Wide band gap high laser damage threshold second-order nonlinear optical film and preparation method thereof

Abstract

The application discloses a wide-bandgap high-laser-damage-threshold second-order nonlinear optical film and a preparation method thereof. The film is a-axis oriented Li-doped Zn 1‑x Mg x O[0.3 < x < 0.56 and 0 < Li / (Zn+Mg+Li) < 0.09] film, which has a high χ (2) (2) and a high laser damage threshold while having a 4.5 eV band gap. The preparation method comprises the following steps: epitaxially growing an a-axis oriented Li-doped Zn 1‑x Mg x O film on an R-face Al2O3 substrate by radio frequency magnetron co-sputtering of a Mg-doped ZnO ceramic target and a Li-doped ZnO ceramic target; and the crystal direction of the film is parallel to the crystal direction of the Al2O3. The Li-doped Zn 1‑x Mg x O film prepared by the application can be applied to frequency doublers, electro-optical modulators and optical switches and other photonic devices, and has a wide application prospect in the fields of integrated photonics and nonlinear optics.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of nonlinear optical materials, and in particular to a-axis oriented Li-doped Zn 1-x Mg x O[0.3 < x ≤ 0.56 and 0 < Li / (Zn+Mg+Li) ≤ 0.09] thin film. BACKGROUND

[0002] Optical materials with high second-order nonlinear susceptibility (χ (2) ) and high laser damage threshold are the basis of nonlinear optical effects such as second-harmonic generation, electro-optic modulation, sum- and difference-frequency generation, and optical parametric oscillation. High χ (2) increases the efficiency of laser frequency conversion in the above optical processes. High laser damage threshold enables the material to withstand greater laser power or energy, thus achieving stronger frequency conversion laser output.

[0003] Second-order nonlinear optical thin film materials have the advantages of easy formation of strong optical beam confinement waveguide structure, heteroepitaxy and large-area deposition on microelectronic material (e.g. Si) platform, and are key materials in the fields of integrated photonics and nonlinear optics. Zn 1-x Mg x O thin film has a large bandgap (≤ 6.2 eV), low optical transmission loss (< 0.5 dB / cm), and low polarization reversal driving voltage (coercive field of about 1.5 MV / cm), etc. It has great application potential in the field of second-order nonlinear optics in the ultraviolet and even solar blind waveband, and has recently received extensive attention.

[0004] Although the bandgap of Zn 1-x Mg x O thin film can be adjusted to be close to 6.2 eV by doping Mg, recent research by the University of Pennsylvania in the United States shows that Mg doping (x > 0.3) significantly reduces the χ 1-x Mg x of c-axis oriented Zn (2) [R.Zu, G. Ryu, K. P. Kelley, S. M. Baksa, L. C. Jacques, B. Wang, K. Ferri, J. He, L. Chen, I. Dabo, S. Trolier-McKinstry, J. Maria, V. Gopalan, Adv. Phys. Res. 2023, 2300003.]. This will limit the laser frequency conversion efficiency of Zn 1-x Mg x O thin film in the second-order nonlinear optical process. SUMMARY

[0005] In view of the above, the main purpose of the present application is to provide an a-axis oriented Li-doped Zn 1-x Mg x O (0.3 < x ≤ 0.56) epitaxial thin film and a preparation method thereof, so as to at least partially solve the technical problem that Mg doping increases the band gap of ZnO thin film while reducing its second-order nonlinear susceptibility χ (2)

[0006] To achieve the above-mentioned purpose, the technical solutions of the present application are as follows:

[0007] As an aspect of the present application, an a-axis oriented Li-doped Zn 1-x Mg x O epitaxial thin film is provided, 0.3 < x ≤ 0.56, comprising: epitaxially growing an a-axis oriented Li-doped Zn 1-x Mg x O [0.3 < x ≤ 0.56 and 0 < Li / (Zn+Mg+Li) ≤ 0.09] thin film by radio frequency magnetron co-sputtering of a Mg-doped ZnO ceramic target and a Li-doped ZnO ceramic target, the crystal orientation of which is parallel to the crystal orientation of Al2O3.

