Evaluation Of Substrate Material And Cu-doping Effect On The Microstructural And Optical Behavior Of ZnO Films

Porous silicon (PS) is a kind of multifunctional semiconductor materials, ZnO has a difference of optics, electricity and gas sensitive properties. In the present work, porous silicon substrate were prepared by electrochemical anodization using the p-type (100) Si wafers. ZnO and ZnO:Cu thin films were prepared on porous silicon, silicon and glass substrates by radio frequency (RF) magnetron sputtering technique. X-ray diffraction, Scanning electronic microscopy, Lambda35UV/VIS, Photolumine-scence measurements, Raman scattering spectra and Fourier transform infrared spectroscopy were employed to evaluation of substrate material and Cu doping effect on the microstructural and optical behavior of ZnO films. The originality of our work is that the present paper contains three aspects as a whole. Detailed description are given below:1. Explore the preparation process and parameters of producting PS, the mechanical properties of which are suitable for substrate and the luminescence properties of which are efficient;2. Effect of Cu doping concentration on the microstructural and optical properties of ZnO/PS nanocomposite systems;3. Effect of substrate material and Cu doping on the microstructural and optical behavior of ZnO films. The main conclusions are listed as belows:1. Find the preparation process and parameters of producting PS, the mechanical properties of which are suitable for substrate and the luminescence properties of which are efficient. Before the electrochemical anodization procedure, the p-type (100) Si wafers with a resistivity of8-13Ω·cm and a thickness of about390μn were ultrasonically cleaned in a bath of acetone, ethyl alcohol and deionized water. To form high quality PS, aluminum films were deposited on the backside of the Si wafers by RF magnetron sputtering and then annealed at500℃for one hour in vacuum. The anodization was then carried out in HF(40%):C2H5OH(98%)=1:1(by volume) for10minutes at a constant current density of15mA/cm2. The PS samples were rinsed in deionized water and then dried in the N2nozzle.2. ZnO/PS and ZnO:Cu/PS nanocomposite films with strong c-axis preferred orientation have been successfully prepared on porous silicon substrate, formed by electrochemical anodization, using radio frequency reactive magnetron sputtering method. X-ray diffraction measurements showed that new weak (100),(101),(102) and (110) diffraction peaks appeared after doping. Meanwhile the intensity of (002) diffraction peak first decreased and then increased with the Cu doping content increasing. The residual stress of the ZnO:Cu/PS nanocomposite films was compressive stress at first, and then changed into tensile stress with the doping percentage further increasing. SEM measurements indicated that a less uniform grain size was observed after Cu doping and the shape of these grains changed from small ball into ellipsoid. The optical band edge of ZnO:Cu films, deduced from the optical absorption spectra, shifted to a longer wavelength comparing with the undoped sample and we attributed this red shift phenomenon to the decreasing of carrier concentration. The broad light emission from350to800nm was obtained by combining the blue-green emission from ZnO with red-orange emission from porous silicon. This could be used as a source of white light emitting diode chips underlying the importance of our work. The variation and origin of the emission peaks were discussed through the Gaussian deconvolution, and the Raman scattering spectral revealed the characteristics of porous silicon and the improvement of multiphonon processes.3. ZnO and ZnO:Cu thin films were prepared on porous silicon, silicon and glass substrates by radio frequency magnetron sputtering technique. X-ray diffraction measurements revealed that ZnO and ZnO:Cu thin films are c-axis preferred orientation and the particle size of all samples was in the range of11.4-17.6nm. All the samples in this part exhibited a compressive stress. Fourier transform infrared spectroscopy showed the presence of Si-O-Si stretching appeared at1067cm-1, which was assigned to the transverse optical mode of the asymmetric vibration. The E2(high) mode indicating the residual stress was observed in the Raman spectra. The optical transmission and absorption spectra were studied, indicating that the optical band gap value shifted to a longer wavelength after Cu doping. The PL spectra of ZnO and ZnO:Cu thin films deposited on Si and glass substrate revealed three main emission peaks located at around416,481and525nm, while on PS substrate exhibited a broad emission band from400to500nm and three emission peaks centred at530,597and688nm. Effect of substrate material and Cu doping on the phot oluminescence properties of ZnO thin film s, along with the origin of some emission peaks, were discussed in detail. The experiment results indicate that the ZnO and ZnO:Cu thin films grown directly on the Si substrates have a high quality of crystallization and intense blue luminescent properties. From this research, it can be seen that the Cu doping as well as the choice of substrates might be considered as one of the most promising methods for device applications.