Study On Optical Properties Of Amorphous Silicon Films And Aluminum - Induced Crystallization Of Polycrystalline Silicon Thin Films

The wide use of solar cell exhibits important role to solve the resource and environmental crisis. Thin film cells have drawn great interests due to their tow cost and higher efficiency.Among them the polycrystalline silicon(p-Si) thin film has the advantages such as abundant raw materials,low production and energy cost,stable performance,extensive application and so on,which enable it promising in replacing crystalline silicon solar cells and becoming the next generation solar cells.In this thesis,firstly amorphous silicon(a-Si:H) thin films were fabricated by plasma enhanced chemical vapor deposition(PECVD) system.We investigated the optical properties of the a-Si:H film.The spectrophotometer was improved by using a clamp.Transmission spectrum of a-Si:H film were measured by the modified spectrophotometer.Its optical properties are obtained by spectrum curve fitting.And then,the a-Si:H films with a stack of glass/a-Si:H/A1 were crystallized by aluminium-inducing.It were analyzed by Raman spectrum,X-ray diffraction,and Atomic Force Microscope.It has been studied that factors affect on the structures of polycrystalline silicon in the process of aluminum induced crystallization.The study results were obtained as fellow:1.The relation between refractive index and incident wavelength of a-Si:H thin film is: n=1.6×10~5/λ~2+2.88;The relation between absorption coefficient and incident wavelength of a-Si:H thin film is:1gα=6.48×105/λ~2-4.8;The optical band gap of a-Si:H thin film is 1.56eV.2.Higher annealing temperature and longer annealing time are prone to make crystallization appear in the aluminum-induced process.Annealing temperature and time were found to be connected.Higher annealing temperature corresponds to shorter time,lower annealing temperature corresponds to longer time in the process of complete crystallization.3.Two steps annealing was put out first time.There existed an optimal point in the process of the two steps annealing,for example,annealed at 300℃for 2h and then reheated to 500℃annealing for 3h.The results showed that the p-Si thin film had big grain size and smooth surface.It is useful in practice.4.The thicker Si film,the higher crystallized fraction of p-Si films.However,there exist a critical point,crystallized fraction of p-Si films is reduced beyond the thick.5.The oxide layer between the a-Si:H and Al forms a barrier for atomic diffusion.The thicker oxide interface layer,the harder diffusion of Al and Si atoms and the smaller nucleation density of Si could produce the larger Si grain.Otherwise,the thinner oxide interface layer,the higher nucleation density resulted in the smaller Si grain.6.In the aluminum-induced layer exchange(ALILE) process the largest contribution to the driving force for the transformation is the release of the crystallization energy of the amorphous Si. Considering that the Si crystallization process takes place locally,the release of the crystallization energy of the amorphous Si has no contribution to a driving force for the layer exchange.However, The layer exchange may be driven by the release of elastic strain energy associated with the relaxation of macrostress and the microstrain and the grain growth of the A1 phase.