Thermal stability of the Pd-Al alloy Schottky contacts to n-GaAs

Thermal stability of the Pd-Al alloy Schottky contacts to n-GaAs have been investigated by X-ray diffraction (XRD), cross-sectional transmission electron microscopy (XTEM) and Auger depth profiling. Electrical characteristics of the Schottky diodes were assessed by current-voltage measurement. Four different alloy compositions, i.e. Pd40Al60, Pd48Al52, Pd52Al48 and Pd68Al32, were codeposited by dual electron-gun evaporation and then annealed by rapid thermal processing at temperatures 500-1000 degrees C for 20 s. The Al-rich films were chemically stable on GaAs up to 1000 degrees C, however, the contacts degraded and exhibited poor diode characteristics when interfacial diffusion was prominent and the interface became rough. The Pd-rich films were chemically less stable and the interfacial reaction occurred at a lower temperature with increasing Pd content. After high-temperature annealing, more As outdiffused into the Al-rich films. On the other hand, more Ga outdiffused into the Pd-rich films resulting in the chemical reaction and the formation of PdGa compound. The Pd48Al52 contact exhibited the best stability among all Pd-Al alloy metallizations on GaAs. A barrier height of 0.97 V and an ideality factor of 1.09 were obtained for Pd48Al52/n-GaAs Schottky diode annealed at 900 degrees C for 20 s. (C) 1997 Elsevier Science S.A.