Effective Schottky Barrier Height Lowering of Metal/n-Ge with a TiO₂/GeO₂ Interlayer Stack

Abstract

A perfect ohmic contact formation technique for low-resistance source/drain (S/D) contact of germanium (Ge) n-channel metal-oxide-semiconductor field-effect transistors (MOSFETs) is developed. A metal-interlayer-semiconductor (M-I-S) structure with an ultrathin TiO/GeO interlayer stack is introduced into the contact scheme to alleviate Fermi-level pinning (FLP), and reduce the electron Schottky barrier height (SBH). The TiO interlayer can alleviate FLP by preventing formation of metal-induced gap states (MIGS) with its very low tunneling resistance and series resistance and can provide very small electron energy barrier at the metal/TiO interface. The GeO layer can induce further alleviation of FLP by reducing interface state density (D) on Ge which is one of main causes of FLP. Moreover, the proposed TiO/GeO stack can minimize interface dipole formation which induces the SBH increase. The M-I-S structure incorporating the TiO/GeO interlayer stack achieves a perfect ohmic characteristic, which has proved unattainable with a single interlayer. FLP can be perfectly alleviated, and the SBH of the metal/n-Ge can be tremendously reduced. The proposed structure (Ti/TiO/GeO/n-Ge) exhibits 0.193 eV of effective electron SBH which achieves 0.36 eV of SBH reduction from that of the Ti/n-Ge structure. The proposed M-I-S structure can be suggested as a promising S/D contact technique for nanoscale Ge n-channel transistors to overcome the large electron SBH problem caused by severe FLP.

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

“…Although a mere GeO x layer can effectively passivate Ge surface, the metal may penetrate into GeO x and thus FL depinning may fail [17]. It has been reported that inserting 1.5 nm oxygen plasma oxidised GeO x prior to 1 nm TiO 2 deposition, results in a nearly symmetric I-V curve, which shows better electrical characteristics compared with no GeO x case [18]. However, such result was achieved by a process of two steps and with high complexity.…”

Reduced Contact Resistance Between Metal and n-Ge by Insertion of ZnO with Argon Plasma Treatment

“…A thin GeO x interfacial layer is formed between Ge and ZnO, which is much smaller compared to [ 31 ] due to the lower deposition temperature used in this work. This is attributed to the fact that, during the deposition of ZnO, Ge reactive with O precursor, leading to the formation of GeO x IL.…”

“…For the heavily doped n + -Ge contact sample, Al/ZnO/n + -Ge contacts shown the smaller ρ c in comparison with those of Ni/GeSn [ 40 , 41 ], Ni/Ge [ 42 ], Ti/n + -Ge in ref. [ 31 ], and Ti/TiO 2 /GeO 2 /Ge [ 31 ], carbon implanted Ni/Ge [ 42 ], and Ti/n + -SiGe/n-Ge [ 43 ]. Metallic ohmic contacts such as Ni/Ge, Ni/GeSn, Ti/Ge, and carbon implanted Ni/Ge suffer from severe Fermi-level pinning, resulting in the large ρ c .…”

Understanding of multi-level resistive switching mechanism in GeOx through redox reaction in H2O2/sarcosine prostate cancer biomarker detection

“…Voltage shift occurs due to oxidation of GeO x membrane using following oxidation-reduction equation below. From equation ( 3 ), the oxidation state of Ge changes from Ge 0 to Ge 4+ via Ge 1+ , Ge 2+ , Ge 3+ states 51 . First, H 2 O 2 in PBS buffer solution will receive electron (e−) from the GeO x surface (Fig.…”