[0008] As another aspect of the present application, an a-axis oriented Li-doped Zn 1-x Mg x O [0.3 < x ≤ 0.56 and 0 < Li / (Zn+Mg+Li) ≤ 0.09] epitaxial thin film obtained by the preparation method as described above is provided.

[0009] The technical solutions adopted by the present application are a second-order nonlinear optical thin film with wide band gap and high laser damage threshold and a preparation method thereof, which comprises the following steps,

[0010] Step A: target material preparation;

[0011] Step B: substrate cleaning;

[0012] Step C: thin film deposition;

[0013] Step D: heat treatment.

[0014] ​The step A comprises: the target material comprises Mg-doped ZnO ceramic target and Li-doped ZnO ceramic target; specifically, the Mg-doped ZnO ceramic target and the Li-doped ZnO ceramic target are prepared by weighing raw materials according to specific component proportions. The preparation method of the Mg-doped ZnO ceramic target comprises: using ZnO with a purity of 99.99% and MgO with a purity of 99.99% as raw materials, and preparing the target material according to a weight percentage of 91.6%:18.4%; the preparation method of the Li-doped ZnO ceramic target comprises: using ZnO with a purity of 99.99% and Li2CO3 with a purity of 99.99% as raw materials, and preparing the target material according to a weight percentage of 95%:5%.

[0015] The step B comprises: the R-plane Al2O3 substrate is vertically placed in a customized cleaning rack, and is ultrasonically cleaned in acetone, alcohol and pure water respectively; then, the substrate is blown dry by using a nitrogen gun; finally, the substrate is placed in an oven.

[0016] The step C comprises: the process parameters of the radio frequency magnetron co-sputtering technology comprise: when the background vacuum is reduced to 7.4*10 -7 Torr, a mixed gas of O2 and Ar is introduced into the growth chamber, the Ar / (Ar+O2) gas ratio is 50%-75%, the flow range is between 5-10sccm, the substrate temperature range is 200-300℃, the gas pressure range is between 2-5mTorr, the radio frequency power range of the Mg-doped ZnO ceramic target is between 100-150W, the radio frequency power range of the Li-doped ZnO ceramic target is between 50-100W; the distance range between the target material and the sample is 100-150mm, and the substrate rotation speed range is 20rpm.

[0017] The step D comprises: the grown thin film sample is placed in a heat treatment furnace, the temperature is increased from room temperature to a maximum temperature at a speed of 15℃ / min, the maximum temperature range is 400-500℃, and the sample is cooled down after heat preservation.

[0018] From the above technical solution, it can be seen that the a-axis oriented Li-doped Zn 1-x Mg x O epitaxial thin film and the preparation method thereof at least have one or part of the following beneficial effects:

[0019] (1) The radio frequency magnetron co-sputtering technology based on the Mg-doped ZnO ceramic target and the Li-doped ZnO ceramic target can form specific point defects (including Mg occupying Zn lattice sites and Li occupying oxygen octahedral interstitial sites) and more accurately control components compared with the ternary (ZnO, MgO and Li2O) co-sputtering technology.

[0020] (2) The a-axis oriented Li-doped Zn 1-x Mg xO [0.3 < x ≤ 0.56 and 0 < Li / (Zn+Mg+Li) ≤ 0.09] epitaxial thin films can increase χ (2) and laser damage threshold.

[0021] (3) a-axis orientation can realize coplanar electrode structure along in-plane c-axis direction, so as to utilize χ (2) tensor maximum component χ 33 for linear electro-optic modulation.

[0022] (4) the material can be applied to frequency doubler, electro-optic modulator and optical switch and other photonic devices, and has broad application prospect in the fields of integrated photonics and nonlinear optics. BRIEF DESCRIPTION OF DRAWINGS

[0023] Figure 1 is a-axis oriented Li-doped Zn 0.67 Mg 0.33 O [Li / (Zn+Mg+Li) = 0.07] thin film prepared in Example 1 of the present application.

