CN106876532A - A kind of high light-emitting rate, the UV LED of high reliability and its manufacture method - Google Patents

Abstract

The invention discloses an ultraviolet semiconductor light-emitting diode with high light extraction rate and high reliability, comprising an LED chip, in which a graphene transparent conductive layer, a metal conductive layer and a conductive reflective layer are sequentially arranged on a p-type layer in the LED chip The graphene transparent conductive layer is characterized in that it is formed by stacking graphene transferred multiple times, and an ohmic contact is formed between the graphene transparent conductive layer and the metal conductive layer and the p-type layer. The multi-transferred graphene transparent conductive layer is formed by multiple transfers of single-layer or multi-layer graphene, and the metal conductive layer is formed on the graphene layer or between multi-layer graphene. The present invention reduces surface resistance and improves luminous efficiency by transferring stacked graphene multiple times; the metal conductive layer formation process of the present invention is annealed at 400°C for 2 minutes in a nitrogen and oxygen mixed atmosphere to reduce the contact resistivity to 4.3*10 ^‑4 Ω·cm ^‑2 , while maintaining the reflectivity of the Al reflective layer at 90% at 450 nm.

Description

Ultraviolet light-emitting diode with high light extraction rate and high reliability and its manufacturing method

technical field

The invention belongs to the technical field of optoelectronics, and relates to an ultraviolet semiconductor light-emitting device and a manufacturing method thereof.

Background technique

Ultraviolet light-emitting diodes have the potential advantages of small size, long life, high efficiency, environmental protection, and energy saving. They can replace existing mercury lamps, gas lasers, etc. in industrial curing, disinfection, water purification, medical and biochemistry, and high-density optical recording. Light source has important application prospects and broad market demand. Light-emitting diode devices are divided into front-mount, flip-chip and vertical structures.

The flip-chip and vertical structure can have the following advantages by adding a metal conductive reflective layer: the metal conductive reflective layer is used as a current spreading layer to make the current spread from the electrode to the active area more uniformly; at the same time, the heat is directly conducted to the high thermal conductivity The substrate, and then dissipate heat through the radiator, its thermal resistance is much smaller than that of the formal structure, so it has more potential and application value.

UV LEDs with inverted and vertical structures need to use a highly reflective p-type ohmic contact metal layer to improve the light efficiency of the device. The reflectivity of highly reflective ohmic contact metals commonly used in the visible light band, such as Ag, has been greatly reduced in the ultraviolet band. Among the main metals, only Al still has a high reflectivity in the ultraviolet band. However, Al cannot form an ohmic contact with p-GaN or p-AlGaN. The way to use Al as a high reflective layer is to cover Al on the transparent conductive p-GaN or p-AlGaN ohmic contact. In this technology, it is necessary to effectively block the ohmic contact caused by the diffusion of Al to the transparent conductive ohmic contact layer. destroyed. Patent CN104810455A adopts a transparent conductive ohmic contact layer of graphene-Ag composite structure, wherein graphene has a blocking effect, which can further improve its reliability, but it has the following problems: firstly, graphene has a multi-domain structure, and there are gaps between domains , Al will pass through the gap and migrate, especially when it is above 100 ° C, it will degrade rapidly and cause its diffusion, destroying the p-ohmic contact, and greatly affecting the reliability of the device; at the same time, Al and graphene have poor adhesion and are easy to peel off. Currently, no technology can solve the adhesion problem of Al to graphene, which greatly limits the fabrication of flip-chip devices.

Contents of the invention

Aiming at the deficiencies in the prior art, the main purpose of the present invention is to provide an ultraviolet light-emitting diode with high transmittance, low surface resistance, high reflection and good p-type ohmic contact. Another object of the present invention is to provide a method for manufacturing the ultraviolet light emitting diode.

In order to realize the purpose of the present invention to provide high light extraction rate and high reliability ultraviolet light-emitting diodes, the technical scheme adopted in the present invention is:

An ultraviolet light-emitting diode device with high light extraction rate and high reliability, including an epitaxial structure layer mainly composed of an n-type layer, a quantum well layer and a p-type layer, and a p-contact layer, a graphene transparent layer are sequentially arranged on the p-type layer An optical layer and a conductive reflective layer, the ohmic contact layer partially covers the surface of the p-type layer, and the coverage ratio is less than 30%, the graphene light-transmitting layer is formed by stacking graphene transferred multiple times, and the p-contact layer is connected to the p-type layer There are ohmic contacts between the p-type layers, between the p-contact layer and the graphene light-transmitting layer;

Preferably, the ohmic contact layer comprises Ag, or Au, or Ni, or an alloy structure or multilayer structure of the above metals;

