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

Yi Zhang,Haihua Zheng,Genquan Han,Yue Hao,Chang Liu,Hao Wu,Jincheng Zhang,Xiao Wang,Huan Liu,Xue Chen,Yan Liu

doi:10.1186/s11671-018-2650-y

Abstract

We investigate the metal-insulator-semiconductor contacts on n-Ge utilizing a ZnO interfacial layer (IL) to overcome the Fermi-level pinning (FLP) effect at metal/Ge interface and reduce the barrier height for electrons. A small conduction band offset of 0.22 eV at the interface between ZnO and n-Ge is obtained, and the ZnO IL leads to the significant reduced contact resistance (Rc) in metal/ZnO/n-Ge compared to the control device without ZnO, due to the elimination of FLP. It is observed that the argon (Ar) plasma treatment of ZnO can further improve the Rc characteristics in Al/ZnO/n-Ge device, which is due to that Ar plasma treatment increases the concentration of oxygen vacancy Vo, acting as n-type dopants in ZnO. The ohmic contact is demonstrated in the Al/ZnO/n-Ge with a dopant concentration of 3 × 1016 cm−3 in Ge. On the heavily doped n+-Ge with a phosphor ion (P+) implantation, a specific contact resistivity of 2.86 × 10− 5 Ω cm2 is achieved in Al/ZnO/n+-Ge with Ar plasma treatment.

Highlights

Germanium (Ge) has attracted much attention for the advanced metal-oxide-semiconductor field-effect transistors (MOSFETs) due to its higher carrier mobilities compared to Si [1, 2]
The Fermi-level depinning effect induced by Zinc oxide (ZnO) interfacial layer (IL) in the Al/ZnO/n-Ge structures is investigated
X-ray photoelectron spectroscopy (XPS) measurement demonstrated a small conduction band offset (CBO) of 0.22 eV at ZnO/n-Ge, i.e., elimination of Fermi-level pinning (FLP) occurs, which leads to the ohmic metal contacts on n-Ge

Summary

Introduction

Germanium (Ge) has attracted much attention for the advanced metal-oxide-semiconductor field-effect transistors (MOSFETs) due to its higher carrier mobilities compared to Si [1, 2]. Ge n-channel transistors, by contrast, are still facing challenges, which produce the obstacle for the integration of Ge CMOS, including the poor interface quality, resulting in the low electron mobility, and the high S/D resistance due to the limited activation rate of n-type dopants in Ge [12] and the Fermi-level pinning (FLP) at metal/n-Ge interface [13]. It is easy to realize n-type doping in ZnO by introducing nonstoichiometric defects, such as oxygen vacancies Vo [21, 22], which gives rise to an even smaller ZnO depletion region between the metal and n-Ge. So far, in metal/ZnO/n-Ge contacts, the doping of ZnO by Vo was carried out by annealing in nitrogen atmosphere [16], which might resulted to the inter diffusion of ZnO and Ge during the annealing [23], and diffusion of dopant atoms in n-Ge during the annealing [24, 25], causing the degradation of current

Methods

Results

Conclusion