[0024] Figure 2 is a Li-doped Zn 0.67 Mg 0.33 O thin film sample cross-section prepared in Example 1 of the present application.

[0025] Figure 3 is a Li-doped Zn 0.67 Mg 0.33 O thin film sample prepared in Example 1 of the present application. X-ray diffraction (XRD) pattern of (a) 2θ / ω scanning pattern, (b) crystal face rocking curve, (c) polar figure.

[0026] Figure 4 is a Tauc curve of several a-axis oriented thin film samples in Example 1 of the present application.

[0027] Figure 5 is a schematic diagram of second harmonic generation test in Example 1 of the present application. (a) experimental optical path schematic diagram, (b) relative relationship between polarization direction of fundamental light and frequency-doubled light and sample crystal direction. In (a), the laser is PL2210A picosecond Nd:YAG laser, M1-4 is 45° full mirror, W1-2 is l / 2 wave plate, P1-2 is Glan prism, F1-2 is optical filter, L1-3 is focusing lens, S is sample, and the spectrometer is grating spectrometer (Princeton Instruments, Acton SP2500). In (b), k ω and k 2ωand k are the wave vectors of the fundamental and second harmonic light, respectively, E ω and E 2ω are the electric fields of the fundamental and second harmonic light, respectively, L s is the thickness of the sample. a, b and c are the and

[0001] directions of the wurtzite crystal structure, respectively.

[0028] Figure 6 is the normalized second harmonic intensity [SQRT(I s ) / L s ] of several samples in Example 1 of the present application as a function of the fundamental light E p . In the figure, Mg-doped LiNbO3 is X-cut single crystal with a doping concentration of 5 mol.% and a thickness of 500 μm.

[0029] Figure 7 is the second harmonic generation intensity of (a) ZnO, (b) Li-doped Zn 0.67 Mg 0.33 O, and (c) Mg-doped LiNbO3 single crystal as a function of the peak power density of the fundamental light in Example 1 of the present application. The insets are the micrographs of the sample surface measured under the conditions of the lower peak power density.

[0030] Figure 8 is the SEM picture of the cross section of the Li-doped Zn 0.67 Mg 0.33 O thin film sample prepared in Example 2 of the present application.

[0031] Figure 9 is the XRD 2θ / ω scan pattern of the Li-doped Zn 0.67 Mg 0.33 O thin film sample prepared in Example 2 of the present application.

[0032] Figure 10 is the second harmonic generation intensity of the Li-doped Zn 0.67 Mg 0.33 O thin film sample prepared in Example 2 of the present application under the condition of E p = 6.2 GW / cm 2 . DETAILED DESCRIPTION

[0033] In order to make the objects, technical solutions and advantages of the present application clearer, the present application will be further described in detail below with reference to the specific embodiments and with reference to the accompanying drawings.

[0034] Specifically, according to some embodiments of the present application, there is provided an a-axis oriented Li-doped Zn 1-x Mg xA method for preparing an O[0.3 < x ≤ 0.56 and 0 < Li / (Zn+Mg+Li) ≤ 0.09] thin film, comprising:

[0035] Step A: target material preparation;

[0036] Step B: substrate cleaning;

[0037] Step C: thin film deposition;

[0038] Step D: heat treatment.

[0039] Step A comprises: preparing Mg-doped ZnO ceramic targets and Li-doped ZnO ceramic targets according to specific component proportions. The method for preparing the Mg-doped ZnO ceramic targets comprises: using ZnO with a purity of 99.99% and MgO with a purity of 99.99% as raw materials, and preparing the target material according to a weight percentage of 91.6%:18.4%; the method for preparing the Li-doped ZnO ceramic targets comprises: using ZnO with a purity of 99.99% and Li2CO3 with a purity of 99.99% as raw materials, and preparing the target material according to a weight percentage of 95%:5%.

