Detecting Charge Separation in Optoelectronic Materials and Devices Using Planar Microwave Resonators: An Overview

The advent of high Q-factor planar microwave resonators has opened up new possibilities for the electronic characterization of semiconductor heterojunctions and hot carrier plasmonic devices. The high sensitivity of planar microwave resonators to changes in the complex permittivity of semiconductor materials placed in the resonator coupling gap allows detection of both mobile and trapped carriers. Therefore, long-lived excess carriers in relaxation-type semiconductors occurring either due to photoexcitation or hot carrier injection from a plasmonic sensitizer can be detected and quantified. Application of a large signal DC bias on top of the small-signal microwave bias further enables differentiation between trapped electrons and trapped holes. In most cases, characteristic lifetimes for trap-mediated processes can also be extracted.