Narrow Results

In this paper, the microscopic electronic structure and related optical properties of the 4H-SiC (111) surface doped with B, Al, Ga elements are explored by first principles calculation methods. Compared with Al- and Ga-doped systems, the formation energy of B-doped system is found to be very small, showing excellent stability. The bandgaps of doped system decrease obviously, and an indirect bandgap is observed in all the systems. Charge density difference maps show that the covalency is increased after B doping and the iconicity is increased after Al and Ga doping. Moreover, due to the sharp increase in static dielectric constant and dielectric loss, the B-doped system can be used as the candidate for absorbing materials. In addition, the increase in the peak value of the absorption and reflectivity makes the doped systems more promising in the development of solar cells.

The Raman spectra of 4H-SiC with hexagonal defect have been investigated as a function of the excitation wavelength. As the excitation wavelength increases, the excitation wavelength dependence of Raman spectrum of hexagonal defect is very different from that of the free defect zone in 4H-SiC. Four electronic Raman scattering peaks are seen to be significantly enhanced with longer wavelength excitation. In hexagonal defect, the optical modes (E₂(TO), E₁(TO) and A₁(LO)) and the second-order Raman spectrum are broadened and redshifted as the excitation wavelength increased. But the positions of these bands obtained from the free defect zone do not change within our experimental error. Structure defects are regarded as the origin of those abnormal phenomena in hexagonal defect, and the structure ordering of hexagonal defect may have some similarity with SiC monofilaments.