CN112688165A

CN112688165A - Bar semiconductor laser capable of reducing threshold current and preparation method thereof

Info

Publication number: CN112688165A
Application number: CN202011563411.3A
Authority: CN
Inventors: 毛森; 邱智贤; 毛虎; 焦英豪; 谭武烈
Original assignee: Lewei Semiconductor Technology Jiaxing Co ltd
Current assignee: Lewei Semiconductor Technology Jiaxing Co ltd
Priority date: 2020-12-25
Filing date: 2020-12-25
Publication date: 2021-04-20

Abstract

The invention provides a bar semiconductor laser capable of reducing threshold current and a preparation method thereof, wherein the semiconductor laser comprises a first electrode, a second electrode, a substrate, a first limiting layer, a first waveguide layer, an active layer, a second waveguide layer, a second limiting layer, an ohmic contact layer and an insulating layer, wherein the substrate, the first limiting layer, the first waveguide layer, the active layer, the second waveguide layer, the second limiting layer, the ohmic contact layer and the insulating layer are arranged between the first electrode and the second electrode and are sequentially arranged from the first electrode to the second electrode, the ohmic contact layer is provided with an X-ray self-supporting blazed transmission grating layer in contact with the second limiting layer, the contact surface on the substrate is provided with a trapezoidal table, the trapezoidal table is transversely parallel to a cleavage surface of the substrate, the trapezoidal table is longitudinally vertical to the cleavage surface of the substrate, and. The invention can reduce the threshold current and improve the COD power of the cavity surface. And the high resolution of the semiconductor laser can be improved and higher diffraction efficiency can be obtained.

Description

Bar semiconductor laser capable of reducing threshold current and preparation method thereof

Technical Field

The invention relates to the technical field of semiconductor photoelectricity, in particular to a bar semiconductor laser capable of reducing threshold current and a preparation method thereof.

Background

With the development of laser technology, a new application subject, namely laser medicine, is gradually formed, and the unique advantages of laser are achieved, so that many problems which cannot be solved in basic research and clinical application of traditional medicine are solved, and the attention of medical circles at home and abroad is aroused. Semiconductor lasers (DL) are particularly suitable for the manufacture of medical devices due to their small size, light weight, long lifetime, low power consumption, wide wavelength coverage, and the like. In addition, semiconductor lasers are widely used in important fields such as optical fiber communication, optical disc access, spectral analysis, and optical information processing.

The light emitting area of the semiconductor laser is small, and when the semiconductor laser works at high power, the cavity surface needs to bear high optical power density, and the requirement on the anti-disaster-degeneration damage (COD) capacity of the cavity surface is high. The method for improving the COD of the semiconductor laser generally comprises two methods, one is to grow a layer of high band gap material at the cavity surface, the other is to directly form a non-absorption window at the cavity surface by using a quantum well mixing method, and the two methods can reduce the absorption of the cavity surface to light, so that the COD power of the cavity surface is improved.

An AlGaInP semiconductor laser with a growth cavity surface window is described by IEEE JOURNAL OF SELECTED TOPICS IN QUANTUM ELECTRONIC S, VOL.1(1995), pp.728. After the bar is cleaved, a layer of high-band-gap AlGaInP material grows in an MOCVD chamber to reduce the absorption of the chamber surface, so that the COD power is increased by two times, and a semiconductor laser with high power and high reliability is obtained. However, the cleaved bars are small, and a high-precision clamp and a proper tray are needed to realize the growth of the material, so that the method has no strong operability.

The gold transmission grating has simple structure, large solid angle and wide spectrum range, can be conveniently combined with a spatial resolution instrument at the same time, and is widely applied to the fields of laser inertial confinement nuclear fusion plasma diagnosis, X-ray celestial body physics and the like. At present, the use wave band of the gold transmission grating in the fields of plasma diagnosis and astrophysics is required to reach sub-kilo electron volts and even higher energy, and in order to realize high-energy X-ray energy spectrum resolution and obtain higher diffraction efficiency, the groove depth (the height of a gold grating line) is required to be increased to more than 500nm on the basis of improving the linear density of the grating, and the straightness and smoothness of the side wall of the grating line are required to be ensured.

Disclosure of Invention

In view of the above, the present invention is directed to a bar-type semiconductor laser capable of reducing threshold current and a method for manufacturing the same, and aims to improve high resolution, high diffraction efficiency and cavity surface COD power of the semiconductor laser and reduce threshold current.

In view of the above, the present invention provides a bar-type semiconductor laser capable of reducing threshold current, which includes a first electrode, a second electrode, a substrate disposed between the first electrode and the second electrode and sequentially arranged from the first electrode toward the second electrode, a first confinement layer, a first waveguide layer, an active layer, a second waveguide layer, a second confinement layer, an ohmic contact layer, and an insulating layer, wherein the ohmic contact layer is provided with an X-ray self-supporting blazed transmission grating layer in contact with the second confinement layer, the upper contact surface of the substrate is provided with a trapezoidal platform, the trapezoidal platform is transversely parallel to a cleavage surface of the substrate, the trapezoidal platform is longitudinally perpendicular to the cleavage surface of the substrate, and the cleavage surface is a cavity surface of the semiconductor laser.

The transverse section and the longitudinal section of the trapezoid table are isosceles trapezoids, and the lower base angle is 30-60 degrees; the transverse length of the lower bottom surface of the trapezoid table is 5-100 μm, the longitudinal length is 300-1500 μm, and the height of the trapezoid table is 0.2-0.5 μm.

The transverse period of the trapezoidal table distributed on the substrate is 200-.

The first electrode is an N-type electrode, the first limiting layer is an N-type limiting layer, the first waveguide layer is an N-type waveguide layer, the second electrode is a P-type electrode, the second limiting layer is a P-type limiting layer, and the second waveguide layer is a P-type waveguide layer.

The refractive index of the first waveguide layer and the second waveguide layer is lower than that of the active layer.

