Investigation of threshold switching mechanism based on Mn-doped ZnO/GaN heterojunction by photogenerated carrier injection

Highly c-axis oriented ZnO thin films have been prepared on n-type GaN-coated sapphire substrates by radio frequency reactive magnetron sputtering at 100 °C followed by thermal annealing at 740 °C for 2 h. The ZnO/GaN heterojunction devices show a steady threshold switching (TS) characteristic. In addition, Mn-doped ZnO (MZO)/GaN heterojunction has been prepared and it shows lower threshold voltage and higher on/off ratio than those of ZnO/GaN heterojunction. The formation of TS characteristic may be attributed to trapping and detrapping of electrons in heterojunction device. Furthermore, the devices are investigated by the injection of photogenerated carriers, it is illustrated that the external carrier injection may affect the rate of the trapping of electrons and results in the decrease of the threshold voltage.