CN111106534B - Laser diode and manufacturing method thereof - Google Patents

Laser diode and manufacturing method thereof Download PDF

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Publication number
CN111106534B
CN111106534B CN201911047057.6A CN201911047057A CN111106534B CN 111106534 B CN111106534 B CN 111106534B CN 201911047057 A CN201911047057 A CN 201911047057A CN 111106534 B CN111106534 B CN 111106534B
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layer
plane
curved surface
type semiconductor
semiconductor layer
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CN111106534A (en
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兰叶
吴志浩
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Huacan Optoelectronics (Guangdong) Co.,Ltd.
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HC Semitek Corp
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    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01S—DEVICES USING THE PROCESS OF LIGHT AMPLIFICATION BY STIMULATED EMISSION OF RADIATION [LASER] TO AMPLIFY OR GENERATE LIGHT; DEVICES USING STIMULATED EMISSION OF ELECTROMAGNETIC RADIATION IN WAVE RANGES OTHER THAN OPTICAL
    • H01S5/00—Semiconductor lasers
    • H01S5/20—Structure or shape of the semiconductor body to guide the optical wave ; Confining structures perpendicular to the optical axis, e.g. index or gain guiding, stripe geometry, broad area lasers, gain tailoring, transverse or lateral reflectors, special cladding structures, MQW barrier reflection layers
    • H01S5/22—Structure or shape of the semiconductor body to guide the optical wave ; Confining structures perpendicular to the optical axis, e.g. index or gain guiding, stripe geometry, broad area lasers, gain tailoring, transverse or lateral reflectors, special cladding structures, MQW barrier reflection layers having a ridge or stripe structure
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01S—DEVICES USING THE PROCESS OF LIGHT AMPLIFICATION BY STIMULATED EMISSION OF RADIATION [LASER] TO AMPLIFY OR GENERATE LIGHT; DEVICES USING STIMULATED EMISSION OF ELECTROMAGNETIC RADIATION IN WAVE RANGES OTHER THAN OPTICAL
    • H01S5/00—Semiconductor lasers
    • H01S5/005—Optical components external to the laser cavity, specially adapted therefor, e.g. for homogenisation or merging of the beams or for manipulating laser pulses, e.g. pulse shaping
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01S—DEVICES USING THE PROCESS OF LIGHT AMPLIFICATION BY STIMULATED EMISSION OF RADIATION [LASER] TO AMPLIFY OR GENERATE LIGHT; DEVICES USING STIMULATED EMISSION OF ELECTROMAGNETIC RADIATION IN WAVE RANGES OTHER THAN OPTICAL
    • H01S5/00—Semiconductor lasers
    • H01S5/30—Structure or shape of the active region; Materials used for the active region
    • H01S5/32—Structure or shape of the active region; Materials used for the active region comprising PN junctions, e.g. hetero- or double- heterostructures
    • H01S5/323—Structure or shape of the active region; Materials used for the active region comprising PN junctions, e.g. hetero- or double- heterostructures in AIIIBV compounds, e.g. AlGaAs-laser, InP-based laser

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  • Condensed Matter Physics & Semiconductors (AREA)
  • General Physics & Mathematics (AREA)
  • Electromagnetism (AREA)
  • Optics & Photonics (AREA)
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  • Semiconductor Lasers (AREA)

Abstract

The disclosure discloses a laser diode and a manufacturing method thereof, and belongs to the technical field of semiconductors. The LED display device comprises a substrate, an epitaxial layer, an N-type electrode, a P-type electrode, a first reflecting layer and a second reflecting layer; the epitaxial layer comprises a buffer layer, an N-type semiconductor layer, an active layer and a P-type semiconductor layer; the surface of the P-type semiconductor layer is of a ridge waveguide structure, a first groove and a second groove are formed in the P-type semiconductor layer, the P-type semiconductor layer and the active layer form a cylinder structure, the side face of the cylinder structure comprises a first curved surface, a first plane, a second curved surface and a second plane, the first plane and the second plane are parallel to the extending direction of a ridge in the ridge waveguide structure, the curvatures of points on the first curved surface and the second curved surface are firstly reduced to 0 in the direction from the first plane to the second plane, then are kept to 0, and finally are increased from 0; the first reflecting layer and the second reflecting layer are respectively laid on the first curved surface and the second curved surface. The light emitting efficiency of the laser diode can be improved.

Description

Laser diode and manufacturing method thereof
Technical Field
The present disclosure relates to the field of semiconductor technologies, and in particular, to a laser diode and a method for manufacturing the same.
Background
The Laser Diode (LD) comprises a substrate, a semiconductor layer with PN junction, and two reflecting layers with different reflectivity, wherein the two reflecting layers are oppositely arranged on the substrate to form a resonant cavity, the semiconductor layer is arranged on the substrate and positioned between the two reflecting layers, the surface of the semiconductor layer is a ridge waveguide structure, and the extending direction of the ridge in the ridge waveguide structure is perpendicular to the opposite surfaces of the two reflecting layers.
Under the action of an applied voltage, electrons and holes in the PN junction are recombined to release photons, and the photons strike atoms, so that more photons are released. Photons vertically striking the reflective layer on one side will be reflected back along the original path and reflected back again from the reflective layer on the other side under the influence of the ridge waveguide structure, thus moving multiple times between the two reflective layers. Meanwhile, in the moving process of the photons, more atoms release more photons due to the avalanche effect, and finally a very strong laser beam is generated and emitted from the resonant cavity.
