A Investigation of the Schottky Barrier Enhancement to N-Gallium Arsenide.

A systematic study of the Schottky barrier enhancement to n-GaAs has been carried out using a ternary Ni-Al-Ga contact system. The diodes, Al/n-GaAs, Ni/Al/n-GaAs, rm NiAl_{y}Ga_{1 -y}/n-GaAs, Ni_2Al _3/Ni/n-GaAs, NiAl/Ni/n-GaAs, Ni/Al/Ni/n -GaAs and NiAl/Al/Ni/n-GaAs, were prepared by sputter deposition from Ni, Al, rm NiAl_{y}Ga _{1-y} and rm Ni _2Al_3 targets. High Schottky barrier heights ranging from 0.95 to 1.1 eV (deduced from I-V method) were observed for all the annealed contacts. These high Schottky barrier heights were attributed to the formation of a (Al,Ga)As layer at the metal/semiconductor interface. The existence of a thin (Al,Ga)As layer was determined using a (200) dark field XTEM image and from the SAM profiles for the contacts annealed at high temperatures. Two mechanisms have been used to rationalize the formation of (Al,Ga)As and the enhanced barrier heights. One is the exchange reaction mechanism and the other is the regrowth mechanism. The annealed contacts, Al/n-GaAs, rm NiAl_{x}Ga_{1-x}/n -GaAs and Ni/Al/n-GaAs, with enhanced barrier heights belong to the exchange reaction mechanism. The reacted diodes, rm Ni_2Al_3/Ni/n-GaAs, NiAl/Ni/n-GaAs, Ni/Al/Ni/n-GaAs and NiAl/Al/Ni/n-GaAs, with high Schottky barrier heights belong to the regrowth mechanism.