ZnO Interface Electrical Properties-Role of Oxygen Chemisorption
In the present studies single ZnO grain boundary or electrode interfaces are isolated and examined as a function of dopant, temperature, atmosphere, and potential. ZnO-Ag junctions were found to be rectifying but with marked sensitivity to ambient conditions (T, Po2) and applied bias. The I(V) characteristics were examined in relation to the predictions of Sze for a metal-semiconductor junction in which both interface states and the nature of the metal influence the barrier height. Reasonable surface state densities are obtained by application of the model to our data. Difficulties associated with the derivation of thick interfacial layers are discussed. The existence of volatile surface states is confirmed by examination of atmosphere and voltage induced transients in barrier height. Manganese and manganese/praseodymium doped grain boundaries are characterized by varistor-like behavior with 3–4 volt breakdown and nonlinearity factor of three. The apparent non-activated behavior of the leakage current was traced to a strong temperature dependent barrier height characterized by ∂ϕB/∂T = 1.5 × 10−3 eV/k, a result of absorbed oxygen at the boundary.
KeywordsBarrier Height Interfacial Layer Schottky Barrier Reverse Bias Forward Bias
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