limiting layer, the upper contact layer, the side surface of the first type ohmic contact metal layer and the upper surface of the first type ohmic contact metal layer, and the thickness of the connection electrode is greater than that of the first type ohmic contact metal layer.
Optionally, the middle epitaxial layer includes a buffer layer, a lower optical field limiting layer, a lower waveguide layer, an active region, and an upper waveguide layer or a part of the upper optical field limiting layer, which are sequentially disposed on one side of the substrate.
In a second aspect, a method for preparing a distributed feedback laser, for preparing the distributed feedback laser of the first aspect, includes:
Preparing a laser epitaxial structure, wherein the laser epitaxial structure comprises a substrate and a plurality of epitaxial layers positioned on one side of the substrate, and the epitaxial layers comprise a middle epitaxial layer, an upper light field limiting layer and an upper contact layer which are sequentially positioned on one side of the middle epitaxial layer far away from the substrate; the material of the epitaxial layer comprises Al x1Iny1Ga1-x1-y1 N, wherein x1 is more than or equal to 0 and less than or equal to 1, y1 is more than or equal to 0 and less than or equal to 1, and (x1+y1) is more than or equal to 0 and less than or equal to 1;
preparing a first type ohmic contact metal layer on one side of the upper contact layer away from the substrate;
Etching the first type ohmic contact metal layer, the upper contact layer and the upper light field limiting layer to form a ridge structure; the ridge structure extends along the m direction; in the ridge structure, the side surfaces of the upper contact layer and part of the upper light field limiting layer are m surfaces; the m direction is parallel to the plane of the substrate;
preparing a second type ohmic contact metal layer on one side of the substrate away from the epitaxial layer;
And scribing, cleaving, coating and splitting the epitaxial structure to form the distributed feedback laser.
Optionally, etching the first type ohmic contact metal layer, the upper contact layer and the upper light field limiting layer to form a ridge structure includes:
etching the first type ohmic contact metal layer, the upper contact layer and the upper light field limiting layer by adopting a dry etching process to form a ridge structure;
after etching the first type ohmic contact metal layer, the upper contact layer and the upper light field limiting layer to form a ridge structure, the method further comprises:
And carrying out wet etching on the side surfaces of the upper contact layer and the upper light field limiting layer by adopting an alkaline solution.
Optionally, the alkaline solution comprises at least one of ammonium hydroxide, ammonium chloride, ammonium fluoride, and tetramethylammonium hydroxide.
Optionally, after etching the first type ohmic contact metal, the upper contact layer and the upper light field limiting layer to form a ridge structure, the method further comprises:
depositing an insulating layer on one side of the first type ohmic contact metal layer away from the substrate, wherein the insulating layer covers the upper surface of the ridge structure and the side surface of the ridge structure;
removing the insulating layer on the upper surface of the ridge structure by adopting photoetching and etching technology to expose the first type ohmic contact metal layer;
And preparing a connecting electrode on one side of the insulating layer far away from the substrate, wherein the connecting electrode at least covers the exposed first-type ohmic contact metal layer.
Optionally, preparing a laser epitaxial structure, including:
Providing a substrate;
Preparing a buffer layer on one side of the substrate;
preparing a lower light field limiting layer on one side of the buffer layer away from the substrate;
Preparing a lower waveguide layer on a side of the lower optical field confinement layer away from the substrate;
Preparing an active region on a side of the lower waveguide layer away from the substrate;
preparing an upper waveguide layer on the side of the active region away from the substrate;
preparing an upper optical field confinement layer on a side of the upper waveguide layer away from the substrate;
an upper contact layer is prepared on a side of the upper light field confining layer remote from the substrate.
In the ridge structure formed by the upper light field limiting layer, the upper contact layer and the first type ohmic contact metal layer, the ridge structure extends along the m direction to obtain m faces on the side surfaces of the upper contact layer and part of the upper light field limiting layer, when the m faces are corroded by adopting a wet corrosion technology, the m faces can be corroded to be smooth, steep and flat faces, so that surface states and defect damages such as light scattering and the like caused by interface roughness caused by a dry etching method and introduced suspension bonds can be removed, the technical problems such as non-radiative recombination and electric leakage in the laser are reduced, the threshold current of the device is effectively reduced, and the performance and reliability of the device are improved.
Drawings
Other features, objects and advantages of the present invention will become more apparent upon reading of the detailed description of non-limiting embodiments, made with reference to the accompanying drawings in which:
FIG. 1 is a schematic top view of a prior art grating structure of a distributed feedback laser;
FIG. 2 is a schematic diagram illustrating a grating structure of a distributed feedback laser according to an embodiment of the present invention;
FIG. 3 is a schematic cross-sectional view of a grating structure of the distributed feedback laser shown in FIG. 2;
FIG. 4 is a graph of the mode profile of the group III nitride DFB laser shown in FIG. 1 and the DFB laser provided by the embodiment of the invention shown in FIG. 2;
FIG. 5 is a schematic flow chart of a method for manufacturing a distributed feedback laser according to an embodiment of the present invention;
fig. 6 is a schematic flow chart of a preparation method of a distributed feedback laser according to an embodiment of the present invention.