In the course of implementing the present disclosure, the inventors found that the prior art has at least the following problems:
the laser beam emitted by the resonant cavity is a Gaussian beam (English: Gaussian beam), namely the amplitude distribution of the cross section of the radiation field of the fundamental mode obeys the Gaussian function, the change rule of the beam radius along with the transmission distance is a hyperbola, and therefore the beam can be gradually diverged in the process of irradiating the reflecting layer. The opposite surfaces of the two existing reflecting layers are planes perpendicular to the irradiation direction of the light beam, and after divergent light rays in the light beam are reflected on the reflecting layers, the divergent light rays are easy to escape from the resonant cavity, so that oscillation in the resonant cavity is influenced, and the light emitting efficiency of the laser diode is reduced.
Disclosure of Invention
The embodiment of the disclosure provides a laser diode and a manufacturing method thereof, which are beneficial to limiting a Gaussian beam in a resonant cavity for oscillation and improving the light emitting efficiency of the laser diode. The technical scheme is as follows:
in one aspect, the present disclosure provides a laser diode comprising a substrate, an epitaxial layer, an N-type electrode, a P-type electrode, a first reflective layer, and a second reflective layer; the epitaxial layer comprises a buffer layer, an N-type semiconductor layer, an active layer and a P-type semiconductor layer which are sequentially stacked on the substrate; the surface of the P-type semiconductor layer is of a ridge waveguide structure, a first groove extending to the N-type semiconductor layer and a second groove extending to the substrate are formed in the P-type semiconductor layer, a cylinder structure independent of the substrate is formed by the P-type semiconductor layer and the active layer, the side face of the cylinder structure comprises a first curved surface, a first plane, a second curved surface and a second plane which are sequentially connected end to end, the first plane and the second plane are parallel to the extending direction of a ridge in the ridge waveguide structure, the curvature of a point on the first curved surface and the second curved surface is firstly reduced to 0 in the direction from the first plane to the second plane, then is kept to 0, and finally is increased from 0; the first reflecting layer is laid on the first curved surface, and the second reflecting layer is laid on the second curved surface; the N-type electrode is arranged on the N-type semiconductor layer in the groove, and the P-type electrode is arranged on the P-type semiconductor layer.
Optionally, the projected lengths of the points on the first curved surface and the second curved surface in the direction from the first plane to the second plane, where the curvature decreases to 0, the point where the curvature remains 0, and the point where the curvature increases from 0, are equal.
Further, the projection length of the point where the curvature decreases to 0, the point where the curvature remains 0, and the point where the curvature increases from 0 in the direction from the first plane to the second plane on the first curved surface and the second curved surface in the direction from the first plane to the second plane is 40 μm to 60 μm.
Optionally, the laser diode further comprises a third reflective layer and a fourth reflective layer, the third reflective layer being disposed on the first plane, the fourth reflective layer being disposed on the second plane.
Optionally, the laser diode further comprises a stress release layer disposed between the buffer layer and the N-type semiconductor layer; the stress release layer comprises a first superlattice layer, and the first superlattice layer consists of a first sublayer and a second sublayer which are alternately laminated; the first sub-layer and the second sub-layer are N-type GaN layers with different growth rates, and the difference between the growth rates of the first sub-layer and the adjacent second sub-layer gradually decreases along the stacking direction of the first superlattice layer.
Further, the stress release layer further comprises a second superlattice layer laminated on the first superlattice layer, and the second superlattice layer is composed of a third sublayer and a fourth sublayer which are alternately laminated; the third sublayer is an N-type AlGaN layer, and the fourth sublayer is an N-type InGaN layer.
Further, the height of the ridge in the ridge waveguide structure is 1.8 μm to 2.2 μm.
In another aspect, the present disclosure provides a method for manufacturing a laser diode, the method comprising:
growing an epitaxial layer on a substrate, wherein the epitaxial layer comprises a buffer layer, an N-type semiconductor layer, an active layer and a P-type semiconductor layer which are sequentially stacked;
forming a first groove extending to the N-type semiconductor layer on the P-type semiconductor layer;
forming a ridge waveguide structure on the P-type semiconductor layer;
forming a second groove extending to the substrate on the P-type semiconductor layer, wherein the P-type semiconductor layer and the active layer form a cylinder structure independent of the substrate, the side surface of the cylinder structure comprises a first curved surface, a first plane, a second curved surface and a second plane which are sequentially connected end to end, the first plane and the second plane are parallel to the extending direction of the ridge in the ridge waveguide structure, and the curvatures of points on the first curved surface and the second curved surface are firstly reduced to 0 in the direction from the first plane to the second plane, then are kept to 0, and finally are increased from 0;
arranging an N-type electrode on the N-type semiconductor layer in the groove, and arranging a P-type electrode on the P-type semiconductor layer;
and laying a first reflecting layer on the first curved surface, and laying a second reflecting layer on the second curved surface.
Optionally, after the first reflective layer and the second reflective layer are laid, the manufacturing method further includes:
thinning and grinding the substrate;
scribing the substrate to form a plurality of mutually independent chips;
correspondingly, the laying of the first reflective layer on the first curved surface and the laying of the second reflective layer on the second curved surface includes:
and inclining the evaporation equipment by 45 degrees, laying a first reflecting layer on the first curved surface, and laying a second reflecting layer on the second curved surface.
Optionally, the opening of the second groove extending to the substrate on the P-type semiconductor layer includes:
placing a plurality of the substrates on a circular carrier tray of an etching apparatus;
and driving the circular bearing disc to revolve around the circle center of the circular bearing disc, driving the substrates to rotate around the circle center of the substrates, and forming a second groove extending to the substrates on the P-type semiconductor layer.
