Electrical characteristics of metal/n-Ge and Ni/n-GeSn contact
Date Issued
2015
Date
2015
Author(s)
Tsai, Hung-Yi
Abstract
Following the advance of technology, silicon-based metal-oxide-semiconductor field-effect transistors (MOSFETs) are reaching their physical limits. In the recent development, Germanium (Ge) and Germanium-tin (GeSn) alloy have been considered as the possible candidates for the channel materials of MOSFET due to the higher carrier mobility compared to silicon (Si). Nevertheless, many challenges concerning Ge and GeSn still need to overcome. Among these issues, the most difficult is to fabricate a low resistance electrical contact between metal and semiconductor. In this thesis, we investigate the electrical characteristics of metal/n-Ge, Ni/n-GeSn, and Ni/i-GeSn/n-Ge. For the metal/n-Ge system, Fermi level pining has caused a severely influence on the metal/n-Ge interface due to the interface states and the Ge native oxide. Here we show that Ohmic contact of AuSb/n-Ge can be achieved by thermal annealing, and the minimum specific contact resistivity is 0.622 (Ω∙cm^2). The electrical parameters of metal/n-Ge system have been extracted, where the values of Schottky barrier height are in the same order of 0.5 (eV). In order to make a stable metal-oxide-semiconductor (MOS) structure, Al2O3 is placed between Ni/n-Ge with different thickness. From the current-voltage (I-V) and capacitance-voltage (C-V) characteristics, it shows a better trend for Ni/Al2O3/n-Ge with 6.7 and 18.4 nm Al2O3 layer. For the Ni/n-GeSn system, film quality of n-GeSn is measured by different characterization techniques. Ohmic contact to Ni/n-GeSn can be achieved, and the specific contact resistivity is 4.361×10-3 (Ω∙cm^2). We have grown an Al2O3 layer to form Ni/Al2O3/n-GeSn, where the electrical parameters have been extracted by the I-V measurement. In the last section, we discuss the influence of different i-GeSn thickness on the Ni/i-GeSn/n-Ge system. From the I-V measurement, forward current of Ni/i-GeSn/n-Ge is reduced when increasing the thickness of i-GeSn.
Subjects
GeSn alloy
Fermi level pinning
Ohmic contact
specific contact resistivity
Schottky barrier height
Al2O3
Type
thesis
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