The following is a reference numeral description:
Fig. 2:100 is a first sub-ridge structure, 101 is a second sub-ridge structure, and 102 is a third sub-ridge structure;
fig. 3:201 is a substrate, 202 is a buffer layer, 203 is a lower optical field confining layer, 204 is a lower waveguide layer, 205 is an active region, 206 is an upper waveguide layer, 207 is an upper optical field confining layer, 208 is an upper contact layer, 209 is a first type ohmic contact metal layer, 210 is an insulating layer, 211 is a connection electrode, and 212 is a second type ohmic contact metal layer.
Detailed Description
In order to make the objects, technical solutions and advantages of the present invention more apparent, the technical solutions of the present invention will be fully described below by way of specific embodiments with reference to the accompanying drawings in the examples of the present invention. It is apparent that the described embodiments are some, but not all, embodiments of the present invention, and that all other embodiments, which a person of ordinary skill in the art would obtain without making inventive efforts, are within the scope of this invention.
Examples
The embodiment of the invention provides a distributed feedback laser. Fig. 2 is a schematic top view of a grating structure of a distributed feedback laser according to an embodiment of the present invention, and fig. 3 is a schematic cross-sectional view of the grating structure of the distributed feedback laser shown in fig. 2. As shown in fig. 2 and 3, the distributed feedback laser includes: the laser epitaxial structure comprises a substrate 201 and a plurality of epitaxial layers positioned on one side of the substrate 201, wherein each epitaxial layer comprises a middle epitaxial layer, an upper light field limiting layer 207 and an upper contact layer 208 which are sequentially positioned on one side of the middle epitaxial layer away from the substrate; the material of the epitaxial layer comprises Al x1Iny1Ga1-x1-y1 N, wherein x1 is more than or equal to 0 and less than or equal to 1, y1 is more than or equal to 0 and less than or equal to 1, and (x1+y1) is more than or equal to 0 and less than or equal to 1; a first type ohmic contact metal layer 209 on a side of the upper contact layer 208 remote from the substrate 201; wherein the upper light field confining layer 207, the upper contact layer 208 and the first type ohmic contact metal layer 209 form a ridge structure; the ridge structure extends in the m direction; in the ridge structure, the side surfaces of the upper contact layer 208 and part of the upper light field limiting layer 207 are m-plane; the m-direction is parallel to the plane of the substrate 201; a second type ohmic contact metal layer 212 on a side of the substrate remote from the epitaxial layer.
As shown in fig. 3, the distributed feedback laser according to the embodiment of the present invention includes a laser epitaxial structure, where the epitaxial structure is used as a main light emitting structure of the laser, and the laser epitaxial structure includes a substrate 201 and multiple epitaxial layers grown on one side of the substrate 201, where a substrate material may be a group III nitride material, for example: gaN, alN, alGaN, inGaN, alInGaN, sapphire, siC, si, and SOI, and a group III nitride semiconductor DFB laser can be fabricated using a group III nitride substrate.
The multi-layer epitaxial layer comprises an intermediate epitaxial layer, as shown in fig. 3, comprising a buffer layer 202, a lower optical field confining layer 203, a lower waveguide layer 204, an active region 205, an upper waveguide layer 206, and an upper optical field confining layer 207 and an upper contact layer 208, which are in turn located on the side of the intermediate epitaxial layer remote from the substrate 201. Wherein the epitaxial layer material comprises Al x1Iny1Ga1-x1-y1 N, x1 and y1 are larger than or equal to 0 and smaller than or equal to 1, and 0.ltoreq.x1+y1.ltoreq.1, for example, material GaN, inN, alN, and different epitaxial layer materials are selected to prepare the required distributed feedback laser, so that the epitaxial layer has multiple selectable materials.
With continued reference to fig. 3, the first type ohmic contact metal layer 209 is located on a side of the upper contact layer 207 remote from the substrate 201, and the first type ohmic contact metal layer 209 may be any one or a combination of two or more of Ni, ti, pd, pt, au, al, tiN, ITO, auGe, auGeNi, ITO, znO, IGZO and graphene, and has a conductive function.
In the ridge structure formed by the upper light field limiting layer 207, the upper contact layer 208 and the first type ohmic contact metal layer 209, the m direction is parallel to the plane where the substrate 201 is located, the ridge structure extends along the m direction, so that the side surfaces of the upper contact layer 208 and part of the upper light field limiting layer 209 are m surfaces, when the m surfaces are corroded by adopting a wet corrosion technology, the m surfaces can be corroded into smooth, steep and flat surfaces, and by setting the m surfaces, the corrosion smoothness of the surfaces of the ridge structure and the grating structure can be effectively improved, and the laser grating structure is high in stability and still has stable lasing wavelength even under a high-order grating.
