Green laser of blue light LED pump and preparation method thereof

Abstract

The invention relates to a green laser of a blue light LED pump and a preparation method of the green laser, and belongs to the technical field of semiconductor lasers. On the basis of a conventional blue light LED, a liquid polymer film mixed with green light quantum dots covers the surface of the LED; the blue light irradiates and enters the polymer waveguide containing the green quantum dot material to form a polymer waveguide resonant cavity, and finally, the two ends of the waveguide are coated with a film layer green laser, and green laser is output. The defect that the wavelength of an existing GaN material semiconductor laser cannot reach 532 nm is effectively overcome, and laser output with the wavelength ranging from 510 nm to 540 nm can be achieved through selection of the diameter and materials of the quantum dots. Moreover, the method only depends on a conventional LED process, can achieve the large-batch production, and can effectively reduce the cost of the laser.

Description

Technical Field

[0001] The invention relates to a green laser pumped by a blue light LED and a preparation method thereof, belonging to the technical field of semiconductor lasers. Background Art

[0002] Green lasers are widely used in outdoor laser indication, distance measurement marking, laser sensor devices and medical devices due to their excellent photoelectric conversion rate and human eye sensitivity. However, the current semiconductor laser materials in the green light band are mainly GaN / InGaN compound materials, which have a high material band gap, and the lowest tunable band gap is still higher than the 2.33eV of the positive green light 532nm band, causing the output wavelength of such semiconductor lasers to deviate from 532nm, mainly concentrated between 510nm-520nm, and the color deviation is serious. In addition, the current technical solution is to generate 1064nm lasers by pumping crystal materials with semiconductor lasers, and then multiply the frequency through nonlinear crystals to generate 532nm lasers. However, this system includes semiconductor lasers and crystals, with complex optical paths, high costs, and large volumes, which cannot meet the needs of large-scale production in the industry.

[0003] There are several solutions to the above problems: First, through the doping and structural research and development of compound semiconductor materials, the band gap of GaN and InGaN compound materials can be reduced as much as possible, and the wavelength can be as close to 532nm as possible through material doping and laser structural design. However, the physical mechanism has already approached the theoretical limit of the material, which makes it difficult to achieve, and the chip output power and efficiency have dropped significantly. The second solution is to integrate optical components such as semiconductor pumps, crystals, and nonlinear crystals as much as possible to reduce the size of the green laser. However, this solution still belongs to the optical system assembly technology, which cannot achieve chip-level mass production and large-scale production, and the degree of cost control is limited. Summary of the invention

[0004] In view of the shortcomings of the prior art, the present invention provides a green laser pumped by a blue light LED. Based on the conventional blue light LED process, the present invention uniformly mixes the green quantum dot material into the organic liquid polymer material, covers it on the surface of the blue light LED by photolithography, and forms a polymer waveguide structure after curing. The blue light irradiates into the polymer waveguide layer to excite the green light quantum dots mixed in the waveguide layer. The two ends of the polymer waveguide layer are optically coated to form a resonant cavity, and finally the green light output is realized.

[0005] At the same time, the present application also provides a method for preparing the above-mentioned blue light LED pumped green light laser.

[0006] The technical solution of the present invention is as follows:

[0007] A green laser pumped by a blue LED, comprising a blue LED and a polymer solid film structure;

[0008] The blue LED has a structure including a substrate, a lower DBR layer, an active layer, an upper DBR layer, and an electrode layer arranged in sequence from bottom to top; the above layers are grown by epitaxial growth, and the upper DBR layer is etched by photolithography into a light-emitting hole with a circular or rectangular structure, and an electrode layer is covered on the upper part of the light-emitting hole; a polymer solid film structure is arranged above the electrode layer structure.

[0009] Preferably, the electrode layer material is ITO or IZO.

[0010] Preferably, the polymer solid film structure is a solidified quantum dot polymer solution with a thickness of 100 nm - 5 μm.

[0011] More preferably, the selection of quantum dots includes but is not limited to: InAs, InSb, InP, GaAs in the III-V material system, CdS, CdSe, CdZnSe, ZnSeTe, ZnSeS, ZnS, HgTe in the II-VI material system, and SnTe, PbS, PbSe materials in the IV-VI material system. The diameter size of the quantum dots ranges from 2 nm to 20 nm. The selection of quantum dots is mainly based on the position of the peak in their fluorescence emission spectrum. Quantum dots with larger diameters are selected for longer wavelengths, and quantum dots with smaller diameters are selected for shorter wavelengths.