The band gaps of the first waveguide layer and the second waveguide layer are higher than the band gap of the active layer.

The active layer is a quantum well active layer.

The preparation method of the bar semiconductor laser capable of reducing the threshold current comprises the following steps:

the method comprises the following steps that firstly, an N-type limiting layer, an N-type waveguide layer, an active layer, a P-type waveguide layer, a P-type limiting layer and an ohmic contact layer are epitaxially prepared on a substrate in sequence;

etching the middle part of the ohmic contact layer to form a P-type limiting layer so as to form a grating groove;

step three, preparing an X-ray gold transmission grating according to the size of the grating groove;

step four, installing the X-ray gold transmission grating into a grating groove;

growing an insulating layer above the ohmic contact layer;

step six, forming a strip-shaped current injection area on the insulating layer by utilizing a photoetching method, wherein the size and the position of the current injection area are consistent with the upper surface of the trapezoid table of the substrate;

step seven, sputtering a second electrode on the upper surface of the insulating layer, evaporating a first electrode on the lower surface of the substrate, and carrying out alloying;

taking the longitudinal arrangement period of the trapezoidal platform of the substrate as the length of the tube core cavity, cleaving the trapezoidal platform into bars, and performing cavity surface film coating;

and step nine, taking the transverse arrangement period of the trapezoidal table of the substrate as a tube core period, and cleaving the tube core to form the semiconductor laser.

The preparation method of the X-ray gold transmission grating comprises the following steps:

s1, taking an SOI silicon chip as a substrate, sequentially plating a gold film and a chromium film on the upper surface of the substrate, and plating a silicon nitride film on the lower surface of the substrate to form a substrate;

s2, respectively coating photoresist on the upper surface and the lower surface of the substrate, manufacturing a photoresist mask of a supporting structure on the upper surface of the substrate by utilizing ultraviolet lithography, and manufacturing a photoresist mask of a grating outer frame on the lower surface of the substrate;

s3, respectively removing the silicon nitride film and the chromium film in the non-mask areas on the upper surface and the lower surface of the substrate;

s4, removing the photoresist on the upper surface and the lower surface of the substrate;

s5, coating an anti-reflection film and a photoresist on the upper surface of the substrate in sequence;

s6, making a photoresist grating mask by holographic lithography, wherein the extension direction of the grating mask is vertical to the extension direction of the grating support structure;

s7, transferring the photoresist grating mask pattern into the antireflection film through reactive ion etching;

s8, transferring the photoresist grating mask pattern into the gold film through ion beam etching;

s9, removing the residual photoresist, antireflective film and chromium film on the upper surface of the substrate, and coating a protective adhesive on the lower surface;

s10, putting the substrate into etching liquid consisting of hydrofluoric acid and oxidant for metal catalytic etching;

s11, placing the substrate in a gold plating electrolyte, and electroplating and depositing gold on the upper surface;

s12, removing the protective glue on the lower surface of the substrate, and coating the protective glue on the upper surface of the substrate;

s13, etching the monocrystalline silicon in the non-mask area of the bottom layer;

s14, removing the protective glue on the upper surface;

s15, etching the top monocrystalline silicon;

s16, removing the silicon nitride and the middle SiO in the window₂And cleaning and drying the layer to obtain the X-ray gold transmission grating.

The invention has the beneficial effects that:

1. the periphery of the active layer of the light emitting region is provided with the waveguide layer with low refractive index and high band gap, so that the waveguide with lateral refractive index can be formed, the threshold current is reduced, a non-absorption window can be formed, and the COD power of the cavity surface is improved.

2. According to the invention, the X-ray gold transmission grating is arranged between the P-face electrode and the P-type limiting layer, so that the high resolution of the semiconductor laser is improved and higher diffraction efficiency is obtained. Can meet the requirement of manufacturing the gold transmission grating with large groove depth, steep side wall and smoothness. The semiconductor laser with the transmission grating layer can improve the reliability in medical diagnosis and is more beneficial for doctors to find out treatment means in a targeted manner.

3. The current injection region is formed by only one-time photoetching after epitaxial growth, so that the chip manufacturing process of the semiconductor laser is simplified, the production cost is reduced, and the method is suitable for batch production.

Drawings

In order to more clearly illustrate the embodiments of the present disclosure or the technical solutions in the prior art, the drawings used in the description of the embodiments or the prior art will be briefly described below, it is obvious that the drawings in the following description are only one or more embodiments of the present disclosure, and other drawings can be obtained by those skilled in the art without creative efforts.

FIG. 1 is a schematic transverse cross-sectional view of a bar-type semiconductor laser with reduced threshold current according to the present invention;

FIG. 2 is a schematic view of a structure of a substrate;

FIG. 3 is a cross-sectional view of a substrate coated with Au and Cr films on the upper surface and a silicon nitride film on the lower surface according to an embodiment of the present invention;

FIG. 4 is a cross-sectional view of a photoresist mask with a support structure formed on the upper surface and a photoresist mask with a grating outer frame formed on the lower surface according to an embodiment of the present invention;

FIG. 5 is a cross-sectional view of a structure in which a silicon nitride film is etched on a lower surface and a Cr film is etched on an upper surface according to an embodiment of the present invention;

FIG. 6 is a cross-sectional view of a structure after photoresist removal according to an embodiment of the present invention;

FIG. 7 is a cross-sectional view of a structure in which an antireflective film and a photoresist are sequentially coated on an upper surface according to an embodiment of the present invention;

FIG. 8 is a cross-sectional view of a structure of a photoresist grating mask fabricated by holographic lithography according to an embodiment of the present invention;

FIG. 9 is a cross-sectional view of a structure after transferring a photoresist grating mask to an antireflective film according to an embodiment of the invention;

FIG. 10 is a cross-sectional view of a structure after transferring a photoresist grating mask to a gold film according to an embodiment of the present invention;

