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HL: Fachverband Halbleiterphysik

HL 57: Focussed Session: ZnO-based Semiconductors

HL 57.6: Invited Talk

Thursday, March 25, 2010, 15:45–16:15, H17

Interface Induced Gap States and ZnO Schottky Contacts — •Steven M. Durbin and Martin W. Allen — University of Canterbury, Christchurch, New Zealand

Practical aspects of fabricating Schottky contacts, such as lateral inhomogeneity, contaminants, and defects, can complicate the comparison of experimentally obtained barrier heights to theoretical predictions. The diode ideality factor η (which should approach unity for laterally homogeneous interfaces, after accounting for image force effects) is also strongly affected by the same issues, and correlations can be observed between barrier height and η when measuring large numbers of devices. ZnO could prove to be an interesting test case for evaluating various theoretical models, as it is significantly more ionic than most semiconductors, resulting in weaker Fermi pinning due to interface states. ZnO also does not require the removal of a native oxide layer for device processing, thereby avoiding often aggressive cleaning procedures. We have fabricated arrays of rectifying metal-ZnO contacts using bulk wafers and a wide variety of metals, using a technique which results in large barrier heights (typically > 0.8 eV) and low η (approaching the image force limit). Using the electrical characteristics of these diodes, we evaluate both Tung′s chemical bonding and Mönch′s metal induced gap states + electronegativity models, and discuss the limits of our current understanding of metal-ZnO interfaces.