Diode junctions between two ZnO nanoparticles: current rectification and the role of particle size (and bandgap).

We form junctions between two ZnO nanoparticles of two different dopant concentrations. A monolayer of intrinsic (n-type) and a monolayer of Al-doped (n(+)-type) ZnO nanoparticles are deposited in sequence to form the junctions. The size of the nanoparticles (and hence their bandgap) has been varied. Such junctions on a doped Si electrode have been characterized with a scanning tunneling microscope (STM) tip as the other electrode. The junctions show rectifying current-voltage characteristics. Control experiments, such as (1) symmetric characteristics from the components of the junctions and (2) inverse rectification in a junction having the monolayers in reverse sequence, rule out any effect of interfaces in the observed rectification. The results show that rectification is higher in nanodiodes with high bandgap nanoparticles. The ideality factor of the nanodiodes has been calculated.