Investigation On Photoelectric Properties Of Si-Ⅰ,Si-Ⅲ,Si-Ⅻ Low-dimensional Materials By First Principle Method And Experimal Preparation

As one of the most commonly used semiconductor materials,crystalline silicon is widely used in solar cells,photodetectors and other fields because of its abundant reserves and mature technology.However,due to the intrinsic limitation of its photoelectric performance,the photoelectric conversion efficiency is limited in practical application,which hinders the further improvement of the performance of related devices.In order to find potential substitute materials,the photoelectric properties of Si-Ⅰ,Si-Ⅲ and Si-Ⅻ low-dimensional materials are calculated theoretically,meanwhile the Si-Ⅰnanocrystalline films are prepared and analyzed experimentally.The calculated results show that bulk Si-Ⅰ and Si-Ⅻ are indirect bandgap semiconductors and bulk Si-Ⅲ is direct bandgap semiconductor.The optical absorption of bulk Si-Ⅲ is stronger than that of bulk Si-Ⅰ and Si-Ⅻ in the infrared part.The Si-Ⅰ films with thickness below 25 A are semi-metals and Si-Ⅲ films are semiconductors.As the thickness of the film decreases,the energy of the absorption edge becomes lower.At the same thickness,the light absorption of Si-Ⅲ and Si-Ⅻ films is stronger than that of Si-Ⅰ films.The bandgaps of Si-Ⅰ,Si-Ⅲ and Si-Ⅻ all narrow with the increase of Si atom number.When the number of Si atoms is the same,the bandgap of Si-Ⅲ and Si-Ⅻ nanoclusters is smaller than that of Si-Ⅰ nanoclusters.Furthermore,the optical absorption and quantum yields of Si-Ⅲclusters are better than those of Si-Ⅰ and Si-Ⅻ nanoclusters.The aluminum induction method is adopted to prepare the Si-Ⅰ nanocrystalline films by electron beam evaporation equipment.Crystallization states of the films is controlled by experimental conditions such as substrate,film thickness and annealing temperature.The results show that the lowest temperature of aluminum induced amorphous silicon film crystallization is about 220℃.When the thickness of aluminum layer is 75 nm,the silicon layer with thickness of 150 nm,has the best crystallization effect,which implies that the optimal thickness ratio of aluminum to silicon film is about 1:2.Additionally,when the thickness of silicon layer is 200 nm,the aluminum layer with thickness of 80 nm has the best crystallization effect,and the thickness ratio of aluminum to silicon film is about 1:2.5.The simulation results of the interlayer transport of aluminum and silicon atoms and the effect of aluminum atoms taking on the bonding of silicon atoms show that the Coulomb shielding effect of aluminum atoms weakens the bonding strength of the covalent bonds among silicon atoms.This interaction improves the mobility of silicon atoms and reduces the crystallization energy barrier of silicon.