Narrow strip-shaped edge emitting micro light emitting diode

Abstract

The invention provides a structure of a narrow-strip-shaped edge-emitting micro light-emitting diode, which is characterized in that a light-emitting layer, namely an active layer of the light-emitting diode, forms a narrow-strip-shaped structure, and then the upper, lower, left and right parts of the active layer are coated with material layers of which the refractive index is smaller than that of the active layer to form an optical waveguide structure, so that the optical waveguide structure has a function of limiting the propagation direction of light; therefore, the light is mainly emitted to the two ends of the strip-shaped active layer. A reflecting layer capable of reflecting light can also be coated outside the four material layers with small refractive indexes to enhance the limitation of the optical waveguide. The narrow-strip-shaped edge emission micro light-emitting diode with the optical waveguide structure has very good light limitation, so that the radiation intensity of light is high, the beam divergence angle is small, and the loss of light coupled to transmission media such as optical fibers or optical waveguides is relatively small; therefore, advantages are provided in the aspects of miniaturization, thinning and cost reduction of the parallel optical link module.

Description

Technical Field

[0001] The present invention relates to a narrow strip edge-emitting micro-LED applied to a parallel optical link. Since the narrow strip edge-emitting micro-LED has a small light beam divergence angle and the light emission direction is parallel to the optical transmission medium (such as an optical fiber or an optical waveguide), it is easy to align the light source with the optical fiber and the light loss coupled to the optical fiber is small. Therefore, it has the advantages of miniaturization, thinness and low cost of the parallel optical link module. Background Art

[0002] Optical link technology plays an important role in fields that require high-speed computing. Optical links use photons to replace traditional electronic signal transmission. On general circuit boards, electrons usually transmit signals through copper wires, but optical link technology uses photons to transmit signals because photons are faster than electrons and are less likely to generate heat, so they can achieve better transmission effects.

[0003] In the past, most optical link technologies used laser diodes as light sources to transmit optical signals. Although laser diodes can transmit optical signals at high speeds, the production process of laser diodes is difficult and costly, and the size of optical transceivers using laser diodes as light sources is still too large, which is not conducive to integrating them with silicon integrated circuit chips.

[0004] Pezeshki disclosed a technology for chip-to-chip optical signal transmission using micro-LEDs in integrated circuits at the CS MANTECH Conference (May 9-12, 2022). This type of micro-LED has a smaller capacitance effect due to the reduction in component size, which greatly reduces the RC time constant of the micro-LED and improves the modulation bandwidth and data rate of the micro-LED. However, this type of micro-LED is a surface emitting diode, and the light beam has a very large emitting angle, resulting in low efficiency of light coupling to the optical fiber. As the size of the micro-LED decreases, more light is emitted from the four sides than from the surface, which is not conducive to coupling light to the optical fiber. In addition, the direction of light emitted by this surface-emitting micro-LED is perpendicular to the optical transmission medium (optical fiber or optical waveguide), so a 45-degree reflector is required to change the direction of the light to 90 degrees before the light can be coupled to the optical fiber or optical waveguide, which is more complicated in production process. Summary of the invention

[0005] In view of the above known problems, an object of the present invention is to form the active layer of the edge-emitting micro-LED into a narrow strip structure and form it into an optical waveguide structure with light localization, so that the radiation intensity of the light is high, the beam divergence angle is small, and the light loss coupled to the transmission medium such as optical fiber or optical waveguide is also small.

[0006] Another object of the present invention is to make the light emitting direction parallel to the optical transmission medium. This makes it easy to align the light source with the optical fiber or optical waveguide, and the light loss of the coupling is small, which has the advantages of miniaturizing, thinning and low cost of the parallel optical link module.

[0007] The present invention provides a narrow strip edge-emitting micro-LED, which emits light from two end faces before and after the narrow strip structure. The micro-LED includes: a refractive index structure, which provides an optical waveguide effect in all directions perpendicular to the light-emitting direction, and the refractive index structure is formed by the refractive index difference of a semiconductor epitaxial layer grown in a direction perpendicular to an electrode surface, and the semiconductor epitaxial layer includes at least one active layer, an upper cladding layer and a lower cladding layer, and the active layer has a refractive index difference with the upper cladding layer and the lower cladding layer respectively, and the refractive index of the active layer is greater than the refractive index of the upper and lower cladding layers, and an insulating layer is coated on at least one side of the semiconductor epitaxial layer, and the insulating layer has a smaller refractive index than the semiconductor epitaxial layer, and the narrow strip structure has a width less than 10 microns, and the area of ​​the active layer is less than 1000 square microns.

[0008] In a preferred embodiment, the refractive index structure has one or more optical microstructures.

[0009] In a preferred embodiment, the narrow strip edge-emitting micro LED further includes a waveguide layer located between the active layer and the upper cladding layer, and between the active layer and the lower cladding layer.

[0010] Furthermore, in a preferred embodiment, the waveguide layer is a gradient refractive index waveguide layer.

