CN117748291A

CN117748291A - Vertical cavity surface emitting laser and manufacturing method thereof

Info

Publication number: CN117748291A
Application number: CN202311620437.0A
Authority: CN
Inventors: 请求不公布姓名
Original assignee: Zhejiang Laoying Semiconductor Technology Co ltd
Current assignee: Zhejiang Laoying Semiconductor Technology Co ltd
Priority date: 2023-11-29
Filing date: 2023-11-29
Publication date: 2024-03-22

Abstract

A Vertical Cavity Surface Emitting Laser (VCSEL) and a manufacturing method thereof, a VCSEL array and a light emitting device, including: a substrate, a first reflecting mirror, an active region, a second reflecting mirror and a composite grating formed on the substrate; the active area is located between the first reflector and the second reflector, the composite grating comprises a grating structure formed in the first material layer and a dielectric layer formed on the surface of the grating structure, the first material layer is a surface layer of the first reflector or is formed on the surface layer of the first reflector, the first surface of the dielectric layer has a shape corresponding to the surface of the grating structure, and the first surface is a surface of the dielectric layer far away from the grating structure. The grating of the VCSEL is a composite grating with optical mode selection and surface passivation protection, can realize more stable VCSEL polarization direction control, is compatible with the conventional VCSEL production process, and thus obtains the VCSEL with better polarization locking effect at lower manufacturing cost.

Description

Vertical cavity surface emitting laser and manufacturing method thereof

Technical Field

The present disclosure relates to the field of optical technology, and more particularly, to a Vertical Cavity Surface Emitting Laser (VCSEL) and a method for fabricating the same.

Background

A vertical cavity surface emitting laser (vertical cavity surface emitting laser, VCSEL), also known as a vertical cavity surface emitting laser, is a semiconductor laser. The VCSEL has characteristics of a narrow spectrum, low power consumption, low temperature drift, etc. compared to an infrared light emitting diode (infrared light emitting diode, IR LED), an edge emitting laser (edge emitting laser, EEL), etc., and in addition, can be tested during manufacturing, and thus is widely used in various fields, for example, fields of optical communication, optical storage, laser printing, biomedical, optical sensing, etc.

The polarization direction of the VCSEL output laser light is generally random, and in many application fields, a laser output with a stable polarization direction is very important for the whole system, so polarization control of the VCSEL is desired.

Disclosure of Invention

It is an object of the present application to provide a Vertical Cavity Surface Emitting Laser (VCSEL) and a method of manufacturing the same, a vertical cavity surface emitting laser array and a light emitting device to improve stability of polarization control of the VCSEL.

In a first aspect, there is provided a Vertical Cavity Surface Emitting Laser (VCSEL) comprising: a substrate, and a first mirror, an active region and a second mirror formed on the substrate, the active region being located between the first mirror and the second mirror; the VCSEL also includes a grating comprising a grating structure formed within the first material layer and a dielectric layer (or dielectric film) formed on a surface of the grating structure.

The VCSEL has the composite grating, the composite grating can be understood as a single-chip integrated composite grating, compared with the traditional grating, the composite grating integrates the functions of optical mode selection and passivation protection on the surface of a device of the traditional grating, and the passivation protection participates in the optical mode selection function, so that the limitation on the technological parameters of a grating structure is greatly reduced, the technological difficulty is reduced, the conventional VCSEL production process can be adopted to finish manufacturing, and the VCSEL with better polarization locking effect is obtained at lower manufacturing cost.

In one implementation, the first surface of the dielectric layer has a shape corresponding to a surface of the grating structure, and the first surface is a surface of the dielectric layer remote from the grating structure. Therefore, the dielectric layer has shape change which is consistent with the grating structure, the structure change which is consistent with the structure change can enable the composite grating to have good polarization inhibition effect, in addition, filling of the dielectric layer is not needed to be considered in the subsequent manufacturing process, and the process difficulty and the manufacturing cost are synchronously reduced.

In one implementation, the grating structure has a depth of 30-250 nanometers. The depth can reduce the problems of bubbles or incomplete protection and the like caused by over-deep etching depth in the formation process of the grating structure, greatly improves the reliability, realizes more stable polarization control, reduces the requirement of the grating structure with respect to the etching process, can adopt lower-level etching equipment to realize the etching of the grating structure, and greatly reduces the manufacturing cost and difficulty of the grating

In one implementation, the dielectric layer has a thickness of 200-600 nanometers. The combination of the dielectric layer with the thickness range and the grating structure can better control polarization, and particularly can realize a very high rejection ratio at 300-500 nanometers.

In one implementation, the thickness of the dielectric layer is greater than the depth of the grating structure, so that the process requirements on the grating structure can be reduced, polarization can be better controlled, and a very high rejection ratio is realized.

