Emission Kinetics of Surface (Bi)Excitons in ZnO Thin Films

Abstract

The kinetics of near-edge photoluminescence (PL) in ZnO nanofilms prepared by the atomic layer deposition has been investigated. It is established that the kinetics of near-edge PL in 4-nm films is determined to a great extent by surface 2D-exciton (SX) and biexciton (SXX) complexes. The contribution from surface biexcitons is estimated based on a photostimulated change in the surface potential in ZnO films with different thicknesses. Ultrafast dynamics of surface biexcitons in thin films are revealed. It is shown that biexcitons localized near the surface have the shortest radiative lifetime (less than 100 ps) among all bound exciton complexes, which is explained by the large oscillator strength.