[0011] Furthermore, in a preferred embodiment, the upper cladding layer or the lower cladding layer has an optical microstructure, or both the upper cladding layer and the lower cladding layer have an optical microstructure.

[0012] In a preferred embodiment, the insulating layer may be covered with a light reflecting layer.

[0013] Furthermore, in a preferred embodiment, the light reflecting layer is a metal layer with high light reflectivity, or a Bragg reflector formed by stacking multiple layers of high and low dielectric materials.

[0014] In a preferred embodiment, the semiconductor epitaxial layer is made of AlGaInN, AlGaInP, AlGaAs, InGaAsP, InGaAs or AlGaInAs compounds.

[0015] In a preferred embodiment, one of the two end surfaces of the narrow strip structure is covered with the insulating layer and the light reflecting layer, so that light is emitted from the other end surface.

[0016] Furthermore, in a preferred embodiment, the other end surface from which the light is emitted has an optical microstructure.

[0017] Furthermore, in a preferred embodiment, the light reflecting layer is a metal layer with high light reflectivity, or a Bragg reflector formed by stacking multiple layers of high and low refractive index dielectric materials.

[0018] Furthermore, in a preferred embodiment, the lower cladding layer includes a plurality of protrusions, the plurality of protrusions are arranged in an array, and the refractive index structure is formed on each of the protrusions, so that the micro-LED has a plurality of refractive index structures.

[0019] Furthermore, the array is arranged in a horizontal manner, a vertical manner, or a combination of the horizontal and vertical manners.

[0020] Furthermore, in a preferred embodiment, the narrow strip edge-emitting micro-LED also includes an optical lens or an optical microstructure, and the optical lens or the optical microstructure is arranged on the light-emitting end surface of the refractive index structure, so that the emitted light can be focused or guided by the optical lens or the optical microstructure. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] Figure 1 It is a schematic diagram of a simple three-dimensional structure of a known edge light-emitting diode.

[0022] Figure 2A It is a simplified cross-sectional structural schematic diagram of the first preferred embodiment of the present invention.

[0023] Figure 2B It is a simplified cross-sectional structural schematic diagram of the second preferred embodiment of the present invention.

[0024] Figure 2C It is a simplified three-dimensional structural schematic diagram of the second preferred embodiment of the present invention.

[0025] Figure 3A It is a simplified cross-sectional structural schematic diagram of the third preferred embodiment of the present invention.

[0026] Figure 3B This is a simplified cross-sectional structural diagram of a third preferred embodiment of the present invention in which both the upper cladding layer and the lower cladding layer have optical microstructures.

[0027] Figure 4 It is a simplified cross-sectional structural schematic diagram of the fourth preferred embodiment of the present invention.

[0028] Figure 5 It is a simplified cross-sectional structural diagram of the fifth preferred embodiment of the present invention.

[0029] Fig. 6A It is a simplified cross-sectional structural schematic diagram of the sixth preferred embodiment of the present invention.

[0030] Figure 6B It is a simplified cross-sectional structural diagram of the seventh preferred embodiment of the present invention.

[0031] Figure 7 It is a simplified cross-sectional structural diagram of the eighth preferred embodiment of the present invention.

[0032] Figure 8 It is a simplified cross-sectional three-dimensional structural schematic diagram of the ninth preferred embodiment of the present invention.

[0033] Explanation of symbols:

[0034] 1: Edge LED

[0035] 11,21: Active layer

[0036] 12,22: Upper cladding layer

[0037] 13,23: Lower cladding layer

[0038] 2: Narrow strip edge emission micro-LED

[0039] 211: Surrounding surface

[0040] 2111: Side

[0041] 2112: End face

[0042] 212: Noodles

[0043] 231: convex part

[0044] 24: Insulation layer

[0045] 241: Sub-insulation layer

[0046] 242: Light reflection layer

[0047] 25: First electrode layer

[0048] 26: Second electrode layer

[0049] 27: Waveguide layer

[0050] 28: Substrate

[0051] 29: Reflection layer

[0052] 30: Silicon substrate

[0053] 4: Semiconductor epitaxial layer

[0054] 5: Refractive index structure

[0055] 7: Electrode surface

[0056] 9: Optical microstructure

[0057] D: Direction

[0058] H: Spacing

[0059] L: Length

[0060] W: width. DETAILED DESCRIPTION

[0061] In order to make the above-mentioned objects, features and advantages of the present invention more obvious and easy to understand, the specific embodiments of the present invention are described in detail below in conjunction with the accompanying drawings. In the following description, many specific details are set forth to facilitate a full understanding of the present invention. However, the present invention can be implemented in many other ways different from those described herein, and those skilled in the art can make similar improvements without violating the connotation of the present invention, so the present invention is not limited by the specific embodiments disclosed below.