[0040] Step B comprises: placing an R-face Al2O3 substrate vertically into a customized cleaning rack, and ultrasonically cleaning the substrate in acetone, alcohol and pure water respectively for 10 minutes; then, using a nitrogen gun to blow dry the substrate; finally, placing the substrate into an oven and keeping it at 120°C for 30 minutes.

[0041] Step C comprises: the process parameters of the radio frequency magnetron co-sputtering technology include: when the background vacuum is reduced to 7.4×10 -7 Torr, introducing a mixed gas of O2 and Ar into the growth chamber, the Ar / (Ar+O2) gas ratio is 50%-75%, the flow rate ranges between 5-10 sccm, the substrate temperature ranges between 200-300°C, the gas pressure ranges between 2-5 mTorr, the radio frequency power of the Mg-doped ZnO ceramic target ranges between 100-150 W, the radio frequency power of the Li-doped ZnO ceramic target ranges between 50-100 W, the distance between the target material and the sample ranges between 100-150 mm, and the substrate rotation speed ranges between 20 rpm.

[0042] Step D comprises: placing the grown thin film sample into a heat treatment furnace, increasing the temperature from room temperature to a maximum temperature at a speed of 15°C / min, the maximum temperature ranges between 400-500°C, the holding time ranges between 1-4 hours, and then cooling down with the furnace.

[0043] According to some embodiments of the present application, an a-axis oriented Li-doped ZnO thin film prepared by the above method is also provided. 1-x Mg xO [0.3 < x ≤ 0.56 and 0 < Li / (Zn+Mg+Li) ≤ 0.09] thin film.

[0044] The following two specific examples are listed to make a detailed description of the technical solutions of the present application. It should be noted that the specific examples below are only for illustration and do not limit the present application.

[0045] Example 1:

[0046] Figure 1 a-axis oriented Li-doped Zn 0.67 Mg 0.33 The flow chart of the preparation method of the O [Li / (Zn+Mg+Li) = 0.07] thin film is shown in Figure 1. The manufacturing method of the present example includes: Figure 1

[0047] Step A, target material manufacturing. The raw materials are weighed according to the component proportions shown in Table 1 and Table 2, and the target materials for growing Zn 0.67 Mg 0.33 O thin film (referred to as ZMO target) and Li-doped (referred to as ZLO target) target materials are respectively manufactured.

[0048] Table 1 Component proportions of the target material for growing Zn 0.67 Mg 0.33 O thin film

[0049]

[0050] Table 2 Component proportions of the target material for Li-doped

[0051]

[0052] Step B, substrate cleaning. The R-face Al2O3 substrate is vertically placed in a customized cleaning rack, and is ultrasonically cleaned in acetone, alcohol and pure water for 10 minutes respectively; then, the substrate is blown dry using a nitrogen gun; finally, it is placed in an oven and kept at 120℃ for 30 minutes.

[0053] Step C, thin film deposition.

[0054] According to the embodiments of the present disclosure, the step B includes the following sub-steps.

[0055] Sub-step B1, the cleaned substrate is placed in a sample holder. Vacuum is extracted until the background vacuum is reduced to 7.4 × 10 -7 Torr. The equipment parameters are set according to the values shown in Table 3.

[0056] Table 3 Magnetic sputtering equipment setting parameters

[0057] ​

[0058] In sub-step B2, after the substrate temperature stabilizes at 300 degrees, pre-sputter the two targets for 10 minutes each.

[0059] Sub-step B3: Open the substrate baffle. Start the timer to begin the actual growth process.

[0060] In sub-step B4, after the expected growth time has been reached, immediately close the substrate baffle. Turn off the substrate heating device. Once the substrate temperature has dropped below 200 degrees Celsius, remove the substrate from the growth chamber.

