Conductivity of Si-ZnO p-n and n-n heterojunctions

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Abstract
Heterojunctions have been prepared by the reactive rf, sputter deposition of n-ZnO on sputter-etched n- and p-type silicon substrates. Measurements of conductance show typical low-reverse breakdown at 18–25 V and forward currents of 2–10 mA at 3 V, both n-n and p-n diodes rectify. At low forward bias, 0–0.3 V, both types of diode have characteristics of the form I=I0[exp(qVA/βkT)−1] with large ideality factors β close to 5 for n-n and 7 for p-n junctions. In the range 0–100 °C β varies by only 15% in each case. Film series resistance predominates above 0.5 V with resistivities close to those measured transversely for films on insulating substrates. A model of highly doped ZnO crystallites with macroscopic mobility controlled by intergranular barriers is coupled with an interface state dominated junction band profile to account for these results.

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