The Electronic Impact of X-Ray on Atomically-Thin Oxide Semiconductor Devices

In the past few years, there has been a significant emphasis on atomically-thin metal oxide semiconductors (OS), driven by their adjustable electrical properties that open up a range of electronic applications [1.2]. However, the mechanisms of transport and electronic tunability in OS remain unclear [3]. X-ray characterization techniques, i.e. X-ray photoelectron spectroscopy (XPS) and X-ray diffractometer (XRD), are considered as non-destructive and are widely used to quantify the chemical and electronic state of OS. In this work, we discovered that X-ray has significant impact on the electronic properties of OS. We observed that low energy X-ray (<2 keV) induces a negative V T offset in OS devices [4]. The variation in V T primarily originates from the chemical interaction of oxygen molecules on the channel surface. OS devices absorb the low-energy X-ray, generating the holes, and they subsequently react with O 2 - on the channel surface, resulting in the production of oxygen and its removal from the channel surface, as shown in Fig 1a. The V T shift caused by low energy X-ray will recover in air over time, as illustrated in Fig 1b. We incorporated the post low-energy X-ray devices into a vacuum environment with a pressure of 10 -6 torr, and the V T of the device exhibited no recovery over time, providing additional support for oxygen absorption mechanism. Time-resolved electrical measurements conducted in different atmospheric conditions reveal that the variations in V T arise from the oxygen absorption mechanism. The research highlights the effect of X-ray on OS and analyzes the mechanism behind the increase in OS carrier concentration induced by the X-ray exposure. [1] Si, M. et al. Scaled indium oxide transistors fabricated using atomic layer deposition. Nat. Electron. 5, 164–170 (2022). [2] Charnas, Adam, et al. Extremely Thin Amorphous Indium Oxide Transistors. Adv. Mater. 2304044 (2023). [3] Conley, J. F. Instabilities in amorphous oxide semiconductor thin-film transistors. IEEE Trans. Device Mater. Rel. 10, 460–475 (2010). [4] Tseng, R., Wang, ST., Ahmed, T. et al. Wide-range and area-selective threshold voltage tunability in ultrathin indium oxide transistors. Nat. Commun. 14, 5243 (2023).