Observation of disorder-driven carrier localization by Auger resonant Raman scattering inn-type doped ZnO

We present direct evidence of carrier localization in (Zn,Al)O by using Auger resonant Raman scattering, which makes use of the competition between the core-hole decay time and the motion of the photoexcited electrons. From the branching ratio of the competing two channels, i.e., normal Auger-like and spectator Auger processes, we found that the average carrier transfer time from a donor site is in the range of 6--140 fs depending on structural disorder. The transfer time shows a rapid increase at a certain energy in the conduction band. This result suggests that the disorder-induced localization limits the electronic conductivity in the heavily $n$-doped ZnO.