[0061] Step D, heat treatment. The grown film sample is placed in a heat treatment furnace and increased from room temperature to 400°C at a rate of 15°C / min. It is held at 400°C for 2 hours and then cooled in the furnace.

[0062] Figure 2 The Li-doped Zn prepared in Example 1 of this invention 0.67 Mg 0.33 Scanning electron microscope (SEM) image of the cross-section of the O thin film sample. The average thickness of the film grown for 100 minutes was determined to be 198.1 nm, and the growth rate was 2.0 nm / min. Figure 3 The Li-doped Zn prepared in Example 1 of this invention 0.67 Mg 0.33 X-ray diffraction (XRD) patterns of the O thin film sample. (a) 2θ / ω scan pattern, (b) Crystal plane rocking curve, (c) Crystal polar diagram. For example... Figure 3 As shown in (a), Li-doped Zn 0.67 Mg 0.33 O-film only presents The diffraction peaks of the crystal planes demonstrate excellent orientation. For example... Figure 3 As shown in (b), Li-doped Zn 0.67 Mg 0.33 O thin film The half-width at half-maximum (FWHM) of the rocking curve is 1.53°, indicating that it has good crystal quality. Figure 3 (c) shows Li-doped Zn 0.67 Mg 0.33 O exhibits a strong second-order rotationally symmetric spot at ψ = 30°, indicating that its Crystal orientation parallel to Al2O3 Crystal orientation. This proves that it was epitaxially grown on an R-plane Al2O3 substrate.

[0063] Figure 4The images show the Tauc curves of several a-axis oriented thin film samples from Example 1 of this invention. The ZnO sample is a 200 nm thick ZnO thin film grown on an R-plane Al2O3 substrate using radio frequency magnetron sputtering and a pure ZnO target (99.99% purity). The optical bandgap (E) was calculated using the Tauc method. opt As shown in the figure, the energy value obtained by extending the linear portion of the Tauc curve and intersecting it with the x-axis is the corresponding E. opt Values. Table 4 lists the optical bandgap values ​​for several samples in the examples. Undoped and Li-doped Zn 0.67 Mg 0.33 E of O thin film opt The values ​​were 3.96 eV and 3.95 eV, respectively. This indicates that Li doping [Li / (Zn+Mg+Li)=0.07] has an effect on E opt The impact is minimal. Furthermore, Li-doped Zn 0.67 Mg 0.33 The O thin film exhibits E properties similar to those of Mg-doped (5 mol.%) LiNbO3 single crystal. opt .

[0064] Table 4 Optical bandgap and laser damage threshold E of ZnMgO thin films pmax and χ (2) component χ 33

[0065] ZnO Zn 0.67 Mg 0.33 O]]> Li-doped Zn 0.67 Mg 0.33 O]]> Mg-doped LiNbO3 E opt (eV) 3.33 3.96 3.95 3.92 E pmax (GW / cm 2 )]]> 81.4 81.2 124.9 93.7 χ 33 (pm / V) a ]]> 26.2 12.5 36.1 27.6

[0066] a) In E p =81.2GW / cm 2 Determination under conditions

[0067] The second-order nonlinear polarizability χ of the thin film sample was characterized by second harmonic generation testing. (2) . Figure 5 This is a schematic diagram of the second harmonic generation test in Embodiment 1 of the present invention. A 1064nm wavelength laser (pulse width and repetition frequency of 25ps and 1kHz, respectively) is used as the fundamental frequency light. The fundamental frequency light energy is controlled by a combination of a half-wave plate and a Glan prism. The fundamental frequency beam is focused into a beam with a radius of approximately 45.2μm at the sample surface using a focusing lens L1. Therefore, according to equation (1), the peak power density (E) of the beam irradiating the sample surface can be calculated. p ).

[0068]

[0069] Where E pulse Let τ be the fundamental frequency optical single pulse energy measured by a power meter after F1, r be the radius of the beam, and τ be the laser pulse width.

