CN114069385A - Edge-emitting semiconductor laser with small divergence angle and preparation method thereof - Google Patents

Abstract

The invention discloses an edge-emitting semiconductor laser with a small divergence angle and a preparation method thereof, wherein the laser comprises: a substrate; an active layer on one side of the substrate; at least two mode extension layers, the mode extension layers and the active layer being located on the same side of the substrate; first spacing layers are arranged between two adjacent mode expansion layers and between the active layer and the mode expansion layer; the mode expansion layer serves to increase the optical field intensity of light leaked out of the active layer to expand the distribution of the optical field in a direction along the active layer toward the mode expansion layer. The invention adds at least two mode expansion layers, can limit the light leaked from the active layer at the periphery of the active layer and expand the light to the outer layer step by step, thereby enlarging the longitudinal optical field distribution of the laser, achieving the effect of reducing the far field divergence angle, replacing the method of integrating a mode spot converter and the method of wide waveguide in the prior art, reducing the divergence angle of a fast axis and simultaneously improving the problems of complex preparation process and overlarge light loss.

Description

Edge-emitting semiconductor laser with small divergence angle and preparation method thereof

Technical Field

The embodiment of the invention relates to the technical field of laser, in particular to an edge-emitting semiconductor laser with a small divergence angle and a preparation method thereof.

Background

The semiconductor laser has the advantages of high conversion efficiency, high power, strong reliability, long service life, small volume, low cost and the like, and is widely applied to the fields of optical communication, optical interconnection, high-power application of optical storage, industrial cutting, distance measurement, Lidar, medical treatment and the like.

Edge emitting lasers in semiconductor lasers, such as Fabry-perot (FP) lasers and Distributed Feedback (DFB) lasers, have a problem that the divergence angle of the fast axis 1/e2 is large, and the large divergence angle of the fast axis brings certain inconvenience or cost increase to applications. For example, in an FP or DFB laser applied in the field of optical communication, an elliptical light spot can be formed when the divergence angle of a fast axis is larger than that of a slow axis, so that the coupling efficiency of the optical fiber is reduced; the high power FP or DFB lasers used in the 3D identification field have a large fast axis divergence, which increases the cost of package beam improvement. The existing methods for reducing the divergence angle of the edge-emitting laser mainly comprise an integrated spot-size converter method and a wide waveguide method, and the methods have the problems of complex preparation process, overlarge optical loss, small divergence angle and the like.

Disclosure of Invention

The embodiment of the invention provides an edge-emitting semiconductor laser with a small divergence angle and a preparation method thereof, which aim to reduce the divergence angle of a fast axis and solve the problems of complex preparation process and overlarge optical loss.

In a first aspect, an embodiment of the present invention provides an edge-emitting semiconductor laser with a small divergence angle, including:

a substrate;

an active layer on one side of the substrate;

at least two layers of mode extension layers, the mode extension layers being on the same side of the substrate as the active layer; first spacing layers are arranged between two adjacent mode expansion layers and between the active layer and the mode expansion layer; the mode expansion layer is used for increasing the light field intensity of light leaked out of the active layer so as to expand the distribution of the light field in the direction pointing to the mode expansion layer along the active layer.

Optionally, each mode extension layer is located between the active layer and the substrate.

Optionally, the active layer includes a quantum well layer, and an upper confinement layer and a lower confinement layer located on opposite sides of the quantum well layer;

the energy band width of the mode expansion layer is between the energy band width of the first spacer layer and the energy band width of the quantum well layer; the mode expansion layer has a refractive index between a refractive index of the first spacer layer and a refractive index of the quantum well layer.

Optionally, in a direction perpendicular to the substrate, a distance from a mode expansion layer closest to the quantum well layer in the mode expansion layers to a light emitting region of the quantum well layer is less than or equal to 1 um.

Optionally, the range of the distance between two adjacent mode expansion layers includes 100nm to 500 nm; the thickness range of the mode extension layer comprises 50-200 nm.

Optionally, the edge-emitting semiconductor laser with a small divergence angle further includes a buffer layer, and the buffer layer and the active layer are located on the same side of the substrate; the buffer layer covers the substrate, and the material of the buffer layer is the same as that of the substrate.

Optionally, the edge-emitting semiconductor laser with small divergence angle further comprises

The second spacer layer is positioned on one side, away from the substrate, of the active layer;

the etching stop layer is positioned on one side, far away from the substrate, of the second spacer layer;

the ridge waveguide structure is positioned on one side of the etching stop layer, which is far away from the substrate, and covers part of the etching stop layer.

Optionally, the edge-emitting semiconductor laser with a small divergence angle further includes:

a dielectric layer covering the sidewalls of the ridge waveguide structure and the exposed etch stop layer of the ridge waveguide structure;

a first electrode layer located on a side of the ridge waveguide structure away from the substrate;

the second electrode layer is positioned on one side, far away from the active layer, of the substrate.

In a second aspect, an embodiment of the present invention provides a method for manufacturing an edge-emitting semiconductor laser having a small divergence angle, including:

providing a substrate;

forming an active layer on one side of the substrate;

forming at least two mode extension layers, the mode extension layers and the active layer being located on the same side of the substrate; a first spacing layer is arranged between two adjacent mode expansion layers; the mode expansion layer is used for increasing the light field intensity of light leaked out of the active layer so as to expand the distribution of the light field in the direction of pointing to the mode expansion layer along the active layer.

