Supporting Information High-Performance MoS 2 /CuO Nanosheet-on-1D Heterojunction Photodetectors Doo-Seung Um, Youngsu Lee, Seongdong Lim, Seungyoung Park, Hochan Lee, and Hyunhyub Ko * School of Energy and Chemical Engineering, Ulsan National Institute of Science and Technology (UNIST), Ulsan 689-798, Korea E-mail: hyunhko@unist.ac.kr S-1
Table S1. Comparison of electrical and optical performances of MoS 2 -based photodetectors. Type Rectification Ratio Dark Current Photoresponsivity Photoresponse Speed Ref. MoS 2 /CuO (PN a ) ~6000 @ ±2 V ~38 fa @ -2 V ~157.6 A/W @ 600nm 34.6 ms (R b ) / 51.9 ms (F c ) This work Single Layer MoS 2 (MSM d ) - - 7.5 ma/w @ 550 nm & 50 V G 50 ms (R) / 50ms (F) 1 Monolayer MoS 2 (MSM) - 2 pa 880 A/W @ 561 nm 4 s (R) / 0.6 s (F) 2 Multi-layer MoS 2 (MSM) - ~10pA @ 1 V 120 ma/w @ 633 nm - 3 MoS 2 HJ by thickness modulation (PN) - ~5 pa @ 1 V & 30 V G 580 ma/w @ 488 nm - 4 MoS 2 /n-si (NN e ) - ~ 20 pa 7.2 A/W @ 365 nm - 5 Bulk MoS 2 /p-si (PN) 42 @ ±0.5 V - - 40 ms (R) / 40 ms(f) 6 MoS 2 /BP (PN) - - 418 ma/w @ 633 nm & 40 V G - 7 MoS 2 /ReSe 2 (PN) 500-6.75 A/W @ 633 nm > 40 s 8 a PN: PN junction photodiode; b R: rise time; c F: falling time (decay time); d MSM: metal-semiconductor-metal photodetector; e NN: NN junction photodiode. S-2
Figure S1. a) and b) Tilted-view and c) and d) top-view SEM images of vertically grown CuO nanowires. S-3
Figure S2. Schematic illustration of wet-transfer printing process for the transfer-printing of MoS 2 nanosheet on top of CuO nanowire. S-4
Figure S3. Encapsulation of CuO NW with MoS 2 nanosheet during the wet-transfer process of MoS 2 nanosheet onto CuO nanowire. a) the exfoliated MoS 2 sheet on the PDMS stamp is covered on top of the CuO NWs/Si substrate. b) Conformal contact between the MoS 2 nanosheet and the CuO NW on Si substrate due to the liquid evaporation. c) As the liquid further evaporates, the MoS 2 sheets uniformly encapsulate the cylindrical CuO NW on the Si substrate, resulting in the tight bonding interface between MoS 2 and CuO NW. S-5
Figure S4. Magnified a) SEM and b) AFM images of CuO NW covered with MoS 2 nanosheet after the wet-transfer of MoS 2 nanosheet onto the CuO NW. The inset AFM analysis indicates the thickness of MoS 2 nanosheet. S-6
Figure S5. Raman spectra of the transferred MoS 2 nanosheet showing two distinctive peaks of MoS 2 for in-plane E 1 2g (382.9 cm -1 ) and out-of-plane A 1g (408.4 cm -1 ) vibration modes. The spacing of ~25.5 cm -1 between E 1 2g and A 1g modes, which indicates the multilayer structure of transferred MoS 2 nanosheet. S-7
Figure S6. Band diagrams of the MoS 2 /CuO NW heterojunction p-n diode a) before and b) after the contact between MoS 2 nanosheet and CuO nanowire. c) Band diagram under the reverse bias of heterojunction p-n diode. When the light is illuminated, the electron-hole pair is generated from the MoS 2 /CuO interface region. S-8
