Characteristics of β-phase PdAl Schottky contacts to n-GaAs

Abstract

Metallurgical and electrical properties of β-phase PdAl Schottky metallizations on n-GaAs after rapid thermal annealing for 20 s in the temperature range 500–1000 °C have been investigated using x-ray diffraction, transmission electron microscopy, Auger depth profiling, film resistivity, and current–voltage measurement. The Al-rich contacts were stable up to 900 °C whereas the Pd-rich contacts were less stable. The thermal stability of β-PdAl exhibited a sharp variation near the stoichiometric composition. The thermal stability of Pd-rich contacts decreased with increasing Pd composition, and the interfacial reaction after high-temperature annealing resulted in the formation of PdGa compound. The interface between Al-rich PdAl film and GaAs substrate remained quite sharp even after 900 °C anneal. The variation of interfacial stability at high temperatures between β-PdAl film and GaAs substrate is correlated to the compositional dependence of Al and Pd activities in PdAl within the β-phase region. The Schottky barrier heights of Al-rich PdAl contacts increased with annealing temperature. The barrier height enhancement in the annealed Al-rich contacts can be attributed to the thin AlxGa1−xAs layer formed at the interface.