CN104810455B - Ultraviolet semiconductor luminescent device and its manufacture method - Google Patents

Abstract

The invention discloses an ultraviolet semiconductor light-emitting device and a manufacturing method thereof. The semiconductor light-emitting device includes an epitaxial structure layer mainly composed of an n-type layer, a quantum well layer and a p-type layer, and p-type and n-type electrodes. The p-type layer is also sequentially provided with a graphene-Ag nanocomposite layer and a conductive A reflective layer, the graphene-Ag nanocomposite layer forms an ohmic contact with the p-type layer. Further, the graphene-Ag nanocomposite layer includes: an Ag nanomaterial layer formed on the p-type layer, the Ag nanomaterial layer comprising Ag nanodots and/or Ag nanowires and covered on the Ag nanomaterial layer of graphene; or, graphene quantum dots supported Ag nanoparticles composite layer. The semiconductor light-emitting device of the invention has the advantages of high external quantum efficiency, high light extraction efficiency, low turn-on voltage, good heat dissipation, high stability, etc., and the preparation process is simple and controllable, with low cost, and is suitable for industrial production.

Description

Ultraviolet semiconductor light-emitting device and manufacturing method thereof

technical field

The invention relates to a semiconductor light-emitting element, in particular to an ultraviolet semiconductor light-emitting device and a manufacturing method thereof. The semiconductor light-emitting device can be used in fields such as transportation, medical treatment, display and white light illumination, and belongs to the field of optoelectronic technology.

Background technique

GaN-based ultraviolet/deep ultraviolet light-emitting diodes (LEDs) have the potential advantages of small size, long life, high efficiency, environmental protection, and energy saving, and they can replace existing ones in industrial curing, disinfection, water purification, medical and biochemistry, and high-density optical recording. There are ultraviolet light sources such as mercury lamps and gas lasers, which have important application prospects and broad market demands.

LED chips are usually divided into front-mount, flip-chip and vertical structures. The existing blue and white LED technologies use ITO as the transparent conductive layer material in the front-mount structure, and Ag as the high-reflection layer material in the flip-chip structure, but they all have the problem of large light absorption in the ultraviolet band.

In order to solve the problem of ultraviolet light absorption, in front-mounted ultraviolet LEDs, some studies have used graphene, carbon nanotubes and Ag nanocomposite structures as transparent conductive layers, which can improve the performance of ultraviolet LEDs. For example, in the published patent (publication number CN104009141A), the photoelectric conversion efficiency of the ultraviolet LED is improved by uniformly hanging Ag nanowires on the carbon nanotube film to form a composite structure as a current spreading layer. When the light transmittance of carbon nanotube film is about 80%, the square resistance is about 10 ³ Ω/sq; while the light transmittance of single-layer and double-layer graphene is above 95%, and the square resistance is about 10 ² Ω /sq order of magnitude. The transparent conductive electrode layer formed by the transferred graphene film covering the silver nanowires further improves the performance of the UV LED. The light transmittance at 375nm is 86.3%, and the surface resistance is about 30Ω/sq, which reduces the operating voltage of the UV LED and improves the light extraction efficiency. (Reference "Graphene-silver nanowire hybrid structure as a transparent and current spreading electrode in ultraviolet light emitting diodes." Applied Physics Letters, 2013, 103(5)).

However, the above-mentioned transparent conductive layer still has a large surface resistance, which leads to limited current spreading ability; the current injected from the electrodes needs to flow through the transparent conductive layer laterally, resulting in current crowding. The turn-on voltage of the formally installed ultraviolet LED is relatively large, and the light extraction efficiency is low.

At the same time, there is a problem of heat dissipation in the front-mounted ultraviolet LED. Generally, due to the low efficiency of the ultraviolet LED, the required optical power is generally large, resulting in a large heat generation of the chip. However, the thermal conductivity of the sapphire substrate is poor (35W/m·K), plus the thermal resistance caused by die bonding, so the thermal resistance of the UV LED chip with the front-mounted structure is relatively large, which is not conducive to the improvement of the luminous efficiency and reliability of the UV LED.

