N. Piluso

Defect Influence on Heteroepitaxial 3C-SiC Young’s Modulus

Heteroepitaxial cubic silicon carbide (3C-SiC) is an extremely promising material for micro- and nano-electromechanical systems due to its large Young’s modulus. Unfortunately, the heteroepitaxy of 3C-SiC on Si substrate is affected by the high mismatch in the lattice parameters and the thermal expansion coefficients between the two dissimilar materials that generate a high number of defects in the material. In this work, through the measurement of natural resonant frequencies and Raman shift analysis, a strong relationship between the mechanical proprieties of the material (Young’s modulus) and the film crystal quality (defect density)

3C-SiC Film Growth on Si Substrates

The aim of this work is to give an overview on 3C-SiC growth on Si substrates. Starting from the reasons why SiC is considered such an interesting innovative material, with a survey of application already demonstrated, we will present data explaining the most important issues in this hetero-epitaxy system and how the chemical vapor deposition process influences the resulting 3C-SiC film properties. 3C-SiC crystal structure is strongly dependent on the process parameters within the reaction chamber during growth as well as the substrate surface properties. Part of this work is then focused on the main crystallographic defects characterizing the 3CSiC/Si system and on the resulting wafer bow due to the large misfit between the materials. Defects and wafer bow, are a direct consequence of the large stress generated at the interface. The work closes discussing the encouraging improvements in 3C-SiC crystal quality obtained by the introduction of compliant Si substrates.

Optical investigation of bulk electron mobility in 3C–SiC films on Si substrates

The dependence between the carrier concentration and electrical mobility has been studied by micro-Raman spectroscopy in n-doped 3C–SiC films grown on (111) and (100) Silicon oriented substrates. Bulk mobility varies between 10 and 510 cm2 V−1 s−1 for a carrier concentration ranging between 1.6×1016 and 5.4×1018 cm−3. Local stacking variations observed on the (111) 3C–SiC surface lead to a worse crystal morphology compared to (100) 3C–SiC films resulting in a decrease in the average bulk mobility. Defects are thus accountable for the dependence between mobility and carrier concentration for different 3C–SiC orientations.

A novel micro-Raman technique to detect and characterize 4H-SiC stacking faults

A novel Micro-Raman technique was designed and used to detect extended defects in 4H-SiC homoepitaxy. The technique uses above band-gap high-power laser densities to induce a local increase of free carriers in undoped epitaxies (n < 1016 at/cm−3), creating an electronic plasma that couples with the longitudinal optical (LO) Raman mode. The Raman shift of the LO phonon-plasmon-coupled mode (LOPC) increases as the free carrier density increases. Crystallographic defects lead to scattering or recombination of the free carriers which results in a loss of coupling with the LOPC, and in a reduction of the Raman shift. Given that the LO phonon-plasmon coupling is obtained thanks to the free carriers generated by the high injection level induced by the laser, we named this technique induced-LOPC (i-LOPC). This technique allows the simultaneous determination of both the carrier lifetime and carrier mobility. Taking advantage of the modifications on the carrier lifetime induced by extended defects, we were able to ...

Fracture property and quantitative strain evaluation of hetero-epitaxial single crystal 3C-SiC membrane

The following paper explores the development of a combined bulge test/micro-Raman analysis. This analysis, together with a refined load-deflection model (valid in both small and large deformation regimes, defined as the regimes in which the ratio between membrane deflection and width is smaller or larger than 1:10), allowed the determination of the elastic and optical properties of high quality single-crystal 3C-SiC squared membranes. Specifically we have evaluated the breaking strain of the membranes by measuring the breaking pressure for various membrane widths. The relation between the shift of the Raman Transverse Optical (TO) mode and the total residual strain (Δa/a) has been determined by measuring the TO shift for different membrane deflections. This relation, which allows determination of the residual strain by simply measuring the TO shift, was known only for thick samples (Olego et al) and high-oriented (100) thin films (Rohmfeld et al). Finally, we have calculated the TO stress-free value of high-quality thin single-crystal 3C-SiC/Si(100) films as 796.71 ± 0.04 cm−1.

Optical characterization of bulk mobility in 3C‐SiC films grown on different orientation of Si substrates

Raman microscopy has been used to study the carrier concentration and mobility in n‐doped 3C‐SiC epilayers grown on different silicon substrates, namely (100) Si and (111) Si on axis and off‐axis towards the [110] direction. By analyzing the longitudinal optical phonon‐plasmon coupled mode (LOPC), we were able to estimate the 3C‐SiC electron bulk mobility (μ) within the range between 5 and 500 cm2/Vs. The carrier concentration (n) was ranging from 2×1016 to 6×1018 cm−3. The observed trend shows a reduction in the electron mobility as the carrier concentration increases for films grown on any substrate considered, accordingly to the existent theory. For equal values of doping concentration, 3C‐SiC epitaxial films grown on (100) Si substrates show a higher mobility than films grown on (111) Si counterparts. This could be ascribed to a higher defect density in (111) Si samples. A deeper characterization by performing Raman maps shows a broadening and a splitting of the 3C‐SiC transverse optical (TO) peaks fo...