Ohmic Contact at Al/TiO2/n-Ge Interface with TiO2 Deposited at Extremely Low Temperature

TiO2 deposited at extremely low temperature of 120 degrees C by atomic layer deposition is inserted between metal and n-Ge to relieve the Fermi level pinning. X-ray photoelectron spectroscopy and cross-sectional transmission electron microscopy indicate that the lower deposition temperature tends to effectively eliminate the formation of GeOx to reduce the tunneling resistance. Compared with TiO2 deposited at higher temperature of 250 degrees C, there are more oxygen vacancies in lower-temperature-deposited TiO2, which will dope TiO2 contributing to the lower tunneling resistance. Al/TiO2/n-Ge metal-insulator-semiconductor diodes with 2 nm 120 degrees C deposited TiO2 achieves 2496 times of current density at -0.1V compared with the device without the TiO2 interface layer case, and is 8.85 times larger than that with 250 degrees C deposited TiO2. Thus inserting extremely low temperature deposited TiO2 to depin the Fermi level for n-Ge may be a better choice.