Probing spatial heterogeneity in silicon thin films by Raman spectroscopy

Abstract

Raman spectroscopy is a powerful technique for revealing spatial heterogeneity in solid-state structures but heretofore has not been able to measure spectra from multiple positions on a sample within a short time. Here, we report a novel Raman spectroscopy approach to study the spatial heterogeneity in thermally annealed amorphous silicon (a-Si) thin films. Raman spectroscopy employs both a galvano-mirror and a two-dimensional charge-coupled device detector system, which can measure spectra at 200 nm intervals at every position along a sample in a short time. We analyzed thermally annealed a-Si thin films with different film thicknesses. The experimental results suggest a correlation between the distribution of the average nanocrystal size over different spatial regions and the thickness of the thermally annealed a-Si thin film. The ability to evaluate the average size of the Si nanocrystals through rapid data acquisition is expected to lead to research into new applications of nanocrystals.

Structural analysis of sputtered amorphous silica thin films: A Raman spectroscopy investigation

“…For film structure investigation, thick films up to the micrometer scale allowing depth profile with confocal Raman microscopy [36]- [37] or materials with a high Raman cross-section are mostly investigated to get an exploitable Raman signal [38]- [39]- [40]. For instance, this technique is frequently used to investigate amorphous thin films with high-intensity Raman answer, in particular silicon, carbon [40]- [41]- [42]- [43] and chalcogenides [44]- [45]. For thin films (<1 µm), specific substrates (fluorides) with a low Raman background signal can be used [46]- [47] and, in some specific cases, surface-enhanced Raman scattering has a beneficial influence on the thin film signal intensity [48]- [49].…”

Thermal conductivity characteristics in polycrystalline silicon with different average sizes of grain and nanostructures in the grains by UV Raman spectroscopy

“…The calculated power density was 1.27 mW μm −2 at 1 mW. For the nanostructure size measuring, the combination of a quasi-line excitation source obtained with a galvano-mirror and a two-dimensional charge-coupled device (CCD) detector system was used 19,27,28) to obtain both spatial and energy information simultaneously using a two-dimensional CCD pixel array. Thus, we can obtain 512 spectra at 200 nm intervals.…”

“…The accuracy of this measurement was compared with that of X-ray diffraction and showed good agreement in general. 19) For the thermal conductivity measurement, the laser-power was controlled by a variable neutral density filter in the incident light path. The exposure time of the UV excitation light was 30 s. Laser-power was measured at the poly-Si sample using a laser-power meter to avoid the damage on the poly-Si from laser heating.…”

“…In the process, it was confirmed that nanocrystals were generated in the grains of the poly-Si thin films. We called the nanocrystals as "nanostructures'' 19) and considered that these nanostructures could also be phonon scatters. In this study, we focused on the "nanostructures" inside the grains and tried to evaluate the thermal conductivity characteristics.…”

Evaluation of Thermal Conductivity Characteristics in Polycrystalline Silicon - The Effect of Nanostructure in the Grains

“…The laser spot size used was approximately 1 m with calculated power density of 1.27 mW/ m 2 at 1 mW. For the nanostructure size evaluation, the combination of a quasi-line excitation source obtained with a galvanomirror and a two-dimensional charge-coupled device (CCD) pixel array detector system was used (17)(18)(19) to obtain both spatial and energy information simultaneously. Thus, we can obtain 512 spectra at 200 nm intervals simultaneously.…”