Annealing effects on the optical and structural properties of Al2O3/SiO2 films as UV antireflection coatings on 4H-SiC substrates

Al2O3/SiO2 films have been prepared by electron-beam evaporation as ultraviolet (UV) antireflection coatings on 4H-SiC substrates and annealed at different temperatures. The films were characterized by reflection spectra, ellipsometer system, atomic force microscopy (AFM), X-ray diffraction (XRD) and Xray photoelectron spectroscopy (XPS), respectively. As the annealing temperature increased, the minimum reflectance of the films moved to the shorter wavelength for the variation of refractive indices and the reduction of film thicknesses. The surface grains appeared to get larger in size and the root mean square (RMS) roughness of the annealed films increased with the annealing temperature but was less than that of the as-deposited. The Al2O3/SiO2 films maintained amorphous in microstructure with the increase of the temperature. Meanwhile, the transition and diffusion in film component were found in XPS measurement. These results provided the important references for Al2O3/SiO2 films annealed at reasonable temperatures and prepared as fine anti-reflection coatings on 4H-SiC-based UV optoelectronic devices. (c) 2008 Elsevier B.V. All rights reserved.

Excitonic photoluminescence properties of nanocrystalline GaSb and Ga0.62In0.38Sb embedded in silica films

The GaSb and Ga0.62In0.38Sb nanocrystals were embedded in the SiO2 films by radio-frequency magnetron co-sputtering and were grown on GaSb and Si substrates at different temperatures. We present results on the 10K excitonic photoluminescence (PL) properties of nanocrystalline GaSb and Ga0.62In0.38Sb as a function of their size. The measurements show that the PL of the GaSb and Ga0.62In0.38Sb nanocrystallites follows the quantum confinement model very closely. By using deconvolution of PL spectra, origins of structures in PL were identified. (C) 2002 Elsevier Science B.V. All rights reserved.

Optical properties of nanometer silicon prepared by silicon ion implanted into SiO2 layers

The samples of silicon nanocrystals (nc-Si) were prepared by Si ion implanted into SiO2 layers. Photoluminescence spectra were measured at room temperature and their dependence on thermal annealing was investigated. The experimental results show that PL peaks originate from the defects in SiO2 layers caused by ion implantation when the thermal annealing temperature is lower than 800 C. The PL peak from nc-Si was observed when the thermal annealing temperature was higher than 900 C, and PL intensity reached its maximum at the thermal annealing temperature of 1100 C. As the annealing temperature increases the red shift of PL peak from nc-Si shows the quantum size effect. The characterized Raman scattering peak of nc-Si was observed at the right angle scattering configuration for the first time. It provides further support for the PL measurements.

Photoluminescence from Erbium-implanted silicon-rich SiO2

Si-rich SiO2 films were deposited by plasma-enhanced chemical vapor deposition on the silicon substrates, and then implanted with 1 x 10(15) cm(-2) 400 keV Er ions. After annealing at 800 degrees C for 5 min the samples show room temperature luminescence around 1.54 mu m, characteristic of intra-4f emission from Er3+, upon excitation using an Ar ion laser.

Heavily doped polycrystalline 3C-SiC growth on SiO2/Si(100) substrates for resonator applications

3C-SiC is a promising material for the development of microelectromechanical systems (MEMS) applications in harsh environments. This paper presents the LPCVD growth of heavily nitrogen doped polycrystalline 3C-SiC films on Si wafers with 2.0 mu m-thick silicon dioxide (SiO2) films for resonator applications. The growth has been performed via chemical vapor deposition using SiH4 and C2H4 precursor gases with carrier gas of H-2 in a newly developed vertical CVD chamber. NH3 was used as n-type dopant. 3C-SiC films were characterized by scanning electron microscopy (SEM), x-ray diffraction (XRD), x-ray photoelectron spectroscopy (XPS), secondary ion mass spectroscopy (SIMS), and room temperature Hall Effect measurements. It was shown that there is no voids at the interface between 3C-SiC and SiO2. Undoped 3C-SiC films show n-type conduction with resisitivity, Hall mobility, and carrier concentration at room temperature of about 0.56 Omega center dot cm, 54 cm(2)/Vs, and 2.0x 10(17) cm(-3), respectively. The heavily nitrogen doped polycrystalline 3C-SiC with the resisitivity of less than 10(-3) Omega center dot cm was obtained by in-situ doping. Polycrystalline SiC resonators have been fabricated preliminarily on these heavily doped SiC films with thickness of about 2 mu m. Resonant frequency of 49.1 KHz was obtained under atmospheric pressure.

Investigation of PL properties of C-doped SiO2/Si samples after high energy Pb ion irradiation

Amorphous SiO2 thin films with about 400-500 nm in thickness were thermally grown on single crystalline silicon. These SiO2/Si samples were firstly implanted at room temperature (RT) with 100 keV carbon ions to 2.0 x 10(17),5.0 X 10(17) or 1.2 x 10(18) ions/cm(2), then irradiated at RT by 853 MeV Pb ions to 5.0 x 10(11), 1.0 X.10(12) 2.0 x 10(12) or 5.0 x 10(12) ions/cm(2), respectively. The variation of photoluminescence (PL) properties of these samples was analyzed at RT using a fluorescent spectroscopy. The obtained results showed that Pb-ion irradiations led to significant changes of the PL properties of the carbon ion implanted SiO2 films. For examples, 5.0 x 10(12) Pb-ions/cm(2) irradiation produced huge blue and green light-emitters in 2.0 x 10(17) C-ions/cm(2) implanted samples, which resulted in the appearance of two intense PL peaks at about 2.64 and 2.19 eV. For 5.0 x 10(17) carbon-ions/cm(2) implanted samples, 2.0 x 10(12) Pb-ions/cm(2) irradiation could induce the formation of a strong and wide violet band at about 2.90 eV, whereas 5.0 x 10(12) Pb-ionS/cm(2) irradiation could,create double peaks of light emissions at about 2.23 and 2.83 eV. There is no observable PL peak in the 1.2 x 10(18) carbon-ions/cm(2) implanted samples whether it was irradiated with Pb ions or not. All these results implied that special light emitters could be achieved by using proper ion implantation and irradiation conditions, and it will be very useful for the synthesis of new type Of SiO2-based light-emission materials.