FIG. 11 is a cross-sectional view of the structure with the photoresist, antireflective film and Cr film removed from the top surface according to an embodiment of the present invention;

FIG. 12 is a cross-sectional view of a structure of applying a protective adhesive to a lower surface according to an embodiment of the present invention;

FIG. 13 is a cross-sectional view of a structure after a top surface metal catalytic etching process according to an embodiment of the present invention;

FIG. 14 is a cross-sectional view of a structure after gold is electroplated on the top surface according to an embodiment of the present invention;

fig. 15 is a cross-sectional view of the structure provided in the embodiment of the present invention, in which the protective adhesive is removed from the lower surface and the protective adhesive is coated on the upper surface;

FIG. 16 is a cross-sectional view of the structure after etching of the bottom layer of single crystal silicon provided by an embodiment of the present invention;

FIG. 17 is a cross-sectional view of the structure with the protective glue removed from the top surface according to the embodiment of the present invention;

FIG. 18 is a cross-sectional view of the structure after etching of the top layer of monocrystalline silicon on the upper surface according to an embodiment of the invention;

FIG. 19 shows an example of removing silicon nitride and SiO in the middle of the window₂And (4) obtaining a structural cross-sectional view of the X-ray gold transmission grating after the layer.

Labeled as:

1. top layer monocrystalline silicon; 2. intermediate layer of SiO₂(ii) a 3. Bottom layer monocrystalline silicon; 4. a SiN film; 5. an Au film; 6. a Cr film; 7. photoresist; 8. a antireflection film; 9. protective glue; 10. an X-ray gold transmission grating layer; 11. a first electrode; 12. a second electrode; 13. a substrate; 14. a first confinement layer; 15. a first waveguide layer; 16. an active layer; 17. a second waveguide layer; 18. a second confinement layer; 19. an ohmic contact layer; 20. an insulating layer; 21. a light emitting region; 22. a trapezoidal table.

Detailed Description

To make the objects, technical solutions and advantages of the present disclosure more apparent, the present disclosure is further described in detail below with reference to specific embodiments.

It should be noted that technical terms or scientific terms used in the embodiments of the present specification should have a general meaning as understood by those having ordinary skill in the art to which the present disclosure belongs, unless otherwise defined. The use of "first," "second," and similar terms in the embodiments of the specification is not intended to indicate any order, quantity, or importance, but rather is used to distinguish one element from another. The word "comprising" or "comprises", and the like, means that the element or item listed before the word covers the element or item listed after the word and its equivalents, but does not exclude other elements or items. The terms "connected" or "coupled" and the like are not restricted to physical or mechanical connections, but may include electrical connections, whether direct or indirect. "upper", "lower", "left", "right", and the like are used merely to indicate relative positional relationships, and when the absolute position of the object being described is changed, the relative positional relationships may also be changed accordingly.

As shown in fig. 1, a bar-type semiconductor laser capable of reducing threshold current includes a first electrode 11, a second electrode 12, a substrate 13 disposed between the first electrode 11 and the second electrode 12 and sequentially arranged from the first electrode 11 toward the second electrode 12, a first confinement layer 14, a first waveguide layer 15, an active layer 16, a second waveguide layer 17, a second confinement layer 18, an ohmic contact layer 19, and an insulating layer 20, wherein the ohmic contact layer 19 is provided with an X-ray self-supporting blazed transmission grating layer in contact with the second confinement layer 18, a trapezoidal mesa 22 is disposed on a contact surface on the substrate 13, the trapezoidal mesa is laterally parallel to a cleavage surface of the substrate 13, the trapezoidal mesa is vertically perpendicular to the cleavage surface of the substrate 13, and the cleavage surface is a cavity surface of the semiconductor laser.

Wherein, the substrate is a GaAs (100) single chip. The substrate may be InP, GaN, or Al₂O₃SiC or Si. The first waveguide layer and the second waveguide layer are made of Al_0.5In_0.5P, band gap 2.3eV, refractive index 3.2. The first limiting layer is tightly contacted with the substrate, and the first waveguide layer at the corner of the trapezoidal table is notCan be broken.

As shown in fig. 2, an upwardly convex trapezoidal mesa 22 is distributed on the surface of the substrate in contact with the first waveguide layer. The trapezoidal mesa has a lateral direction (corresponding to the direction of the side of the substrate positioned at the bottom side in fig. 2) parallel to the cleavage plane of the substrate and a longitudinal direction (corresponding to the vertical direction of the side of the substrate positioned at the bottom side in fig. 2) perpendicular to the cleavage plane of the substrate.

In a preferred embodiment, the transverse section and the longitudinal section of the trapezoid table 22 are isosceles trapezoids, and the lower base angle is 30-60 degrees; the transverse length of the lower bottom surface of the trapezoid table 22 is 5-100 μm, the longitudinal length is 300-1500 μm, and the height of the trapezoid table 22 is 0.2-0.5 μm.

In a preferred embodiment, the trapezoidal mesa 22 is arranged on the substrate with a lateral period of 200-.

In a preferred embodiment, the active layer is (Al)_0.5Ga_0.5)_0.5In_0.5P/Ga_0.5In_0.5The total thickness of the P quantum well structure is 0.1-0.3 μm, and is smaller than the height of the trapezoid table. Quantum well Ga_0.5In _0.5P has a band gap of 1.9eV and a refractive index of 3.6.

In a preferred embodiment, the refractive index of the first waveguide layer and the second waveguide layer is lower than the refractive index of the active layer. The band gaps of the first waveguide layer and the second waveguide layer are higher than the band gap of the active layer 5.

As shown in fig. 1 and 2, the light emitting region 21 generated by the active layer is surrounded by the first waveguide layer. Al (Al)_0.5In_0.5P and Ga_0.5In_0.5The refractive index difference of P is 0.4, a strong-refractive-index waveguide structure is formed, the lateral mode of the laser can be well limited, and the threshold current is reduced. Al (Al)_0.5In_0.5P and Ga_0.5In_0.5The band gap difference of P is 0.4eV, and the quantum well Ga_0.5In_0.5P emitted laser light will notIs covered with Al_0.5In_0.5The P material absorbs, a non-absorption window is formed at the cavity surface, and the COD power is improved.