On the side of the substrate 201 away from the epitaxial layer is a second type ohmic contact metal layer 212, wherein the second type ohmic contact metal comprises the ohmic contact metal material described in the above embodiments, and forms an opposite ohmic contact electrode with the first type ohmic contact metal layer 209, in preparation for subsequent electrical connection of the laser.
In summary, in the distributed feedback laser provided in the embodiment of the present invention, by setting the laser epitaxial structure, in the ridge structure formed by the upper light field limiting layer, the upper contact layer and the first type ohmic contact metal layer, the ridge structure extends along the m direction, and both the upper contact layer and part of the side surfaces of the upper light field limiting layer are m surfaces, when the m surfaces are corroded by adopting the wet etching technology, the m surfaces can be corroded into smooth, steep and flat surfaces, so that the surface state and defect damage such as light scattering and the like caused by interface roughness caused by the dry etching method, the surface state and defect damage such as suspension bond introduction and the like can be removed, the technical problems such as non-radiative recombination and electric leakage in the laser are reduced, the threshold current of the device is effectively reduced, and the device performance and reliability are improved; meanwhile, the laser grating structure has high stability, and even under the condition of a high-order grating, the laser grating structure still has stable lasing wavelength.
Optionally, with continued reference to fig. 2, the ridge structure includes a plurality of sub-ridge structures connected in sequence along an m-direction, the m-direction being parallel to a plane in which the substrate is located; the sub-ridge structure comprises a first sub-ridge structure, a second sub-ridge structure and a third sub-ridge structure which are sequentially connected along the m direction; along the direction a, the extension width of the first sub-ridge structure is larger than that of the second sub-ridge structure and the third sub-ridge structure; and along the m direction, the extension width of the second sub-ridge structure in the a direction is gradually reduced, and the extension width of the third sub-ridge structure in the a direction is gradually increased; the a direction is parallel to the plane of the substrate and intersects the m direction.
The embodiment of the invention (shown in fig. 2) is different from the prior art (shown in fig. 1), and takes a group III nitride semiconductor laser grating structure as an example, the ridge structure comprises a plurality of sub-ridge structures sequentially connected along the m direction to form the laser grating structure, and when the width of the sub-ridge structure is changed, the change of the refractive index of the grating structure can be realized, so that the required laser grating structure is obtained. Specifically, as shown in fig. 2, along the m direction parallel to the plane where the substrate is located, the sub-ridge structure includes a first sub-ridge structure 100, a second sub-ridge structure 101, and a third sub-ridge structure 102 that are sequentially connected, where the first sub-ridge structure 100 is a wide ridge region, the second sub-ridge structure 101 is a ridge width graded region, and the third sub-ridge structure 102 is a ridge width graded region. Specifically, in the a direction parallel to the plane of the substrate and intersecting the m direction, the extension width D1 of the first sub-ridge structure 100 (wide ridge region) of the ridge structure is larger than the extension width D2 of the second sub-ridge structure 101 (ridge width graded region) and the extension width D3 of the third sub-ridge structure 102 (ridge width graded region); and along the m direction, the extending width D2 of the second sub-ridge structure 101 (ridge width graded region) in the a direction is gradually reduced, the extending width D3 of the third sub-ridge structure 102 (ridge width graded region) in the a direction is gradually increased, and the changing of the refractive index of the laser grating structure is realized by adjusting the extending width of the sub-ridge structure.
Optionally, along the direction a, the width D of the ridge structure satisfies 0 < D less than or equal to 200 μm; along the direction a, the extension width of the first sub-ridge structure is D1, the extension width of the second sub-ridge structure is D2, and the extension width of the third sub-ridge structure is D3, wherein D1-D2 is more than 0 and less than or equal to 100 mu m, and D1-D3 is more than 0 and less than or equal to 100 mu m.
Specifically, to further optimize the grating structure, the width of the ridge structure may be defined along the direction a in fig. 2, by setting the width D of the ridge structure to satisfy 0 < d+.200 μm, and the extension width D1 of the first sub-ridge structure 100, the extension width D2 of the second sub-ridge structure 101, and the extension width D3 of the third sub-ridge structure 103 satisfy: D1-D2 is more than 0 and less than or equal to 100 mu m, D1-D3 is more than 0 and less than or equal to 100 mu m. In actual preparation, the width of the wide ridge region 100, the width of the ridge region 101 from large to small and the width of the ridge region 102 from small to large are all larger than 0 and smaller than 10 μm, and the grating structure with special structure can be obtained by the arrangement, so that the preparation requirements of the DFB grating structure with special requirements can be met.
Furthermore, the first sub-ridge structure 100 and the second sub-ridge structure 101, the second sub-ridge structure 101 and the third sub-ridge structure 102, and the third sub-ridge structure 102 and the first sub-ridge structure 100 may all have an included angle of 60 ° or 120 °, that is, all the surfaces corresponding to the side walls of the ridge structures are m surfaces of the group III nitride semiconductor, which is favorable for wet etching the grating structure to smooth the surface, and improving the stability of the laser mode.