[0070] As Figure 5 shown in Fig. (b), when the polarization direction, i.e. the electric field direction, of both fundamental light and second harmonic light is parallel to the c-axis, i.e. the

[0001] direction, of the sample, a 500 μm thick Y-cut quartz single crystal is used as a reference sample, and according to equation (2), the χ (2) component of the χ 33 tensor along the c-axis direction of the sample can be obtained.

[0071]

[0072] where L c represents the coherence length [L c = λ / (4(n 2ω -n ω ))], λ is the wavelength of the fundamental light, n(ω) and n(2ω) represent the refractive indices of the fundamental light and the second harmonic light, respectively, I is the energy of the second harmonic light, T represents the transmittance of the sample, the subscripts q and s represent the quartz single crystal and the thin film sample, respectively, χ 11,q is the χ (2) tensor component of the quartz single crystal (0.67 pm / V).

[0073] Figure 6 is the normalized second harmonic light intensity [SQRT(I s ) / L s ] of several samples in Example 1 of the present application as a function of the fundamental light E p . Figure 7 is the second harmonic generation intensity of several samples in Example 1 of the present application as a function of the peak power density of the fundamental light. As Figure 6 shown in Fig. (a), when E p increases from 50 GW / cm 2 to 81.2 GW / cm 2 , the normalized second harmonic light intensity of the ZnO sample remains essentially unchanged. As Figure 7 shown in Fig. (b), when E p increases from 81.2 GW / cm 2 to 87.4 GW / cm 2 , the second harmonic light intensity of the ZnO sample decreases by 22%, and a significant morphology change is found at the sample surface where the fundamental light is irradiated. This indicates that the sample is severely damaged by the laser. In the present application, the peak power density of the fundamental light at which the second harmonic light intensity decreases by 20% and the surface morphology changes significantly is defined as the laser damage threshold E pmax under picosecond pulsed laser irradiation. The E pmax values of several samples in Example 1 of the present application are listed in Table 1. Compared with ZnO, the pure Mg doping (x = 0.33) decreases the normalized second harmonic light intensity by 42.4%. However, after further Li doping, i.e. Li-doped Zn 0.67Mg 0.33 Sample O not only exhibits the strongest normalized frequency-doubled light intensity, but also has the largest Eo. pmax (124.9GW / cm 2 ). with ZnO and Zn 0.67 Mg 0.33 Compared to O, Li-doped Zn 0.67 Mg 0.33 E of O sample pmax An increase of 53.8%. Additionally, Li-doped Zn... 0.67 Mg 0.33 E of O sample pmax E exceeding that of Mg-doped LiNbO3 single crystals pmax (93.7GW / cm 2 Table 4 lists several samples in E. p =81.2GW / cm 2 χ² measured under the conditions 33 Value. Li-doped Zn 0.67 Mg 0.33 χ of O thin film sample 33 It reached 36.1 pm / V. This value is for Zn. 0.67 Mg 0.33 The χ² value of the O sample was 2.9 times that of the Mg-doped LiNbO3 single crystal, and exceeded that of the Mg-doped LiNbO3 single crystal. 33 .

[0074] I used first-principles calculations based on density functional theory and X-ray photoelectron spectroscopy (XPS) to analyze the reasons for the above phenomena. First, from the perspective of defect formation energy, the calculation results show that Mg atoms tend to occupy Zn lattice sites, while Li atoms tend to occupy oxygen octahedral interstitial sites. Furthermore, calculations were performed corresponding to ZnO and Zn... 0.67 Mg 0.33 O and Li-doped Zn 0.67 Mg 0.33 The structural model of O[Li / (Zn+Mg+Li)=0.07] was used to calculate the respective electronic density of states and the d-band center (ε) of Zn. d ) and the p-band center of O (ε p Mg doping (x = 0.33) causes ε d and ε p The shifts of 0.22 and 0.35 eV towards higher energy directions indicate that Mg doping (x = 0.33) reduces the stability of the ZnO crystal structure; further Li doping causes ε d and ε p The shifts to lower energy directions by 3.48 and 3.37 eV, respectively, indicate that Li doping [Li / (Zn+Mg+Li)=0.07] significantly improves Zn... 0.67 Mg0.33 O crystal structure stability. In addition, the XPS test results show that, compared with the Zn 0.67 Mg 0.33 O, Li doping [Li / (Zn+Mg+Li)=0.07] makes the peak position of O1s move 1.02 eV to the high energy direction. This reveals that Li doping significantly enhances the interaction between metal and oxygen. Therefore, the author speculates that the increase in crystal structure stability and the enhancement of metal-oxygen interaction caused by Li doping are the reasons for the increase in the laser damage threshold of Zn 0.67 Mg 0.33 O.

