Thin polytype inclusions in 4H silicon carbide epitaxial films and isotope and anharmonic effects in carbon-hydrogen vibrational centers of silicon carbide

More than ten distinct intrinsic exciton spectra with exciton bandgaps ranging from 2.18 to 3.03 eV are observed due to polytype inclusions in 4H SiC homoepitaxial films grown in hot-wall chemical vapor deposition reactors. A correlation is found between the appearance of these spectra and reduced carrier lifetime as well as electron microscopic evidence for stacking faults. A 4H/3C/4H-SiC quantum well was observed in a high-resolution transmission electron microscopy image consisting of thirteen 3C-SiC bilayers. The optical emission energy of the quantum well is more than 200 meV below the exciton bandgap of bulk 3C SiC. The large redshift of the emission energy is explained by the quantum-confined Stark effect which is induced by a strong internal electric field on the order of 1 MV/cm in the quantum well. The origin of this field is discussed in terms of the spontaneous polarization difference between 3C and 4H SiC. The stretch frequencies of the C-H and C-D modes in the (V_Si + H) complex of SiC are measured out to the third harmonic using the low temperature photoluminescence. A Morse Potential model is found to account well for both the anharmonicity and the isotope effect of the C-H and C-D vibrational centers. A first principles calculation was carried out by A. Gali et. al. for the (V_Si + H) complex of 3C SiC. Their calculation shows excellent agreement with our experiment for the C-H vibrational frequencies. The isotope shift of the no-phonon line of the C-H and C-D center is discussed in terms of the ground and excited states of the (V_Si + H) and (V_Si + D) complex of SiC. We propose that the isotope shift of the no-phonon line is related to the difference of the zero-point energies of the vibrations in both the electronic ground and excited states of the complex.