Exemplary, fig. 4 is a schematic diagram of a group III nitride DFB laser shown in fig. 1 and a DFB laser provided by an embodiment of the present invention shown in fig. 2, where a straight line a in fig. 4 is a laser wavelength range obtained in the prior art, a broken line B is a wavelength range of the DFB laser provided by the embodiment of the present invention, and a broken line C is a mode distribution of the laser. As shown in fig. 1, 2 and 4, compared with the ridge shape of the DFB laser in the prior art, which is formed by alternately arranging wide ridge shapes and narrow ridge shapes, the ridge shape of the DFB laser provided by the invention comprises a wide ridge region 100, a gradual change region 101 with a ridge width from large to small and a gradual change region 102 with a ridge width from small to large, and the change of the ridge width forms the change of the effective refractive index of the DFB laser. That is, the grating of the DFB laser according to the present invention is not formed by alternately arranging conventional two refractive index materials, but is formed by refractive index retardation, so that the high-reflectivity region of the grating structure is narrowed, as shown in fig. 4, to be much smaller than the width of the high-reflectivity region of the conventional DFB laser. For a conventional DFB laser, a high-order grating structure is generally adopted, and a high-reflectivity region of the high-order grating structure comprises a plurality of modes, so that the lasing mode of the laser is unstable and the mode is easy to jump; in the grating structure provided by the invention, the high reflectivity area is narrowed, as shown in fig. 4, the wavelength of the laser adopting the grating structure provided by the embodiment of the invention is narrower in the wavelength range of 400nm-430nm, and only one mode is contained inside, so that the lasing mode of the laser is very stable, and stable lasing wavelength can be output even under the condition of a high-order grating.
Optionally, with continued reference to fig. 3, the distributed feedback laser further includes a connection electrode 211; the connection electrode 211 covers the upper light field limit 207, the upper contact layer 208, the side surface of the first type ohmic contact metal layer 209, and the upper surface of the first type ohmic contact metal layer 209, and the thickness of the connection electrode is greater than that of the first type ohmic contact metal layer 209.
Illustratively, since the ridge structure has a width on the order of μm and the ohmic contact electrode is relatively thin, it is not advantageous for practical production of electrical connection, and the connection electrode 211 having a thickness greater than that of the first type ohmic contact metal layer is prepared by a metal deposition method, so as to cover the upper optical field limit 207, the upper contact layer 208, the side surface of the first type ohmic contact metal layer 209 and the upper surface of the first type ohmic contact metal layer 209, thereby forming a thickened connection electrode 211, which is convenient for laser preparation.
The embodiment of the invention provides a preparation method of a distributed feedback laser, which is used for preparing the distributed feedback laser shown in the embodiment. Fig. 5 is a schematic flow chart of a preparation method of a distributed feedback laser according to an embodiment of the present invention, where, as shown in fig. 5, the preparation method of the distributed feedback laser includes:
s101, preparing a laser epitaxial structure, wherein the laser epitaxial structure comprises a substrate and a plurality of epitaxial layers positioned on one side of the substrate, and each epitaxial layer comprises a middle epitaxial layer, an upper light field limiting layer and an upper contact layer which are sequentially positioned on one side of the middle epitaxial layer far away from the substrate; the material of the epitaxial layer comprises Al x1Iny1Ga1-x1-y1 N, wherein x1 is more than or equal to 0 and less than or equal to 1, y1 is more than or equal to 0 and less than or equal to 1, and (x1+y1) is more than or equal to 0 and less than or equal to 1.
Specifically, as shown in fig. 3, a laser epitaxial structure is prepared, and a plurality of epitaxial layers are sequentially grown and prepared on one side of a substrate 201 material, wherein the epitaxial layers comprise a buffer layer 202, a lower optical field limiting layer 203, a lower waveguide layer 204, an active region 205, an upper waveguide layer 206, an upper optical field limiting layer 207 and an upper contact layer 208, the epitaxial layers comprise an Al x1Iny1Ga1-x1-y1 N material, and the conditions are satisfied: x1 and y1 are both greater than or equal to 0 and less than or equal to 1, 0.ltoreq.x1+y1.ltoreq.1.
S102, preparing a first type ohmic contact metal layer on one side of the upper contact layer far away from the substrate.
Specifically, as shown in fig. 3, the epitaxial structure is cleaned, a first type ohmic contact metal is deposited on the side, away from the substrate 201, of the upper contact layer 207 of the epitaxial wafer structure, the first type ohmic contact metal comprises Pt/Au, and rapid thermal annealing in an air atmosphere is performed to form a better ohmic contact, and finally, a first type ohmic contact metal layer 209 is prepared on the side, away from the substrate 201, of the upper contact layer 208, so as to form an ohmic contact electrode of the epitaxial structure.
