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Silicon carbide (SiC) powders are studied by current-voltage measurements and the influences of grain size and doping are investigated. The macroscopic current characteristics of green and black SiC powders can be described by the transport mechanisms at the grain contacts and Schottky-like barriers can model the contacts, where the effective barrier height appears to be in the range 0.4-0.5 eV.

The fundamental band gap, the crystal field splitting, the spin-orbit splitting and the effective electron and hole masses in the hexagonal polytypes 2H, 4H, and 6H of SiC have been computed for various lattice constants and basis atom positions. Results indicate that the exact positions of the hexagonal planes have a strong impact on the crystal-field splitting. However, the hexagonal planes have no effect on the band gap, spin-orbit splitting and the effective electron and hole masses.

Research was conducted to calculate the energy shifts of the conduction band minimum and of the valence band maximum as functions of ionized impurity concentration for both n-type and p-type 3C, 2H-, 4H-, 6H-SiC, and Si. The true energy dispersions and overlap integrals were taken into consideration. Results reveal that the nonparabolicity of the valence band curvatures influences the calculated self-energies of the valence band maximum.

Doping-induced band edge displacements and band gap narrowing in both n-type and p-type, 3C-, 4H- and 6H-SiC were modeled for the first time. The models are an extension of the theory presented by Jain and Roulston in 1991 and consider the three different electron effective mass components related to hexagonal lattices. Also, a more extensive analysis of minority carrier correlation energy was conducted, using a two-band model for the dielectric function of a hole gas in the plasmon-pole approximation.

Researchers demonstrate their derivations of the densities of states for hexagonal SiC polytypes 2H, 4H and 6H. The derivations take into account the nonparabolicities of the energy dispersions, the particular structure of the lowest conduction bands in 6H, and the uppermost valence bands of all three hexagonal polytypes. It would be possible to use the derivations in investigations of other materials with energy dispersions which are similar to those of SiC.

A theoretical study helps derive a heat conduction/generation equation for electrical and electrothermal simulation of semiconductors within the drift-diffusion approximation for anisotropic materials. Generalization of heat generation source in the heat conduction equation facilitates the description of anisotropic materials. Extension of the mathematical form of the equations makes them applicable to all semiconductor materials with a Bravais lattice.

Subjection of degenerate heterostructure substrates to general conditions helps derive relations between electron and hole current-density. The general conditions include Fermi-Dirac statistics, conduction band minima, position-dependent band structure and nonconstant temperature. The derivation also involves the determination of electrical boundary conditions at ohmic contacts. Nonisothermal effect on boundary conditions is also specified.

Heat conduction equations for nonisothermal semiconductor device simulations are analyzed using a general heat generation model on cubic semiconductors with position-dependent, multivalley and multiband structures. The model uses Fermi-Dirac statistics to accurately determine electron hole scattering. Boltzmann transport equation forms the basis for the generalization of the model.

Ab initio supercell calculations of cubic inclusions in 6H-SiC are performed. The cubic inclusions can be created in perfect 6H-SiC by the propagation of successive partial dislocations having the same Burgers vector in neighboring basal planes, i.e., multiple stacking faults. We have studied the electronic structures and the total energies of 6H-SiC single crystals that contain one, two, three, and four stacking faults, based on density functional theory in local density approximation. Our total energy calculations have revealed that the second stacking fault energy in 6H-SiC is about six to seven times larger than that of an isolated stacking fault, which is actually opposite the trend recently obtained for 4H-SiC [J. Appl. Phys. 93, 1577 (2003)]. The effects of spontaneous polarization on the electronic properties of stacking disorders are examined in detail. The calculated positions of the quantum-well-like localized bands and stacking fault energies of 3C inclusions in 6H-SiC are compared with those previously determined in 4H-SiC, and the possibility of local hexagonal to cubic polytypic transformations is discussed in light of the formation energy and quantum-well action. © 2003 American Institute of Physics. [ABSTRACT FROM AUTHOR]

In conventional Monte Carlo simulations of electron and hole transport in semiconductors, the possibility of electric-field induced interband transitions between scattering events is not taken into account. In this article we study the effects of interband transitions on the electron (or hole) velocity and on the distance traveled by the charge carrier. The resulting quantum velocity, defined as the expectation value of the velocity operator for a state which is a superposition of Bloch states, contains an average group velocity and a quantum interference term. We calculate these terms for two cases, namely, for a simple parameterized two-band k·p model and for hole motion in wurtzite GaN, and compare with the one-band group velocity used in the conventional Monte Carlo method. The results show that interband transitions around closely spaced energy bands, which may arise in crystals with relatively large unit cells, like wurtzite GaN and hexagonal and rhombohedral SiC polytypes, may have a major effect on the particle velocity and particle trajectory, and therefore constitute a major influence on, for instance, electrical breakdown. [ABSTRACT FROM AUTHOR]

The ohmic transport of holes in p-type Al-doped 4H–SiC samples is investigated using a Monte Carlo tool based on a full-potential band structure. The temperature and doping dependence of the hole mobility and its anisotropy are calculated and discussed from a physical point of view, where we stress the importance of considering two-band conduction. Acoustic and optical phonon scattering, as well as ionized and neutral impurity scattering, have been considered. The Monte Carlo program also considers incomplete ionization of impurity atoms compatible with an Al ionization energy of 0.2 eV. © 2002 American Institute of Physics. [ABSTRACT FROM AUTHOR]

A first-principles study of cubic inclusions and stacking fault (SF)-SF interactions in 6H -SiC, based on density functional theory (DFT) in local density approximation (LDA) is reported. The study confirms that the simple rectangular quantum-well picture can describe the quantum-well (QW)-like features quite well, but the effects of spontaneous polarizations can modify them to some extent.

Calculates the full-potential band structure for the polytypes 3C, 2H, 4H and 6H of silicon carbide. Local density approximation to the density functional theory; Agreement of calculated effective electron masses with experimental values; Estimation of electron-optical phonon coupling; Influence of spin-orbit interaction on the value of the effective hole masses.

Silicon carbide (SiC) powder is used in nonlinear field grading materials. The composite material, consisting of an insulating polymer matrix filled with the SiC-grains, is usually a percolated system with established conducting paths. In order to explain the properties, the electrical characteristic and conduction mechanisms of the SiC powder itself are of interest. SiC powders have been studied by current–voltage measurements and the influences of grain size and doping have been investigated. The macroscopic current characteristics of green and black SiC powders can be described by the transport mechanisms at the grain contacts, which can be modeled by Schottky-like barriers. The SiC is heavily doped and tunneling by field emission is the dominating conduction mechanism over the major part of the nonlinear voltage range. It is suggested that preavalanche multiplication influences the current at the highest voltages, especially for p-type black SiC. © 2001 American Institute of Physics. [ABSTRACT FROM AUTHOR]