The technical scheme provided by the embodiment of the disclosure has the following beneficial effects:
the cylinder structure comprising the active layer is formed by adopting a first curved surface, a first plane, a second curved surface and a second plane which are sequentially connected end to end, the first plane and the second plane are parallel to the extending direction of a ridge in the ridge waveguide structure, the curvature of points on the first curved surface and the second curved surface is firstly reduced to 0 and then kept to 0 in the direction from the first plane to the second plane, and finally increased from 0, and a first reflecting layer and a second reflecting layer are respectively laid on the first curved surface and the second curved surface, for divergent light rays in a resonant cavity, two sides of the first reflecting layer and two sides of the second reflecting layer are tilted, the whole body is concave, the divergent light rays can be effectively prevented from escaping, the light rays are limited in the resonant cavity to oscillate, meanwhile, for non-divergent light rays in the resonant cavity, the middle of the first reflecting layer and the second reflecting layer is a plane, and the light rays which are vertically incident can be reflected back as they are, the light is prevented from being diffused. That is to say, the first reflective layer and the second reflective layer of the embodiment of the present disclosure limit the non-divergent light originally in the resonant cavity and the divergent light originally escaping from the resonant cavity to oscillate in the resonant cavity, and finally improve the light-emitting efficiency of the laser diode.
Drawings
In order to more clearly illustrate the technical solutions in the embodiments of the present disclosure, the drawings needed to be used in the description of the embodiments are briefly introduced below, and it is obvious that the drawings in the following description are only some embodiments of the present disclosure, and it is obvious for those skilled in the art to obtain other drawings based on the drawings without creative efforts.
Fig. 1 is a schematic structural diagram of a laser diode provided in an embodiment of the present disclosure;
FIG. 2 is a cross-sectional view taken along line A-A of FIG. 1 provided in an embodiment of the present disclosure;
fig. 3 is a schematic structural diagram of a first curved surface provided by the embodiment of the present disclosure;
FIG. 4 is a schematic structural diagram of a stress relieving layer provided by an embodiment of the present disclosure;
fig. 5 is a flowchart of a method for manufacturing a laser diode according to an embodiment of the present disclosure.
Detailed Description
To make the objects, technical solutions and advantages of the present disclosure more apparent, embodiments of the present disclosure will be described in detail with reference to the accompanying drawings.
The disclosed embodiments provide a laser diode. Fig. 1 is a schematic structural diagram of a laser diode provided in an embodiment of the present disclosure, and fig. 2 is a sectional view taken along a direction a-a of fig. 1 provided in an embodiment of the present disclosure. Referring to fig. 1 and 2, the laser diode includes a substrate 10, an epitaxial layer, an N-type electrode 31, a P-type electrode 32, a first reflective layer 41, and a second reflective layer 42. The epitaxial layer includes a buffer layer 21, an N-type semiconductor layer 22, an active layer 23, and a P-type semiconductor layer 24 sequentially stacked on the substrate 10. The surface of the P-type semiconductor layer 24 is a ridge waveguide structure, a first groove 100 extending to the N-type semiconductor layer 22 and a second groove 200 extending to the substrate 10 are arranged on the P-type semiconductor layer 24, the P-type semiconductor layer 24 and the active layer 23 form a cylinder structure independent of the substrate 10, the side surface of the cylinder structure comprises a first curved surface, a first plane, a second curved surface and a second plane which are sequentially connected end to end, the first plane and the second plane are parallel to the extending direction of a ridge in the ridge waveguide structure, the curvature of points on the first curved surface and the second curved surface is firstly reduced to 0 in the direction from the first plane to the second plane, then is kept to 0, and finally is increased from 0. The first reflective layer 41 is laid on the first curved surface, and the second reflective layer 42 is laid on the second curved surface. An N-type electrode 31 is disposed on the N-type semiconductor layer 22 within the recess 100 and a P-type electrode 32 is disposed on the P-type semiconductor layer 24.
The embodiment of the disclosure adopts the first curved surface, the first plane, the second curved surface and the second plane which are connected end to end in sequence to form a cylinder structure comprising an active layer, the first plane and the second plane are parallel to the extending direction of the ridge in the ridge waveguide structure, the curvature of points on the first curved surface and the second curved surface is firstly reduced to 0 and then kept to 0 in the direction from the first plane to the second plane, and finally increased from 0, and the first reflecting layer and the second reflecting layer are respectively laid on the first curved surface and the second curved surface, for divergent light rays in the resonant cavity, two sides of the first reflecting layer and two sides of the second reflecting layer are tilted, the whole is concave, the divergent light rays can be effectively blocked from escaping, the light rays are limited in the resonant cavity to oscillate, meanwhile, for non-divergent light rays in the resonant cavity, the middle of the first reflecting layer and the second reflecting layer is a plane, and the light rays which are vertically incident can be reflected back in the original way, the light is prevented from being diffused. That is to say, the first reflective layer and the second reflective layer of the embodiment of the present disclosure limit the non-divergent light originally in the resonant cavity and the divergent light originally escaping from the resonant cavity to oscillate in the resonant cavity, and finally improve the light-emitting efficiency of the laser diode.
In the present embodiment, the substrate mainly serves to provide a substrate for epitaxial material growth, and the substrate may be made of sapphire (Al is a main component)2O3) Preferably, a patterned sapphire substrate (english: pattern Sapphire Substrate, abbreviated as: PSS). Furthermore, the pattern in the PSS can be a cone with the diameter of 2.5 μm and the height of more than 1.5 μm, and the distance between two adjacent patterns can be 1 μm, so that the overall effect of stress release and light extraction improvement of the PSS is better.
The buffer layer serves primarily to provide nucleation centers for epitaxial growth and additionally to mitigate lattice mismatch between the substrate material and the epitaxial material. Further, the buffer layer may include an aluminum nitride (AlN) buffer layer and a gallium nitride (GaN) buffer layer, which are sequentially stacked. The aluminum nitride buffer layer may have a thickness of 1800 angstroms to 2200 angstroms, such as 2000 angstroms; the thickness of the gallium nitride buffer layer can be 30 nm-50 nm, such as 40nm, and the realization effect is good.