S103, etching the first type ohmic contact metal layer, the upper contact layer and the upper light field limiting layer to form a ridge structure; the ridge structure extends in the m direction; in the ridge structure, the side surfaces of the upper contact layer and part of the upper light field limiting layer are m surfaces; the m-direction is parallel to the plane of the substrate.
Specifically, the laser epitaxial structure is subjected to glue spreading and other methods, a DFB grating pattern and a ridge structure are prepared by using a stepping photoetching technology, photoresist is further used as a mask, and a reactive coupling plasma (ICP) etching technology is used for preparing the ridge and the grating structure of the laser. Specifically, as shown in fig. 3, a ridge structure forming a DFB laser is prepared by dry etching the upper optical field confining layer 207, the upper contact layer 208, and the first type ohmic contact metal layer 209, and a desired grating structure is obtained by controlling the width of the ridge structure, etc. Specifically, the m direction is parallel to the plane where the substrate 201 is located, the ridge structure extends along the m direction, in the ridge structure, the side surfaces of the upper contact layer and the light field limiting layer on part are both m surfaces, by setting the side surfaces to be m surfaces, the corrosion smoothness of the surfaces of the ridge structure and the grating structure can be effectively improved, and the laser grating structure is high in stability, and has stable lasing wavelength even under the high-order grating.
S104, preparing a second type ohmic contact metal layer on one side of the substrate away from the epitaxial layer.
Illustratively, as shown in fig. 3, the prepared epitaxial structure is further thinned, ground and polished, and a second type ohmic contact metal layer 212 is prepared by depositing metal on the side of the substrate away from the epitaxial layer so as to be disposed opposite to the first type ohmic contact metal layer 209, thereby preparing an ohmic contact electrode pair.
S105, scribing, cleaving, coating and splitting the epitaxial structure to form the distributed feedback laser.
Specifically, according to the production requirement of the laser, reasonable scribing, cleaving, coating and splitting processes are further carried out on the epitaxial structure, and the required distributed feedback laser is prepared.
In summary, in the preparation method of the distributed feedback laser provided by the embodiment of the invention, the first type ohmic contact metal layer, the upper contact layer and the upper optical field limiting layer obtained by the etching method form a ridge structure, the ridge structure extends along the m direction, in the ridge structure, the side surfaces of the upper contact layer and part of the upper optical field limiting layer are both m surfaces, the m surfaces are arranged, when the m surfaces are corroded by adopting a wet corrosion technology, the m surfaces can be corroded into smooth, steep and flat surfaces, the corrosion smoothness of the surfaces of the ridge and grating structures can be effectively improved, and the laser grating structure has high stability and stable lasing wavelength even under a high-order grating.
Optionally, fig. 6 is a schematic flow chart of a preparation method of a distributed feedback laser according to an embodiment of the present invention, where, as shown in fig. 6, the preparation method of the distributed feedback laser includes:
S201, preparing a laser epitaxial structure, wherein the laser epitaxial structure comprises a substrate and a plurality of epitaxial layers positioned on one side of the substrate, and each epitaxial layer comprises a middle epitaxial layer, an upper light field limiting layer and an upper contact layer which are sequentially positioned on one side of the middle epitaxial layer far away from the substrate; the material of the epitaxial layer comprises Al x1Iny1Ga1-x1-y1 N, wherein x1 is more than or equal to 0 and less than or equal to 1, y1 is more than or equal to 0 and less than or equal to 1, and (x1+y1) is more than or equal to 0 and less than or equal to 1.
S202, preparing a first type ohmic contact metal layer on one side of the upper contact layer far away from the substrate.
S203, etching the first type ohmic contact metal layer, the upper contact layer and the upper light field limiting layer by adopting a dry etching process to form a ridge structure; the ridge structure extends in the m direction; in the ridge structure, the side surfaces of the upper contact layer and part of the upper light field limiting layer are m surfaces, and the m direction is parallel to the plane where the substrate is located.
By way of example, the processes such as gluing are carried out on the epitaxial structure, a step-by-step lithography technology is utilized to prepare a DFB grating pattern and a ridge structure, then a photoresist is utilized as a mask, a dry etching technology is utilized to prepare the ridge and the grating structure of the laser, the ridge structure extends along the m direction, and the sides of the upper contact layer and part of the upper light field limiting layer are both m surfaces.
And S204, carrying out wet etching on the side surfaces of the upper contact layer and the upper light field limiting layer by adopting alkaline solution.
Specifically, wet etching technology is adopted, ammonium hydroxide solution is adopted to carry out wet etching, the m-plane side wall of the ridge and the grating structure of the laser prepared by dry etching is subjected to wet etching, and due to the arrangement of the m-plane, smooth, steep and flat surfaces can be obtained, the corrosion smoothness of the surfaces of the ridge and the grating structure can be effectively improved, the problems of non-radiative recombination, electric leakage and the like caused by dry etching damage can be solved, the non-radiative recombination, electric leakage and the like in the laser are reduced, further the threshold current of a device is effectively reduced, and the performance and reliability of the device are improved.