In one implementation, the thicknesses of the dielectric layers of the composite grating tend to be uniform, i.e., the difference in thicknesses of the dielectric layers throughout the grating structure is within a first range, which is the range of process errors during formation of the dielectric layers. The dielectric layer may be formed by deposition, but for process reasons there may be differences in thickness of the dielectric layer throughout the grating structure, but experiments have found that the differences do not affect the stability of the control of the polarization of the grating, and thus the need for additional process steps may also be reduced.

In one implementation, the first material layer is a surface layer of the first mirror, i.e. the grating structure is formed in the surface layer of the first mirror. The surface layer of the first reflecting mirror is a semiconductor material layer, so that a grating structure can be formed on the semiconductor material through an etching process, a good polarization direction locking effect can be achieved, and the process is simple and the manufacturing cost is lower.

In one implementation, the grating structure is a periodic grating structure, the dielectric layer is a periodic dielectric layer, and the period of the grating structure is the same as that of the dielectric layer.

In one implementation, the grating structure has a grating period of 550-1200 nanometers.

In one implementation, the duty cycle of the grating structure is 0.3-0.7.

In a second aspect, a method for manufacturing a vertical cavity surface emitting laser is provided, including:

grating etching is carried out on the first material layer to form a grating structure, wherein the first material layer is a surface layer of the first reflecting mirror or is formed on the surface layer of the first reflecting mirror;

and depositing or extending a dielectric layer on the surface of the grating structure, so that the first surface of the dielectric layer has a shape corresponding to the surface of the grating structure, and forming the composite grating comprising the dielectric layer and the grating structure.

Further, by controlling the process parameters, the fabricated vertical cavity surface emitting laser of the second aspect may be provided with a composite grating as achieved by any of the above first aspects.

According to the manufacturing method of the vertical cavity surface emitting laser, the dielectric film is deposited on the surface of the grating layer, the thickness of the dielectric film at each position of the grating layer is ensured to be equal, the dielectric film can form a wave structure with the same shape as the grating layer, the composite grating formed by combining the grating layer and the dielectric film does not additionally increase the production process, the stable control of the polarization direction of the vertical cavity surface emitting laser and the higher inhibition ratio of the polarization mode are achieved based on the existing grating etching process and the existing dielectric film deposition process; the manufacturing process of the composite grating can be completely compatible with the existing vertical cavity surface emitting laser production process, so that the reliability of a product is guaranteed, the cost is not increased, and the competitiveness of the product is improved.

In addition, the etching process and the photoetching equipment for carrying out grating etching on the surface of the wafer of the vertical cavity surface emitting laser and the deposition process or the epitaxy process for carrying out medium layer growth on the surface of the grating structure can adopt the processes and the equipment which are common to the existing vertical cavity surface emitting laser manufacturers, realize compatibility with the existing vertical cavity surface emitting laser production process, and are beneficial to improving the stability of VCSELs and reducing the cost; the formed monolithic integrated composite grating can realize more stable control of the polarization direction of the vertical cavity surface emitting laser, and has higher inhibition ratio to the polarization mode.

In a third aspect, there is also provided a vertical cavity surface emitting laser array comprising a plurality of VCSELs arranged in an array. The array may be a multi-row multi-column array, or may be a single-row multi-column array, or may be a multi-row single-column array.

In one implementation, the linear polarization of each VCSEL surface output laser in the VCSEL array is independently controllable. For example, the VCSEL array includes a first VCSEL and a second VCSEL having a composite grating of different orientations, e.g., perpendicular. Thus, the application scene of the VCSEL can be further expanded.

In a fourth aspect, there is provided a light emitting device comprising the vertical cavity surface emitting laser of any one of the first aspects and a drive circuit for supplying a drive current to the vertical cavity surface emitting laser.

Drawings

The drawings that accompany the description can be briefly described as follows:

fig. 1 is a schematic structural diagram of a VCSEL according to an embodiment of the present application;

FIG. 2 is a schematic structural diagram of a composite grating according to an embodiment of the present disclosure;

FIG. 3 is a schematic diagram of a VCSEL test result provided in an embodiment of the present application

Fig. 4 is a schematic flow chart of a method for manufacturing a vertical cavity surface emitting laser according to an embodiment of the present application;

fig. 5 is a schematic diagram of a production stage in a VCSEL fabrication process according to an embodiment of the present application;

fig. 6 is a schematic diagram of another stage in the fabrication of a VCSEL according to an embodiment of the present application;

fig. 7 is a schematic diagram of yet another stage in the fabrication of a VCSEL according to an embodiment of the present application;

fig. 8 is a partial cross-sectional view of a VCSEL array according to an embodiment of the present application;

fig. 9 is a top view of a portion of a composite grating of a VCSEL array according to an embodiment of the present application.

Detailed Description

In order to more clearly illustrate the embodiments of the present application or the technical solutions in the prior art, the following description will explain specific embodiments of the present application with reference to the accompanying drawings. The drawings described below are only examples of the present application, and it is apparent to those skilled in the art that other drawings and other embodiments can be obtained from the drawings without inventive effort, and modifications and improvements made without departing from the spirit and scope of the present application.

