A lead-free perovskite vertical cavity surface emitting dual-wavelength laser and its preparation method

Abstract

The present invention relates to the field of laser devices, and more specifically to a lead-free perovskite vertical-cavity surface-emitting dual-wavelength laser and a method for manufacturing the same. The laser comprises a bottom Bragg reflector, a first active region, an intermediate Bragg reflector, a second active region, and a top Bragg reflector, all grown sequentially on a substrate. The first active region and / or the second active region comprise a ternary copper halide perovskite and / or a multinary copper halide perovskite. The perovskite laser of the present invention is lead-free and has high chemical and thermal stability.

Description

Technical Field

[0001] The present invention relates to the field of laser devices, and in particular to a lead-free perovskite vertical cavity surface emitting dual-wavelength laser and a preparation method thereof. Background Art

[0002] Lasers have been widely used in many fields such as medical equipment, displays, optical communications and industrial manufacturing. Lasers used to emit lasers can emit lasers of a single wavelength or multiple wavelengths. Among them, multi-wavelength visible light lasers have been a hot research topic in recent years. They have the following advantages: First, the laser emission spectrum is a linear spectrum of multiple wavelengths, with high color saturation and color resolution, and clear and bright visual colors; second, the emitted wavelength is optional, and a specific wavelength can be selected using a polarization beam splitter or filter; third, frequency mixing and high-brightness laser display can be achieved, and compared with ordinary light sources of the same brightness, the utilization rate of lasers is higher, which is more in line with the sustainable development plan of the environmentally friendly earth. Based on this, multi-wavelength lasers have broad application prospects in display, medical analysis, precision laser spectroscopy, nonlinear optical mixers and other fields.

[0003] Multi-wavelength lasers are usually composed of a pump source, a gain medium, and a resonant cavity. The gain medium is a necessary condition for the emission of multi-wavelength lasers. Different gain media correspond to specific output wavelengths. Perovskite is considered to be a very promising laser gain material due to its unique optical properties, tunable spectrum, high defect tolerance, low cost, and easy processing. The resonant cavity of perovskite lasers is mainly realized by whispering gallery wall mode (WGM), distributed feedback (DFB) or distributed Bragg reflector (DBR). Among them, vertical cavity surface emitting lasers (VCSELs) with Bragg reflector resonators have attracted much attention due to their single-mode output performance and easy integration. At present, vertical cavity surface emitting lasers usually use lead-based perovskites as the gain material of the laser, combined with a spectrally matched Bragg reflector resonator to realize perovskite VCSELs (Pe-VCSELs); for example, using 10 pairs of alternating HfO2 / SiO2 layers to form a Bragg reflector resonator and using FAPbBr3 as the gain material, a low threshold (18.3μJ / cm) was prepared. 2 ) 552.4nm green Pe-VCSEL. Eleven layers of perovskite nanocrystals (CsPbX3, X = Cl, Br, I) were prepared on a Bragg reflector using a solution process. The top Bragg reflector was then bonded together to create red, green, and blue Pe-VCSELs.

[0004] However, the lead-based perovskite materials used for lasers (including CsPbBr3, MAPbI3, FAPbI3, CsPbCl3) have poor thermal stability due to the toxicity of Pb, which affects the large-scale application and commercialization of lead-based perovskite materials. 2+ Can be Sn 2+ and Ge 2+ Plasma substitution, but the above-mentioned substitution ions are easily oxidized to tetravalent ions, and the prepared perovskite material is also easy to decompose; therefore, the environmental stability and thermal stability of the corresponding perovskite material prepared are better than those using Pb 2+ The performance is even worse, making it difficult to apply to lasers.

[0005] Currently, the high photoluminescence quantum yield (PLQY) and thermal stability of ternary copper halide perovskite materials (Cs3Cu2I5, Cs3Cu2Br5, Cs3Cu2Cl5, Cs1Cu2I3, Cs1Cu2Br3, Cs1Cu2Cl3) have been demonstrated. For example, Cs3Cu2I5 NCs have been used to fabricate high-efficiency deep-blue light-emitting diodes (LEDs) with a turn-on voltage of 4.5V at 7.5V and a maximum brightness of 262.6cd / m 2 ; CsCu2I3 single crystals and yellow-emitting CsCu2I3 nanorods have a PLQY of up to 15.7%; in addition, although ternary copper halide perovskite materials such as Cs3Cu2I5 have a strong quantum confinement effect that makes them laser gain materials, they have self-trapped exciton (STEs) emission characteristics. The STEs effect will cause the photoluminescence spectrum (PL) of the material to be broadened, making it difficult to meet the conditions for achieving laser emission. Summary of the Invention

[0006] In order to improve the deficiencies of the prior art, the present invention provides a lead-free perovskite vertical cavity surface emitting dual-wavelength laser, which can be lead-free and has high environmental stability and thermal stability.