Optionally, each mode extension layer is located between the active layer and the substrate;

the mode expansion layer forming at least two layers includes:

sequentially and alternately forming a mode expansion layer and a first spacing layer on one side of the substrate; among the mode expansion layers and the first spacing layers which are alternately formed, the mode expansion layer which is closest to the substrate is the first spacing layer, and the first spacing layer which is farthest from the substrate is the first spacing layer;

the forming the active layer includes:

sequentially forming a lower limiting layer, a quantum well layer and an upper limiting layer on one side, far away from the substrate, of the first spacing layer far away from the substrate; wherein the energy band width of the mode extension layer is between the energy band width of the first spacer layer and the energy band width of the quantum well layer; the mode expansion layer has a refractive index between a refractive index of the first spacer layer and a refractive index of the quantum well layer.

Optionally, after the forming the active layer, the method further includes:

forming a second spacer layer, wherein the second spacer layer is positioned on one side of the active layer away from the substrate;

forming an etching stop layer, wherein the etching stop layer is positioned on one side of the third interlayer far away from the substrate;

and forming a ridge waveguide structure, wherein the ridge waveguide structure is positioned on one side of the etching stop layer, which is far away from the substrate, and covers part of the etching stop layer.

The embodiment of the invention provides an edge-emitting semiconductor laser with a small divergence angle and a preparation method thereof, wherein the edge-emitting semiconductor laser with the small divergence angle comprises the following components: a substrate; an active layer on one side of the substrate; at least two mode extension layers, the mode extension layers and the active layer being located on the same side of the substrate; first spacing layers are arranged between two adjacent mode expansion layers and between the active layer and the mode expansion layer; the mode expansion layer serves to increase the optical field intensity of light leaked out of the active layer to expand the distribution of the optical field in a direction along the active layer toward the mode expansion layer. On the basis of not changing the design of energy bands and refractive indexes around the active layer, the invention introduces a plurality of mode expansion layers, can limit the light leaked by the active layer at the periphery of the active layer and expand the light to the outer layers step by step, thereby enlarging the longitudinal light field distribution of the laser and further playing the role of reducing the far field divergence angle. The method replaces an integrated spot size converter method and a wide waveguide method in the prior art, reduces the divergence angle of a fast axis, and simultaneously improves the problems of complex preparation process and overlarge optical loss.

Drawings

FIG. 1 is a schematic diagram of an optical near-field spot of an edge-emitting laser provided in the prior art;

FIG. 2 is a schematic diagram of a longitudinal optical field distribution of an edge-emitting laser provided in the prior art;

FIG. 3 is a schematic diagram of the conduction band energy level of a partial film structure of an edge-emitting laser provided in the prior art;

FIG. 4 is a schematic illustration of a refractive index gradient of the film layer structure shown in FIG. 3;

fig. 5 is a schematic structural diagram of an edge-emitting semiconductor laser with a small divergence angle according to an embodiment of the present invention;

FIG. 6 is a schematic diagram of an outgoing near-field spot of an edge-emitting laser with a small divergence angle according to an embodiment of the present invention;

FIG. 7 is a schematic diagram of the longitudinal optical field distribution of an edge-emitting laser with a small divergence angle provided by an embodiment of the present invention;

FIG. 8 is a schematic diagram of conduction band energy levels of a partial film structure of an edge-emitting laser with a small divergence angle, according to an embodiment of the present invention;

FIG. 9 is a schematic illustration of a refractive index gradient of the film layer structure shown in FIG. 8;

fig. 10 is a schematic structural diagram of another edge-emitting semiconductor laser with a small divergence angle according to an embodiment of the present invention;

fig. 11 is a flow chart of a method for fabricating an edge-emitting semiconductor laser with a small divergence angle according to an embodiment of the present invention;

fig. 12 is a flow chart of another method for fabricating an edge-emitting semiconductor laser with a small divergence angle according to an embodiment of the present invention;

fig. 13 is a cross-sectional view of the structure corresponding to step S260 in the method shown in fig. 12.

Detailed Description

The present invention will be described in further detail with reference to the accompanying drawings and examples. It is to be understood that the specific embodiments described herein are merely illustrative of the invention and are not limiting of the invention. It should be further noted that, for the convenience of description, only some of the structures related to the present invention are shown in the drawings, not all of the structures.

