Analyzing the Contact-Doping Effect in In₂O₃ FETs: Unveiling the Mechanisms Behind the Threshold-Voltage Roll-Off in Oxide Semiconductor Transistors

In this work, the contact-doping effect (CDE) and its impact on the threshold voltage ( ${V}_{\text {T}}$ ) roll-off in indium oxide (In2O3) field-effect transistors (FETs) are systematically studied. By analyzing the long channel length ( ${L} _{\text {ch}}$ ) and short ${L}_{\text {ch}}$ devices separately using a modified transfer length method (TLM), $\boldsymbol {\Delta }{L}$ can be extracted to quantify the CDE. The correlation between $\Delta {L}$ and the ${L}_{\text {ch}}$ at which ${V}_{\text {T}}$ roll-off occurs suggests that CDE may be a key factor contributing to the ${V}_{\text {T}}$ roll-off in In2O3 transistors. Next, the underlying mechanisms of CDE are investigated. It is found that oxygen scavenging reactions (OSRs) during the deposition of source/drain (S/D) metals on the In2O3 channel is one of the reasons behind CDE. S/D metals can scavenge oxygen atoms from In2O3, creating oxygen vacancies and increasing the carrier density near the S/D regions. Additionally, the Schottky barrier height ( $\boldsymbol {\Phi }_{\text {SB}}$ ) of metal/In2O3 contacts might also influence the CDE: a positive $\boldsymbol {\Phi }_{\text {SB}}$ depletes carriers, while a negative $\boldsymbol {\Phi }_{\text {SB}}$ accumulates them in the In2O3 channel under the S/D. This study provides a new approach to investigating CDE and highlights its critical role in understanding the ${V}_{\text {T}}$ roll-off in oxide semiconductor (OS) transistors.