Asymmetric Broadening and Enhanced Photoluminescence Emission in ZnO Due to Electron–Phonon Coupling

The ultraviolet emission of ZnO has great advantages for realizing applications in optoelectronics. Recent efforts to enhance their photoluminescence (PL) intensity have a profound importance to device efficiency. Enhanced PL spectra are always accompanied by large asymmetric broadening, and the recombination mechanism remains unclear. In this paper, the emission of ZnO thin films is enhanced by Ar and H2plasma treatments, showing an increase of 30-fold in the intensity and 4-fold in the full width at half-maximum (FWHM). The systematic time-resolved photoluminescence measurements illustrate an extraordinary recombination mechanism, as a wide range of photon energies possess identical dynamic features and temperature-dependent characteristics. The asymmetric broadening is attributed to strong electron–phonon coupling introduced by the variation of carrier distribution. As a theoretical confirmation, the multimode Brownian oscillator (MBO) model is used to quantitatively describe the line shape of spectra with a perfect agreement and evaluates the coupling strength between the primary oscillator and LO phonon. The recombination mechanism of enhanced and broadened PL spectrum is applicable to other materials with strong phonon interaction, which will be beneficial to improving the performance of optoelectronic devices.