As in the background art, edge-emitting lasers in semiconductor lasers, such as FP lasers and DFB lasers, have a problem of a large divergence angle of the fast axis 1/e 2. Fig. 1 is a schematic diagram of an optical near-field spot of an edge-emitting laser provided in the prior art, fig. 2 is a schematic diagram of a longitudinal optical field distribution of an edge-emitting laser provided in the prior art, fig. 3 is a schematic diagram of a conduction band energy level of a partial film structure of an edge-emitting laser provided in the prior art, and fig. 4 is a schematic diagram of a refractive index gradient of the film structure shown in fig. 3. Wherein fig. 3 exemplarily shows a conduction band energy level diagram of a film layer around a quantum well (MQW), such as an etch stop layer 7, and an N-type epitaxial layer (e.g., a buffer layer) made of InP on one side of the active layer, and a P-type epitaxial layer (e.g., a conductive layer) made of InP on the other side of the active layer 4; FIG. 4 is an exemplary graph showing the refractive index gradient of the above-described film structure around the quantum well (MQW). In order to obtain high quantum efficiency in a side-emitting laser, it is necessary to confine both photons and electrons in a quantum well (MQW) light-emitting region of the active layer 4, and therefore, in general, in the mechanical design of a laser, it is necessary to set the refractive index of the quantum well region to the maximum and the energy band width to the minimum. Due to the small thickness of the active layer 4, the optical field of the light emitting region is further limited to a narrow region in the longitudinal direction Y (direction perpendicular to the substrate), typically only in the order of 1 um. Referring to fig. 1 and 2, the pattern of the spot 100 is that of the laser in the near field, where the optical field intensity is greatest in the region of the active layer 4 in the direction perpendicular to the substrate, and decreases rapidly in the direction pointing from the active layer to both sides. Because the light field in the light emitting region is limited in a narrow region in the longitudinal direction Y, a strong diffraction effect can be generated on the light emitting surface, and further, the divergence angle of the light spot in the far field in the longitudinal direction Y is larger and can reach more than 40 degrees. And a larger fast axis divergence angle brings certain inconvenience or cost increase to the application. For example, in an FP or DFB laser applied in the field of optical communication, an elliptical light spot can be formed when the divergence angle of a fast axis is larger than that of a slow axis, so that the coupling efficiency of the optical fiber is reduced; the high power FP or DFB lasers used in the 3D identification field have a large fast axis divergence, which increases the cost of package beam improvement. The existing methods for reducing the divergence angle of the edge-emitting laser mainly comprise an integrated spot-size converter method and a wide waveguide method, and the methods have the problems of complex preparation process, overlarge optical loss, small divergence angle and the like.

In view of this, an embodiment of the present invention provides an edge-emitting semiconductor laser with a small divergence angle, fig. 5 is a schematic structural diagram of an edge-emitting semiconductor laser with a small divergence angle provided by an embodiment of the present invention, fig. 6 is a schematic light-emitting near-field spot of an edge-emitting semiconductor laser with a small divergence angle provided by an embodiment of the present invention, fig. 7 is a schematic longitudinal optical field distribution diagram of an edge-emitting semiconductor laser with a small divergence angle provided by an embodiment of the present invention, and referring to fig. 5 to 7, the edge-emitting semiconductor laser with a small divergence angle includes:

a substrate 10;

an active layer 40 on one side of the substrate 10;

at least two layers of mode extension layer 20, mode extension layer 20 being on the same side of substrate 10 as active layer 40; first spacer layers 30 are disposed between two adjacent mode expansion layers 20 and between the active layer 40 and the mode expansion layer 20; the mode expansion layer 20 serves to increase the optical field intensity of light leaked out of the active layer 40 to expand the distribution of the optical field in a direction along the active layer 40 toward the mode expansion layer 20.

Specifically, the substrate 10 may be any material suitable for forming an edge-emitting semiconductor laser, such as indium phosphide (InP). The substrate 10 may be conductive or insulating. If two electrode layers for supplying power to the active layer 40 for generating laser light are located on opposite sides of the substrate 10, the substrate 10 should function as a conductor to conduct the two electrode layers, the substrate 10 may have conductivity, and the substrate 10 may be made conductive by heavily doping. If the two electrode layers supplying power to the active layer 40 are located on the same side of the substrate 10, the substrate 10 does not need to function as a conductor to conduct the two electrode layers, as opposed to the case where the two electrode layers are formed on opposite sides of the substrate 10, and the substrate 10 is less conductive or non-conductive.

The active layer 40 serves to convert electrical energy into optical energy, thereby generating laser light. Edge-emitting lasers confine both photons and electrons in the light-emitting region of the active layer 40 in order to achieve high quantum efficiency, and can sufficiently perform the double-core light emission of electrons and holes confined therein. Therefore, the refractive index of the active layer 40 needs to be set to the maximum and the energy band width needs to be set to the minimum with respect to other film layer structures of the laser. The intensity of the light field is maximized in the region where the active layer 40 is located, in a direction perpendicular to the substrate 10. In order to improve the problem that the optical field of the light emitting region is longitudinally limited to a narrow region, which results in a strong diffraction effect and a large divergence angle of the far field, the active layer 40 is set to have a small thickness, for example, 2 μm, in the embodiment of the present invention, at least two mode expansion layers 20 are added, and the mode expansion layers 20 are used to increase the optical field intensity of the light leaked from the active layer 40. It will be appreciated that the mode expansion layer 20 may draw light generated by the active layer 40 to be confined therein, which may have the effect of increasing the intensity of the light field outside the active layer 40 at the location of the mode expansion layer 20, thereby expanding the distribution of the light field in a direction along the active layer 40 towards the mode expansion layer 20. The light leaked from the active layer 40 is limited at the periphery of the active layer 40 and is diffused gradually towards the mode expansion layer 20 which is far away from the active layer 40, so that the longitudinal optical field distribution of the laser can be enlarged, and the effect of reducing the far field divergence angle is achieved.

