CN112490848A - Distributed feedback laser and preparation method thereof - Google Patents

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 the plurality of epitaxial layers comprise a middle epitaxial layer and an upper optical field limiting layer and an upper contact layer which are sequentially positioned on one side of the middle epitaxial layer, which is far away from the substrate; the material of the epitaxial layer comprises Al_x1In_y1Ga_1‑x1‑y1N, 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; the first type ohmic contact metal layer is positioned on one side, far away from the substrate, of the upper contact layer; wherein, the upper optical 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 the side surfaces of the upper contact layer and part of the optical field limiting layer in the ridge structure are m surfaces; is located on the substrateAnd a second type ohmic contact metal layer on the side far away from the epitaxial layer. The invention solves the technical problems of non-radiative recombination and electric leakage of dry etching ridge-shaped side walls and unstable laser wavelength.

Description

Distributed feedback laser and preparation method thereof

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

Group III nitride semiconductors, which are referred to as third-generation semiconductor materials, have advantages such as large forbidden bandwidth and high light emission efficiency; the light-emitting wavelength of the material covers the range from deep ultraviolet to near infrared, and the material can be used for manufacturing semiconductor light-emitting devices such as light-emitting diodes, lasers and the like. The DFB laser based on the group III nitride semiconductor has a very narrow output spectrum and a very good single mode characteristic, and has very important application prospects in the fields of atomic clocks, laser radars, sensing mapping, and the like, and thus has attracted attention and becomes a research hotspot in the academic and industrial fields at home and abroad.

Early group III nitride semiconductor DFB lasers generally adopted mask gratings, namely gratings are manufactured in the DFB lasers, so that multiple times of epitaxial growth is needed, the manufacturing process is complex, the cost is high, and the secondary epitaxial growth interface is easy to generate contamination of carbon, oxygen, silicon and the like, so that the performance and the reliability of devices are seriously influenced. Therefore, the conventional DFB laser mainly adopts a surface grating, i.e., a ridge-shaped sidewall grating structure, and as shown in fig. 1, the grating structure with alternately arranged effective refractive indexes is formed by controlling the width of ridge-shaped strips. In general, in order to ensure flatness of the cavity surface of the DFB laser, the ridge of the laser is disposed along the m-plane direction, i.e., the cavity surface of the laser is the m-plane, so that the side wall of the ridge is the a-plane. As for the conventional (0001) plane III-group nitride semiconductor material, the chemical stability is good, the acid and alkali resistance is good, and the corrosion is not easy, so that the ridge of the DFB laser needs to be formed by dry etching. The dry etching not only causes rough interface to cause light dispersion and the like, but also introduces surface states and defects such as dangling bonds and the like, and the surface states and the defects not only can become non-radiative recombination centers and influence the internal quantum efficiency of the laser; it can also be a leakage path, affecting the reliability and stability of the device. In the prior art, researchers use strong alkali to carry out high-temperature wet etching so as to remove the dry etching damage of the side wall. However, the strong alkali high-temperature wet etching not only corrodes the dislocation pits on the a-plane of the group III nitride semiconductor to form a leakage channel, but also corrodes the a-plane of the group III nitride semiconductor to be serrated, which greatly increases the light scattering loss of the DFB laser, and thus the wet etching technique is not adopted.

In addition, since the operating wavelength of the group III nitride semiconductor DFB laser is short and the effective refractive index thereof is small, the grating period thereof is short, and it is difficult to prepare a low-order grating using a conventional photolithography technique, so that a high-order grating is often used. And the high-order grating contains a plurality of lasing modes, so that the mode of the DFB laser is unstable when the DFB laser works, mode hopping is easy to occur, and the mode stability and the application scene of the III-nitride semiconductor DFB laser are seriously influenced.

Disclosure of Invention

In view of this, embodiments of the present invention provide a distributed feedback laser and a method for manufacturing the same, so as to solve technical problems in the prior art that non-radiative recombination and leakage influence reliability and stability of a device and an unstable lasing wavelength under a high-order grating structure, which are caused by surface states and defects such as light scattering and the like due to interface roughness caused by a ridge-shaped sidewall of a DFB laser manufactured by dry etching, and a dangling bond introduced.

