电场调控高响应度超快宽谱石墨烯光电探测器研究

As one of two-dimensional (2D) atomic crystals, graphene is considered to be one of promising materials for ultrafast broadband photodetector because of its high mobility (200,000cm2V-1s-1) and broadband absorption from visible to far-infrared. However, the responsivity of graphene photodetector is still as low as several mA/W due to the short exciton lifetime (ps) and low absorption (2.3%). Here, we propose to improve the responsivity of graphene photodetector by appling an electric field by the following two ways: 1) In the field effect transistor structure, a pair of in-plane untouched electrodes are planned to constructed perpendicular to graphene channel. Then the photo induced exciton could be separated efficiently in the applied electric field. 2) For the suspending graphene FET photodetector, the carrier density in the graphene can be adjusted by the gate voltage, and electrostatic force could form between graphene and gate electrode, and this strain is nonliner, thus a bandgap could be opened in this situation. The opening of this bandgap could significantly enhance photo induced bolometric effect and decrease exiton recombination and then increase the responsivity. The goal of the present project is realizing the high photoresponsivity, broadband response and fast detection from graphene photodetector, as well as elucidating the transport and recombination mechanism of carrier in the novel devices. Meanwhile, these strategies could also be applied in other 2D materials based photodetector and thus this project is significant for the applications of graphene and other 2D materials in optoelectronic devices.

二维原子晶体石墨烯具有高达200,000cm2V-1s-1的载流子迁移率及从可见光到中红外的超宽光谱吸收，是制备宽光谱超快光电探测器的最佳候选材料之一。然而，相对较弱的光吸收率（2.3%）及较短的激子寿命（ps量级）使得石墨烯光电探测器的响应度徘徊在mA/W量级。本项目中，我们拟采用外置电场调控的办法提高其响应度：在石墨烯探测器沟道面内垂直方向制备非接触电极，通过施加面内静电场促使石墨烯光生激子分离；构建悬空状态石墨烯探测器，通过施加法向垂直栅压调控石墨烯内电荷浓度，借助电荷受到的静电力在石墨烯上施加非均匀力场进而调控石墨烯能带结构，增强辐射热效应且降低激子复合，提高光电响应度。通过该项目我们期望实现超快宽谱响应石墨烯光电探测器的高效光电转化，揭示新型器件结构中载流子在特定电场下输运与复合机制，同时该思路也可拓展到其它二维光电材料，为实现石墨烯及其它二维原子晶体材料的光电子学应用奠定基础。

石墨烯是制备宽光谱超快光电探测器的最佳候选材料之一。然而，相对较弱的光吸收率（2.3%）及较短的激子寿命（ps量级）使得石墨烯光电探测器的响应度徘徊在mA/W量级。本项目中，首先完成制备可实现面内垂直电场施加的石墨烯光电探测器。面内垂直电场的施加，可有效地降低器件暗电流。进而完成制备可实现法向垂直电场施加的石墨烯光电探测器。法向垂直电场的施加，可有效打开石墨烯带隙。当底栅栅压为-1V时，光响应度为4.33A/W。提高石墨烯探测器光响应度三个数量级，同时器件响应时间到百毫秒级别。随后完成制备可同时施加面内垂直电场，法向垂直电场的石墨烯光电探测器。双场的施加，实现了光电流提升的同时，暗电流也被有效调控，器件探测率可达到1.518×10^9Jones。双场调控石墨烯光电探测器实现了宽光谱，快速探测，高响应度的石墨烯光电探测器。将项目推广到二硫化钼光电探测器之中。在二硫化钼垂直电场光电探测器中，实现器件响应速度可调。在-1V底栅栅压下，二硫化钼器件的响应时间可以缩短至40ms。随后在面内垂直电场调控思路的启发下，设计了面内同质结二硒化钼光电探测器。-50V栅压时，器件的响应度可达到519A/W，该方法有效地改善了单纯的二硒化钼光电探测器性能。最后在法向方向垂直电场调控思路的启发下，设计了一种级联能带结构的硫化铅量子点黑磷光电探测器。黑磷光电探测器的性能被有效改善，光响应度达到1.1×10^7A/W，探测率达到1.75×10^15Jones，等效噪声功率下降到4.3×10^-7pW/Hz^1/2。对本项目成功推广，更加印证了本项目的可行性。本项目初步实现了石墨烯及其它二维原子晶体材料的光电子学应用，为进一步推广本项目打下坚实基础。