Preparation And Characterization Of Transparent Conducting Yttrium-doped Zinc Oxide Films

As the optoelectronics industry develops fast, various optoelectronic materials have been found. Because of its good conductivity and high transparency in the visible light range, the transparent conducting films have been widely used. At present, Indium-Tin Oxide (ITO) film manufactured by mature technologies is the most widely used. However, ITO is expensive, and the Indium can diffuses easily under high temperature, so ITO performance deteriorates. Compared with ITO, zinc oxide has been gained much attention due to its unique advantages, such as low costs, rich resources, non-poisonous, high thermal and chemical stabilities in the field of transparent conducting films.In this dissertation, YZO film has been prepared on the glass substrate by RF magnetron sputtering for the first time. The influence of deposition parameters (sputtering pressure, RF power) and film thickness on the structure, optical, and electrical properties of the YZO film was studied systematically. The structure, surface morphology, and electrical and the optical properties of YZO film have been measured with XRD, SEM, Hall Effect, and UV-Vis Spectrophotometer.1. The influence of film thickness on the properties of the filmFive samples have been prepared with a pressure of 2.0 Pa, power of 100W and unheated substrate. Theirs thickness is 200 nm,400 nm,600 nm, and 800 nm. The growth rate of these five samples is about 52 nm/min, and it will not change as time goes on. As the thickness of the film increases, the crystallization becomes better and the intensity of the (002) peak rises, so the size of the grain has increased from 30.4 nm to 34.6 nm. The grain size is bigger than other grain size of transparent conducting films, but its increasing is unobvious. For the YZO films, with the crystallization of films changing better, Hall mobility increases, the resistivity continue to decline, and the minimum resistivity of 8.36×10-4Ω·cm is available, with a Hall mobility of 15.3 cm2V-1s-1and a carrier concentration of 4.88×1020 cm-3. As the thickness of the film increases, the average transparency of the film decreases, but the average transparency of all the samples is above 90% in the wavelength range of 500 nm to 800 nm.2. The influence of the sputtering pressure on the properties of the YZO filmUnder the condition, the thickness of all films is 600 nm, the sputtering power is 100W, and the substrate is unheated. When the sputtering pressure is 0.8 Pa,1.0 Pa, 1.6 Pa,2.0 Pa and 3.0 Pa, respectively, and YZO films have been prepared. As the sputtering pressure increases from 0.8Pa to 3.0 Pa, the growth rate of the film decreases from 56 nm/min to 43 nm/min yet the size of the grains decreases from 47.4 nm to 31.5 nm, which shows that the crystal quality of the films has deteriorated. When the pressure is 1.0 Pa, the growth rate of the films is faster, more oxygen vacancies exist in the films, and the carrier concentration is 5.2×1020 cm-3., Hall mobility decreases due to ionized impurity scattering, it is 10.8 cm2V-1s-1. When the sputtering pressure is 2.0 Pa, the films with resistivity of 8.9×10-4Ω·cm, a carrier concentration of 4.92×1020 cm-3 and a Hall mobility of 14.2 cm2V"1s"1, has been obtained. With the sputtering pressure increasing, the transmittance of the films decreases. But the average transmittance of all films exceeds 89% in the visible range.3. The influence of the sputtering power on the properties of the YZO filmThe average thickness of the films is about 600 nm, the sputtering pressure is 2.0 Pa, the substrate is unheated, and the sputtering power is 40 W,50 W,60 W,90 W and 110W, respectively. As the sputtering power increasing from 40 W to 110 W, the growth rate increases from 15 nm/min to 56 nm/min obviously, but the grain size changes little between 33 nm and 38 nm. When the sputtering power is 90W, the maximum carrier concentration is 4.99×1020 cm-3, with a Hall mobility of 14 cm2V-1s-1. The optimum power is 50 W, and the resistivity of 8.71×10"4Ω·cm is available with a carrier concentration of 4.25×1020 cm-3 and a Hall mobility of 16.8 cm2V-1s-1. With sputtering power increasing, the crystal quality degenerates. That causes increasing of light scattered by the surface and the photon absorbtion so that the average transparency decreases. The point of view from band gap, as the sputtering power increases, band gap tends to rise. The band gap increases from 3.54 eV to 3.64 eV when the sputtering power increases from 40 W to 110 W.