[0012] More preferably, the selected quantum dots have an emission peak at 510 nm - 540 nm.

[0013] More preferably, the selection of polymers includes but is not limited to PMMA, PSU, PET, COC, TPX, PS, NAS, ADC. The original state of the polymer is liquid. To ensure that it must have the ability to transmit light in the required laser wavelength range and can achieve light focusing and passing through.

[0014] The preparation method of the above green laser pumped by a blue LED includes the following steps:

[0015] (1) Use the MOCVD method to grow the lower DBR layer, the active layer, and the upper DBR layer on the substrate in sequence;

[0016] (2) Use electron beam evaporation or magnetron sputtering technology to grow an ITO or IZO layer on the light-emitting layer;

[0017] (3) Put the quantum dots into the liquid polymer, stir, and at the same time put the solution into an ultrasonic oscillation device for treatment until the quantum dots are evenly mixed with the liquid polymer and the quantum dots can be evenly dispersed to form a stable polymer mixture;

[0018] (4) The liquid polymer mixture is spin-coated onto the P-side metal. Using a thermal oven or photo-curing method, the liquid polymer mixture is solidified into a polymer solid film. The thickness of the polymer solid film is controlled by the spin-coating technique, and the thickness of the polymer thin film is 100 nm - 5 μm; the polymer viscosity value is 10 cp - 100 cp;

[0019] (5) By spin-coating a photoresist on the polymer solid film and through photolithography and etching, the polymer solid film is etched into a rectangular waveguide structure. The width of the polymer waveguide is 1 μm - 50 μm;

[0020] (6) Use a saw blade tool to cut the wafer according to the LED partition, and a smooth plane is formed on the polymer cutting surface;

[0021] (7) Use an optical coating equipment to perform optical coating on the polymer cutting surface. A high-reflection film with a wavelength band of 510 nm - 540 nm (reflectivity greater than or equal to 99%) is evaporated at one end, and a partial reflection film with a reflectivity of 5% - 50% in the 510 nm - 540 nm band is coated at the other end to form the output cavity surface of the green laser, and finally a green laser pumped by a blue LED is obtained.

[0022] Preferably, in step (4), a spotlight emitting ultraviolet or blue light in the wavelength range of 300 nm - 450 nm is selected for photo-curing, or a thermal oven with a temperature range of 100 °C - 450 °C is used for thermal curing.

[0023] Preferably, in step (5), the width of the polymer waveguide is 5 μm.

[0024] The present invention has no CMOS wafer structure, no red light quantum dot deposition process, and has a waveguide structure formed by a polymer above the blue LED. The light emission direction of the invention is the same as that of the LED, perpendicular to the LED light-emitting surface, and the polymer waveguide adopted by the invention oscillates and emits light along the polymer waveguide direction.

[0025] The beneficial effects of the present invention are as follows:

[0026] The present invention provides a green laser pumped by a blue LED. Based on a conventional blue LED, by covering the surface of the LED with a liquid polymer thin film mixed with green quantum dots, blue light irradiates into the polymer waveguide containing green quantum dot materials to form a polymer waveguide resonant cavity, and finally a green laser is formed by coating layers at both ends of the waveguide and green laser is output. The invention effectively makes up for the defect of insufficient wavelength of the existing GaN material, and can realize laser output with a wavelength of 510 nm - 540 nm by selecting the quantum dot diameter and material. Moreover, this technology relies on the conventional LED process, can realize mass production and effectively reduce the cost of the laser at the same time. Description of the Drawings

[0027] Figure 1 Schematic diagram of the green laser pumped by a blue LED provided by the present invention before lithography is performed on the solid polymer film to form a polymer waveguide;

[0028] Figure 2 Schematic diagram of the green laser pumped by a blue LED provided by the present invention;

[0029] 1. Substrate, 2. Lower DBR layer, 3. Active layer, 4. Upper DBR layer, 5. Electrode layer, 6. Polymer solid film, 7. Polymer waveguide, 8. Green quantum dots. Detailed implementation manners

[0030] The present invention will be further described below by way of examples in conjunction with the drawings, but not limited thereto.