Optionally, the alkaline solution comprises at least one of ammonium hydroxide, ammonium chloride, ammonium fluoride, and tetramethylammonium hydroxide.
Exemplary, the wet etching solution for preparing the DFB laser in this embodiment may be an amino alkaline solution, including at least one of ammonium hydroxide, ammonium chloride, ammonium fluoride and tetramethylammonium hydroxide, and specifically, the wet etching is performed on the group III nitride semiconductor by using a tetramethylammonium hydroxide weak alkaline solution, so that not only the dry etching damage of the group III nitride semiconductor can be removed, but also the m-plane can be etched into a smooth, steep and flat plane; in addition, the amino weak alkaline solution does not react with the substrate, the epitaxial layer and the metal severely, so that the amino weak alkaline solution can be used for preparing a DFB laser.
And S205, preparing a second type ohmic contact metal layer on one side of the substrate away from the epitaxial layer.
S206, scribing, cleaving, coating and splitting the epitaxial structure to form the distributed feedback laser.
In summary, according to the preparation method of the distributed feedback laser provided by the embodiment of the invention, the m-surface obtained by an etching method is subjected to wet etching by adopting an alkaline solution, and is etched into a smooth, steep and flat surface, so that the technical problems of light scattering and the like caused by interface roughness, surface state and defect damage caused by suspension bonds and the like introduced into the laser, non-radiative recombination, electric leakage and the like in the laser are solved, the threshold current of the device is effectively reduced, and the performance and reliability of the device are improved; meanwhile, the laser grating structure has high stability, and even under the condition of a high-order grating, the laser grating structure still has stable lasing wavelength.
Optionally, in order to further protect the ridge structure, in the method for manufacturing the distributed feedback laser, after etching the first type ohmic contact metal, the upper contact layer and the upper optical field limiting layer to form the ridge structure, the method further includes:
An insulating layer is deposited on a side of the first-type ohmic contact metal layer remote from the substrate, the insulating layer covering an upper surface of the ridge structure and a side of the ridge structure.
And removing the insulating layer on the upper surface of the ridge structure by adopting photoetching and etching technology, and exposing the first type ohmic contact metal layer.
And preparing a connecting electrode on one side of the insulating layer away from the substrate, wherein the connecting electrode at least covers the exposed first-type ohmic contact metal layer.
Specifically, the insulating dielectric film used for the insulating layer is any one or a combination of more than two of SiO2、SiNx、SiON、Al2O3、AlON、SiAlON、TiO2、Ta2O5、ZrO2、HfO2、Si, polysilicon and other materials. As shown in fig. 3, an insulating layer 210 is deposited on a side of the first type ohmic contact metal layer 209 remote from the substrate 201 by depositing a metal such that the insulating layer 210 covers an upper surface of the ridge structure and sides of the ridge structure. Further, the insulating layer 210 on the upper surface of the ridge structure is removed by photolithography and etching techniques, the first type ohmic contact metal layer 209 is exposed, and the connection electrode 211 is further prepared on the side of the insulating layer 210 away from the substrate 201, so that the upper surface of the ridge structure is used for electrical connection, and the side surface of the ridge structure has electrical insulation property and plays a role in protecting the ridge structure. The connection electrode 211 at least covers the exposed first type ohmic contact metal layer 209, and the connection electrode 211 is provided as a thickened electrode, which is beneficial to the process designs such as electrical connection of the first type ohmic contact metal layer 209 and other devices of the laser, and circuit spot welding.
Alternatively, referring to fig. 3, a laser epitaxial structure is prepared comprising:
A liner 201 is provided.
A buffer layer 202 is prepared on the substrate side.
A lower light field confining layer 203 is prepared on the side of the buffer layer 202 remote from the substrate 201.
A lower waveguide layer 204 is prepared on the side of the lower optical field confinement layer 203 remote from the substrate 201.
An active region 205 is prepared on the side of lower waveguide layer 204 remote from substrate 201.
An upper waveguide layer 206 is prepared on the side of the active region 205 remote from the substrate 201.
An upper optical field limiter layer 207 is prepared on the side of upper waveguide layer 206 remote from substrate 201.
An upper contact layer 208 is prepared on the side of the upper light field confining layer 207 remote from the substrate 201.
Illustratively, a substrate material, which may be any one or a combination of two or more of GaN, alN, alGaN, inGaN, alInGaN, sapphire, siC, si, and SOI, is provided to fabricate an epitaxial structure in a direction away from the side of the substrate 201. Specifically, a lower optical field confinement layer 203 is prepared on a side of the buffer layer 202 away from the substrate 201, a lower waveguide layer 204 is prepared on a side of the lower optical field confinement layer 203 away from the substrate 201, an active region 205 is prepared on a side of the lower waveguide layer 204 away from the substrate 201, an upper waveguide layer 206 is prepared on a side of the active region 205 away from the substrate 201, an upper optical field confinement layer 207 is prepared on a side of the upper waveguide layer 206 away from the substrate 201, and an upper contact layer 209 is prepared on a side of the upper optical field confinement layer 207 away from the substrate 201. The epitaxial layer material of the DFB laser is Al x1Iny1Ga1-x1-y1 N, wherein x1 and y1 are greater than or equal to 0 and less than or equal to 1, and the requirements are: 0.ltoreq.x1+ y 1) is less than or equal to 1.