Figure S7. a, b) SEM images of photodiode based on the heterojunction of CuO NW above the MoS 2 nanosheet (CuO/MoS 2 1D-on-nanosheet heterojunction). S-9
Figure S8. The light absorption area of MoS 2 /CuO nanosheet-on-1d heterojunction photodetectors. The absorption area is defined as the junction area between CuO NW and MoS 2 nanosheet, which can be obtained by multiplying the arc length (l arc ) and the length of junction between CuO NW and MoS 2 nanosheet (l nanowire ). S-10
a) b) c) Anode current (na) 0.02 0.00-0.02 MoS 2 /CuO Heterojunction -0.04 Dark current Photocurrent -0.06-2.0-1.5-1.0-0.5 0.0 Anode voltage (V) Anode current (na) 1.0 0.8 0.6 0.4 0.2 0.0 CuO MSM 0.0 0.5 1.0 1.5 2.0 Anode voltage (V) Dark current Photocurrent Anode current (na) 1.5 1.0 0.5 0.0 MoS 2 MSM Dark current Photocurrent 0.0 0.5 1.0 1.5 2.0 Anode voltage (V) Figure S9. Dark and photocurrent comparison of a) MoS 2 sheet/cuo nanowire heterojunction p- n diode, b) CuO MSM photodetector, and c) MoS 2 MSM photodetector in dark state and under the 570 nm LED light. S-11
Figure S10. Photo-switching behavior of a) CuO MSM photodetector and b) MoS 2 MSM photodetector under the pulsed 570 nm LED light. S-12
References 1. Yin, Z.; Li, H.; Li, H.; Jiang, L.; Shi, Y.; Sun, Y.; Lu, G.; Zhang, Q.; Chen, X.; Zhang, H. Single-Layer MoS 2 Phototransistors. ACS Nano 2011, 6 (1), 74-80. 2. Lopez-Sanchez, O.; Lembke, D.; Kayci, M.; Radenovic, A.; Kis, A. Ultrasensitive Photodetectors based on Monolayer MoS 2. Nat. Nanotechnol. 2013, 8, 497-501. 3. Choi, W.; Cho, M. Y.; Konar, A.; Lee, J. H.; Cha, G. B.; Hong, S. C.; Kim, S.; Kim, J.; Jena, D.; Joo, J. High Detectivity Multilayer MoS2 Phototransistors with Spectral Response from Ultraviolet to Infrared. Adv. Mater. 2012, 24 (43), 5832-5836. 4. Tosun, M.; Fu, D.; Desai, S. B.; Ko, C.; Kang, J. S.; Lien, D.-H.; Najmzadeh, M.; Tongay, S.; Wu, J.; Javey, A. MoS 2 Heterojunctions by Thickness Modulation. Sci. Rep. 2015, 5, 10990. 5. Li, Y.; Xu, C.-Y.; Wang, J.-Y.; Zhen, L. Photodiode-Like Behavior and Excellent Photoresponse of Vertical Si/Monolayer MoS 2 Heterostructures. Sci. Rep. 2014, 4, 7186. 6. Hao, L.; Liu, Y.; Gao, W.; Han, Z.; Xue, Q.; Zeng, H.; Wu, Z.; Zhu, J.; Zhang, W. Electrical and Photovoltaic Characteristics of MoS 2 /Si pn Junctions. J. Appl. Phys. 2015, 117 (11), 114502. 7. Deng, Y.; Luo, Z.; Conrad, N. J.; Liu, H.; Gong, Y.; Najmaei, S.; Ajayan, P. M.; Lou, J.; Xu, X.; Ye, P. D. Black Phosphorus Monolayer MoS 2 van der Waals Heterojunction p n Diode. ACS Nano 2014, 8 (8), 8292-8299. 8. Wang, X.; Huang, L.; Peng, Y.; Huo, N.; Wu, K.; Xia, C.; Wei, Z.; Tongay, S.; Li, J. Enhanced Rectification, Transport Property and Photocurrent Generation of Multilayer ReSe 2 /MoS 2 p n Heterojunctions. Nano Res. 2016, 9 (2), 507-516. S-13