Multi-junction light-emitting diode, and light-emitting apparatus

Abstract

Disclosed in the present invention is a multi-junction light-emitting diode. The multi-junction light-emitting diode at least comprises: a first epitaxial structure, wherein the first epitaxial structure comprises a first N-type semiconductor layer, a first light-emitting layer and a first P-type semiconductor layer that are stacked in sequence; a second epitaxial structure, wherein the second epitaxial structure comprises a second N-type semiconductor layer, a second light-emitting layer and a second P-type semiconductor layer that are stacked in sequence; and a tunneling junction, wherein the tunneling junction is located between the first epitaxial structure and the second epitaxial structure. The first P-type semiconductor layer includes a first P-type capping layer, and the second P-type semiconductor layer includes a second P-type capping layer and a second P-type window layer. The multi-junction light-emitting diode is characterized in that the material of the first P-type capping layer is Alx1Ga1-x1As, wherein 0<X1<1; and the material of the second P-type capping layer is Alx2Ga1-x2InP or Alx3Ga1-x3As, wherein 0<X2<1, and 0<X3<1. The present invention can solve the technical problems of the high voltage, low brightness and poor reliability of AlGaInP-based red multi-junction light-emitting diodes, thereby improving the light emission efficiency of red multi-junction light-emitting diodes.

Description

Multi-junction light emitting diode and light emitting device TECHNICAL FIELD

[0001] The present application relates to a multi-junction light emitting diode and light emitting device, belonging to the field of semiconductor optoelectronic devices and technology. BACKGROUND

[0002] With the continuous development of modern society, display technology has become the most important window for human-computer interaction in the intelligent society. Compared with liquid crystal display and organic electroluminescent display technology which dominate the display market, micro-size light emitting diode (Micro LED) display technology has the advantages of high efficiency, high brightness, high resolution, low energy consumption, high reliability, etc. and is expected to become the mainstream of future display technology. However, the Micro LED at the present stage still faces many technical challenges, one of which is the efficiency decay effect of light emitting diode chip size reduction.

[0003] Specifically, as the size of red Micro LED decreases, the ratio of the sidewall area to the front light emitting area gradually increases, causing the sidewall of the red Micro LED chip to produce dangling bonds, contaminants or structural damage during the ICP (dry etching) process. Since the carrier diffusion coefficient of the phosphor-based material used in red light is relatively larger than that of the traditional nitrogen-based material, these defects on the sidewall will become non-radiative recombination centers for carriers, resulting in a decrease in the light emitting efficiency of the red Micro LED chip, making the efficiency decay effect of the red Micro LED very serious. Therefore, how to solve the efficiency decay problem of the red Micro LED has become one of the urgent problems to be solved by the technical personnel in the field.

[0004] Light emitting diodes still face other technical challenges, one of which is the efficiency droop effect of light emitting diodes. Specifically, when the light emitting diode is operated in a low current density range, it corresponds to a peak value of external quantum efficiency (EQE). However, as the current density of the light emitting diode continues to rise, the external quantum efficiency will decrease, which is the efficiency droop effect of the light emitting diode.

[0005] Generally speaking, in order to achieve high-brightness light emission, the current density of medium and high-power light emitting diodes is usually in a high current density operating range. Due to the above-mentioned efficiency decay effect, the external quantum efficiency of medium and high-power light emitting diodes in a high current density operating range is limited, and the light emitting efficiency of medium and high-power light emitting diodes cannot be further improved. Therefore, how to improve the light emitting efficiency of medium and high-power light emitting diodes is also one of the problems to be solved by the technical personnel in the field.

[0006] It should be understood that all the information in the Background section is only intended to increase an understanding of the general background of the application and is not intended to be a SUMMARY

[0007] To solve at least one of the above problems, the present application provides a multi-junction light emitting diode, comprising at least: a first epitaxial structure comprising a first N-type semiconductor layer, a first light emitting layer and a first P-type semiconductor layer stacked in sequence; a second epitaxial structure comprising a second N-type semiconductor layer, a second light emitting layer and a second P-type semiconductor layer stacked in sequence; a tunnel junction between the first and second epitaxial structures, the tunnel junction comprising a P-type heavily doped layer connected to the first P-type semiconductor layer and an N-type heavily doped layer connected to the second N-type semiconductor layer; the first P-type semiconductor layer comprising a first P-type cap layer; the second P-type semiconductor layer comprising a second P-type cap layer and a second P-type window layer; characterized in that: the material of the first P-type cap layer is Al x1 Ga 1-x1 As, wherein 0 x2 Ga 1-x2 InP or Al x3 Ga 1-x3 As, wherein 0

[0008] In some preferred embodiments, the material of the first P-type cap layer is Al x1 Ga 1-x1 As, wherein 0.5

[0009] In some preferred embodiments, the thickness of the first P-type cap layer is 0.15-1 μm.

[0010] In some preferred embodiments, the dopant of the first P-type cap layer is C, and the doping concentration of the first P-type cap layer is 3E17-1E19 / cm 3 .

[0011] In some preferred embodiments, the material of the second P-type cap layer is Al x3 Ga 1-x3 As, wherein 0.5

[0012] In some preferred embodiments, the dopant of the second P-type cap layer is C, and the doping concentration of the first P-type cap layer is 3E17-1E19 / cm3.

[0013] In some preferred embodiments, the material of the second P-type cladding layer is Al x2 Ga 1-x2 InP, wherein 0 3 .

[0014] In some preferred embodiments, the P-type heavily doped layer is AlmGa1-mAs, wherein 0

[0015] In some preferred embodiments, the dopant of the P-type heavily doped layer is C, and the doping concentration of the P-type heavily doped layer is greater than 1E20 / cm 3 .