The N-type semiconductor layer mainly functions to provide electrons for composite light emission, and may include an N-type buffer layer, an N-type contact layer, an N-type cladding layer, and an N-type light guiding layer, which are sequentially stacked. The N-type buffer layer is low-temperature gallium nitride and has the thickness of 0.5 micrometer; the N-type contact layer is high-temperature gallium nitride and has the thickness of 3 microns; the N-type cladding layer is an aluminum-gallium-nitrogen layer containing 10% of aluminum and has the thickness of 5000 angstroms; the N-type guide layer is a gallium nitride layer, and the thickness of the N-type guide layer is 0.2 micrometer; the doping concentration of the N-type dopant in the N-type semiconductor layer may be 1020/cm3. The N-type dopant can adopt silane, silicon element in the silane is used for doping, and after the silicon element replaces gallium element in a gallium nitride covalent bond, surplus electrons are formed due to the existence of the surplus electrons, so that the semiconductor with the electron carriers is obtained.
The active layer may be composed of a plurality of periodic structures, for example, 6 periodic structures, which are sequentially stacked, each periodic structure is composed of an InGaN well layer and a GaN barrier layer, which are sequentially stacked, and the GaN barrier layer or the AlGaN barrier layer confines electrons and holes in the InGaN well layer for radiative recombination light emission.
The P-type semiconductor layer mainly functions to provide holes for recombination light emission, and may include a P-type high barrier layer, a P-type light guiding layer, a P-type cladding layer, and a P-type contact layer, which are sequentially stacked. The P-type high barrier layer is an aluminum gallium nitride layer with the thickness of 50 angstroms; the P-type light guide layer is a gallium nitride layer with the thickness of 0.2 micron; the P-type cladding layer is an aluminum gallium nitride layer with the thickness of 0.5 micron; the P-type contact layer is a gallium nitride layer with a thickness of 500 angstroms.
The N-type electrode and the P-type electrode are used for being respectively connected with the anode and the cathode of a power supply and injecting current into the chip, and the materials can be Cr/Al/Cr/Ti/Au, namely the N-type electrode and the P-type electrode respectively comprise a Cr layer, an Al layer, a Cr layer, a Ti layer and an Au layer which are sequentially stacked.
Further, the thickness of the Au layer can be larger than 1.5 microns, so that the reliability of subsequent processing is ensured; the thickness of the bottom Cr layer is less than or equal to angstroms to reduce light absorption and ensure brightness. In addition, the thickness of the Cr layer in the P-type electrode can be smaller than that of the Cr layer in the N-type electrode, the thickness of the Cr layer in the P-type electrode is smaller, the light emitting efficiency is improved, and the stability of the electrode is improved due to the fact that the thickness of the Cr layer in the N-type electrode is larger.
Fig. 3 is a schematic structural diagram of a first curved surface provided in the embodiment of the present disclosure. Referring to fig. 3, alternatively, a projection length a of a point of the first curved surface in the direction from the first plane to the second plane, where the curvature decreases to 0, a projection length b of a point of the first curved surface in the direction from the first plane to the second plane, where the curvature remains 0, where the curvature in the direction from the first plane to the second plane, where the curvature increases from 0, may be equal.
Accordingly, a projected length of a point on the second curved surface in the direction from the first plane to the second plane, the projected length of a point on the second curved surface, the curvature of which is kept at 0 in the direction from the first plane to the second plane, a projected length of a point on the second curved surface, the curvature of which is increased from 0 in the direction from the first plane to the second plane, may be equal.
The part that the camber keeps to be 0 on first curved surface and the second curved surface equals with the partial length that both sides camber changes for first curved surface and second curved surface are at the non-divergence department camber of gaussian beam and are kept 0, can carry out the vertical reflection to non-divergent light, avoid reflecting non-divergent light out the resonant cavity, shelter from divergent light in gaussian beam divergence department simultaneously, avoid divergent light to escape. To sum up, first reflection stratum and second reflection stratum lay along first curved surface and second curved surface respectively, can be to the characteristics of gaussian beam, and furthest is oscillated light restriction in the resonant cavity, improves laser diode's luminous efficacy.
Further, a projected length a of a point of the first curved surface in the direction from the first plane to the second plane, where the curvature decreases to 0, in the direction from the first plane to the second plane, a projected length b of a point of the first curved surface, where the curvature remains 0, in the direction from the first plane to the second plane, where the curvature increases from 0, in the direction from the first plane to the second plane, and a projected length c of a point of the first curved surface, where the curvature increases from 0, in the direction from the first plane to the second plane, may be 40 μm to 60 μm.
Accordingly, a projected length of a point on the second curved surface in a direction from the first plane to the second plane, the projected length of a point on the second curved surface, the curvature of which is decreased to 0 in the direction from the first plane to the second plane, the projected length of a point on the second curved surface, the curvature of which is maintained to 0 in the direction from the first plane to the second plane, and the projected length of a point on the second curved surface, the curvature of which is increased from 0 in the direction from the first plane to the second plane, in the direction from the first plane to the second plane may be 40 μm to 60 μm.
The size of the first curved surface and the size of the second curved surface are set by combining the size of the chip and the divergence condition of the Gaussian beam, so that the light is limited in the resonant cavity to oscillate to the maximum extent, and the light emitting efficiency of the laser diode is improved.
