Photoluminescence Of The Complex Materials Of Porous Silicon/Nano Zinc Oxide

With the development of information technology, the speed of information transportation and the storage function of management are not increased enough to meet the demands of the markets. If the photoelectric technology could be introduced in silicon chip, which uses photons instead of electron as carrier, the transportation speed and dealing ability of information can be greatly enhanced, and information technology such as computer, communication and display technologies, etc would get into new phase. But unfortunately silicon integrate circuit chip is limited to the size of the devices and the electron speed in bulk silicon. Materials of photoluminescence grown on silicon substrate have attracted attention of scientists because of their potential usage in silicon photoelectron chip. In order to make silicon emit visible light, one has tried many methods, such as vaporizing, sputtering, molecular beam epitaxying (MBE), etc. to develop heterogeneous luminescent materials on silicon wafers. According to the engineering of defects mechanism, single crystal silicon has been doped by elements of equivalent valent electrons or rare metals such as Er to improve its photoelectronic characteristics. Considering changing of the energy band of silicon with the adjustment of the material structure, Ge-Si super crystal lattice material has been tried, based on the engineering of energy band structure. But the effects of above methods have not get promising results up to now in their luminescent characters. The porous silicon (PS) has attracted increasing interest for a wide spectrum of potential applications since the discovery of the unexpected optical properties of the microporous Si in 1990. As to the emission mechanism of porous silicon, many models have been proposed, for example the quantum (size) confinement effect model, the surface recombination center model, the impure silicon model, the surface chemical bond restrict-quantum confinement effect model and quantum confinement-surface recombination center model. At present, more and more experiments indicate that the excitation of porous silicon has some thing to do with the quantum (size) confinement effect and the emission recombination mechanism has more things to do with the surface recombination. In the application research, we can easily obtain porous silicon with red to yellow photoluminescence, but its emitting efficiency is still very low (its quanta efficiency is 1% to 10%), and the light emission is unstable which is very sensitive to the preparing processes and keeping conditions. Hence, how to increase the emitting efficiency, enhance its stability and extend the wavelength range of light emitting have become very important in the field in recent years. In this paper, we first use a new electrochemical method to create zinc oxide nanoparticles in ethonal, which have strong photoluminescence at room temperature. We have investigated the formation condition and mechanism of them systematically. X-ray diffraction and electron diffraction pattern analysis were used to affirm that the nanoparticles of zinc oxide have a structure of wurtzite. The photoluminescence character was analyzed using 960CRT and PERKIN ELMER Luminescence Spectrometer. As a result, at room temperature, their chief luminescent peaks are at about 392 nm,420 nm,448 nm,489 nm,513 nm,570 nm and 662 nm when different wavelengths of exciting lights were used. We found that the ultraviolet light emission was enhanced and the visible emission weakened, some of the peaks have even disappeared after samples were annealed separately at 350 ℃for 1 hour in an atmosphere of nitrogen and oxygen.. Ultraviolet-visible absorption spectrum shows that the samples have a strong absorption in ultraviolet light. At the same time, we deduced 3.58 eV of optical band gap of the zinc oxide according to the light absorption coefficient equation. It is larger than the theoretic figure 3.36 eV, which might be the result of quantum confinement effect. light absorption coefficient equation: α(hυ)=A(hυ-Eopt)1/2+αoαmeans absorption coefficient, which is a function of light frequency, hυis the photon energy, Eopt is the optical band gap, A is a coefficient based on the nature of the material, it is commonly a constant figure for direct energy band semiconductors, αo is a constant. Secondly, we use zinc oxide nanoparticles to modify porous silicon. There are two methods we have used, one is electrochemical deposition method, and the other is magnetron sputtering. In electrochemical deposition method, we use as-prepared porous silicon as cathode, pure zinc (99.999%) as anode, and ethanol electrolyte, to form a thin zinc oxide film on porous silicon surface. In magnetron sputtering method, we use analysis-grade zinc oxide as target, to form the zinc oxide film. Then the samples of PS/ZnO were annealed at 300 ℃for 30 minutes, The samples annealed and unannealed were observed by metallographic microscope and compared subsequently, and the photoluminescence spectra was measured by PERKIN ELMER Luminescence Spectrometer. It has been found that the ZnO nanoparticles can enter into the pores of the PS for the electrochemical deposition samples but not for those deposited by magnetron sputtering. The results of the luminescent measurements indicated that the deposited samples show some new peaks different from PS, which are in agreement with morphological results. A new model about the mechanism of the photoluminescence has been brought out according to the articles delivered formerly. Lastly, nanocrystalline zinc silicate doped with manganese (Zn2SiO4: Mn) has been formed. As we all know that silicate luminescent materials have characters of high stability and luminescent efficiency. If we can change porous silicon to porous silicate, we can obtain materials of photoluminescence grown on silicon substrate with stable character and high luminescent efficiency. Zn2SiO4: Mn is relatively common among the luminescent silicate materials. It has widely used in plasma displays (PDP). Zn2SiO4: Mn has become one of the best green light emitting luminescent materials because of its high luminance and pure green light emitting. It...