For simplicity of the drawing, only the parts relevant to the present application are schematically shown in the drawings in the embodiments of the present application, and they do not represent the actual structure thereof as a product. In addition, in order to simplify the drawings for ease of understanding, in some drawings, only one or a portion of a structure or component is schematically depicted (or labeled), and in fact, more identical or similar structures or components may exist.

In the embodiment shown in the drawings, the directions (such as up, down, left, right, front, rear, etc.) are not absolute but relative in describing the respective structures, and are not intended to limit the directions in which the product is actually used.

In this application, ordinal terms such as "first," "second," and the like, are used solely to distinguish between the associated objects and are not to be construed as indicating or implying a relative importance or order between such associated objects unless otherwise expressly specified and defined; in addition, the number of associated objects is not represented. "and/or" is used to describe a relationship between associated objects that includes any of the relationships of associated objects, e.g., "a and/or b" includes: "a alone", "b alone", or "a and b".

The Vertical Cavity Surface Emitting Laser (VCSEL) is a semiconductor laser, has the characteristics of narrow spectrum, low power consumption, low temperature drift and the like, and can be tested in the manufacturing process, so that the VCSEL is widely applied. VCSELs mainly include two mirrors, such as an N-type distributed bragg reflection (distributed Bragg reflector, DBR) and a P-type DBR, and an active region formed between the two mirrors, the active region using, for example, a quantum well structure as a gain medium. An optical cavity (or resonant cavity) is formed between the two reflectors, electrons and holes are combined in the quantum well during current injection to generate photons, the photons are reflected in the optical cavity for multiple times to form laser, and the laser is emitted vertically to the top or bottom of the VCSEL.

The optical cavity structure of the above VCSEL may cause random switching of the polarization mode (or polarization state) of the VCSEL with changes in current and/or temperature. The two reflectors of the conventional VCSEL have isotropy for polarization mode selection, so that the polarization light emitting directions are random, particularly in different current and temperature ranges, frequent polarization mode jumps are easy to occur, the stability of the VCSEL is not facilitated, and the use scene of the VCSEL is limited or the performance of the VCSEL in the use scene is influenced.

In view of the above, the embodiments of the present application utilize dichroism (dichroism) of a grating, so that polarization directions of optical cavities of VCSELs are controlled by different reflection and absorption of polarization modes of different directions of the grating. In addition, in consideration of the manufacturing cost and the effect of polarization control on the VCSEL, the embodiments of the present application propose a composite grating, and the VCSEL with the composite grating, capable of realizing the manufacturing of the VCSEL with the composite grating based on the conventional VCSEL production process on the basis of improving the suppression ratio of the polarization mode of the VCSEL. The following detailed description will be made with reference to the accompanying drawings:

please refer to fig. 1, which is a schematic diagram of a VCSEL structure according to an embodiment of the present application. As shown in fig. 1, the VCSEL100 includes: a substrate 110, a first mirror 120, an active region 130, a second mirror 140, and a composite grating 150 formed on the substrate 110. The active region 130 is located between the first mirror 120 and the second mirror 140; the composite grating 150 includes a grating structure 151 formed within a first material layer and a dielectric layer 152 formed on a surface of the grating structure 151.

In one embodiment, the first material layer is a surface layer 141 of the first mirror 140. I.e. the grating structure 151 is formed in the surface layer 141 of the first mirror 140. The surface layer 141 of the first reflecting mirror 140 is a semiconductor material layer, so that the grating structure 151 can be formed on the semiconductor material through an etching process, and compared with the formation of a dielectric grating on the surface of the semiconductor material through deposition and etching, a better polarization direction locking effect can be achieved, and the process is simple and the manufacturing cost is lower, so that more stable polarization control is realized through a simpler and lower-cost process.

In another embodiment, the first material layer is formed on a surface layer of the first mirror. The first material layer is, for example, a dielectric layer (e.g., siO2 or Si3N 4) deposited on the surface layer of the first mirror, and the grating structure is formed in the dielectric layer by etching, and the dielectric layer of the composite grating is further deposited on the surface of the grating structure.

The VCSEL has the composite grating, the composite grating can be understood as a single-chip integrated (monolithic) composite grating, compared with the traditional grating, the composite grating integrates the function of optical mode selection of the traditional grating and the function of passivation protection on the surface of a device, and the passivation protection participates in the function of optical mode selection, so that the limitation on the technological parameters of a grating structure is greatly reduced, the technological difficulty is reduced, the manufacturing can be completed by adopting the conventional VCSEL production technology, and the VCSEL with better polarization locking effect is obtained with lower manufacturing cost.

