The unique properties of SiC, such as high thermal conductivity, thermal stability and chemical inertness combined with high concentration, wide bandgap, and high mobility, make them materials of choice for high-frequency/high power/high temperature applications. To take the full advantage of this material, high quality thermally stable Schottky contacts to SiC are required. Up to now, Ti, Al, and Ni were tried as the most widely used n-type Schottky contacts in SiC-based devices. While successfully used in standard conditions, in high temperature and harsh environment they survive rather low time because of their degradation. Therefore, it was necessary to seek other materials for high quality thermally stable Schottky contacts.

In this work we report on optimisation of Ir and IrO₂ Schottky contacts to n-type 4H-SiC and their performance under high temperature stress. Ir and IrO₂ contact metallization was deposited by magnetron sputtering from metallic Ir target. Ir films were dc sputtered in Ar, IrO₂ films were formed by reactive rf process in Ar-O mixture. The deposition parameters (the ratio of Ar/O₂ flow, power, oxygen partial pressure) were adjusted with the goal to obtain film conductivity as high as possible. Schottky contacts were heat treated in Ar atmosphere up to 900^oC to evaluate thermal stability of the contact. Thermal tests of the contacts were conducted in air and Ar at 600^oC for time up to 100 hours. Surface morphology of Ir and IrO₂ films was characterized by optical and atomic force microscopies, crystal structure was examined using x-ray diffraction. Sheet resistance of metallization was measured by four-point-probe. The Schottky barrier heights of iridium and iridium oxide on 4H-SiC were investigated as a function of annealing temperature and ageing time by current-voltage (I-V) and capacitance-voltage (C-V) techniques.

The Schottky barriers of the as-deposited Ir/n-SiC and IrO₂/n-SiC are 1.40 eV and 1.53 eV, respectively. Annealing at 600ºC for 10 min. increases slightly the barrier height but the subsequent annealing does not influence on that barrier height. The long-term stability of Ir/SiC and IrO₂/SiC Schottky barrier heights will be discussed.

The research is partially supported by the Ministry of Science and Information Society Technologies, Poland, under the grant 3T11B 042 30.

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