Schottky contacts to ZnO layers grown by Atomic Layer Deposition: effects of H_2O_2 functionalization and transport mechanisms

摘要

Vertical structures based on Pd Schottky contacts to a ZnO/AZO bilayer have been realized and electrically characterized. Following a preliminary annealing study on the separated ZnO and AZO layers the ZnO/AZO bilayer was first annealed at 450 degrees C for 30 min to reduce the carrier concentration and then functionalized with a H2O2 dip prior to Pd deposition. On the basis of Atomic Force Microscopy, Transmission electron Microscopy and Capacitance vs Voltage measurements it has been found that the H2O2 treatment lowers the surface roughness and creates a similar to 200 nm thick layer formed by ZnO crystallites with grain size less than or similar to 10 nm embedded into an amorphous matrix with reduced carrier concentration. However, contrary to what previously reported no formation of ZnO2 has been observed. The obtained Schottky contacts showed a rectification ratio greater than or similar to 10(2) at -2 V/+2 V with a detailed analysis based on the differential approach pointing to field enhanced emission from defective channels as the main leaking mechanisms.