The substrate 110 is, for example, a gallium arsenide (GaAs) substrate, an indium phosphide (InP) substrate, or a gallium nitride (GaN) substrate, and the like, and the present application is not limited to a substrate material and may be selected according to a desired wavelength. The first mirror 120 may also be referred to as a lower mirror, the second mirror 140 may also be referred to as an upper mirror, and both the first mirror 120 and the second mirror 140 may be DBRs, e.g., the first mirror 120 is an N-DBR and the second mirror 140 is a P-DBR; for another example, the first mirror 120 is a P-DBR and the second mirror 140 is an N-DBR. The DBR is used as a mirror of an optical cavity, and includes alternately formed high and low refractive index medium or semiconductor material layers, for example, the DBR is formed by alternately epitaxial growth of the high and low refractive index medium or semiconductor material, and is generally a quarter DBR, the thickness of each material layer corresponds to a quarter wavelength, the wavelength is a wavelength for which a targeted increase of reflectivity is desired, and the greater the refractive index difference of the two materials, the higher the reflection efficiency. The light exit surface DBR may be adapted to allow laser light to be emitted through a small reflection coefficient by appropriately reducing the number of layers thereof, for example, the number of layers of the second mirror 140 is smaller than that of the first mirror 120, and in the flip-chip VCSEL, the number of layers of the first mirror 120 is smaller than that of the second mirror 140. The active region 130 may employ, for example, a quantum well structure or a double heterojunction structure, which may be understood as a PN junction formed between the first mirror 120 and the second mirror 140.

Dielectric layer 152, which may also be referred to as a dielectric film, may be formed by deposition or atomic layer epitaxy (atom layer deposition, ALD), which may be formed of a material selected to have passivation protection, such as silicon nitride (Si 3N 4) or silicon dioxide (SiO 2).

Fig. 1 is presented in a cross-sectional view, and a partial structure of the VCSEL is omitted for clarity. For example, the VCSEL further includes a P-type ohmic contact electrode (or P-type contact layer) electrically connected to the P-type DBR, and an N-type ohmic contact electrode (or N-type contact layer) electrically connected to the N-type DBR. For another example, the VCSEL further includes a confinement layer 161 positioned in the second mirror 140, the confinement layer 161 can be formed in one or more layers to reduce the junction capacitance of the VCSEL and increase its modulation bandwidth. Further, the restriction layer 161 has a restriction hole 162. In one implementation, the confinement layer 161 may be an oxidation confinement layer and the oxide holes 161 formed therein, and in another implementation, the confinement layer 161 may be a non-oxidation confinement layer and the non-oxide holes 162 formed therein (as shown in fig. 8). The above composite grating 150 may be formed only over the oxide or non-oxide holes 162 and have a size equal to or greater than the oxide or non-oxide holes 162, which may reduce the difficulty of the post-process. The specific positions of the restriction layer 161 and the restriction hole 162 are not limited herein, for example, the restriction layers on both sides of the restriction hole 162 may have the same size or different sizes, i.e., the restriction hole 162 may be formed at a middle position of the restriction layer or biased to one side.

The embodiment of the application does not simply consider the composite grating formed by the traditional grating and the dielectric layer, but synchronously considers the grating production process and the requirement on polarization suppression of the VCSEL, utilizes the grating structure and the dielectric layer formed on the surface of the grating structure to jointly realize the polarization suppression, achieves better suppression effect, and is compatible with the production process of the traditional VCSEL. The structure of the composite grating is described in further detail below with reference to the accompanying drawings.

Please refer to fig. 2, which is a schematic diagram of a structure of a composite grating according to an embodiment of the present application. As shown in fig. 2, in an embodiment, the first surface 1521 of the dielectric layer 152 has a shape corresponding to the surface 1511 of the grating structure 151, and the first surface 1521 is a surface of the dielectric layer 152 away from the grating structure 151. In this way, the dielectric layer 152 has a shape change which is consistent with the grating structure 151, and the consistent structure change can enable the composite grating to have a good polarization inhibition effect, and in addition, filling of the dielectric layer 152 is not needed to be considered in the subsequent manufacturing process, so that the process difficulty and the manufacturing cost are synchronously reduced.

In one embodiment, the thicknesses of the dielectric layers 152 of the composite grating 150 tend to be uniform, i.e., the difference in thicknesses of the dielectric layers 152 across the grating structure 151 is within a first range, which is a range of process errors during formation of the dielectric layers 152. The dielectric layer may be formed by deposition, but for process reasons there may be differences in thickness of the dielectric layer throughout the grating structure, but experiments have found that the differences do not affect the stability of the control of the polarization of the grating, and thus the need for additional process steps may also be reduced.

With continued reference to fig. 2, in one embodiment, the depth D of the grating structure 151 is 30-250 nm (including the boundary value). The depth D can reduce the problems of bubbles or incomplete protection and the like caused by over-deep etching depth in the formation process of the grating structure, greatly improves the reliability, realizes more stable polarization control, reduces the requirement of the grating structure on the etching process, can adopt lower-level etching equipment to realize the etching of the grating structure, and greatly reduces the manufacturing cost and difficulty of the grating.

