Effect of Sputtering Pressure on the Properties of Li-W Co-doped ZnO Film

Li-W co-doped ZnO thin films (LWZO) were prepared on quartz substrates by RF magnetron sputtering in different sputtering pressure environments. Perform X-ray diffraction (XRD), scanning electron microscopy (SEM), transmittance and resistivity tests on the samples. The results show that the proper sputtering pressure environment can help improve the crystalline quality of the LWZO film; SEM results show that with the increase of the sputtering pressure, the surface grain size of the LWZO film is smaller and the surface is flatter; the light transmittance of the film is maintained at Around 85%. The photoluminescence spectrum shows that the photoluminescence of LWZO is composed of intrinsic luminescence and defect luminescence, with high crystallinity, good preferred orientation, and strong intrinsic luminescence intensity. At the same time, the lowest resistivity of the film has also reached 6.9 × 10-3 Ωcm.

Zinc oxide (ZnO) is a kind of direct wide bandgap oxide semiconductor. The crystal structure belongs to the hexagonal wurtzite structure. Its band gap can reach 3.37 eV at room temperature and the exciton binding energy can reach 60 meV. It can be used to prepare blue light and ultraviolet photoelectrons. Ideal material for devices. At the same time, ZnO can also be widely used in related fields such as transparent conductive films, flat panel displays, solar cell front electrodes, chemical sensing agents, surface acoustic wave devices and organic light-emitting diodes. Under normal circumstances, undoped ZnO films exhibit n-type conductivity, which is mainly caused by intrinsic defects such as oxygen vacancies (VO) and zinc interstitial atoms (Zni) inside the ZnO film; through Ga, Al, W, Donor doping such as In can also realize the control of the carrier concentration in the ZnO film. As a high-priced element, tungsten (W) can form more oxygen vacancies (Vo) inside the ZnO film and increase the carrier concentration; at the same time, lithium (Li) can be doped into the ZnO film as an acceptor, which can effectively increase the ZnO film Stability of electrical performance. In this paper, Li-W co-doped films (LWZO) were prepared at different sputtering gas pressures, and the influence of sputtering gas pressure on the crystalline properties, surface morphology, optical properties and electrical properties of LWZO films was analyzed.

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In this experiment, the quartz glass was used as the substrate and the radio frequency magnetron sputtering method was used. The substrate temperature was 100 ℃ and the LWZO was deposited under different sputtering pressure conditions. Materials used: target material (Li-W co-doped ZnO ceramic target: 99.99%, molar ratio: ZnO: Li2O: WO3 = 97.5:1. 5:1), sputtering gas Ar: 99.99% . Target base distance: 70 mm; background pressure: 5 × 10-4 Pa; working pressure is 1 Pa, total gas flow is 30.0 mL/min (standard state) (Ar), sputtering power is 250 W, sputtering deposition Time: 60 min; pre-sputter 15 min before depositing the LWZO film to ensure that the target surface is clean. We obtained 1# sample LWZO film (0.6 Pa), 2# sample LWZO film (0.8 Pa), 3# sample LWZO film (1.0 Pa), 4# sample LWZO film (1.2 Pa) and 5# sample LWZO film (1.4 Pa). ).

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The crystal structure of the LWZO film was analyzed using the D8Advance X-ray diffractometer (XRD) from Bruker, Germany. Test conditions: Cu target Kα radiation, tube voltage 40 kV, current 40mA, λ = 0.15418 nm, scanning step frequency 0.02°, scanning range 10°～60°. The FEI QuanTA-200F environmental electron microscope (ESEM) was used to observe the surface morphology and structure of the LWZO film. A Backman-Du 8B UV-Visible Spectrophotometer was used to measure the optical transmittance of the LWZO film. The resistivity of all LWZO films is measured with a four-probe resistivity tester. The photoluminescence (PL) spectrum of the sample was measured with a Hitachi F-7000 fluorescence spectrophotometer, the excitation source was a 150 W Xe lamp, and the excitation wavelength was 325 nm. All tests are done at room temperature.

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LWZO thin films were prepared on quartz substrates by RF magnetron sputtering, and the crystallinity, surface morphology, optical transmittance and resistivity of the thin films were studied. According to XRD, as the sputtering pressure increases, the crystallinity of the obtained LWZO film first increases and then decreases, and the 2θ values of the (002) and (100) peaks shift to a small angle. SEM results show that with the increase of sputtering pressure, the surface grain size of the LWZO film is smaller and the surface is smoother. In the wavelength range of 400 to 1200 nm, the average transmittance of LWZO is over 85%. PL analysis at room temperature found that the luminescence of the LWZO film sample is composed of intrinsic luminescence and defect luminescence. When the sputtering pressure is around 1.0 Pa, the intrinsic luminescence intensity of the LWZO film is significantly enhanced, indicating that a proper sputtering pressure is beneficial to improve the crystalline quality of the film and the preferential growth of the film. As the crystallinity of the LWZO film increases, the resistivity of the film also decreases significantly.

Founded in 2015,Zunhua Baorui Titanium Equipment Co.,Ltd. is a manufacturer specializing in pvd vacuum ion coating equipment. The company’s products mainly include large plate coating machine, large tube collating machine, tool coating machine and LOW-E glass production line. Mr.Wang baijiang ,general manager of the company ,has been engaged in vacuum coating industry for more than 30 years. He continuously improve production technology, improve product performance and devote himself to provide customers with better product experience and higher production efficiency.