CHARACTERISTICS OF TA AND TA-AL ALLOY SCHOTTKY CONTACTS TO N-GAAS

The metallurgical stability and the electrical characteristics of Ta and Ta-Al alloy metallizations on n-GaAs have been investigated. The compositions of electron-gun-evaporated alloy films were Ta55Al45, Ta37Al63, and Ta30Al70. The contacts were annealed by rapid thermal processing in the temperature range 400-900-degrees-C for 20 s. X-ray diffraction, transmission electron microscopy, and Auger depth profiling analysis were used to study the structural properties. The sheet resistance and the electrical characteristics of the Schottky diodes were assessed using four-point probe and current-voltage measurements, respectively. The Ta-Al alloy metallizations were substantially more stable than pure Ta. The interfaces of Ta-Al/GaAs contacts were metallurgically stable and the surface remained smooth and lustrous up to 900-degrees-C anneal, while interfacial reactions occurred and the surface became rough in Ta/GaAs contact after annealing above 600-degrees-C. The Schottky barrier heights of all thermally stable Ta-Al/GaAs diodes increased with temperature after annealing above 700-degrees-C. The variation of the electrical characteristics of the contacts as a function of annealing temperature can be correlated to the crystallization transformation of the film, and the interfacial diffusion and reaction.