[0062] It should be noted that when an element is referred to as being "fixed to" or "disposed on" another element, it may be directly on the other element or there may be a central element. When an element is considered to be "connected to" another element, it may be directly connected to the other element or there may be a central element at the same time. The terms "vertical", "horizontal", "upper", "lower", "left", "right" and similar expressions used in the present specification are for illustrative purposes only and do not represent the only implementation method.

[0063] In addition, the terms "first" and "second" are used for descriptive purposes only and should not be understood as indicating or implying relative importance or implicitly indicating the number of the indicated technical features. Therefore, the features defined as "first" and "second" may explicitly or implicitly include at least one of the features. In the description of the present invention, "multiple" and "plurality" mean at least two, such as two, three, etc., unless otherwise clearly and specifically defined.

[0064] In the present invention, unless otherwise clearly specified and limited, a first feature being “above” or “below” a second feature may mean that the first feature is directly in contact with the second feature, or the first feature and the second feature are indirectly in contact through an intermediate medium. Moreover, a first feature being “above”, “above” or “above” a second feature may mean that the first feature is directly above or obliquely above the second feature, or simply means that the first feature is higher in level than the second feature. A first feature being “above”, “above” or “above” a second feature may mean that the first feature is directly below or obliquely below the second feature, or simply means that the first feature is lower in level than the second feature.

[0065] Unless otherwise defined, all technical and scientific terms used in the specification of the present invention have the same meaning as those commonly known to those skilled in the art of the present invention. The terms used in the specification of the present invention are only for the purpose of describing specific embodiments and are not intended to limit the present invention. The term "and / or" used in the specification of the present invention includes any and all combinations of one or more related listed items.

[0066] Please refer to Figure 1 , which shows a known edge emitting LED 1, which adopts a double heterostructure in structure, that is, the upper and lower side layers of an active layer 11 are respectively sandwiched by a cladding layer (12, 13) with a larger energy bandgap but a smaller refraction index. Electrons and holes are injected and confined into the active layer 11 through the upper cladding layer 12 and the lower cladding layer 13, so that electrons and holes have a greater probability of radiative recombination in the active layer 11 to emit light. When the light travels up and down, most of it will be totally reflected and can only be emitted to the two ends of the active layer 11.

[0067] In addition, since the refractive index of the active layer 11 is greater than the refractive index of the cladding layer (12, 13), the light generated by the radiation recombination of electrons and holes in the active layer 11 can also be mostly confined to the active layer 11 for transmission. Since the light is limited in the direction perpendicular to the active layer 11, the divergence angle of the light beam perpendicular to the active layer 11 is also small, about 30 degrees. However, on the left and right sides parallel to the active layer 11, since there is no structural design to limit the light, the radiation distribution of the light source in the direction parallel to the active layer 11 is similar to the Lambertian distribution, and therefore the divergence angle of the light beam parallel to the active layer 11 is large, about 120 degrees.

[0068] Reference Figure 2A As shown, it is a simplified cross-sectional structural diagram of the first embodiment of the present invention. The present invention discloses a narrow strip edge emitting micro-LED 2, which emits light from two end surfaces of the narrow strip structure. The narrow strip edge emitting micro-LED 2 includes: a refractive index structure 5, which provides an optical waveguide effect in all directions perpendicular to the light emission direction. The refractive index structure 5 has a semiconductor epitaxial layer 4 grown in a direction perpendicular to an electrode surface 7. The refractive index of each layer structure in the semiconductor epitaxial layer 4 is different. The semiconductor epitaxial layer 4 includes at least an active layer 21, an upper cladding layer 22 and a lower cladding layer 23. The active layer 21 is located between the upper cladding layer 22 and the lower cladding layer 23. The active layer 21 has a refractive index difference with the upper cladding layer 22 and the lower cladding layer 23 respectively. An insulating layer 24 is coated on at least one side surface of the semiconductor epitaxial layer 4. In a preferred embodiment, the insulating layer 24 at least covers the range of the left and right sides of the active layer 21, but is not limited thereto, and the insulating layer 24 has a lower refractive index than the semiconductor epitaxial layer 4.

[0069] Additional references Figure 2B as well as Figure 2C , which is a simplified cross-sectional structural schematic diagram and a simplified three-dimensional structural schematic diagram of the second embodiment of the present invention. The active layer 21 also includes a surrounding surface 211 and two corresponding surfaces 212 above and below, the surrounding surface 211 is connected to the two surfaces 212, the surrounding surface 211 has two side surfaces 2111 corresponding to the left and right and two end surfaces 2112 corresponding to the front and back, the two surfaces 212 are respectively connected to the upper cladding layer 22 and the lower cladding layer 23, the two side surfaces 2111 are respectively connected to the insulating layer 24, and the active layer 21 only projects a light energy through the two end surfaces 2112 corresponding to the front and back.

[0070] In addition to the above, in this embodiment, the lower cladding layer 23 has a protrusion 231 , the active layer 21 is located on the protrusion 231 , and the active layer 21 projects light energy only from the two end surfaces 2112 corresponding to each other at the front and rear.