In this embodiment, the first electrode 11 is an N-type electrode, the first confinement layer 14 is an N-type confinement layer, the first waveguide layer 15 is an N-type waveguide layer, the second electrode 12 is a P-type electrode, the second confinement layer 18 is a P-type confinement layer, and the second waveguide layer 17 is a P-type waveguide layer. The N-type limiting layer is made of an N-type AlGaAs material, and can effectively limit an optical field. The P-type limiting layer is made of AlxGa 1-xAs. The P-type confinement layer is formed on the P-type waveguide layer.

The invention also provides a preparation method of the bar semiconductor laser capable of reducing the threshold current, which comprises the following steps:

the method comprises the following steps that firstly, an N-type limiting layer, an N-type waveguide layer, an active layer 16, a P-type waveguide layer, a P-type limiting layer and an ohmic contact layer 19 are epitaxially prepared on a substrate 13 in sequence; the N-type substrate is a gallium arsenic substrate with a (100) plane deviated from a <111> direction by 15 degrees of an N-type deviation angle. On one hand, the formation of a metastable state ordered structure in the growth process can be inhibited by selecting a (100) plane 15-degree N-type deflection angle gallium arsenic substrate deviating from the <111> direction; on the other hand, the doping concentration of P-type impurities in the limiting layer can be improved, the effective potential barrier of electrons is improved, the electron leakage of the active layer is inhibited, and the preparation of a high-power semiconductor laser is facilitated.

Etching the middle part of the ohmic contact layer 19 to form a P-type limiting layer so as to form a grating groove;

growing an insulating layer above the ohmic contact layer;

step seven, thinning the back of the substrate to 80-120 mu m, sputtering a second electrode on the upper surface of the insulating layer, evaporating a first electrode on the lower surface of the substrate, and alloying;

s1, taking an SOI silicon chip as a substrate, sequentially plating a gold film and a chromium film on the upper surface of the substrate, and plating a silicon nitride film on the lower surface of the substrate to form a substrate; in the embodiment of the invention, the top layer monocrystalline silicon can be<110>The crystal orientation,<111>Crystal orientation or<100>Crystal orientation of wherein<100>The top layer of the crystal orientation has the best effect, and the bottom layer of the crystal orientation can be monocrystalline silicon<110>Crystal orientation or<100>And (4) crystal orientation. The structural parameters of the SOI silicon wafer adopted in the embodiment of the invention are as follows: the top layer of monocrystalline silicon is<100>The crystal orientation is 2-10 microns thick; intermediate layer of SiO₂The thickness of (A) is 1-2 microns; the bottom layer of monocrystalline silicon is<100>Crystal orientation, thickness of 300-500 micron, wherein, top layer monocrystalline silicon, middle layer SiO₂And the thickness of the underlying monocrystalline silicon is designed based on the requirements of the product. FIG. 2 is a cross-sectional view of a substrate with an Au film 5 and a Cr film 6 plated on the upper surface and a SiN film 4 (silicon nitride film) plated on the lower surface, according to an embodiment of the present invention, wherein the Au film is deposited by magnetron sputtering, ion beam sputtering, or electron beam evaporation, and the thickness of the Au film is 15nm to 30 nm; because the Cr film is easy to be stripped from the SOI silicon wafer under the action of the Cr removing liquid, the Cr film is used as an intermediate layer of a transfer grating supporting structure, the Cr film is plated by adopting an electron beam evaporation or ion beam sputtering method, the thickness of the Cr film must be larger than that of the catalytic metal so as to protect the catalytic metal under the Cr film from being etched, and experiments prove that the requirement can be met when the thickness is larger than 100 nm; the silicon nitride film and the monocrystalline silicon have similar structures, so that the silicon nitride film and the monocrystalline silicon have strong adhesive force, the silicon nitride film and the monocrystalline silicon do not fall off in the later ultrasonic cleaning process, and the silicon nitride does not react with the potassium hydroxide etching solution for windowing the lower surface of the silicon wafer, so that the silicon nitride film is used as a protective layer for manufacturing the grating outer frame structure, and the PECVD (plasma enhanced chemical vapor deposition) method can be adopted for manufacturing the grating outer frame structurePlating to a thickness of more than 40 nm.

S2, respectively coating photoresist 7 on the upper surface and the lower surface of the substrate, manufacturing a supporting structure photoresist 7 mask on the upper surface of the substrate by utilizing ultraviolet lithography, and manufacturing a grating outer frame photoresist 7 mask on the lower surface of the substrate; FIG. 3 is a structural cross-sectional view of a grating support structure mask made on the upper surface and a grating outer frame mask made on the lower surface, wherein the grating support structure mask is a line array, the period is preferably 10-20 micrometers, the line width is 2-3 micrometers, the grating outer frame mask image is an orthogonal grid, the width of the grid bars is 1-2 millimeters, and the interval of the grid bars is 4-6 millimeters.

The photoresist is a positive photoresist, such as AZ MIR-701, the coating thickness (500-1000) nm is preferred, the photoresist is coated by using a rotary coating method, and the thickness can be adjusted by adjusting the rotating speed and the proportion of a solvent in the photoresist according to the use instruction of the photoresist. The gluing process is as follows: coating the surface, and baking; then coating the lower surface, and then baking the glue. The baking condition can refer to the photoresist application instruction, and for the AZ MIR-701 photoresist, the single baking parameter is baking for 2 minutes at 90 ℃ of a hot table. The ultraviolet lithography uses a URE-2000/35 type ultraviolet lithography machine of photoelectric technology research institute of Chinese academy of sciences, and the specific process conditions can refer to the photoresist use instruction and the lithography machine use instruction. Because the selected positive photoresist is adopted, the pattern of the photoetching mask is consistent with the target pattern. The process of ultraviolet photoetching comprises the following steps: exposing the upper surface in a contact manner; lower surface contact exposure; and (6) developing.