[0016] In some preferred embodiments, the N-type heavily doped layer is Ga n1 In 1-n1 P or Al n2 Ga 1-n2 As, wherein 0

[0017] In some preferred embodiments, the dopant of the N-type heavily doped layer is Te, and the doping concentration of the N-type heavily doped layer is greater than 1E19 / cm 3 .

[0018] In some preferred embodiments, the first epitaxial structure further comprises a first P-type spacer layer, which is located between the first P-type cladding layer and the first light emitting layer, and the first P-type spacer layer is Al a1 Ga 1-a1 As, wherein 0.5

[0019] In some preferred embodiments, the thickness of the first P-type spacer layer is less than 0.4 μm.

[0020] In some preferred embodiments, the first light emitting layer and the second light emitting layer are a structure formed by alternately stacking a plurality of well layers and barrier layers, the well layer is Al p1 Ga 1-p1 InP, the barrier layer is Al q1 Ga 1-q1 InP, wherein 0

[0021] In some preferred embodiments, the first and second epitaxial structures radiate red light with a wavelength of 570-650 nm.

[0022] The application also discloses a light emitting device, characterized in that the light emitting device comprises the multi-junction light emitting diode according to any one of the preceding embodiments.

[0023] The P-type cover layer material of the first epitaxial structure is AlGaAs material, and P-type doping is realized by C doping, so that the technical problems of high voltage, low brightness and poor reliability of the AlInP doped Mg material used as the P-type material in the original AlGaInP red multi-junction light emitting diode are solved, and the light emitting efficiency of the red multi-junction LED is improved.

[0024] Other features and advantages of the present application will be set forth in the following description, and in part will become apparent to those skilled in the art from the description, or can be learned by practice of the present application. The objects and other advantages of the present application can be realized and attained by the structure particularly pointed out in the description, claims and drawings. BRIEF DESCRIPTION OF DRAWINGS

[0025] The accompanying drawings are included to provide a further understanding of the present application, and constitute a part of the specification, illustrate embodiments of the present application, and are used to explain the present application, and do not constitute a limitation of the present application. In addition, the drawing data is a description summary, and is not drawn to scale.

[0026] Fig. 1 is a schematic diagram of the epitaxial structure mentioned in the embodiment 1 of the present application.

[0027] Fig. 2 is a schematic diagram of the structure of the light emitting diode mentioned in the embodiment 1 of the present application.

[0028] Fig. 3 is a schematic diagram of the structure of the micro light emitting element mentioned in the embodiment 1 of the present application.

[0029] Figs. 4-9 are schematic diagrams of the structure of the micro light emitting element in the preparation process mentioned in the embodiment 1 of the present application.

[0030] Fig. 10 is a schematic diagram of the cross section of the micro light emitting element of the embodiment 3 of the present application.

[0031] Fig. 11 is a schematic diagram of the cross section of the micro light emitting diode of the embodiment 4 of the present application.

[0032] Fig. 12 is a schematic diagram of the cross section of the multi-junction light emitting diode of the embodiment 5 of the present application.

[0033] Fig. 13 is a schematic diagram of the cross section of the micro light emitting diode of the embodiment 6 of the present application.

[0034] Fig. 14 is a schematic diagram of the light emitting device of the embodiment 7 of the present application.

[0035] Growth substrate: 100; Buffer layer: 101; Etch stop layer: 102; First epitaxial structure: 200; Tunnel junction: 300; Second epitaxial structure: 400; First N-type window layer: 201; First N-type cladding layer: 202; First N-type spacer layer: 203; First light emitting layer: 204; First P-type spacer layer: 205; First P-type cladding layer: 206; P-type heavily doped layer: 301; N-type heavily doped layer: 302; Second N-type cladding layer: 401; Second N-type spacer layer: 402; Second light emitting layer: 403; Second P-type spacer layer: 404; Second P-type cladding layer: 405; Second P-type window layer: 406; Second P-type ohmic contact layer: 407; Substrate: 901; Bonding layer: 902; First electrode: 501; Ohmic contact portion of the first electrode: 501a; Ohmic contact portion of the second electrode: 502a; Second electrode: 502; Pad electrode of the first electrode: 501b; Pad electrode of the second electrode: 502b; Insulating protective layer: 600; Horizontal portion of the insulating protective layer: 2071; Sacrificial layer: 800; Base frame: 900; Bridge arm: 700; Light emitting device: 300; Micro light emitting diode: 1. DETAILED DESCRIPTION

[0036] In order to make the objects, technical solutions and advantages of the embodiments of the present application clearer, the technical solutions in the embodiments of the present application will be described clearly and completely below with reference to the drawings in the embodiments of the present application. Obviously, the described embodiments are some but not all of the embodiments of the present application. Based on the embodiments in the present application, all other embodiments obtained by a person of ordinary skill in the art without creative work fall within the protection scope of the present application. Embodiment 1

[0037] Referring to FIG. 1, the present application provides a multi-junction LED epitaxial structure, and a double-junction LED epitaxial structure is taken as an example in the embodiment, which comprises a first epitaxial structure 200, a tunnel junction 300 and a second epitaxial structure 400 stacked in turn on a growth substrate 100 from bottom to top. The first epitaxial structure 200 comprises a first N-type semiconductor layer, a first light emitting layer and a first P-type semiconductor layer stacked in turn; the second epitaxial structure 400 comprises a second N-type semiconductor layer, a second light emitting layer and a second P-type semiconductor layer stacked in turn; the tunnel junction 300 is located between the first epitaxial structure 200 and the second epitaxial structure 300, and the tunnel junction comprises a P-type heavily doped layer 301 and an N-type heavily doped layer 302, the P-type heavily doped layer 301 is connected to the first P-type semiconductor layer, and the N-type heavily doped layer 302 is connected to the second N-type semiconductor layer.

