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 × 10
⁷
, and subthreshold slopes close to the thermal limit. The ON-voltage can be shifted from -3.5 to ~0 V when the channel thickness is decreased from 80 to 10 nm. At elevated temperatures of up to 100 °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.