CAREER: Understanding Photo-thermoelectric Phenomena in Bulk and Nanomaterials for Better Optical Sensing

Nontechnical

Infrared detectors have important uses in industry, agriculture, healthcare, and national security. Most detectors are based on absorption of infrared light by a semiconductor that in turn generates an electrical current. However, their sensitivity decreases, and the noise increases, as the wavelength increases.

A different phenomenon involving both light and heat shows promise for infrared detectors with high sensitivity across a wide range of wavelengths. This phenomenon, called the photo-thermoelectric effect, is the electronic response of a material when exposed to both light and a temperature gradient. This CAREER award will advance the fundamental understanding of the photo-thermoelectric effect, including underlying causes and impact of materials properties.

The PI’s team will synthesize single crystal films and nanomaterials and study them by a suite of advanced characterization techniques. The aim of this project is to develop materials that would enable infrared of detectors with unprecedented light-sensing performance and spectral response. The project has a multi-pronged educational effort to address the nation’s semiconductor workforce needs.

The PI will develop training modules and rapid certificate programs and explore curriculum reform focused on problem-solving. Undergraduate students will participate in research and the PI will engage in outreach to K-12 students themed in semiconductor technology. Technical

Photo-thermoelectric phenomena arise from varied mechanisms. While some can be described with classic frameworks, others occur far from equilibrium and are not well understood. In order to address this knowledge gap, the PI will develop strategies and techniques to separate contributions from different mechanisms, allowing for the quantification and interpretation of each.

The drift of photon-generated carriers will be examined using modified scanning photocurrent microscopy. Contributions from hot carriers will be distinguished using transient photo-thermoelectric voltage measurements. The influence of materials properties will be studied using lead sulfide as an archetype, comparing single crystalline thin films with nanoparticles assemblies of interest for slow hot carrier cooling caused by phonon bottlenecks.

The nature of defects and their influence will be studied using a modified thermoelectric spectroscopy technique. These research efforts will be complemented by pump-probe spectroscopy, and synchrotron diffraction and absorption. This research will enable rational design of infrared sensing devices based on photo-thermoelectric effects where different factors constructively contribute.

This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.