[0071] In addition, the narrow strip edge-emitting micro-LED 2 further includes a first electrode layer 25 and a second electrode layer 26. The first electrode layer 25 extends along the electrode surface 7 and is connected to the upper cladding layer 22 in a direction D, and the direction D is perpendicular to the electrode surface 7. The second electrode layer 26 is connected to the lower cladding layer 23 along the direction D. In addition, the insulating layer 24 covers part or all of the upper cladding layer 22, the insulating layer 24 completely covers the two side surfaces 2111 of the active layer 21, and the insulating layer 24 covers part or all of the lower cladding layer 23.

[0072] That is to say, the present invention provides a light waveguide function with the narrow strip refractive index structure 5, and emits light from the two end faces 2112 of the narrow strip active layer 21. Since most of the light will be totally reflected when traveling on the four surfaces of the upper, lower, left and right, and is confined in the refractive index structure of the light waveguide, it can only travel along the long axis direction of the two front and rear end faces 2112. The formation of the refractive index structure 5 is to form the semiconductor epitaxial layer in the direction D perpendicular to the active layer 21 by epitaxial growth, and grow an N-type and P-type cladding layer (22, 23) with a larger energy band gap on the two faces 212 of the active layer 21 with a smaller energy band gap, and the two side faces 2111 of the active layer 21 are respectively connected to the insulating layer 24 to form a double heterostructure to confine the light in the active layer 21, and project a light energy from the two end faces 2112, or project a light energy from one of the two end faces 2112.

[0073] Additional References Figure 3A and Figure 3B , which is a simplified cross-sectional structural diagram of the third preferred embodiment of the present invention, and a simplified cross-sectional structural diagram of the upper cladding layer and the lower cladding layer both having optical microstructures. Of course, in addition to the double heterostructure, a separate confinement heterostructure can also be used, wherein the structure includes an optical waveguide structure composed of the active layer 21, at least one waveguide layer 27 and the two insulating layers 24. Preferably, in this preferred embodiment, the structure includes an optical waveguide structure of five semiconductor layers composed of the active layer 21, the two waveguide layers 27 and the two insulating layers 24, and the two waveguide layers 27 are respectively located between the active layer 21 and the upper cladding layer 22 and between the active layer 21 and the lower cladding layer 23. The structure can confine carriers and photons in the active layer 21 and the waveguide layer 27, respectively. The efficiency of radiation recombination of electrons and holes in the active layer 21 is high, and the generated photons travel and propagate in the waveguide layer 27 with a larger energy band gap and a thicker thickness, and the reabsorption loss by the active layer 21 is also small. It is additionally explained that at least one of the upper cladding layer 22 and the lower cladding layer 23 can have an optical microstructure 9. Preferably, the optical microstructure 9 can be disposed on the top of the upper cladding layer 22 or the bottom of the lower cladding layer 23, but is not limited thereto. Since the light is mainly confined to the active layer 21 and the waveguide layer 27 for propagation, some light that is not confined in the active layer 21 and the waveguide layer 27 needs to rely on the optical microstructure 9 to change its direction and re-enter the active layer 21 and the waveguide layer 27. In other words, the optical microstructure 9 further controls the path of light conduction, improves conduction efficiency, and reduces reabsorption loss. In addition, the optical microstructure 9 can also be applied to the refractive index structure 5.

[0074] Additional References Figure 4 As shown, it is a simplified cross-sectional structural schematic diagram of the fourth preferred embodiment of the present invention. In addition, Figure 4 Another graded-index separate confinement heterostructure is shown. Like the separate confinement heterostructure, the carrier confinement and the photon confinement are designed separately, but the main difference is that for photon confinement, a waveguide layer 27 with a gradient energy band gap is used instead of the waveguide layer 27 with a fixed energy gap. Since the change of the semiconductor energy gap also corresponds to the change of the refractive index, when the compound grows on the semiconductor epitaxially, the waveguide layer 27 can continuously change the size of the energy band gap by continuously changing the composition of the epitaxial layer, thereby achieving the purpose of using the waveguide layer 27 with a gradient refractive index and also making the light confinement better.

[0075] In particular, Figure 2B as well as Figure 2C The disclosed narrow strip structure of the narrow strip edge emission micro-LED is formed by etching away the upper cladding layer 22, the active layer 21 and part of the lower cladding layer 23 outside the narrow strip, Figure 2B as well as Figure 2C The grain structure shown is wide at the bottom and narrow at the top. This narrow strip edge-emitting micro-LED grain that is wide at the bottom and narrow at the top has the advantage of being less likely to fall over. The main claim of the present invention is a narrow strip edge-emitting micro-LED, especially the light emitting direction of the active layer 21, and the four surfaces parallel to the light emitting direction, which are related to the optical waveguide structure formed by the refractive index difference. Therefore, in the production of the grain of the narrow strip edge-emitting micro-LED of the present invention, the upper cladding layer 22, the active layer 21 and the lower cladding layer 23 outside the narrow strip structure can also be completely etched away to form a narrow strip edge-emitting micro-LED grain with the same width at the top and bottom. In addition, due to the factors of the etching manufacturing process, the two side surfaces of the narrow strip edge-emitting micro-LED grain are not necessarily perpendicular to the semiconductor epitaxial layer or the electrode surface, but are slightly inclined, but this does not affect the characteristics of the optical waveguide formed by the refractive index difference.