With continued reference to fig. 2, in one embodiment, the dielectric layer 152 has a thickness N of 200-600 nm (including the boundary value). Further, 300-500 nanometers (including boundary values). The combination of dielectric layer 152 with a thickness range with grating structure 151 allows better control of polarization, especially at 300-500 nm, and very high rejection ratios.

In an embodiment, the thickness N of the dielectric layer 152 is greater than the depth D of the grating structure 151, so that the process requirement on the grating structure can be reduced, and the polarization can be better controlled, so as to achieve a very high suppression ratio.

With continued reference to fig. 2, in one embodiment, the grating structure 151 is a periodic grating structure, the dielectric layer 152 is a periodic dielectric layer, and the period of the grating structure 151 and the period of the dielectric layer 152 are the same, so that the composite grating 150 is a periodic grating. The grating structure includes a periodic grating structure and an aperiodic grating structure, and the control of the polarization direction of the VCSEL is easier to implement with the periodic grating structure. In other embodiments, the grating structure may also be configured as a non-periodic grating structure, without limitation.

In one embodiment, the grating period P of the grating structure 151 is 550-1200 nanometers (including boundary values). Correspondingly, the period of the dielectric layer 152 is 550-1200 nanometers (including boundary values). In one embodiment, the duty cycle M/P of the grating structure 151 is 0.3-0.7 (including the boundary value).

In the prior art, the grating structure is arranged on the surface of the semiconductor material, and the following technical routes are mainly provided: 1. directly etching a surface grating on a surface layer of a semiconductor material; 2. forming a dielectric grating on the surface layer of the semiconductor material by utilizing deposition and etching; 3. a grating structure with extremely complex processes is introduced, such as a high contrast grating (high contrast grating, HCG). However, the above technical route has at least the following technical problems: 1. the effectiveness of polarization control is difficult to ensure; 2. the compatibility with the existing process is low; 3. high costs associated with the introduction of complex processes, such as Deep Ultra Violet (DUV) lithography, electron beam, or nanoimprint, and the like, as well as high reliability risks, and the like. For example, when the surface grating is directly etched on the surface layer of the semiconductor material, for example, the polarization of near infrared light of 850-1200 nm is used as an example, the deep etching is required on the wafer surface of the VCSEL, at least 80 nm-level lithography equipment is required, and in the actual VCSEL production process, the lithography equipment used by common manufacturers is 320 nm-level lithography equipment, which not only requires to replace lithography equipment with higher precision and higher price, but also requires to replace and upgrade the whole production process, personnel and the like, thereby increasing the cost by several times; similarly, introducing a grating structure with more complex process can also cause high cost caused by the complex process, and for a mature industrial production line, upgrading and replacing part of the process can also easily cause the reduction of product stability; for another example, the dielectric grating is manufactured by adopting the processes of deposition and etching, so that uneven grating grooves are easily caused, and the effectiveness of polarization control cannot be ensured.

Therefore, from the standpoint of the actual production process of the manufacturer, if VCSELs that can be put into production and have better polarization suppression effects are to be produced, they have better cost and stability benefits under at least the following conditions: 1. the conventional VCSEL production process and production equipment are not changed, or the conventional VCSEL production process or production equipment can be used for production, and the conventional VCSEL production process and production equipment can be used for realizing the VCSEL with controllable polarization direction and high suppression ratio, so that the production cost of the VCSEL can be reduced or the production cost of the VCSEL is not increased, and the VCSEL performance can be more stable; 2. the grating introduced into the VCSEL is not a complex structure, the grating with the complex structure is realized by a complex production process or photoetching equipment, and the like, so that on one hand, the production cost is increased, on the other hand, the stability of a product is easily reduced, and the grating with the controllable polarization direction and high inhibition ratio of a target can be realized is a relatively simple and easy-to-realize structure; 3. the performance of the VCSEL is excellent enough, that is, not only the polarization direction can be controlled stably, but also the suppression ratio to the polarization mode is high enough. The composite grating provided by the embodiment of the application can not only be put into production in a large quantity but also produce the VCSEL with advantages because the conditions are met.

The above dielectric layer 152 assists the polarization of the grating structure 151, and when the same suppression ratio for the laser polarization is reached, the depth of the trench of the grating structure 151 is reduced. By comprehensively considering the depth of the grating structure 151 and the thickness of the dielectric layer 152 and selecting proper parameter values, the suppression ratio of the VCSEL to the laser polarization can reach extremely high degree even if the conventional grating etching process and the conventional dielectric layer 152 deposition process are adopted. For example, when the polarization control is performed on the near infrared light of 850-1200 nanometers, the suppression ratio of the polarization modes of the produced VCSEL can reach 80:1 by adopting the 320 nanometer-level photoetching equipment commonly used by the existing VCSEL manufacturers, and the suppression ratio which can generally meet the basic requirement of the application end is 9:1, so that the polarization suppression effect of the VCSEL is more obvious and the application scene is wider; if the conventional grating is adopted to achieve the same inhibition ratio, the required lithography equipment is at least 80 nanometers, and the lithography equipment with higher precision and higher price is required to be replaced, and the whole production process is required to be replaced or upgraded.

