High-temperature electric contacts for AlGaInP/GaInP photon-enhanced thermionic emisson cathodes

Three metals (Ag, Au, and Ti) and a carbide (WC) were studied to verify their suitability to act as high-temperature electric contacts for photon-enhanced thermionic emission cathodes based on an AlGaInP/GaInP heterostructure. Transfer length method measurements, performed in the temperature range 25-350°C, showed that the lowest specific contact resistivity values were found for Au (4.0 × 10-4 O cm-2 @350°C) and Ti (1.2 × 10-3 O cm-2 @350°C). A further selection was made on the basis of film adhesion tests performed after the thermal cycles, in which Ti demonstrated an excellent mechanical robustness.