Preferably, the at least two layers of graphene that constitute the graphene light-transmitting layer also include a partially covered intercalation metal layer, and the coverage ratio of the metal layer is lower than 10%; preferably, the interposition metal guide layer is tiled Ag or Au nano dots or nano wires; further preferably, the Ag or Au nano dots in the metal insertion layer have a particle size of 10 nm to 1 μm, and the Ag or Au nano wires have a diameter of 5 to 100 nm and a length of 5～100μm;

Preferably, the thickness of the conductive reflective layer is 0.1-3 μm, and the conductive reflective layer has high conductivity and reflectivity, and the material of the conductive reflective layer is preferably Al.

For realizing another object of the present invention, the technical scheme that the present invention adopts is:

A method for manufacturing an ultraviolet light-emitting diode device with high light extraction rate and high reliability, comprising the following steps:

Step S1, growing an epitaxial structure layer on the substrate, the epitaxial layer sequentially includes a p-type layer, an n-type layer and a quantum well layer;

Step S2, performing etching and other processing on the epitaxial structure layer to form n contact holes;

Step S3, forming a p-contact layer on the p-type layer by evaporation or sputtering, and annealing;

Step S4, forming a graphene light-transmitting layer on the p-contact layer by transferring graphene stacks multiple times;

Step S5, evaporating a highly reflective metal conductive reflective layer on the graphene light-transmitting layer, preferably, the highly reflective conductive metal layer is aluminum with a thickness of more than 150 nm;

Step S6, preparing an n-region ohmic contact layer on the n contact hole;

Step S7, forming p and n electrodes respectively on the p-region highly reflective metal conductive layer and the n-region ohmic contact layer

Preferably, the p-contact layer in step S3 is a single layer of Ag, Au, or Ni with a thickness of 1-5 nm, or the above-mentioned metal multilayer structure is quickly annealed in nitrogen or a mixed atmosphere of nitrogen and oxygen. After annealing, the metal aggregates and covers rate to below 30%;

Alternatively, step S3 consists of the following steps: step S3a, evaporating or sputtering 3-100nm Ag, Au, Ni, ITO single layer or multi-layer, forming a circular or polygonal metal dot array by photolithography and etching or lift-off process , the diameter or diagonal length of metal dots is 2-10 μm, and the distance between the centers of adjacent metal dots is twice or more than the diameter or diagonal length of metal dots; step S3b, rapid annealing in nitrogen or a mixed atmosphere of nitrogen and oxygen;

Preferably, step S4 includes the following steps: S4a, transferring single-layer or multi-layer graphene to the p contact layer; S4b, also inserting a metal layer on the transfer graphene, the insertion metal layer is Ni, Au of 1-2nm Or Ti, or the alloy structure or multilayer structure of the above metals; S4c, repeating S4a-S4b or S4a, to reach the required number of transfer layers; in addition, the subsequent process of inserting the metal layer in step S4b also includes rapid annealing under nitrogen atmosphere.

Compared with the prior art, the advantages of the present invention include:

(1) The ability of the present invention to block Al diffusion through multiple transfers of graphene is also greatly enhanced, which improves the contact, reflection performance and reliability of the device;

(2) The coverage ratio of the P contact layer is less than 30%, ensuring that it forms an ohmic contact while having a high light transmittance;

(3) The preferred scheme improves the electrical connection between the graphene layers and solves the problem of poor adhesion between graphene and Al reflective layers by adding intercalated metal layers between graphene layers and between graphene and Al .

In summary, compared with the prior art, the formed ultraviolet semiconductor light-emitting device has the advantages of high transmittance, high external quantum efficiency, high light extraction efficiency, good p-type ohmic contact, low turn-on voltage, good heat dissipation, and high reliability. .

Description of drawings

Fig. 1 is the structural representation of multiple transfer graphene flip-chip GaN-based ultraviolet LED chip in embodiment 1 of the present invention;

Fig. 2 is the structure schematic diagram of direct annealing multiple transfer graphene flip-chip GaN-based ultraviolet LED chip in the embodiment 2 of the present invention;

3 is a schematic structural view of a multi-transfer graphene flip-chip GaN-based ultraviolet LED chip containing a metal layer inserted in Example 3 of the present invention;

FIG. 4 is a schematic diagram of the structure of the p-contact layer.

detailed description

In order to make the object, technical solution and advantages of the present invention clearer, the following examples will be described in detail. It should be understood that the specific embodiments described here are only used to explain the present invention, not to limit the present invention.