Wherein the mode extension layer 20 is located on the same side of the substrate 10 as the active layer 40. The mode expansion layer 20 may be located on a side of the active layer 40 away from the substrate 10, or may be located on a side of the active layer 40 close to the substrate 10 (refer to fig. 5); or partially on the side of the active layer 40 away from the substrate 10 and partially on the side of the active layer 40 close to the substrate 10. The number of layers of the mode expanding layer 20 includes at least two layers, and the effect of reducing the far field divergence angle can be further improved as compared with a single layer of the mode expanding layer 20. In addition, the first spacing layer 30 is arranged between the mode expansion layers 20 of two adjacent layers to space the mode expansion layers 20 apart, so that the mode expansion layers 20 are prevented from being connected to form a thick integral film layer, excessive light leakage in the active layer is caused, and the light spot of the laser is shifted from the position of the active layer 40 to the mode expansion layer 20, so that the laser cannot emit laser normally, and the normal operation of the laser is influenced. Moreover, the first spacer layer 30 is disposed between the mode expansion layers 20 of two adjacent layers, and the effect of stretching the optical field can be changed by adjusting the thickness of the mode expansion layer 20 and the thickness of the first spacer layer 30, thereby playing a role in adjusting the magnitude of the far-field divergence angle. It should be noted that the mode expansion layer 20 and the active layer 40 also need to be separated by the first spacer layer 30, so as to avoid large optical loss due to wide waveguide.

The edge-emitting semiconductor laser with a small divergence angle provided by the embodiment of the invention comprises: a substrate; an active layer on one side of the substrate; at least two mode extension layers, the mode extension layers and the active layer being located on the same side of the substrate; first spacing layers are arranged between two adjacent mode expansion layers and between the active layer and the mode expansion layer; the mode expansion layer serves to increase the optical field intensity of light leaked out of the active layer to expand the distribution of the optical field in a direction along the active layer toward the mode expansion layer. On the basis of not changing the design of energy bands and refractive indexes around a quantum well in the active layer, the design of an epitaxial structure is improved in the direction vertical to the substrate, and a plurality of mode expansion layers are introduced, so that light leaked from the active layer can be limited at the periphery of the active layer and can be expanded towards an outer layer step by step, the longitudinal optical field distribution of the laser can be enlarged, and the effect of reducing the far field divergence angle is achieved. The method replaces an integrated spot size converter method and a wide waveguide method in the prior art, reduces the divergence angle of a fast axis, and simultaneously improves the problems of complex preparation process and overlarge optical loss.

Alternatively, referring to fig. 5, each mode extension layer 20 is positioned between the active layer 40 and the substrate 10.

Specifically, in the at least two mode expansion layers 20, each mode expansion layer 20 is located between the active layer 40 and the substrate 10, and the first spacer layer 30 is disposed between two adjacent mode expansion layers 20 and between the active layer 40 and the mode expansion layer 20. In the process of manufacturing the laser, the mode extension layer 20 and the first spacer layer 30 are alternately formed on one side of the substrate 10 in sequence, so that the manufacturing process of the mode extension layer 20 and the first spacer layer 30 can be simplified. Of the alternately formed mode extension layers 20 and first spacer layers 30, the layer closest to the substrate 10 is the mode extension layer 20, and the layer farthest from the substrate 10 is the first spacer layer 30, i.e., the mode extension layer 20 is disposed in pair with the first spacer layer 30. The mode expansion layer 20 may be bulk materials (bulk materials) with a thickness in a range of 50nm to 500nm, and has the characteristics of simple structure and simple preparation process. The material of the mode extension layer 20 may include InGaAsP or AlGaInAs materials; the material of the first spacer layer 30 may comprise InP.

In the embodiment of the present invention, the mode expansion layer 20 is an N-type mode expansion layer, and the first spacer layer 30 is an N-type spacer layer. The N-type doping can reduce the absorption of the mode extension layer 20 to light, and avoid the loss of light, compared to the P-type doping. Since one side of the epitaxial structures on the two opposite sides of the active layer 40 is doped P-type and the other side is doped N-type, each mode extension layer 20 is located between the active layer 40 and the substrate 10, and loss of light by the N-type mode extension layer can be avoided compared with the structure having the mode extension layer 20 on the side of the active layer 40 away from the substrate 10. On the basis of not changing the design of energy bands and refractive indexes around the active layer 40, the mode expansion layers 20 are introduced below the active layer 40 (the side of the active layer 40 close to the substrate 10), the mode expansion layers 20 can be epitaxial layers with higher refractive indexes, light leaked from a quantum well region in the active layer 40 can be limited at the periphery of a quantum well and can be expanded to lower layers step by step, and therefore the longitudinal optical field distribution of the laser can be enlarged, and the effect of reducing the far field divergence angle is achieved.

Alternatively, fig. 8 is a schematic diagram of a conduction band energy level of a partial film structure of an edge-emitting laser with a small divergence angle according to an embodiment of the present invention, fig. 9 is a schematic diagram of a refractive index gradient of the film structure shown in fig. 8, and referring to fig. 8 to 9, and fig. 5, the active layer 40 includes a quantum well layer, and an upper confinement layer and a lower confinement layer on opposite sides of the quantum well layer;

the energy band width of the mode expansion layer 20 is between the energy band width of the first spacer layer 30 and the energy band width of the quantum well layer; the refractive index of the mode expansion layer 20 is between the refractive index of the first spacer layer 30 and the refractive index of the quantum well layer.

