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 °C for 20 s. The Al-rich films were chemically stable on GaAs up to 1000 °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 °C for 20 s.