HUANG Zhijuan , YU Zhinong ,＊, LI Yan , WANG Jizheng

1 Beijing Engineering Research Center of Mixed Reality and Advanced Display, School of Optoelectronics, Beijing Institute of Technology, Beijing 100081, P. R. China.

2 Key Laboratory of Organic Solids, Institute of Chemistry, Chinese Academy of Sciences, Beijing 100190, P. R. China.

Abstract: ZnO is an ideal material for ultraviolet (UV)detection due to its wide direct-bandgap, high exciton binding energy, and high internal photoconductive gain. However, ZnO UV detectors have the disadvantages of slow response speed and low detectivity. Graphdiyne (GD) is a novel carbonaceous allotrope, and possesses excellent electronic performance in air.In this study, the metal-semiconductor-metal (MSM) structured lateral ZnO UV detectors were prepared, and GD was employed to modify the ZnO surface. The effects of GD deposited 1–3 times (viz. 1T, 2T, and 3T GD) on the performance of ZnO ultraviolet detector were carefully investigated. The results show that the dark current of the bare ZnO detector is 24 μA under a bias of 10 V, while that of the graphdiyne-modified detector is ～0.34 μA (about two orders of magnitude reduction). The dark current remains almost the same for the 1T, 2T and 3T GD films. The photocurrents of 1–3T GD-modified detectors were 0.21, 0.32, 0.27 mA,respectively. The device modified with 2T GD displays the highest photocurrent, which is significantly enhanced in comparison to the unmodified device (0.08 mA) under a 365-nm UV radiation of 100 μW·cm−2. Meanwhile, the responsivity and detectivity are improved remarkably. Under a bias of 10 V, the 2T-GD-modified detector displays high responsivity of 1759 A·W−1 and detectivity of 4.23×1015 Jones. The detectivity is thus far the highest for ZnO UV detectors prepared by the sol-gel method. The improved performance of the GD-modified detector is attributed to the p-n junction formed between the GD and the ZnO film. At dark, the p-n junction is formed between the ZnO film and the GD, which greatly decreases the dark current of the detector. Under UV illumination, photogenerated holes accumulate in the GD,reducing electron-hole recombination; thus, the photocurrent is significantly increased. Furthermore, desorption and absorption of oxygen on the ZnO surface are much reduced due to the GD attached on the ZnO surface, thus improving the response speed of the detector. However, the intensive distribution of GD slightly hinders the UV absorption of ZnO thin films, reducing the responsivity of the detector. Careful optimization shows that the use of 2T GD gives the best output,and the corresponding ZnO UV detector exhibits very good performance. Overall, this study demonstrates that using GD can effectively improve the performance of ZnO UV detector.

Key Words: Graphdiyne; Zinc oxide; Ultraviolet detector; Responsivity; Detectivity

1 引言

ZnO是一种直接宽带隙的 II-VI族半导体材料，自然状态下为纤锌矿结构，禁带宽度为3.3 eV，激子束缚能为60 meV，远高于室温下的26 meV1，且具有独特的光学和电学特性，以及良好的热稳定性和化学稳定性，因此在紫外探测领域获得了很高的关注2,3。对于未封装的ZnO紫外探测器，空气中的氧分子会在ZnO薄膜表面进行吸附和解吸附，这一定程度上有利于探测器响应度的提高，然而氧的吸附和解吸附需要很长的时间，导致器件响应速度很慢3。因此近年来，大量研究人员采用不同方法对ZnO紫外探测器的光电特性进行改善，例如利用Au4,5，Ag6，Al7,8等金属材料和石墨烯9,10，碳纳米点11等碳质材料对 ZnO进行掺杂或表面修饰。由于这些材料导电率均高于ZnO，对ZnO进行掺杂可以降低ZnO材料的电阻率，提高器件的光电流。而表面修饰可以为光生载流子提供快速传输通道，同时抑制ZnO表面氧的吸附和解吸附过程，因此可有效地改善紫外探测器的响应度，响应速度等性能。

石墨炔被认为是一种新的碳质同素异形体，它是由二炔键将 6个苯环共轭连接形成的全碳分子12,13，其sp与sp2杂化态的成键方式决定了其独特的二维平面网络构型14。它天然三角孔状结构，丰富的碳化学键、可调控的电子结构和良好的化学稳定性，使其在信息技术、电子、能源、催化以及光电等领域具有重要的应用前景。研究结果表明，石墨炔具有0.46 eV的天然带隙，良好的空穴传输特性15,16，这有助于促进探测器光生电子空穴对的分离，提高探测器性能。……