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 plurality of epitaxial layers comprise a middle epitaxial layer and an upper optical field limiting layer and an upper contact layer which are sequentially positioned on one side, far away from the substrate, of the middle epitaxial layer; the material of the epitaxial layer comprises Al_x1In_y1Ga_1-x1-y1N, 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;

the first type ohmic contact metal layer is positioned on one side, far away from the substrate, of the upper contact layer; wherein the upper optical field confining 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 optical 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 far 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;

in the a direction, the extension width of the first sub-ridge structure is greater than the extension widths 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 gradually decreases, and the extension width of the third sub-ridge structure in the a direction gradually increases.

Optionally, along the a direction, the width D of the ridge structure 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 μm, and D1-D3 is more than or equal to 0 and less than or equal to 100 μm.

Optionally, the distributed feedback laser further includes a connection electrode;

the connection electrode covers the upper optical 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 larger 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 portion of the upper optical field limiting layer, which are sequentially disposed on one side of the substrate.

In a second aspect, a method for manufacturing a distributed feedback laser is used to manufacture the distributed feedback laser of the first aspect, and 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 plurality of epitaxial layers comprise a middle epitaxial layer and a plurality of epitaxial layers sequentially positioned in the middleAn upper optical field limiting layer and an upper contact layer on one side of the inter-epitaxial layer far away from the substrate; the material of the epitaxial layer comprises Al_x1In_y1Ga_1-x1-y1N, 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, which is far away from the substrate;

etching the first type ohmic contact metal layer, the upper contact layer and the upper optical 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 optical 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 far away from the epitaxial layer;

and carrying out processes of scribing, cleavage, coating and splitting on 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 optical field limiting layer to form a ridge structure, including:

etching the first type ohmic contact metal layer, the upper contact layer and the upper optical field limiting layer by adopting a dry etching process to form a ridge structure;

after the first type ohmic contact metal layer, the upper contact layer and the upper optical field limiting layer are etched to form a ridge structure, the method further comprises the following steps:

and carrying out wet etching on the side surfaces of the upper contact layer and the upper optical field limiting layer by adopting an alkaline solution.

Optionally, the alkaline solution includes at least one of ammonium hydroxide, ammonium chloride, ammonium fluoride, and tetramethylammonium hydroxide.

Optionally, after the first type ohmic contact metal, the upper contact layer, and the upper optical field limiting layer are etched to form a ridge structure, the method further includes:

depositing an insulating layer on one side of the first type ohmic contact metal layer, which is far 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 technologies to expose the first type ohmic contact metal layer;

and preparing a connecting electrode on one side of the insulating layer, which is 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 includes:

providing a substrate;

preparing a buffer layer on one side of the substrate;

preparing a lower optical field limiting layer on one side of the buffer layer far away from the substrate;

preparing a lower waveguide layer on the side of the lower optical field limiting layer far away from the substrate;

preparing an active region on the side of the lower waveguide layer away from the substrate;

preparing an upper waveguide layer on one side of the active region far away from the substrate;

preparing an upper optical field limiting layer on the side of the upper waveguide layer away from the substrate;

and preparing an upper contact layer on the side of the upper optical field limiting layer far away from the substrate.

In the distributed feedback laser provided by the embodiment of the invention, in the ridge structure formed by the upper optical field limiting layer, the upper contact layer and the first type ohmic contact metal layer, the ridge structure extends along the m direction, and the side surfaces of the upper contact layer and part of the upper optical field limiting layer are m surfaces.

Drawings

Other features, objects and advantages of the invention will become more apparent upon reading of the detailed description of non-limiting embodiments made with reference to the following drawings:

FIG. 1 is a schematic diagram of a prior art grating structure of a distributed feedback laser in a top view;

fig. 2 is a schematic top view of a grating structure of a distributed feedback laser according to an embodiment of the present invention;

FIG. 3 is a cross-sectional view of a grating structure of the distributed feedback laser shown in FIG. 2;

FIG. 4 is a graph showing the mode profiles 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 method for manufacturing a distributed feedback laser according to an embodiment of the present invention.

