Lyle Patrick

Localized vibrational modes of a persistent defect in ion-implanted SiC☆

Abstract The low-temperature luminescence spectrum of an intrinsic defect in ion-implanted cubic SiC reveals a number of high-energy localized modes. One has an energy of 164·7 meV, equivalent to the highest lattice frequency in diamond, and far above the 120·5 meV lattice limit of SiC. A carbon di-interstitial is a plausible model for the defect, which appears after a 1300°C anneal, and persists after a 1700°C anneal.

Refractive Index and Low-Frequency Dielectric Constant of 6H SiC

The ordinary refractive index of 6H SiC has been measured from 2.43 μ (0.51 eV) to 0.336 μ (3.69 eV), using the transmission interference fringes of thin plates. Thibault’s data in the visible were used to normalize the dispersion curve. The index goes from 2.530 at 0.51 eV to 2.868 at 3.69 eV. The residual-ray and interband contributions to the index are evaluated. The extrapolated interband index plus residual-ray contribution yield a low-frequency dielectric constant of 9.8, compared with a measured 10.2. As possible reasons for the disagreement, four allowed but unreported infrared transitions are considered.

Electron Mobilities in SiC Polytypes

Electron‐scattering mechanisms in SiC polytypes are discussed. It is shown that the mechanism which limits mobility from 300° to 800°K in n‐type SiC is probably intervalley scattering (in relatively pure samples). The dependence of electron mass on polytype enables one to study the scattering mechanisms by a comparison of Hall mobilities in two polytypes.

High Electron Mobility of Cubic SiC

The high mobility of electrons in cubic SiC is shown to be due to selection rules which severely restrict intervalley scattering. Only longitudinal acoustic (LA) phonons are permitted, and these have such a high energy (79.4 meV) that they are unimportant at room temperature. On the other hand, electron mobility in the common SiC polytypes, 6H and 15R, is limited by intervalley scattering.

Magneto-Optical Measurements on H-Implanted 6H SiC

Magneto-optical measurements were made at 4.2°K on two kinds of luminescence spectra found in H-implanted 6H SiC. Both spectra are attributed to the same center, an H atom bonded to a C atom at a Si vacancy. One spectrum (called secondary) is due to exciton recombination at a charged center, and its magnetic response is explained by effective-mass theory with gh = 2.8 and ge = 1.8. The other spectrum (called primary) is due to recombination of an exciton strongly bound to the neutral center. Its magnetic splittings are explained by a strong-exchange model, with a singlet level 6.5 meV above the triplet level.

DEPENDENCE OF PHYSICAL PROPERTIES ON POLYTYPE STRUCTURE

ABSTRACT The physical properties of SiC are classified according to the degree of their dependence on polytype. The relationship of polytype dependence to wave-vector dependence is explained, and is illustrated by a number of examples. The correlation of polytype properties with hexagonality is also considered.