Generation of super high frequencies by graphene on piezoelectric buffer layer upon applied nanosecond electrical pulse

Abstract

An unforeseen phenomenon occurred when measuring the current–voltage (I–U) characteristics of graphene samples in the pulsed regime. The graphene monolayer of the samples was grown by chemical vapor deposition and transferred onto 50 nm buffer HfO2 and AlO3 layers. Bilayer graphene was obtained from epitaxial graphene grown on SiC and was transferred onto 100 nm SiO2. The distance between contacts varied from 5 to 25 µm. The measurements were performed employing cables of 50 Ω impedance to transmit the pulses and a 0–12 GHz bandwidth sampling scope was used to register them. The transmitted registered pulses through graphene/HfO2 and graphene/SiO2 samples were superposed with super high frequency (SHF) oscillations. The wave packet oscillations of about 2 ns in duration appeared on the pulses passed through graphene/HfO2. On the passed-through graphene/SiO2 pulses, the appearing wave packet turns into continuous generation along the pulse length. Spectral decomposition reveals that the base frequency of the oscillations is about 10 GHz; however, bisected frequencies are also present in the spectra. Preliminary analysis of the SHF oscillations occurrence shows that the wave packets appear as an inverse piezoelectric response to a rapidly rising voltage of the pulses. It is proposed that due to acoustic–electronic interaction, the oscillating wave packet in graphene/SiO2 turns into the continued generation, which consumes three-quarters of the pulse energy. These results show that the coupling between graphene and the piezoelectric buffer layer combined with acoustic–electronic interaction brings forth novel effects that are in demand for practical applications.