Thickness modulated structural and photo-luminescence properties of magnetron sputtered nanocrystalline SiC ultrathin films (original) (raw)
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The paper presents the results of porous SiC study using photoluminescence and scanning electronic microscopy. It is shown that the intensity of defect-related PL bands (2.08, 2.27, 2.44 and 2.63 eV) increases monotonically with the rise of PSiC thickness from 2.1 up to 12.0 lm. These luminescence centers are assigned to surface defects which appear at the PSiC etching process. Photoluminescence intensity stimulation for surface defects is attributed to rise of defect concentrations with increasing of porous layer thickness and to realization of the hot carrier ballistic mechanism at surface defect excitation. Intensity enhancement for exciton-related PL bands (2.79, 2.98 and 3.26 eV) is attributed to increasing the exciton recombination rate as result of exciton weak confinement in big size SiC NCs of different polytypes (6H-PSiC with inclusions of 15R-and 4H-PSiC).
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SiC nanopowder has been formed using an original technological approach based on grinding of bulk porous SiC nanostructures. The initial porous SiC nanostructures were obtained by anodization of n + -type 4H-SiC substrate in HF/Ethanol solution under UV illumination. Large single SiC nanoparticles (~ 30 nm in diameter) constituting the nanopowder have a porous structure which can be clearly visible. On the other hand, small single SiC nanoparticles (~ 4 nm in diameter) exhibit a clear crystalline structure. A broad and very intense luminescence band (400 -900 nm) provided from the nanopowder corresponds to the radiative processes involving nanoparticle surface states. A smaller photoluminescence peak centred at 358 nm may correspond to radiative recombination of the photogenerated excitons confined in the individual and spatially separated 4H-SiC nanoparticles.
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We report the formation of the continuous b-SiC layers on Si by means of C þ implantation into Si followed by pulsed ion-beam treatment (C þ , 300 keV, 50 ns). Transmission electron microscopy and electron diffraction indicate the formation of a polycrystalline b-SiC layers with a grain size of up to 100 nm. Porous SiC/Si structures were prepared by anodization and were studied by photoluminescence (PL) at room temperature. Three PL bands were observed at 460, 520 and 615 nm and were ascribed to the SiC nanocrystals, C-rich clusters and Si nanocrystals, respectively. The time constant s ¼ 40 ns was deduced from time-resolved PL measurements. It is close to the value for direct band gap semiconductors and is shorter nearly by 3 orders of magnitude than that for porous Si.
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Structural changes in diamond films of different qualities caused by annealing in vacuum up to 1600ЊC have been studied by IR and UV-visible optical absorption, Raman and photoluminescence spectroscopy. An internal degradation of the diamond films and a strong optical absorption enhancement in the whole UV-vis-IR range take place at T) 1300ЊC, and correlate with the loss of bonded hydrogen. At least 25% of the total amount of hydrogen is found to be in the unbound state in some of the as-grown Ž. untreated films. The diamond darkening is ascribed to appearance of graphite-like phases presumably at grain boundaries. Ž. Activation energy of GB transformation process is much lower 250᎐530 kJrmol compared to surface graphitization of single 0 Ž crystal diamond. No evidence of charge transfer altering the concentration of substitutional nitrogen N and N y N in S A D. Ž B-doped films upon annealing was found. Thermal conductivity measured by laser flash technique remains almost constant 20. WrcmK even after annealing to 1575ЊC, then catastrophically drops because of crack development in the film.
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Applied Physics Letters, 1993
Continuous, ultrathin silicon carbide (Sic) films of less than 10 nm have been grown on Si by rapid thermal chemical vapor deposition carbonization with high propane flow rates at IlOO-1300 "C. X-ray and electron diffraction techniques indicated a monocrystalline structure for these nanometer-scale films. High-resolution transmission electron microscopy reveals that five Sic planes are aligned with four Si planes at the SiC/Si interface. The Fourier transform infrared spectrum of the Sic films exhibits the characteristic SGC absorption peak at around 800 cm-', with a FWHM of 45 cm-'.
Modern Physics Letters B, 2008
In this paper, we present a comparative study of structural and optical properties of polycrystalline p-type 6H-SiC and thin SiC layer growth onto Si. The thin SiC layer was grown on a p-type Si(100) substrate by pulsed laser deposition (PLD) using KrF excimer laser from a 6H-SiC hot pressed target. The properties of polycrystalline 6H-SiC and thin SiC layer were investigated by scanning electronic microscopy (SEM), high resolution X-Ray Diffraction (XRD), secondary ion mass spectrometry (SIMS), FT-IR spectroscopy and photoluminescence spectrometry. XRD analysis showed that the two materials have the same hexagonal structure (6H-SiC) as identified by ASTM 72-0018. In addition, a SIMS analysis gives a ratio Si/C of the thin SiC layer around 1.15 but the ratio Si/C of the target was found equal to 1.06, whereas one should have 1.0. This is due to the higher ionization efficiency of Si by the report of C atoms and in photoluminescence, the two materials exhibit the same emission bands (blue and green). Finally, a crystalline thin SiC layer of 1.6 µm was elaborated using the PLD method at low-temperature indicating that the technique reproduces the same macroscopic property (optical, structural, mechanical, etc.) of the target.
Solid State Communications, 2005
Hydrogenated amorphous SiC thin films deposited at low substrate temperature (100 8C) show the different bonding configurations and microstructures which depend on the carbon concentrations in the films controlled by the gas ratio R of methane to silane during the deposition. Photoluminescence characteristics are investigated for these samples with different structures. A strong luminescence in red light region can be observed for samples deposited with low gas ratio R which is significantly reduced its intensity with increasing the carbon concentrations in the films. On the other hand, the luminescence bands located at blue-green light region are detected under UV light excitation for samples deposited with high gas ratio R, which can be associated with the existence of amorphous SiC clusters in the films. q
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