Preparation And Structure Properties Of Si-rich Silicon Nitride Thin Films Containing Si Quantum Dots By Hot Wire Method

The third generation solar cell based on the quantum size effect of semiconductor quantum dots is one of the hot spots in the current research.The spacing and size of silicon quantum dots have a great influence on the absorption of light and the migration of carriers.The nanometer silicon quantum dot thin film material,because of its high conductivity and low conductance activation energy,so can be prepared by proper scale,uniform silicon quantum dots better nano thin film materials is key to the preparation of the third generation of silicon quantum dot solar cells.Preparation of silicon quantum dots in silicon nitride matrix in embedded film material,usually by magnetron sputtering and plasma enhanced chemical vapor deposition method by annealing after condensation by silicon quantum dots,and by hot wire chemical vapor deposition?HWCVD?technology for preparation of silicon quantum dot thin film materials are few.Silicon quantum dot films deposited by hot wire chemical vapor deposition,the hot wire temperature can be as high as 1700 Centigrade,the vapor deposition process,not only can generate a large number of Si-N bond,but also directly generated Si-Si bond,that is to say in the process of formation of silicon nitride is directly generated silicon quantum dots,such as saves the treatment process after high temperature annealing process.Based on the above reasons,the hot wire chemical vapor deposition method was used to prepare silicon nitride thin films.Gas source is used for the purity of 99.9999% NH₃,N₂,SiH₄,and H₂ combination,in the P type monocrystalline silicon and Corning7059 glass deposition of the experimental data of the three groups.The structure and properties of the films were characterized by Fourier transform infrared spectroscopy,UV-Vis transmission spectra,photoluminescence spectra and X ray diffraction spectra.Experimental results show:? Using SiH₄,NH₃ and N₂ as reaction gases,SiH₄,NH₃ gas flow rateremains unchanged,by changing the flow rate of N₂ for the preparation of thin film samples,The results showed that,the thin films are mainly composed of Si-N bond structure,and the H atoms are mainly bonded with N atoms in the nitrogen rich samples.With the increase of nitrogen flow rate,the nitrogen atom has the characteristic of doping,and the number of N atoms bound to a Si atom decreases,and the peak value of the N-H bond is weak until it disappears.Due to the high electronegativity of N atoms,the asymmetric stretching mode of the Si-N bond is blue shifted.The nitrogen in the reaction process of nitrogen atom in the film played the role of dilution.When the nitrogen flow rate is less than 60 sccm,the width of the band gap is not changed,and the band gap of 4.3eV is close to the ideal Si3N4 band gap.With the increase of the nitrogen flow rate,the Eg of the films decreases gradually,the order of the films increases,and the silicon nitride grains increase.When the nitrogen flow rate reaches 150 sccm,the film has a sharp diffraction peak of the crystallization ?-Si3N4 at 69.5°?2??,and preferential growth orientation along?322?crystal orientation,with increasing of the silicon nitride crystal grains significantly.? Using SiH₄,NH₃,and H₂ as reaction gas,In the optimization of other parameters unchanged,only change the H₂ flow for the preparation of thin film samples.The results showed that,the thin films are mainly composed of Si-N bond structure,with the increase of hydrogen flow rate,hydrogen atom density excess H atoms can be fully integrated with N,Si,N-H bond and Si-H bond increase,carrier recombination rate reduced life enhancement,played a good effect on the passivation film.When the hydrogen flow rate is less than40 sccm,the band gap broadening slow.When hydrogen flow rate changes from 40 sccm to 60 sccm,the band gap broadening change,the high energy Si-N bond increased,the refractive index decreases,gradually changing to the structure of Si3N4 thin films.When the hydrogen flow rate reaches 150 sccm,the film has a sharp diffraction peak of the crystallization ?-Si3N4 at 64.5°?2??,and preferential growth orientation along?311?crystal orientation.The phenomenon of silicon nitride crystals appeared in the thin films,and theamorphous silicon nanoclusters needed for quantum dots were formed.The hydrogen flow rate has a great influence on the passivation effect of the film,and the increase of the hydrogen flow rate can increase the probability of N atoms into the film and promote the formation and increase of the silicon nitride grain.? Using SiH₄,NH₃,and H₂ as reaction gas,In the optimization of other parameters unchanged,by changing the hot wire temperature to prepare thin film samples.The results showed that,with the increase of the hot wire temperature,the N-H bond and Si-H bond rupture,which makes the Si-H,N-H bond density decreased,H atoms overflow the film,Si and N dangling bonds can not be passivated,prompting Si-N bond recombination,increased Si-N bond density in the films,stability and compactness of the film get promotion.However,the decrease of H atom leads to the decrease of the adsorption of H atoms and the increase of the density of defect states.the widening of the band gap,the enhancement of the valence band in the conduction band to the forbidden band,the decrease of the order of the film,and the occurrence of the silicon rich state.With the increase of hot wire temperature,the silicon and nitrogen atoms in the films can be fully relaxed.It is favorable for the order of the silicon nitrogen network,the bond between the silicon atoms is more compact,and the formation of more small size silicon clusters,the direct formation of nano scale silicon quantum dot clusters.In this way,the nano scale silicon quantum dot thin film material is prepared by using the high temperature annealing effect of the hot wire without further annealing.