Specifically, the active layer 40 includes a quantum well layer, and an upper confinement layer and a lower confinement layer on opposite sides of the quantum well layer; wherein the quantum well layer can be a single layer or multiple layers. The refractive index of the quantum well region is set to be maximum, the energy band width is set to be minimum, and the refractive indices of the upper confinement layer and the lower confinement layer are smaller than the refractive index of the quantum well region. Photons and electrons can be confined simultaneously in the quantum well light emitting region, and high quantum efficiency is obtained. The energy band width of the mode expansion layer 20 is between the energy band width of the first spacer layer 30 and the energy band width of the quantum well layer; the refractive index of the mode expansion layer 20 is between the refractive index of the first spacer layer 30 and the refractive index of the quantum well layer. The material of the first spacer layer 30 may be InP, the material of the quantum well layer may be InGaAsP or AlGaInAs, the mode extension layer 20 may have a band width between the band width of InP and the band width of the quantum well layer, for example, a 1310nm band laser may have InGaAsP or AlGaInAs with an emission wavelength in the range of 1100nm to 1200nm as the material of the mode extension layer 20. That is, the material of the quantum well layer and the material of the mode expansion layer 20 may be both InGaAsP or AlGaInAs, but the energy band width of the quantum well layer is smaller than that of the mode expansion layer 20, and the refractive index of the quantum well layer is larger than that of the mode expansion layer 20, which can be achieved by adjusting the ratio of each element in the materials. In addition, the mode expansion layer 20 needs to be lattice-matched to InP (first spacing) to reduce crystal defects due to lattice mismatch.

Alternatively, referring to fig. 5, in a direction perpendicular to the substrate 10, a distance from the mode expansion layer 20 closest to the quantum well layer among the mode expansion layers 20 to the light emitting region of the quantum well layer is less than or equal to 1 um.

Specifically, the closer the first mode expansion layer 20 (the mode expansion layer 20 closest to the quantum well layer) is to the light emitting region of the quantum well layer, the stronger the mode expansion effect is, and the distance between the first mode expansion layer 20 and the light emitting region of the quantum well layer is set to be within 1um, so that the mode expansion effect can be ensured. However, the closer the distance between the first mode expanding layer 20 and the quantum well layer light emitting region is, the greater the light loss is, and the distance between the first mode expanding layer 20 and the quantum well layer light emitting region can be adjusted according to the light confinement factor of the quantum well region.

Optionally, referring to fig. 5, the range of the distance between two adjacent mode expansion layers 20 includes 100nm to 500nm, and the range of the thickness of the mode expansion layer 20 includes 50nm to 200 nm.

Specifically, the thickness range of the mode expansion layer 20 includes 50 to 200nm, which can be adjusted according to the refractive index of the adopted material and the distance from the active region, and the thicker the mode expansion layer 20 is, the smaller the divergence angle in the longitudinal direction is. The distance between the mode expanding layers 20 is in the range of 100nm to 500nm to have a more gradual mode expanding effect. The distance between the mode expansion layers 20 ranges from 100nm to 500nm, i.e., the thickness of the first spacer layer 30 ranges from 100nm to 500 nm. The main purpose of limiting the distance is to enhance the mode expansion effect of the mode expansion layer, if the distance of the mode expansion layer 20 is too small, the effect is equivalent to that of an integral mode expansion layer 20 with a larger thickness, and the light spot generated by the active layer 40 is shifted downwards, so that the laser cannot emit laser normally; if the distance is too large, the light confinement factor of the mode expansion layer 20 under the active layer 40 becomes small and the mode expansion effect is reduced.

Optionally, with continued reference to fig. 5, the edge-emitting semiconductor laser with a small divergence angle further includes a buffer layer 50, the buffer layer 50 and the active layer 40 being located on the same side of the substrate 10; the buffer layer 50 covers the substrate 10, and the material of the buffer layer 50 is the same as that of the substrate 10.

Specifically, before the mode extension layer 20 and the active layer 40 are formed, a buffer layer 50 may be formed on the substrate 10, and the material of the buffer layer 50 may be the same as that of the substrate 10. For example, the material of the buffer layer 50 and the material of the substrate 10 are both InP. Defects on the surface of the substrate 10 can be reduced by forming a buffer layer 50 on the substrate 10 to avoid affecting subsequent fabrication of the laser.

Optionally, with continuing reference to fig. 5, the edge-emitting semiconductor laser with a small divergence angle further includes:

a second spacer layer 60, the second spacer layer 60 being located on a side of the active layer 40 away from the substrate 10;

an etch stop layer 70, the etch stop layer 70 being located on a side of the second spacer layer 60 remote from the substrate 10;

a ridge waveguide structure 80, wherein the ridge waveguide structure 80 is located on the side of the etch stop layer 70 away from the substrate 10 and covers a portion of the etch stop layer 70.

Specifically, for each laser with the mode expansion layer 20 located between the active layer 40 and the substrate 10, the second spacer layer 60, the etch stop layer 70 and the ridge waveguide structure 80 are further sequentially disposed on the side of the active layer 40 away from the substrate 10. Wherein the second spacer layer 60 is a P-type spacer layer. The material of the second spacer layer 60 may be the same as the first spacer layer 30, for example InP. The etch stop layer 70 serves to prevent the etching liquid from damaging a film layer under the ridge waveguide structure 80 in the process of forming the ridge waveguide structure 80. The ridge waveguide structure 80 is a channel for injecting electrons, and the ridge waveguide structure 80 comprises a p-type conducting layer 81 and a p-type electrode contact layer 82; the material of the p-type conductive layer 81 may be InP and the material of the p-type electrode contact layer 82 may be InGaAs. It may be made conductive by means of doping. Wherein the p-type InGaAs electrode contact layer 82 is in contact with the electrode layer for injecting electrons. The width of the ridge waveguide structure 80 in a direction parallel to the substrate 10 defines the width of the injected electron channel. The ridge waveguide structure 80 is arranged at a small distance from the active layer 40, so that the area where electrons enter the active layer 40 is approximately equal to the width of the ridge waveguide structure 80. By adjusting the width of the ridge waveguide structure 80, the distribution range of the lateral light field of the laser light can be adjusted, and thus the divergence angle in the lateral direction in the far field can be adjusted. In addition, it should be noted that, each mode extension layer 20 is disposed between the active layer 40 and the substrate 10, and with respect to the structure having the mode extension layer 20 on the side of the active layer 40 away from the substrate 10, or with respect to the structure having each mode extension layer 20 on the side of the active layer 40 away from the substrate 10, the mode extension layer 20 can be prevented from increasing the distance between the ridge waveguide structure 80 and the active layer 40, so as to prevent electrons flowing out from the ridge waveguide structure 80 from diffusing in the lateral direction, and ensure that the width of the ridge waveguide structure 80 defines the range of electrons flowing into the active layer 40.

