Annealing temperature dependency of the electrical and microstructural properties of Ti and Pt contacts to n-type Ge substrates

We have investigated the rapid thermal annealing behavior of electrical and microstructural properties of Ti (30 nm) and Pt (30 nm) contacts to n-type Ge substrates before and after rapid thermal annealing (RTA) at the temperatures in the range of 500-700 °C for 30 s under N₂ ambient. Despite low work function, Ti contacts exhibited Schottky behavior at low RTA temperatures due to strong Fermi level pinning (FLP) effect. However, the Ti contacts showed Ohmic behavior after annealing at 700 °C. Similarly, the Pt contacts formed at low temperatures annealing showed Schottky behavior as usually expected from Schottky-Mott theory. However, the annealing of Pt contacts at higher temperature (700 °C) resulted in the Ohmic behavior. For both contacts, the abrupt transition of Schottky to Ohmic behavior could be associated with the significant increase in the leakage current under reverse bias condition caused by structural degradation of Ti- and Pt-germanide films.