3D Band Diagram and Photoexcitation of 2D鈥?D Semiconductor Heterojunctions

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• 作者：Bo Li ; Gang Shi ; Sidong Lei ; Yongmin He ; Weilu Gao ; Yongji Gong ; Gonglan Ye ; Wu Zhou ; Kunttal Keyshar ; Ji Hao ; Pei Dong ; Liehui Ge ; Jun Lou ; Junichiro Kono ; Robert Vajtai ; Pulickel M. Ajayan
• 刊名：Nano Letters
• 出版年：2015
• 出版时间：September 9, 2015
• 年：2015
• 卷：15
• 期：9
• 页码：5919-5925
• 全文大小：450K
• ISSN：1530-6992

文摘

The emergence of a rich variety of two-dimensional (2D) layered semiconductor materials has enabled the creation of atomically thin heterojunction devices. Junctions between atomically thin 2D layers and 3D bulk semiconductors can lead to junctions that are fundamentally electronically different from the covalently bonded conventional semiconductor junctions. Here we propose a new 3D band diagram for the heterojunction formed between n-type monolayer MoS₂ and p-type Si, in which the conduction and valence band-edges of the MoS₂ monolayer are drawn for both stacked and in-plane directions. This new band diagram helps visualize the flow of charge carriers inside the device in a 3D manner. Our detailed wavelength-dependent photocurrent measurements fully support the diagrams and unambiguously show that the band alignment is type I for this 2D-3D heterojunction. Photogenerated electron鈥揾ole pairs in the atomically thin monolayer are separated and driven by an external bias and control the 鈥渙n/off鈥?states of the junction photodetector device. Two photoresponse regimes with fast and slow relaxation are also revealed in time-resolved photocurrent measurements, suggesting the important role played by charge trap states.