Reduction of persistent photoconductivity in a few-layer MoS 2 field-effect transistor by graphene oxide functionalization Neha Rathi,† a Servin Rathi,† a Inyeal Lee, a Jianwei Wang, b Moonshik Kang, ac Dongsuk Lim, d Muhammad Atif Khan, a Yoontae Lee a and Gil-Ho Kim * a We functionalized two-dimensional few-layer MoS 2 based FET with graphene oxide (GO) in order to improve its persistent photoconductivity and photoresponse time. Both pristine and GO functionalized devices show n-type semiconductor behavior with high on/off ratio exceeding 10 5 . The photoresponse of the GO–MoS 2 hybrid device shows almost complete recovery from persistent photoconductivity and a substantial decrease in response time from 15 s in the pristine MoS 2 device to 1 s in the GO–MoS 2 device. The reasons behind this improvement have been explored and discussed on the basis of electrostatic and photo interaction between GO and MoS 2 . As GO is a strong candidate for various sensing applications, therefore this intelligent hybrid system, where GO interacts electrostatically with the underlying MoS 2 channel, has tremendous potential to add more functionalities to a pristine MoS 2 device for realizing various smart nanoscale FET-based biochemical and gas sensors for myriad applications. Introduction Two-dimensional (2D) material based heterostructures con- sisting of various combinations like graphene–MoS 2 and MoS 2 – WSe 2 have resulted in various new device architectures for novel applications and transport studies. 1–7 Of these heterostructures, those involving MoS 2 are of particular interest due to their multi-functional properties, such as decent mobility, good photoresponsivity, and application in bio, and gas sensing. 8–11 The photo applications of MoS 2 and its heterostructures have attracted particular attention due to their highly responsive photo-detecting properties, however, various issues such as persistent photoconductivity (PPC) have plagued the photo- response of MoS 2 based photodetectors. 2,7,12–15 Recently, several studies have point out the role of defects and sulfur vacancy within the material which can trap the photo activated carriers resulting in a longer recombination lifetimes, thus leading to PPC, however the role of interface charge and defects at SiO 2 and air interface with MoS 2 can also play detrimental effect in prolonging PPC. 12,13,15 Although, several methods like measurement in vacuum and encapsulating MoS 2 layers have been demonstrated to reduce PPC but a practical and simple method is still evading. 15 Further, heterostructures constituting 2D materials involves complex device fabrication and process intensive techniques which make them impractical for scalable production thereby limiting the application scope for such devices. In the present study, we have proposed and demon- strated a facile fabrication method which involves direct depo- sition of graphene oxide (GO) onto MoS 2 layers to address the critical issue of PPC in MoS 2 based devices. The fabricated devices with GO show comparative electrical characteristics aer GO deposition and negligible PPC as compared to pristine MoS 2 devices, which display considerable PPC in their photo- current. In addition to improving the photo properties, such hybrid devices holds huge potential to add further functional- ities which can be readily applied for other applications like gas, bio and chemical sensing. Experimental GO solution preparation GO nanostructures used in the experiment were synthesized using a modied Hummer's method. In this method, 4 g of graphite akes were added to a 250 mL round-bottom ask containing 120 mL of H 2 SO 4 and stirred for 1 h. A KMnO 4 aqueous solution was added to the mixture every 20 min while stirring. The mixture was then slowly heated to, and maintained at 40  C for 5 h in order to oxidize the graphite. Subsequently, a School of Electronic and Electrical Engineering, Sungkyunkwan Advanced Institute of Nanotechnology (SAINT), Sungkyunkwan University, Suwon 16419, South Korea. E-mail: ghkim@skku.edu b School of Mechanical and Electrical Engineering, Guizhou Normal University, Guiyang, 550002, China c Manufacturing Engineering Team, Memory Division, Samsung Electronics Co., Hwasung 18396, South Korea d School of Advanced Materials Science and Engineering, Sungkyunkwan University, Suwon 16419, South Korea † N. R. and S. R. are equal contributing authors. Cite this: RSC Adv. , 2016, 6, 23961 Received 5th February 2016 Accepted 20th February 2016 DOI: 10.1039/c6ra03436e www.rsc.org/advances This journal is © The Royal Society of Chemistry 2016 RSC Adv. , 2016, 6, 23961–23967 | 23961 RSC Advances PAPER Published on 22 February 2016. Downloaded by Sungkyunkwan University on 02/03/2016 05:04:13. View Article Online View Journal | View Issue