S3, respectively removing the silicon nitride film and the chromium film in the non-mask areas on the upper surface and the lower surface of the substrate; FIG. 4 is a cross-sectional view of a structure in which a silicon nitride film is etched on a lower surface and a Cr film is etched on an upper surface according to an embodiment of the present invention; for the etching of the silicon nitride film, an ICP-98A type induction coupling plasma etching machine developed by microelectronics of Chinese academy of sciences is used, the etching depth of the silicon nitride film is controlled by controlling the flow rate of reaction gas, the power of an excitation power supply, the power of a bias power supply and the etching time, and a large number of experiments prove that for the silicon nitride film with the thickness of 40nm, the adopted etching conditions are as follows: reaction gas CF₄(ii) a Flow rate of 20sccm, laserExcitation power 300W, bias power 75W, time 90 s. And (3) etching the Cr film by using a Cr removing liquid wet method, wherein the Cr removing liquid is prepared by mixing cerium ammonium nitrate: glacial acetic acid: water is mixed according to the mass ratio of 20:3: 100. Since the etching is isotropic, the etching time cannot be too long, otherwise the lateral undercutting effect will cause the Cr mask lines to disappear. The specific etching time can be obtained by experiment.

S4, removing the photoresist 7 on the upper surface and the lower surface of the substrate; the photoresist on the upper surface and the lower surface is removed by acetone ultrasonic, and the structural cross-sectional view after the photoresist is removed is shown in fig. 5.

S5, coating an antireflective film 8 and a photoresist 7 on the upper surface of the substrate in sequence; fig. 6 is a cross-sectional view of a structure in which an antireflective film and a photoresist are sequentially coated on an upper surface according to an embodiment of the present invention, in order to reduce a standing wave effect in holographic exposure, before a photoresist 7 is coated, a layer of antireflective film 8 is coated on a prepared substrate, the antireflective film is selected from a series of Brewer Science, and a positive photoresist is selected from AZ MIR-701. The thickness of the antireflective film is about 150nm, and the thickness of the photoresist is about 300 nm. The specific process conditions can refer to the application specifications of the antireflective film and the photoresist.

S6, making a photoresist 7 grating mask by holographic lithography, wherein the extension direction of the grating mask is vertical to the extension direction of the grating support structure; fig. 7 is a cross-sectional view of a structure of a grating mask manufactured by holographic lithography according to an embodiment of the present invention, which is obtained by performing holographic exposure on an exposure light path of a laemon lens, developing the exposure light path to obtain a photoresist grating mask, wherein an extending direction of the support structure mask is parallel to an optical platform during exposure, and an extending direction of interference fringes that generate a pattern of the photoresist grating mask is perpendicular to the optical platform, so that the photoresist grating mask obtained by development is naturally perpendicular to the support structure, and the holographic lithography is a conventional process means, and detailed description of a specific operation process is omitted.

S7, transferring the grating mask pattern of the photoresist 7 into the antireflection film 8 through reactive ion etching; fig. 8 is a structural cross-sectional view of transferring a photoresist grating mask to an antireflective film according to an embodiment of the present invention, in which an ICP-98A type inductively coupled plasma etcher developed by microelectronics of the chinese academy of sciences is used, and the etching depth of the antireflective film is controlled by controlling the reaction gas flow, the excitation power, the bias power, and the etching time, and finally the photoresist grating mask pattern is transferred to the antireflective film to form the antireflective film 8 of the grating structure.

S8, transferring the photoresist 7 grating mask pattern into the gold film through ion beam etching; fig. 9 is a cross-sectional view of the structure after transferring the photoresist grating mask to the gold film according to the embodiment of the present invention, in which the photoresist grating mask pattern is transferred to the gold film by using the conventional ion beam etching.

S9, removing the residual photoresist 7, the antireflective film 8 and the chromium film on the upper surface of the substrate, and coating the protective glue 9 on the lower surface; FIG. 10 is a cross-sectional view of the structure after the photoresist, the antireflective film and the Cr film have been removed according to the embodiment of the present invention; in particular to

The photoresist and the antireflective coating (ARC) were removed by acetone sonication, and the Cr coating was removed by Cr removal liquid sonication. FIG. 11 is a cross-sectional view of a structure of the protective adhesive coated on the lower surface according to an embodiment of the present invention, wherein the protective adhesive 9 is made of the protective adhesive of Brewer Science. The specific process conditions of coating the Primer first and then coating can refer to the use instruction.

S10, putting the substrate into etching liquid consisting of hydrofluoric acid and oxidant for metal catalytic etching; fig. 12 is a cross-sectional view of the structure after the catalytic etching process of the upper surface metal provided by the present invention. The oxidant can be hydrogen peroxide, potassium permanganate or silver nitrate, the concentration and the etching temperature of each component of the specific etching solution can be obtained through a contrast experiment, the optimal target is to etch a grating structure with a smooth and steep side wall, the hydrogen peroxide is taken as the oxidant for example, the concentration of hydrofluoric acid in the etching solution is (4-6) mol/L, the concentration of hydrogen peroxide is (0.2-0.3) mol/L, when the temperature of the etching solution is (5-15) DEG C, the obtained grating structure is steep and the side wall is smooth, the roughness of the grating side wall is about 1nm, the etching time is determined by the etching depth and the etching rate, the etching depth is the thickness of the top silicon, and the etching rate can be measured through experiments.

S11, placing the substrate in a gold plating electrolyte, and electroplating and depositing gold on the upper surface; FIG. 13 is a cross-sectional view of the structure after gold is electroplated on the upper surface.

