Based on the thermodynamic/kinetic model of the exchange mechanism, the ternary intermetallic compound NiAl x Ga 1Ϫx ͑where 0Ͻxр1) 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 NiAl x Ga 1Ϫx 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 NiAl x Ga 1Ϫx metallizations, with compositions corresponding to xϭ0.00, 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 nm͒ interfacial region of Al x Ga 1Ϫx As was formed in annealed contacts for which xϾ0.00, in accordance with the exchange mechanism model. Schottky barrier enhancement was also observed in all annealed contacts for which xϾ0.00. 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°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.

Thermally stable Al/n-GaAs Schottky contacts, up to annealing temperature at 500 °C for 20 seconds, have been realized by sputter deposition from an Al target to (100) n-GaAs at a base pressure ∼2×10−7 Torr. The Schottky barrier height was 0.75 eV (0.9 eV) when using the I-V (C-V) method with an ideality factor of 1.09 for the as-deposited samples. The Schottky barrier height increased to 0.97 eV (1.06 eV) with an ideality factor of 1.07 after annealing at 400 °C for 20 seconds. This barrier height, 0.97 eV, is the highest value reported for Al/n-GaAs diodes. The interfacial stability between Al and GaAs has been examined by cross section transmission electron microscopy. A (200) dark field cross section transmission electron microscopy image of the contact after annealing at 600 °C showed that the (Ga,Al)As phase formed at the interface and the enhancement of the Schottky barrier height was due to the formation of this phase.