Indirect Band Gap Emission by Hot Electron Injection in Metal/MoS2 and Metal/WSe2 Heterojunctions

详细信息    查看全文

• 作者：Zhen Li ; Goutham Ezhilarasu ; Ioannis Chatzakis ; Rohan Dhall ; Chun-Chung Chen ; Stephen B. Cronin
• 刊名：Nano Letters
• 出版年：2015
• 出版时间：June 10, 2015
• 年：2015
• 卷：15
• 期：6
• 页码：3977-3982
• 全文大小：348K
• ISSN：1530-6992

文摘

Transition metal dichalcogenides (TMDCs), such as MoS₂ and WSe₂, are free of dangling bonds and therefore make more 鈥渋deal鈥?Schottky junctions than bulk semiconductors, which produce Fermi energy pinning and recombination centers at the interface with bulk metals, inhibiting charge transfer. Here, we observe a more than 10脳 enhancement in the indirect band gap photoluminescence of transition metal dichalcogenides (TMDCs) deposited on various metals (e.g., Cu, Au, Ag), while the direct band gap emission remains unchanged. We believe the main mechanism of light emission arises from photoexcited hot electrons in the metal that are injected into the conduction band of MoS₂ and WSe₂ and subsequently recombine radiatively with minority holes in the TMDC. Since the conduction band at the K-point is 0.5 eV higher than at the 危-point, a lower Schottky barrier exists for the 危-point band, making electron injection more favorable. Also, the 危 band consists of the sulfur p_z orbital, which overlaps more significantly with the electron wave functions in the metal. This enhancement in the indirect emission only occurs for thick flakes of MoS₂ and WSe₂ (鈮?00 nm) and is completely absent in monolayer and few-layer (鈭?0 nm) flakes. Here, the flake thickness must exceed the depletion width of the Schottky junction, in order for efficient radiative recombination to occur in the TMDC. The intensity of this indirect peak decreases at low temperatures, which is consistent with the hot electron injection model.