Papers by Author: Satoshi Yamasaki

Abstract: The long-term reliability of Schottky pn diodes (SPNDs) on diamond having widely used Ti/Pt/Au electrodes was investigated at 500°C in order to identify degradation phenomena at higher temperatures. A vital degradation event was observed after the passage of about 100 hours in that both forward and reverse currents were progressively reduced. AES depth profiling and X-STEM-EELS analyses revealed that this occurred because the Ti contact material changed to insulating (or semiconductive) TiO₂, causing large series resistance.

Abstract: A new rectifier, called SPND or SNPD (Schottky-PN or -NP junction diode) and inherently showing low on-resistance and unipolar operation, was experimentally demonstrated for the first time on 4H-SiC. It is structured with an n^– or a p^– region of very low doping that is sandwiched and completely depleted between a Schottky junction and a one-sided PN junction. Either electrons or holes, but not both, contribute to the current conduction process. Clear and sharp rectifying properties are observed over the entire range of applied voltage.

Abstract: Calculations of lattice constant of 4H-SiC and diamond have been carried out. Lattice constant of 4H-SiC trends to decrease when nitrogen concentration increases. On the other hand, lattice constant of 4H-SiC trends to increase when aluminum concentration increases. Lattice constant of boron and phosphorus doped diamond trends to increase when impurity concentration increases. The effect of phosphorus on diamond lattice constant is about six times larger than that of boron.

Abstract: Shallow N donors in n-type 4H-SiC were studied by electron paramagnetic resonance (EPR) and electron nuclear double resonance (ENDOR). For the N donor at the cubic site (Nk) in 4H-SiC, the hyperfine (hf) constants of the interaction with the nearest neighbour (NN) 29Si atom along the c axis were determined as A = 41.07 MHz and A^ = 41.31 MHz. For other three NN Si atoms in the basal plane, the hf tensor has C1h symmetry and the principal values Axx = 5.94 MHz, Ayy = 5.06 MHz and Azz = 14.25 MHz. Our EPR and ENDOR observations unambiguously confirm that the N donor occupies the C site in 4H-SiC lattice and also reveal a considerable amount of the spin density of Nk (~23.9%) which was not obtained in previous studies.