S12, removing the protective adhesive 9 on the lower surface of the substrate, and coating the protective adhesive 9 on the upper surface of the substrate; and (3) removing the alkali-resistant protective glue by using a Piranha solution, and removing the alkali-resistant protective glue by using a water bath for 30 minutes at the water bath temperature of 80 ℃, wherein fig. 14 is a structural cross-sectional view of the protective glue removed from the lower surface and the protective glue coated on the upper surface. The protective glue 9 is the protective glue of Brewer Science. The specific process conditions of coating the Primer first and then coating can refer to the use instruction.

S13, etching the monocrystalline silicon in the non-mask area of the bottom layer; fig. 15 is a cross-sectional view of the structure after etching the lower surface single crystal silicon according to the embodiment of the present invention, in which a KOH aqueous solution with a mass fraction of 30% is used as an etching solution, the etching temperature is 80 ℃, and the etching time is longer than 6 hours. Etching to intermediate SiO₂In the case of the layer, a smooth bottom surface is visible, at which point the etching can be stopped.

S14, removing the protective glue 9 on the upper surface; the alkali-resistant protective glue is removed by using a Piranha solution, the alkali-resistant protective glue can be removed by water bath for 30 minutes at the water bath temperature of 80 ℃, and the structural cross-sectional view of the upper surface of the protective glue removed is shown in fig. 16.

S15, etching the top monocrystalline silicon 1; fig. 17 is a cross-sectional view of the structure after etching the top-layer single-crystal silicon, which is provided by the embodiment of the present invention, and a KOH aqueous solution with a mass fraction of 30% is used as an etching solution, the etching temperature is 80 ℃, and the etching time is longer than 6 hours. Etching to intermediate SiO₂In the case of the layer, a smooth bottom surface is visible, at which point the etching can be stopped.

And S16, removing the silicon nitride and the middle SiO2 layer in the window, cleaning and drying to obtain the X-ray gold transmission grating. Soaking in 48% hydrofluoric acid for 8 min to remove silicon nitride and SiO in the window₂Layer, removal of silicon nitride and intermediate SiO₂The cross-sectional view of the structure after lamination is shown in fig. 18. And (3) cleaning with deionized water, and drying the sample by using a carbon dioxide critical point dryer so as to solve the problem of grating line adhesion caused by drying in the air. The dryer is a carbon dioxide critical point dryer of Quorum E3100 in UK, and the specific operation method can refer to the specification.

The preparation method further comprises the steps of after edge lines of the epitaxial wafer with the electrodes are cleaved, depositing a highly compact passivation layer on the front cavity surface and the rear cavity surface of the semiconductor laser through an atomic layer deposition method, then depositing an antireflection film on the passivation layer on the front cavity surface, and depositing a high reflection film on the passivation layer on the rear cavity surface.

the method comprises the following steps that firstly, an N-type limiting layer, an N-type waveguide layer, an active layer 6, a P-type waveguide layer, a P-type limiting layer and an ohmic contact layer 9 are epitaxially prepared on a substrate 3 in sequence; the N-type substrate is a gallium arsenic substrate with a (100) plane deviated from a <111> direction by 15 degrees of an N-type deviation angle. On one hand, the formation of a metastable state ordered structure in the growth process can be inhibited by selecting a (100) plane 15-degree N-type deflection angle gallium arsenic substrate deviating from the <111> direction; on the other hand, the doping concentration of P-type impurities in the limiting layer can be improved, the effective potential barrier of electrons is improved, the electron leakage of the active layer is inhibited, and the preparation of a high-power semiconductor laser is facilitated.

Etching the middle part of the ohmic contact layer 9 to form a P-type limiting layer so as to form a grating groove;

step three, preparing a transmission grating according to the size of the grating groove;

step four, installing the transmission grating into the grating groove;

preparing a P-type electrode on the epitaxial wafer;

and seventhly, thinning and polishing the substrate 3 to prepare the N-type electrode. And preparing a P-type electrode and an N-type electrode on the epitaxial wafer, wherein the electrodes are electrode materials capable of forming good ohmic contact with gallium arsenic materials, the P-type electrode is prepared by adopting a sputtering method, and the N-type electrode is prepared by adopting an evaporation method.

The preparation method of the transmission grating comprises the following steps:

s1, taking an SOI silicon chip as a substrate, plating a Cr film 14 on the upper surface of the substrate, and plating a silicon nitride film 15 on the lower surface of the substrate; the structural parameters of the SOI silicon wafer adopted in the embodiment of the invention are as follows: the top layer of monocrystalline silicon is<100>Crystal orientation, thickness (2-10) micron; intermediate layer of SiO₂Thickness ofIs (1-2) micron; the bottom layer of monocrystalline silicon is<100>Crystal orientation and thickness (300-500) microns, wherein the top layer of monocrystalline silicon and the middle layer of SiO₂And the thickness of the underlying single crystal silicon is designed based on the requirements of the product. Fig. 2 is a structural cross-sectional view of a substrate with a Cr-plated upper surface and a silicon nitride-plated lower surface according to an embodiment of the present invention, in which the Cr film is easily peeled off from the SOI wafer by a Cr-removing solution, and thus the Cr film is used as an intermediate layer of a transfer grating support structure, the Cr film is plated by an electron beam evaporation or ion beam sputtering method, the thickness of the Cr film must be greater than that of a catalytic metal, so that the Cr film can be removed by the Cr-removing solution, and experiments prove that a thickness greater than 100nm can meet requirements; the silicon nitride film and the monocrystalline silicon have similar structures, so that the silicon nitride film and the monocrystalline silicon have strong adhesive force, the silicon nitride film and the monocrystalline silicon do not fall off in the later ultrasonic cleaning process, and the silicon nitride does not react with the potassium hydroxide etching solution for windowing the lower surface of the silicon wafer, so that the silicon nitride film is used as a protective layer for manufacturing the grating outer frame structure, and can be plated by adopting a PECVD (plasma enhanced chemical vapor deposition) method, and the thickness is more than 40 nm.