The following are the reference signs:

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 clearer, the technical solutions of the present invention will be fully described by the detailed description with reference to the accompanying drawings in the embodiments of the present invention. It is obvious that the described embodiments are a part of the embodiments of the present invention, not all embodiments, and all other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present invention without inventive efforts fall within the scope of the present invention.

Examples

The embodiment of the invention provides a distributed feedback laser. Fig. 2 is a schematic plan 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 the plurality of epitaxial layers comprise a middle epitaxial layer, and an upper optical field limiting layer 207 and an upper contact layer 208 which are sequentially positioned on one side of the middle epitaxial layer, which is far away from the substrate; the material of the epitaxial layer comprises Al_x1In_y1Ga_1-x1-y1N, 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 optical field limiting layer 207, the upper contact layer 208 and the first type ohmic contact metal layer 209 form a ridge structure; the ridge structure extends along the m direction; in the ridge structure, the side surfaces of the upper contact layer 208 and part of the upper optical field limiting layer 207 are m surfaces; 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.

Illustratively, as shown in fig. 3, the distributed feedback laser provided by 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 a plurality of epitaxial layers grown on one side of the substrate 201, where the substrate material may be a group III nitride material, such as: any one or a combination of two or more of GaN, AlN, AlGaN, InGaN, AlInGaN, sapphire, SiC, Si and SOI, and a group III nitride semiconductor DFB laser can be produced by using a group III nitride as a substrate.

The multi-layer epitaxial layer comprises an intermediate epitaxial layer, which, as shown in fig. 3, comprises 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 sequentially located on a side of the intermediate epitaxial layer remote from the substrate 201. Wherein the epitaxial layer material comprises Al_x1In_y1Ga_1-x1-y1N, x1 and y1 are both greater than or equal to 0 and less thanOr equal to 1, and 0 ≦ (x1+ y1) ≦ 1, e.g., the materials GaN, InN, AlN, different epitaxial layer materials are selected to make the desired distributed feedback laser with multiple material choices for its epitaxial layer.

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 away 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 function of conducting electricity.

Wherein, in the ridge structure that last optical field restriction layer 207, last contact layer 208 and first type ohmic contact metal layer 209 formed, the m direction is parallel with substrate 201 place plane, the ridge structure extends along the m direction, the side that obtains last contact layer 208 and partial last optical field restriction layer 209 is the m face, when adopting wet etching technique to corrode the m face, can corrode the m face into smooth steep and smooth face, be the m face through setting up, can effectively improve the corrosion smoothness on ridge and grating structure surface, laser grating structure stability is high, even under high-order grating, still have stable lasing wavelength.

On the side of the substrate 201 away from the epitaxial layer, a second-type ohmic contact metal layer 212 is formed, wherein the second-type ohmic contact metal layer includes 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, so as to prepare for the subsequent preparation of laser electrical connection.

In summary, according to the distributed feedback laser provided by the embodiment of the present invention, by providing the laser epitaxial structure, in the ridge structure formed by the upper optical field limiting layer, the upper contact layer and the first type ohmic contact metal layer, the ridge structure extends along the m direction, and the side surfaces of the upper contact layer and part of the upper optical field limiting layer are m surfaces, when the m surface is etched by using the wet etching technique, the m surface can be etched into a smooth, steep and flat surface, so that surface states and defect damages such as light scattering and the like caused by interface roughness caused by the dry etching method, introduction of a dangling bond and the like can be removed, technical problems such as non-radiative recombination and leakage in the laser can be reduced, the threshold current of the device can be effectively reduced, and the performance and reliability of the device can be improved; meanwhile, the grating structure of the laser has high stability, and even under a high-order grating, the laser still has stable lasing wavelength.

