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

The absence of a high-performance p-channel oxide thin-film 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 ∼2.8 ×1013 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 × 1012 cm–2 eV–1 and demonstrated the Cu2O-TFT with a saturation mobility of 1.38 ± 0.7 cm2 V–1 s–1, a s-value of 2.35 ± 1.22 V decade–1, and an on/off current ratio of ∼4.1 × 106. 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 ∼230 at VDD = 70 V.