Admittance Spectroscopy of 6H, 4H, and 15R Silicon Carbide

Abstract

By analyzing the temperature dependence of the capacitance and AC conductance of a zero-biased Schottky diode one obtains the activation energy of the primary shallow dopant in a semiconductor. This technique has become known as Thermal Admittance Spectroscopy. Thermal admittance spectroscopy has been used to characterize nitrogen donors in 4H-, 6H-, and 15R-SiC. p-type dopants (Al, B) have also been characterized in 6H-SiC. In addition, an activation energy attributable to hopping conduction has been obtained in n-type specimens of all three polytypes. The change in the admittance of a Schottky diode caused by illumination, measured as a function of wavelength, is called Optical Admittance Spectroscopy. Optical admittance spectroscopy has been used to study deep centers in silicon carbide where traditional electrical detection is made difficult by the requirement for very high measurement temperatures. Using this technique, the energies of the midgap donor-like levels attributed to vanadium atoms substitutionally occupying the inequivalent lattice sites have been determined. The bandgaps of 6H- and 4H-SiC polytypes have been measured, and the phonon spectra associated with the indirect transitions from the valence band to the conduction band have been determined.