Determination of donor and acceptor level energies by admittance spectroscopy in 6H SiC

Admittance and deep level transient spectroscopy (DLTS) measurements were taken on n- and p-type Schottky diodes in order to determine the activation energies of both shallow (aluminium and nitrogen) and deep levels in 6H SiC epitaxial layers. A dependence on the lattice sites is found for N and suggested for Al. For N the activation energies are 82 and 137 meV in the hexagonal and cubic sites respectively. For Al, the values could be 0.22 and 0.25 eV respectively. DLTS analysis shows the presence of deep levels in low concentrations. Finally, we show that assuming a two-level structure of the doping impurities, the carrier concentration can be well predicted as a function of temperature so that it is possible, from current-voltage measurements of junction field effect transistors, to determine the power law dependence of mobility on temperature in n-type material.