[0031] Example 1:

[0032] A green laser pumped by a blue LED includes a blue LED and a polymer solid film structure;

[0033] For the blue LED, its structure from bottom to top includes a substrate, a lower DBR layer, an active layer, an upper DBR layer, and an electrode layer arranged in sequence; the above layers are grown by epitaxial growth, and the upper DBR layer is etched by lithography into an out-coupling hole with a circular or rectangular structure, and an electrode layer is covered on the upper part of the out-coupling hole; a polymer solid film structure is arranged above the electrode layer structure.

[0034] The material of the electrode layer is ITO or IZO. The polymer solid film structure is a solidified quantum dot polymer solution with a thickness of 2 μm.

[0035] The selection of quantum dots includes but is not limited to: InAs, InSb, InP, GaAs in the III-V material system, CdS, CdSe, CdZnSe, ZnSeTe, ZnSeS, ZnS, HgTe in the II-VI material system, and SnTe, PbS, PbSe materials in the IV-VI material system. The diameter of the quantum dots ranges from 2 nm to 20 nm. The selection of quantum dots is mainly based on the position of the peak of their fluorescence emission spectrum. Quantum dots with a larger diameter are selected for longer wavelengths, and quantum dots with a smaller diameter are selected for shorter wavelengths. In this example, CdSe material quantum dots are selected, with a quantum dot diameter of 10 nm and a concentration of 1% mg / mL in the liquid polymer. The selected quantum dots have an emission peak at 530 nm.

[0036] The selection of polymers includes but is not limited to PMMA, PSU, PET, COC, TPX, PS, NAS, ADC, and PC. The polymers are in a liquid state originally. To ensure the ability to transmit light within the required laser wavelength range and to achieve light focusing and passing through, the polymers should be able to do so. In this example, COC material is used. This material is liquid above 170 °C and is suitable for mixing with quantum dot powder.

[0037] Example 2:

[0038] A green laser pumped by a blue LED has the same structure as described in Example 1, except that the thickness of the polymer solid film structure is 100 nm. In this example, CdS material quantum dots are selected, with a quantum dot diameter of 2 nm and a quantum dot concentration of 2% mg / mL in the liquid polymer. The selected quantum dot emission peak is at 510 nm. The polymer used is PMMA material.

[0039] Example 3:

[0040] A green laser pumped by a blue LED has the same structure as described in Example 1, except that the thickness of the polymer solid film structure is 5 μm. In this example, CdZnSe material quantum dots are selected, with a quantum dot diameter of 20 nm and a quantum dot concentration of 5% mg / mL in the liquid polymer. The selected quantum dot emission peak is at 540 nm. The polymer used is PC material.

[0041] Example 4:

[0042] A preparation method for the green laser pumped by the blue LED described in Example 1 includes the following steps:

[0043] (1) Use the MOCVD method to sequentially grow the lower DBR layer, active layer, and upper DBR layer on the substrate;

[0044] (2) Use electron beam evaporation or magnetron sputtering technology to grow an ITO or IZO layer on the light-emitting layer;

[0045] (3) Put the quantum dots into the liquid polymer, stir, and at the same time put the solution into an ultrasonic oscillation device for treatment until the quantum dots are evenly mixed with the liquid polymer and the quantum dots can be evenly dispersed to form a stable polymer mixture;

[0046] (4) The liquid polymer mixture is spin-coated onto the P-side metal. Using a thermal oven or photo-curing method, a spotlight emitting ultraviolet or blue light with a wavelength range of 300 nm - 450 nm is selected for photo-curing, or a thermal oven with a temperature range of 100 °C - 450 °C is used for thermal curing, so that the liquid polymer mixture solidifies into a polymer solid film. The thickness of the polymer solid film is controlled by the spin-coating technique, and the thickness of the polymer thin film is 2 μm; the polymer viscosity value is 10 cp - 100 cp;

[0047] (5) By spin-coating a photoresist on the polymer solid film and through photolithography and etching, the polymer solid film is etched into a rectangular waveguide structure, and the width of the polymer waveguide is 5 μm;

[0048] (6) The wafer is cut according to the LED partition using a saw blade tool, and a smooth plane is formed on the polymer cutting surface;

[0049] (7) An optical coating is applied to the polymer cutting surface using an optical coating device. A high-reflection film with a wavelength band of 510 nm - 540 nm (reflectivity greater than or equal to 99%) is evaporated at one end, and a partial reflection film with a wavelength of 510 nm - 540 nm (reflectivity 5% - 50%) is deposited at the other end. In this example, a reflection film with a reflectivity of 30% is selected to form the output cavity surface of the green laser, and finally a green laser pumped by a blue LED is obtained.