Optionally, with continued reference to fig. 2, the ridge structure includes a plurality of sub-ridge structures sequentially connected along the m direction, and the m direction is parallel to the plane of the substrate; 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 that of the third sub-ridge structure; 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.

Illustratively, the embodiment of the present invention (as shown in fig. 2) is different from the prior art (as shown in fig. 1), taking the grating structure of the group III nitride semiconductor laser as an example, the ridge structure includes a plurality of sub-ridge structures sequentially connected along the m direction to form the grating structure of the laser, and when the width of the sub-ridge structures is changed, the change of the refractive index of the grating structure can be realized, so as to obtain the required grating structure of the laser. Specifically, as shown in fig. 2, in the m direction parallel to the plane of the substrate, the sub-ridge structure includes a first sub-ridge structure 100, a second sub-ridge structure 101, and a third sub-ridge structure 102, which are connected in sequence, where the first sub-ridge structure 100 is a wide ridge region, the second sub-ridge structure 101 is a gradual ridge width region, and the third sub-ridge structure 102 is a gradual ridge width 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 greater 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 extension width D2 of the second sub-ridge structure 101 (ridge width gradual change region) in the a direction gradually decreases, the extension width D3 of the third sub-ridge structure 102 (ridge width gradual change region) in the a direction gradually increases, and the change of the refractive index of the laser grating structure is realized by adjusting the extension width of the sub-ridge structure.

Optionally, along the direction a, the width D of the ridge structure satisfies that D is more than 0 and 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 μm, and D1-D3 is more than 0 and less than or equal to 100 μm.

Specifically, with continued reference to fig. 2, in order 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 to satisfy: D1-D2 of more than 0 and less than or equal to 100 mu m, and D1-D3 of more than 0 and less than or equal to 100 mu m. In actual preparation, the widths of the wide ridge region 100, the gradual change region 101 with the ridge width from large to small and the gradual change region 102 with the ridge width from small to large are all larger than 0 and smaller than 10 μm, and according to the arrangement, the grating structure with a special structure can be obtained, and the preparation requirement of the DFB grating structure with special requirements can be met.

Furthermore, included angles between the first sub-ridge structure 100 and the second sub-ridge structure 101, included angles between the second sub-ridge structure 101 and the third sub-ridge structure 102, and included angles between the third sub-ridge structure 102 and the first sub-ridge structure 100 are both 60 degrees or 120 degrees, namely, all surfaces corresponding to the side walls of the ridge structures are m surfaces of the group III nitride semiconductor, so that the wet etching grating structure is favorably smooth in surface, and the laser mode stability is improved.

Illustratively, fig. 4 is a diagram showing the mode distribution of the group III nitride DFB laser shown in fig. 1 and the DFB laser provided by the 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 prior art where the ridge of the DFB laser is formed by alternately arranging wide ridges and narrow ridges, the ridge of the DFB laser provided by the present invention includes a wide ridge region 100, a gradual change region 101 with a gradually decreasing ridge width, and a gradual change region 102 with a gradually decreasing ridge width, and the change in ridge width forms a change in the effective refractive index of the DFB laser. That is, the grating of the DFB laser proposed by the present invention is not formed by alternately arranging two conventional refractive index materials, but is formed by gradual refractive index change, so that the high reflectivity region of the grating structure becomes narrow, as shown in fig. 4, which is 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 usually adopted, and a high-reflectivity area of the high-reflectivity area comprises a plurality of modes, so that a lasing mode of the laser is unstable and mode hopping is easy; in the grating structure provided by the invention, the high-reflectivity region is narrowed, as shown in fig. 4, in the wavelength range of 400nm-430nm, the laser adopting the grating structure provided by the embodiment of the invention has narrower wavelength, and only one mode is contained in the laser, so that the lasing mode of the laser is very stable, and even under a high-order grating, the stable lasing wavelength can still be output.

Optionally, with continued reference to fig. 3, the distributed feedback laser further comprises a connecting electrode 211; the connection electrode 211 covers the upper optical field confinement 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 has a thickness greater than that of the first-type ohmic contact metal layer 209.

