Determining the crystalline degree of silicon nanoclusters/SiO2 multilayers by Raman scattering

Abstract

We use Raman scattering to investigate the size distribution, built-in strains and the crystalline degree of Si-nanoclusters (Si-nc) in high-quality Si-rich oxynitride/SiO 2 multilayered samples obtained by plasma enhanced chemical vapor deposition and subsequent annealing at 1150 C. An initial structural characterization of the samples was performed by means of energy-filtered transmission electron microscopy (EFTEM) and X-ray diffraction (XRD) to obtain information about the cluster size and the presence of significant amounts of crystalline phase. The contributions to the Raman spectra from crystalline and amorphous Si were analyzed by using a phonon confinement model that includes the Si-nc size distribution, the influence of the matrix compressive stress on the clusters, and the presence of amorphous Si domains. Our lineshape analysis confirms the existence of silicon precipitates in crystalline state, in good agreement with XRD results, and provides also information about the presence of a large compressive stress over the Si-nc induced by the SiO 2 matrix. By using the Raman spectra from low temperature annealed samples (i.e., before the crystallization of the Si-nc), the relative scattering cross-section between crystalline and amorphous Si was evaluated as a function of the crystalline Si size. Taking into account this parameter and the integrated intensities for each phase as extracted from the Raman spectra, we were able to evaluate the degree of crystallization of the precipitated Si-nc. Our data suggest that all samples exhibit high crystalline fractions, with values up to 89% for the biggest Si-nc. The Raman study, supported by the EFTEM characterization, indicates that this system undergoes a practically abrupt phase separation, in which the precipitated Si-nanoclusters are formed by a crystalline inner part surrounded by a thin amorphous shell of approximately 1-2 atomic layers. V

Structural parameters effect on the electrical and electroluminescence properties of silicon nanocrystals/SiO2 superlattices

“…t SiO2 is reduced) results in an increasing interaction of the carrier wavefunctions that leads to a current increase. It is also remarkable that similar J(V) curves were obtained for ), taking into account the formalism described in [10]. The error bars account for a 2% fitting uncertainty of the Raman spectra.…”

“…The resulting Raman spectra acquired for the different sets of devices are displayed in figures 2(a) and (b). The spectra exhibit three main features: (i) a sharp peak around 517 cm −1 corresponding to the crystalline Si TO-LO mode, (ii) a broad shoulder growing at lower frequencies than the crystalline peak, coming from the amorphous Si phases present within the SL, and (iii) an overall background ascribed to disorder-activated SiO 2 or acoustic amorphous Si modes [10,11]. Looking at figure 2(a), which shows the spectra corresponding to devices with different barrier thickness, no obvious variation exists when decreasing t SiO2 .…”

“…The structural and optical properties from Si NCs have been extensively studied in the past, as a function of the nanostructure size and the stoichiometry of the Si-rich layers, with the nanostructures embedded either in bulk matrix [8,9] or in conveniently arranged ensembles (SL structures) [7,10,11]. The assessment of the electrical behavior of NCs is more complex, requiring the deposition of metallic contacts to design a metal-oxide-semiconductor (MOS) device, for instance, which allows for a proper charge injection and extraction.…”

Optical emission fromSiO2-embedded silicon nanocrystals: A high-pressure Raman and photoluminescence study

“…In both figures we have also included Raman spectra corresponding to the as-grown structures outside the DAC, before the mechanical polishing of the substrates. The ambient-pressure Raman spectra of these Si NCs have been discussed in detail elsewhere [20]. In Fig.…”

“…In this way, Si NCs of average sizes L = 4.1 and 3.3 nm as determined by transmission electron microscopy (see Ref. [20] for details) were precipitated in samples A and B, respectively. Further details of the sample preparation can be found in Ref.…”