Large Piezoresistive Effect in a Ti/n-4H-SiC Schottky Junction

Silicon carbides (SiC) are promising alternatives to conventional silicon (Si) for sensors working in harsh environments due to their wide bandgap, high Young's modulus, exceptional chemical resistance, thermal stability, and reliability. This study investigates the strain-sensitive behavior of a Ti/n-4H-SiC Schottky junction under external bias. When uniaxial strain is applied to the junction along the [101-0] orientation on the (0001) plane of n-4H-SiC, experimental results reveal a linear relationship between the relative change of forward current and the applied strain. At a forward bias of 0.65 V, the Schottky junction exhibited a transverse gauge factor (GF) of -31, representing a 40% improvement over the highest GF reported for n-4H-SiC piezoresistors. Notably, traditional piezoresistive theory predicted negligible conductivity changes in this orientation. To elucidate the origin of this strong enhancement, first-principles calculations are conducted to quantitatively elucidate the strain-induced modifications to the conduction band structure (electron energy ellipsoids) of n-4H-SiC. The results show a piezoresistive mechanism in the Schottky junction: strain-induced shifts of the conduction band modulate the Schottky barrier height, thereby altering the current transport through the junction. These findings not only highlight the potential of Ti/n-4H-SiC Schottky junctions for highly sensitive and robust mechanical sensors but also advance our fundamental understanding of the piezoresistive phenomenon in wide-bandgap metal/semiconductor Schottky junctions.