Flip-chip and vertical structures can effectively solve the above-mentioned shortcomings of front-mounted LEDs by adding a metal conductive reflective layer. The metal conductive reflective layer is used as the current spreading layer, so that the current spreads from the electrode to the active area more uniformly; at the same time, the heat is directly conducted to the substrate with high thermal conductivity, and then dissipated through the radiator, and its thermal resistance is smaller than that of the formal structure Therefore, it has more potential and application value.

However, UV LEDs with flip-chip and vertical structures must use p-type ohmic contacts with high reflection and low resistance, so as to improve the light efficiency of the device, and the existing technology still lacks effective solutions. The significant decrease in the reflectivity of Ag in the ultraviolet band and the strong absorption of ultraviolet light by ITO are no longer suitable as p-type ohmic contact materials for UV LEDs with flip-chip and vertical structures. At the same time, metal Al, which has a high reflectivity in the ultraviolet band, It is difficult to form a good ohmic contact with p-GaN or p-AlGaN.

Contents of the invention

The main purpose of the present invention is to provide an ultraviolet semiconductor light-emitting device with the advantages of high reflection, low resistance p-type ohmic contact, etc., so as to overcome the deficiencies in the prior art.

Another object of the present invention is to provide a method for manufacturing the ultraviolet semiconductor light emitting device.

In order to realize the aforementioned object of the invention, the technical solutions adopted in the present invention include:

An ultraviolet semiconductor light-emitting device, including an epitaxial structure layer mainly composed of an n-type layer, a quantum well layer and a p-type layer, and p-type and n-type electrodes, is characterized in that the p-type layer is also sequentially provided with graphene- An Ag nanocomposite layer and a conductive reflective layer, the graphene-Ag nanocomposite layer forms an ohmic contact with the p-type layer.

As one of the more preferred embodiments, the graphene-Ag nanocomposite layer includes:

An Ag nanomaterial layer formed on the p-type layer, the Ag nanomaterial layer comprising Ag nanodots and/or Ag nanowires;

And, a graphene film covering the Ag nano material layer.

In a more specific embodiment, the Ag nanomaterial layer is an Ag nanodot layer. For example, the graphene-Ag nanocomposite layer is an Ag nanodot layer obtained by annealing a thin layer of Ag covered by a graphene film.

In a more specific embodiment, the Ag nanomaterial layer is an Ag nanowire layer.

More preferably, the aforementioned Ag nano-dots have a particle size of 10 nm˜1 μm.

More preferably, the aforementioned Ag nanowires have a diameter of 5-100 nm and a length of 5-100 μm.

More preferably, the number of layers of the aforementioned graphene film is a single layer or multiple layers, such as 2-10 layers.

As one of the more preferred embodiments, the graphene-Ag nanocomposite layer includes a graphene quantum dot-supported Ag nanoparticle composite layer.

Further, the particle size of the Ag nanoparticle composite supported by graphene quantum dots is preferably 5-100 nm.

As one of the more preferred embodiments, an intermediate layer and a conductive reflective layer are sequentially formed on the graphene-Ag nanocomposite layer.

As one of the more preferred embodiments, an intermediate layer is formed between the Ag nanomaterial layer and the graphene film.

In a specific embodiment, the epitaxial structure layer may include a buffer layer, an n-type AlGaN layer, a multi-quantum well layer, a p-type layer, etc. formed in sequence.

Further, the conductive reflective layer is electrically connected to the p-type electrode.

Further, the conductive reflective layer may be selected from but not limited to a metal reflective layer, such as an Al reflective layer, but not limited thereto.

More preferably, the aforementioned conductive reflective layer has a thickness of 0.1-3 μm.

Further, the material of the intermediate layer is preferably Cr, but not limited thereto.

Further, the material of the p-type layer is preferably p-AlGaN, but not limited thereto.

Further, the semiconductor light emitting device is preferably a flip-chip structure or a vertical structure, but not limited thereto.

Further, the semiconductor light emitting device is a GaN-based LED chip.

A method of manufacturing the ultraviolet semiconductor light-emitting device, comprising:

growing an epitaxial structure layer on the substrate;

Process the epitaxial structure layer, form an n-type electrode on the n-type layer, form a graphene-Ag nanocomposite layer on the p-type layer, and make the graphene-Ag nanocomposite layer form an ohmic contact with the p-type layer ;

And, forming a conductive reflective layer on the graphene-Ag nanocomposite layer, and then making a p-type electrode on the conductive reflective layer.

