Self-driven near infrared photoelectric detector based on C<sub>14</sub>H<sub>31</sub>O<sub>3</sub>P-Ti<sub>3</sub>C<sub>2</sub>/Au Schottky junction
Authors: Du Li-Jie , Chen Jing-Wen , Wang Rong-Ming ,   Beijing Advanced Innovation Center for Materials Genome Engineering, State Key Laboratory for Advanced Metals and Materials, Beijing Key Laboratory for Magneto-Photoelectrical Composite and Interface Science, School of Mathematics and Physics, University of Science and Technology Beijing, Beijing 100083, China
Published: May 2023

Ti<sub>3</sub>C<sub>2</sub>T<sub><i>x</i></sub>, as one of new two-dimensional materials MXene, has abundant surface functional groups (—OH, —F, and —O, etc.) and can exhibit semiconductor properties through further surface functionalization. In addition, it has excellent absorption capabilities for both infrared and visible light. Currently, there is limited research on applying the semiconductor properties of Ti<sub>3</sub>C<sub>2</sub>T<sub><i>x</i></sub> to infrared photodetectors. In this study, a self-driven near-infrared photodetector based on a C<sub>14</sub>H<sub>31</sub>O<sub>3</sub>P-Ti<sub>3</sub>C<sub>2</sub>/Au Schottky junction is developed. The modified C<sub>14</sub>H<sub>31</sub>O<sub>3</sub>P-Ti<sub>3</sub>C<sub>2</sub> two-dimensional semiconductor is prepared by a simple solution method, in which the phosphonic acid group reacts with the hydroxyl group on the Ti<sub>3</sub>C<sub>2</sub>T<sub><i>x</i></sub> surface. The C<sub>14</sub>H<sub>31</sub>O<sub>3</sub>P-Ti<sub>3</sub>C<sub>2</sub>/Au photodetector is constructed by using a drop-coating method at room temperature. The observation of an S-shaped curve in the <i>I</i>-<i>V</i> characteristics indicates the formation of a Schottky junction between C<sub>14</sub>H<sub>31</sub>O<sub>3</sub>P-Ti<sub>3</sub>C<sub>2</sub> nanosheets and the Au electrode. The device exhibits good detection performance in the near-infrared band (808–1342 nm), with a maximum responsivity of 0.28 A/W, a detectivity of 4.3×10<sup>7</sup> Jones and an external quantum efficiency (EQE) of 32.75% under 1064 nm infrared light illumination. The <i>I</i><sub>on</sub>/<i>I</i><sub>off</sub> ratio is 10.4, which is about 7.3 times higher than that under 1342 nm light. The response time and the recovery time of the device are 0.9 s and 0.5 s, respectively. After 10 cycles of <i>I</i>-<i>t</i>, the photocurrent does not show any significant decay, indicating excellent repeatability and cycle stability of the device. Owing to the built-in electric field formed by the Schottky junction, photo-generated electrons and holes can quickly separate and produce photocurrent in the external circuit without the need for external voltage driving. In addition, the C<sub>14</sub>H<sub>31</sub>O<sub>3</sub>P-Ti<sub>3</sub>C<sub>2</sub> film obtained by drop-casting on Au is composed of several layers of nanosheets that are randomly stacked, which can effectively relax the plasma momentum limitation, promote the generation of hot electrons, and contribute to the photocurrent. As the C<sub>14</sub>H<sub>31</sub>O<sub>3</sub>P-Ti<sub>3</sub>C<sub>2</sub>/Au Schottky junction photodetector possesses self-driven characteristics and simple fabrication process, it exhibits great potential applications in detecting weak light signals, such as in the fields of astronomy and biomedical science. The successful fabrication of this photodetector provides a new approach for designing and developing MXene-based near-infrared detectors, thus promoting further advancements in this field.