S2, respectively coating photoresist 19 on the upper surface and the lower surface of the substrate, manufacturing a grating supporting structure mask on the upper surface by utilizing ultraviolet lithography, and manufacturing a grating outer frame mask on the lower surface; FIG. 3 is a structural cross-sectional view of a grating support structure mask made on the upper surface and a grating outer frame mask made on the lower surface, wherein the grating support structure mask is a line array, the period is preferably 10-20 micrometers, the line width is 2-3 micrometers, the grating outer frame mask image is an orthogonal grid, the width of the grid bars is 1-2 millimeters, and the interval of the grid bars is 4-6 millimeters. The photoresist is a positive photoresist, such as AZ MIR-701, the coating thickness (500-1000) nm is preferred, the photoresist is coated by using a rotary coating method, and the thickness can be adjusted by adjusting the rotating speed and the proportion of a solvent in the photoresist according to the use instruction of the photoresist. The gluing process is as follows: coating the surface, and baking; then coating the lower surface, and then baking the glue. The baking condition can refer to the photoresist application instruction, and for the AZ MIR-701 photoresist, the single baking parameter is baking for 2 minutes at 90 ℃ of a hot table. The ultraviolet lithography uses a URE-2000/35 type ultraviolet lithography machine of photoelectric technology research institute of Chinese academy of sciences, and the specific process conditions can refer to the photoresist use instruction and the lithography machine use instruction. Because the selected positive photoresist is adopted, the pattern of the photoetching mask is consistent with the target pattern. The process of ultraviolet photoetching comprises the following steps: exposing the upper surface in a contact manner; lower surface contact exposure; and (6) developing.

S3, etching the silicon nitride film 15 on the lower surface through reactive ions, and etching the Cr film 14 on the upper surface through a wet method; FIG. 4 is a cross-sectional view of a structure in which a silicon nitride film is etched on a lower surface and a Cr film is etched on an upper surface according to an embodiment of the present invention; for the etching of the silicon nitride film, an ICP-98A type induction coupling plasma etching machine developed by microelectronics of Chinese academy of sciences is used, the etching depth of the silicon nitride film is controlled by controlling the flow rate of reaction gas, the power of an excitation power supply, the power of a bias power supply and the etching time, and a large number of experiments prove that for the silicon nitride film with the thickness of 40nm, the adopted etching conditions are as follows: reaction gas CF₄(ii) a The flow rate is 20sccm, the excitation power supply power is 300W, the bias power supply power is 75W, and the time is 90 s. And (3) etching the Cr film by using a Cr removing liquid wet method, wherein the Cr removing liquid is prepared by mixing cerium ammonium nitrate: glacial acetic acid: water is mixed according to the mass ratio of 20:3: 100. Since the etching is isotropic, the etching time cannot be too long, otherwise the lateral undercutting effect will cause the Cr mask lines to disappear. The specific etching time can be obtained by experiment.

S4, removing the photoresist 19 on the upper surface and the lower surface; the photoresist on the upper surface and the lower surface is removed by acetone ultrasonic, and the structural cross-sectional view after the photoresist is removed is shown in fig. 5.

S5, coating an antireflective film 18 and a photoresist 19 on the upper surface of the substrate in sequence; fig. 6 is a cross-sectional view of a structure in which an antireflective film and a photoresist are sequentially coated on an upper surface according to an embodiment of the present invention, in order to reduce a standing wave effect in holographic exposure, before the photoresist is coated, a layer of antireflective film is coated on a prepared substrate, the antireflective film is selected from a series of Brewer Science, and the positive photoresist is selected from AZ MIR-701. The thickness of the antireflective film is about 150nm, and the thickness of the photoresist is about 300 nm.

S6, holographic photoetching is carried out to manufacture a grating mask, and the extending direction of the grating mask is vertical to the extending direction of the grating support structure mask; fig. 7 is a cross-sectional view of the photoresist grating mask according to the embodiment of the present invention, in which a holographic exposure is performed on a laemoscope exposure light path, and the photoresist grating mask is obtained after development, and when exposure is performed, the extending direction of the support structure mask is parallel to the optical platform, and the extending direction of the interference fringes that generate the photoresist grating mask pattern is perpendicular to the optical platform, so that the photoresist grating mask obtained by development is naturally perpendicular to the support structure.

S7, transferring the grating mask pattern of the photoresist 19 into the antireflection film 18 by reactive ion etching; fig. 8 is a structural cross-sectional view of transferring a photoresist grating mask to an antireflective film according to an embodiment of the present invention, where an etching depth of the antireflective film is controlled by controlling a reaction gas flow rate, an excitation power supply power, a bias power supply power, and an etching time, and finally, a photoresist grating mask pattern is transferred to the antireflective film to form the antireflective film of the grating structure.

S8, depositing catalytic metal on the upper surface of the substrate vertically downwards, where fig. 9 is a cross-sectional view of the structure after plating the catalytic metal according to the embodiment of the present invention, where the catalytic metal is gold, silver, or platinum; and depositing by adopting an ion beam sputtering or electron beam evaporation coating method to obtain the grating structure of the catalytic metal film.

S9, removing the photoresist 19, the antireflective film 18, the Cr film 14 and the catalytic metal attached to the photoresist 19 and the Cr film 14; the anti-reflective coating (ARC), the photoresist and the catalytic metal on the photoresist are removed by using acetone ultrasound, the Cr and the catalytic metal on the Cr are removed by using Cr-removing liquid ultrasound, and fig. 10 is a cross-sectional view of a structure for removing the anti-reflective coating, the photoresist, the Cr film and the catalytic metal attached to the photoresist and the Cr film according to an embodiment of the present invention.

S10, coating alkali-resistant protective glue 21 on the upper surface of the substrate; as shown in fig. 11.

