Scanning Photocurrent Microscopy in MoS2/Graphene Heterojunction Devices
Scanning Photocurrent Microscopy in MoS2/Graphene Heterojunction Devices
초록/요약
We performed imaging of the MoS2/graphene heterojunction device fabricated by chemical vapor deposition (CVD) method by using scanning photocurrent microscopy (SPCM). We measured the diffusion length, carrier lifetime, and mobility of each layers. The heterostructure device exhibited n-type operation, due to the lower mobility of MoS2 layer than that of graphene layer. The SPCM signal showed the depletion layer at the MoS2 and graphene heterojunction. The graphene edge offered nucleation site for MoS2 growth and an excellent electrical contact for the MoS2 layer without performing rectifying behavior. The potential barrier at the junction have been extracted from the polarity switching of the photocurrent signals as a function of drain–source bias. Bias-dependent SPCM allowed us to simultaneously measure the diffusion lengths of both electron and hole carriers for the respective MoS2 and graphene layers. Combining them with the lifetimes measured by femtosecond SPCM, we determined the localized electron and hole mobilities in MoS2 and graphene layers. The electron mobility (µe) and hole mobility (µh) yielded µe = 8800 cm2 V-1 s-1 and µh = 15000 cm2 V-1 s-1 for graphene. Similarly, the results for MoS2 yielded µe = 160 cm2 V-1 s-1 and µh = 80 cm2 V-1 s-1 for the electron and holes, respectively. Our work will be beneficial to the understanding of the transport phenomenon in two-dimensional materials and nanoscale devices.
more목차
I. Introduction 1
II. Background 3
1. Two-dimensional crystalline materials 3
1.1 Molybdenum disulfide (MoS2) 5
1.2 Graphene 5
2. Carrier dynamics in semiconductors 7
3. Device characterization using scanning photocurrent microscopy 9
4. The basic principles of the pump-probe technique including some studies 14
III. Device fabrication and carrier transport measurement setup 18
1. Device fabrication 18
2. SPCM setup 22
3. Femto-second SPCM setup 22
IV. Imaging carrier transport in MoS2/graphene FET 24
1. Device characterization 24
2. Determinization of electronic band alignment in MoS2/graphene FET through SPCM 30
3. Study of Schottky contact through SPCM 36
4. Diffusion lengths of both majority and minority carriers for both MoS2 and graphene layers 40
5. Carrier transport parameters obtained from femtosecond SPCM measurement 46
V. Conclusion 50
References 52
