新穎二維材料在電晶體、光感測器及發光二極體上的應用

Abstract

層狀二維材料因著獨特的量子性質被廣泛的運用在各種元件，像是高靈敏度感測器、人工組織工程、催化劑和儲能元件。因此，開發合適的二維材料成為當前最優先的目標。本研究中，我們成長高品質單晶新穎二維材料：硒化銦和硫化鍺，並且研究這兩者材料的電性和光學性質，且組裝成多層硒化銦電晶體和硫化鍺電晶體。 多層硒化銦電晶體在室溫下展現優異的電子遷移率>1000 cm2/Vs，此項數據高於先前已被報導的許多二維金屬二硫屬化物。本研究中探討多種基板，包括聚甲基丙烯酸甲酯(PMMA)、氧化矽、頓化氧化矽和氮化矽，皆用來製作多層硒化銦電晶體元件。 利用背閘極和霍爾測量探討二維材料的本質傳導特性和介電基板效應，當量測溫度從20−300 K時，多層硒化銦電晶體電子遷移率和霍爾遷移率從0.1變化至2.0 × 103 cm2/Vs。 多層硫化鍺光感測器展現出高的光響應率206 安培/瓦，觀察到的光電流高於先前所發表的硒化鍺和硫化錫光感測器，再者，硫化鍺光感測器表現出高外部量子效率(EQE)達4.0 × 104 %和比探測率(D*)達2.35 × 1013 Jones，所量測到的比探測率和目前商用的矽和砷化鎵光感測器是相當的，硫化鍺光測器擁有很好的常時間光開關穩定性。另外，將多層硫化銦組裝在硬質矽晶片和軟質聚對苯二甲酸(PET)薄膜上，能夠偵測廣範圍光波長偵測，從可見多(450奈米)到近紅外光(785 奈米)，硬質矽晶片上的光響應率利用波長450奈米光照射時可達12.3 AW−1；軟質聚對苯二甲酸薄膜利用波長為633奈米光照射時，光響應可達3.9 AW−1。 本研究中最後部分，我們利用單閘極和不同功函數金屬當做電極，能夠在電性量測上得到雙極傳導行為(ambipolar behavior)，一系列的實驗顯示透過特定功函數電極和硒化銦進行接觸，可以有效的控制載子的傳遞。接者，我們利用不同功函數金屬當作源極和汲極可以減少肖特基勢壘(Schottky barriers)，因此，透過選擇合適的金屬當做電極，即可達到載子雙極傳遞的行為。 多層硒化銦和硫化鍺因著擁有獨特的性質，是未來開發高效能奈米元件適宜的材料，因著這些優點，我們可想像多層硒化銦和硫化鍺不僅可運用在許多光電元件和可撓曲元件，也可在二維異質結構元件上扮演重要的角色。

The exotic quantum properties of two-dimensional (2D) layered materials are used for various potential applications, such as nanoscale electronics, optoelectronics for ultrasensitive sensors, tissue engineering, catalysis, and energy storage. Pursuing the 2D materials is a high priority in the discovery of suitable and promising candidates for fabricating the devices. In this study, we report the growth of novel 2D materials, such as indium selenide (InSe) and germanium sulfide (GeS) high-quality single crystals. The electrical and optical properties of both these single crystals were investigated. The main focus of this thesis is the careful fabrication and demonstration of multi-layered as well as few-layered InSe- or GeS-based field-effect transistors (FETs). The multi-layered InSe-FET shows a mobility of >1000 cm2/Vs at room temperature, which is higher than that of recently reported FETs made of widely studied 2D transition metal dichalcogenides. In this work, various substrates, such as PMMA, bare silicon oxide, passivated silicon oxide, and silicon nitride were used to fabricate multilayer InSe-FET devices. Through back gating and Hall measurement in four-probe configuration, the device’s field-effect mobility and intrinsic Hall mobility were extracted at various temperatures to study the material’s intrinsic transport behavior and the effect of the dielectric substrate. The sample’s field-effect and Hall mobilities over the range of 20−300 K fall in the range of 0.1−2.0 × 103 cm2/Vs. The multi-layered GeS-FET photodetector exhibits a high photoresponsivity about 206 AW-1. The observed photocurrent is higher than the known GeSe and SnS2 photodetectors. Moreover, the multi-layered GeS photodetector exhibits high external quantum efficiency (EQE ~ 4.0 × 104 %) and specific detectivity (D* ~ 2.35 × 1013 Jones). The measured D* is comparable to those of the advanced commercial Si- and InGaAs-based photodiodes. The GeS photodetector also shows an excellent long-term photo switching stability over a long period of operation (>1 h). 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 photoresponsivity of up to 12.3 AW−1 at 450 nm (on SiO2/Si) and 3.9 AW−1 at 633 nm (on PET). These InSe devices can also operate on a flexible substrate with or without bending and reveal comparable performance to those devices on SiO2/Si. In the final part, we propose a simple structure adopting single-gate electrode and different work function metals as contacts to achieve ambipolar behavior. A series of experiments were conducted to demonstrate that the designated metal-InSe junctions can lead the carrier behavior of FETs. The results indicate that the polarity of InSe-FET can be controlled by different metal work functions. Furthermore, we adopt asymmetric metal with different work functions as source-drain electrode to reduce Schottky barriers for electron-hole recombination. We also conducted experiments to demonstrate 2D materials-based FETs with carefully selected metal electrode contacts can achieve ambipolar behavior. These extraordinary properties of InSe and GeS show that the materials are highly qualified candidates for the future high performance nanoelectronics devices. With these excellent optoelectronic merits, we envision that the nanoscale InSe and GeS layers will not only find applications in optoelectronics and flexible devices but also act as an active component to configure versatile 2D heterostructures devices.