| AVS 55th International Symposium & Exhibition | |
| Electronic Materials and Processing | Tuesday Sessions |
| Session EM-TuM |
| Session: | ZnO Materials and Devices |
| Presenter: | S.M. Durbin, University of Canterbury, New Zealand |
| Authors: | M.W. Allen, University of Canterbury, New Zealand S.M. Durbin, University of Canterbury, New Zealand |
| Correspondent: | Click to Email |
Historically, most attempts to fabricate Schottky contacts to ZnO have resulted in devices with relatively high ideality factors, and barrier heights in the 0.6 – 0.8 eV range regardless of the Schottky metal used.1 For ZnO applications, such as UV photodiodes, power diodes, and field effect transistors, homogeneous Schottky contacts with low ideality factors, high barrier heights and low reverse leakage currents are required. Recently, significant progress has been made towards understanding the conditions necessary for the reproducible fabrication of high quality Schottky contacts. In particular, studies into the effects of oxidation treatments, such as remote oxygen plasmas, hydrogen peroxide, and ozone, have established the link between improved Schottky contact performance and a reduction in surface hydroxide concentration,2 while the importance of reducing intrinsic point defects plus additional defects introduced by the metallization process has been established.3 We have fabricated ‘almost ideal’ Schottky contacts, with ideality factors approaching the image force limit, on hydrothermally grown bulk ZnO using a number of different Schottky metals. In this paper, we examine the key factors contributing to the success of these contacts. In particular, the polar and non-polar surfaces of bulk ZnO are naturally terminated by a hydroxide layer. Mechanisms for the removal of this accumulation layer are discussed, including the use of a reactive oxygen ambient in the fabrication of silver rich, silver oxide Schottky contacts which produce the highest reported Schottky barriers (1.00 - 1.20 eV) to ZnO. We will also provide evidence for the dominating influence of oxygen vacancies in Schottky contact formation via a relationship between the barrier heights of Ge, Ni, Ir, Pd, Pt Schottky contacts (on the same hydrothermal ZnO material) and the free energy of formation of their metal oxides.
1 K Ip. et al., J. Crys. Growth 287, 149 (2006).
2 B. J. Coppa et al., J. Appl. Phys. 97, 103517 (2005).
3 L. J. Brillson et al., Appl. Phys. Lett. 90, 102116 (2007).