A Study Of The Evolution Of The Silicon Nanocrystallites In The Amorphous Silicon Carbide Under Argon Dilution Of The Source Gases (original) (raw)
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Nanoscale, 2010
Nanophase nc-Si/a-SiC films that contain Si quantum dots (QDs) embedded in an amorphous SiC matrix were deposited on single-crystal silicon substrates using inductively coupled plasma-assisted chemical vapor deposition from the reactive silane and methane precursor gases diluted with hydrogen at a substrate temperature of 200 C. The effect of the hydrogen dilution ratio X (X is defined as the flow rate ratio of hydrogen-to-silane plus methane gases), ranging from 0 to 10.0, on the morphological, structural, and compositional properties of the deposited films, is extensively and systematically studied by scanning electron microscopy, high-resolution transmission electron microscopy, X-ray diffraction, Raman spectroscopy, Fourier-transform infrared absorption spectroscopy, and X-ray photoelectron spectroscopy. Effective nanophase segregation at a low hydrogen dilution ratio of 4.0 leads to the formation of highly uniform Si QDs embedded in the amorphous SiC matrix. It is also shown that with the increase of X, the crystallinity degree and the crystallite size increase while the carbon content and the growth rate decrease. The obtained experimental results are explained in terms of the effect of hydrogen dilution on the nucleation and growth processes of the Si QDs in the high-density plasmas. These results are highly relevant to the development of next-generation photovoltaic solar cells, lightemitting diodes, thin-film transistors, and other applications.
ACS Omega
Silicon carbide (SiC) has become an extraordinary photonic material. Achieving reproducible self-formation of silicon quantum dots (SiQDs) within SiC matrices could be beneficial for producing electroluminescent devices operating at high power, high temperatures, or high voltages. In this work, we use a remote plasmaenhanced chemical vapor deposition system to grow SiC thin films. We identified that a particular combination of 20 sccm of CH 4 and a range of 58−100 sccm of H 2 mass flow with 600°C annealing allows the abundant and reproducible self-formation of SiQDs within the SiC films. These SiQDs dramatically increase the photoluminescenceintegrated intensity of our SiC films. The photoluminescence of our SiQDs shows a normal distribution with positive skewness and well-defined intensity maxima in blue regions of the electromagnetic spectrum (439−465 nm) and is clearly perceptible to the naked eye.
Journal of Alloys and Compounds, 1999
Two series of hydrogenated amorphous silicon carbide (a-SiC:H) films have been prepared by using plasma-enhanced chemical-vapor deposition (PECVD) with the gas mixture of methane (CH ) and silane (SiH ). The influence of the r.f. power density on the structural 4 4 and optical properties of the films has been investigated with the CH gas ratio in the total gas flow rate ranging from 50 to 90%. The r.f. 4 power density is an important parameter which affects both the carbon content and the structures of the films. Under high r.f. power condition, the samples are Si-rich and the structure of them is described as a disordered amorphous silicon network in which hydrogen 3 atoms are incorporated in the form of Si-CH and Si-CH entities and carbon atoms are in a sp carbon-related configuration. The 2 3
Journal of Applied Physics, 2003
Nanocrystalline silicon carbide ͑SiC͒ thin films were deposited by plasma enhanced chemical vapor deposition technique at different deposition temperatures (T d) ranging from 80 to 575°C and different gas flow ratios ͑GFRs͒. While diethylsilane was used as the source for the preparation of SiC films, hydrogen, argon and helium were used as dilution gases in different concentrations. The effects of T d , GFR and dilution gases on the structural and optical properties of these films were investigated using high resolution transmission electron microscope ͑HRTEM͒, micro-Raman, Fourier transform infrared ͑FTIR͒ and ultraviolet-visible optical absorption techniques. Detailed analysis of the FTIR spectra indicates the onset of formation of SiC nanocrystals embedded in the amorphous matrix of the films deposited at a temperature of 300°C. The degree of crystallization increases with increasing T d and the crystalline fraction (f c) is 65%Ϯ2.2% at 575°C. The f c is the highest for the films deposited with hydrogen dilution in comparison with the films deposited with argon and helium at the same T d. The Raman spectra also confirm the occurrence of crystallization in these films. The HRTEM measurements confirm the existence of nanocrystallites in the amorphous matrix with a wide variation in the crystallite size from 2 to 10 nm. These results are in reasonable agreement with the FTIR and the micro-Raman analysis. The variation of refractive index ͑n͒ with T d is found to be quite consistent with the structural evolution of these films. The films deposited with high dilution of H 2 have large band gap (E g) and these values vary from 2.6 to 4.47 eV as T d is increased from 80 to 575°C. The size dependent shift in the E g value has also been investigated using effective mass approximation. Thus, the observed large band gap is attributed to the presence of nanocrystallites in the films.
