Optimizing Pd-Ge ohmic contact to GaAs through microstructure control

The microstructure evolution and the corresponding solid state reactions th at take place during the formation of the Pd-Ge ohmic contact on GaAs were determined. By combining constant-heating-rate differential calorimetry (DS C) and cross-sectional transmission electron microscopy (XTEM) to study the behavior of the Pd (50 nm)/Ge (150 nm)/Pd (20 nm) thin film stack on GaAs, we identified four solid state reactions that take place during annealing: Pd-Ge interdiffusion, hexagonal Pd2Ge formation, PdGe transformation, and excess Cre crystallization. Specimens heated to temperatures that coincided with the DSC peaks were quenched in a I-Ie atmosphere and the resulting mi crostructure was characterized by XTEM and specific contact resistivity mea surements. Based on these correlations, the mechanisms that contribute to t he formation of optimal microstructure for ohmic contact were identified. ( C) 1999 American Vacuum Society. [S0734-211X(99)06405-7].