[0038] The first N-type semiconductor layer comprises a first N-type window layer 201, a first N-type cover layer 202 and a first N-type isolation layer 203; the first P-type semiconductor layer comprises a first P-type isolation layer 205 and a first P-type cover layer 206; and the first light-emitting layer 204 is located between the first N-type isolation layer 203 and the first P-type isolation layer 205.

[0039] Specifically, referring to FIG. 1, the material of the growth substrate 100 includes but is not limited to GaAs, and other materials such as GaP, InP, etc. can also be used. In this embodiment, the GaAs growth substrate 100 is taken as an example. Optionally, a buffer layer 101 and an etching stop layer 102 are sequentially arranged between the growth substrate 100 and the first N-type window layer 201; since the lattice quality of the buffer layer 101 is better than that of the growth substrate 100, growing the buffer layer 101 on the growth substrate 100 is beneficial to eliminate the influence of the lattice defects of the growth substrate 100 on the semiconductor epitaxial stack; and the etching stop layer 102 is used as a stop layer for chemical etching in a later step. In some optional embodiments, the etching stop layer 102 is an n-type etching stop layer, and the material is n-GaInP. In order to facilitate the subsequent removal of the growth substrate 100, the thickness thereof is controlled to be within 500 nm, and more preferably within 200 nm.

[0040] The double-junction LED epitaxial structure can be formed on the growth substrate 100 by means of physical vapor deposition (PVD), chemical vapor deposition (CVD), epitaxial growth (Epitaxy Growth Technology) and atomic layer deposition (ALD), etc. The double-junction LED epitaxial structure is a semiconductor material capable of providing conventional radiation such as ultraviolet, blue, green, yellow, red, infrared light, etc. Specifically, it can be a material of 200-950 nm, such as a common nitride, specifically a gallium nitride-based semiconductor epitaxial stack, which is commonly doped with elements such as aluminum and indium, and mainly provides radiation in the 200-550 nm band; or a common aluminum gallium indium phosphorus-based or aluminum gallium arsenide-based semiconductor epitaxial stack, which mainly provides radiation in the 550-950 nm band. In this embodiment, the materials of the first epitaxial structure and the second epitaxial structure are preferably aluminum gallium indium phosphorus materials or aluminum gallium arsenide materials, and the wavelengths of the radiation of the first epitaxial structure and the second epitaxial structure are red light of 570-650 nm.

[0041] The first N-type semiconductor layer and the first P-type semiconductor layer can be respectively doped with n-type dopants or p-type dopants to provide electrons or holes. The n-type semiconductor layer can be doped with n-type dopants such as Si, Ge or Sn, and the p-type semiconductor layer can be doped with p-type dopants such as Mg, Zn, Ca, Sr, C or Ba. The first N-type semiconductor layer, the first light-emitting layer and the first P-type semiconductor layer can be made of materials such as aluminum gallium indium nitride, gallium nitride, aluminum gallium nitride, aluminum indium phosphide, aluminum gallium indium phosphide or gallium arsenide or aluminum gallium arsenide. In this embodiment, the first N-type semiconductor layer, the first light-emitting layer and the first P-type semiconductor layer are preferably made of aluminum indium phosphide, aluminum gallium indium phosphide or gallium arsenide or aluminum gallium arsenide.

[0042] The first N-type semiconductor layer and the first P-type semiconductor layer respectively include a first N-type cladding layer 202 and a first P-type cladding layer 206 for providing electrons or holes for the first light-emitting layer 204, such as aluminum gallium indium phosphide or aluminum indium phosphide or aluminum gallium arsenide. More preferably, when the material of the first light-emitting layer 204 is aluminum gallium indium phosphide, aluminum indium phosphide is used as the first N-type cladding layer 202 and the first P-type cladding layer 206 to provide electrons and holes. In order to improve the uniformity of current spreading, the first N-type semiconductor layer further includes a first N-type window layer 201.

[0043] Since the hole mobility is smaller than the electron mobility, the electrons and holes tend to recombine and emit light in the active region near the P-type cladding layer end, resulting in a waste of the active region area and thus reducing the internal quantum efficiency of the light-emitting chip. In order to adjust the position of the recombination and light emission of the electrons and holes in the active region (MQW) of the light-emitting diode and make full use of the active region area, this embodiment preferably includes a first N-type spacer layer 203 between the first N-type cladding layer 201 and the first light-emitting layer 204, and a first P-type spacer layer 205 between the first P-type cladding layer 206 and the first light-emitting layer 204.

[0044] The first N-type window layer 201 plays a role in current spreading, and its spreading ability is related to the thickness. In this embodiment, the material is preferably Al y1 Ga 1-y1 InP, where 0 < y1 < 1, the thickness is 0-6000 nm, preferably 2500-4500 nm, and the n-type doping concentration is 2E17-5E18 / cm 3 , preferably 3E17-4E18 / cm 3 . The n-type doping is commonly Si doping, and other element doping is not excluded.

[0045] The first N-type spacer layer 203 is located between the first N-type cladding layer 202 and the first light-emitting layer 204, and the material is preferably Al b1 Ga 1-b1InP, the thickness of the first N-type spacer layer 203 is preferably 120 nm or less, the Al component content b1 is in the range of 0.2 ~ 1; in the present embodiment, the first N-type spacer layer 203 is preferably n-type doped, and the doping concentration is less than 2E17 / cm 3 .

[0046] The first N-type cover layer 202 provides electrons for the first light emitting layer 204, and the material of the first N-type cover layer is Al c1 Ga 1-c1 InP, wherein 0 < c1 ≤ 1, and the preferred material is AlInP, and the thickness is 100 ~ 2000 nm; the n-type doping concentration is 3E17 ~ 2E18 / cm 3 The n-type doping is commonly Si doping, and other element equivalent doping is not excluded.

