The UT team used a different method for quantifying these lifetimes by placing small volumes of the materials in specially designed microwave resonator circuits. Samples are exposed to concentrated microwave fields while inside the resonator. When the sample is hit with light, the microwave circuit signal changes, and the change in the circuit can be read out on a standard oscilloscope. The decay of the microwave signal indicates the lifetimes of photoexcited charge carriers in small volumes of the material placed in the circuit.
"Measuring the decay of the electrical (microwave) signal allows us to measure the materials' carrier lifetime with far greater accuracy," Wasserman said. "We have discovered it to be a simpler, cheaper and more effective method than current approaches."
Carrier lifetime is a critical material parameter that provides insight into the overall optical quality of a material while also determining the range of applications for which a material could be used when it's integrated into a photodetector device structure. For example, materials that have a very long carrier lifetime may be of high optical quality and therefore very sensitive, but may not be useful for applications that require high-speed.
"Despite the importance of carrier lifetime, there are not many, if any, contact-free options for characterizing small-area materials such as infrared pixels or 2D materials, which have gained popularity and technological importance in recent years," Wasserman said.