Cryogenic Microwave Imaging of Metal-Insulator Transition in Doped Silicon

TL;DR

This paper presents a cryogenic microwave impedance microscope capable of spatially resolving the metal-insulator transition in doped silicon, revealing effects of thermal energy and electric fields on local charge carriers.

Contribution

It introduces a novel cryogenic scanning microwave impedance microscopy technique for imaging phase transitions in doped silicon at low temperatures.

Findings

Successful spatial resolution of the metal-insulator transition.

Data agrees with finite-element simulation.

Observation of thermal and electric field effects on charge carriers.

Abstract

We report the instrumentation and experimental results of a cryogenic scanning microwave impedance microscope. The microwave probe and the scanning stage are located inside the variable temperature insert of a helium cryostat. Microwave signals in the distance modulation mode are used for monitoring the tip-sample distance and adjusting the phase of the two output channels. The ability to spatially resolve the metal-insulator transition in a doped silicon sample is demonstrated. The data agree with a semi-quantitative finite-element simulation. Effects of the thermal energy and electric fields on local charge carriers can be seen in the images taken at different temperatures and DC biases.