Structural modification of C-doped SiO2 induced by swift heavy ion irradiations

Thermally grown amorphous SiO2 samples were implanted at room temperature (RT) with 120 keV C-ions to a dose ranging from 1.0 x 10(16) to 8.6 x 10(17)C ions/cm(2), then irradiated at RT with 950 MeV Pb, 345 or 1754 MeV Xe ions to a fluence in the region from 1.0 x 10(11) to 3.8 x 10(12) ions/cm(2), respectively. The irradiated samples were investigated using micro-FTIR and micro-Raman spectroscopes. It was found that new chemical bonds such as Si-C, C=C(O), C C and Si(C)-O-C bonds formed significantly in the C-doped SiO2 films after heavy ion irradiations. The evolution of Si-O-C bonds and possible mechanism of structural modification in C-doped SiO2 induced by swift heavy ion irradiations were discussed.

Study on Er3+ emission from the erbium-doped hydrogenated amorphous silicon suboxide film

The erbium-doped hydrogenated amorphous silicon suboxide films containing amorphous silicon clusters were prepared. The samples exhibited photoluminescence peaks at around 750 nm and 1.54 mum, which could be assigned to the electron-hole recombination in amorphous silicon clusters and the intra-4f transition in Er3+, respectively. Correlations between the intensities of these two photoluminescence peaks and oxidation and dehydrogenation of the films during annealing were studied. It was found that the oxidation is triggered by dehydrogenation of the films even at low annealing temperatures, which decisively changes the intensities of the two photoluminescence peaks. On the other hand, the increase of Er content in the erbium-doped hydrogenated amorphous silicon suboxide film will enhance Er3+ emission at 1.54 mum, while quench amorphous silicon cluster emission at 750 nm, such a competitive relationship, was also observed in the erbium-doped silicon nanocrystals embedded in SiO2 matrix. Moreover, we found that Er3+ emission is not sensitive to whether silicon clusters are crystalline or amorphous. The amorphous silicon clusters can be as sensitizer on Er3+ emission as that of silicon nanocrystals. (C) 2003 American Institute of Physics.

Investigation of absorption of nanocrystalline silicon

Nanocrystalline silicon embedded SiO2 matrix is formed by annealing the SiO2 films fabricated by plasma enhanced chemical vapor deposition technique. In conjunction with the micro-Ramam spectra, the absorption spectra of the films have been investigated. The blue-shift of absorption edge with decreasing size of silicon crystallites is due to quantum confinement effect. It is found that nanocrystalline silicon is of an indirect band structure, and that the absorption presents an exponential dependance absorption coefficient on photon energy ii! the range of 2.0-3.0 eV, and a sub-band appears in the the range of 1.0-1.5 eV. We believe that the exponential absorption is due to the indirect band-to-band transition of electrons in silicon nanocrystallites, while the Sub-band absorption is ascribed to transitions between the amorphous silicon states existing in the films.

Essential and Non-Essential Work of Fracture of PI/SiO2 Hybrid Thin Films

Essential work of fracture (EWF) analysis is used to study the effect of the silica doping level on fracture toughness of polyimide/silica (PI/SiO2) hybrid films. By using double-edge-notched-tension (DENT) specimens with different ligament lengths, it seems that the introduction of silica additive can improve the specific essential work of fracture (w (e) ) of PI thin films, but the specific non-essential work of fracture (beta w (p) ) will decease significantly as the silica doping level increasing from 1 to 5 wt.%, and even lower than that of neat PI. The failure process of the fracture is investigated with online scanning electron microscope (SEM) observation and the parameters of non-essential work of fracture, beta and w (p) , are calculated based on finite element (FE) method.

Optical transmission larger than 1 (T > 1) through ZnS-SiO2/AgOx/ZnS-SiO2 sandwiched thin films

Optical transmission through flat media should be smaller than 1. However, we have observed optical transmission up to T=1.18. The samples were ZnS-SiO2/AgOx/ZnS-SiO2 sandwiched thin films on glass substrate. The supertransmission could only be observed in the near field. We attribute the supertransmission to the lateral propagation relayed by the laser activated and decomposed Ag nanoparticles. (c) 2006 American Institute of Physics.

The study on the interface adhesion comparison of the MgF2, Al2O3, SiO2 and Ag thin films

Adhesion between the interface of pure silver thin film and three kinds of low refractive index coatings MgF2, Al2O3, SiO2 were compared in this article. The results indicated that the adhesion of Al2O3 and Ag was evidently superior to that of MgF2 and Ag, and the adhesion of MgF2 and Ag was evidently superior to that Of SiO2 and Ag. Reasons were analyzed accordingly. On the other hand, we compared the effect on the optical characteristic of Ag film when these three kinds of films were used as protective coatings and enhanced coatings. Considering the difference of the adhesion between Ag and MgF2, Al2O3, SiO2, suited uses are given for each other. © 2004 Elsevier B.V. All rights reserved.