[0047] The first light emitting layer 204 provides a light radiation region for electron and hole recombination, and different materials can be selected according to different light emitting wavelengths. The first light emitting layer 204 can be a single quantum well or a periodic structure of multiple quantum wells. In the present embodiment, the first light emitting layer 204 is a quantum well structure of n1 periods, each quantum well structure comprising a well layer and a barrier layer deposited in sequence, wherein the barrier layer has a larger band gap than the well layer. By adjusting the composition ratio of the semiconductor material in the first light emitting layer 204, light of a desired wavelength can be radiated. The first light emitting layer 204 is a material layer for providing electroluminescence radiation, such as aluminum gallium indium phosphorus or aluminum gallium arsenide, and more preferably aluminum gallium indium phosphorus. The aluminum gallium indium phosphorus is a single quantum well or a multiple quantum well. In the present embodiment, the multi-junction red LED epitaxial structure is composed of AlGaInP-based materials, and the first light emitting layer 204 radiates light with a wavelength of 550 ~ 750 nm.

[0048] In the present embodiment, the number of periods n1 of the first light emitting layer 204 is 2 ~ 100. The well layer is composed of Al p1 Ga 1-p1 InP materials; the barrier layer is composed of Al q1 Ga 1-q1 InP materials, wherein 0 ≤ p1 ≤ q1 ≤ 1. The thickness of the well layer is 2 ~ 25 nm, and is preferably 3 ~ 10 nm; the thickness of the barrier layer is 2 ~ 25 nm, and is preferably 3 ~ 10 nm. The Al component content y of the barrier layer is in the range of 0.3 ~ 0.85.

[0049] In existing red epitaxial structures, the P-type capping layer is generally made of AlInP material, with Mg doping to achieve P-type doping. However, Mg material suffers from segregation, memory effect, and severe diffusion problems, leading to reduced luminous efficiency and decreased reliability of the first epitaxial structure. Furthermore, the memory effect of Mg material results in excessively high residual Mg concentration in the second epitaxial structure, causing high voltage, low luminous efficiency, and poor reliability. Therefore, in this embodiment, the first P-type capping layer 206 material of the first epitaxial structure is Al. x1 Ga 1-x1 As, where 0 < X1 < 1; preferably 0.5 < X1 < 1, to reduce the light absorption effect of the first P-type capping layer 206. The thickness of the first P-type capping layer 206 is 0.15~1μm, preferably 0.2μm or more and 0.8μm or less. The dopant of the first P-type capping layer 206 is C, and the doping concentration of the first P-type capping layer 206 is 3E17~1E19 / cm. 3 The preferred value is 5E17 / cm 3 That's all. In this embodiment, the P-type capping layer material of the first epitaxial structure is AlGaAs material. P-type doping is achieved by C doping, which can solve the technical problems of high voltage, low brightness and poor reliability that occurred when AlInP-doped Mg material was used as the P-type material in the original AlGaInP-based red multi-junction LED, thereby improving the luminous efficiency of red multi-junction LED.

[0050] The first P-type spacer layer 205 is located above the first light-emitting layer 204, and the material of the first P-type spacer layer 205 is preferably Al. a1 Ga 1-a1 As, where 0.5 < a1 < 1. The doping concentration of the first p-type spacer layer 205 is less than 2E17 / cm. 3 Because the first P-type capping layer uses Al a Ga 1-a As material with C doping, C element does not have a diffusion effect, so the thickness of the first P-type spacer layer 205 can be reduced. The first P-type spacer layer 205 is preferably less than 40 nm. Reducing the thickness of the first P-type spacer layer 205 allows holes to quickly enter the first light-emitting layer for radiative recombination, reducing the sidewall effect and thus improving the luminous efficiency of the multi-junction light-emitting diode.

[0051] A tunnel junction 300 is located between the first epitaxial structure 200 and the second epitaxial structure 400. The tunnel junction 300 includes a heavily p-type doped layer 301 and an heavily n-type doped layer 302. The heavily p-type doped layer 301 is connected to the first p-type semiconductor layer, and the heavily n-type doped layer 302 is connected to the second n-type semiconductor layer. The heavily p-type doped layer 301 is Al. m Ga 1-mAs, where 0 < m < 1, the thickness of the P-type heavily doped layer 301 is 0.01-0.03 μm. The dopant of the P-type heavily doped layer 301 is C, and the doping concentration of the P-type heavily doped layer 301 is greater than 1E20 / cm 3 . The N-type heavily doped layer 302 is Ga n1 In 1-n1 P or Al n2 Ga 1-n2 As, where 0 < n1 < 1, 0 < n2 < 1; the thickness of the N-type heavily doped layer 302 is 0.01-0.03 μm. The dopant of the N-type heavily doped layer 302 is Te, and the doping concentration of the N-type heavily doped layer is greater than 1E19 / cm 3 .

[0052] The second epitaxial structure 400 comprises a second N-type semiconductor layer, a second light-emitting layer and a second P-type semiconductor layer stacked in sequence; the second N-type semiconductor layer comprises a second N-type cover layer 401 and a second N-type isolation layer 402 stacked from bottom to top, and the second P-type semiconductor layer comprises a second P-type isolation layer 404, a second P-type cover layer 405, a second P-type window layer 406 and a second P-type ohmic contact layer 407 stacked from bottom to top.

[0053] The second N-type cover layer 401 provides electrons for the second light-emitting layer 403, and the preferred material is Al y1 Ga 1-y1 InP, where 0 < y1 < 1, the preferred material is AlInP, and the thickness is 150-300 nm; the n-type doping concentration is 3E17-2E18 / cm 3 The n-type doping is commonly Si doping, and other element equivalent substitution doping is not excluded.