Preferably, a projected length a of a point in the direction from the first plane to the second plane, where the curvature of the first curved surface decreases to 0 in the direction from the first plane to the second plane, a projected length b of a point in the direction from the first plane to the second plane, where the curvature of the first curved surface remains 0 in the direction from the first plane to the second plane, and a projected length c of a point in the direction from the first plane to the second plane, where the curvature of the first curved surface increases from 0 in the direction from the first plane to the second plane may be 50 μm.
Accordingly, a projected length of a point on the second curved surface in a direction from the first plane to the second plane, the projected length of a point on the second curved surface, the curvature of which is decreased to 0 in the direction from the first plane to the second plane, the projected length of a point on the second curved surface, the curvature of which is maintained to 0 in the direction from the first plane to the second plane, and the projected length of a point on the second curved surface, the curvature of which is increased from 0 in the direction from the first plane to the second plane, in the direction from the first plane to the second plane may be 50 μm.
Experiments prove that when the first curved surface and the second curved surface adopt the sizes, the light emitting efficiency of the laser diode reaches the highest.
Optionally, the laser diode may further include a third reflective layer 43 and a fourth reflective layer 44, the third reflective layer 43 being laid on the first plane, and the fourth reflective layer 44 being laid on the second plane.
By additionally arranging the reflecting layers on the two sides of the resonant cavity, light can be further prevented from escaping from the resonant cavity, and the light emitting efficiency of the laser diode is improved.
Alternatively, the first reflective layer 41, the second reflective layer 42, the third reflective layer 43, and the fourth reflective layer 44 may each include a plurality of periodic metal oxide thin films, the plurality of periodic metal oxide thin films are sequentially stacked, each periodic metal oxide thin film includes at least two kinds of metal oxide thin films, the metal oxide thin films of different materials have different refractive indexes, the metal oxide thin films of at least two kinds of materials are sequentially stacked, and the stacking order of the metal oxide thin films of at least two kinds of materials in the metal oxide thin films of different periods is the same.
In the present embodiment, the number of cycles of the metal oxide thin film in the first reflective layer 41 is greater than the number of cycles of the metal oxide thin film in the second reflective layer 42, and the number of cycles of the metal oxide thin film in the third reflective layer 43 and the fourth reflective layer 44 may be equal to the number of cycles of the metal oxide thin film in the second reflective layer 42.
The difference in the number of cycles of the metal oxide thin film in the first reflective layer and the second reflective layer is advantageous for the laser beam formed in the resonant cavity to be emitted from the reflective layer having a small number of cycles of the metal oxide thin film. The light rays emitted to the third reflecting layer and the fourth reflecting layer are less, the third reflecting layer and the fourth reflecting layer adopt the metal oxide thin film with less cycles to achieve good reflecting effect, and meanwhile, the realization cost is reduced.
For example, the number of cycles of the metal oxide thin film in the first reflective layer 41 may be 24, and the number of cycles of the metal oxide thin film in the second, third, and fourth reflective layers 42, 43, and 44 may be 2.
Furthermore, the thickness D1 of the metal oxide thin film of N1 cycles in the first reflective layer is λ × (2 × k-1)/4, the thickness D2 of the metal oxide thin film of N2 cycles in the reflective layer is λ × (1+ a) × (2 × k-1)/4, the thickness D3 of the metal oxide thin film of N3 cycles in the reflective layer is λ (1+ b) × (2 × k-1)/4, λ is a set wavelength, -0.1 < a < 0, 0 < b < 0.1, N1, N2, N3, k1, k2, and k3 are positive integers, N1+ N2+ N3 is not more than N, and N is the number of cycles of the metal oxide thin film in the first reflective layer.
Illustratively, λ ═ 455nm, λ ═ 1+ a ═ 450nm, λ × (1+ b) ═ 460nm, the thickness of the metal oxide thin film of 5 cycles can be set to be an odd multiple of one quarter of 452.5nm, the thickness of the metal oxide thin film of 10 cycles can be set to be an odd multiple of one quarter of 455nm, and the thickness of the metal oxide thin film of 5 cycles can be set to be an odd multiple of one quarter of 457.5nm, and the light emission efficiency of the LED can be improved to the maximum.
In addition, the thickness of the 2 periods of the metal oxide thin film in the second reflective layer is an odd multiple of one quarter of 455 nm.
Further, magnesium difluoride (MgF) can be used as a material for the metal oxide thin film2) Tantalum pentoxide (Ta)2O5) Zirconium dioxide (ZrO)2) Aluminum oxide (Al)2O3) Titanium dioxide (TiO)2) Or silicon dioxide (SiO)2). Wherein the refractive index of magnesium difluoride is 1.22, the refractive index of tantalum pentoxide is 2.06, the refractive index of zirconium dioxide is 1.92, the refractive index of aluminum oxide is 1.77, the refractive index of titanium dioxide is 2.35, and the refractive index of silicon dioxide is 1.46.
Illustratively, the metal oxide film of each period may include a metal oxide film of two materials, the metal oxide film of one material being titanium dioxide, and the metal oxide film of the other material being magnesium difluoride. The refractive indexes of the titanium dioxide and the magnesium difluoride have the largest difference, and the reflection effect is the best.
Further, the first reflective layer 41 may further include a metal thin film stacked on the metal oxide thin films in a plurality of periods, so as to enhance the reflection effect and improve the light extraction efficiency of the laser diode.
Illustratively, the material of the metal thin film may be one of aluminum, silver and platinum, and the reflection effect is good.
Alternatively, the laser diode may further include a stress relief layer disposed between the buffer layer 21 and the N-type semiconductor layer 22. Fig. 4 is a schematic structural diagram of a stress relief layer provided in an embodiment of the disclosure. Referring to fig. 4, the stress relieving layer 25 includes a first superlattice layer 251, and the first superlattice layer 251 is composed of first and second sub-layers 251a and 251b alternately stacked. The first sublayer 251a and the second sublayer 251b are N-type GaN layers having different growth rates, and the difference in growth rate between the first sublayer 251a and the adjacent second sublayer 252b gradually decreases in the stacking direction of the first superlattice layer 2.