In a more specific embodiment, a method for manufacturing a GaN-based ultraviolet LED chip may include the following steps:

Firstly, the main structural layers including buffer layer, n-type layer, multi-quantum well layer and p-type contact layer are grown on the substrate by MOCVD process.

Then, the obtained epitaxial wafer undergoes a series of process steps such as photolithography, etching, and metal layer deposition to form an n-type electrode on the LED chip, and fabricate a graphene-Ag nanocomposite layer on the p-type layer. Depositing a conductive reflective layer Al or a composite structure layer formed by Al and an intermediate layer on the nanocomposite layer, making a p-type electrode on the conductive reflective layer, and thinning and splitting the epitaxial wafer to form a chip.

Further, the n-type and p-type electrodes can be electrically connected to the outside through bumps, solder, conductive glue or metal wires.

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

(1) By adopting a flip-chip or vertical structure, the thermal resistance of the ultraviolet semiconductor light-emitting device of the present invention and its junction temperature during operation are effectively reduced, and the light efficiency and reliability of the device are improved;

(2) Using metal as the conductive reflective layer can effectively overcome the shortcomings of the large resistance of the transparent conductive layer, making the current diffuse from the electrode to the active area more uniform, and improving the expansion of the current;

(3) Through the graphene-Ag nanocomposite layer on the p-type layer, combined with the conductive reflective layer, it has low ohmic contact resistance and high reflectivity in the ultraviolet band; at the same time, due to the existence of graphene, the compound The interdiffusion between the structure and the reflective layer is suppressed, which improves the contact, reflection performance and reliability of the device, so that the formed ultraviolet semiconductor light-emitting device has high external quantum efficiency, high light extraction efficiency, low turn-on voltage, and good heat dissipation. High reliability and other advantages;

(4) The preparation process of the ultraviolet semiconductor light-emitting device of the present invention is simple and controllable, the cost is low, and it is suitable for industrial production.

Description of drawings

Fig. 1 is a schematic structural view of a GaN-based ultraviolet LED chip in Embodiment 1 of the present invention;

2 is a schematic structural view of a GaN-based ultraviolet LED chip in Embodiment 2 of the present invention;

3 is a schematic structural view of a GaN-based ultraviolet LED chip in Embodiment 3 of the present invention;

FIG. 4 is a schematic structural diagram of a GaN-based ultraviolet LED chip in Embodiment 4 of the present invention.

detailed description

The technical solution of the present invention will be further described below in conjunction with the accompanying drawings and several specific implementation examples.

Embodiment 1 Referring to FIG. 1, the structure of the GaN-based ultraviolet LED chip is as follows from bottom to top: a sapphire substrate 101, and the epitaxial layer includes an AlN buffer layer 102, an n-AlGaN layer 103, an n-AlGaN electron expansion layer 104, a multilayer Quantum well layer 105, AlGaN electron blocking layer 106, p-AlGaN layer 107, and graphene film covering Ag nano-dot layer 108 (wherein Ag nano-dot layer 108a, graphene film layer 108b), conductive reflection layer 109, n-type electrode 110. A p-type electrode 111.

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

Step S1: On the sapphire substrate, use the MOCVD process to grow epitaxial layers in sequence. The epitaxial layers include a GaN buffer layer with a thickness of about 2.0 μm, an n-AlGaN layer with a thickness of about 2.0 μm, and an n-AlGaN electron expansion layer with a thickness of about 200 nm. layer, an InGaN/AlGaN multiple quantum well layer with a thickness of about 100 nm, an AlGaN electron blocking layer with a thickness of about 20 nm, and a p-AlGaN contact layer with a thickness of about 0.1 μm;

Step S2: On the substrate (wafer) on which the epitaxial layer is grown, etch from the p-AlGaN layer to the n-AlGaN layer by photolithography and etching processes, to form an n-AlGaN mesa;

Step S3: forming a Ti (about 50 nm thick)/Al (about 300 nm thick) ohmic contact on the n-AlGaN mesa by photolithography, electron beam evaporation, lift-off, and annealing processes;