Example 1

Referring to FIG. 1 , the GaN-based ultraviolet LED structure is mainly composed of a sapphire substrate 101 , an epitaxial layer grown on the substrate, and a contact electrode. From the substrate upwards, the epitaxial layer includes: an AlN buffer layer 102 , an n-AlGaN electronic layer 103 , a quantum well layer 104 , and a p-type layer 105 . After the epitaxial growth, the epitaxial layer is etched to form a mesa and an n contact hole, the surface of the mesa is the surface of the original epitaxial layer, and the surface of the n contact hole is the n-AlGaN layer. A p-contact layer 106, a graphene light-transmitting layer 107 and a conductive reflective layer 108 formed by multiple transfers of graphene stacks, and a p-type electrode 109 are sequentially arranged on the mesa, which together constitute a reflective ohmic contact electrode of the p-type layer. Wherein, the p-contact layer 106 is an array of metal dots, the diameter or diagonal length of the metal dots is 2-10 μm, and the distance between the centers of adjacent metal dots is twice or more than the diameter or diagonal length of the metal dots. An n-type ohmic contact electrode 110 is disposed in the n-contact hole.

The manufacturing steps of the GaN-based ultraviolet LED chip are described in detail below:

Step S1: on the sapphire substrate 101, using the MOCVD process, sequentially grow epitaxial layers, the epitaxial layers include AlN buffer layer 102, n-AlGaN electronic layer 103, InGaN/AlGaN multi-quantum well layer 104, and AlGaN p-type layer 105.

Step S2, etching from the p-AlGaN layer to the n-AlGaN layer by photolithography and etching processes to form n-AlGaN mesas and n contact holes;

Step S3a, 3nm Ag is evaporated, and a circular or polygonal metal dot array is formed by photolithography and etching processes, the diameter or diagonal length of the metal dots is 2-10 μm, and the distance between the centers of adjacent metal dots is 1/2 of the diameter or diagonal length of the metal dots Twice or more, distributed in a matrix of dots in Figure 4, of which 41 are metal dots and 42 are p-type layers;

Step S3b, rapid annealing in nitrogen;

The contact layer in the above step S3a can be replaced by evaporated or sputtered 3-100nm Ag, Au, Ni, ITO single layer or multilayer, and the annealing in step S3b can be replaced by rapid annealing in a nitrogen and oxygen mixed atmosphere.

Step S4, forming a graphene light-transmitting layer 107 on the p-contact layer by stacking graphene transferred multiple times; details are as follows:

The graphene transfer method can be a wet transfer or a dry transfer. The wet transfer uses the organic material polymethyl methacrylate (PMMA) or polydimethylsiloxane (PDMS) as the corrosion substrate method of the transfer medium, and the dry transfer The method adopts Roll To Roll or Hot pressing (Reference: Efficient Transfer of Large-Area Graphene Films onto Rigid Substrates by Hot Pressing. (2012). Acs Nano 6 (6): 5360-5365.). Preferably adopt wet method to transfer by utilizing organic material polymethyl methacrylate (PMMA) as the corrosion substrate method of transfer medium, transfer monoatomic layer or polyatomic layer graphene to contact layer, then carry out next transfer, transfer The number of times is controlled at 2-5 times, preferably 3 times, to form the graphene light-transmitting layer 107 .

Step S5, forming a conductive reflective layer 108 by evaporating a highly reflective metal on the graphene light-transmitting layer, preferably, the highly reflective conductive metal layer is aluminum above 150 nm;

Step S6, preparing an n-region ohmic contact layer on the n contact hole by photolithography, stripping, and annealing, and the contact material is Ti/Al, Cr/Al or Cr/Au;

Step S7, depositing a SiO2 passivation layer on the surface of the sample by PECVD, opening holes on the passivation layer by photolithography and corrosion methods to expose the metal layer under the p and n electrodes; using electron beam evaporation or sputtering to deposit electrode metal, Preferably Ti (50nm)/Au (1000nm), combined with photolithography and lift-off methods, form p and n metal electrodes 109, 110 above the opening of the passivation layer;

Step S8, further, thinning and splitting the epitaxial wafer to form a single chip.

In this embodiment, the ability to block Al diffusion through multiple transfers of graphene is also greatly enhanced, which improves the contact, reflection performance and reliability of the device; at the same time, the lattice distribution of the p-contact layer is formed by photolithography, so that the p-contact layer is a partial Coverage, the coverage ratio is less than 25%, which ensures that it has a high light transmittance while forming an ohmic contact.