Alternatively, fig. 10 is a schematic structural diagram of another edge-emitting semiconductor laser with a small divergence angle according to an embodiment of the present invention, and with reference to fig. 10, the edge-emitting semiconductor laser further includes: a dielectric layer 93, the dielectric layer 93 covering the sidewall of the ridge waveguide structure 80 and the etching stop layer 70 exposed by the ridge waveguide structure 80; a first electrode layer 91, the first electrode layer 91 being located on a side of the ridge waveguide structure 80 away from the substrate 10; and a second electrode layer 92, wherein the second electrode layer 92 is positioned on the side of the substrate 10 far away from the active layer 40. The first electrode layer 91 and the second electrode layer 92 are located on opposite sides of the substrate 10, and the substrate 10 has conductivity.

An embodiment of the present invention further provides a method for manufacturing an edge-emitting semiconductor laser with a small divergence angle, which is used to form an edge-emitting semiconductor laser with a small divergence angle according to any of the above embodiments, and fig. 11 is a flowchart of a method for manufacturing an edge-emitting semiconductor laser with a small divergence angle according to an embodiment of the present invention, and with reference to fig. 1, the method includes:

and S110, providing a substrate.

In particular, the substrate may be any material suitable for forming an edge-emitting semiconductor laser, such as indium phosphide (InP). The substrate may be conductive or insulating. If the two electrode layers for supplying power to the active layer for generating laser light are located on opposite sides of the substrate, the substrate needs to function as a conductor to conduct the two electrode layers, and the substrate may have conductivity and may be made conductive by heavily doping. If the two electrode layers supplying power to the active layer are located on the same side of the substrate, the substrate does not need to function as a conductor to conduct the two electrode layers, as opposed to the case where the two electrode layers are formed on opposite sides of the substrate, and the substrate is less conductive or non-conductive.

And S120, forming an active layer, wherein the active layer is positioned on one side of the substrate.

Specifically, the active layer is located on one side of the substrate to convert electrical energy into optical energy, thereby generating laser light. The active layer comprises a quantum well layer, an upper limiting layer and a lower limiting layer which are positioned on two opposite sides of the quantum well layer; wherein the quantum well layer can be a single layer or multiple layers. The refractive index of the quantum well region is set to be maximum, the energy band width is set to be minimum, and the refractive indices of the upper confinement layer and the lower confinement layer are smaller than the refractive index of the quantum well region. Photons and electrons can be confined simultaneously in the quantum well light emitting region, and high quantum efficiency is obtained. The intensity of the light field in the region of the active layer is maximized in the direction perpendicular to the substrate. The thickness of the active layer is small, for example 2 microns.

S130, forming at least two mode expansion layers, wherein the mode expansion layers and the active layer are positioned on the same side of the substrate; a first spacing layer is arranged between two adjacent mode expansion layers; the mode expansion layer is used to increase the optical field intensity of the light leaked out of the active layer to expand the distribution of the optical field in a direction along the active layer towards the mode expansion layer.

Specifically, at least two mode expansion layers are added, and the mode expansion layers are used for increasing the light field intensity of light leaked out of the active layer. It can be understood that the mode expansion layer can attract the light generated by the active layer to be limited in the mode expansion layer, the effect of increasing the light field intensity outside the active layer at the position of the mode expansion layer can be achieved, and then the distribution of the light field is expanded in the direction pointing to the mode expansion layer along the active layer. Light leaked from the active layer is limited at the periphery of the active layer and is diffused to the mode expansion layer which is further away from the active layer step by step, so that the longitudinal light field distribution of the laser can be enlarged, and the effect of reducing the far field divergence angle is achieved.

Wherein the mode extension layer and the active layer are on the same side of the substrate. The mode expansion layer can be positioned on the side of the active layer far away from the substrate or positioned on the side of the active layer close to the substrate. Or partially on the side of the active layer away from the substrate and partially on the side of the active layer close to the substrate. The mode expansion layer comprises at least two layers, and the effect of reducing the far field divergence angle can be further improved compared with a single-layer mode expansion layer. In addition, a first spacing layer is arranged between the mode expansion layers of the two adjacent layers to separate the mode expansion layers, so that the mode expansion layers can be prevented from being connected to form a thick film layer, and light spots of the laser can not normally emit laser light due to the fact that the light spots are shifted to the mode expansion layers from the position of the active layer, and the normal work of the laser is influenced. The effect of stretching the optical field can be changed by adjusting the thickness of the mode expanding layer and the thickness of the first spacing layer, and the effect of adjusting the size of the far-field divergence angle is achieved. It should be noted that the mode expansion layer and the active layer also need to be separated by the first spacer layer to avoid large optical loss due to wide waveguide.

