Anomalous splitting has been observed in the photoreflectance (PR) response of SI:GaAs in the vicinity of the exciton at 78 K. Photoluminescence (PL) measurements suggest the splitting is correlated with the EL2 content of the samples. Separation between the two peaks in PR measurements range from about 2 to 4 meV. A striking effect is that each peak is maximized by a different phase setting of the lock-in. The splitting is sample dependent and is also affected by several other factors including surface conditions, temperature, pump beam intensity, and modulation frequency.

Measurements of the temperature dependence of N‐Al donor‐acceptor pair photoluminescence spectra in cubic SiC films demonstrate that the thermal activation energy for the nitrogen donors is equivalent to the 54 meV binding energy for nitrogen determined from the spectral energies of the sharp‐line close pair spectra. It follows that the 15–20 meV donor which dominates the electrical properties of n‐type films is not isolated, substitutional nitrogen. Spatial variations observed in the intensity of a new 2.368 eV luminescence band demonstrate that the radiative recombination centers are inhomogeneously distributed in the films.

Electron Spin Resonance (ESR), temperature dependent Hall effect measurements and photoluminesence (PL) are used to examine the assumption that the residual donor in β-SiC films is nitrogen. At low temperatures the ESR has a three line isotropic spectrum which is characteristic of a central hyperfine interaction with nitrogen. The temperature dependence of the intensity of the nitrogen ESR signal correlates with the concentration of un-ionized donors measured by the Hall effect. Donor-Acceptor pair PL spectra are used to establish that the binding energy of the dominant donor in the films is the same as the nitrogen donor observed in Lely-grown samples. Neither PL nor ESR provide any evidence for the presence of a shallower donor.

Defects in β-SiC films grown on Si substrates by chemical-vapor deposition have been investigated using x-ray double-crystal topography. Varying levels of dislocations are often observed in the form of channels, originating at the SiC/Si interface, which can be detected topographically regardless of the visible roughness in the film surface. It is found that rough surfaces are crystallographically more ‘‘flat,’’ on a macroscopic scale, compared to smooth surfaces which are often curved. Films in the latter group also contain fewer defects than the former, and are characterized mostly by misfit striations along [110] directions. A model for defect propagation is proposed connecting the observed topographic detail to the lattice mismatch, differences in thermal expansion, and the relative thickness of film and substrate.

: The invention pertains to a method for preparing a substrate for subsequent liquid-phase epitaxial layer growth whereby the substrate traverses molten solvent metal of the substrate, or an unsaturated solution thereof, in an inert atmosphere at a temperature lying within a range from the melting point of the solvent metal to the melting point of the substrate.