Example 2

Referring to FIG. 2 , the present GaN-based ultraviolet LED structure is mainly composed of a sapphire substrate 201 , an epitaxial layer grown on the substrate, and a contact electrode. From the substrate upwards, the epitaxial layer includes: an AlN buffer layer 202 , an n-AlGaN electronic layer 203 , a quantum well layer 204 , and a p-type layer 205 . After the epitaxial growth, the epitaxial layer is etched to form a mesa and an n contact hole, the surface of the mesa is the surface of the original epitaxial layer, and the surface of the n contact hole is the n-AlGaN layer. A p-contact layer 206, a graphene light-transmitting layer 207, a conductive reflective layer 208 formed by multiple transfers of graphene stacks, and a p-type electrode 209 are sequentially arranged on the mesa, which together constitute a reflective ohmic contact electrode of the p-type layer. The p-contact layer 206 is randomly distributed metal points, and the n-type ohmic contact electrode 210 is arranged in the n-contact hole.

The difference between the structure and the process of this embodiment and embodiment 1 is as follows:

The p-contact layer in Example 1 is a single layer or multiple layers of Ag, Au, Ni, ITO evaporated or sputtered 3-100nm, and a circular or polygonal metal dot array is formed by photolithography and etching or lift-off process. After the metal dot array is formed after photolithography and etching, the p-contact layer is further formed by rapid annealing in nitrogen or a mixed atmosphere of nitrogen and oxygen.

The difference between embodiment 2 and embodiment 1 is that embodiment 2 does not form a regular array of metal dots in the p contact layer as shown in FIG. The metal is Ag, Ni or Au, the thickness of the metal layer is 1-3nm before annealing, and the metal aggregates to form nanometer-sized metal dots after annealing, and the metal dot coverage rate is lower than 30%.

The difference between embodiment 2 and embodiment 1 process is: step S3 of embodiment 2 is:

Step S3a, evaporating 3nm Ag;

Step S3b, rapid annealing in nitrogen;

The contact layer in step S3a above can be replaced by evaporated or sputtered 1-3nm Ag, Au, Ni single layer or multi-layer, and the annealing in step S3b can be replaced by rapid annealing in a mixed atmosphere of nitrogen and oxygen.

Other processing steps are identical with embodiment 1.

Example 3

Referring to FIG. 3 , the present GaN-based ultraviolet LED structure is mainly composed of a sapphire substrate 301 , an epitaxial layer grown on the substrate, and a contact electrode. From the substrate upwards, the epitaxial layer includes: an AlN buffer layer 302 , an n-AlGaN electronic layer 303 , a quantum well layer 304 , and a p-type layer 305 . After the epitaxial growth, the epitaxial layer is etched to form a mesa and an n contact hole, the surface of the mesa is the surface of the original epitaxial layer, and the surface of the n contact hole is the n-AlGaN layer. A p-contact layer 306 is sequentially arranged on the table, and a graphene light-transmitting layer 307 formed by stacking graphene transferred multiple times, wherein 307a, 307b, and 307c are all transferred graphene, and a metal layer 308 is inserted on the transferred graphene (308a, 308b, 308c), the conductive reflective layer 309, and the p-type electrode 310 together constitute a reflective ohmic contact electrode of the p-type layer. An n-type ohmic contact electrode 311 is disposed in the n contact hole.

The difference between the fabrication method of Example 3 and the structure of Example 1 is that in step S4, an insertion metal layer 308 (308a, 308b, 308c) is added to the graphene layer. Step S4 includes the following steps:

S4a, transferring single-layer or multi-layer graphene to the p-contact layer;

S4b, there is also an inserted metal layer on the transferred graphene, and the inserted metal layer is Ni, Au or Ti of 1-2nm, or an alloy structure or a multilayer structure of the above metals;

S4c. Repeat S4a-S4b or S4a to reach the required number of transfer layers.

In addition, the subsequent process of inserting the metal layer in step S4b also includes rapid annealing in a nitrogen atmosphere, or a mixed atmosphere of argon and hydrogen.

Other processing steps are identical with embodiment 1.

In this embodiment, the electrical connection between the graphene layers and the adhesion between the graphene and the Al reflective layer can be improved by inserting metal layers between the graphene layers and between the graphene and Al.

In the previous three embodiments, the flip-chip structure that emits light from one side of the sapphire substrate is adopted, which greatly reduces the light loss and increases the light extraction rate; at the same time, the ability to block the diffusion of Al by using the method of transferring graphene multiple times is also improved. It is greatly strengthened, making it easier to form ohmic contacts and improving reliability. In addition, the above three embodiments also have the advantages of low turn-on voltage, high heat dissipation, and high external quantum efficiency.