According to the preparation method of the edge-emitting semiconductor laser with the small divergence angle, provided by the invention, on the basis of not changing the design of the energy band and the refractive index around the quantum well in the active layer, the design of the epitaxial structure is improved in the direction vertical to the substrate, and the plurality of mode expansion layers are introduced, so that the light leaked from the quantum well region can be limited at the periphery of the quantum well and can be expanded towards the outer layer step by step, and thus the longitudinal optical field distribution of the laser can be enlarged, and the effect of reducing the far field divergence angle is further achieved. The method replaces an integrated spot size converter method and a wide waveguide method in the prior art, reduces the divergence angle of a fast axis, and simultaneously improves the problems of complex preparation process and overlarge optical loss.

Fig. 12 is a flowchart of another method for manufacturing an edge-emitting semiconductor laser having a small divergence angle according to an embodiment of the present invention, and referring to fig. 12, the method for manufacturing includes:

s210, providing a substrate, and forming a buffer layer on the substrate.

S220, alternately forming a mode expansion layer and a first spacing layer on one side of the buffer layer far away from the substrate in sequence; among the mode expansion layers and the first spacing layers which are alternately formed, the mode expansion layer is closest to the substrate, and the first spacing layer is farthest from the substrate.

Specifically, each mode extension layer of the at least two mode extension layers is located between the active layer and the substrate, and first spacing layers are arranged between two adjacent mode extension layers and between the active layer and the mode extension layers. The mode expansion layer can be bulk materials (bulk materials) with the thickness ranging from 50nm to 500nm, and has the characteristics of simple structure and simple preparation process. The mode expansion layer is an N-type mode expansion layer, and the first spacing layer is an N-type spacing layer. Compared with P-type doping, the N-type doping can reduce the absorption of the mode expansion layer to light, and avoid the loss of light. Because one side of the epitaxial structures on the two opposite sides of the active layer is doped in a P type mode, and the other side of the epitaxial structures is doped in an N type mode, each mode extension layer is positioned between the active layer and the substrate, and the problem of light loss caused by the N type mode extension layer can be avoided compared with the structure that the mode extension layer is arranged on the side, far away from the substrate, of the active layer.

And S230, sequentially forming a lower limiting layer, a quantum well layer and an upper limiting layer on the side, away from the substrate, of the first spacing layer farthest from the substrate.

Specifically, the energy band width of the mode expansion layer is between the energy band width of the first spacer layer and the energy band width of the quantum well layer; the refractive index of the mode expansion layer is between the refractive index of the first spacer layer and the refractive index of the quantum well layer. The material of the first spacer layer may be InP, the material of the quantum well layer may be InGaAsP or AlGaInAs, the material of the mode extension layer may be InGaAsP or AlGaInAs with a band width between InP and the light emitting wavelength of the laser, for example, a 1310nm band laser may use InGaAsP or AlGaInAs with a light emitting wavelength in the range of 1100nm to 1200nm as the material of the mode extension layer. That is, the material of the quantum well layer and the material of the mode extension layer may be both InGaAsP or AlGaInAs, but the energy band width of the quantum well layer is smaller than that of the mode extension layer, and the refractive index of the quantum well layer is greater than that of the mode extension layer. Can be realized by adjusting the proportion of each element in the material. In addition, the mode-expanding layer needs to be lattice-matched to InP (first spacer layer) to reduce crystal defects due to lattice mismatch.

And S240, forming a second spacer layer on one side of the upper limiting layer far away from the substrate.

Specifically, the second spacer layer is a P-type spacer layer. The material of the second spacer layer may be the same as the material of the first spacer layer, for example InP.

And S250, forming an etching stop layer on one side of the second spacer layer, which is far away from the substrate.

And S260, forming a ridge waveguide structure, wherein the ridge waveguide structure is positioned on one side of the etching stop layer, which is far away from the substrate, and covers a part of the etching stop layer.

Specifically, fig. 13 is a cross-sectional view of the structure corresponding to step S250 in the method shown in fig. 12, and referring to fig. 12, after an etching stop layer is formed on the side of the second spacer layer away from the substrate, a p-type conductive layer 81 and a p-type electrode contact layer 82 are sequentially formed on the side of the etching stop layer away from the substrate. The p-type conductive layer 81 and the p-type electrode contact layer 82 may be etched by an etching solution under the action of a mask until the etching stop layer is exposed. Referring to fig. 5, the p-type conductive layer 81 and the p-type electrode contact layer 82 remaining after the etching constitute a ridge waveguide structure 80. The width of the ridge waveguide structure 80 in the direction parallel to the substrate defines the width of the injected electron channel.

And S270, forming a dielectric layer, wherein the dielectric layer covers the side wall of the ridge waveguide structure and the etching stop layer exposed by the ridge waveguide structure.

Specifically, referring to fig. 10, a dielectric layer 93 of SiNx or SiO2 is fabricated, and the dielectric layer above the ridge waveguide structure 80 is removed to leak out of the electrode contact layer 82.

S280, forming a first electrode layer on one side of the ridge waveguide structure, which is far away from the substrate; and forming a second electrode layer on one side of the substrate far away from the active layer.

