Comprehensive study of the ultrafast photoexcited carrier dynamics in Sb₂Te₃-GeTe superlattices

Abstract Chalcogenide superlattices Sb2Te3-GeTe is a candidate for interfacial phase-change memory (iPCM) data storage devices. By employing terahertz emission spectroscopy and the transient reflectance spectroscopy together, we investigate the ultrafast photoexcited carrier dynamics and current transients in Sb2Te3-GeTe superlattices. Sample orientation and excitation polarization dependences of the THz emission confirm that ultrafast thermo-electric, shift and injection currents contribute to the THz generation in Sb2Te3-GeTe superlattices. By decreasing the thickness and increasing the number of GeTe and Sb2Te3 layer, the interlayer coupling can be enhanced, which significantly reduces the contribution from circular photo-galvanic effect (CPGE). A photo-induced bleaching in the transient reflectance spectroscopy probed in the range of ~1100 nm to ~1400 nm further demonstrates a gapped state resulting from the interlayer coupling. These demonstrates play an important role in the development of iPCM-based high-speed optoelectronic devices.