Distinguishing Thermal and Electronic Effects in Ultrafast Optical Spectroscopy Using Oxide Heterostructures

Abstract

Measuring time-resolved photoexcited properties in semiconductors is critical to the design and improvement of light-harvesting devices. Although ultrafast pump–probe spectroscopy offers a promising route to understand carrier recombination mechanisms and quantify lifetimes, thermal contributions to the transient optical response can be significant and need to be properly accounted for to isolate carrier-induced contributions. We demonstrate the use of broadband ultrafast optical spectroscopy on type I heterostructures as a means to isolate transient effects that are solely thermal in nature. Specifically, we use transient absorption and reflectance spectroscopy to measure the time-resolved optoelectronic changes in photoexcited epitaxial bilayers of LaFeO3/LaMnO3 and monolithic thin films of these materials. Experiments and complementary numerical modeling reveal that thermal effects dominate the transient absorption and reflectance spectra above the band gap. Fitting the dynamics with a thermal diffusio...