[0007] To overcome the wide photoluminescence (PL) spectrum of ternary copper halide perovskite materials, the inventors implemented a specific structural design. In this design, a vertical cavity emitting laser with an intermediate Bragg reflector and a second active region was added to the conventional three-layer structure of a bottom Bragg reflector, a first active region, and a top Bragg reflector, thereby achieving dual-wavelength emission.

[0008] A lead-free perovskite vertical cavity surface emitting dual-wavelength laser, the laser comprising a bottom Bragg reflector, a first active region, an intermediate Bragg reflector, a second active region and a top Bragg reflector sequentially grown on a substrate;

[0009] The first active region and / or the second active region includes ternary copper halide perovskite and / or multinary copper halide perovskite.

[0010] In the present invention, for each individual active region, it can be considered that all other layers located on both sides of the active region together constitute the Bragg reflectors on both sides, forming the resonant cavity of the active region (i.e., the light-emitting layer). Therefore, according to an embodiment of the present invention, the bottom Bragg reflector, the first active region, and (the middle Bragg reflector, the second active region, and the top Bragg reflector) constitute the first resonant cavity, and the (bottom Bragg reflector, the first active region, the middle Bragg reflector), the second active region, and the top Bragg reflector constitute the second resonant cavity. The resonant cavity is used to perform mode selection on photons emitted by the gain medium to achieve near-monochromatic laser output.

[0011] It should be noted that, in this application, “active region” and “gain region” have the same meaning and can be used interchangeably.

[0012] According to an embodiment of the present invention, the reflectivity of the bottom Bragg reflector is greater than 0.9999; the reflectivity of the top Bragg reflector is greater than 0.9, and the reflectivity of the middle Bragg reflector is less than 0.9.

[0013] According to an embodiment of the present invention, the ternary copper halide perovskite is selected from Cs x Cu y I x+y 、Cs x Cu y Br x+y 、Cs x Cu y Cl x+y , Rb x Cu y I x+y , Rb x Cu y Br x+y , Rb x Cu y Cl x+y At least one of the following, wherein 0.5≤x≤3.5, 1.5≤y≤2.5, and 2.5≤x+y≤5.5.

[0014] It should be noted that, in the present application, the multi-component copper halide perovskite refers to a compound and / or mixture formed by two or more ternary copper halide perovskites.

[0015] For example, the ternary copper halide perovskite is Cs3Cu2I5 or Cs3Cu2Br5.

[0016] For example, the multi-element copper halide perovskite is Cs3Cu2I2Br3, Cs1Rb2Cu2I2Br3, Cs 2.4 Rb0.6 Cu2I5, Cs3Cu2I 4.9 F 0.1 .

[0017] According to an embodiment of the present invention, the thermal decomposition temperature of the ternary copper halide perovskite and the polyvalent copper halide perovskite is greater than 200 °C and less than 300 °C. For example, it can be greater than 220 °C, greater than 250 °C. Further, for example, the decomposition temperature of Cs3Cu2I5 is greater than 250 °C.

[0018] According to an embodiment of the present invention, the thickness d1 of the first active region and the thickness d2 of the second active region are the same or different, and preferably different.

[0019] According to an embodiment of the present invention, the thickness d1 of the first active region and the thickness d2 of the second active region are different. For example, the thickness d2 of the second active region is greater than the thickness d1 of the first active region.

[0020] According to an embodiment of the present invention, the thickness d1 of the first active region is 100 nm to 200 nm, for example, 130 nm.

[0021] According to an embodiment of the present invention, the thickness d2 of the second active region is 100 nm to 200 nm, for example, 150 nm.

[0022] According to an embodiment of the present invention, the refractive index n1 of the material of the first active region ranges from 1.3 < n2 < 3.5, and the refractive index n2 of the material of the second active region ranges from 1.3 < n2 < 3.5.

[0023] According to an embodiment of the present invention, the refractive index n1 of the material of the first active region and the refractive index n2 of the material of the second active region can be the same or different. Preferably, the refractive index n1 of the material of the first active region and the refractive index n2 of the material of the second active region are the same.

[0024] According to an embodiment of the present invention, the optical thickness (the product of the refractive index and the thickness) value L1 = n1 * d1 of the first active region and the optical thickness value L2 = n2 * d2 of the second active region. The relationship between L1, L2 and the emission wavelengths λ1 and λ2 of the dual-wavelength laser is: N1 = 4 * L1 / λ1, N2 = 4 * L2 / λ2, and 1 < N1 < 3, 1 < N2 < 3. Preferably, N1 = 2.186 and N2 = 2.45.

[0025] According to an embodiment of the present invention, the first active region and the second active region are film structures, for example, a single-layer film structure or a film structure formed by alternately stacking several layers of films.

[0026] According to an embodiment of the present invention, in a membrane structure formed by alternately stacking several membrane layers, the materials of the several membrane layers may be the same or different, preferably different.

[0027] According to an embodiment of the present invention, the thicknesses of the several layers of film may be the same or different, preferably different.

[0028] For example, the first active region and / or the second active region may be a five-layer film structure formed by alternating stacking of Cs3Cu2I5 and Cs3Cu2Br5.