As a possible embodiment, a specific example is exemplified, and the gallium nitride GaN-based near-ultraviolet DFB laser is prepared based on the preparation method provided in the above example, as shown in fig. 2 to 6, and the specific preparation method is as follows:
A GaN substrate 201 material is provided and a group III nitride semiconductor laser structure is grown on the GaN substrate 201, specifically comprising a1 μm n-GaN buffer layer 201, a 1.5 μm n-AlGaN lower optical field confinement layer 202, a 0.1 μm n-InGaN lower waveguide layer 203, an InGaN/GaN multiple quantum well active region 205, a 0.1 μm p-InGaN upper waveguide layer 206, a 0.8 μm p-AlGaN upper optical field confinement layer 207, and a 20nm p-GaN upper contact layer 208.
And cleaning the epitaxial wafer, depositing ohmic contact metal Pt/Au on the surface of the epitaxial wafer to form a first ohmic contact metal layer 209, and performing rapid thermal annealing in an air atmosphere to form better ohmic contact.
Gluing is performed, and a step-by-step lithography technique is used to prepare the DFB grating pattern and ridge structure, as shown in fig. 2.
And preparing the ridge and grating structure of the laser by using the photoresist as a mask and adopting a reactive coupling plasma (ICP) etching technology.
And (3) carrying out wet etching by adopting ammonium hydroxide solution, and etching the side walls of the ridge and the grating structure m of the laser prepared by dry etching.
And growing a 200nm silicon dioxide SiO 2 insulating passivation film on the surface of the laser epitaxial wafer to passivate the side wall of the device.
The insulating passivation film over the ridge-shaped upper surface is stripped to expose the first type ohmic contact metal layer 209.
A thickened electrode 211 is formed over the laser epitaxial wafer using photolithographic, deposition and lift-off techniques, and the electrode material may be Cr/Au.
The epitaxial wafer is thinned, ground and polished, and then a second type ohmic contact electrode 212 is prepared on the back side of the GaN substrate 201, and the ohmic metal material may be Cr/Pt/Au as shown in fig. 3.
Dicing, cleaving, coating and splitting to form the laser tube core.
The gallium nitride GaN-based near ultraviolet DFB laser is prepared by adopting a preparation mode of combining dry etching and wet etching, the ridge-shaped side wall of the obtained laser is smooth, steep and flat and free of dry etching damage, the threshold current of the device can be greatly reduced, and the stability and reliability of the device are effectively improved; in addition, the mode stability of the DFB laser structure is very good, and the DFB laser structure still has stable lasing wavelength even under the high-order grating, so that the practical application requirement of high requirements is met.
Note that the above is only a preferred embodiment of the present invention and the technical principle applied. Those skilled in the art will appreciate that the invention is not limited to the specific embodiments described herein, and that features of the various embodiments of the invention may be partially or fully coupled or combined with each other and may be co-operated and technically driven in various ways. Various obvious changes, rearrangements, combinations and substitutions can be made by those skilled in the art without departing from the scope of the invention. Therefore, while the invention has been described in connection with the above embodiments, the invention is not limited to the embodiments, but may be embodied in many other equivalent forms without departing from the spirit or scope of the invention, which is set forth in the following claims.
Claims (9)
1. A distributed feedback laser, comprising:
The laser epitaxial structure comprises a substrate and a plurality of epitaxial layers positioned on one side of the substrate, wherein the epitaxial layers comprise a middle epitaxial layer, an upper light field limiting layer and an upper contact layer which are sequentially positioned on one side of the middle epitaxial layer far away from the substrate; the material of the epitaxial layer comprises Al x1Iny1Ga1-x1-y1 N, wherein x1 is more than or equal to 0 and less than or equal to 1, y1 is more than or equal to 0 and less than or equal to 1, and (x1+y1) is more than or equal to 0 and less than or equal to 1;
a first type ohmic contact metal layer located on a side of the upper contact layer away from the substrate; wherein the upper light field limiting layer, the upper contact layer and the first type ohmic contact metal layer form a ridge structure; the ridge structure extends along the m direction; in the ridge structure, the side surfaces of the upper contact layer and part of the upper light field limiting layer are m surfaces; the m direction is parallel to the plane of the substrate; the ridge structure comprises a plurality of sub ridge structures which are sequentially connected along the m direction; the sub-ridge structure comprises a first sub-ridge structure, a second sub-ridge structure and a third sub-ridge structure which are sequentially connected along the m direction; the first sub-ridge structure is a wide ridge region; the extension width of the first sub-ridge structure is larger than that of the second sub-ridge structure and the third sub-ridge structure along the direction a; and along the m direction, the extension width of the second sub-ridge structure in the a direction gradually decreases, and the extension width of the third sub-ridge structure in the a direction gradually increases; the a direction is parallel to the plane of the substrate and intersects with the m direction;
And the second type ohmic contact metal layer is positioned on one side of the substrate away from the epitaxial layer.