Illustratively, since the width of the ridge structure is in the order of μm and the ohmic contact electrode is relatively thin, which is not beneficial for practical electrical connection production, the connection electrode 211 having a thickness greater than that of the first-type ohmic contact metal layer is prepared by depositing metal so as to cover the upper optical field confinement 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 form a thickened connection electrode 211, which facilitates 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 method for manufacturing a distributed feedback laser according to an embodiment of the present invention, and as shown in fig. 5, the method for manufacturing a 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 the plurality of epitaxial layers comprise a middle epitaxial layer, an upper optical field limiting layer and an upper contact layer which are sequentially positioned on one side, far away from the substrate, of the middle epitaxial layer; the material of the epitaxial layer comprises Al_x1In_y1Ga_1-x1-y1N, 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, a laser epitaxial structure is prepared, and as shown in fig. 3, a plurality of epitaxial layers are sequentially grown and prepared on one side of a substrate 201 material, and each epitaxial layer comprises 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, and the epitaxial layer material comprises Al_x1In_y1Ga_1-x1-y1N material, satisfies the condition: x1 and y1 are both greater than or equal to 0 and less than or equal to 1, with 0 ≦ (x1+ y1) ≦ 1.

And S102, preparing a first type ohmic contact metal layer on one side of the upper contact layer, which is far away from the substrate.

Specifically, the epitaxial structure is cleaned, as shown in fig. 3, 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 includes Pt/Au, rapid thermal annealing is performed in an air atmosphere 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 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 optical 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 optical field limiting layer are m surfaces; the m direction is parallel to the plane of the substrate.

Specifically, the method for coating the epitaxial structure of the laser comprises the steps of utilizing a stepping photoetching technology to prepare a DFB grating pattern and a ridge structure, further utilizing photoresist as a mask, and adopting a reaction coupled plasma (ICP) etching technology to prepare the ridge and grating structure of the laser. Specifically, as shown in fig. 3, a ridge structure of the DFB laser is formed 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 of the substrate 201, the ridge structure extends along the m direction, the side surfaces of the upper contact layer and the optical field limiting layer on the part obtained by etching are m surfaces in the ridge structure, the side surfaces are m surfaces through setting, the corrosion smoothness of the surfaces of the ridge structure and the grating structure can be effectively improved, the stability of the grating structure of the laser is high, and the laser still has stable lasing wavelength even under high-order gratings.

And S104, preparing a second type ohmic contact metal layer on one side of the substrate far 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 opposite to the first type ohmic contact metal layer 209, and thus, an ohmic contact electrode pair is prepared.

And S105, carrying out scribing, cleavage, coating and splitting processes on the epitaxial structure to form the distributed feedback laser.

Specifically, according to the production requirement of the laser, reasonable scribing, cleavage, coating and splitting processes are further carried out on the epitaxial structure, and the required distributed feedback laser is prepared.

In summary, in the method for manufacturing a distributed feedback laser according to the embodiments of the present invention, in the first type ohmic contact metal layer, the upper contact layer, and the upper optical field limiting layer obtained by the etching method, a ridge structure is formed, the ridge structure extends along the m direction, and in the ridge structure, the side surfaces of the upper contact layer and a part of the upper optical field limiting layer are both m surfaces, and are both m surfaces.

Optionally, fig. 6 is a schematic flow chart of a method for manufacturing a distributed feedback laser according to an embodiment of the present invention, and as shown in fig. 6, the method for manufacturing a 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 the plurality of epitaxial layers comprise a middle epitaxial layer, an upper optical field limiting layer and an upper contact layer which are sequentially positioned on one side, far away from the substrate, of the middle epitaxial layer; the material of the epitaxial layer comprises Al_x1In_y1Ga_1-x1-y1N, 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, which is far away from the substrate.

S203, etching the first type ohmic contact metal layer, the upper contact layer and the upper optical field limiting layer by adopting a dry etching process 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 optical field limiting layer are m surfaces, and the m direction is parallel to the plane of the substrate.