By the first sublayer and the second sublayer with larger difference in growth rate, stress extension generated by lattice mismatch between the substrate and the epitaxial layer can be effectively relieved by using rapid growth, and the difference of the first sublayer and the second sublayer in growth rate is gradually reduced subsequently, so that epitaxial growth gradually tends to be stable.
Illustratively, the growth rate of the first sub-layer 251a may be 6-10A/s, and the growth rate of the second sub-layer 251b may be 1-3A/s. For example, the growth rate of each sublayer in the first superlattice layer 251 is 10 angstroms/second (first sublayer 251a), 3 angstroms/second (second sublayer 251b), 8 angstroms/second (first sublayer 251a), 2 angstroms/second (second sublayer 251b), 6 angstroms/second (first sublayer 251a), and 1 angstroms/second (second sublayer 251b) in this order.
Further, as shown in fig. 4, the stress relieving layer 25 may further include a second superlattice layer 252 stacked on the first superlattice layer 251, and the second superlattice layer 252 is composed of third sublayers 252a and fourth sublayers 252b which are alternately stacked. The third sublayer 252a is an N-type AlGaN layer, and the fourth sublayer 252b is an N-type InGaN layer.
On the basis that the first superlattice structure reduces the extension stress, the influence caused by lattice mismatch of the substrate and the epitaxial layer is further overcome by adopting the alternate growth of lattices with different atomic radii, so that the quality of the laser diode can be effectively improved, and the service life of the laser diode is prolonged.
Illustratively, the content of the Al component In the third sublayer 252a may be 3%, and the content of the In component In the fourth sublayer 252b may be 5%.
Further, as shown in FIG. 2, the height h of the ridge in the ridge waveguide structure may be 1.8 μm to 2.2 μm.
Preferably, the height h of the ridge in the ridge waveguide structure may be 2 μm.
On the basis of improving the quality of the laser diode, the height of the ridge in the ridge waveguide structure is increased to about 2 mu m, so that the guiding effect of the ridge waveguide on the light transmission direction in the resonant cavity can be effectively improved, the ratio of high-order transverse modes is reduced, and the light emitting effect of the laser diode is favorably improved.
Alternatively, as shown in fig. 2, the laser diode may further include a passivation protection layer 50, and the passivation protection layer 50 is disposed on a region other than the region where the N-type electrode 31 is located within the groove 100 and on a region other than the region where the P-type electrode 32 is located on the P-type semiconductor layer 24.
Further, the passivation protection layer may include a first silicon oxynitride layer, a second silicon oxynitride layer, and a silicon dioxide layer, which are sequentially stacked, wherein the content of nitrogen components in the first silicon oxynitride layer is greater than the content of nitrogen components in the second silicon oxynitride layer; the passivation protection layer may have a thickness of 1.5 μm, and the first silicon oxynitride layer, the second silicon oxynitride layer, and the silicon dioxide layer may have equal thicknesses.
Illustratively, the content of the nitrogen component in the first silicon oxynitride layer may be 20%, and the content of the nitrogen component in the second silicon oxynitride layer may be 10%, which is beneficial to improving the protective effect of the passivation protective layer.
The embodiment of the disclosure provides a manufacturing method of a laser diode, which is suitable for manufacturing the laser diode shown in fig. 1 and 2. Fig. 5 is a flowchart of a method for manufacturing a laser diode according to an embodiment of the present disclosure. Referring to fig. 5, the manufacturing method includes:
step 201: an epitaxial layer is grown on a substrate, and the epitaxial layer comprises a buffer layer, an N-type semiconductor layer, an active layer and a P-type semiconductor layer which are sequentially stacked.
Optionally, the step 201 may include:
sputtering an aluminum target in a nitrogen atmosphere to form an aluminum nitride layer on a substrate;
and sequentially growing an N-type semiconductor layer, an active layer and a P-type semiconductor layer on the buffer layer by using a Metal Organic Chemical Vapor Deposition (MOCVD) technology.
Optionally, before the step 201, the manufacturing method may further include:
and cleaning the substrate.
By cleaning the substrate, a clean surface is provided for subsequent epitaxial growth, the crystal quality of epitaxial growth is improved, and the luminous efficiency of the LED is improved.
Specifically, the substrate may be cleaned with a sulfuric acid solution.
Step 202: a first groove extending to the N-type semiconductor layer is formed in the P-type semiconductor layer.
Optionally, this step 202 may include:
forming photoresist with a certain pattern on the P-type semiconductor layer by adopting a photoetching technology, wherein the photoresist is arranged on the region of the P-type semiconductor layer except the region where the groove is located;
adopting an inductively Coupled Plasma etching (ICP) device to dry-Etch the P-type semiconductor layer and the light-emitting layer which are not covered by the photoresist to form a first groove;
and removing the photoresist.
By adopting the ICP equipment for dry etching, the plasma density is higher, higher etching speed and smaller photoresist loss can be obtained, and the yield of the LED chip can be improved.
Specifically, the etching gas may employ Cl2、BCl3And the mixed gas of Ar has good realization effect.
In a specific implementation, the forming of the patterned photoresist by using the photolithography technique may include:
laying a layer of photoresist;
exposing the photoresist through a mask plate with a certain pattern;
and soaking the exposed photoresist in a developing solution to dissolve part of the photoresist, wherein the remained photoresist is the photoresist with the required pattern.
Step 203: a ridge waveguide structure is formed on the P-type semiconductor layer.
