Characteristics On Preparation And Properties Of Germanium/conductive Oxide Optical Films

Recently a new type of subwavlength optical coatings was demonstrated by researchers of Havard University, which breaked the traditional views of highly absorbing dielectiric will destroy interference effects and the thickness of optical coatings must be multiple quarter-wave thickness. When the thickness of highly absorbing dielectric layer was from 5 to 25 nm, interference effects still existed. These coatings selectively absorb various frequency range of incident light and therefore show different colors with different Ge thickness, with low sensitivity to the surface roughness and angle of incidence. This new kind of optical structure consists of highly absorbing dielectric and conducting films opens up a new research route for optical coatings. On the other hand, traditional fabrication of optical coatings needs highly vacuum condition, precision mechical instrument, or expensive large mocular metal organic source, the cost is high. Metal Organic Deposition(MOD for short) method needs no vacuum environment and its instrument is cheap and simple, with advantages of high deposition efficiency, source unilization rate, easy control of element, and most importantly large scale uniformly depostion which fits massive industial manufacture. As a result, the fabircation of optical coatings with MOD method is highly commercial perspective.Dielectric/metal layered structure is one of the most widely used optical structures. Some advanced functions like perfect mirror(highly reflective films) and Fabry-perot interferometer(filter) can be achieved by wisely ultilizing this structure. Tradiontal researches on optical structures were to change optical property of dielectric layer, however we found the property of conducting layer also have large influence on the optical property of dielectric/metal layers structure. Thus, this dissertation changed different kind of conducting materials based on highly absorbing Ge/conducting film system, and study the influence of conducting layer on properties of the optical system. In particular, YBa2Cu3O7-δ(YBa2Cu3O7-δ,YBCO for short) superconducting films with zero resistence(for perfect electric conductor), and GaZnO(GaZnO compound, GZO for short) transparent conducting oxide films were chosen to replace highly reflective Au layer. Focusing on optical property changing and potential applications of Ge/YBCO and Ge/GZO film system, following works were carried out in this dissertation:(1) YBCO superconducting films were prepared on LaAlO3(LAO) substrates by MOD method. The effects of experiment parameters on the film structure and properties of YBCO films were systematically studied. High performance of YBCO films were stably fabricated by optimizing heating rate and eliminating a-axis oriented grains. The critical current density Jc≥1.8 MA/cm2 was achieved. La2Zr2O7(LZO for short) buffer layers were prepared by MOD method on Ni-W substrate for cost reduction and future flexible optical applications. In order to improve performance of YBCO films, flux pinning were achieved by surface decoration using Y2O3 nano amorphous films, by this way, high Jc with thicker YBCO films and as a result zero transparent of YBCO films were guarentied.(2) GZO transparent conducting oxide films were prepared by MOD method. The effects of growth temperature, thickness and the doping concentration on structural, morphology, optical and electrical properties of GZO films were systematically studied. GZO films with transparency of over 85% at visible wavelength and resistivity of 5.42×10-3 ?cm were successfully fabricated. By changing the component of the precursor, ZnO films, Ga2O3 ultraviolet absorbing films and MOD-Ga2O3 based solar blind ultraviolet photodetectors were fabricated.(3) Verification experiments of Ge/Au system were carried out. Reflectivity was observed varying with the changing Ge thickness(and therefore coloring effect). Compared with theoretical calculation results, the experimental results fit well with theoretical results. Then the visible absorbing Ge films were replaced by ultraviolet aborbing Ga2O3 films, similar results were found that the peaks of reflectivity at ultraviolet region shifted with changing Ga2O3 thickness. The application area of subwavelength optical coating was successfully extended to UV region.(4) Reflective Au layer was replaced by YBCO superconductor films, and the optical properties of Ge/YBCO system were studyed. It was found that YBCO films nearly absorb all light at visible region at room temperature, which differs from intial anticipation of Perfect Electric Conductor. Ge/YBCO system has near 90% absorption at visible region, and the absorption getting higher at lower temperature, which permits its application in solar cells and ultrathin photodetectors.(5) Reflective Au layer was replaced by transparent conductive GZO films, and the optical properties including reflectivity and absorption of Ge/GZO system were studied. When the resistivity of GZO films was relatively low(in the magnitude of 10-3 ?cm), the phenomenom of peak shift of reflectivity with changing Ge thickness and therfore coloring effect was observed. Meanwhile GZO films can obsorb UV light effectively, so UV protection functions of decroarive UV sunglasses were successfully realized by Ge/GZO system. Since Au is highly reflective and non-transparent in visible region, the application of Ge/Au system limited in decoration fields. By changing non-transparent Ge/Au system to half transparent Ge/GZO system, a new structure was expored and its application of subwavelength optical coatings was expanded.