DOPANT LEVEL FREEZE-OUT AND NONIDEAL EFFECTS IN 6H-SIC EPILAYER JUNCTIONS

Experimental results obtained from current-voltage (I-V) and capacitan ce-voltage techniques along with admittance spectroscopy have been qua litatively correlated to achieve a more comprehensive picture of dopan t freeze-out and conduction mechanisms in a 6H-SiC n(+)p-type junction . Special attention was paid to the temperature range of 100-200 K. Th e dependence of the ideality factor, n, on the temperature was obtaine d experimentally from the I-V measurements. Two contributions have bee n considered in its evolution. At room temperature, n is very close to 2, indicating that recombination processes dominate the forward condu ction mechanism. This result may be related to the SiC sample preparat ion process: structural defects may be present at the junction interfa ce giving rise to interface states which act as recombination centers. At low temperatures (100-200 K), the Poole-Frenkel effect on the impu rity level is the main effect responsible for the nonideal behavior of the junction. We have carried out a quantitative estimation of the n factor predicted by this effect incorporating partial ionization of th e dopant. These calculations agree very well with the experimental val ues. At these temperatures the thermal excitation is low, the traps re main inactive, and their contribution to the conduction mechanisms is negligible. When the temperature increases, traps become thermally act ivated and then the recombination processes participate in the conduct ion mechanisms and they become dominant at room temperature. The admit tance analysis allows numerical values of the aluminum emission rate t o be obtained at different temperatures. (C) 1996 American Institute o f Physics.