The temperature dependent electrical properties of Ag Schottky contacts to a -plane bulk ZnO single crystal were investigated in the temperature range of 100-300 K. The variation in the barrier heights was described by a double Gaussian distribution with two different regions in the temperature range of 200-300 and 100-180 K. The modified Richardson plot in the temperature range of 200-300 K produced the Richardson constant of 29 A cm-2 K -2 which is similar to the theoretical value of 32 A cm-2 K-2 for n-type ZnO, indicating that the inhomogeneous barrier height with the thermionic emission model can explain the current transport well in this region. Below 200 K, the bulk carriers start to freeze out and the induced oxygen vacancies in the interface region, probably due to the formation of silver oxide at the Ag-ZnO interface, will influence significantly the current transport by creating very thin interfacial layer that is susceptible to electron tunneling.
Bibliographical noteFunding Information:
This work was supported by Basic Science Research Program (Grant No. 2010-0003594) and in part by the Pioneer Research Center Program (Grant No. 2010-0002231) through the National Research Foundation of Korea funded by the Ministry of Education, Science, and Technology (MEST).