Comprehensive study of the ultrafast photoexcited carrier dynamics in Sb 2 Te 3 –GeTe superlattices

Chalcogenide superlattices Sb 2 Te 3 –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 Sb 2 Te 3 –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 Sb 2 Te 3 –GeTe superlattices. By decreasing the thickness and increasing the number of GeTe and Sb 2 Te 3 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.