MgO/Mg/MgO Multilayer Structure Of Deep Ultraviolet Transparent Conductive Thin Film

Traditional transparent conductive films have high transmittance in the visible region and excellent conductivity,which have been applied to flat liquid crystal display, touch screen, solar cells and other fields. However, traditional transparent conductive films are difficult to be penetrated by the deep ultraviolet which wavelength is less than 300nm because of the band gap limit (less than 4eV). At present, the transparent conductive of Si and Sn doped β-Ga2O3 thin films have the ability of deep ultraviolet transparent conductivity.However when the bandgap is larger, the dope of conductive materials become more difficult, which leads to preparing single Ga2O3 based films with excellent electrical properties of deep ultraviolet transparent conductive film not easy. Therefore, developing a new deep ultraviolet transparent conductive film with high performance is a hot issue in the field of optoelectronic devices.In this paper, MgO/Mg/MgO multilayer structure of deep ultraviolet transparent conductive film was fabricated on the sapphire substrate using high pure Mg target, high purity of argon and oxygen sputtering gas via RF magnetron sputtering. The optical and electrical properties of single Mg layer and MgO/Mg/MgO multilayer structure were characterized and analyzed by X-ray diffraction, optical transmittance spectra and Hall effect measurement, were characterized by metallographic microscope, X-ray diffraction, optical transmittance spectra and Hall effect measurement. Main works as follows:(1) Mg thin films of 3nm,5nm,7nm and 9nm were prepared on sapphire substrate by RF magnetron sputtering technique. The electrical resistance of Mg films decreased to the thickness increasing. When the thickness became from 3nm to 5nm, Mg film’s sheet resistance reduced significantly from 104.9ohm/sq to 30.11ohm/sq. The resistance of Mg films no longer decreased obviously when the thickness continued to increase. At the same time, with the increase of thickness, the transmittance of Mg films at the same wavelength decreased gradually. When the thickness of Mg was 5nm, the conductivity and the transmittance reached an optimum state with the sheet resistance 30.11ohm/sq and transmission 82.6% at wavelength of 300nm.(2) MgO/Mg/MgO multilayer structure of deep ultraviolet transparent conductive film was fabricated on the sapphire substrate by RF magnetron sputtering. The metal layer thickness of Mg was 5nm and the thickness of MgO layer was 40nm. The trend of the transmission curve of MgO/Mg/MgO multilayer structure was basically the same with single-layer Mg film, that was increasing gradually along the short length direction. The prepared MgO/Mg/MgO transparent conductive film had good optical performance. It’s sheet resistance was 57.35ohm/sq and the transmittance was more than 85% at the deep ultraviolet spectral wavelength range of 200-300nm.(3) The MgO/Mg/MgO multilayer structure deep ultraviolet transparent conductive thin films of mentioned conditions were annealed in N2 atmosphere at 200 ℃,300 ℃,400 ℃, 500 ℃ annealing temperature respectively. The sheet resistance of samples which annealed under 500 ℃ decreased comparing to ground ones. The sheet resistance of annealed samples became larger while annealing temperature becoming higher. The sample after 500 ℃ annealing temperature showed a high resistance. When annealing temperature became higher, the transmittance of MgO/Mg/MgO multilayer structure at 200-300nm deep ultraviolet range decreased gradually, which were all less than ground ones. Thin films achieved a photoelectric properties after 200 ℃ annealing with transmittance 80% at 300nm and resistivity 31.78ohm/sq.