Characterization of nanocrystalline silicon carbide films
Journal of Non-Crystalline Solids, 2006
Amorphous silicon carbide films were obtained by plasma enhanced chemical vapor deposition (PECVD) technique using a gas mixture of silane, methane, and hydrogen with a high excitation frequency and a high hydrogen dilution ratio. The high temperature annealing behavior of the amorphous silicon carbide films was studied by annealing at 1373 K for 1 h in nitrogen atmosphere. A very thin Au film was deposited on part of the films to investigate the metal induced crystallization effect. Well aligned nanotubes were found on the silicon carbide films covered by a thin gold layer after the high temperature annealing by atomic force microscopy. Further study is necessary to identify the nature of the nanotubes and elucidate their growth mechanism.
Silicon nanocrystals in carbide matrix
Solar Energy Materials and Solar Cells, 2014
Ordered silicon nanocrystals in silicon carbide are produced by Plasma Enhanced Chemical Vapor Deposition by means of the multilayer approach followed by annealing at 1100 1C. The crystallization is verified by Raman scattering, X-ray diffraction, Transmission Electron Microscopy, and UV-vis spectroscopy. The conditions for the periodic structure to survive the high temperature annealing and for the SiC barrier to confine the Si crystal growth are examined by energy-filtered transmission electron microscopy and X-ray reflection. The final layout appears to be strongly influenced by the structural features of the as-deposited multilayer. Threshold values of Si-rich carbide sublayer thickness and Si-to-C ratio are identified in order to preserve the ordered structure. The crystallized fraction is observed to be correlated with the total silicon volume fraction. The constraints are examined through the use of abinitio calculations of matrix-embedded silicon nanocrystals, as well as in terms of existing models for nanocrystal formation, in order to establish the role played by the interface energy on nanocrystal outgrowth, residual amorphous fraction, and continuous crystallization. A parameter space of formation of ordered Si nanocrystals is proposed. The diffusivity of carbon in the crystallized material is evaluated, and estimated to be around 10 -16 cm 2 /s at 1100 1C.
Low temperature deposition of nanocrystalline silicon carbide thin films
Applied Physics Letters, 2000
Nanocrystalline silicon carbide ͑SiC͒ thin films were deposited by plasma enhanced chemical vapor deposition technique at different deposition temperatures (T d) ranging from 80 to 575°C and different gas flow ratios ͑GFRs͒. While diethylsilane was used as the source for the preparation of SiC films, hydrogen, argon and helium were used as dilution gases in different concentrations. The effects of T d , GFR and dilution gases on the structural and optical properties of these films were investigated using high resolution transmission electron microscope ͑HRTEM͒, micro-Raman, Fourier transform infrared ͑FTIR͒ and ultraviolet-visible optical absorption techniques. Detailed analysis of the FTIR spectra indicates the onset of formation of SiC nanocrystals embedded in the amorphous matrix of the films deposited at a temperature of 300°C. The degree of crystallization increases with increasing T d and the crystalline fraction (f c) is 65%Ϯ2.2% at 575°C. The f c is the highest for the films deposited with hydrogen dilution in comparison with the films deposited with argon and helium at the same T d. The Raman spectra also confirm the occurrence of crystallization in these films. The HRTEM measurements confirm the existence of nanocrystallites in the amorphous matrix with a wide variation in the crystallite size from 2 to 10 nm. These results are in reasonable agreement with the FTIR and the micro-Raman analysis. The variation of refractive index ͑n͒ with T d is found to be quite consistent with the structural evolution of these films. The films deposited with high dilution of H 2 have large band gap (E g) and these values vary from 2.6 to 4.47 eV as T d is increased from 80 to 575°C. The size dependent shift in the E g value has also been investigated using effective mass approximation. Thus, the observed large band gap is attributed to the presence of nanocrystallites in the films.
Characterization of silicon carbide thin films prepared by VHF-PECVD technology
Journal of Non-Crystalline Solids, 2004
A series of hydrogenated amorphous silicon carbide films were prepared by plasma enhanced chemical vapor deposition (PECVD) using a gas mixture of silane, methane, and hydrogen as the reactive source and an excitation frequency of 27.12 MHz. Compared to the typical radio frequency deposition technique, the very high plasma excitation frequency increases the density of the electrons and decreases the electron temperature, which helps the dissociation of the SiH 4 and CH 4 , and reduces the energetic ion impact on the growth surface of the thin film. Thus, dense-films with lower bulk density of states and higher growth rate are expected, as confirmed by spectroscopic ellipsometry data. Apart from that, a substantial reduction of bulk defects is achieved, allowing an improvement of the valence controllability (widening of the optical gap from about 1.9 to 3.6 eV). In this work results concerning the microstuctural and photoelectronic properties of the silicon carbide films will be discussed in detail, correlating them with the deposition process conditions used as well as with the gas phase composition of the mixtures used.