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 (TiO 2)/GeO x. Cross-sectional transmission electron microscope results confirm the thickness of the 30 PEALD cycles TiO 2 /GeO x is 1.62/1.38 nm. By inserting 1.62/1.38 nm TiO 2 /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 cm 2 for Al/IL/n-Ge with an n-Ge concentration of 6 × 10 16 cm −3 was achieved. ρ c reduced by a factor 83 compared with no TiO 2 IL, and it also shows 4.72 times reduction compared with ρ c extracted from samples inserting thermal ALD-deposited TiO 2. 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 TiO 2 was oxygen-vacancies rich, which may dope TiO 2 and may contribute to lower tunnelling resistance. All of the characteristics will be beneficial for low contact resistivity.

Bendable Single Crystal Silicon Nanomembrane Thin Film Transistors with Improved Low-Temperature Processed Metal/n-Si Ohmic Contact by Inserting TiO2 Interlayer

“…Figure 3a shows the XPS results of Ti 2p of samples for 20 cycles and 300 cycles of ALD process and all the XPS results are calibrated with C 1 s peak at 284.8 eV [23,24]. The two curves have two distinct peaks at about 458–459 eV and 464–465 eV, which represent for Ti 2p3/2 and Ti 2p1/2 peaks and are consistent with typical values of TiO 2 .…”

“…However, with the increase of the cycle (the thickness of TiO 2 ), the contact resistance becomes greater and greater. The explanation for this is that the thickness of titanium dioxide exceeds a certain value leading to carriers passing through the insertion layer at lower tunneling rate [23,24]. This will reduce the current, with presenting a larger contact resistance.…”

“…It can be seen that the peak of oxygen vacancies is not obvious. In conclusion, there are some oxygen vacancies in thin TiO 2 film, which will dope TiO 2 and make it more conductive [24]. Due to the presence of a donor band related to oxygen vacancies which can provide more electrons, TiO 2 behaves as an n-type semiconductor and exhibits good electrical conductivity.…”

“…This result is consistent with results of Figure 2c and Figure 4d. Thin TiO 2 which restrains the Fermi energy level pinning effect of n-Si can improve the interface contact between Ti/n-Si contributing to increase I ds [23,24,25]. I off of 0 cycle is largest, 5 cycles is smallest and 10 cycles is medium.…”