[0029] According to an embodiment of the present invention, the substrate is made of a material with low absorption to the emission wavelength and the pump source, such as quartz, silicon or sapphire.

[0030] According to an embodiment of the present invention, the bottom Bragg reflector, the middle Bragg reflector, and the top Bragg reflector include first structure layers and second structure layers that are alternately stacked.

[0031] According to an embodiment of the present invention, the total number of the first structure layer and the second structure layer in the bottom Bragg reflector and the top Bragg reflector is an odd number, and the total number of the first structure layer and the second structure layer in the middle Bragg reflector is an odd number or an even number.

[0032] For example, the bottom Bragg reflector includes 16 first structure layers and 15 second structure layers.

[0033] For example, the intermediate Bragg reflector includes three first structure layers and two second structure layers.

[0034] For example, the top Bragg reflector includes 6 first structure layers and 5 second structure layers.

[0035] According to an embodiment of the present invention, the thickness of the first structure layer in each Bragg reflector is the same or different, for example, different.

[0036] According to an embodiment of the present invention, the thickness of the second structure layer in each Bragg reflector is the same or different, for example, different.

[0037] According to an embodiment of the present invention, the optical thickness L of the first structure layer in each Bragg reflector is a and the optical thickness L of the second structural layer b The same or different, the relationship with the dual-wavelength laser emission wavelengths λ1 and λ2 is: N a =4*L a / λ1,N b =4*L b / λ2,N a The difference from the nearest even number is greater than 0.9 and less than 1.1, Nb The difference from the nearest even number is greater than 0.9 and less than 1.1, that is: 0.9 + the nearest even number <N a <1.1+closest even number, 0.9+closest even number <N b <1.1+nearest even number, such as N a =0.99 or 2.99, N b =1.01 or 3.01.

[0038] For example, the thickness of the first structure layer in the bottom Bragg reflector is 54.7 nm, the thickness of the first structure layer in the middle Bragg reflector is 54.8 nm, and the thickness of the first structure layer in the top Bragg reflector is 54.8 nm.

[0039] For example, the thickness of the second structure layer in the bottom Bragg reflector is 76.7 nm, the thickness of the second structure layer in the middle Bragg reflector is 84.3 nm, and the thickness of the second structure layer in the top Bragg reflector is 84.3 nm.

[0040] According to an embodiment of the present invention, in each Bragg reflector, the refractive index n3 of the first structure layer and the refractive index n4 of the second structure layer are different, preferably n3 is greater than n4, for example, n3 is 2.0-2.6, and n4 is 1.3-1.6.

[0041] According to an embodiment of the present invention, in each Bragg reflector, the first structure layer and the second structure layer are made of materials with low absorption of the pump source and emission wavelength.

[0042] According to an embodiment of the present invention, the materials of the first structural layer and the second structural layer include oxides, halides, and sulfides. The oxides include TeO2, Ta2O5, SiOx (x=1~2), and SiNx (x=1~1.5). The halides include LiF and MgF. The sulfides include ZnS. For example, the material of the first structural layer is TeO2, and the material of the second structural layer is LiF.

[0043] According to an embodiment of the present invention, the emission wavelength range of the laser is in the visible light band, for example: the laser whose gain medium is Cs3Cu2I5 has an emission wavelength in the blue light region; the laser whose gain medium is Cs3Cu2Cl5 has an emission wavelength in the green light region.

[0044] According to an embodiment of the present invention, the blue light region refers to a region with a wavelength of 410 nm to 490 nm, and the green light region refers to a region with a wavelength of 490 nm to 570 nm.

[0045] According to an embodiment of the present invention, the laser of the present invention is a low-threshold dual blue-light emitting vertical cavity surface laser.

[0046] It should be noted that, in this application, low threshold means that laser emission can be achieved with lower pump energy, for example: under optical pumping, the pump energy is less than or equal to 10μJ, for example: 4.95μJ, 5.69μJ, 6.98μJ.

[0047] The present invention also provides a method for preparing the above-mentioned laser, which comprises the following steps:

[0048] Step 1: Depositing a bottom Bragg reflector on the substrate surface;

[0049] Step 2: depositing ternary copper halide perovskite and / or multinary copper halide perovskite on the surface of the bottom Bragg reflector to form a first active region;

[0050] Step 3: depositing an intermediate Bragg reflector on the surface of the first active region;

[0051] Step 4: depositing ternary copper halide perovskite and / or multinary copper halide perovskite on the surface of the intermediate Bragg reflector to form a second active region;

[0052] Step 5: Deposit a top Bragg reflector on the surface of the second active region.

[0053] According to an embodiment of the present invention, step 2 includes: placing the evaporation source material corresponding to the ternary copper halide perovskite and / or the multi-component copper halide perovskite into a coating machine for evaporation.

[0054] According to an embodiment of the present invention, in step 2, the evaporation source material includes CuX and at least one selected from CsX and RbX, and X is selected from any one or more of F, Cl, Br, and I. X in different evaporation source materials may be the same or different.

[0055] Preferably, the evaporation source material is, for example, CsI or CuI.

