Microstructure evolution study of Pd–Ge ohmic contact formation on GaAs

Abstract

Listen

Translate article

The microstructure evolution and the corresponding solid-state reactions that take place during the formation of the Pd–Ge ohmic contacts on GaAs were studied using constant-heating-rate differential calorimetry (DSC) and cross-sectional transmission electron microscopy (XTEM). DSC analysis at different scan rates was performed on Pd(20 nm)/Ge(150 nm)/Pd(50 nm) thin film stacks that were lifted off the substrate and four solid-state reactions were identified. Specimens heated at temperatures that coincide with the DSC peaks were quenched in a He atmosphere and the resulting microstructure was characterized by XTEM. Variable constant-heating-rate DSC experiments allowed us to determine the activation energy associated with each solid-state reaction by the Kissinger plot method. The results were as follows: for Pd:Ge interdiffuson, the activation energy Q=1.03 eV, for hexagonal Pd2Ge formation Q=1.12 eV, for orthorhombic PdGe formation Q=1.33 eV and for Ge crystallization Q=1.8 eV. Based on these correlations, the mechanisms that contribute to the formation of an optimal ohmic contact microstructure were identified.