In an embodiment, the grating structure 151 is formed by etching the surface layer 141 of the first reflecting mirror 140 based on the existing etching process for performing grating etching on the wafer surface of the VCSEL, and then the dielectric layer 152 is formed on the surface of the grating structure 151 based on the existing deposition process or epitaxial process of the dielectric layer 152, so that the compatibility between the manufacturing process of the monolithically integrated composite grating 150 and the existing VCSEL production process can be realized, the reliability of the product can be improved, and the cost can not be increased; the composite grating with optical mode selection and surface passivation protection can realize stable VCSEL polarization direction control; in addition, the composite grating can improve the inhibition proportion of the polarization mode of the VCSEL without using high-precision photoetching equipment and production technology, and further improves the performance of the product under the condition of not increasing the production cost. In addition, the production and preparation process of the composite grating provided by the embodiment of the application can be decomposed into a process with each step being accurate and controllable, so that the accuracy and the performance of the whole VCSEL are higher.

Of course, if the technology development, such as the popularization of high-precision lithography equipment, brings about the upgrade of the VCSEL production process, the composite grating according to the embodiments of the present application is also applicable, so that the polarization direction of the VCSEL can be controlled more stably, and the suppression ratio of the polarization mode is higher.

In an embodiment, the cross-section of the grating structure 151 is square, which has low requirements on the process, can reduce the difficulty of the process, and has good inhibition effect. Of course, in other embodiments, the grating structure 151 may be configured in other shapes, such as, but not limited to, an arc shape on the side of each slit of the grating structure, if desired.

For example, the above VCSEL can perform polarization control on near infrared light of 850-1200 nanometers, and near infrared light of 850-1200 nanometers wavelength is a common light of VCSELs. Because the polarization conditions of different wavelengths are different, the parameters of the composite grating can also be different, for example, the embodiment of the application can adopt the combination of accurate strict coupled wave analysis (rigorous coupled wave analysis, RCWA) simulation calculation and process optimization to design the VCSEL with specific light wavelength. The strict coupled wave analysis is a direct and effective electromagnetic field theory, and is widely used in analysis design of gratings of various shapes all the time, by strictly solving maxwell's equations in a grating area, converting the solution problem of maxwell's equations into a solution problem of a characteristic function, obtaining an electromagnetic field expression of the grating area coupled by the characteristic function, and then solving boundary conditions on interfaces of the grating area and other areas to obtain a final diffraction efficiency value. In addition, parameters such as grating period of the grating structure, duty ratio of the grating structure, depth of the grating structure, thickness of the dielectric layer and the like can be flexibly adjusted according to different application scenes of the VCSEL, and the method is not limited.

In one embodiment, reference is made to fig. 3 of the accompanying specification, which shows the power and power ratio (polarization suppression ratio) of VCSELs with the above composite gratings at different temperatures and currents for different polarization directions. As shown in fig. 3, the solid line represents a light power (or power of S polarized light) curve representing the S polarization direction, and the broken line represents a light power (power of P polarized light) curve of the P polarization direction. The abscissa in the drawing represents the current, and the unit is not limited, and is, for example, ampere (a). The ordinate of the graph in the upper left corner represents power, and the unit is not limited, for example, watt (W), which represents the change of the optical power in the P polarization direction and the optical power in the S polarization direction with the current at the temperature of 25 ℃, and it can be seen from the graph that the above composite grating has a good suppression effect on the P polarization direction, so that the optical power in the P polarization direction is close to 0. Similarly, as shown in the upper right corner graph, the composite grating still has good effect of suppressing the P polarization direction at the temperature of 85 ℃. The lower two graphs in the figure show the ratio of the optical power in the S polarization direction to the optical power in the P polarization direction at 25 ℃ and 85 ℃ respectively, so that the polarization suppression ratio is further shown, and the VCSEL with the composite grating can achieve the suppression ratio of the polarization mode as high as 80:1 and is far higher than the suppression ratio 9:1 meeting the basic requirements of an application end, so that the VCSEL has more excellent performance and wider application scene.

The above composite grating can be used not only for the VCSEL shown in fig. 1, but also for flip-chip VCSELs, and also for VCSELs having a multi-junction structure, which can be called multi-junction VCSELs.

In one embodiment, please refer to fig. 4, which is a method for manufacturing a Vertical Cavity Surface Emitting Laser (VCSEL) according to an embodiment of the present application, the method at least includes the following steps:

s410, forming a first reflecting mirror, an active area and a second reflecting mirror on a substrate, wherein the active area is positioned between the first reflecting mirror and the second reflecting mirror.