[0056] According to an embodiment of the present invention, in step 2, a dual-source co-evaporation method is adopted when depositing a ternary copper halide perovskite, and a multi-source co-evaporation method is adopted when depositing a multi-element copper halide perovskite. For example, a three-source co-evaporation method is adopted when depositing a quaternary copper halide perovskite.

[0057] According to an embodiment of the present invention, in step 2, when the evaporation source material corresponding to the ternary copper halide perovskite and / or the multi-element copper halide perovskite is placed in the coating machine for evaporation, the evaporation rate of the evaporation source material is

[0058] According to an embodiment of the present invention, if the active region is a multi-layer copper halide perovskite thin film structure, the film layer is evaporated.

[0059] According to an embodiment of the present invention, during evaporation, the rotation speed of the sample stage on which the substrate is placed is 5 rpm to 25 rpm; and the rotation speed of the sample stage can be the same or different in different steps.

[0060] According to an embodiment of the present invention, the evaporation rates of different evaporation source materials are different. For example, the evaporation rate of CsI is The evaporation rate of CuI is

[0061] According to an embodiment of the present invention, when Cs3Cu2I5 is formed, the molar ratio of CsI and CuI is 3:(1.5-2.5). Further, the molar ratio of CsI and CuI is 3:(1.8-2.1), for example, 3:2.

[0062] Preferably, in step 2, the vacuum degree during evaporation in the coating machine is below 5E-4Pa.

[0063] According to an embodiment of the present invention, the evaporation source materials in step 4 and step 2 may be the same or different, for example, the same.

[0064] Preferably, the evaporation conditions in step 4 and step 2 may be the same or different, for example, the same.

[0065] According to an embodiment of the present invention, in step 1, before depositing the bottom Bragg reflector on the substrate surface, the following steps are also included: cleaning the substrate, for example, ultrasonically cleaning the substrate in acetone, isopropyl alcohol, and deionized water for 5 to 20 minutes, and then treating it with ultraviolet ozone for 10 to 20 minutes.

[0066] According to an embodiment of the present invention, in step 1, depositing a bottom Bragg reflector on the substrate surface includes: alternately evaporating a first structure layer material and a second structure layer material on the substrate surface.

[0067] Preferably, the materials of the first structural layer and the second structural layer are defined as above.

[0068] According to an embodiment of the present invention, in step 1, evaporating the first structural layer material and the second structural layer material on the surface of the substrate includes: placing the first structural layer material and the second structural layer material as evaporation source materials into a coating machine, and when the vacuum degree reaches below 5E-4Pa, alternately evaporating the first structural layer material and the second structural layer.

[0069] For example, the cleaned substrate is placed in a vacuum coating machine, Ta2O5 and SiO2 are placed in a crucible as evaporation source materials, the vacuum system of the coating machine is turned on, and when the vacuum degree of the vacuum system of the coating machine reaches below 5E-4Pa, 15.5 pairs of Ta2O5 and SiO2 are alternately evaporated to obtain a bottom Bragg reflector.

[0070] According to an embodiment of the present invention, in step 3, forming the intermediate Bragg reflector by deposition on the surface of the first active area includes: alternately evaporating a first structural layer material and a second structural layer material on the surface of the first active area.

[0071] According to an embodiment of the present invention, in step 5, forming a top Bragg reflector by deposition on the surface of the second active area includes: alternately evaporating a first structure layer material and a second structure layer material on the surface of the second active area.

[0072] According to an embodiment of the present invention, step 5 is followed by the following steps: venting and depressurizing the coating machine, taking out the device, and obtaining a low-threshold dual-blue-light-emitting vertical-cavity surface laser.

[0073] The present invention provides a lead-free perovskite vertical cavity surface emission dual-wavelength laser, which is prepared by adopting the above method.

[0074] Beneficial effects

[0075] The present invention is based on a lead-free perovskite material with high chemical and thermal stability, and can obtain a lead-free perovskite laser with high chemical and thermal stability. Moreover, by adding an intermediate Bragg reflector and a second active region to a conventional three-layer structure of a bottom Bragg reflector, a first active region, and a top Bragg reflector, the defect of a wide photoluminescence spectrum (PL) of the material caused by the STEs effect of the copper halide perovskite can be overcome, and a vertical cavity emitting laser capable of achieving dual-wavelength emission can be obtained. BRIEF DESCRIPTION OF THE DRAWINGS

[0076] Figure 1 Schematic diagram of the structure of the lead-free perovskite vertical cavity surface emitting dual-wavelength laser of the present invention;

[0077] Figure 2 This is a scanning electron microscope image of the lead-free perovskite vertical cavity surface emitting dual-wavelength laser in Example 1 of the present invention (the scale is 2 microns);

[0078] Figure 3 is a scanning electron microscope image of the lead-free perovskite vertical cavity surface emitting dual-wavelength laser in Example 2 of the present invention (scale is 400 nm);

[0079] Figure 4 The XRD patterns of Cs3Cu2I5 at room temperature and after heating at 200 and 300 degrees in the test example of the present invention are shown below:

[0080] Figure 5 This is an emission spectrum diagram of the laser in Example 1 of the present invention. DETAILED DESCRIPTION

[0081] The following will further describe the embodiments of the present invention in detail with reference to specific examples. It should be understood that the following examples are merely illustrative and explanations of the present invention and should not be construed as limiting the scope of protection of the present invention. All technologies implemented based on the above content of the present invention are encompassed within the scope of protection intended by the present invention.

