Effect of ozone cleaning on Pt/Au and W/Pt/Au Schottky contacts to n-type ZnO

The role of UV ozone cleaning on the characteristics of Pt contacts on n-type (n similar to 10(17) cm(-3)) bulk single-crystal zinc oxide (ZnO) is reported. The contacts are Ohmic for samples that were not exposed to ozone prior to Pt deposition, but exhibit excellent rectifying behavior with ozone cleaning. The barrier height of these contacts obtained from current-voltage measurements was 0.70 +/- 10.04 eV at 25 degreesC with an ideality factor of 1.49 and a saturation current density of 6.17 x 10(-6) A cm(-2). There is a significant decrease in surface carbon concentration after the ozone cleaning (29.5 at.% down to 5.8 at.%, as determined from Auger electron spectroscopy). The measured barrier height for Pt on ZnO is similar to the value reported for both An and Ag rectifying contacts on this material. By sharp contrast, sputter-deposited W contacts are Ohmic, independent of the use of ozone cleaning and become rectifying after 700 degreesC annealing to repair sputter-induced damage. The barrier height is similar to 0.45 - 0.49 eV, with the ozone cleaning producing values at the high end of this range. (C) 2004 Elsevier B.V. All rights reserved.