Spanning Femtoseconds to Seconds in the Photoinduced Response of Antimony Thin Films

The observable dynamics in electrical devices based on phase change materials span nanoseconds to decades. Any processes on timescales below nanoseconds are obscured by the limited time resolution of electronic circuits. Photonic circuits do not share this limitation [1]. Material<br/>dynamics on much shorter timescales are accessible, but must be understood in order to be exploitable in applications. This study investigates the photoinduced dynamics of the phase change material antimony in the time range from femtoseconds to seconds using optical pump-probe spectroscopy.<br/><br/>Certain aspects of the response of crystalline antimony to excitation with short laser pulses have been examined in the past [2]. The short-timescale response is characterized by the displacive excitation of a damped coherent phonon mode [3], the coupling of the hot electron system to the lattice initially leads to a non-thermal population of phonons [4], and in the long-timescale limit the optical contrast between an amorphous and the crystalline state exhibits a film thickness dependence [5]. However, there is no individual study that attempts to elucidate the photoinduced response of antimony in its entirety. Furthermore, the large parameter space of e.g. film thickness, pump fluence, or probe wavelength remains largely unexplored. Exploring, for instance, the role of the film thickness is expected to be especially important in antimony, where confinement below 10 nm already has been shown to influence a range of material properties such as the crystallization kinetics [6], phonon mode frequencies [5] or electronic structure [7]. Varying the thickness of the antimony film, its structural state through in-situ switching, the probing wavelength, pump fluence and base temperature, we measured the complete photoinduced response until its return to equilibrium. Comparison of the different processes across this broad parameter space is enabled by deriving a phenomenological model that can capture the entire response.<br/><br/>REFERENCES<br/>1. T. Yu et al., arXiv:2102.10398 (2021)<br/>2. J. Tominaga et al., Appl. Phys. Lett. 75 (1999) 3114<br/>3. M. Hase et al., J. Phys. Soc. Jpn. 84 (2015) 024708<br/>4. L. Waldecker et al., Phys. Rev. B 95 (2017) 054303<br/>5. Z. Cheng et al., Sci. Adv. 7 (2021) 7097<br/>6. M. Salinga et al., Nat. Mat. 17 (2018) 681<br/>7. P. Zhang et al., Phys. Rev B 85 (2012) 201410