I am performing C-V using SPA on two In contacts made on ZnO film. At first, it was observed to give a step increase in capacitance as the applied voltage is changed from negative to positive. After annealing these samples in vacuum, the capacitance dips near the transition of voltage from negative to positive and than returns to same capacitance level as voltage is further increased. It is baffling me, because both nature of capacitance represent very different film and contact properties. Please suggest what could be a probable reason for such capacitance in ohmic contacts, which is repeatedly confirmed by I-V measurements.
The most probable reason is that there is large stray capacitance effect. Two adjacent conductors can function as a capacitor, but this capacitance is typically small unless these conductors are close to each other over a large area.
Mohamed Ghoneim
Thank you very much for your detailed answer. I have some very confusing results working with ZnO for transistor application. I will definitely look into your work for further explanations.
Dear Mohammed,
When the measured capacitance changes with the bias voltage it points out on the presence of rectifying contacts. In order to verify if your contacts are ohmic or rectifying Schottky contacts as hinted by Martin yo can use the three electrode method. Then you need to make a third contact. You derive a current between two of them and and measure the voltage between one of them and the third electrode.
The details of this method is given in the paper at the link: Article A. Zekry and G. El-Dllal, “ effect of MS contact on the elec...
Best wishes
Thank you Abdelhalim abdelnaby Zekry Sir, your information is highly helpful.
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