[0054] In some embodiments, the second epitaxial structure comprises a second N-type isolation layer 402 between the second N-type cover layer 401 and the second light-emitting layer 403. The preferred material of the second N-type isolation layer 402 is Al b2 Ga 1-b2 InP, the thickness of the second N-type isolation layer 302 is preferably less than 120 nm, and the Al component content b1 is in the range of 0.2-1; the doping concentration of the second N-type isolation layer 402 in this embodiment is less than 2E17 / cm 3 .

[0055] The second light emitting layer 403 provides a light radiation region for electron and hole recombination. Different materials can be selected according to different light emitting wavelengths. The second light emitting layer 403 can be a single quantum well or a periodic structure of multiple quantum wells. In the embodiment, the second light emitting layer 403 is a quantum well structure with n2 periods, each quantum well structure comprising a well layer and a barrier layer deposited in sequence, wherein the barrier layer has a larger band gap than the well layer. The composition ratio of the semiconductor material in the second light emitting layer 403 is adjusted to radiate light with a target wavelength. The second light emitting layer 403 is a material layer for providing electroluminescence radiation, such as aluminum gallium indium phosphorus or aluminum gallium arsenide, and more preferably aluminum gallium indium phosphorus. The aluminum gallium indium phosphorus is a single quantum well or a multiple quantum well. In the embodiment, the multi-junction red LED epitaxial structure is composed of AlGaInP-based materials, and the second light emitting layer 402 radiates light with a wavelength of 550-750 nm.

[0056] In the embodiment, the number n2 of periods of the second light emitting layer 403 is 1-100. The well layer is composed of Al p2 Ga 1-p2 InP materials; and the barrier layer is composed of Al q2 Ga 1-q2 InP materials, wherein 0≤p2≤q2≤1. The thickness of the well layer is 2-25 nm, and preferably 3-10 nm. The thickness of the barrier layer is 2-25 nm, and preferably 3-10 nm. The Al composition content y of the barrier layer ranges from 0.3 to 0.85.

[0057] The second P-type cladding layer 405 provides holes for the second light emitting layer 403. In some embodiments, the material of the second P-type cladding layer 405 is AlInP, and the thickness is 150-2000 nm. The P-type doping is commonly Mg doping, and other element equivalent doping is not excluded. In some embodiments, the material of the second P-type cladding layer 405 is AlGaAs, and the thickness is 150-2000 nm. The P-type doping is commonly C doping, and other element equivalent doping is not excluded. The doping concentration of the second P-type cladding layer 405 is 3E17-2E18 / cm 3 , and preferably 5E17 / cm 3 .

[0058] In some embodiments, a second P-type spacer layer Al a2 Ga 1-a2 InP is preferably provided between the second light emitting layer 403 and the second P-type cladding layer 405, wherein 0 3 .

[0059] The second P-type window layer 406 plays a role of current spreading, and its spreading capability is related to its thickness, so in this embodiment, its thickness can be selected according to the size of the device, and preferably, the thickness is controlled to be greater than 200 nm and less than 800 nm. In this embodiment, the thickness of the second P-type window layer 406 is preferably 300-500 nm. In this embodiment, the preferred material is GaP, and the p-type doping concentration is 5E17-2E18 / cm 3 The p-type doping is commonly C doping, and other element equivalent doping is not excluded.

[0060] The second P-type ohmic contact layer 407 is covered on the second P-type window layer 406, and the preferred material is GaP, and the thickness is 10-50 nm, and the preferred doping concentration is 1E20 / cm 3 The second P-type ohmic contact layer 407 is covered on the second P-type window layer 406, and the preferred material is GaP, and the thickness is 10-50 nm, and the preferred doping concentration is 1E20 / cm

[0061] In some embodiments, the multi-junction light emitting diode belongs to a micro light emitting diode, that is, a light emitting diode with a size of microns. Due to the small size of the micro light emitting diode, its manufacturing process is very different from that of a traditional light emitting diode. The micro light emitting diode in this application mainly refers to a size of less than or equal to 100 microns. The size, for example, includes a range of length, width, or height from greater than or equal to 2 μm to less than 5 μm, from greater than or equal to 5 μm to less than 10 μm, from greater than or equal to 10 μm to less than 20 μm, from greater than or equal to 20 μm to less than 50 μm, or from greater than or equal to 50 μm to less than or equal to 100 μm. The micro light emitting diode can be widely used in display, lighting, and other fields.

[0062] In some embodiments, the multi-junction light emitting diode belongs to a high-power light emitting diode, which can have a power of 1 W, 2 W, or even tens of watts, and a working current of tens of milliamperes to hundreds of milliamperes. The high-power light emitting diode has the advantages of small size, low power consumption, low heat generation, long service life, fast response speed, low voltage, good weather resistance, good directivity, etc. It can be applied to most lighting fields, such as medical devices and display screen back lighting sources. It meets the high requirements of brightness and luminous efficiency of LEDs required by current applications.

[0063] Figure 2 shows a schematic diagram of a light emitting diode in an embodiment, which employs the epitaxial structure shown in Figure 1. The light emitting diode is a micro light emitting diode, which comprises: a semiconductor epitaxial stack, containing a first epitaxial structure 200, a tunnel junction 300 and a second epitaxial structure 400 stacked in sequence; a first mesa, which is composed of the first N-type window layer 201 exposed by the semiconductor epitaxial stack; a second mesa S2, which is composed of the second P-type semiconductor layer; a first electrode 501, which is formed on the first mesa and electrically connected with the first N-type window layer; and a second electrode 502, which is formed on the second mesa and electrically connected with the second P-type semiconductor layer.

[0064] The conductive metal that contacts the first N-type window layer 201 of the first electrode 501 can be selected from gold, platinum or silver, or a transparent conductive oxide, specifically ITO, ZnO, etc. More preferably, the first electrode 501 can be a multi-layer material, such as an alloy material comprising at least one of gold germanium nickel, gold beryllium, gold germanium, gold zinc, etc. More preferably, the first electrode 501 can further comprise a reflective metal, such as gold or silver, which reflects the light radiated from the active layer and penetrating through the first N-type semiconductor layer back to the semiconductor epitaxial stack and out of the light emitting side.

