Exciton–phonon coupling in resonant Raman scattering: intrinsic attributes and extrinsic tunability in ZnTe of different dimensionalities*

The dependence of electron-phonon coupling (EPC) on nanostructure size has been controversial over three decades. Often, the EPC was probed by resonant Raman scattering (RRS) using the 2LO to 1LO intensity ratio R21 to extract the Huang-Rhys factor (S) by applying Albrecht’s theory, where the bulk reference S was calculated using a theoretical model developed for a bound exciton with Fröhlich interaction. We show that in ZnTe, in contrast to the previous reports, R21 exhibits a much larger intrinsic value and minimal change from bulk to 30 nm nanowire, indicating previously reported size dependences were likely affected by extrinsic mechanisms. In fact, the ratio can be tuned extrinsically over one order in magnitude controllably either during or post growth, allowing for programing EPC in nanoscale devices. We point out that R21 is not directly related to Huang-Rhys factor, lattice relaxation is minimal for bulk and moderately small nanostructures, and Albrecht’s theory is not applicable to RRS [1,2]. This work provides unambiguous experimental results for validating EPC theories with reduced dimensionality.
[1] Y. Zhang, Journal of Semiconductors 40, 091102 (2019).
[2] Y. Yi et al., Phys. Rev. Appl.-Lett. 13, 011001 (2020).