Studies On Preparation And Properties Of Si-rich Silicon Nitride And Amorphous Silicon Quantum Dot Thin Films

Based on the quantum confinement effect,the silicon quantum dots embedded in silicon-rich nitride thin films can be adjusted at various wavelength bands after reasonable design,and the luminous efficiency and photovoltaic conversion efficiency of solar cells can be greatly improved,which makes it have a great application prospect in solar cells and other optoelectronic devices.But the application of silicon quantum dots in solar cells is only at the initial stage of the oretical and experimental research,most of the films containing silicon quantum dots are prepared by deposition of silicon rich silicide films at first,and then condensed by high temperature annealing to form amorphous or crystalline silicon quantum dots.In this paper Si-rich silicon nitride thin films were prepared by plasma enhanced chemical vapor deposition?PECVD?method firstly.Secondly the thin film samples were annealed under nitrogen protection.The internal structures,composition and crystallization of the film samples were characterized by FTIR,UV-Vis spectrum,PL,X-ray diffraction spectrum and Raman scattering spectroscopy,respectively.The luminescent properties of silicon quantum dots formed in the thin films after annealing were studied.The main contents and results of this paper are as follows.1.With NH₃?SiH₄ and N₂ as reaction gas,silicon-rich nitride thin films were produced by plasma enhanced chemical vapor deposition method.In the case of optimizing other depositional parameters,the effects of NH₃ flow rates on the structures and optical properties of silicon-rich SiN_x thin films were studied.The bonding situation and band gap structures of the film samples were characterized and analyzed by Fourier transform infrared absorption,ultraviolet-visible absorption spectrum and XRD.The research results show that,with the increasing of NH₃ flow rates,the Si-N bond and N-H bond in the films are strengthened,but the Si-H bond is descended and moved to high wave-number.Meanwhile,the film transformation occurs from amorphous SiN_x phase to small crystal Si₃N₄ phase.Besides,with the increasing of NH₃ flow rates,the optical band gap of the film is widened gradually and the order degree of the microscopic structures is decreased.In addition,the analysis of XRD pattern shows that the size of the average crystal grain in the films increases gradually with the increasing of NH₃ flow rates.Based on the above analysis,the conclusion comes that an appropriate increasing of NH₃ flow rates will contribute to the transformations of films from amorphous Si N_x phase to small crystal Si₃N₄ phase.2.Silicon-rich nitride thin films were deposited by plasma enhanced chemical vapor deposition with NH₃?SiH₄ and N₂ as reaction gas.When the other parameters remain unchanged,we changed the two parameters of radio frequency?RF?power and deposition pressure.The thin films were characterized by UV-Vis spectra?FTIR and X-ray diffraction spectra.The results show that the increasing of RF power and deposition pressure all contribute to the deposition rate of the films.However,the increase of RF power leads to the decrease of the optical band gap and the increase of refractive index,and the increase of deposition pressure leads to the widening of the optical band gap.The increase of RF power leads to the increase of the probability of si-atom joining into the thin films,the transition of the films to silicon-rich state,the increase of deposition pressure leading to the increase of the probability of n-atom joining into the films and the transition of the films to nitrogen-rich state.XRD pattern shows that the average grain size in the film decreases.Based on the above results,the deposition pressure and RF power have important effects on the microstructure and optical properties of the films.The silicon nitride films with good densification and excellent properties can be obtained by adjusting these two parameters properly.3.Si-rich silicon nitride films were prepared on n-type silicon substrates?100?by plasma enhanced chemical vapor deposition method?SiH₄and NH₃?and annealed at 600¹000?for 60 minutes in a annealing furnace filled with nitrogen protection.Fourier transform infrared spectroscopy?FTIR?is used to analyze the bonding structure in the films.The results show that the Si-H bond and N-H bond decrease with the increase of annealing temperature,and disappear completely at 900?.At the same time,with the increase of annealing temperature,the Si-N bond increases and the blue shift occurs,the Si-Si bond increases and the si content in the film increases.By further analysis of Raman spectra,The Raman peak of amorphous silicon appeared in the 480cm^-11 of the annealed film at 700?,then the Raman peak of crystalline silicon particles at 497 cm^-11 was found by fitting the two peaks of Raman at the annealing temperature of 1000?.It shows that with the increase of annealing temperature,the silicon phase in the film changes from amorphous to crystalline.The PL spectra were used to analyze the photoluminescence properties of the films.There are five emission peaks in each sample at different annealing temperature in PL spectrum.Combined with Raman and FTIR spectra,it is found that the characteristic photoluminescence peaks of Si quantum dots was observed in the wavelength range of 525⁵55nm?P4?,and the other photoluminescence peaks?p1,p2,p3and p5?are all come from the defect states in the films.Finally,we calculated the relationship between the size of silicon quantum dots and annealing temperature.