[0076] That is to say, when using a narrow strip micro-LED with an optical waveguide structure, since the four upper, lower, left, and right surfaces of the active layer 21 are covered with materials with a relatively low refractive index, most of the light traveling to the four upper, lower, left, and right surfaces will be totally reflected and can only be emitted from the two ends of the narrow strip edge-emitting micro-LED. As a result, the divergence angle of the light is small, and the light loss of butt coupling to a transmission medium such as a single-mode optical fiber or an optical waveguide is also small.

[0077] Since the core layer (core) of a single-mode optical fiber or a single-mode optical waveguide is smaller than 10 microns, the strip width of the narrow strip edge-emitting micro-LED of the present invention must also be smaller than 10 microns to effectively couple the light emitted from the end face 2112 to the single-mode optical fiber. If the efficiency of butt-coupling is to be high, the narrow strip width W of the narrow strip edge-emitting micro-LED is as narrow as possible, and it is best that the width is less than half of the core diameter of the single-mode optical fiber, that is, less than 5 microns.

[0078] In addition, if the light-emitting diode has a high modulation bandwidth, it can have a high data transmission rate, and the modulation bandwidth of the light-emitting diode is related to the carrier lifetime and the RC time constant. To improve the modulation bandwidth of the light-emitting diode, the carrier lifetime can be shortened by optimizing the epitaxial structure, or the size of the LED can be reduced, that is, the capacitance is reduced, and therefore, the RC time constant of the light-emitting diode is reduced, so as to achieve the purpose of improving the modulation bandwidth of the light-emitting diode. Referring to the paper "Bandwidth Analysis of High-Speed ​​InGaN, Micro-LEDs by an Equivalent Circuit Model" (IEEE ELECTRON DEVICE LETTERS, VOL. 44, NO. 5, MAY 2023) published by Z. Li et al. in IEEE Electron Device Letters on May 1, 2023, it shows that for a 20-micron device, according to the theoretical value of RC, the transmission speed of the device can reach 4 GHz, and the experimental measurement results are also around 3.5 GHz. The device area of ​​20 microns x 20 microns is equal to 400 square microns. If its area is enlarged by 2.5 times, its -3dB bandwidth is estimated to be 1.4 GHz, which can achieve the design goal of greater than 1 GHz. The following example is given: In order to achieve a modulation bandwidth greater than 1 GHz, the light-emitting area of ​​the LED must be less than 1000 square microns, which is equivalent to the size of a surface-emitting micro-LED of about 32 microns x 32 microns. If converted to the narrow strip edge-emitting micro-LED of the present invention, the width of the narrow strip structure is 10 microns and the length is 100 microns. Of course, using the current chip manufacturing process technology of the present invention, it is also possible to produce a narrow strip edge-emitting micro-LED of a smaller size, such as a micro-LED grain of 2 microns wide and 20 microns long, or a micro-LED grain of 1 micron wide and 10 microns long, and the light-emitting end of a very narrow micro-LED grain can be easily embedded or coupled into a very narrow optical waveguide to achieve the requirement of high bandwidth density.

[0079] In addition, the P-type and N-type metal electrodes of the narrow strip edge-emitting micro-LED are made on the upper and lower surfaces and do not cover the light-emitting surface. In the structural design of the known surface-emitting micro-LED, the metal electrodes are inevitably plated on the light-emitting surface. In order to avoid the metal electrodes shading the light, resulting in poor light-emitting efficiency of the LED, the metal electrodes are generally only partially plated on the light-emitting surface, but this also causes problems such as large contact resistance and uneven current distribution.

[0080] Additional References Figure 5 , which is a simplified cross-sectional structural diagram of the fifth preferred embodiment of the present invention. In this preferred embodiment, the insulating layer 24 includes a sub-insulating layer 241 and a light reflecting layer 242, the sub-insulating layer 241 is attached to the upper cladding layer 22, the light reflecting layer 242 covers the sub-insulating layer 241, and the light reflecting layer 242 is a metal layer with high light reflectivity or a Bragg reflection layer.

