Construction And Optical Properites Of Ge Ordered Macroporous Structure

Germanium is an important semiconductor material, with a high dielectric constant (ε= 16), and excellent transparent in the near infrared region (λ>1.87μm). These properties make it suitable for preparation of completely photonic band gap three-dimensional photonic crystals. Especially, it is still a challenge to produce sub-micron magnitude Ge three-dimensional photonic crystal with photonic band gap in the visible and near-infrare region. Chemical vapor deposition (CVD) is the most common filling in the interstice between the colloidal crystal template for Ge photonic crystal. But this method has some problem, such as expensive, complex process, less filling rate and easy to form core-shell structure.Therefore, this paper studies a new preparation method of Ge photonic crystals. An electrodeposition from ionic liquids for the first time is raised assisted by colloidal crystal templates to propare Ge photonic crystals. It systematically studied the electrodeposition processes in two kinds of ionic liquids, [HMIm] FAP and [EMIm] Tf2N in, as well as micro-structure, surface valence, dielectric properties, spectral characteristics and photoluminescence properties of the Ge film and Ge photonic crystal. The content and conclusions of this paper are as following:By the theory analysis of colloidal crystal template growth, it explained that the increase of the higher temperature could cause the decreas of thickness fluctuating in the vertical deposition process, high concentration of latex particles could result in thick wet films. Verified by the experiments, under the condition of temperature of 65℃and the volume fraction of 0.25% concentration, it can grow a highly ordered multi-layered centered cubic stacking PS template with smooth surface.It could effectively resolve deep cracks of PS microspheres during the growth by femtosecond laser micro-machining method etching parallel grooves with the width of 5um, slot spacing of 100um on glass substrates, because it will release the tensile stress in the disordered structures of PS microspheres Three different particle sizes of the PS template served as substrates, it uses magnetron sputtering method to fill Ge; Experimental results shows Ge only aggregating in the surface of PS, and format composite structure of Ge/PS. But it is interesting to find that the growth of Ge film has a duplicating phenomenon with same shape as the PS template, and simply explaining of this phenomenon as well.By cyclic voltammetry electrochemical windows of ionic liquids [HMIm] FAP were studied on the surface of ITO glass and gold substrate. By Field Emission Scanning Electron Microscopy (SEM), Energy Dispersive Spectroscopy (EDX), X- ray diffraction (XRD) and Raman Spectroscopy (Raman), the morphology, composition and microstructure of Ge thin film were characterized and analyzed. Experimental results show that it has the same electrochemical properties on two different substrates, SEM and EDX results prove that Ge film can be deposited in the [HMIm] FAP and the Ge films are amorphous approved by the XRD and Raman spectra results.Influence of different scan rates, deposition potential, deposition time are discussed to the electrodeposition Ge films from [EMIm] Tf2N by Cyclic Voltammetry, SEM and EDX. XPS analyze the valence variation of germanium membrane surface by different argon ion sputtering time. The optical constants of Ge films are tested by Ellipsometer, according to effective medium model fitting 380-900nm of the dispersion relation of the Ge films are obtained.By contact angle tester, laser scanning confocal microscope, SEM and EDX analysis, it is studied that wetting properties between ionic liquids [HMIm] FAP and [EMIm] Tf2N and PS colloidal crystal template, while micro-morphology and elemental composition of photonic crystal Ge prepared from electrodeposition. As well as the spectral character and dielectric properties of Ge photonic crystals are studied. The results showed that it is different wetting between two ionic liquids and the PS template. Ge three-dimensional photonic crystals could be deposited both from two ionic liquids, but the deposition rate in [EMIm] Tf2N is higher than [HMIm] FAP. The Ge photonic crystal has the reflective properties similar to Bragg grating. based on effective medium theory, it is fitted that the 380-900nm Ge photonic crystal dispersion relations along the x, y, z directions.The photoluminescence properties of the Ge film, Ge photonic crystal and Ge/PS composite structure are studied by confocal microscopy Raman - Fluorescence Spectroscopy. SEM, XPS and TEM characterize their microstructure and surface valence states. The results show that Ge/PS composite structure has a strong yellow green luminescence enhancement effect. Laser thermal effect on the Ge photonic crystal and Ge/PS composite structure show step-like effects of the luminous intensity and the light-emitting-level model is established to explain this phenomenon.