Van der Waals Interface-Enabled Fabrication of Selenide-Based Two-Dimensional Transition Metal Semiconductors

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题名:	Van der Waals Interface-Enabled Fabrication of Selenide-Based Two-Dimensional Transition Metal Semiconductors
作者:	娜歐蜜;Paylaga, Naomi Tabudlong
贡献者:	物理學系
关键词:	凡德瓦界面;二維材料;過渡金屬硫族化合物;二硒化鎢;硒化銦;場效電晶體;van der Waal Interface;2D material;transition metal chalcogenide;WSe2;InSe;FET
日期:	2025-07-30
上传时间:	2025-10-17 11:56:52 (UTC+8)
出版者:	國立中央大學
摘要:	本研究利用凡德瓦界面特性探討二維半導體的兩大挑戰──單層 InSe 中暗激子的操控與 WSe₂ 場效電晶體（FET）之p型傳導高電阻接觸問題。首先，針對從單層到塊材的 h-BN 封裝 InSe 進行系統性光致發光（PL）測量，發現單層 InSe 的動量間接 A 激子能夠被偵測到強烈、直接能隙的發光。透過增強的激子–聲子耦合與延伸的動量空間波函數，該原本暗激子得以轉為亮激子，並以載子局部化模型精確擬合非對稱 PL 光譜及其厚度相關性。其次，在 Pd/WSe₂ 接觸界面下方引入熱蒸鍍生長的 Sb₂O₃ 犧牲層，以抑制電子束蒸鍍過程中產生的缺陷誘導能隙態。具有 Sb₂O₃ 犧牲層的 Pd/WSe₂ 元件在低溫下展現以直接穿隧為主的歐姆型 p 型傳輸行為，XPS、拉曼與 PL 分析皆證實介面具原子級潔淨度。這些成果提供了 InSe 暗激子發光操控與 WSe₂ 低電阻p型傳導的電接觸工程之策略，為實現全方位整合的二維光電元件平台奠定基礎。;Two-dimensional (2D) semiconductors have drawn intense interest for both optoelectronic applications in the nanoscale. Among these materials, indium selenide (InSe) is distinguished by its strongly layer-dependent band gap and tightly bound excitons, which together enable spectral coverage from the visible to the near-infrared in atomically thin films. However, as the number InSe layers decreases, it undergoes a direct-to-indirect band-gap transition that typically suppresses emission from the ground state A exciton, rendering monolayer (ML) photoluminescence (PL) vanishingly weak or undetectable. To clarify the nature of “dark” excitons in ML InSe, systematic PL measurements were carried out on hexagonal boron nitride encapsulated samples ranging from ML to bulk. Unexpectedly, ML InSe exhibited a bright luminescence attributed to the A exciton despite its indirect band gap nature. This anomalous brightening is due to two principal factors. One is strong exciton-phonon coupling, which enables momentum-indirect radiative recombination. Second factor is the extended exciton wave functions in k-space, which increases spatial overlap between electron and hole states. Moreover, the line shape of A exciton emission becomes increasingly asymmetric in thinner flakes, which is well described by a carrier localization model. In parallel, transition metal dichalcogenides (TMDs) such as WSe2 face persistent challenges due to Fermi-level pinning at the metal-semiconductor interface, arising from defect-induced gap states (DIGS) and metal-induced gap states (MIGS). These gap states cause the formation Schottky barriers that impede charge injection which degrading FET performance. Thermally evaporated Sb₂O₃ is introduced as a sacrificial interlayer beneath Pd contacts on WSe₂ to suppress defect-induced gap states during e-beam evaporation. Pd/WSe₂ with Sb2O3 sacrificial layer devices exhibit ohmic p-type behavior dominated by direct tunneling at low temperature. X-ray photoelectron spectroscopy (XPS), Raman scattering, PL measurements, TEM, and EDS confirmed preservation of the pristine Pd/WSe₂ interface, with no evidence of new defect states or chemical degradation. DFT calculations have shown that the Pd/WSe2 is governed by orbital overlap with intermediate interaction. Thus, this work puts forward a strategy to the formation of ohmic p-type contacts despite the presence of MIGS. These body of work advances two complementary fronts: established strategies to advance research in achieving ohmic p-type contacts in TMDs but may also be applied in TMCs like InSe for the manipulation of dark excitons in future optoelectronic applications.
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