In one implementation, the first mirror, the active region, and the second mirror may be grown on the substrate using an epitaxial process. The epitaxial process includes, for example, a metal organic chemical vapor deposition (metal organic chemical vapor deposition, MOCVD), a molecular layer epitaxy (molecular layer epitaxy, MLE), or an atomic layer epitaxy (atom layer deposition, ALD), or the like. A wafer with a VCSEL grown in a multilayer structure is obtained.

And S420, carrying out grating etching on the first material layer to form a grating structure, wherein the first material layer is a surface layer of the first reflecting mirror or is formed on the surface layer of the first reflecting mirror.

The first material layer is a surface layer of the first reflecting mirror, and grating etching can be performed on the surface of the wafer of the VCSEL to form a grating structure; when the first material layer is formed on the surface layer of the first mirror, epitaxial growth or deposition may be performed on the wafer surface of the VCSEL to form the first material layer. Before etching, the wafer surface of the VCSEL can be cleaned; referring to fig. 5, the surface of the first mirror of the VCSEL is prepared for cleaning in a manner that uses a general cleaning process known in the art to make the surface of the first mirror sufficiently smooth and clean without affecting subsequent etching.

Referring to fig. 6, in one implementation, a conventional etching process for performing grating etching on a wafer surface of a VCSEL may be used to etch a surface of a first mirror to form a grating structure, where a grating period, a duty cycle, and a depth of the grating structure are adjusted according to an outgoing wavelength of the VCSEL to be produced, and a range of values may refer to the above embodiments.

And S430, depositing or extending a dielectric layer on the surface of the grating structure to form the composite grating comprising the dielectric layer and the grating structure.

For example, deposition or epitaxy of a dielectric layer is performed on the surface of the grating structure, so that the shape of the dielectric layer tends to be uniform in the grating structure, or the thickness tends to be uniform in all parts of the grating structure.

Referring to fig. 7, after the etching of the grating structure on the wafer surface of the VCSEL is completed, a dielectric layer is deposited or epitaxially deposited on the surface of the grating structure based on the existing deposition or epitaxy process, and the thickness of the dielectric layer is adjusted according to the specific wavelength of the light emitted by the VCSEL to be produced, and the grating period, duty cycle, and depth of the grating structure, which can be specifically referred to the above embodiments.

In addition, the manufacturing method of the VCSEL can further comprise the following steps: etching process to form trenches between different VCSELs; an evaporation process for forming ohmic electrodes in electrical contact with the first and second mirrors, respectively; and a side oxygen process to form an oxidation limiting hole, etc. The embodiments of the present application are not limited thereto.

In the embodiment of the application, grating etching can be performed on the wafer surface of the VCSEL to form a grating structure, and then a deposition or epitaxy process of a dielectric layer is performed on the surface of the grating structure.

Experiments show that the VCSEL manufactured by adopting 320-nanometer-level photoetching equipment commonly used by the existing VCSEL manufacturers through the manufacturing process of the VCSEL has the advantages that when the polarization of near infrared light of 850-1200 nanometers is controlled, the suppression ratio of the polarization mode of the VCSEL is far higher than the suppression ratio which can generally meet the basic requirement of an application end group, and the suppression ratio is 9:1, so that the VCSEL has more excellent performance and wider application scene; if the conventional grating is adopted to achieve the same inhibition ratio, the required lithography equipment is at least 80 nanometers, so that the lithography equipment with higher precision and higher price is required to be replaced, the whole production process is required to be replaced and upgraded, and the production cost is greatly increased.

The method adopts the common process and equipment of the prior VCSEL manufacturer to realize the complete compatibility of the manufacturing process of the single-chip integrated composite grating and the prior VCSEL production process by carrying out grating etching on the surface of the wafer of the VCSEL, photoetching equipment and carrying out dielectric layer deposition or epitaxy on the surface of the grating structure, thereby being beneficial to improving the reliability of products and not increasing the cost; the composite grating with optical mode selection and surface passivation protection can realize more stable VCSEL polarization direction control; in addition, the composite grating can improve the inhibition proportion of the polarization mode of the VCSEL without using high-precision photoetching equipment and production technology, and further improves the performance of the product under the condition of not increasing the production cost; in addition, the dielectric deposition of the composite grating provided by the embodiment of the application can be decomposed into a multi-step deposition process according to the special requirements of different product light-emitting wavelength or reliability protection or the process itself. And each step is accurate and controllable, so that the accuracy and the performance of the whole VCSEL are higher.

In one embodiment, the present application also provides a VCSEL array having integrated thereon a plurality of VCSELs having any of the above composite gratings, the plurality of VCSELs arranged in an array. The array may be a multi-row multi-column array, or may be a single-row multi-column array, or may be a multi-row single-column array, and the input current may be independently controlled.

In one embodiment, the linear polarization of each VCSEL surface output laser in the VCSEL array is independently controllable. For example, the VCSEL array includes a first VCSEL and a second VCSEL having a composite grating of different orientations, e.g., perpendicular.