Claims

1. A green laser pumped by a blue LED, characterized in that: Including blue LED and polymer solid film structure; The structure of the blue light LED includes, from bottom to top, a substrate, a lower DBR layer, an active layer, an upper DBR layer, and an electrode layer arranged in sequence; the upper DBR layer is etched into a light-emitting hole with a circular or rectangular structure, and the electrode layer is laid on the upper part of the light-emitting hole; A polymer solid film structure is arranged above the electrode layer structure.

2. The blue LED-pumped green laser according to claim 1, characterized in that: The electrode layer material is ITO or IZO.

3. The blue LED-pumped green laser according to claim 1, characterized in that: The polymer solid film structure is a solidified quantum dot polymer solution with a thickness of 100nm-5um.

4. The blue LED-pumped green laser according to claim 3, characterized in that: The selection of quantum dots includes but is not limited to: InAs, InSb, InP, GaAs in the III-V group material system, CdS, CdSe, CdZnSe, ZnSeTe, ZnSeS, ZnS, HgTe in the II-VI group material system, and SnTe, PbS, PbSe materials in the IV-VI group material system, and the quantum dot diameter size ranges from 2nm to 20nm.

5. The blue LED-pumped green laser according to claim 4, characterized in that: The emission peak of the selected quantum dots is between 520nm and 540nm.

6. The blue LED-pumped green laser according to claim 3, characterized in that: The choice of polymer includes but is not limited to PMMA, PSU, PET, COC, TPX, PS, NAS, ADC.

7. A method for preparing a green laser pumped by a blue LED, characterized in that: The steps include: (1) using MOCVD to sequentially grow a lower DBR layer, an active layer, and an upper DBR layer on a substrate; (2) growing an ITO or IZO layer on the light-emitting layer using electron beam evaporation or magnetron sputtering technology; (3) placing the quantum dots into the liquid polymer and stirring the mixture, while placing the mixture into an ultrasonic oscillation device for treatment until the quantum dots and the liquid polymer are evenly mixed to form a polymer mixture; (4) The liquid polymer mixture is spin-coated onto the P-side metal, and the liquid polymer mixture is solidified into a polymer solid film by a heat oven or light curing. The thickness of the polymer solid film is controlled by spin coating technology, and the polymer film thickness is 100nm-5um; the polymer viscosity value is 10cp-100cp; (5) spin coating a photoresist on the polymer solid film, and etching the polymer solid film into a rectangular waveguide structure through photolithography and etching, wherein the polymer waveguide has a width of 1 um to 50 um; (6) Using a saw blade tool to cut the wafer according to the LED partitions, the polymer cut surface forms a smooth plane; (7) Optical coating equipment is used to perform optical coating on the cut surface of the polymer. A high-reflection film in the wavelength range of 510 nm to 540 nm is evaporated on one end, and a partial reflection film in the wavelength range of 510 nm to 540 nm is deposited on the other end to form the output cavity surface of the green laser. Finally, a green laser pumped by a blue LED is obtained.

8. The method for preparing a green laser pumped by a blue LED according to claim 7, characterized in that: In step (4), a spotlight emitting ultraviolet or blue light in the wavelength range of 300nm-450nm is selected for light curing, or a hot oven with a temperature range of 100°C-450°C is used for heat curing.

9. The method for preparing a green laser pumped by a blue LED according to claim 7, characterized in that: In step (5), the width of the polymer waveguide is 5 um.

10. The method for preparing a green laser pumped by a blue LED according to claim 7, characterized in that: In step (7), the reflectivity of the high-reflection film is greater than or equal to 99%, and the reflectivity of the partial-reflection film is 5%-50%.

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