[0082] Unless otherwise specified, the raw materials and reagents used in the following examples are commercially available or can be prepared by known methods.

[0083] Example 1

[0084] The preparation process of lead-free perovskite vertical cavity surface emitting dual-wavelength laser is as follows:

[0085] Step 1: The quartz substrate was ultrasonically cleaned in acetone, isopropanol, and deionized water for 15 minutes, and then treated with UV-ozone for 20 minutes.

[0086] Step 2: Place the substrate processed in step 1 into a vacuum coating machine, place Ta2O5 and SiO2 as evaporation source materials into the crucible, and start the vacuum system of the coating machine.

[0087] Step 3: When the vacuum degree of the vacuum system of the coating machine in step 2 reaches below 5E-4Pa, start to alternately evaporate 15.5 pairs of Ta2O5 layers and SiO2 layers (one Ta2O5 layer and one SiO2 layer as a pair), and the rotation speed of the sample stage on which the substrate is placed is 15 rpm; a bottom Bragg reflector is obtained, in which the first and last layers are both Ta2O5 layers, that is, there are 16 Ta2O5 layers, and the thickness of each Ta2O5 layer is 54.7nm, and there are 15 SiO2 layers, and the thickness of each SiO2 layer is 76.7nm.

[0088] Step 4: Take out the substrate after coating the bottom Bragg reflector in step 3, put it into a dual-source co-evaporation coating machine, put CsI and CuI as evaporation source materials into a quartz crucible, and start the vacuum system of the coating machine.

[0089] Step 5: When the vacuum degree of the vacuum system of the dual-source co-evaporation coating machine in step 4 reaches below 5E-4Pa, adjust the evaporation power supply current to make the evaporation rate of CsI The evaporation rate of CuI is The rotation speed of the sample stage on which the substrate sheet is placed is 15 revolutions per minute.

[0090] Step 6: After the evaporation rate in step 5 stabilizes, open the substrate stage baffle and start evaporating the Cs3Cu2I5 perovskite film with a film thickness of 130nm to obtain the first active region (first gain region) with a refractive index of 1.86.

[0091] Step 7: After the evaporation of the perovskite film in the first gain zone in step 6 is completed, the coating machine is vented and depressurized, the evaporation source materials are replaced with TeO2 and LiF, and the vacuum system of the coating machine is reopened.

[0092] Step 8: When the vacuum degree of the vacuum system of the coating machine in step 7 reaches below 5E-4Pa, start alternately evaporating 2.5 pairs of TeO2 layers and LiF layers to obtain an intermediate Bragg reflector, in which the first and last layers are both TeO2 layers, that is, there are 3 TeO2 layers, and the thickness of each TeO2 layer is 54.8nm, and there are 2 LiF layers, and the thickness of each LiF layer is 84.3nm.

[0093] Step 9: After the intermediate Bragg reflector evaporation in step 8 is completed, vent the air and pressure of the coating machine, put CsI and CuI again, turn on the vacuum system of the dual-source co-evaporation coating machine, and evaporate the Cs3Cu2I5 perovskite film again according to steps 5 and 6 to obtain the second active region (second gain region). However, the difference is that the thickness of the second active region is 150nm and the refractive index of the second active region is 1.85.

[0094] Step 10: After the second gain region is evaporated in step 9, 5.5 pairs of TeO2 layers and LiF layers are alternately evaporated again according to steps 7 and 8 to serve as a top Bragg reflector. In the top Bragg reflector, there are 6 TeO2 layers and 5 LiF layers; the thickness of each TeO2 layer is 54.8 nm, and the thickness of each LiF layer is 84.3 nm.

[0095] Step 11: After the top Bragg reflector is fabricated in Step 10, the coating machine is vented and the device is removed. This results in a low-threshold dual-blue-emission vertical cavity surface laser. Under fs pulsed laser pumping, the pump threshold energy is 4.95 μJ.

[0096] The structure diagram of the laser obtained in this embodiment can be found in Figure 1 .

[0097] Figure 2 This is a scanning electron microscope image of the vertical cavity surface laser prepared in this embodiment. It can be seen from the image that the vertical cavity surface laser includes a bottom Bragg reflector (including 15.5 pairs of Ta2O5 layers and SiO2 layers), a first active region, an intermediate Bragg reflector (2.5 pairs of TeO2 layers and LiF layers), a second active region and a top Bragg reflector (5.5 pairs of TeO2 layers and LiF layers) grown in sequence on the substrate.

[0098] The emission spectrum of the laser obtained in this example is shown in Figure 5 .