Specifically, referring to fig. 10, a metal electrode layer formed on the front surface is used as the first electrode layer 91. After the InP substrate 10 is thinned, a metal electrode layer may be formed on the back surface of the substrate 10, and used as the second electrode layer 92. The wafer can be cut into Bar strips according to the designed length of the resonant cavity of the laser. And plating an antireflection film or a reflecting film on the front/back light-emitting surface of the laser. And cutting the coated Bar strip into single laser chips.

On the basis of not changing the design of an energy band and a refractive index around the active layer, the embodiment of the invention introduces a plurality of mode expansion layers below the active layer (the side of the active layer close to the substrate), wherein the mode expansion layers can be epitaxial layers with higher refractive indexes, and can limit light leaked from a quantum well region in the active layer to the periphery of the quantum well and expand the light to lower layers step by step, so that the longitudinal optical field distribution of the laser can be enlarged, and the effect of reducing the far field divergence angle is achieved.

It is to be noted that the foregoing is only illustrative of the preferred embodiments of the present invention and the technical principles employed. It will be understood by those skilled in the art that the present invention is not limited to the particular embodiments described herein, but is capable of various obvious changes, rearrangements and substitutions as 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 (11)

1. An edge-emitting semiconductor laser having a small divergence angle, comprising:

a substrate;

an active layer on one side of the substrate;

at least two layers of mode extension layers, the mode extension layers being on the same side of the substrate as the active layer; first spacing layers are arranged between two adjacent mode expansion layers and between the active layer and the mode expansion layer; the mode expansion layer is used for increasing the light field intensity of light leaked out of the active layer so as to expand the distribution of the light field in the direction pointing to the mode expansion layer along the active layer.

2. An edge-emitting semiconductor laser with a small divergence angle as claimed in claim 1 wherein each said mode spreading layer is located between said active layer and said substrate.

3. An edge-emitting semiconductor laser having a small divergence angle as claimed in claim 2, wherein the active layer comprises a quantum well layer and upper and lower confinement layers on opposite sides of the quantum well layer;

the energy band width of the mode expansion layer is between the energy band width of the first spacer layer and the energy band width of the quantum well layer; the mode expansion layer has a refractive index between a refractive index of the first spacer layer and a refractive index of the quantum well layer.

4. An edge-emitting semiconductor laser having a small divergence angle according to claim 2, wherein a distance from a mode expansion layer closest to the quantum well layer among the mode expansion layers to a light emitting region of the quantum well layer is less than or equal to 1um in a direction perpendicular to the substrate.

5. An edge-emitting semiconductor laser having a small divergence angle according to claim 1, wherein a distance between adjacent two mode expanding layers ranges from 100nm to 500 nm; the thickness range of the mode extension layer comprises 50-200 nm.

6. An edge-emitting semiconductor laser with a small divergence angle as claimed in claim 1 further comprising a buffer layer on the same side of the substrate as the active layer; the buffer layer covers the substrate, and the material of the buffer layer is the same as that of the substrate.

7. An edge-emitting semiconductor laser with a small divergence angle as claimed in claim 2 further comprising

The second spacer layer is positioned on one side, away from the substrate, of the active layer;

the etching stop layer is positioned on one side, far away from the substrate, of the second spacer layer;

the ridge waveguide structure is positioned on one side of the etching stop layer, which is far away from the substrate, and covers part of the etching stop layer.

8. An edge-emitting semiconductor laser having a small divergence angle as claimed in claim 7, further comprising:

a dielectric layer covering the sidewalls of the ridge waveguide structure and the exposed etch stop layer of the ridge waveguide structure;

a first electrode layer located on a side of the ridge waveguide structure away from the substrate;

the second electrode layer is positioned on one side, far away from the active layer, of the substrate.

9. A method of fabricating an edge-emitting semiconductor laser having a small divergence angle, comprising:

providing a substrate;

forming an active layer on one side of the substrate;

forming at least two mode extension layers; the mode extension layer and the active layer are positioned on the same side of the substrate; a first spacing layer is arranged between two adjacent mode expansion layers; the mode expansion layer is used for increasing the light field intensity of light leaked out of the active layer so as to expand the distribution of the light field in the direction of pointing to the mode expansion layer along the active layer.

10. A method for fabricating an edge-emitting semiconductor laser having a small divergence angle as claimed in claim 9 wherein each of said mode expansion layers is located between said active layer and said substrate; the mode expansion layer forming at least two layers includes:

sequentially and alternately forming a mode expansion layer and a first spacing layer on one side of the substrate; among the mode expansion layers and the first spacing layers which are alternately formed, the mode expansion layer which is closest to the substrate is the first spacing layer, and the first spacing layer which is farthest from the substrate is the first spacing layer;

the forming the active layer includes:

sequentially forming a lower limiting layer, a quantum well layer and an upper limiting layer on one side, far away from the substrate, of the first spacing layer far away from the substrate; wherein the energy band width of the mode extension layer is between the energy band width of the first spacer layer and the energy band width of the quantum well layer; the mode expansion layer has a refractive index between a refractive index of the first spacer layer and a refractive index of the quantum well layer.

11. A method for fabricating an edge-emitting semiconductor laser with a small divergence angle as claimed in claim 10 further comprising, after said forming an active layer:

forming a second spacer layer, wherein the second spacer layer is positioned on one side of the active layer away from the substrate;

forming an etching stop layer, wherein the etching stop layer is positioned on one side of the second spacer layer, which is far away from the substrate;

and forming a ridge waveguide structure, wherein the ridge waveguide structure is positioned on one side of the etching stop layer, which is far away from the substrate, and covers part of the etching stop layer.

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