Back-Channel Defect Termination by Sulfur for p-Channel Cu2O Thin-Film Transistors

The absence of a high-performance p-channel oxide thinfilm transistor (TFT) is the major challenge faced in the current oxide semiconductor device technology. Simple solution-based back-channel subgap defect termination using sulfur was developed for p-channel cuprous oxide (Cu2O)-TFTs. We investigated the origin of poor device characteristics in conventional Cu2O-TFTs and clarified that it was mainly because of a back-channel donor-like defect of similar to 2.8 X10(13) cm(-2) eV(-1), which originated from the interstitial Cu defect. Sulfur ion treatment using thiourea effectively reduced the back-channel defect down to <3 X 10(12) cm(-2) eV(-1) and demonstrated the Cu2O-TFT with a saturation mobility of 1.38 +/- 0.7 cm(2) V-1 s(-1), a s-value of 2.35 +/- 1.22 V decade(-1), and an on/off current ratio of similar to 4.1 X 10(6). The improvement of device characteristics was attributed to the reduction of back-channel defect by the formation of a thin CuSO4 back-channel passivation layer by the chemical reaction of interstitial Cu with S and O ions. An oxide-based complementary inverter using a p-channel Cu2O-TFT and a n-channel a-In-Ga-Zn-O-TFT was demonstrated with a high voltage gain of similar to 230 at V-DD = 70 V.