Transparent JFETs Based on p-NiO/n-ZnO Heterojunctions

The fabrication of all-oxide junction-FETs consisting of n-type ZnO channels and p-type NiO gate electrodes with high optical transmission in the visible spectral range is reported. The influence of the channel layer thickness on the transfer characteristics in terms of ON-voltage, current ON/OFF ratio, and subthreshold slope was investigated. Best devices showed channel mobilities of around 4 cm(2) V-1 s(-1), ON/OFF ratios of up to 3 x 10(7), and subthreshold slopes close to the thermal limit. The ON-voltage can be shifted from -3.5 to similar to 0 V when the channel thickness is decreased from 80 to 10 nm. At elevated temperatures of up to 100 degrees C, the devices remain fully operational. After the annealing cycle, the OFF-current is only slightly increased irreversibly. The frequency dependence of the switching behavior was investigated (gate-lag effect), and a high-frequency cutoff frequency at f(c) = 123 kHz was determined.