Thermostable Ti/Au/Pt/Ti Schottky contacts to n-type 4H-SiC

The electrical properties and interface chemistry of Ti/Au/Pt/Ti Schottky contacts to n-type 4H-SiC have been investigated with respect to their utilization for MESFETs operated at high temperatures. The electrical properties of these contacts were studied at room temperature as well as during thermal treatment. The barrier height determined from I-V characteristics was calculated to be 1.17 eV with an ideality factor of 1.09. These parameters were examined by ageing and temperature dependence tests as criteria for the thermal stability and reliability of the contacts. The barrier height and ideality factor did not change after prolonged heating at a constant temperature of 500 degrees C and operating temperatures up to 350 degrees C, which confirmed the contact stability. Diodes used in the measurements showed a low leakage current at 100 V reverse voltage and room temperature (2.48 x 10(-9) A) as well as at 350 degrees C (2.15 x 10(-5) A) and breakdown voltage above 400 V. The chemical interface properties were studied by x-ray photoelectron spectroscopy for as-deposited, annealed and heated contacts. Annealing at 575 degrees C for 10 min led to formation of TIC and Pt,Si in a restricted region close to the SIC interface. The data revealed a chemically stable Ti/SiC interface after annealing, which is of importance for stable rectifying characteristics during long-term operation.