Abstract
The Cox–Strack method is commonly applied to assess the contact resistivity between a metal and a semiconductor since the 1960s, while the underlying assumptions have not yet been rigorously assessed. In this article, a combination of finite-element modeling and mathematical analysis is used to investigate the accuracy of the conventional Cox–Strack equation for generic metal–semiconductor junctions. A systematic error in the spreading resistance equation is quantified, and alternative, more accurate equations are presented. Furthermore, it is shown that commonly used experimental configurations can lead to highly overestimated contact resistivities. Guidelines are formulated for accurate extraction of the contact resistivity from the Cox–Strack measurements.
Highlights
S EMICONDUCTOR devices rely on high-quality contacts between external, metallic leads and the semiconductor.As the device performance may be limited by these contacts, the resistance occurring at the interface between metal and semiconductor must be low and well-controlled in a fabrication process
This interface resistivity is, difficult to quantify precisely, as any measurement suffers from series resistance and current spreading effects [1]
This is problematic when the contact resistivity is very low, as we find in contemporary silicon-integrated circuit technology [2]
Summary
S EMICONDUCTOR devices rely on high-quality contacts between external, metallic leads and the semiconductor. As the device performance may be limited by these contacts, the resistance occurring at the interface between metal and semiconductor must be low and well-controlled in a fabrication process This interface resistivity (contact resistivity) is, difficult to quantify precisely, as any measurement suffers from series resistance and current spreading effects [1]. Two commonly used methods to quantify the contact resistivity between metal and semiconductor are the transfer length method (TLM, sometimes called transmission line method) [4] and the Cox–Strack method [5] The latter was proposed in 1967 and is often used for compound semiconductor technologies [6]–[8] and photovoltaic cells [9]–[12]. We formulate general guidelines to obtain accurate contact resistivity values with the Cox–Strack method
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