過渡金屬氮化物閘極增強電場調控單層二硫化鉬之激子—電漿子耦合

Abstract

近年來，隨著對於元件尺度的要求以達到單位面積數量的提升，層狀二維材料被認定是相當具有潛力的新興半導體，尤其單層大面積的過渡金屬二硫族化物(TMDCs)為光電整合提供良好的機會與未來性，原因在於單層時其能帶結構為直接能隙，使得發光效率明顯提升。此外，當傳統多晶矽逐漸縮小至奈米尺度，載子的遷移率將顯著下降，而過渡金屬二硫族化物仍保持相當好的電子遷移率。最後，由於單層引致較弱的介電屏蔽效應(Dielectric Screening Effect)，電子與電洞具有較強的激子束縛能，因此能在室溫下穩定發光；而相對較大的激子半徑則使其易與表面載子發生作用，而可透過施加閘極電壓調制其自發輻射發光。 過往研究並未著重於電閘極調制光致發光的實際應用，原因在於大多數研究使用手撕製備單層二硫化鉬以利得到優良的發光性質，然而手撕製備之單層二硫化鉬十分不便與現今元件製程整合，因此我們透過氮化鉿與化學氣相沉積之單層大面積二硫化鉬之異質結構接面以簡便的製程初步實現了元件整合並透過氮化鉿作為良好反射層以及作為閘極與二硫化鉬之功函數匹配實現高發光強度以及高閘極調制能力。立基於此結果，我們更進一步利用過渡金屬氮化物作為耐熱材料以及置於大氣下的高環境穩定性，運用隙電漿震盪的局域強場增強二維材料的自發輻射發光以致調控光的程度增強。 在實驗上，我們透過比較氮化鉿與p型矽作為金屬閘極，並透過相關電性檢測一步步地確認元件運作機制。最後我們成功驗證功函數機制能有效調控二硫化鉬的光致發光，同時運用電漿震盪強場優勢，增加光與物質的交互作用實現發光強度增強；然由於奈米共振金屬結構直接接觸二硫化鉬表面中和了累積之載子而導致調制幅度減弱。 總結以上，我們實現過渡金屬氮化物閘極調控載子濃度與隙電漿共振的整合並驗證閘極調致發光的機制。最後，我們期望此元件同時具備良好閘極光調制能力也維持元件的電性，以其做到單位面積室溫下光調制元件做Li-Fi 可見光通訊應用。

In recent years, with the increasing demand for smaller device scales to enhance the number of units per unit area, layered two-dimensional (2D) materials have been identified as highly promising emerging semiconductors. Particularly, single-layer large-area transition metal dichalcogenides (TMDCs) offer excellent opportunities and prospects for optoelectronic integration. This is because their band structure in a single layer forms a direct bandgap, significantly improving light emission efficiency. Additionally, as traditional polysilicon is scaled down to the nanoscale, the carrier mobility decreases significantly, whereas TMDCs maintain good electron mobility. Finally, due to the weaker dielectric screening effect in a single layer, electrons and holes exhibit stronger exciton binding energy, allowing for stable light emission at room temperature. Moreover, the relatively large exciton radius facilitates interactions with surface carriers, enabling modulation of spontaneous radiative emission through gate voltage application. Previous research has not focused on practical applications of gate modulation of photoluminescence because most studies used mechanically exfoliated monolayer molybdenum disulfide (MoS₂) to achieve excellent luminescent properties. However, mechanically exfoliated monolayer MoS₂ is inconvenient for integration with current device fabrication processes. Therefore, we have achieved initial device integration through a simple process using hafnium nitride and chemical vapor deposition of large-area monolayer MoS₂ with heterostructure interfaces. Hafnium nitride serves as a good reflective layer and matches the work function with MoS₂ to achieve high light emission intensity and high gate modulation capability. Based on this result, we further utilized transition metal nitrides as refractory materials with high environmental stability under atmospheric conditions. We employed local strong field enhancement of spontaneous emission of two-dimensional materials via plasmonic resonance to enhance the extent of light modulation. In our experiments, we compared hafnium nitride and p-type silicon as metal gates and verified the device operation mechanism through related electrical tests. We successfully confirmed that the work function mechanism effectively modulates the photoluminescence of MoS₂. Simultaneously, we used plasmonic resonance to enhance light-matter interactions, resulting in enhanced light emission intensity. However, the direct contact of the nano-plasmonic metal structure with the MoS₂ surface neutralized the accumulated carriers, leading to reduced modulation amplitude. In summary, we have achieved integration of transition metal nitride gate modulation of carrier concentration and plasmonic resonance and verified the gate-tuned light emission mechanism. We hope this device will combine excellent gate-tunable light modulation capability with maintained device electrical properties, enabling unit-area room-temperature light modulation devices for Li-Fi visible light communication applications.