[0099] Example 2

[0100] The preparation process of lead-free perovskite vertical cavity surface emitting dual-wavelength laser is as follows:

[0101] Step 1: The silicon substrate was ultrasonically cleaned in acetone, isopropanol, and deionized water for 10 minutes, and then treated with UV-ozone for 15 minutes.

[0102] Step 2: Place the substrate processed in step 1 into a vacuum coating machine, place Ta2O5 and SiO2 as evaporation source materials into the crucible, and start the vacuum system of the coating machine.

[0103] Step 3: When the vacuum degree of the vacuum system of the coating machine in step 2 reaches below 5E-4Pa, start to alternately evaporate 17.5 pairs of Ta2O5 layers and SiO2 layers (one Ta2O5 layer and one SiO2 layer as a pair), and the rotation speed of the sample stage on which the substrate is placed is 10 rpm; a bottom Bragg reflector is obtained, in which the first and last layers are both Ta2O5 layers, that is, there are 18 Ta2O5 layers, and the thickness of each Ta2O5 layer is 55.8nm, and there are 17 SiO2 layers, and the thickness of each SiO2 layer is 78.2nm.

[0104] Step 4: Take out the substrate after coating the bottom Bragg reflector in step 3, put it into a dual-source co-evaporation coating machine, put CsBr and CuI as evaporation source materials into a quartz crucible, and start the vacuum system of the coating machine.

[0105] Step 5: When the vacuum degree of the vacuum system of the dual-source co-evaporation coating machine in step 4 reaches below 5E-4Pa, adjust the evaporation power supply current to make the evaporation rate of CsBr The evaporation rate of CuI is The sample stage on which the substrate sheet is placed rotates at a speed of 18 revolutions per minute.

[0106] Step 6: After the evaporation rate in step 5 stabilizes, open the substrate stage baffle and start evaporating the Cs3Cu2Br3I2 perovskite film with a film thickness of 100nm to obtain the first active region (first gain region) with a refractive index of 1.9.

[0107] Step 7: After the evaporation of the perovskite film in the first gain zone in step 6 is completed, the coating machine is vented and depressurized, the evaporation source materials are replaced with TeO2 and LiF, and the vacuum system of the coating machine is reopened.

[0108] Step 8: When the vacuum degree of the vacuum system of the coating machine in step 7 reaches below 5E-4Pa, start alternately evaporating 2.5 pairs of TeO2 layers and LiF layers to obtain an intermediate Bragg reflector, in which the first and last layers are both TeO2 layers, that is, there are 3 TeO2 layers, and the thickness of each TeO2 layer is 53.7nm, and there are 2 LiF layers, and the thickness of each LiF layer is 85.2nm.

[0109] Step 9: After the intermediate Bragg reflector evaporation in step 8 is completed, the coating machine is vented and depressurized, and CsI and CuI are added again. The vacuum system of the dual-source co-evaporation coating machine is turned on to make the evaporation rate of CsI The evaporation rate of CuI is The Cs3Cu2I5 perovskite film is evaporated again according to steps 5 and 6 to obtain a second active region (second gain region). However, the difference is that the thickness of the second active region is 140 nm and the refractive index of the second active region is 1.88.

[0110] Step 10: After the second gain region is evaporated in step 9, 3.5 pairs of TeO2 layers and LiF layers are alternately evaporated again according to steps 7 and 8 to serve as a top Bragg reflector. In the top Bragg reflector, there are four TeO2 layers and three LiF layers; the thickness of each TeO2 layer is 50.1 nm, and the thickness of each LiF layer is 78.3 nm.

[0111] Step 11: After the top Bragg reflector is fabricated in Step 10, the coating machine is vented and the device is removed. This results in a low-threshold dual-blue-emission vertical cavity surface laser. Under fs pulsed laser pumping, the pump threshold energy is 5.69 μJ.

[0112] Figure 3 This is a scanning electron microscope image of the vertical cavity surface laser prepared in this embodiment. It can be seen from the image that the vertical cavity surface laser includes a bottom Bragg reflector (including 15.5 pairs of Ta2O5 layers and SiO2 layers), a first active region, an intermediate Bragg reflector (2.5 pairs of TeO2 layers and LiF layers), a second active region and a top Bragg reflector (3.5 pairs of TeO2 layers and LiF layers) grown in sequence on the substrate.

[0113] Example 3

[0114] The preparation process of the lead-free perovskite vertical cavity surface emitting dual-wavelength laser is as follows:

[0115] Step 1: The sapphire substrate was ultrasonically cleaned in acetone, isopropyl alcohol, and deionized water for 10 minutes, and then treated with UV-ozone for 15 minutes.

[0116] Step 2: Place the substrate processed in step 1 into a vacuum coating machine, place Ta2O5 and SiO2 as evaporation source materials into the crucible, and start the vacuum system of the coating machine.