[0075] In addition, the calculation of the electronic state density shows that Li doping significantly affects the orbital hybridization between metal and oxygen, thereby affecting the electron distribution outside the nucleus. This is very likely to increase the contribution of electron polarization to χ (2) under the action of an optical frequency electric field, thereby increasing χ (2) .

[0076] Example 2:

[0077] According to the flowchart shown in Figure 1 , the manufacturing method of this embodiment includes:

[0078] Step A, target material manufacturing. Weigh the raw materials according to the component proportions shown in Tables 1 and 2 to manufacture the target material for growing Zn 0.67 Mg 0.33 O film (referred to as ZMO target) and Li doping (referred to as ZLO target) target material.

[0079] Step B, substrate cleaning. Place the R-face Al2O3 substrate vertically into a custom-made cleaning rack, and ultrasonically clean it in acetone, alcohol, and pure water for 10 minutes each time; then, use a nitrogen gun to blow dry the substrate; finally, place it in an oven and keep it at 120°C for 30 minutes.

[0080] Step C, thin film deposition.

[0081] According to the embodiment of the present disclosure, the step B includes the following sub-steps.

[0082] Sub-step B1, place the cleaned substrate into a sample holder. Vacuumize it to reduce the background vacuum to below 7.4×10 -7 Torr. Set the equipment parameters according to the values shown in Table 5.

[0083] Table 5. Setting parameters of the magnetron sputtering equipment

[0084]

[0085] Sub-step B2, after the substrate temperature stabilizes at 300 degrees, pre-sputter the two target materials for 10 minutes respectively.

[0086] Sub-step B3, open the substrate shutter. Start timing and begin the formal growth.

[0087] Sub-step B4, close the substrate shutter as soon as the expected growth time is reached. Turn off the substrate heater. When the substrate temperature drops to below 200°C, remove the substrate from the growth chamber.

[0088] Step D, thermal treatment. Place the grown film sample in a thermal treatment furnace, increase the temperature from room temperature to 400°C at a rate of 15°C / min, hold at 400°C for 2 hours, and then cool down with the furnace.

[0089] Figure 8 Li-doped Zn 0.67 Mg 0.33 O film sample. The average thickness of the film grown for 100 minutes was measured to be 187.5 nm, and the growth rate was 1.87 nm / min. The method of increasing the Li doping amount by increasing the ZLO target power [Li / (Zn+Mg+Li) > 0.09] resulted in a decrease in the growth rate of the film.

[0090] Figure 9 Li-doped Zn 0.67 Mg 0.33 O film sample. As shown in Figure 9 , the Li-doped Zn 0.67 Mg 0.33 O film prepared in Example 2 did not exhibit any diffraction peaks, indicating poor orientation. This indicates that the method of increasing the Li doping amount by increasing the ZLO target power [Li / (Zn+Mg+Li) > 0.09] resulted in a decrease in the crystalline quality of the film.