The above VCSELs with monolithically integrated compound gratings may be integrated on an array chip, enabling each VCSEL of the array chip to have a locked polarization direction. Furthermore, through the arrangement of the grating direction, the polarization direction of each VCSEL can be independently controlled, and the use prospect of the VCSEL is enriched.

Referring to fig. 8 and 9, fig. 8 is a partial cross-sectional view of a VCSEL array according to an embodiment of the present application, and fig. 9 is a top view of a partial composite grating of a VCSEL array according to an embodiment of the present application. For clarity, only 2 VCSELs are shown, and many more VCSELs are possible in the actual product. The VCSEL array 800 includes a plurality of VCSELs, the different VCSELs being isolated by trenches 830, wherein the first VCSEL810 and the second VCSEL820 are independently polarization controlled by respective composite gratings 150-1 and 150-2, and the grating directions of the two composite gratings 150-1 and 150-2 are perpendicular. The composite grating illustrated in fig. 9 is generally circular, and the overall shape of the composite grating is not limited by the present application, and may be, for example, elliptical, polygonal (e.g., triangular, quadrilateral, pentagonal, etc.), or other irregular patterns.

The above figures are for illustration only, as in the above embodiments, there may be more or fewer structural layers in the actual structure, and furthermore, the morphology of the surface layers on both sides of the grating 150-1 and the grating 150-2 is not limited in any way.

The VCSEL or the VCSEL array can be applied to various scenes, such as a laser radar, data communication, consumer electronic products (such as a mobile phone) and the like as a light emitting device, so that a stable light source is provided for the application products, and the performance of the application products is improved, for example, the detection performance of the laser radar is improved; for another example, the 3D perception function of the consumer electronic product is improved, and even the screen can emit light for perception in a required direction while emitting light; for another example, the signal-to-noise ratio of optical communications is improved.

The embodiment of the application also provides a light emitting device, which comprises the VCSEL with the composite grating and a driving circuit, wherein the driving circuit is used for providing driving current for the VCSEL.

In the foregoing embodiments, the descriptions of the embodiments are focused on, and the parts of a certain embodiment that are not described or depicted in detail may be referred to in the related descriptions of other embodiments. Furthermore, the above embodiments can be freely combined as needed. While only a few embodiments of the present application have been shown and described, it will be appreciated by those skilled in the art that changes and modifications may be made without departing from the principles of the present application, such changes and modifications are to be considered as within the scope of the present application.

Claims

1. A vertical cavity surface emitting laser, comprising:

a substrate;

a first mirror, an active region, and a second mirror formed on the substrate, the active region being located between the first mirror and the second mirror;

the composite grating comprises a grating structure formed in a first material layer and a dielectric layer formed on the surface of the grating structure, wherein the first material layer is a surface layer of the first reflecting mirror or is formed on the surface layer of the first reflecting mirror, the first surface of the dielectric layer has a shape corresponding to the surface of the grating structure, and the first surface is the surface of the dielectric layer far away from the grating structure.

2. The vcl laser of claim 1, wherein the grating structure has a depth of 30-250 nm.

3. The vcl according to claim 1 or 2, wherein the dielectric layer has a thickness of 200-600 nm.

4. A vcl as claimed in any of claims 1 to 3, wherein the dielectric layer has a thickness greater than the depth of the grating structure.

5. The vcl as recited in any one of claims 1-4, wherein a difference in thickness of the dielectric layer across the grating structure is within a first range.

6. The vcl laser of any of claims 1-5, wherein the grating structure is a periodic grating structure and the dielectric layer is a periodic dielectric layer.

7. The vcl laser of claim 6, wherein the grating structure has a grating period of 550-1200 nm.

8. The vcl according to claim 6 or 7, wherein the grating structure has a duty cycle of 0.3-0.7.

9. The vcl laser of any of claims 1-8, wherein the first material layer is a surface layer of the first mirror, the surface layer being a semiconductor material layer.

10. A method of fabricating a vertical cavity surface emitting laser, comprising:

forming a first mirror, an active region, and a second mirror on a substrate, the active region being located between the first mirror and the second mirror;

performing grating etching on a first material layer to form a grating structure, wherein the first material layer is a surface layer of the first reflecting mirror or is formed on the surface layer of the first reflecting mirror;

and depositing or extending a dielectric layer on the surface of the grating structure, so that a first surface of the dielectric layer has a shape corresponding to the surface of the grating structure, and forming the composite grating comprising the dielectric layer and the grating structure, wherein the first surface is the surface of the dielectric layer far away from the grating structure.

11. A vcsels array comprising a plurality of vcsels according to any of claims 1-9, the plurality of vcsels being arranged in an array.

12. The vcsel array of claim 11, wherein the plurality of vcsels includes a first vcsels and a second vcsels, wherein a direction of a composite grating of the first vcsels is perpendicular to a direction of a composite grating of the second vcsels.

13. A light emitting device comprising the vertical cavity surface emitting laser according to any one of claims 1 to 9 and a driving circuit for supplying a driving current to the vertical cavity surface emitting laser.