Time-Domain Observation of Spectral Diffusion in Defective ZnO

Defects can affect all aspects of materials by altering their electronic structures and mediating the carrier dynamics. However, in the past decades, most research efforts were restricted to nonstoichiometric defects, while the effects of high-density defects on the carrier dynamics of semiconductors remained elusive. In this work, using transient absorption spectroscopy, we have observed for the first time a hybrid carrier relaxation dynamics with the feature of a Poisson-like retard shoulder in a time-domain profile in highly defective ZnO crystals. This novel behavior has been attributed to the spectral diffusion within continuum defect states, which is further confirmed by a proposed diffusion (in energy space) controlled carrier dynamic model. Our results thus reveal an alternative energy decay channel in highly defective crystals and may provide a new route for defect engineering.