Step S4: Deposit a thin layer of Ag (Ag thickness 1nm-200nm, preferably 30nm) on the p-AlGaN layer by electron beam evaporation, and anneal for 10s-30min at 300-500°C (preferably 400°C) in _N2 atmosphere (preferably 1min) forming Ag nano dots, the average particle size of which is about 250nm;

Step S5: Prepare graphene on the copper foil by CVD, spin-coat PMMA with a thickness of about 1.5 μm, then corrode the copper foil substrate with _FeCl3 solution, and after the corrosion is complete, use deionized water to corrode the formed PMMA/ The graphene film is cleaned, and then the PMMA/graphene film is transferred to the surface of the epitaxial wafer after being processed in step S4;

Step S6: Remove PMMA with hot acetone solution, then clean, and then realize the patterning of graphene film by photolithography and oxygen plasma etching (reference "Large-scale patterned multi-layer graphene films as transparent conducting electrodes for GaN light -emitting diodes."Nanotechnology, 2010, 21(17));

Step S7: Depositing an Al reflective layer with a thickness of about 500 nm by electron beam evaporation, and then depositing a _SiO2 passivation layer on the surface of the sample;

Step S8: Open contact holes on the passivation layer in the p-type and n-type regions by photolithography etching process, and form Ti (about 50 nm in thickness)/Au (about 50 nm in thickness) on the contact holes by photolithography, electron beam evaporation and lift-off process 250nm) electrodes, after which the epitaxial wafers are thinned, polished, cut and split to form discrete LED chips.

Further, the electrodes on the LED chip can be electrically connected to the pads on the flip-chip substrate through bumps or solder.

Embodiment 2 Referring to FIG. 2, the structure of the GaN-based ultraviolet LED chip is as follows from bottom to top: a silicon carbide substrate 201, and the epitaxial layer includes an AlN buffer layer 202, an n-AlGaN layer 203, an n-AlGaN electron expansion layer 204, Multi-quantum well layer 205, p-AlGaN electron blocking layer 206, p-GaN layer 207, and coated graphene quantum dot loaded Ag nanoparticle layer 208 (graphene quantum dot loaded Ag nanoparticle composite layer 208a, intermediate layer 208b ), a conductive reflective layer 209, an n-type electrode 210, and a p-type electrode 211.

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

Step S1: The purified graphene quantum dots and silver nitrate mixed solution are heated and refluxed to prepare the graphene quantum dots loaded Ag nanoparticle complex (reference "Synthesis of Silver Nanoparticles Supported onGraphene Quantum Dots for Oxygen Reduction Reaction," Journal of Electrochemistry , vol.20, pp.353-359, 2014);

Step S2: On the silicon carbide substrate, use the MOCVD process to sequentially grow epitaxial layers, the epitaxial layers sequentially include an AlN buffer layer with a thickness of about 2.0 μm, an n-AlGaN layer with a thickness of about 2.0 μm, and an n-AlGaN electron layer with a thickness of about 200 nm. An expansion layer, an InGaN/AlGaN multiple quantum well layer with a thickness of about 100nm, an AlGaN electron blocking layer with a thickness of about 20nm, and a p-GaN contact layer with a thickness of about 0.1μm;

Step S3: Etching from the p-GaN layer to the n-AlGaN layer by photolithography and etching processes to form an n-AlGaN mesa, and preparing an n-type electrode on the n-AlGaN mesa;

Step S4: Take the graphene quantum dot-loaded Ag nanoparticle composite prepared in step S1, and evenly spin-coat it on the p-GaN layer. The average particle size of the graphene quantum dot-loaded Ag nanoparticle composite is about 30nm;

Step S5: Then deposit a Cr (Cr thickness of about 25-50 nm, preferably about 30 nm) intermediate layer and an Al reflective layer with a thickness of about 1 μm by electron beam evaporation, and prepare a p-type electrode on the Al reflective layer;

Step S6: Add a metal layer of Ti (about 50nm thick)/Au (about 250nm thick), passivate and open to form electrodes, and the electrodes can be electrically connected to the outside through bumps, solder, conductive glue or metal bonding wires.