[0065] The second electrode 502 is preferably made of a conductive metal, such as gold, platinum or silver, to form a good ohmic contact with the second P-type ohmic contact layer 407 of the second P-type semiconductor layer. More preferably, the second electrode 502 can be a multi-layer material, which comprises an alloy material comprising at least one of gold germanium nickel, gold beryllium, gold germanium, gold zinc, etc. More preferably, to improve the ohmic contact effect between the second electrode 502 and the second P-type ohmic contact layer 407, at least one metal capable of diffusing to the side of the second P-type ohmic contact layer 407 can be included to improve the ohmic contact resistance, and a fusion temperature of at least 300°C can be selected to facilitate the diffusion. The diffusing metal can be a metal that can directly contact the side of the second P-type ohmic contact layer 407, such as gold, platinum or silver.

[0066] To improve the reliability of the micro light emitting diode, an insulating protective layer (not shown in Figure 2) is provided on the first mesa, the second mesa S2 and the sidewall of the micro light emitting diode, which is a single layer or a multi-layer structure formed by at least one of SiO2, SiN x , Al2O3, Ti3O5. In some alternative embodiments, the insulating protective layer is a Bragg reflection layer structure, for example, the insulating protective layer is formed by alternately stacking Ti3O5 or titanium dioxide and SiO2. In this embodiment, the material of the insulating protective layer can be SiNx or SiO2, and the thickness is at least 1 μm.

[0067] In this embodiment, the first electrode 501 and the second electrode 502 are located on the opposite side of the light emitting side, and the first electrode 501 and the second electrode 502 can be in contact with the external electrical connector through the opposite side of the light emitting side, forming an inverted structure. Therefore, the first electrode 501 and the second electrode 502 include ohmic contact portions 501a and 502a and pad electrodes 501b and 502b, which can be at least one layer such as gold, aluminum, or silver to realize die bonding of the first electrode 501 and the second electrode 502. The first electrode 501 and the second electrode 502 can be equal in height or not equal in height, and the pad metal layers of the first electrode and the second electrode do not overlap in the thickness direction.

[0068] Figure 3 is a schematic diagram of a micro light emitting element formed using the multi-stage light emitting diode of the present embodiment, which also includes a base frame 900 supporting the micro light emitting diode, the base frame 900 being located on the lower side of the micro light emitting diode, and a bridge arm 700 connecting the micro light emitting diode and the base frame 900; the base frame 900 includes a substrate 901 and a bonding layer 902, and in this embodiment the material of the bonding layer 902 is BCB glue, silicone glue, UV ultraviolet glue, or resin, and the material of the bridge arm 700 includes dielectric, metal, or semiconductor material. In some embodiments, the horizontal portion of the insulating protective layer can be used as the bridge arm 700, bridging the bonding layer 902 and connecting the micro light emitting diode and the base frame 900.

[0069] The micro light emitting diode is separated from the base frame 900 by printing a stamp, and the printing stamp material is PDMS, silicone glue, pyrolytic glue, or UV ultraviolet glue. In some cases, the micro light emitting diode and the base frame have a sacrificial layer 800 therebetween, and at least in some cases the removal efficiency of the sacrificial layer 800 is higher than that of the micro light emitting diode, and the specific cases include chemical decomposition or physical decomposition, such as ultraviolet light decomposition, etching removal, or impact removal, etc. Embodiment 2

[0070] Figures 4-9 show schematic diagrams of the manufacturing process of the micro light emitting element according to the present embodiment, and the manufacturing method of the micro light emitting diode of the present embodiment will be described in detail below in conjunction with the schematic diagrams.

[0071] First, as shown in Fig. 1, an epitaxial structure is provided, which specifically comprises the following steps: providing a growth substrate 100, epitaxially growing a semiconductor epitaxial stack on the growth substrate 100 by epitaxial growth such as MOCVD, the semiconductor epitaxial stack comprising a buffer layer 101 and an etch stop layer 102 successively stacked on the surface of the growth substrate 100, for removing the epitaxial growth substrate 100, then growing a first epitaxial structure 200, a tunnel junction 300 and a second epitaxial structure 400. The first epitaxial structure 200 comprises, from bottom to top, a first N-type window layer 201, a first N-type cover layer 202, a first N-type isolation layer 203, a first light emitting layer 204, a first P-type isolation layer 205 and a second P-type cover layer 206 successively stacked; the tunnel junction comprises a P-type heavily doped layer 301 and an N-type heavily doped layer 302. The second epitaxial structure 400 comprises, from bottom to top, a second N-type cover layer 401, a second N-type isolation layer 402, a second light emitting layer 403, a second P-type isolation layer 404, a second P-type cover layer 405, a second P-type window layer 406 and a second P-type ohmic contact layer 407 successively stacked.

[0072] Then, as shown in Fig. 4, a part of the semiconductor epitaxial stack is removed by dry etching to form a first mesa and a second mesa, the first mesa being composed of the first N-type window layer exposed by the recess of the semiconductor epitaxial stack, and the second mesa being composed of the second P-type semiconductor layer; a side wall is formed at the outer edge of the semiconductor epitaxial stack between the first mesa and the second mesa.

[0073] Next, as shown in Fig. 5, a first electrode 501 and a second electrode 502 are respectively fabricated on the first mesa and the second mesa; wherein the first electrode 501 and the second electrode 502 comprise an ohmic contact part 501a and 502a, an insulating protective layer 600 is covered on the ohmic contact part, and a pad electrode 501b and 502b is respectively formed on the insulating protective layer 600 to contact the ohmic contact part 501a and 502a. The material of the ohmic contact part 501a and 502a can be Au / AuZn / Au or AuGeNi, for example, and the ohmic contact part 501a and 502a can be fused in this step to form a good ohmic contact with the semiconductor epitaxial stack. The insulating protective layer 600 is preferably SiNx or SiO2, and the thickness is more than 1 μm. In other alternative embodiments, the insulating protective layer 600 can adopt a Bragg reflection layer structure formed by two materials with different refractive indexes alternately stacked.