Illustratively, the epitaxial structure is subjected to processes such as glue coating, a DFB grating pattern and a ridge structure are prepared by using a step-by-step lithography technology, then a photoresist is used as a mask, a dry etching technology is used for preparing the ridge structure and the grating structure of the laser, the ridge structure extends along the m direction, and the side surfaces of the upper contact layer and part of the optical field limiting layer obtained by etching are m surfaces.

And S204, carrying out wet etching on the side surfaces of the upper contact layer and the upper optical field limiting layer by adopting an alkaline solution.

Specifically, adopt wet process corrosion technique, adopt ammonium hydroxide solution to carry out wet process corrosion, carry out wet process corrosion with laser instrument ridge shape and the grating structure m face lateral wall that dry process etching prepared, because the setting of m face, can obtain smooth steep and smooth face, effectively improve the corruption smoothness on ridge shape and grating structure surface, can get rid of the nonradiative recombination and the electric leakage scheduling problem that the dry process etching damage arouses, reduce nonradiative recombination and electric leakage etc. in the laser instrument, and then effectively reduce the threshold current of device, promote device performance and reliability.

Optionally, the alkaline solution comprises at least one of ammonium hydroxide, ammonium chloride, ammonium fluoride, and tetramethylammonium hydroxide.

For example, in this embodiment, the wet etching solution for preparing the DFB laser may be an amino alkaline solution, including at least one of ammonium hydroxide, ammonium chloride, ammonium fluoride and tetramethylammonium hydroxide, specifically, the tetramethylammonium hydroxide weak alkaline solution is used to perform wet etching on the group III nitride semiconductor, 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 to a smooth, steep and flat surface; in addition, the amino weak alkaline solution does not react with the substrate, the epitaxial layer and the metal violently, so that the preparation method can be used for preparing the DFB laser.

And S205, preparing a second type ohmic contact metal layer on the side of the substrate far away from the epitaxial layer.

And S206, carrying out scribing, cleavage, film coating and splitting processes on the epitaxial structure to form the distributed feedback laser.

In summary, in the preparation method of the distributed feedback laser provided by the embodiment of the present invention, the m-plane obtained by the etching method is subjected to wet etching by using the alkaline solution, and the m-plane is etched to be a smooth, steep and flat surface, so that surface states and defect damages such as light scattering and the like, introduction of dangling bonds and the like caused by interface roughness caused by the dry etching method can be removed, technical problems such as non-radiative recombination and 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; meanwhile, the grating structure of the laser has high stability, and even under a high-order grating, the laser still has stable lasing wavelength.

Optionally, in order to further protect the ridge structure, in the method for manufacturing a distributed feedback laser, after the first type ohmic contact metal, the upper contact layer, and the upper optical field limiting layer are etched to form the ridge structure, the method further includes:

and depositing an insulating layer on one side of the first type ohmic contact metal layer, which is far away from the substrate, wherein the insulating layer covers the upper surface of the ridge structure and the side surface of the ridge structure.

And removing the insulating layer on the upper surface of the ridge structure by adopting photoetching and etching technologies to expose the first type ohmic contact metal layer.

And preparing a connecting electrode on one side of the insulating layer, which is far away from the substrate, wherein the connecting electrode at least covers the exposed first type ohmic contact metal layer.

Specifically, the insulating dielectric film adopted by the insulating layer is SiO₂、SiN_x、SiON、Al₂O₃、AlON、SiAlON、TiO₂、Ta₂O₅、ZrO₂、HfO₂And one or a combination of two or more of materials such as Si and polysilicon. As shown in fig. 3, an insulating layer 210 is deposited on the first-type ohmic contact metal layer 209 on the side away from the substrate 201 by depositing metal, such that the insulating layer 210 covers the upper surface of the ridge structure and the side surfaces of the ridge structure. Further, the insulating layer 210 on the upper surface of the ridge structure is removed by using 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 and plays a role in protecting the ridge structure. The connecting electrode 211 at least covers the exposed first-type ohmic contact metal layer 209, and the connecting electrode 211 is a thickened electrode, which is beneficial to the process design of electrical connection between the first-type ohmic contact metal layer 209 and other devices of the laser, spot welding of circuits and the like.

