Papers by Keyword: Si Nanocrystals

Abstract: In this work, Hydrogenated silicon rich nitride (SRN) films were deposited by varying NH3/SiH4 ratio and thermally annealed within the temperature range of 700-1000 °C in N2 ambient to precipitate silicon nanocrystals in the film. The optical and structural properties of SiNx:H films were studied. Chemical composition and structural investigations were performed by Secondary ion mass spectrometry (SIMS), Infrared and Raman spectrometry experiments.Fourier Transform Infrared Spectroscopy (FTIR) indicates a new band which appeared as a “shoulder” in the 850-900 cm−1 range and is attributed to a reordering in the films towards an increased SiN4 bonding configuration resulting from the precipitation of silicon nanocrystals.The Raman analysis clearly evidences a high density of Si nanoclusters as shown by the broadened and asymmetric Raman peak approaching 520 cm-1.Strong visible photoluminescence (PL) can be observed in silicon nitride and the evolution of the photoluminescence with annealing temperature is correlated to the evolution of the structure. Radiative defects in the films and the quantum confinement effect in silicon nanoparticles were proposed to explain the origin of light emission from the samples.

Abstract: The effect of annealing temperature on the properties of c-Si wafer/SiO_x interface (x = 1.15 and 1.3) is studied by Transmission Electron Microscopy and Capacitance/Conductance-Voltage measurements. Furnace annealing for 60 min at 700 and 1000 °C is used to grow amorphous or crystalline Si nanoparticles. The high temperature process leads to an epitaxial overgrowth of the Si wafer and an increase of the interface roughness, 3-4 monolayers at 700 °C and 4-5 monolayers at 1000 °C. The increased surface roughness is in correlation with the higher density of electrically active interface states.

Abstract: Metal-Oxide-Semiconductor structures with semitransparent Au top electrode and containing Si nanocrystals in the gate dielectric are fabricated and studied. The structures can be charged negatively or positively by injecting or extracting electrons from the top electrode. Illumination with 395-400 nm, 10.4 mW UV light source causes discharge of previously charged structures with rate which varies between 2 mV/s and 12 mV/s. The discharge rate depends on the sign of the trapped charge, as well on the internal electric field in the gate dielectric.

Abstract: Er-dispersed silicon-rich silicon oxide (SRSO:Er) films have been fabricated by pulsed laser ablation technique. After deposition, the films were annealed in Ar ambient at different temperatures for 30 min to generate SiO₂ films containing Si nanocrystals (Si-nc) and Er ions. The relationship between Er photoluminescence (PL) intensity and annealing temperature was investigated by PL spectrums analysis at room temperature. Transmission Electron Microscopy (TEM) and Energy Dispersive X-ray Spectrometer (EDS) were used to observe the samples. Experimental results show that high-density Si-nc generate when the annealing temperature increases to 1000°C, however, PL intensity of Er decreases due to Er atoms segregated out in SiO₂ film and formed large particles.

Abstract: Silicon substrates were implanted with Si ions at an energy of 60 keV to a dose of 5×10¹⁵ cm^-2 followed by a thermal annealing at various temperatures up to 950 oC. Photoluminescence (PL) and infrared absorption (IRA) techniques have been used to characterize these samples. The PL peak positions at 2.07 eV and 1.93 eV undergo redshifts with the increasing annealing temperature. The two IRA peaks at 1080 cm^-1 and 800 cm^-1 are ascribed to the Si-O-Si asymmetric stretching and the Si-O bending vibration, respectively. The experimental results indicate that Si nanocrystals embedded in silicon oxide layer can be formed at the annealing temperature 800 oC or higher.

Abstract: Metal-Oxide-Semiconductor structures with silicon nanocrystals in the oxide layer are prepared and characterized by Transmission Electron Microscopy and electrical measurements. High temperature annealing of SiO_1.15 films at 1000 °C for 30 or 60 min leads to formation of silicon nanocrystals with diameters of 2-3 or 4-6 nm. The processes used to obtain the multilayer gate dielectric and to grow nanocrystals do not deteriorate the properties of the cSi wafer/thermal SiO₂ interface. For the interface defect density and the fixed oxide charge values 10¹⁰ cm^-2 eV^-1 and ~ 10¹⁰ cm^-2 were obtained.

Abstract: A physical picture of swift heavy ion irradiation effects on ensembles of silicon nanocrystallites (NCs) embedded in a dielectric SiO₂ matrix is given following our study of the experimental investigation of structural, electrical and photoluminescence properties of that system We found that ion irradiation can drastically change the structure of the layer by forming an ordered NC chains along the ion tracks in the 400-1000 nm thick layer. The ion energy and dose are then the main tools for functionalization of our system, from changing the size and the concentration of the NCs, to managing the optical and electrical properties.

Abstract: In the Current Study, the Structural Characteristics of Siox Thin Films Grown by Magnetron Sputtering on Si Substrates Are Reported. High Resolution Transmission Electron Microscopy Revealed the Formation of Amorphous Siox Films for the as-Deposited Samples, as Well as the Ones Annealed in Ambient Air for 30 Min at 950oC and of Si Nanocrystals, Embedded in Amorphous Siox, after Ar Annealing for 1-4 Hours at 1000oC. the Nanocrystals, with Sizes up to 6 Nm, Predominately Exhibit {111} Lattice Planes. Energy-Dispersive X-Ray Analysis Showed that the Si/O Ratio Is between 0.5-1, I.e. the Amorphous Films Comprise of a Mixture of Sio2 and Sio. Phase Images and Corresponding Strain Maps Created Using Fourier Filtering Revealed a Uniform Contrast in the Nanocrystals, which Shows that the Si Lattice Constant Does Not Vary Significantly. the Residual Strain Variations, around 4%, May Account for the Possible Existence of a Small Percentage of Highly Disordered Si or Siox Residual Clusters inside the Regular Si Matrix, in Full Agreement with Photoluminescence Measurements Performed on the same Materials.

Abstract: Photoluminescence mechanisms (models) are reviewed and experimental data are analyzed based on our model, related to direct radiative transitions from the second conduction sub-band to the first one.