S11, corroding the monocrystalline silicon on the lower surface until the corrosion is stopped to reach the middle SiO2 layer; fig. 12 is a cross-sectional view of the structure after etching the lower surface single crystal silicon according to the embodiment of the present invention, in which a KOH aqueous solution with a mass fraction of 30% is used as an etching solution, the etching temperature is 80 ℃, and the etching time is longer than 6 hours. Etching to intermediate SiO₂When the layer is formed, the smooth bottom surface can be seen,at this point, the etching is stopped.

S12, removing the alkali-resistant protective glue 21; the alkali-resistant protective glue is removed by using a Piranha solution, and the alkali-resistant protective glue can be removed by using a water bath for 30 minutes at the water bath temperature of 80 ℃, and the structural cross-sectional view after the alkali-resistant protective glue is removed is shown in fig. 13.

S13, removing the silicon nitride and the middle SiO in the window₂A layer; soaking in 48% hydrofluoric acid for 8 min to remove silicon nitride and SiO in the window₂A cross-sectional view of the structure after removal of the silicon nitride and intermediate SiO2 layers is shown in fig. 14.

S14, putting the substrate into etching liquid consisting of hydrofluoric acid and oxidant for metal catalytic etching; the oxidant can be hydrogen peroxide, potassium permanganate or silver nitrate, the concentration of each component of the specific etching solution and the etching temperature can be obtained through a contrast experiment, the optimal target is to etch a grating structure with a smooth and steep side wall, the hydrogen peroxide is taken as the oxidant, the concentration of hydrofluoric acid in the etching solution is (4-6) mol/L, the concentration of hydrogen peroxide is (0.2-0.3) mol/L, and when the temperature of the etching solution is (5-15) DEG C, the obtained grating structure is steep and the side wall is smooth.

And S15, removing the catalytic metal, rinsing and drying to obtain the X-ray self-supporting blazed transmission grating.

In addition, as a further improvement, the preparation method further comprises the steps of cleaving an edge line of the epitaxial wafer with the electrode, depositing a highly dense passivation layer on the front cavity surface and the rear cavity surface of the semiconductor laser through an atomic layer deposition method, then depositing an anti-reflection film on the passivation layer on the front cavity surface, and depositing a high-reflection film on the passivation layer on the rear cavity surface. The highly dense passivation layer has a thickness of 10nm and is made of Si₃N₄. The passivation layer is highly dense, so that the highly dense passivation layer can more effectively prevent other atoms from entering the cavity surface material through the passivation layer compared with the conventional passivation method, thereby preventing optical catastrophe of the cavity surface, improving the damage threshold of the cavity surface, improving the power of the semiconductor laser and prolonging the service life of the semiconductor laser. Prevent oxygen in the air from oxidizing and damaging the cavity surface, and can omit the cleaning step before preparing the passivation film, thereby preventing the cleaning step from damaging the cavity surfaceThis preserves the integrity of the facet structure to the maximum extent possible.

Those of ordinary skill in the art will understand that: the discussion of any embodiment above is meant to be exemplary only, and is not intended to intimate that the scope of the disclosure, including the claims, is limited to these examples; within the idea of the present disclosure, also technical features in the above embodiments or in different embodiments may be combined, steps may be implemented in any order, and there are many other variations of the different aspects of the embodiments of the present description as described above, which are not provided in detail for the sake of brevity.

The embodiments of the present description are intended to embrace all such alternatives, modifications and variances that fall within the broad scope of the appended claims. Therefore, any omissions, modifications, equivalents, improvements, and the like that may be made within the spirit and principles of the embodiments described herein are intended to be included within the scope of the disclosure.

Claims

1. A bar semiconductor laser capable of reducing threshold current is characterized by comprising a first electrode, a second electrode, a substrate, a first limiting layer, a first waveguide layer, an active layer, a second waveguide layer, a second limiting layer, an ohmic contact layer and an insulating layer, wherein the substrate, the first limiting layer, the first waveguide layer, the active layer, the second waveguide layer, the second limiting layer, the ohmic contact layer and the insulating layer are arranged between the first electrode and the second electrode and are sequentially arranged from the first electrode to the second electrode, the ohmic contact layer is provided with an X-ray self-supporting blazed transmission grating layer in contact with the second limiting layer, the contact surface on the substrate is provided with a trapezoidal table, the trapezoidal table is transversely parallel to a cleavage surface of the substrate, the trapezoidal table is longitudinally vertical to the cleavage surface of the substrate, and the cleavage surface is a.

2. The laser as claimed in claim 1, wherein the transverse section and the longitudinal section of the trapezoid table are isosceles trapezoids, and the lower base angle is 30-60 degrees; the transverse length of the lower bottom surface of the trapezoid table is 5-100 μm, the longitudinal length is 300-1500 μm, and the height of the trapezoid table is 0.2-0.5 μm.

3. The BAR semiconductor laser as claimed in claim 1, wherein the trapezoid mesa has a lateral period of 200-500 μm and a longitudinal period of 350-1550 μm.

4. The laser as claimed in claim 1, wherein the first electrode is an N-type electrode, the first confinement layer is an N-type confinement layer, the second electrode is a P-type electrode, and the second confinement layer is a P-type confinement layer.

5. The barcoded semiconductor laser of claim 1, wherein the first and second waveguide layers have a refractive index lower than that of the active layer.

6. The barcoded semiconductor laser of claim 1, wherein the bandgaps of the first and second waveguide layers are higher than the bandgap of the active layer.

7. The laser of claim 1, wherein the active layer is a quantum well active layer.

8. The method for manufacturing a semiconductor laser device of the bar type capable of reducing the threshold current according to claim 1, comprising the steps of:

growing an insulating layer above the ohmic contact layer;

9. The method for manufacturing a semiconductor laser device of the bar type capable of reducing threshold current according to claim 8, wherein the method for manufacturing the X-ray gold transmission grating comprises the following steps:

s14, removing the protective glue on the upper surface;

s15, etching the top monocrystalline silicon;