Thermal sensitivity and barrier height inhomogeneity in thermally annealed and un-annealed Ni/n-6H-SiC schottky diodes

Abstract

The Ni/n-6 H-SiC Schottky barrier diodes (SBDs) have been fabricated. Then, they have been thermally annealed at 700 degrees C for 2 min. Their forward bias voltage versus measurement temperature (V-T) curves in 100-500 K range have been studied to determine the thermal sensitivity at current levels from 1.0 nA to 100 mu A for as deposited SBD and from 10 pA to 1.0 mu A for the annealed SBD. The V-T curves of both SBDs have exhibited the linear behavior at the mentioned current levels. The thermal sensitivity coefficient (alpha) calculated from the slope of the V-T curves has ranged from 2.15 mV/K at 1.0 nA to 1.79 mV/K at 10 mu A for the un-annealed diode, and from 1.75 mV/K at 10 pA to 1.27 mV/K at 1.0 mu A for the annealed diode. Furthermore, the alpha versus current level (I) graph of the un-annealed diode has given a straight line from 1.0 nA to 10 mu A. The linearity of the V-T and alpha-I graphs is a very crucial factor for a good thermal sensor in the thermal sensitivity. It can be said that the un-annealed diode can operate adequately as a temperature sensor in the range of 100-500 K and of 1.0 nA-10 mu A, considering studies in literature. The annealed diode did not exhibit a linear alpha versus current level curve. This has been ascribed to the formation of a highly resistive inhomogeneous layer at the Ni/n-6 H-SiC interface due to thermal annealing to 700 degrees C. The interfacial inhomogeneity has been explained by Gaussian distribution of the barrier heights.