Electrical properties of a Cu-germanide Schottky contact to n-type Ge depending on its microstructural evolution driven by rapid thermal annealing

The electrical properties of Cu-germanide(Cu₃Ge)/n-type Ge Schottky contacts formed as a result of a solid state reaction between Cu and n-type Ge were investigated as a function of the rapid thermal annealing (RTA) temperature and correlated with its microstructural evolution driven by the RTA process. The variations of the barrier height of Cu₃Ge/n-type Ge Schottky rectifiers caused by the RTA process were determined using current-voltage (I-V) and capacitance-voltage (C-V) methods. The Cu₃Ge film formed after annealing at 400 °C exhibited a relatively uniform surface and interface morphology. This led to the formation of a laterally homogenous Schottky barrier in the Cu₃Ge/n-type Ge Schottky diode, resulting in an improvement of its rectifying I-V behavior. On the other hand, after annealing above 500 °C, the Cu₃Ge film was severely agglomerated without film continuity and eventually evolved into isolated islands at 600 °C. Such structural degradation of Cu₃Ge led to a rapid decrease in the barrier height and an increase in the reverse leakage current of the Cu₃Ge/n-type Ge Schottky diode. The electric field dependence of the reverse current showed that the reverse leakage current in the Cu₃Ge/n-type Ge Schottky diodes was dominated by a Poole-Frenkel emission mechanism, regardless of the RTA temperatures.