Embodiment 3 Referring to FIG. 1, the structure of the GaN-based ultraviolet LED chip is as follows from bottom to top: a sapphire substrate 301, and the epitaxial layer includes an AlN buffer layer 302, an n-AlGaN layer 303, an n-AlGaN electron expansion layer 304, a multilayer Quantum well layer 305, AlGaN electron blocking layer 306, p-AlGaN layer 307, graphene film covering silver nanowire layer 308 (Ag nanowire layer 308a, graphene film layer 308b), conductive reflection layer 309, n-type electrode 310, p-type electrode 311 .

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

Step S1: On the sapphire substrate, use the MOCVD process to grow epitaxial layers in sequence. The epitaxial layers include an AlN buffer layer with a thickness of about 2.0 μm, an n-AlGaN layer with a thickness of about 2.0 μm, and an n-AlGaN electron expansion layer with a thickness of about 200 nm. layer, an InGaN/AlGaN multiple quantum well layer with a thickness of about 100 nm, an AlGaN electron blocking layer with a thickness of about 20 nm, and a p-AlGaN contact layer with a thickness of about 0.1 μm;

Step S2: Etching from the p-AlGaN layer to the n-AlGaN layer by photolithography and etching processes to form an n-AlGaN mesa, and preparing an n-type electrode on the n-AlGaN mesa;

Step S3: spin coating an Ag nanowire film on the p-AlGaN layer, the diameter of the Ag nanowire film is about 20 nm, and the length is about 10-30 μm;

Step S4: prepare graphene by CVD method on copper foil, after spin _- coating PMMA, then corrode the copper foil substrate with FeCl3 solution, after the corrosion is complete, clean the PMMA/graphene film formed by corrosion with deionized water , and then transfer the PMMA/graphene film to the p-AlGaN layer containing Ag nanowires;

Step S5: Remove PMMA with hot acetone solution, then clean, and then realize patterning of graphene film by photolithography and oxygen plasma etching

Step S6: Depositing an Al reflective layer with a thickness of about 1.5 μm by electron beam evaporation, and preparing a p-type electrode on the Al reflective layer;

Step S7: Add a metal layer Ti (about 50nm thick)/Au (about 200nm thick), passivate and open to form electrodes, and the electrodes can be electrically connected to the outside through bumps, solder, conductive glue or metal bonding wires.

Embodiment 4 With reference to Fig. 4, the structure of this GaN base ultraviolet LED chip comprises: n-GaN401, quantum well layer 402, p-GaN layer 403, graphene film cover Ag nano-dot layer 404 (Ag nano-dot layer 404a, graphene Thin film layer 404b), conductive reflective layer 405, p-type electrode 406, metal bonding layer 407, metal substrate 408, n-type electrode 409.

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

Step S1: On the sapphire substrate, a GaN buffer layer with a thickness of about 2.0 μm, an n-GaN layer with a thickness of about 2.0 μm, an InGaN/AlGaN multiple quantum well layer with a thickness of about 100 nm, and a p - GaN layer;

Step S2: Deposit a thin layer of Ag (Ag thickness is about 1nm-200nm, preferably about 40nm) on the p-GaN layer by electron beam evaporation, and anneal it in a _N2 atmosphere at 300-500°C (preferably about 400°C) About 1min to form Ag nano dots, the average particle size is about 300nm;

Step S3: prepare graphene by CVD method on copper foil, after spin-coating PMMA, then corrode copper foil substrate with FeCl ₃ solution, etch copper foil substrate, after corrosion is thorough, corrode to form PMMA/graphite with deionized water The olefin film is cleaned, and then the PMMA/graphene film is transferred to the p-GaN layer containing Ag nano-dots;

Step S4: After removing the PMMA with a hot acetone solution, then cleaning, and then patterning the graphene film by photolithography and oxygen plasma etching, and removing the graphene between the unit chips;

Step S5: Depositing an Al reflective layer with a thickness of about 2.5 μm by electron beam evaporation;

Step S6: further deposit a Ti (about 50nm thick)/Au (about 200nm thick) metal layer on the surface of the Al reflective layer, photolithography and corrosion to form the p-electrode of each chip, and then vapor-deposit metal Au/Sn, and further photolithography , corrosion, forming the bonding layer of each chip;

