How It Works

Photo-generated charge alters the microwave reflection coefficient of semiconductor materials. When constructed properly, microwave based lifetime measurements have orders of magnitude more sensitivity than other approaches for infrared materials. In many scientific fields, time-resolved photoluminescence (TRPL) or other light analysis based measurements using visible light are highly successful in quantifying the response dynamics of materials.

There are several key reasons microwave measurements are superior in general to TRPL for infrared devices:

• In typical measurements of IR materials, microwave based measurements are 1000x more sensitive than TRPL. Cooled IR detectors used to analyze light in TRPL experiments are not very sensitive compared to detectors in the visible portion of the spectrum where TRPL can be more effective. This enhanced sensitivity translates to greater measurement speed.

• Charge vs Photon sensing: To characterize the minority carrier lifetime of a material, the injection level must be below the doping level of the material. This means the injection level for valid measurements, and subsequently the number of PL photons available to measure, is essentially fixed. As your materials improve and lifetimes increase, TRPL suffers from reduced signal levels. Microwave based measurements sensing the charge in the material have no such limitations.

• IR materials often don’t emit light well, especially in the material development stages or when growth problems occur. This complicates using light analysis techniques.

• Cooled IR detectors with adequate performance for TRPL require liquid nitrogen

No light, no problem: Sometimes materials that may emit in the visible are just naturally poor emitters. Microwave measurements can be implemented to replace many light analysis based techniques for material characterization, not just lifetime measurements.

There can be good reasons for desiring TRPL as a supplement to or in place of TMR depending on your material or application and these needs can be accommodated in the 8D Wafer Mapping System.

While we specialize in low temperature measurement systems, high temperatures are not a problem if that is needed for your application. Want to learn more? Just contact us below.