Optionally, this step 203 may comprise:
placing a plurality of substrates on a circular carrier tray of an etching apparatus;
and driving the circular bearing disc to revolve around the circle center of the circular bearing disc, and simultaneously driving each substrate to rotate around the circle center of the substrate to form a ridge waveguide structure on the P-type semiconductor layer.
The revolution and the rotation of the substrate are performed, so that the uniform etching of the P-type semiconductor layer is facilitated, and the sawtooth can be prevented from being formed on the ridge waveguide structure.
Step 204: and a second groove extending to the substrate is formed on the P-type semiconductor layer, and the P-type semiconductor layer and the active layer form a column structure independent of the substrate.
In this embodiment, the side surface of the pillar structure includes a first curved surface, a first plane, a second curved surface and a second plane connected end to end in sequence, the first plane and the second plane are parallel to the extending direction of the ridge in the ridge waveguide structure, and the curvature of the point on the first curved surface and the second curved surface is firstly reduced to 0, then kept to 0, and finally increased from 0 in the direction from the first plane to the second plane.
Optionally, this step 204 may include:
placing a plurality of substrates on a circular carrier tray of an etching apparatus;
the circular bearing disc is driven to revolve around the circle center of the circular bearing disc, the substrates are driven to rotate around the circle center of the substrates, second grooves extending to the substrates are formed in the P-type semiconductor layer, and second grooves extending to the substrates are formed in the P-type semiconductor layer.
And the substrate is revolved and rotated, so that uniform etching is facilitated.
In practical application, the over-etching is performed in the process of forming the second groove, so that the side wall of the second groove is fully etched and is perpendicular to the surface of the substrate.
Step 205: an N-type electrode is arranged on the N-type semiconductor layer in the groove, and a P-type electrode is arranged on the P-type semiconductor layer.
Optionally, this step 205 may include:
forming photoresist with a set pattern in the groove and on the P-type semiconductor layer by adopting a photoetching technology;
an electrode material is laid on the photoresist, the P-type semiconductor layer and the N-type semiconductor layer which are not covered by the photoresist by adopting a Physical Vapor Deposition (PVD for short);
and removing the photoresist and the electrode material on the photoresist, wherein the electrode material left on the P-type semiconductor layer forms a P-type electrode, and the electrode material left on the N-type semiconductor layer forms an N-type electrode.
Illustratively, the electrode material may be laid down using an evaporation technique. Reaction during evaporationThe vacuum degree of the chamber is 5 x 10-6torr or more.
Further, before the P-type electrode is formed, the manufacturing method may further include:
a transparent conductive layer is formed on the P-type semiconductor layer.
Specifically, the transparent conductive layer mainly has the functions of improving the transverse expansion capability of current and expanding the region acted by the current; the transparent conductive layer can be made of Indium Tin Oxide (ITO) or zinc oxide (ZnO), and has good conductivity and transmittance and low manufacturing cost. Taking ITO as an example, the molar content ratio of indium oxide to tin oxide is 19:1, indium in indium oxide is mainly in valence 3, tin in tin oxide is mainly in valence 4, and the molar content of tin oxide in ITO reaches 5%, so that more electrons can be generated and good conductivity can be obtained.
Furthermore, oxygen can be introduced when the transparent conductive layer is formed, so as to ensure the crystal quality. Preferably, the flow rate of oxygen can be 8sccm, on one hand to avoid that too large a flow rate of oxygen leads to an increase in resistivity, and on the other hand to avoid that too small a flow rate of oxygen leads to a decrease in transmittance.
During specific implementation, firstly, oxygen is not introduced, ITO is sputtered at normal temperature, then oxygen-containing annealing is carried out, and finally, ITO is patterned.
Accordingly, the P-type electrode is disposed on the transparent conductive layer.
Optionally, after step 205, the manufacturing method may further include:
and forming a passivation protective layer on the region of the P-type semiconductor layer except the region where the P-type electrode is located and the region of the first groove except the region where the N-type electrode is located.
In practical application, the passivation protection layer is processed by a Plasma Enhanced Chemical Vapor Deposition (PECVD), wherein the gases are silane, laughing gas and ammonia gas, the silane is a mixed gas with a ratio of 10%, the laughing gas is pure laughing gas, and the ammonia gas is pure ammonia gas.
It should be noted that the process of patterning a layer (transparent conductive layer or passivation protection layer) by using photolithography and etching techniques may be similar to the process of forming the groove, and therefore, the detailed description is omitted.
Step 206: and laying a first reflecting layer on the first curved surface and laying a second reflecting layer on the second curved surface.
Optionally, after step 206, the manufacturing method may further include:
thinning and grinding the substrate;
scribing the substrate to form a plurality of mutually independent chips;
accordingly, this step 206 may include:
and inclining the evaporation equipment by 45 degrees, laying a first reflecting layer on the first curved surface, and laying a second reflecting layer on the second curved surface.
By forming the reflecting layer between the two chips without separation, compared with the reflecting layer formed after splitting, the reflecting layer can be effectively prevented from being polluted by impurities generated in the splitting process, the adhesion of the reflecting layer is enhanced, and the forming speed of the reflecting layer can be ensured.
Further, dicing the substrate to obtain at least two chips independent of each other may include:
carrying out invisible cutting on the substrate, wherein scratches are formed at least two depth positions in the substrate under the action of a laser focus;
and splitting the substrate to obtain at least two mutually independent chips.
Through the multiple invisible cutting, the collapse damage of the crack edge is reduced, the scribing width is reduced, and finally the light emitting brightness of the LED chip is improved.
Illustratively, the power of the laser may be 5W, and the wavelength of the laser may be 1024 nm.
