220 ISSN 1063-7850, Technical Physics Letters, 2020, Vol. 46, No. 3, pp. 220–223. © Pleiades Publishing, Ltd., 2020. Russian Text © The Author(s), 2020, published in Pis’ma v Zhurnal Tekhnicheskoi Fiziki, 2020, Vol. 46, No. 5, pp. 19–22. Photoresponse in Multilayer Graphene during the Passage of a Surface Acoustic Wave O. V. Kononenko a *, E. V. Emelin a , V. N. Matveev a , and D. V. Roshchupkin a a Institute of Microelectronics Technology and High-Purity Materials, Russian Academy of Sciences, Chernogolovka, Moscow oblast, 142432 Russia *e-mail: oleg@iptm.ru Received October 28, 2019; revised October 28, 2019; accepted November 28, 2019 Abstract—In this Letter, we studied the photoresponse in multilayer graphene on a lithium niobate (LiNbO 3 ) crystal under the conditions of an electric potential applied to graphene and transmission of a surface acoustic wave. The acoustoelectric current in graphene when irradiated with light is shown to either increase or decrease depending on the polarity of the potential applied to graphene. A surface acoustic wave causes the appearance of a periodic charge lattice in graphene that enhances the interaction with incident light, which leads to an increase in the photoresponse. Keywords: graphene, surface acoustic wave, acoustoelectric current, photoresponse. DOI: 10.1134/S1063785020030086 Acoustoelectronic devices are actively used as sen- sors of physical quantities, the principle of operation of which is based on a change in the resonant frequen- cies of excitation of acoustic waves under specific physical conditions (pressure, acceleration, tempera- ture, humidity, etc.). Humidity sensors and gas sen- sors based on graphene oxide and graphene, in which surface acoustic waves (SAWs) were used, were recently reported in [1, 2]. Lately, the interaction of SAWs with charge carriers in graphene was of interest to researchers. The interaction of electric charges and SAWs leads to the appearance of an acoustoelectric (AE) current in graphene [3–7]. It was also shown that the acoustic wave can be controlled under the condi- tions of an electric potential applied to the graphene film [8], and the photoresponse in graphene and graphene nanoribbons under the conditions of the AE current flow was demonstrated [9, 10]. Here, we study the photoresponse in a multilayer graphene film under conditions of application to the film of an electric potential of different polarity and of interaction with the SAW. Samples for studying the photoresponse were pre- pared as follows. On the surface of the YZ-section of a LiNbO 3 crystal, for the excitation and detection of SAWs with a wavelength of 30 μm at a resonant fre- quency of 114.7 MHz, aluminum interdigital trans- ducers (IDTs) were fabricated by photolithography and electron beam deposition. The IDTs consisted of 50 pairs of pins. Graphene films were synthesized by chemical vapor deposition at low pressure with a single injection of acetylene. Deposited on oxidized silicon wafers by laser pulsed deposition, pure nickel films with a thickness of 0.3 μm were used as a catalyst. After the synthesis, a layer of polymethyl methacrylate (PMMA) with a thickness of 0.8 μm, which later served as a supporting film for graphene, was depos- ited on the surface of nickel films with grown graphene. Samples were immersed in a 1%-aqueous solution of hydrochloric acid to dissolve the nickel film. During etching, graphene, together with the sup- porting PMMA film, was separated from the sub- strate. After the nickel was completely dissolved, graphene with PMMA was washed in deionized water and transferred to the surface of LiNbO 3 crystals between two IDTs. PMMA was removed from the graphene surface by dissolution in acetone. Raman spectroscopy was used to characterize graphene films. The spectra were measured at from eight to ten different points on the sample surface using a SENTERRA Bruker Raman microscope with a laser wavelength of 488 nm. The diameter of the laser beam was about 1 μm. Figure 1 shows a typical Raman spectrum obtained for a graphene film. Clear G and 2D peaks indicating the presence of graphene are visi- ble in the spectrum. A weak D peak indicates a low content of defects. The intensity ratio of the 2D and G peaks equal to 0.75 and the half maximum width of the 2D peak equal to 65 cm –1 indicate that the film con- tains three or four graphene monolayers. To study the electrical properties of graphene under SAW propagation, two platinum electrodes on the sur- face of the graphene film were formed by electron beam lithography. The distance between the elec-