Alternatively, referring to fig. 3, a laser epitaxial structure is prepared, including:

a liner 201 is provided.

A buffer layer 202 is prepared on the substrate side.

A lower optical 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 confining layer 203 remote from the substrate 201.

An active region 205 is prepared on a side of the lower waveguide layer 204 remote from the substrate 201.

An upper waveguide layer 206 is prepared on the side of active region 205 remote from substrate 201.

An upper optical field confining layer 207 is fabricated on a side of upper waveguide layer 206 remote from substrate 201.

An upper contact layer 208 is prepared on the side of the upper optical field confining layer 207 remote from the substrate 201.

Illustratively, a substrate material is provided, which may be any one or a combination of two or more of GaN, AlN, AlGaN, InGaN, AlInGaN, sapphire, SiC, Si, and SOI, and an epitaxial structure is fabricated in a direction away from the substrate 201 side. Specifically, a lower optical field confining 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 confining 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 confining 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 confining layer 207 away from the substrate 201. The epitaxial layer of the DFB laser is made of Al_x1In_y1Ga_1-x1-y1N, wherein x1 and y1 are both greater than or equal to 0 and less than or equal to 1, and satisfy: 0 is less than or equal to (x1+ y1) is less than or equal to 1.

As a possible embodiment, a specific example is given, and a GaN-based near-uv DFB laser is fabricated based on the fabrication method provided in the above example, as shown in fig. 2 to 6, and the specific fabrication method is as follows:

a GaN substrate 201 material is provided, and a III-nitride semiconductor laser structure is grown on the GaN substrate 201, and specifically comprises a 1-micron n-GaN buffer layer 201, a 1.5-micron n-AlGaN lower optical field limiting layer 202, a 0.1-micron n-InGaN lower waveguide layer 203, an InGaN/GaN multi-quantum well active region 205, a 0.1-micron p-InGaN upper waveguide layer 206, a 0.8-micron p-AlGaN upper optical field limiting layer 207 and a 20nm p-GaN upper contact layer 208.

And cleaning the epitaxial wafer, depositing an 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 a better ohmic contact.

And gluing, and preparing the DFB grating pattern and the ridge structure by using a step-by-step lithography technology, as shown in figure 2.

The ridge and grating structure of the laser is prepared by using the photoresist as a mask and adopting a reactive coupled plasma (ICP) etching technology.

And (3) carrying out wet etching by adopting an ammonium hydroxide solution, and etching the ridge of the laser and the side wall m of the grating structure prepared by dry etching.

Growing 200nm silicon dioxide SiO on the surface of the laser epitaxial wafer₂And the insulating passivation film passivates the side wall of the device.

The insulating passivation film over the upper surface of the ridge is stripped to expose the first-type ohmic contact metal layer 209.

Thickened electrodes 211 are formed on the laser epitaxial wafer by photolithography, deposition and lift-off techniques, and the electrode material can 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 surface of the GaN substrate 201, and the ohmic metal material may be Cr/Pt/Au, as shown in fig. 3.

And scribing, 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 combining dry etching and wet etching, the ridge-shaped side wall of the obtained laser is smooth, steep and flat and has no 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 high-order grating, thereby meeting the high-requirement practical application requirement.

It is to be noted that the foregoing is only illustrative of the preferred embodiments of the present invention and the technical principles employed. Those skilled in the art will appreciate that the present invention is not limited to the specific embodiments described herein, and that the features of the various embodiments of the invention may be partially or fully coupled to each other or combined and may be capable of cooperating with each other in various ways and of being technically driven. Numerous variations, rearrangements, combinations, and substitutions will now become apparent to those skilled in the art without departing from the scope of the invention. Therefore, although the present invention has been described in greater detail by the above embodiments, the present invention is not limited to the above embodiments, and may include other equivalent embodiments without departing from the spirit of the present invention, and the scope of the present invention is determined by the scope of the appended claims.

