Interaction between Thin Films of Zinc and (100) GaAs

Abstract

Zinc is currently being used as a dopant element in ohmic contact metallization systems to p-type GaAs. The results of our recent studies on interfacial reactions occurring during formation of Au(Zn)/p-GaAs ohmic contact indicate that Zn plays a more universal role facilitating the dispersion of the native oxide on GaAs [1]. On the other hand, in plating and soldering technologies zinc is widely used as a component enabling one the of metallic surfaces before further processing [2, 3]. To our knowledge, the precise mechanism of these cleaning action of zinc has not been yet established. The aim of the present work is to elucidate the metallurgical behavior of Zn in contact with GaAs. The microstuctural analysis of the Zn/GaAs interface, under as-deposited state and annealed conditions, was carried out by transmission electron microscopy (TEM) methods. Emphasis was placed on the determination of the stucture and composition of reaction products. High resolution electron microscopy (ΗREM) images were recorded with the JEOL JEM 2000EΧ (200 keV). The substrates used in this study were (100) oriented p-type GaAs wafers doped with Zn to a concentration of 8 x 10 17 cm-3 . Prior to metal deposition the samples were degreased in trichloroethylene (TCE), acetone and isopropyl alcohol, and then etched in solution of ΝΗ4OH:H2O2:H2O (20:7:973), followed by a rinse in deionized H2 O and immersion into ΝH4 OH:H2O (1:10) for 10 s. Zinc fflms, 150 nm thick, were deposited by vacuum thermal evaporation using 99.999% Zn source, in