[0091] Figure 10 Li-doped Zn 0.67 Mg 0.33 O film sample produced a second harmonic generation intensity under E p = 6.2 GW / cm 2 conditions. This intensity was only 7.5% of the intensity of the Li-doped Zn 0.67 Mg 0.33 O film sample prepared in Example 1. This indicates that the method of increasing the Li doping amount by increasing the ZLO target power [Li / (Zn+Mg+Li) > 0.09] resulted in a significant decrease in the second harmonic generation intensity of the film.

[0092] The a-axis oriented Li-doped Zn 1-x Mg xO[0.3 < x ≤ 0.56 and 0 < Li / (Zn+Mg+Li) ≤ 0.09] thin film can be applied to frequency doubler, electro-optical modulator and optical switch and other photonic devices, and has great application prospect in the fields of integrated photonics and nonlinear optics.

[0093] The above-described specific embodiments further illustrate the purpose, technical solutions and beneficial effects of the present application. It should be understood that the above-described specific embodiments are merely examples of the present application and are not intended to limit the present application. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present application shall be included in the protection scope of the present application.

Claims

1. A wide bandgap, high laser damage threshold, second-order nonlinear optical thin film, characterized in that, This thin film is an a-axis oriented Li-doped Zn. 1-x Mg x O thin film; the preparation method of this thin film includes: Step A: Fabricate a dual ceramic target with adjustable thin film bandgap and Li doping concentration; Step B: Clean the R-side Al2O3 substrate; Step C: Growth of a-axis oriented Li-doped Zn by RF magnetron co-sputtering 1-x Mg x O thin film; Step D: Heat treatment of α-axis oriented Li-doped Zn 1-x Mg x O thin film; The a-axis oriented Li-doped Zn 1-x Mg x The composition of the O thin film is: 0.3 <x≤0.56,0<Li / (Zn+Mg+Li)≤0.09; Step A includes: weighing raw materials according to the component ratio to prepare Mg-doped ZnO ceramic targets and Li-doped ZnO ceramic targets. Step C includes: the process parameters of the RF magnetron co-sputtering technology include: when the background vacuum is reduced to 7.4 × 10⁻⁶. -7 When the Torr is below a certain value, a mixture of O2 and Ar gas is introduced into the growth chamber. The Ar / (Ar+O2) gas ratio is 50%-75%, the flow rate is between 5-10 sccm, the substrate temperature is between 200-300℃, the gas pressure is between 2-5 mTorr, the RF power of the Mg-doped ZnO ceramic target is between 100-150W, the RF power of the Li-doped ZnO ceramic target is between 50-100W, the distance between the target and the sample is between 100-150mm, and the substrate rotation speed is between 20rpm.

2. The wide bandgap, high laser damage threshold second-order nonlinear optical thin film according to claim 1, characterized in that, Step B includes: placing the R-side Al2O3 substrate vertically into a custom cleaning rack, and ultrasonically cleaning it for 10 minutes each in acetone, alcohol, and pure water; then, drying the substrate with a nitrogen gun; and finally, placing it in an oven and maintaining it at 120°C for 30 minutes.

3. The wide bandgap, high laser damage threshold second-order nonlinear optical thin film according to claim 1, characterized in that, Step D includes: placing the grown thin film sample into a heat treatment furnace, increasing the temperature from room temperature to the maximum temperature at a rate of 15°C / min, with the maximum temperature ranging from 400 to 500°C, holding the temperature for 1 to 4 hours, and then cooling it with the furnace.

4. The wide bandgap, high laser damage threshold second-order nonlinear optical thin film according to claim 1, characterized in that, The method for fabricating the Mg-doped ZnO ceramic target includes: using ZnO with a purity of 99.99% and MgO with a purity of 99.99% as raw materials, and fabricating the target material in a weight percentage of 91.6%:18.4%.

5. The wide bandgap, high laser damage threshold second-order nonlinear optical thin film according to claim 1, characterized in that, The method for fabricating the Li-doped ZnO ceramic target includes: using ZnO with a purity of 99.99% and Li2CO3 with a purity of 99.99% as raw materials, and fabricating the target material in a weight percentage of 95%:5%.

Images