[0081] That is to say, in order to achieve the confinement of light on both sides, a layer of low refractive index insulating dielectric (dielectric) or high molecular polymer material is covered on both sides of the narrow strip structure, that is, the refractive index difference between the middle compound semiconductor layer and the sub-insulating layer 241 on both sides is used to achieve the purpose of confining light on both sides. The present invention can also cover the insulating sub-insulating layer 241 with another layer of the light reflecting layer 242, and the light reflecting layer 242 is a metal layer with high reflectivity, or a distributed Bragg reflector (DBR) formed by stacking multiple layers of high and low dielectric materials, so that a better confinement effect can be achieved when light propagates. The present invention forms a narrow strip structure of the edge-emitting micro-LED 2 grain in a direction parallel to the active layer 21, and its width is related to the size of the optical fiber or optical waveguide to be coupled. The narrower the width, the easier it is to couple light to the optical fiber or optical waveguide.

[0082] It should be additionally explained that, since the core diameter of a single-mode optical fiber or a single-mode optical waveguide is less than 10 microns, the strip width of the narrow strip edge-emitting micro-LED of the present invention must also be less than 10 microns to effectively butt-couple the light to the single-mode optical fiber. If the efficiency of butt-coupling is to be further improved, the width of the narrow strip edge-emitting micro-LED is preferably less than half the diameter of the core layer of the single-mode optical fiber, that is, less than 5 microns. Even its width is preferably less than one-quarter the diameter of the core layer of the single-mode optical fiber, that is, less than 2 microns. In this way, even if there are some deviations during butt-coupling, the light can still be effectively coupled to the single-mode optical fiber.

[0083] Also, see Fig. 6A as well as Figure 6B As shown, it is a simplified cross-sectional structural schematic diagram of the sixth preferred embodiment of the present invention, and a simplified cross-sectional structural schematic diagram of the seventh preferred embodiment of the present invention. Fig. 6A This is a 650 nanometer (nm) aluminum gallium arsenide edge-emitting micro-LED structure, showing a cross-sectional view perpendicular to the light emission direction. Figure 6B The narrow strip edge-emitting micro-LED 2 also includes a substrate 28 and a reflective layer 29, the sub-insulating layer 241 is a protective layer with a low refractive index and the light reflective layer 242 is a layer with a high light reflectivity, the substrate 28 is connected to the second electrode layer 26 in the direction D, the reflective layer 29 is connected to the substrate 28 in the direction D, and the lower cladding layer 23 is the convex portion 231 and protrudes from the reflective layer 29.

[0084] That is to say, to illustrate with a more specific embodiment, Fig. 6A The epitaxial structure of the edge-emitting micro-LED can be seen, which includes, from bottom to top, the second electrode layer 26, the substrate 28 of N-type gallium arsenide, the reflective layer 29 of N-type aluminum gallium arsenide (AlGaAs) / aluminum arsenide (AlAs), the lower cladding layer 23 of N-type aluminum gallium indium phosphide (AlInGaP), the active layer 21 of gallium indium phosphide (InGaP), the upper cladding layer 22 of P-type aluminum gallium indium phosphide, and the first electrode layer 25 of P-type high-reflectivity metal, wherein the reflective layer 29 is a distributed Bragg reflector.

[0085] In addition, the two sides of the epitaxial structure are covered with the insulating layer 24, which includes the sub-insulating layer 241 formed by the protective layer of silicon dioxide (SiO2) with a low refractive index, and the metal layer with high light reflectivity covered thereon, or the light reflection layer 242 of the distributed Bragg reflector formed by stacking multiple layers of high and low dielectric materials. Since the four upper, lower, left and right sides of the narrow strip-shaped active layer 21 are respectively surrounded by the upper cladding layer 22, the lower cladding layer 23 and the insulating layer 24 with a smaller refractive index, and the outer periphery of the upper cladding layer 22 and the lower cladding layer 23 is respectively covered by the first electrode layer 25 and the reflection layer P, at the same time, the outer layer of the insulating layer 24 on the left and right sides has a metal layer with high light reflectivity, or the light reflection layer 242 of the distributed Bragg reflector formed by stacking multiple layers of high and low dielectric materials. Therefore, an excellent optical waveguide structure is formed. Most of the light generated by the radiation recombination of electrons and holes in the active layer 21 will be totally reflected when it hits the optical waveguide structure covering the upper, lower, left and right sides thereof, and emitted toward the two ends of the narrow strip structure.

[0086] In addition, if Figure 6BAs shown in the cross-sectional view, the insulating layer 24 can also be covered on one end of the narrow strip edge emitting micro-LED 2, and the sub-insulating layer 241 covered with silicon dioxide and the light reflecting layer 242 with high light reflectivity can cause the light to finally only be emitted from the other end of the edge emitting micro-LED, and the optical microstructure 9 can be made at the light outlet to increase the light emitting and light guiding properties. Therefore, the narrow strip edge emitting micro-LED 2 with a small beam divergence angle and a higher light radiation intensity can be obtained.

[0087] That is to say, the insulating layer 24 is also coated on one of the second end faces 2112 in the same direction of the upper cladding layer 22, the active layer 21 and the lower cladding layer 23, and the active layer 21 only projects the light energy with the other second end face 2112, so as to obtain the narrow strip edge-emitting micro-LED 2 with a small light beam divergence angle and a higher light radiation intensity.

