Papers by Keyword: Si Nanocrystal

Abstract: X-ray Diffraction and Reflectivity, Transmission Electron Microscopy and Atomic Force Microscopy were applied to study the effect of thermal annealing on the properties of thin SiOx films (~ 15 nm) prepared by thermal evaporation of SiO in vacuum. It has been shown that furnace annealing at 1000 oC causes phase separation and formation of uniformly distributed Si nanocrystals into a SiO2 matrix. Clockwise hysteresis has been observed in the C-V curves measured and explained by assuming charging and discharging of the NCs with carriers, which tunnel from the Si substrate.

Abstract: Photoluminescence (PL) from silicon nanocrystals deposited on top of silica-glass template and from silicon nanocrystals in nc_Si/SiO2 multilayer films were studied as a function of ultraviolet (UV) laser irradiation time in vacuum. Both the films exhibit intense visible PL at room temperature under laser excitation. It was found that upon prolong irradiation time using a He-Cd laser (325 nm) the PL intensity of the films was spectacularly enhanced. The process is reversible and does not happen with excitation wavelength longer than 400 nm. Upon introducing air into the measurement chamber, a rapid decrease of the PL intensity was recorded. This observation suggests that the UV light may lead to modification of nonradiative recombination centers in the films and thus improves the emission yield of silicon nanocrystals.

Abstract: Samples with layer of silicon nanocrystals embedded in SiO2 (the single phase Si content in oxide ranged between 5 and 92 volume %) were subjected to high energy ion implantation. Implantation-induced modifications of SiO2-ncSi properties discussed in this paper include a shift of the major ncSi-related photoluminescence peak and intensification of the high-photon energy peaks, that accompany the change in amount and type of the charge trapped on the nanocrystals. A unified model is suggested for all these phenomena.

Abstract: Silicon suboxide, SiOx thin films with different oxygen contents (1.15≤x≤1.70) were prepared by thermal evaporation of silicon monoxide at a residual oxygen pressure of 1·10-3 Pa and deposition rates of 0.2, 1.0, 3.0 and 6.0 nm/s. Rapid thermal annealing (RTA) of films was carried out at 1100°C in vacuum for 15 and 30 s and the films were analyzed by infrared (FTIR) and photoluminescence (PL) spectroscopy. In the FTIR spectra of SiOx annealed samples, a blue-shift of the stretching band with initial oxygen content, x, is observed. This band is shifted to a much lower frequency with prolonged RTA time. This behavior can be interpreted in terms of the partial decrease of oxygen content and film density upon annealing in vacuum. With annealing time increase a new band at 1106 cm-1 appears. Therefore, infrared spectra of SiOx films are significantly affected by the oxygen content. PL spectra of these films also change drastically with increasing annealing time. In the PL spectra of films annealed for 15 s two bands are easily visible: broad redorange band at 2.2 eV and a green band at 2.4 eV, while for 30 s annealing only low-energy band exists. Green band is connected with the defects in the SiOx matrix while red-orange band can be deconvoluted into several bands at 2.0, 2.3 and 2.5 eV. Two types of defects can be responsible for the PL band at about 2 eV: defects in a-Si (amorphous silicon) nanoparticles separated during RTA, and nonbridging oxygen hole recombination centers (NBOHC) formed by loosing of oxygen during RTA. The PL band at 2.3 eV is associated with the defects formed at a-Si/SiOx interfaces while a hardly visible band at 2.5 eV is related to the defects connected with the oxygen deficiency formed in the SiOx matrix during RTA.

Abstract: Scanning probe microscope (SPM) with a conducting tip was used to electrically probe silicon nanocrystals (Si NCs) embedded in a SiO2 layer. The Si NCs were generated by the laser ablation method with compressed Si powder followed by a sharpening oxidation. The size of Si NCs is in the range of 10-50 nm, and the density is around 1011 /cm2. Using a conducting tip, the charge was injected directly into each Si NC, and the image contrast change and dC/dV curve shift caused by the trapped charges were monitored. The results were compared with those of the conventional MOS capacitor.

Abstract: A quantitative approach to determination of depth profiles of optical properties of Si-implanted SiO2 films based on spectroscopic ellipsometry (SE) is presented. From the SE measurements, the depth profiles of the complex refractive index of SiO2 films containing Si nanocrystals (Si-nc) are obtained with an effective medium approximation (EMA) in the wavelength range of 400-1200nm. The optical profiles obtained imply the existence of a wave-guide in the Si-doped SiO2 films.

Abstract: Laser-induced etching of silicon is used to generate silicon nanocrystals. The pore structure depends on the substrate type and etching laser wavelength. Porous silicon (PS) samples prepared by Nd:YAG laser (1.16 eV) etching of n-type substrate showed a fairly uniform and highly interconnected network of nearly circular pores separated by thin columnar boundaries, while no circular pits were produced by argon- ion laser (2.41 eV) etching under similar conditions. The size and size distribution of the nanocrystals are investigated by Raman and photoluminescence spectroscopies and analyzed within the framework of quantum confinement models.