Mixed mode, ionic-electronic diode using atomic layer deposition of V₂O₅ and ZnO films

We demonstrate high current rectification in a new system comprising 30 nm of hydrated vanadium pentoxide and 100 nm of zinc oxide (V₂O₅·nH₂O–ZnO) thin film structures. The devices are prepared using a low temperature (<150 °C), all atomic layer deposition process. A key element in the rectifying properties comes from anomalous p-type conductivity in V₂O₅ – an otherwise well known n-type semiconductor. Experimental evidence points to protonic (H⁺) conductivity due to intercalated water in V₂O₅ as the source for p-type behaviour, while the ZnO is known to be electronically n-type. Thus, the diode behaves as a novel, mixed mode ionic-electronic rectifier. Further, we show that the diode characteristics are strongly dependent on the electrode material in contact with V₂O₅·nH₂O. A high I_on/I_off ratio (598) at ± 2 V is obtained for oxygen-free Pt electrodes, whereas a low I_on/I_off ratio (19) is obtained for oxygen-rich ITO electrodes, suggesting the deleterious effects of oxygen atom reactivity to device characteristics.