Contactless measurement of electrical conductance of a thin film of amorphous germanium

TL;DR

This paper introduces a contactless method using a nanoscale silicon MOSFET to measure the conductance of amorphous germanium films, enabling precise measurements even with blocking contacts and at very low conductance levels.

Contribution

The authors develop a novel contactless charge sensing technique for amorphous germanium, allowing conductance measurements unaffected by contact resistance and applicable at extremely low conductance levels.

Findings

Conductance measurement agrees with direct current at high bias.

Temperature and field dependence match Mott variable-range hopping model.

Achieves measurement of conductance as low as 10^-19 S.

Abstract

We present a contactless method for measuring charge in a thin film of amorphous germanium (a-Ge) with a nanoscale silicon MOSFET charge sensor. This method enables the measurement of conductance of the a-Ge film even in the presence of blocking contacts. At high bias voltage, the resistance of the contacts becomes negligible and a direct measurement of current gives a conductance that agrees with that from the measurement of charge. This charge-sensing technique is used to measure the temperature- and field-dependence of the conductance, and they both agree with a model of Mott variable-range hopping. From the model, we obtain a density of states at the Fermi energy of 1.6 x 10^18 eV^-1 cm^-3 and a localization length of 1.06 nm. This technique enables the measurement of conductance as low as 10^-19 S.