[0088] See also Figure 7 , which is a simplified cross-sectional structural diagram of the eighth preferred embodiment of the present invention. The micro-LED further includes a silicon substrate 30, the silicon substrate 30 is connected to the second electrode layer 26 in the direction D, the lower cladding layer 23 is connected to the silicon substrate 30 in the direction D, and the insulating layer 24 is a distributed Bragg reflector formed by a multi-layer film, and the active layer 21 is a multi-quantum well layer.

[0089] In this embodiment, the present invention is applied to an edge-emitting micro-LED of blue light. Figure 7 As shown, on a silicon substrate 30, the lower cladding layer 23 of N-type aluminum gallium nitride (AlGaN), the waveguide layer 27 of N-type gallium nitride (GaN), the active layer 21 of indium gallium nitride (InGaN) or gallium nitride multiple quantum well layer, another waveguide layer 27 of P-type gallium nitride and the upper cladding layer 22 of P-type aluminum gallium nitride are sequentially grown or wafer bonded to form a separated and confined heterostructure. The insulating layer 24 is coated on the two side surfaces, and the insulating layer 24 is a distributed Bragg reflection layer formed by a multilayer film of silicon dioxide and titanium dioxide (SiO2 / TiO2) staggered and stacked. Due to the waveguide structure formed by the separated and confined heterostructure and the distributed Bragg reflection layer, the propagation of light in the vertical and horizontal directions is limited, so that the narrow strip edge-emitting micro-LED 2 with a small beam divergence angle and high light radiation intensity can be obtained.

[0090] In addition to being able to generate red to yellow-green light, that is, aluminum gallium indium phosphide (AlGaInP) with a wavelength of 560nm to 650nm and aluminum gallium indium nitride (AlGaInN) that can generate blue to green light, the present invention is also applicable to infrared narrow strip edge emitting micro-LEDs made of materials such as AlGaAs, InGaAs, InGaAsP, AlGaInAs, etc.

[0091] See also Figure 8 , which is a simplified cross-sectional three-dimensional structural diagram of the ninth preferred embodiment of the present invention. In this embodiment, the lower cladding layer 23 includes a plurality of convex portions 231, and the plurality of convex portions 231 are arranged in an array manner, and the array manner can be arranged in a horizontal manner, a vertical manner, or a horizontal and vertical arrangement manner, and the refractive index structure 5 is formed on each of the convex portions, so that the narrow strip edge emitting micro-LED 2 has the plurality of refractive index structures 5, the refractive index structure 5 has a width W, the micro-LED 2 has a length L, and two adjacent strip portions 7 are spaced apart by a spacing H.

[0092] That is, this embodiment is an edge-emitting micro-LED array, which uses the plurality of protrusions 231 to be arranged in an array, and the array arrangement is a horizontal arrangement, a vertical arrangement, or a horizontal and vertical arrangement. In this embodiment, the width W is 2 microns, the length L is 10 microns, and the spacing H is 10 microns. Since the beam divergence angle of this embodiment is small, when the light-emitting surface of the narrow strip-shaped edge-emitting micro-LED 2 is very close to the end face of the single-mode optical fiber or polymer waveguide and is positioned and aligned, most of the light emitted from the narrow strip-shaped edge-emitting micro-LED 2 will be able to be more effectively coupled to the single-mode optical fiber or polymer waveguide than the known micro-LED. It is additionally explained that the light-emitting surface of the narrow strip-shaped edge-emitting micro-LED 2 can also be provided with an optical lens or an optical microstructure (not shown in the figure), and the optical lens or the optical microstructure allows the emitted light to be concentrated or guided by the optical lens or the optical microstructure, which can improve the positioning alignment with the end face of the single-mode optical fiber or polymer waveguide.

[0093] In addition, it is worth mentioning that when the total width of the narrow strip edge-emitting micro-LED array of the present invention is 1 millimeter (mm), there will be 100 refractive index structures 5 on the edge-emitting micro-LED array to project the light energy. Assuming that the transmission rate of each narrow strip micro-LED 2 can reach 10 billion bits per second (10Gbps), the overall high bandwidth density of 1Tbps / mm can be achieved.

[0094] If the width W of the narrow strip edge emitting micro-LED 2 is reduced to 1 micron, and the distance H between two adjacent narrow strip edge emitting micro-LEDs is also reduced to 5 microns, then on a 1 mm wide narrow strip edge emitting micro-LED array, there will be 200 narrow strip edge emitting micro-LEDs 2, and the corresponding coupled optical waveguide width is about 3 microns, which is 3 times larger than the narrow strip edge emitting micro-LED 2. Therefore, the efficiency of butt coupling is high. When the data transmission rate of each edge emitting micro-LED 2 can be increased to 15 billion bits per second (15Gbps), a high bandwidth density of 3Tbps / mm can be achieved.