[0117] Step 3: When the vacuum degree of the vacuum system of the coating machine in step 2 reaches below 5E-4Pa, start alternately evaporating 20.5 pairs of Ta2O5 layers and SiO2 layers (one Ta2O5 layer and one SiO2 layer as a pair), and the rotation speed of the sample stage on which the substrate is placed is 14 rpm; a bottom Bragg reflector is obtained, in which the first and last layers are both Ta2O5 layers, that is, there are 21 Ta2O5 layers, and the thickness of each Ta2O5 layer is 53.8nm, and there are 20 SiO2 layers, and the thickness of each SiO2 layer is 75.1nm.

[0118] Step 4: Take out the substrate after coating the bottom Bragg reflector in step 3, put it into a three-source co-evaporation coating machine, put CsI, RbI and CuI as evaporation source materials into the quartz crucible, and start the vacuum system of the coating machine.

[0119] Step 5: When the vacuum degree of the vacuum system of the three-source co-evaporation coating machine in step 4 reaches below 5E-4Pa, adjust the evaporation power supply current to make the evaporation rate of CsI The evaporation rate of RbI is The evaporation rate of CuI is The sample stage on which the substrate sheet is placed rotates at a speed of 12 revolutions per minute.

[0120] Step 6: After the evaporation rate in step 5 stabilizes, open the substrate stage baffle and start evaporating Cs 2.4 Rb 0.6 The Cu2I5 perovskite film has a thickness of 180 nm, and a first active region (first gain region) is obtained. The refractive index of the first active region is 1.87.

[0121] Step 7: After the evaporation of the perovskite film in the first gain zone in step 6 is completed, the coating machine is vented and depressurized, the evaporation source materials are replaced with TeO2 and LiF, and the vacuum system of the coating machine is reopened.

[0122] Step 8: When the vacuum degree of the vacuum system of the coating machine in step 7 reaches below 5E-4Pa, start alternately evaporating 1.5 pairs of TeO2 layers and LiF layers to obtain an intermediate Bragg reflector, in which the first and last layers are both TeO2 layers, that is, there are 2 TeO2 layers, and the thickness of each TeO2 layer is 53.7nm, and there is 1 LiF layer, and the thickness of each LiF layer is 85.2nm.

[0123] Step 9: After the intermediate Bragg reflector evaporation in step 8 is completed, the coating machine is vented and depressurized, and CsI and CuI are added again. The vacuum system of the dual-source co-evaporation coating machine is turned on to make the evaporation rate of CsI The evaporation rate of CuI is According to steps 5 and 6, the Cs3Cu2I5 perovskite film is evaporated again to obtain a second active region (second gain region). However, the difference is that the thickness of the second active region is 160 nm and the refractive index of the second active region is 1.85.

[0124] Step 10: After the second gain region is evaporated in step 9, 5.5 pairs of TeO2 layers and LiF layers are alternately evaporated again according to steps 7 and 8 to serve as a top Bragg reflector. In the top Bragg reflector, there are 6 TeO2 layers and 5 LiF layers; the thickness of each TeO2 layer is 53.7 nm, and the thickness of each LiF layer is 4 layers, and the thickness of each LiF layer is 85.2 nm.

[0125] Step 11: After the top Bragg reflector is fabricated in Step 10, the coating machine is vented and the device is removed. This results in a low-threshold dual-blue-emission vertical cavity surface laser. Under fs pulsed laser pumping, the pump threshold energy is 6.98 μJ.

[0126] Test Case

[0127] Environmental stability and thermal stability test of laser

[0128] Environmental and thermal stability testing methods: In air, during the VCSEL fabrication process as described in Example 1, an additional Si wafer was placed on the sample stage in step 4 as a companion wafer. The companion Si wafer, coated with the active layer, was placed in air for one week, then placed on a heating table and heated for at least 5 minutes. The XRD diffraction patterns before and after heating were compared, as well as the degree of match with the standard diffraction pattern.

[0129] See also Figure 4 As shown in the figure, the lead-free perovskite material of the present invention can still maintain good stability at room temperature and when the temperature reaches 200 degrees. It decomposes into CsI only when the temperature reaches 300 degrees. Its stability is significantly higher than that of the existing Sn 2+ and Ge 2+ The corresponding perovskite material (decomposition temperature in air is lower than 130 degrees). This result proves that the lead-free perovskite material of the present invention has good environmental stability and thermal stability, and thus the vertical cavity surface laser of the present invention using the lead-free perovskite material also has good environmental stability and thermal stability.

[0130] In contrast, CsGeI3 perovskite films exhibit slow decomposition (i.e., about 45% decomposition within 48 hours) after exposure to air (see Chen, L.-J., 2018. Synthesis and optical properties of lead-free cesium germanium halide perovskite quantum rods. RSC Advances 8, 18396–18399.. doi:10.1039 / c8ra01150h).

