Richard Nader

Effect of introducing gettering sites and subsequent Au diffusion on the thermal conductivity and the free carrier concentration in n-type 4H-SiC

We report on the application of introducing gettering sites by helium implantation prior to an annealing and subsequent gold diffusion as an approach to control the thermal conductivity and the charge carrier concentration in n-type 4H-SiC. Rutherford backscattering spectroscopy showed high diffusion of gold impurities to the introduced gettering sites which implied a success in introducing gettering sites. Data obtained from the measurements of the specific heat, thermal diffusivity, and room temperature density were used to deduce the thermal conductivity of the samples investigated. The thermal conductivity modeling showed that introducing gettering sites can increase the thermal conductivity in n-type 4H-SiC due to the reduction of phonon-impurity scattering. Raman measurements showed the presence of the desired defects introduted by ion implantation at 20°C. The analysis of the Fourier transform infrared reflectivity showed that the gettering sites can act as majority carrier traps and reduce the rec...

Tuning Residual Stress in 3C-SiC(100) on Si(100)

Germanium modified silicon surfaces in combination with two step epitaxial growth technique consisting in conversion of the Si(100) substrate near surface region into 3C-SiC(100) followed by an epitaxial growth step allows the manipulation of the residual strain. The morphology and the residual strain in dependence on the Ge coverage are only affected by the Ge quantity and not by the growth technique. The positive effect of the Ge coverage is attributed to changes in the morphology during the conversion process, as well as to a reduced lattice and thermal mismatch between SiC and Si in consequence of alloying the near surface region of the Si substrate with Ge.

SiC Polytype Stability Influenced by Ge Impurities

In this paper we present a methodology to affect the stability of polytypes formation during heteroepitaxial growth of SiC on Si. This methodology is based on the investigation of growth related parameters. These parameters involve substrate temperature, effect of impurities on surface diffusion, strain, and super-saturation conditions as solved by using SSMBE growth (Solid Source molecular beam epitaxy).

Direct mathematical method for calculating the photofraction and intrinsic efficiency of 4πNaI(Tl) borehole cylindrical detectors

Abstract A direct mathematical method for calculating the photofraction and intrinsic efficiency of a borehole cylindrical detector is derived using a direct mathematical method. This method depends on the photon path length inside the detector active volume and the geometrical solid angle Ω subtended by the source to the detector. The comparisons with the experimental and Monte Carlo method data reported in the literature indicated that the present method is useful in the efficiency calibration of the borehole detector.

Quantitative Evaluation of Strain in Epitaxial 2H-AlN Layers

To improve the quality of AlN layer deposit on SiC/Si, different Ge amounts (0.25, 0.5, 1, 2ML) were deposited before the carbonization process at the silicon substrate in order to reduce the lattice parameters mismatch between Si and SiC grown layers. The residual stress of the hexagonal AlN layers derives from the phonon frequency shifts of the E1(TO) phonon mode. The crystalline quality of the AlN layer is correlated to and investigated by the full width of the half maximum (FWHM) and the intensity of E1(TO) mode of the 2H-AlN. Best crystalline quality and lower stress value are found in the case where 1ML of Ge amount is predeposited. The E1(TO) mode phonon frequency shifts-down by 3 cm-1/GPa with respect to an unstrained layer.