Ultrafast sensing of photoconductivity decay using microwave resonators

TL;DR

This paper introduces a high-speed, contactless method using microwave resonators to measure photoconductivity decay in semiconductors with nanosecond resolution, overcoming previous electronic bandwidth limitations.

Contribution

It presents a novel time-resolved resonator measurement technique that captures transient responses during photoconductivity decay, achieving ultimate time resolution limited by the resonator's time constant.

Findings

Achieved measurement of photoconductivity decay with ~100 ns resolution.

Demonstrated stable, high-accuracy measurements using a fixed-frequency oscillator.

Overcame electronic bandwidth limitations of traditional resonator methods.

Abstract

Microwave reflectance probed photoconductivity (or $\mu$-PCD) measurement represents a contactless and non-invasive method to characterize impurity content in semiconductors. Major drawbacks of the method include a difficult separation of reflectance due to dielectric and conduction effects and that the $\mu$-PCD signal is prohibitively weak for highly conducting samples. Both of these limitations could be tackled with the use of microwave resonators due to the well-known sensitivity of resonator parameters to minute changes in the material properties combined with a null measurement. A general misconception is that time resolution of resonator measurements is limited beyond their bandwidth by the readout electronics response time. While it is true for conventional resonator measurements, such as those employing a frequency sweep, we present a time-resolved resonator parameter readout method which overcomes these limitations and allows measurement of complex material parameters and to enhance $\mu$-PCD signals with the ultimate time resolution limit being the resonator time constant. This is achieved by detecting the transient response of microwave resonators on the timescale of a few 100 ns \emph{during} the $\mu$-PCD decay signal. The method employs a high-stability oscillator working with a fixed frequency which results in a stable and highly accurate measurement.