2. A distributed feedback laser as in claim 1 wherein the width D of the ridge structure in the a-direction satisfies 0 < d+.200 μm;
Along the a direction, the extension width of the first sub-ridge structure is D1, the extension width of the second sub-ridge structure is D2, and the extension width of the third sub-ridge structure is D3, wherein D1-D2 is more than 0 and less than or equal to 100 mu m, and D1-D3 is more than 0 and less than or equal to 100 mu m.
3. A distributed feedback laser as defined in claim 1 wherein, the distributed feedback laser also comprises a connecting electrode;
The connection electrode covers the upper light field limiting layer, the upper contact layer, the side surface of the first type ohmic contact metal layer and the upper surface of the first type ohmic contact metal layer, and the thickness of the connection electrode is greater than that of the first type ohmic contact metal layer.
4. A distributed feedback laser as in claim 1 wherein the intermediate epitaxial layer comprises a buffer layer, a lower optical field confinement layer, a lower waveguide layer, an active region, and an upper waveguide layer or a portion of the upper optical field confinement layer disposed sequentially on one side of the substrate.
5. A method of preparing a distributed feedback laser for preparing the distributed feedback laser of any of claims 1-4, comprising:
Preparing a laser epitaxial structure, wherein the laser epitaxial structure comprises a substrate and a plurality of epitaxial layers positioned on one side of the substrate, and the epitaxial layers comprise a middle epitaxial layer, an upper light field limiting layer and an upper contact layer which are sequentially positioned on one side of the middle epitaxial layer far away from the substrate; the material of the epitaxial layer comprises Al x1Iny1Ga1-x1-y1 N, wherein x1 is more than or equal to 0 and less than or equal to 1, y1 is more than or equal to 0 and less than or equal to 1, and (x1+y1) is more than or equal to 0 and less than or equal to 1;
preparing a first type ohmic contact metal layer on one side of the upper contact layer away from the substrate;
Etching the first type ohmic contact metal layer, the upper contact layer and the upper light field limiting layer to form a ridge structure; the ridge structure extends along the m direction; in the ridge structure, the side surfaces of the upper contact layer and part of the upper light field limiting layer are m surfaces; the m direction is parallel to the plane of the substrate;
preparing a second type ohmic contact metal layer on one side of the substrate away from the epitaxial layer;
And scribing, cleaving, coating and splitting the epitaxial structure to form the distributed feedback laser.
6. The method of manufacturing of claim 5, wherein etching the first type ohmic contact metal layer, the upper contact layer, and the upper optical field confining layer to form a ridge structure comprises:
etching the first type ohmic contact metal layer, the upper contact layer and the upper light field limiting layer by adopting a dry etching process to form a ridge structure;
after etching the first type ohmic contact metal layer, the upper contact layer and the upper light field limiting layer to form a ridge structure, the method further comprises:
And carrying out wet etching on the side surfaces of the upper contact layer and the upper light field limiting layer by adopting an alkaline solution.
7. The method of preparing according to claim 6, wherein the alkaline solution comprises at least one of ammonium hydroxide, ammonium chloride, ammonium fluoride, and tetramethylammonium hydroxide.
8. The method of manufacturing of claim 5, further comprising, after etching the first type ohmic contact metal, the upper contact layer, and the upper light field confining layer to form a ridge structure:
depositing an insulating layer on one side of the first type ohmic contact metal layer away from the substrate, wherein the insulating layer covers the upper surface of the ridge structure and the side surface of the ridge structure;
removing the insulating layer on the upper surface of the ridge structure by adopting photoetching and etching technology to expose the first type ohmic contact metal layer;
And preparing a connecting electrode on one side of the insulating layer far away from the substrate, wherein the connecting electrode at least covers the exposed first-type ohmic contact metal layer.
9. The method of manufacturing as claimed in claim 5, wherein preparing the laser epitaxial structure comprises:
Providing a substrate;
Preparing a buffer layer on one side of the substrate;
preparing a lower light field limiting layer on one side of the buffer layer away from the substrate;
Preparing a lower waveguide layer on a side of the lower optical field confinement layer away from the substrate;
Preparing an active region on a side of the lower waveguide layer away from the substrate;
preparing an upper waveguide layer on the side of the active region away from the substrate;
preparing an upper optical field confinement layer on a side of the upper waveguide layer away from the substrate; an upper contact layer is prepared on a side of the upper light field confining layer remote from the substrate.
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| CN214899326U (en) * | 2020-12-03 | 2021-11-26 | 因林光电科技(苏州)有限公司 | Distributed feedback laser |
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