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

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 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 film's 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 diffusion model yields thermal conductivities of 6.4 W m(-1) k(-1) for LaFeO3 and 2.2 W m(-1) k(-1) for LaMnO3. In LaFeO3, an additional photoinduced absorption feature below the band gap at X1.9 eV is assigned primarily to photoexcited carriers and persists for over 3 ns. This work provides a direct demonstration of how thermal and electronic contributions can be separated in transient optical spectroscopies, enabling new insights into dynamical optical properties of semiconductors.