Effects Of Hot Wire Chemical Vapor Deposition Paramaters On The Preparation And Microstructure Of Microcrystalline Silicon Thin Films

In the filed of photovoltaic,crystalline silicon?including monocrystalline and polycrystalline silicon?solar cells have always occupied a dominant position in the market?accounting for more than95%?.However,since crystalline silicon is a bulk material,a large amount of raw materials are consumed during the preparation of solar cells.In order to reduce the consumption of raw materials,people have been hoping to obtain silicon solar cells with high conversion efficiency.Among them,microcrystalline silicon film material as a new type of solar photovoltaic material has attracted much attention.The microcrystalline silicon thin film material has both the high absorption of the amorphous silicon thin film material and the good stability of the crystalline silicon material.At the same time,it has a longer carrier life and a smaller photo-induced attenuation effect.In addition,the microcrystalline silicon thin film material preparation equipment is simple,suitable for large area and low cost production.Therefore,people hope to use microcrystalline silicon thin film materials instead of crystalline silicon materials to prepare high conversion efficiency,low cost and low consumable silicon thin film solar cells.At present,plasma-enhanced chemical vapor deposition?PECVD?technology is widely used in the preparation of microcrystalline silicon films,but its low deposition rate leads to an increase in the production cost.The hot wire chemical vapor deposition?HWCVD?technology can not only decompose molecules through high temperature,but also play a catalytic role in the reaction process,so its deposition rate is fast.At the same time,the hot wire equipment is simple and suitable for large area growth on inexpensive substrates?glass,stainless steel,etc.?,which is currently considered as a better technology for depositing silicon thin film.In this paper,HWCVD technology is used to prepare microcrystalline silicon thin film materials on glass substrates and n-type single crystal silicon substrates.The effects of three important parameters of silane flow rate,deposition time and hot wire temperature on the preparation of microcrystalline silicon thin film materials and their microstructure characteristics during microcrystalline silicon materials were studied.The main contents include the following three parts:1.In the process of preparing microcrystalline silicon thin films by HWCVD,hydrogen ions play a key role in the growth of crystal grains.The change of the silane flow rate indirectly affects the concentration of hydrogen plasma,and thus affects the quality of the thin film.In the experiment,SiH₄ and H₂ were used as the reaction gas sources.Under the condition that the hot wire temperature was about 1600??current was14A?,the deposition pressure was 30 Pa,and the hydrogen flow rate was30 sccm,the silicon thin film material was deposited on N-type monocrystalline silicon wafer with crystal direction of?100?and and Corning 7059 glass wafer by changing the silane flow.X-ray diffraction experiments found that the deposited silicon thin film had preferential orientation growth in the?111?crustal plane direction.With the increase of silane flow rate,the grain size decreases and the band gap broadens.When the silane flow rate was 1.02 sccm,a better deposition rate?0.239nm/s?was obtained,and the grain size?18.7nm?and band gap?1.483eV?of samples were also improved to a certain extent.2.In order to understand the characteristics of the longitudinal growth of thin films prepared by hot-wire chemical vapor deposition technology,the changes of the structure and optical characteristics of microcrystalline silicon thin films with deposition time were studied.In the experiment,when the hot wire temperature was about 1600?,a series of microcrystalline silicon thin films were prepared by changing the deposition time?50min?70min?90min?110min?with silane and hydrogen as the reaction gas sources.The results show that with the increase of deposition time,the thickness of the silicon thin film increases,but the deposition rate dose not change monotonously.It shows non-uniform growth in the longitudinal direction.The grain size of the silicon thin film sample in the direction of the characteristic peak of the?111?plane first increased and tended to be basically unchanged.When the deposition time was 90 min,the grain size was the largest,the optical band gap was the smallest and the oxidation degree of the thin film was the lowest.In summary,with the change of deposition time,the grains of the thin film as a whole show a tendency to grow within a certain range.3.The hot wire temperature affects the product of silane decomposition and the efficiency of catalysis,so it is important influence on the structure of the thin film.In the process of preparing microcrystalline silicon thin films,the influence of the hot wire temperature?corresponding to the hot wire current of 14A,16A,18A?on the structure and optical properties of microcrystalline silicon thin films was studied by controlling the hot wire current.The experimental results show that the crystal plane orientation of microcrystalline silicon thin film gradually changes from?111?to?220?with the increase of the hot wire temperature.The grain size of?111?plane shows a trend of decreasing,while the grain size of?220?plane shows a trend of increasing.At the same time,the characteristic diffraction peak of silicon oxide appeared when the hot wire current reached 14A.The higher the temperature of hot wire,the better the crystalline property of the silicon thin film.The grains show a large-sized multilateral pyramid shape.However,the larger the size of the polygonal pyramid,the lager the voids in the thin film.The oxygen content in the thin film obtained at high temperature was the highest when the thin film was characterized by Fourier infrared absorption spectroscopy.In order to suppress oxygen,the thin films prepared by the hot wire chemical vapor deposition were treated with hydrogen plasma.It was found that the external hydrogen plasma could get rid of a certain amount of oxygen.Bue XRD characterization found that silicon oxide still exists,so it is speculated that the oxygen treated by the hydrogen plasma is mainly distributed on the surface of the film.