Improving metal/ n ‐Ge ohmic contact by inserting TiO 2 deposited by PEALD

Abstract

A simple method is used to improve metal/n-germanium (Ge) contact characteristics by inserting plasma-enhanced atomic layer deposition (PEALD) deposited titanium dioxide (TiO2)/GeO x . Cross-sectional transmission electron microscope results confirm the thickness of the 30 PEALD cycles TiO2/GeO x is 1.62/1.38 nm. By inserting 1.62/1.38 nm TiO2/GeO x between aluminium (Al) and n-Ge, current densities increased by about 1800 times at −0.1 V compared with contacts without insertion layer (IL). With IL, ρ c of 9.52 × 10−3 Ω cm2 for Al/IL/n-Ge with an n-Ge concentration of 6 × 1016 cm−3 was achieved. ρ c reduced by a factor 83 compared with no TiO2 IL, and it also shows 4.72 times reduction compared with ρ c extracted from samples inserting thermal ALD-deposited TiO2. X-ray photoelectron spectroscopy (XPS) results shows that the valence state for GeO x was 3.682, thus Ge surface may be passivated. It was also determined by XPS that TiO2 was oxygen-vacancies rich, which may dope TiO2 and may contribute to lower tunnelling resistance. All of the characteristics will be beneficial for low contact resistivity.