[0095] Since the width W of the narrow strip edge-emitting micro-LED 2 of the present invention is less than 10 microns, the light coupling efficiency of butt coupling to the single-mode optical fiber is high. Even in a short-distance optical link, the light-emitting end of the narrow strip edge-emitting micro-LED 2 can be embedded coupled to the optical waveguide, which is not only a simple light coupling technology, but also can effectively couple most of the light into the optical waveguide.

[0096] In summary, the present invention uses a narrow strip edge light-emitting micro-LED, utilizes a low refractive index or insulating material, and forms an optical waveguide structure around the upper, lower, left and right sides of the active layer to limit the light source to be transmitted in one direction. At the same time, the light source is absorbed and lost less, thereby achieving a micro-LED with a small beam divergence angle and a higher light radiation intensity.

[0097] In addition, the present invention further limits the size of each dimension by using a narrow strip-shaped edge-emitting micro-LED. The narrower the width, the easier it is to couple the light to the optical fiber or optical waveguide, making it easier to align the light source with the optical fiber to be coupled, and the light loss coupled to the optical fiber is smaller. Therefore, the parallel optical link module has the advantages of being miniaturized, thin, and low-cost.

[0098] The above detailed description is a specific description of the feasible embodiments of the present invention. However, the aforementioned embodiments are not intended to limit the patent scope of the present invention. Any equivalent implementation or modification that does not deviate from the technical spirit of the present invention should be included in the patent scope of this case.

Claims

1. A narrow strip edge emitting micro light emitting diode, emitting light from two end surfaces of the narrow strip structure, the micro light emitting diode comprising: A refractive index structure provides an optical waveguide effect in all directions perpendicular to the light emitting direction. The refractive index structure is formed by the refractive index difference of a semiconductor epitaxial layer grown in a direction perpendicular to an electrode surface. The semiconductor epitaxial layer includes at least an active layer, an upper cladding layer and a lower cladding layer. The active layer has a refractive index difference with the upper cladding layer and the lower cladding layer respectively, and the refractive index of the active layer is greater than the refractive index of the upper and lower cladding layers. An insulating layer is coated on at least one side of the semiconductor epitaxial layer. The insulating layer has a smaller refractive index than the semiconductor epitaxial layer. The narrow strip structure has a width less than 10 microns, and the area of ​​the active layer is less than 1000 square microns.

2. The narrow strip edge-emitting micro-LED according to claim 1, characterized in that: The refractive index structure has one or more optical microstructures.

3. The narrow strip edge-emitting micro-LED according to claim 1, characterized in that: The narrow strip edge-emitting micro-LED further comprises a waveguide layer located between the active layer and the upper cladding layer, and between the active layer and the lower cladding layer.

4. The narrow strip edge-emitting micro-LED as claimed in claim 3, characterized in that: The waveguide layer is a graded refractive index waveguide layer.

5. The narrow strip edge-emitting micro-LED as claimed in claim 3, characterized in that: The upper cladding layer or the lower cladding layer has an optical microstructure, or both the upper cladding layer and the lower cladding layer have an optical microstructure.

6. The narrow strip edge-emitting micro-LED according to claim 1, characterized in that: The insulating layer may also be covered with a light reflecting layer.

7. The narrow strip edge-emitting micro-LED according to claim 6, characterized in that: The light reflection layer is a metal layer with high light reflectivity, or a Bragg reflection mirror formed by stacking multiple layers of high and low dielectric materials.

8. The narrow strip edge-emitting micro-LED according to claim 1, characterized in that: The semiconductor epitaxial layer is made of AlGaInN, AlGaInP, AlGaAs, InGaAsP, InGaAs or AlGaInAs material.

9. The narrow strip edge-emitting micro-LED according to claim 1, characterized in that: One of the two end surfaces of the narrow strip structure is covered with the insulating layer and a light reflecting layer, so that light is emitted from the other end surface.

10. The narrow strip edge-emitting micro-LED according to claim 9, characterized in that: The other end surface from which the light is emitted is provided with an optical microstructure.

11. The narrow strip edge-emitting micro-LED according to claim 9, characterized in that: The light reflection layer is a metal layer with high light reflectivity, or a Bragg reflection mirror formed by stacking multiple layers of high and low refractive index dielectric materials.

12. The narrow strip edge-emitting micro-LED according to claim 1, characterized in that: The lower cladding layer includes a plurality of convex portions arranged in an array, and the refractive index structure is formed on each of the convex portions, so that the micro light emitting diode has the plurality of refractive index structures.

13. The narrow strip edge-emitting micro-LED according to claim 12, characterized in that: The array is arranged in a horizontal manner, a vertical manner, or a combination of the horizontal and vertical manners.

14. The narrow strip edge-emitting micro-LED according to claim 12, characterized in that: The narrow strip edge-emitting micro-LED further comprises an optical lens or an optical microstructure, and the optical lens or the optical microstructure is arranged on the light-emitting end surface of the refractive index structure.

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