Gold Schottky contacts on oxygen plasma-treated, n-type ZnO(000(1)over-bar)

Reverse bias current-voltage measurements of similar to100-mum-diameter gold Schottky contacts deposited on as-received, n-type ZnO(000 (1) over bar) wafers and those exposed for 30 min to a remote 20% O-2/80% He plasma at 525+/-20 degreesC and cooled either in vacuum from 425 degreesC or the unignited plasma gas have been determined. Plasma cleaning resulted in highly ordered, stoichiometric, and smooth surfaces. Contacts on as-received material showed muA leakage currents and ideality factors >2. Contacts on plasma-cleaned wafers cooled in vacuum showed similar to36+/-1 nA leakage current to -4 V, a barrier height of 0.67+/-0.05 eV, and an ideality factor of 1.86+/-0.05. Cooling in the unignited plasma gas coupled with a 30 s exposure to the plasma at room temperature resulted in decreases in these parameters to similar to20 pA to -7 V, 0.60+/-0.05 eV, and 1.03+/-0.05, respectively. Differences in the measured and theoretical barrier heights indicate interface states. (0001) and (000 (1) over bar) are used in this letter to designate the polar zinc- and oxygen-terminated surfaces, respectively. (C) 2003 American Institute of Physics.