Schottky enhancement of contacts to n-GaAs via the exchange mechanism using NiAlxGa1-x as a metallization

Based on the thermodynamic/kinetic model of the exchange mechanism, the ternary intermetallic compound NiAlxGa1-x (where 0 < x less than or equal to 1)was identified as a metallization that may be used to fabricate Schottky enhanced contacts to n-GaAs. Experimental: phase equilibrium:studies of the quaternary Al-Ga-Ni-As system, in conjunction with diffusion data available in the literature, indicated that the phase NiAlxGa1-x fulfills the thermodynamic and kinetic requirements necessary for participation in an exchange reaction with GaAs. Contacts to n-GaAs were fabricated by sputter deposition of NiAlxGa1-x metallizations, with compositions corresponding to x = 0.00, 0.25, 0.50, 0.75 and 1.00. These contacts were subjected to rapid thermal processing, and analyzed using cross-sectional high resolution transmission electron microscopy and I-V characterization. Electron microscopy and concomitant electron dispersive spectroscopic analysis indicated that a very thin (2.5 nm) interfacial region of AlxGa1-xAs was formed in annealed contacts for which x > 0.00, in accordance with the exchange mechanism model. Schottky barrier enhancement was also observed in all annealed contacts for which x > 0.00. The degree of Schottky barrier enhancement was shown to be dependent upon the initial composition of the metallization, again in,accordance with the prediction of the exchange mechanism model. Schottky barrier heights as high:as 0.96 eV were obtained under the optimum annealing conditions of 400 degrees C for 1 min. However, these experimentally determined Schottky barrier heights were somewhat smaller than the values that were anticipated based upon the exchange mechanism model. Potential reasons for these discrepancies were discussed. Overall, it was demonstrated that the thermodynamic/kinetic model of the exchange mechanism is a powerful tool for identifying metallizations that may be used to enhance the Schottky barriers of contacts to n-GaAs. (C) 1999 American Vacuum Society. [S0734-211X(99)04602-8].