[0131] Moreover, Sn 2+ It is easily oxidized by trace amounts of oxygen, producing high-density Sn 4+ defects and lead to material degradation. (See Chen, J., Luo, Z., Fu, Y., Wang, X., Czech, K. J., Shen, S., Guo, L., Wright, J. C., Pan, A., Jin, S., 2019. Tin(IV)-Tolerant Vapor-Phase Growth and Photophysical Properties of Aligned Cesium Tin Halide Perovskite(CsSnX3; X=Br, I) Nanowires. ACS Energy Letters 4, 1045–1052.. doi:10.1021 / acsenergylett.9b00543)

[0132] The above describes the embodiments of the present invention. However, the present invention is not limited to the above embodiments. Any modifications, equivalent replacements, improvements, etc. made within the spirit and principles of the present invention shall be included in the scope of protection of the present invention.

Claims

1. A lead-free perovskite vertical cavity surface emitting dual-wavelength laser, characterized in that: The laser includes a bottom Bragg reflector, a first active region, an intermediate Bragg reflector, a second active region, and a top Bragg reflector that are sequentially grown on a substrate. The first active region and / or the second active region includes ternary copper halide perovskite and / or multi-component copper halide perovskite; The ternary copper halide perovskite is Cs3Cu2I5 or Cs3Cu2Br5, and the multi-component copper halide perovskite is Cs3Cu2I2Br3, Cs1Rb2Cu2I2Br3, Cs 2.4 Rb 0.6 Cu2I5 or Cs3Cu2I 4.9 F 0.1 ; The reflectivity of the bottom Bragg reflector is greater than 0.9999, the reflectivity of the top Bragg reflector is greater than 0.9, and the reflectivity of the intermediate Bragg reflector is less than 0.9; The thermal decomposition temperature of the ternary copper halide perovskite and the multi-component copper halide perovskite is greater than 200 °C and less than 300 °C; The thickness d1 of the first active region is 100 nm to 200 nm; the thickness d2 of the second active region is 100 nm to 200 nm; The refractive index n1 of the material of the first active region ranges from 1.3 < n2 < 3.5, and the refractive index n2 of the material of the second active region ranges from 1.3 < n2 < 3.5; The optical thickness value of the first active region is L1 = n1 * d1, the optical thickness value of the second active region is L2 = n2 * d2, and the relationship between L1, L2 and the emission wavelengths λ1 and λ2 of the dual-wavelength laser is: N1 = 4 * L1 / λ1, N2 = 4 * L2 / λ2, and 1 < N1 < 3, 1 < N2 < 3.

2. The lead-free perovskite vertical cavity surface emitting dual-wavelength laser according to claim 1, characterized in that: The first active region and the second active region are film structures; The bottom Bragg reflector, the intermediate Bragg reflector, and the top Bragg reflector include alternately stacked first structural layers and second structural layers; The total number of the first structural layer and the second structural layer in the bottom Bragg reflector and the top Bragg reflector is odd.

3. The lead-free perovskite vertical cavity surface emitting dual-wavelength laser according to claim 2, characterized in that: The optical thickness of the first structure layer in the bottom Bragg reflector, the middle Bragg reflector and the top Bragg reflector is L a , the optical thickness of the second structural layer is L b , and the relationship between the emission wavelengths λ1 and λ2 of the dual-wavelength laser is: N a =4*L a / λ1,N b =4*L b / λ2, and 0.9+ is the closest even number <N a <1.1+closest even number, 0.9+closest even number <N b <1.1+nearest even number; The materials of the first structural layer and the second structural layer include oxides, halides, or sulfides.

4. A method for preparing a lead-free perovskite vertical cavity surface emitting dual-wavelength laser according to any one of claims 1 to 3, the preparation method comprising the following steps: Step 1: Deposit and form a bottom Bragg reflector on the surface of the substrate; Step 2: Deposit ternary copper halide perovskite and / or multi-component copper halide perovskite on the surface of the bottom Bragg reflector to form a first active region; Step 3: Deposit and form an intermediate Bragg reflector on the surface of the first active region; Step 4: Deposit ternary copper halide perovskite and / or multi-component copper halide perovskite on the surface of the intermediate Bragg reflector to form a second active region; Step 5: Deposit and form a top Bragg reflector on the surface of the second active region.

5. The preparation method according to claim 4, characterized in that Step 2 includes: putting the evaporation source materials corresponding to the ternary copper halide perovskite and / or the multi-component copper halide perovskite into a coating machine for evaporation coating; In step 2, the evaporation source materials include CuX and at least one selected from CsX and RbX, and X is selected from any one or more of F, Br, and I; In step 2, when depositing the ternary copper halide perovskite, a dual-source co-evaporation method is used, and when depositing the multi-component copper halide perovskite, a multi-source co-evaporation method is used, and the evaporation rate of the evaporation source materials is 0.5 - 2 Å / s.

6. The preparation method according to claim 4 or 5, characterized in that In step 1, depositing and forming the bottom Bragg reflector on the surface of the substrate includes: alternately evaporating the first structural layer material and the second structural layer material on the surface of the substrate; In step 3, forming the intermediate Bragg reflector by deposition on the surface of the first active area includes: alternately evaporating a first structural layer material and a second structural layer material on the surface of the first active area; In step 5, depositing the top Bragg reflector on the surface of the second active area includes: alternately evaporating the first structure layer material and the second structure layer material on the surface of the second active area.

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