[0074] Next, as shown in Fig. 6, a sacrificial layer 800 is covered on the surface of the micro-LED; preferably, the thickness of the sacrificial layer 800 covered on the side wall is more than 1 μm, and the material of the sacrificial layer 800 can be an oxide, a nitride or a material that can be selectively removed relative to other layers.

[0075] Next, referring to Fig. 7, a bonding glue, such as BCB glue, is bonded on the sacrificial layer 800 of the micro-LED, forming a bonding layer 902.

[0076] Next, referring to Fig. 8, the wafer of the distributed micro-LED is bonded to the substrate 901.

[0077] Next, referring to Fig. 9, the growth substrate 100 is peeled off, and the buffer layer 101 and the etching stop layer 102 are removed.

[0078] Next, by masking and etching, the first type semiconductor layer at the edge of the micro-LED is removed, and the etching is stopped on the insulating protective layer, forming an independent core particle, facilitating the separation of the subsequent core particle, and obtaining the micro-LED element as shown in Fig. 3.

[0079] Finally, the formed micro-LED element is separated from the substrate 901 by transfer printing and transferred to a packaging substrate. (Not shown in the figure) Example 3

[0080] Compared with the micro-LED element shown in Fig. 3 of Example 1, in order to further improve the efficiency of the light emitted from the active layer 106 from the light-emitting surface, as shown in Fig. 10, the surface of the first N-type window layer 201 has a roughening structure composed of regular or irregular protrusions. Example 4

[0081] Compared with the micro-LED shown in Fig. 2 of Example 1, as shown in Fig. 11, the first electrode 501 and the second electrode 502 are on different sides, and the micro-LED in this embodiment is a vertical structure. The side of the second P-type ohmic contact layer 407 away from the second light-emitting layer 403 is the light-emitting surface, and the space between the first N-type window layer 201 and the first electrode 502 can be covered with a reflective metal or a reflective insulating dielectric layer (not shown in the figure). The part of the light radiated from the first light-emitting layer 204 and penetrating through the first N-type window layer 201 is reflected back to the semiconductor epitaxial layer, and is emitted from the light-emitting side. Example 5

[0082] Fig. 12 shows a schematic diagram of a multi-junction light-emitting diode in another embodiment, which adopts the epitaxial structure shown in Fig. 1, and the current density of the light-emitting diode is greater than 10 A / cm 2 The size of the light-emitting diode is preferably greater than 100 μm, that is, the length of at least one side of the light-emitting tube is greater than 100 μm, preferably greater than 300 μm or more. The light-emitting diode is mainly applied to outdoor display screens, plant lighting, stage lights and other fields.

[0083] The light emitting diode comprises a substrate 901, a semiconductor epitaxial stack is bonded to the substrate 901 through a bonding layer 902, the semiconductor epitaxial stack comprises a second P-type ohmic contact layer 407, a second P-type window layer 406, a second P-type cover layer 405, a second P-type isolation layer 404, a second light emitting layer 403, a second N-type isolation layer 402, a second N-type cover layer 401, an N-type heavily doped layer 302, a P-type heavily doped layer 301, a first P-type cover layer 206, a first P-type isolation layer 205, a first light emitting layer 204, a first N-type isolation layer 203, a first cover layer 202 and a first N-type window layer, which are sequentially stacked on the substrate 901.

[0084] The substrate 901 is a conductive substrate, which can be a silicon, silicon carbide or metal substrate, and the metal substrate is preferably a copper, tungsten or molybdenum substrate. In order to support the semiconductor epitaxial stack with sufficient mechanical strength, the thickness of the substrate 901 is preferably greater than 50 μm. In addition, in order to facilitate the mechanical processing of the substrate 901 after bonding to the semiconductor epitaxial stack, the thickness of the substrate 901 is preferably less than 300 μm. In the present embodiment, the substrate 901 is preferably a silicon substrate.

[0085] The first electrode 501 is disposed on the first N-type window layer 201, and a first N-type ohmic contact layer (not shown in the figure) is further disposed between the first N-type window layer and the first electrode 501. The first electrode 501 forms an ohmic contact with the first N-type ohmic contact layer to realize current flow.

[0086] A mirror layer 1000 can be disposed between the semiconductor epitaxial stack and the substrate 901, and the mirror layer 1000 comprises a P-type ohmic contact metal layer 1000a and a dielectric material layer 1000b, which cooperate to form an ohmic contact with the second P-type ohmic contact layer 407 on one hand, and to reflect the light beams emitted by the first light emitting layer and the second light emitting layer to the light emitting surface of the first N-type window layer 201 or the sidewall of the semiconductor epitaxial stack on the other hand.

[0087] The light emitting diode further comprises a second electrode 502. In some embodiments, the second electrode 502 is disposed on the back surface of the substrate 901. Alternatively, the second electrode 502 is disposed on the substrate 901 on the same side as the semiconductor epitaxial stack.

[0088] The first electrode 501 and the second electrode 502 comprise a transparent conductive material and / or a metal material. The transparent conductive material comprises a transparent conductive layer such as ITO or IZO, and the metal material comprises at least one of GeAuNi, AuGe, AuZn, Au, Al, Pt and Ti.