The embodiments described above in conjunction with the accompanying drawings are only preferred implementations of the present invention, rather than limiting the protection scope of the present invention. Any improvement made based on the spirit of the present invention should fall within the protection scope of the present invention.

Claims (10)

1. An ultraviolet light-emitting diode device with high light extraction rate and high reliability, comprising an epitaxial structure layer mainly composed of an n-type layer, a quantum well layer and a p-type layer, on which a p-type layer is successively provided with a p-contact layer, a graphite Graphene light-transmitting layer and conductive reflective layer, characterized in that the ohmic contact layer partially covers the surface of the p-type layer, and the coverage ratio is less than 30%, the graphene light-transmitting layer is formed by stacking graphene transferred multiple times, the Ohmic contact is established between the p-contact layer and the p-type layer, and between the p-contact layer and the graphene light-transmitting layer. 2. The ultraviolet semiconductor light-emitting device according to claim 1, characterized in that the ohmic contact layer comprises Ag, or Au, or Ni, or an alloy structure or multilayer structure of the above metals. 3. A kind of high light extraction rate, high reliability ultraviolet light-emitting diode device according to claim 1, it is characterized in that between the at least two layers of graphene that constitute the graphene light-transmitting layer, also include the insertion metal of partial coverage layer, the metal layer coverage ratio is less than 10%. 4. A high-efficiency, high-reliability ultraviolet light-emitting diode device according to claim 3, characterized in that the inserted metal guide layer is flat Ag or Au nano-dots or nano-wires. 5. The ultraviolet light-emitting diode device with high light extraction rate and high reliability according to claim 4, characterized in that the Ag or Au nano-dots in the metal insertion layer have a particle size of 10 nm to 1 μm, Ag or Au The diameter of the Au nanowire is 5-100 nm, and the length is 5-100 μm. 6. A high light extraction rate and high reliability ultraviolet light-emitting diode device according to claim 1, characterized in that the thickness of the conductive reflective layer is 0.1-3 μm, and the conductive reflective layer has high conductivity and For reflectivity, the material of the conductive reflective layer is preferably Al. 7. A method for manufacturing an ultraviolet light-emitting diode device with high light extraction rate and high reliability, characterized in that it comprises the following steps: Step S1, growing an epitaxial structure layer on the substrate, the epitaxial layer sequentially includes a p-type layer, an n-type layer and a quantum well layer; Step S2, performing etching and other processing on the epitaxial structure layer to form n contact holes; Step S3, forming a p-contact layer on the p-type layer by evaporation or sputtering, and annealing; Step S4, forming a graphene light-transmitting layer on the p-contact layer by transferring graphene stacks multiple times; Step S5, evaporating a highly reflective metal conductive reflective layer on the graphene light-transmitting layer, preferably, the highly reflective conductive metal layer is aluminum with a thickness of more than 150 nm; Step S6, preparing an n-region ohmic contact layer on the n contact hole; Step S7, forming p and n electrodes respectively on the p-region highly reflective metal conductive layer and the n-region ohmic contact layer. 8. The manufacturing method of a high light extraction rate and high reliability ultraviolet light-emitting diode device according to claim 7, characterized in that: the p-contact layer in step S3 is a single layer of Ag, Au, Ni of 1-5nm layer, or the above-mentioned metal multilayer structure is formed by rapid annealing in nitrogen or a mixed atmosphere of nitrogen and oxygen. After annealing, the metal aggregates and the coverage is reduced to below 30%. 9. A method for manufacturing a high-efficiency, high-reliability ultraviolet light-emitting diode device according to claim 7, characterized in that: Step S3 consists of the following steps: Step S3a, evaporating or sputtering 3-100nm Ag, Au, Ni, ITO monolayer or multilayer, forming a circular or polygonal metal dot array by photolithography and etching or lift-off process, the metal dot diameter or diagonal length is 2 ~10μm, the distance between the centers of adjacent metal dots is twice or more than the diameter or diagonal length of the metal dots; Step S3b, rapid annealing in nitrogen or a mixed atmosphere of nitrogen and oxygen. 10. A method for manufacturing a high light extraction rate and high reliability ultraviolet light-emitting diode device according to claim 7, characterized in that: Step S4 comprises the following steps: S4a, transferring single-layer or multi-layer graphene to the p-contact layer; S4b, there is also an inserted metal layer on the transferred graphene, and the inserted metal layer is Ni, Au or Ti of 1-2nm, or an alloy structure or a multilayer structure of the above metals; S4c. Repeat S4a-S4b or S4a to reach the required number of transfer layers. In addition, the subsequent process of inserting the metal layer in step S4b also includes rapid annealing under nitrogen atmosphere.