Ta Overlayer Research Articles

Reaction of Amorphous Minb Films with Crystalline Metal Overlayers

AbstractIn many cases the stability of amorphous films is influenced by interaction with metallic crystalline overlayers. Such interactions between Au, Ni, Nb and Ta overlayers and a-(Ni-Nb) films are reported. During interdiffusion Au overlayers reacted with a-(Ni-Nb) to form two different adjacent crystalline layers. In order to study the influence of relaxation of the amorphous film on overlayer reaction several a-(Ni-Nb) samples were pre-annealed prior to Au deposition. High depth resolution Rutherford Backscattering Spectrometry (RBS) demonstrates that preannealing lowers the diffusion poefficient of Au in a-(Ni-Nb) at 4500C from 7.5×10−22 m2/s to 8.7×10−23 m22/s. During interdiffusion Ta was discovered to be substantially more inert than Au. For example, negligible interdiffusion between Ta and a-(Ni-Nb) at 505°C after 25 hours implies a diffusivity of less than 5×10−24 m2/s. These observations allow assessment of some of the requirements for increasing the stability of crystalline-amorphous metal film layered structures.

Development ot ohmic contacts for GaAs devices using epitaxial Ge films

Ohmic contacts to n-type GaAs have been developed using epitaxial Ge films on GaAs alloyed with Ni overlayers by solid-state diffusion at temperatures of 450/spl deg/C-650/spl deg/C. These contacts have applications to high reliability, high temperature microwave devices. Reflection electron diffraction of the Ge layers prior to deposition of the Ni overlayers reveals the presence of high quality single-crystalline films. Even after sintering, there is very little penetration of Ge into GaAs in the absence of Ni. With the presence of a Ni overlayer, significant interdiffusion between Ge and GaAs is revealed by Auger electron spectroscopic profiles. These results, together with the current-voltage characteristics of similar contacts prepared on p-type GaAs, indicate the presence of a Ge-doped n/SUP +/ layer at the Ni/Ge-GaAs interface. Ohmic contacts using epitaxial Ge films with Ta and Mo overlayers have also been investigated.