| 摘要: | 近年來「二維單晶奈米薄膜」之蓬勃發展，以蔚為風潮。在這些發展中，石墨烯固然扮演領銜之角色，然而石墨烯雖有其特殊之物理、化學、機械、光電特性，但因石墨烯的極弱吸光係數（~2.3%）、短暫之光載子生命期，導致其僅具頗低之光響應率（photoresponsivity, 5*10-4 AW-）與內在量子效率（intrinsic quantum efficiency, 6-16%）。又因石墨烯不具能隙（energy bandgap），使其無明顯之開關態（on/off state）、並擁較高之暗電流（dark current），致使石墨烯在光偵測（photodetection）應用上呈現缺點、與無謂之能量消耗。相對的，「二維單晶半導體奈米薄膜（2D single-crystalline semiconductor nanomembranes）」材料卻能克服上述石墨烯之諸多光
電（opto-electronic）缺點，在我們最近研究的「二維單晶半導體奈米薄膜」，例如：InSe，GeS ， GeS/InSe p-n junction 等 材 料 ， 我 們 可 以 這 些 材 料 製 備 奈 米 薄 膜 光 感 測 元 件
（photodetector），並選擇將這些奈米薄膜光感測元件製備於堅硬之 SiO2/Si 晶片、或撓曲之聚對苯二甲酸乙二酯（polyethylene terephthalate, PET）的基板上。這些奈米薄膜做成之光感測元件，
有極寬之波長響應範圍（photoresponse range），適用於可見光至遠紅外光之偵測，且具極高之光響應率（photoresponsivity），並擁有快速對光響應（~300 μs）及穩定持久（目前實驗以小時計）光控開關（photo-switching）之優點。
近來發展之「二維單晶半導體奈米薄膜」材料，展現其具有獨特之維度、超薄、與原子等級平坦表面之結構特性。利用「二維單晶半導體奈米薄膜」可製備成超小、但擁有優良光響應率、量子效率、比探測率之光電元件。在這研究計劃裡，我們將利用個別之「二維單晶半導體奈米薄膜」、以及不同之「二維單晶半導體奈米薄膜」組合成奈米元件，例如：p-n 接面二極體、光伏效應、發光二極管、場效電晶體等，以做為光電儀器與生物感測之應用。;Two-dimensional crystals with a wealth of exotic dimensional-dependent properties are promising candidates for next-generation ultrathin and flexible optoelectronic devices. First, we demonstrate that few-layered InSe photodetectors, fabricated on both a rigid SiO2/Si substrate and a flexible polyethylene terephthalate (PET) film, are capable of conducting broadband photodetection from the visible to near-infrared region (450−785 nm) with high photoresponsivities of up to 12.3 AW−1 at 450 nm (on SiO2/Si) and 3.9 AW−1 at 633 nm (on PET). These photoresponsivities are superior to those of other recently reported two-dimensional (2D) crystal-based (graphene, MoS2, GaS, and GaSe) photodetectors. The InSe devices fabricated on rigid SiO2/Si substrates possess a response time of ∼50 ms and exhibit long-term stability in photoswitching. These InSe devices can also operate on a flexible substrate with or without bending and reveal comparable performance to those devices on SiO2/Si. With these excellent optoelectronic merits, we envision that the nanoscale InSe layers will not only find applications in flexible optoelectronics but also act as an active component to configure versatile 2D heterostructure devices.
Next, we demonstrate that three types of Van der Waal based heterojunctions, they are isotype (n-n) junction, anisotype (p-n) junction and iso-anisotype hetero junction (n –ambipolar semiconductor). The fabricated isotype junction between the few layered flakes of n- InSe and multilayer n-MoTe2 exhibits rectification kind of behavior in forward bias and shows non-saturated current in reverse bias mode. The highest rectification ratio of the Isotype junctions is around 10 at zero gate voltage. Further, we demonstrate the temperature dependent current transport mechanism in isotype junction from 77K to 300 K. Next, the anisotype junction between few layered flakes of n-InSe and p-GeS shows the rectification behavior in forward bias and saturation current in reverse bias mode. The measured rectification ratio and ideality factor of the anisotype junction are 2.3 and 105 at Vg= -80 V Then, we studied the optical properties of the anisotype junction and the achieved responsivity and quantum efficiency are 2 AW-1 and 40. Next, we demonstrate the fabrication and characterization of a new kind of a junction, named it as an iso-anisotype junction between n-InSe and ambipolar graphene. Further, it has been demonstrated that the output characteristics of the iso-type junction could be modulated by applied gate voltage. The gate dependent electrical characteristics proves that, we can create isotype and anisotype hetero junctions within the same device, by simply tuning the fermi level of ambipolar (MoTe2) semiconductor by using back gate voltage . Further we demonstrate the application of the iso-anisotype device as a photovoltaic cell and the measured fill factor of the device is 0.28. |