Claims (10)

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 plurality of epitaxial layers comprise a middle epitaxial layer and an upper optical field limiting layer and an upper contact layer which are sequentially positioned on one side, far away from the substrate, of the middle epitaxial layer; the material of the epitaxial layer comprises Al_x1In_y1Ga_1-x1-y1N, 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;

the first type ohmic contact metal layer is positioned on one side, far away from the substrate, of the upper contact layer; wherein the upper optical field confining 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 optical 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 far away from the epitaxial layer.

2. The distributed feedback laser as claimed in claim 1, wherein the ridge structure comprises a plurality of sub-ridge structures connected in series 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;

in the a direction, the extension width of the first sub-ridge structure is greater than the extension widths 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.

3. The distributed feedback laser as claimed in claim 2, wherein the width D of the ridge structure along 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 μm, and D1-D3 is more than or equal to 0 and less than or equal to 100 μm.

4. The distributed feedback laser of claim 1 further comprising a connecting electrode;

the connection electrode covers the upper optical 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 larger than that of the first-type ohmic contact metal layer.

5. A distributed feedback laser as claimed in claim 1 wherein said intermediate epitaxial layer comprises a buffer layer, a lower optical field confining layer, a lower waveguide layer, an active region and an upper waveguide layer or part of said upper optical field confining layer disposed in that order on one side of said substrate.

6. A method for manufacturing a distributed feedback laser, for manufacturing a distributed feedback laser according to any one of claims 1 to 5, 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 plurality of epitaxial layers comprise a middle epitaxial layer and an upper optical field limiting layer and an upper contact layer which are sequentially positioned on one side, far away from the substrate, of the middle epitaxial layer; the material of the epitaxial layer comprises Al_x1In_y1Ga_1-x1-y1N, 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)≤1；

Preparing a first type ohmic contact metal layer on one side of the upper contact layer, which is far away from the substrate;

etching the first type ohmic contact metal layer, the upper contact layer and the upper optical 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 optical 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 far away from the epitaxial layer;

and carrying out processes of scribing, cleavage, coating and splitting on the epitaxial structure to form the distributed feedback laser.

7. The method of claim 6, wherein etching the first type ohmic contact metal layer, the upper contact layer and the upper field limiting layer to form a ridge structure comprises:

etching the first type ohmic contact metal layer, the upper contact layer and the upper optical field limiting layer by adopting a dry etching process to form a ridge structure;

after the first type ohmic contact metal layer, the upper contact layer and the upper optical field limiting layer are etched to form a ridge structure, the method further comprises the following steps:

and carrying out wet etching on the side surfaces of the upper contact layer and the upper optical field limiting layer by adopting an alkaline solution.

8. The method of claim 7, wherein the alkaline solution comprises at least one of ammonium hydroxide, ammonium chloride, ammonium fluoride, and tetramethylammonium hydroxide.

9. The method of claim 6, wherein etching the first type of ohmic contact metal, the upper contact layer, and the upper field limiting layer to form a ridge structure further comprises:

depositing an insulating layer on one side of the first type ohmic contact metal layer, which is far 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 technologies to expose the first type ohmic contact metal layer;

and preparing a connecting electrode on one side of the insulating layer, which is far away from the substrate, wherein the connecting electrode at least covers the exposed first type ohmic contact metal layer.

10. The method of manufacturing according to claim 6, wherein manufacturing a laser epitaxial structure comprises:

providing a substrate;

preparing a buffer layer on one side of the substrate;

preparing a lower optical field limiting layer on one side of the buffer layer far away from the substrate;

preparing a lower waveguide layer on the side of the lower optical field limiting layer far away from the substrate;

preparing an active region on the side of the lower waveguide layer away from the substrate;

preparing an upper waveguide layer on one side of the active region far away from the substrate;

preparing an upper optical field limiting layer on the side of the upper waveguide layer away from the substrate;

and preparing an upper contact layer on the side of the upper optical field limiting layer far away from the substrate.

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