Synchrotron white-beam X-ray topography studies, in conjunction with Nomarski optical microscopy, have been carried out on 6H-SiC single crystals grown by the sublimation physical vapour transport technique. Two kinds of dislocations were observed using topography: dislocations exhibiting bimodal images of various widths and with line directions approximately parallel to the (0001) axis and dislocations confined to the basal plane, which appear to have emanated from the former dislocations. The larger bimodal image width dislocations were found to have hollow cores, known as 'micropipes'. Detailed contrast analysis of topographic images obtained in transmission and back-reflection geometries establishes that 'micropipes' are Frank-type hollow-core screw dislocations with Burgers vectors typically equal to 3-7 times the c lattice parameter. X-ray topography also revealed many line defects approximately parallel to the (0001) axis that were determined to be screw dislocations with Burgers vectors equal to the c lattice parameter and there were no discernible 'micropipes' associated with these latter screw dislocations.

Correlation between morphological defects, electron beam-induced current imaging, and the electrical properties of 4H-SiC Schottky diodes J. Appl. Phys. 97, 013540 (2005); 10.1063/1.1829784 X-ray photoelectron spectroscopy study of the heating effects on Pd/6H-SiC Schottky structure Analytic calculations of electron transport across a Schottky barrier in 6H-silicon carbide are presented. The treatment includes the effect of barrier height fluctuations and image charge lowering on both the thermionic emission and electron tunneling processes. The results show that barrier height inhomogeneities are very important, and can lead to reverse current densities that are orders of magnitude higher than obtained from a simple theory. Formation of detrimental filamentary currents are predicted. The results are in very good agreement with published experimental data at 300 K. Finally, under forward biasing conditions, the analytical theory yields ideality factors of 1.037 in close agreement with measurements.

Calculations of the electronic mobility and drift velocity have been carried out for bulk GaN and AlGaN–GaN heterojunctions based on a Monte Carlo approach. The bulk calculations were intended to serve as a validity check of the simulation model. For the heterojunction electron mobility calculations, polarization effects, degeneracy, and interface roughness scattering were all taken into account. Degeneracy is shown to play an important role, especially at large gate bias. Very good agreement with available experiments has been obtained, and yields a set of best-fit transport parameters. Our results underscore the dominance of interface roughness scattering, and demonstrate that a parameterized model based on weak-perturbation, Born approximation theory can yield sufficiently accurate results.

The temperature dependent thermal conductivity of silicon carbide has been calculated taking into account the various phonon scattering mechanisms. The results compared very well with available experimental data. The inclusion of four-phonon processes is shown to be necessary for obtaining a good match. Several important phonon scattering parameters have been extracted in this study. Dislocations are shown to have a strong effect at 300 K, but not as much at the higher temperatures.

No abstract

We report the observation of anomalous reverse breakdown behavior in moderately doped (2-3x 1017 cm -3) small-area micropipe-free 4H-and 6H-SiC pn junction diodes. When measured with a curve tracer, the diodes consistently exhibited very low reverse leakage currents and sharp repeatable breakdown knees in the range of 140-150 V. However, when subjected to single-shot reverse bias pulses (200 ns pulsewidth, 1 ns risetime), the diodes failed catastrophically at pulse voltages of less than 100 V. We propose a possible mechanism for this anomalous reduction in pulsed breakdown voltage relative to dc breakdown voltage. This instability must be removed so that SiC high-field devices can operate with the same high reliability as silicon power devices.[S0021-8979(96)06114-2]

No abstract

No abstract