Preparation And Characterization Of Germanium Films On Heterogeneous Substrate

In 21st century,due to the exhaustion of traditional fossil energy,the energy crisis and environmental pollution has become the urgent problems for human society.However,with the development of renewable energy technology,the renewable energy,especially solar energy,has become an inevitable choice for social and economic development.Because of its inexhaustible characteristics,solar energy has been highly valued and strongly supported by all countries in the world.In the future,solar energy will occupy a dominant position in the energy market.In that situation,how to improve the efficiency of solar cells and reduce the cost of solar power generation has become the point of research in the field of photovoltaic power generation.At present,the multi-junction solar cells based on GaAs have the highest conversion efficiency,and Ge is usually used as the substrate material for multi-junction solar cells.However,Ge is one of the typical scattered metal with high price.In order to reduce the cost of multi-junction solar cells,we consider Si as the substrate material for multi-junction solar cells which is much cheaper than Ge.The main content of this paper is to prepare Ge thin films with high preferred orientation and prefect crystal quality on Si substrate.Based on the Bragg equation,this paper proves the applicable range of Scherrer formula and its maximum value for measuring the grain size of Ge material.Ge thin films were prepared on silicon substrates by magnetron sputtering and conventional thermal annealing.The quality of Ge thin films was characterized by X-ray diffraction,Raman spectroscopy.The main findings are as follows:(1)It is proved that the grain size calculated by Scherrer formula is only the grain height that perpendicular to the crystal plane,and the maximum value of Scherrer formula for the grain size of Ge(111)is 115 nm.(2)Al and Ge films were deposited on Si substrate by magnetron sputtering,and the samples were annealed by conventional annealing equipment to investigate the effect of annealing temperature on the microstructure of Ge films.Raman measurements show that the Ge films are amorphous at annealing temperature of 200?and begin to crystallize when annealing temperature is above 250?.indicating that the minimum annealing temperature for Al-induced crystallization of Ge films is 250?,and the Ge films whose grain size exceeded 100nm and has more than 99%preferred orientation were successfully prepared at 250?.(3)The effect of annealing time on the crystallization of Ge thin films was studied by annealing the samples at 250? and 400? for different times.XRD results show that annealing time has great effect on the crystallization of Ge thin films.With the increase of annealing time,the crystalline quality of the samples increases.At 400?,the preferred orientation of Ge(111)peak becomes more obvious with the increase of annealing time.(4)The samples were annealed at different annealing temperatures to investigate the effect of temperature on the crystallization of Ge films.XRD results show that the preferred orientation of Ge(111)decreases and the grain size decreases with the increase of annealing temperature.