Through testing and comparing the laser diode chip provided by the embodiment with a chip processed by a traditional mode, the beam radius of the laser diode chip provided by the embodiment is reduced by 9.2% compared with that of the traditional chip, the light effect is improved to 8.6% from 8.1% of the traditional chip, and the stability of the chip is obviously improved.
The above description is intended to be exemplary only and not to limit the present disclosure, and any modification, equivalent replacement, or improvement made without departing from the spirit and scope of the present disclosure is to be considered as the same as the present disclosure.

Claims (10)

1. A laser diode, characterized in that it comprises a substrate (10), an epitaxial layer, an N-type electrode (31), a P-type electrode (32), a first reflective layer (41) and a second reflective layer (42); the epitaxial layer comprises a buffer layer (21), an N-type semiconductor layer (22), an active layer (23) and a P-type semiconductor layer (24) which are sequentially laminated on the substrate (10); the surface of the P-type semiconductor layer (24) is of a ridge waveguide structure, a first groove (100) extending to the N-type semiconductor layer (22) and a second groove (200) extending to the substrate (10) are formed in the P-type semiconductor layer (24), the P-type semiconductor layer (24) and the active layer (23) form a cylinder structure independent of the substrate (10), the side face of the cylinder structure comprises a first curved surface, a first plane, a second curved surface and a second plane which are sequentially connected end to end, the first plane and the second plane are parallel to the extending direction of ridges in the ridge waveguide structure, the curvature of points on the first curved surface and the second curved surface is firstly reduced to 0 in the direction from the first plane to the second plane, then is kept to 0, and finally is increased from 0; the first reflecting layer (41) is laid on the first curved surface, and the second reflecting layer (42) is laid on the second curved surface; the N-type electrode (31) is arranged on the N-type semiconductor layer (22) in the first groove (100), and the P-type electrode (32) is arranged on the P-type semiconductor layer (24).
2. The laser diode according to claim 1, wherein the projected lengths of the points on the first curved surface and the second curved surface, at which the curvature decreases to 0, keeps at 0, and increases from 0 in the direction from the first plane to the second plane, are equal.
3. The laser diode according to claim 2, wherein a projection length of a point on the first curved surface and the second curved surface in a direction from the first plane to the second plane, at which a curvature decreases to 0, a point at which the curvature remains 0, and a point at which the curvature increases from 0, in the direction from the first plane to the second plane is 40 μm to 60 μm.
4. A laser diode according to any of claims 1 to 3, further comprising a third reflective layer (43) and a fourth reflective layer (44), the third reflective layer (43) lying on the first plane and the fourth reflective layer (44) lying on the second plane.
5. The laser diode according to any of claims 1 to 3, further comprising a stress relief layer (25), wherein the stress relief layer (25) is disposed between the buffer layer (21) and the N-type semiconductor layer (22); the stress release layer (25) includes a first superlattice layer (251), the first superlattice layer (251) being composed of first and second sub-layers (251a, 251b) that are alternately stacked; the first sublayer (251a) and the second sublayer (251b) are N-type GaN layers having different growth rates, and the difference in growth rate between the first sublayer (251a) and the adjacent second sublayer (251b) gradually decreases in the stacking direction of the first superlattice layer (251).
6. The laser diode according to claim 5, wherein the stress release layer (25) further comprises a second superlattice layer (252) stacked on the first superlattice layer (251), the second superlattice layer (252) being composed of third and fourth sub-layers (252a, 252b) stacked alternately; the third sublayer (252a) is an N-type AlGaN layer, and the fourth sublayer (252b) is an N-type InGaN layer.
7. The laser diode of claim 6, wherein the height of the ridge in the ridge waveguide structure is between 1.8 μm and 2.2 μm.
8. A method for manufacturing a laser diode, the method comprising:
growing an epitaxial layer on a substrate, wherein the epitaxial layer comprises a buffer layer, an N-type semiconductor layer, an active layer and a P-type semiconductor layer which are sequentially stacked;
forming a first groove extending to the N-type semiconductor layer on the P-type semiconductor layer;
forming a ridge waveguide structure on the P-type semiconductor layer;
forming a second groove extending to the substrate on the P-type semiconductor layer, wherein the P-type semiconductor layer and the active layer form a cylinder structure independent of the substrate, the side surface of the cylinder structure comprises a first curved surface, a first plane, a second curved surface and a second plane which are sequentially connected end to end, the first plane and the second plane are parallel to the extending direction of the ridge in the ridge waveguide structure, and the curvatures of points on the first curved surface and the second curved surface are firstly reduced to 0 in the direction from the first plane to the second plane, then are kept to 0, and finally are increased from 0;
arranging an N-type electrode on the N-type semiconductor layer in the first groove, and arranging a P-type electrode on the P-type semiconductor layer;
and laying a first reflecting layer on the first curved surface, and laying a second reflecting layer on the second curved surface.
9. The method of manufacturing according to claim 8, wherein after the first and second reflective layers are laid, the method of manufacturing further comprises:
thinning and grinding the substrate;
scribing the substrate to form a plurality of mutually independent chips;
correspondingly, the laying of the first reflective layer on the first curved surface and the laying of the second reflective layer on the second curved surface includes:
and inclining the evaporation equipment by 45 degrees, laying a first reflecting layer on the first curved surface, and laying a second reflecting layer on the second curved surface.
10. The method according to claim 8 or 9, wherein the forming of the second groove extending to the substrate on the P-type semiconductor layer comprises:
placing a plurality of the substrates on a circular carrier tray of an etching apparatus;
and driving the circular bearing disc to revolve around the circle center of the circular bearing disc, driving the substrates to rotate around the circle center of the substrates, and forming a second groove extending to the substrates on the P-type semiconductor layer.
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