Non-nitridated oxides: abnormal behaviour of n-4H-SiC/SiO2 capacitors at low temperature caused by near interface states

Comparative studies of gate oxides on a N+ pre-implanted area (N-interface similar to 1x10(19)cm(-3)) and on a virgin Si face 4H-SiC material (N-interface similar to 1x10(16)cm(-3)) have been undertaken by means of Capacitance-Voltage (C-V) characteristics, performed at different temperatures and frequencies, and Thermal Dielectric Relaxation Current technique. In the non implanted samples, the stretch out of the C-V curves get larger as the temperature is lowered to 150K, while for lower temperatures the C-V characteristics become steeper and some discontinuities occur. These discontinuities are specific for the non-implanted sample and are associated with charging of the fast near interface states (NIToxfast) via a tunneling from the shallow interface states (D-it). The tunneling from the shallow D-it to NIToxfast supress the a.c. response of D-it, which is recovered only after most of the NIToxfast are charged with electrons.