[0089] In some embodiments, the surface of the first N-type window layer has a rough surface, which can improve the light extraction efficiency of the multi-junction light emitting diode, thereby improving the light emitting efficiency. Embodiment 5

[0090] Compared with the micro light emitting element described in Figure 3 in Embodiment 1, as shown in Figure 13, the micro light emitting diode is bonded on a substrate 901 through a bonding layer 902, which can be BCB glue or PI. The substrate 901 can be a sapphire substrate. The micro light emitting element in this embodiment can be transferred to a packaging substrate by laser peeling and the like. (not shown in the figure) Embodiment 6

[0091] This embodiment provides a light emitting device 300, please refer to Figure 14, the light emitting device 300 includes a plurality of array arranged micro light emitting diodes 1 as any of the preceding embodiments, a part of the micro light emitting diodes 1 is shown in Figure 16 in a schematic way of enlarged display.

[0092] In this embodiment, the light emitting device 300 is a display panel corresponding to the display screen of a smart phone. In other embodiments, the light emitting device 300 can be a display panel of other types of electronic products, such as a display panel of a computer display screen, or a display panel of a smart wearable electronic product display screen, etc.

[0093] In the light emitting diode and the light emitting device of the embodiments of the present application, the P-type cover layer material of the first epitaxial structure adopts AlGaAs material, and P-type doping is realized by C doping, which can solve the technical problems of high voltage, low brightness and poor reliability of the original AlGaInP red light multi-junction light emitting diode using AlInP doped Mg material as P-type material, and improve the light emitting efficiency of the multi-junction light emitting diode and the light emitting device.

[0094] It should be noted that the above embodiments are only used to illustrate the present application, and are not used to limit the present application. Those skilled in the art can make various modifications and changes to the present application without departing from the spirit and scope of the present application. Therefore, all equivalent technical solutions belong to the scope of the present application, and the patent protection scope of the present application should be limited by the scope of the claims.

Claims

1. A multi-junction light emitting diode, comprising at least: a first epitaxial structure comprising a first N-type semiconductor layer, a first light emitting layer and a first P-type semiconductor layer stacked in sequence; a second epitaxial structure comprising a second N-type semiconductor layer, a second light emitting layer and a second P-type semiconductor layer stacked in sequence; a tunnel junction between the first and second epitaxial structures, the tunnel junction comprising a P-type heavily doped layer connected to the first P-type semiconductor layer and an N-type heavily doped layer connected to the second N-type semiconductor layer; the first P-type semiconductor layer comprises a first P-type cover layer; the second P-type semiconductor layer comprises a second P-type cover layer and a second P-type window layer; Its characteristic is that: the first P-type capping layer material is Al. x1 Ga 1-x1 As, where 0 < X1 < 1; the second P-type capping layer material is Al. x2 Ga 1-x2 InP or Al x3 Ga 1-x3 As, where 0 < X2 ≤ 1, 0 < X3 < 1.

2. The multijunction light emitting diode of claim 1, wherein: The first P-type cladding layer material is Al x1 Ga 1-x1 As, where 0.50 ≤ X1 ≤ 1.

3. The multijunction light emitting diode of claim 1, wherein: the first P-type cover layer has a thickness of 0.15-1 μm.

4. The multijunction light emitting diode of claim 1, wherein: The dopant of the first P-type cladding layer is C, and the doping concentration of the first P-type cladding layer is 3E17~1E19 / cm 3 .

5. The multijunction light emitting diode of claim 1, wherein: The material of the second P-type cladding layer is Al x3 Ga 1-x3 As, wherein 0.50≤X3≤1.

6. The multijunction light emitting diode of claim 5, wherein: The dopant of the second P-type cladding layer is C, and the doping concentration of the first P-type cladding layer is 3E17~1E19 / cm 3 .

7. The multijunction light emitting diode of claim 1, wherein: The material of the second P-type cladding layer is Al x2 Ga 1-x2 InP, wherein 0 < X2≤ 1, the dopant of the second P-type cladding layer is Mg, and the doping concentration of the second P-type cladding layer is 3E17~2E18 / cm 3 .

8. The multijunction light emitting diode of claim 1, wherein: The P-type heavily doped layer is Al m Ga 1-m As, where 0 < m < 1; the thickness of the P-type heavily doped layer is 0.01-0.03 μm.

9. The multijunction light emitting diode of claim 8, wherein: The dopant of the P-type heavily doped layer is C, and the doping concentration of the P-type heavily doped layer is greater than 1E20 / cm 3 .

10. The multijunction light emitting diode of claim 1, wherein: The N-type heavily doped layer is Ga n1 In 1-n1 P or Al n2 Ga 1-n2 As, wherein 0 < n1 < 1, 0 < n2 < 1; the thickness of the N-type heavily doped layer is 0.01-0.03 μm.

11. The multijunction light emitting diode of claim 10, wherein: The dopant of the N-type doped layer is Te, and the doping concentration of the N-type heavily doped layer is greater than 1E19 / cm 3 .

12. The multijunction light emitting diode of claim 1, wherein: The first epitaxial structure further comprises a first P-type isolation layer between the first P-type cladding layer and the first light emitting layer, the first P-type isolation layer is Al a1 Ga 1-a1 As, wherein 0.5 < al < 1.

13. The multijunction light emitting diode of claim 12, wherein: the first P-type isolation layer has a thickness of less than 0.4 μm.

14. The multijunction light emitting diode of claim 1, wherein: The first light emitting layer and the second light emitting layer are a structure of a plurality of periodical well layers and barrier layers stacked alternately, the well layer is Al p1 Ga 1-p1 InP, the barrier layer is Al q1 Ga 1-q1 InP, wherein 0 The thickness of the well layer is 3-10 nm, and the thickness of the barrier layer is 3-10 nm.

15. The multijunction light emitting diode of claim 1, wherein: the first and second epitaxial structures emit red light with a wavelength of 570-650 nm.

16. A light-emitting device, characterized in that: use of the multi-junction light emitting diode according to any one of claims 1-16.

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