Impacts of extended defects on performance and reliability of SiC power devices are reviewed. Threading dislocations in the state-of-the-art SiC wafers do not work as the major leakage paths and ...macroscopic defects generated during epitaxial process are more harmful. A basal plane dislocation is a killing defect in SiC bipolar devices because a Shockley-type stacking fault (SSF) is expanded from the dislocation when the electron-hole recombination energy is given. After classification of SSF-expansion patterns, the major types of SSFs (triangular-shaped and bar-shaped SSFs) and their origins are identified. Based on these understandings, two approaches to eliminate the "bipolar degradation" in SiC devices are presented. In particular, it is demonstrated that a "recombination-enhancing layer" is effective for substantial reduction of bipolar degradation in SiC devices.
The impact of how to model phonon scattering on hole transport in Si nanowires was studied based on Boltzmann's transport equation. Boundary conditions for atomistic description of phonons in ...nanowires and approximation by bulk acoustic and optical phonons were analyzed in terms of their impacts on high-field hole transport. The boundary conditions for phonons influence the drift velocity and momentum relaxation time, especially at low electric field, but the energy relaxation time hardly depends on the boundary conditions. The impacts by the change of boundary conditions can be approximated by the change of the strength of acoustic phonon scattering in bulk phonon picture, though the behavior of energy relaxation and distribution function of holes can not be reproduced by bulk phonon approximation.
The electronic properties and formation energy of isolated Cl defects in SiC were investigated by first-principles calculations. Chlorine was studied in a substitutional position, in either a carbon ...(Cl(C)) or a silicon site (Cl(Si)), and in two interstitial positions (Cl(i)), either tetrahedral or octahedral configurations. Our calculations revealed that Cl(C) is energetically favored and it is a likely candidate to explain the nature of the experimentally observed Cl incorporation reported in SiC epilayers grown by chloride-based chemical vapor deposition.
Effects of surface defects on performance of kV-class 4H- and 6H-SiC epitaxial p-n junction diodes were investigated. The perimeter recombination and generation, instead of the bulk process, are ...responsible for forward recombination current and reverse leakage current of the diodes, respectively. Mapping studies of surface morphological defects have revealed that triangular-shaped defects severely degrade high-blocking capability of the diodes whereas shallow round pits and scratch give no direct impact. Device-killing defects in SiC epilayers are discussed based on breakdown voltage mapping. Effective minority carrier lifetimes are mainly limited not by bulk recombination but by perimeter recombination.
Hybrid density functional theory was employed in investigating the structural and electronic properties of 14 chiral and 3 armchair SiC nanotubes (SiCNTs). The role of the tube diameter, as well as ...that of the chiral angle theta, was studied in detail by considering nanotubes of diameters varying from 2 to 9 A and chiral angles theta varying between 7 degrees and 30 degrees. The study revealed that all the investigated SiCNTs are semiconductors with a broad spectrum of bandgap values ranging from 0.2 to 2.9 eV and that the structural stability of the nanotubes increases with diameter. By analyzing the behavior of the molecular orbitals, an explanation of the mechanism by which theta affects the determination of such values is put forward.
A novel calamitic mesophase semiconductor based on symmetrically designed thiophene–naphthalene, 2,6‐di(5′‐n‐octyl‐2′‐thienyl)naphthalene, is used as the active layer in a field‐effect transistor and ...the device performance is studied (see figure). This mesogen has an excellently high mobility of 0.14 cm2 V–1s–1 in a polycrystalline film at room temperature.
Hippocampal pyramidal neurons and granule neurons of adult male rats are equipped with a complete machinery for the synthesis of pregnenolone, dehydroepiandrosterone, testosterone, ...dihydrotestosterone and 17β-estradiol. Both estrogens and androgens are synthesized in male hippocampus. These brain steroids are synthesized by cytochrome P450s (P450scc, P45017α and P450arom), hydroxysteroid dehydrogenases and reductases from endogenous cholesterol. The expression levels of enzymes are as low as 1/300–1/1000 of those in endocrine organs. Synthesis is dependent on the acute Ca
2+ influx upon neuron–neuron communication via NMDA receptors. Estradiol is particularly important because estradiol rapidly modulates neuronal synaptic transmission such as long-term potentiation via synaptic estrogen receptors. Xenoestrogens may also act via estrogen-driven signaling pathways.
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