Resonant coupling of bound excitons with LO phonons in ZnO: Excitonic polaron states and Fano interference

Abstract

We report on a photoluminescence observation of robust excitonic polarons due to resonant coupling of exciton and longitudinal optical (LO) phonon as well as Fano-type interference in high quality ZnO crystal. At low enough temperatures, resonant coupling of excitons and LO phonons leads to not only traditional Stokes lines (SLs) but also up to second-order anti-Stokes lines (ASLs) besides the zero-phonon line (ZPL). The SLs and ASLs are found to be not mirror symmetric with respect to the ZPL, strongly suggesting that they are from different coupling states of exciton and phonons. Besides these spectral features showing the quasiparticle properties of exciton-phonon coupling system, the first-order SL is found to exhibit characteristic Fano lineshape, caused by quantum interference between the LO components of excitonic polarons and the continuous phonon bath. These findings lead to a new insight into fundamental effects of exciton-phonon interactions.

Optical properties of homo- and heteroepitaxial single quantum wells grown by pulsed-laser deposition

“…Noticeable is the asymmetric lineshape. A similar phenomena is reported elsewhere [13] and is in that case interpreted as a Fano interference [14]. Another possible explanation could be an absorption edge, related to polarons in ZnO [15].…”

Extinction of the zero-phonon line and the first-order phonon sideband in excitonic luminescence of ZnO at room temperature: the self-absorption effect

“…2a. As the temperature increases, the OPA-PL spectrum evolves as reported previously [19,20], as shown in Fig. 2b.…”

“…2a, both OPA-PL and TPA-PL spectra show similar spectral features at 4 K, e.g. comprising three types of principal emission lines and their LO phonon sidebands: donor-bound-exciton (DX-mLO), free-exciton (FX-mLO), and two-electron-satellite (TES-mLO) emissions with m = 0, 1, 2, 3 [18,19]. However, a noticeable difference between the 4 K OPA-and TPA-PL spectra is the relative intensity between the ZPL lines and their respective LO phonon sidebands.…”

Identification of a Deep Acceptor Level in ZnO Due to Silver Doping

“…4 as well. This phenomenon has been previously observed in ZnO, 32 and is due to resonant coupling of the I 6 exciton with the LO phonons, since the total binding energy of the I 6 complex (60 meV exciton binding energy plus 16 meV exciton localization energy) is comparable to the LO phonon energy (72 meV). Intensity of the 1LO replica of I 6 is significantly reduced as a result of the Fano resonance, sometimes resulting in misidentification of the 2LO peak as a donor-acceptor-pair transition, due to its high relative intensity compared to the 1LO peak.…”