3D Band Diagram and Photoexcitation of 2D-3D Semiconductor Heterojunctions.
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-hole pairs in the atomically thin monolayer are separated and driven by an external bias and control the "on/off" 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.
Bo
B
Li
Gang
G
Shi
Sidong
S
Lei
School of Physical Science and Technology, Lanzhou University , Lanzhou, Gansu 730000, P. R. China.
Yongmin
Y
He
Weilu
W
Gao
Yongji
Y
Gong
Gonglan
G
Ye
Materials Science and Technology Division, Oak Ridge National Laboratory , Oak Ridge, Tennessee 37831, United States.
Wu
W
Zhou
Kunttal
K
Keyshar
Department of Mechanical and Industrial Engineering, Northeastern University , Boston, Massachusetts 02115, United States.
Ji
J
Hao
Pei
P
Dong
Liehui
L
Ge
Jun
J
Lou
Junichiro
J
Kono
Robert
R
Vajtai
Pulickel M
PM
Ajayan
MoS2−Si heterojunction; band diagram; charge generation; exciton relaxation