Scanning tunneling microscope investigation of local density of states in Al-doped ZnO thin films

The electrical properties of grain boundaries in technologically relevant oxide thin films are the subject of both applied and fundamental research. Here we present an investigation of the local density of states (LDOS) in sputtered Al-doped ZnO using a scanning tunneling microscope. We observe a pronounced difference in the tunneling conductivity recorded on- and off-grain, with the grain boundary LDOS peaked ~600 meV below the Fermi level. This provides a direct measurement of the distribution of charge traps that is of relevance in advancing understanding of carrier conduction in this transparent conducting oxide.