Step S7: Deposit SiO ₂ , and remove the area between the chips by photolithography etching, use this as a protective layer to etch the InGaN/AlGaN material to the sapphire to form isolation grooves between the chips, and then etch and remove the surface SiO ₂ ;

Step S8: using the bonding layer as the contact surface to realize large-area wafer bonding with the Cu/W alloy substrate;

Step S9: using a KrF excimer laser to scan each chip one by one from the side of the sapphire substrate and peel off the sapphire substrate;

Step S10: Remove the GaN buffer layer by plasma etching, roughen the surface of n-GaN, and prepare Ti (50nm)/Al (250nm) ohmic contacts on the surface of n-GaN layer by photolithography, electron beam evaporation, and lift-off methods Electrodes, after dicing, obtain LED chips with a metal support vertical structure.

In the foregoing embodiments 1-4, the resistance of the conductive reflective layer is less than 0.1Ω/sq, and the reflective structure composed of the graphene-Ag nanocomposite layer and the conductive reflective layer is about 84% on average for 375nm light reflectance, and for 280nm The light reflectance is about 80% on average. In addition, it is found through testing that the LED chips formed in Examples 1-4 also have the advantages of high external quantum efficiency, high light extraction efficiency, low turn-on voltage, good heat dissipation, and high reliability.

It should be understood that the present invention is not limited to the above-mentioned embodiments, if the various changes or deformations of the present invention do not depart from the spirit and scope of the present invention, if these changes and deformations belong to the claims and equivalent technical scope of the present invention, then The present invention is intended to cover such modifications and variations as well.

Claims (10)

1. An ultraviolet semiconductor light-emitting device, comprising an epitaxial structure layer mainly composed of n-type layer, quantum well layer and p-type layer and p-type, n-type electrodes, characterized in that graphite is also arranged successively on the p-type layer A graphene-Ag nanocomposite layer and a conductive reflective layer, the graphene-Ag nanocomposite layer forms an ohmic contact with the p-type layer. 2. The ultraviolet semiconductor light-emitting device according to claim 1, wherein the graphene-Ag nanocomposite layer comprises: An Ag nanomaterial layer formed on the p-type layer, and a graphene film covering the Ag nanomaterial layer, the Ag nanomaterial layer comprising Ag nanodots and/or Ag nanowires; Alternatively, graphene quantum dots supported Ag nanoparticle composite layers. 3. The ultraviolet semiconductor light-emitting device according to claim 2, characterized in that the Ag nano-dots have a particle diameter of 10 nm to 1 μm, the Ag nanowires have a diameter of 5 to 100 nm and a length of 5 to 100 μm, and the The particle size of the graphene quantum dot-loaded Ag nano particle composite is 5-100 nm. 4. according to claim 2 or 3 described ultraviolet semiconductor light-emitting devices, it is characterized in that an intermediate layer is also formed between the Ag nanomaterial layer and the graphene film, Alternatively, an intermediate layer and a conductive reflective layer are sequentially formed on the graphene-Ag nanocomposite layer. 5. The ultraviolet semiconductor light-emitting device according to claim 1, characterized in that the thickness of the conductive reflective layer is 0.1-3 μm, and the material of the conductive reflective layer includes Al. 6. The ultraviolet semiconductor light-emitting device according to claim 4, characterized in that the material of the intermediate layer comprises Cr. 7. The ultraviolet semiconductor light emitting device according to claim 1, characterized in that the material of the p-type layer comprises p-AlGaN. 8. The ultraviolet semiconductor light-emitting device according to claim 1, characterized in that the semiconductor light-emitting device is a flip-chip structure or a vertical structure. 9. The ultraviolet semiconductor light-emitting device according to any one of claims 1-3, 6-8, characterized in that the semiconductor light-emitting device is a GaN-based LED chip. 10. A method for manufacturing an ultraviolet semiconductor light-emitting device according to any one of claims 1-9, characterized in that it comprises: growing an epitaxial structure layer on the substrate; Process the epitaxial structure layer, form an n-type electrode on the n-type layer, form a graphene-Ag nanocomposite layer on the p-type layer, and make the graphene-Ag nanocomposite layer form an ohmic contact with the p-type layer ; And, forming a conductive reflective layer on the graphene-Ag nanocomposite layer, and then making a p-type electrode on the conductive reflective layer.