Acoustoelectric transport at gigahertz frequencies in coated epitaxial graphene

The strain and piezoelectric potentials accompanying surface acoustic waves (SAWs) provide a powerful tool for the manipulation of elementary excitations (carriers, spins, excitons, flux quanta, etc.) in low-dimensional structures. In the case of a two-dimensional electron gas lying close to the surface of a piezoelectric substrate, the interaction between the SAW and electric charges can induce electric currents. We have recently demonstrated these acoustically induced electric currents in epitaxial graphene on SiC [1]. The weak piezoelectricity of the SiC substrate, however, lead to acoustoelectric currents of only a few pA.

Fig. 1(a) Experimental setup. The structured graphene on SiC is coated with a dielectric HSQ/SiO2 and a piezoelectric ZnO layer before deposition of interdigital transducers for SAW excitation (IDT1) and detection (IDT2). (b) Dependence of the acoustoelectric current measured in graphene, Iae, on the frequency and power of the RF signal applied to IDT1 to generate SAWs.

In this contribution, we study structures for the efficient generation of SAWs in epitaxial graphene with frequencies compatible with those of radio-frequency (RF) electronic devices (>> 1 GHz). For that purpose, we coated our graphene Hall bar structures with a hydrogen-silsesquioxane (HSQ) layer and a piezoelectric ZnO/SiO2 layers stack, cf. Fig. 1(a). Finally, acoustic delay lines with interdigital transducers (IDTs) were deposited at the opposite edges of the graphene Hall bars for the excitation and detection of SAWs. We have measured the acoustoelectric current, Iae, along the graphene structures for the different acoustic modes generated by the IDTs. Figure 1(b) shows the dependence of Iae on the frequency and nominal power of the RF signal applied to the IDT for the case of a SAW of 1.99 GHz frequency. The observed current levels are about 300 times larger than the ones previously obtained in samples with uncoated graphene Hall bars [1]. We attribute this large current enhancement to the stronger piezoelectric fields induced by the piezoelectric ZnO layer in the graphene with respect to the ones originated only by the weak piezoelectric SiC substrate.

2 Author A. Hernández-Mínguez , A. Tahraoui , J. M. J. Lopes , P. V. Santos

Acoustoelectric transport at gigahertz frequencies in coated epitaxial graphene

Source Appl. Phys. Lett. , 108 , 193502 ( 2016 )
DOI : 10.1063/1.4949756 | Download: PDF | 2779 Cite : Bibtex RIS
A. Hernández-Mínguez, A. Tahraoui, J. M. J. Lopes, and P. V. Santos

1 Author P. V. Santos , T. Schumann , M. H. Oliveira Jr. , J. M. J. Lopes , H. Riechert

Acousto-electric transport in epitaxial monolayer graphene on SiC

Source Appl. Phys. Lett. , 102 , 221907 ( 2013 )
Download: PDF | 2405 Cite : Bibtex RIS
P. V. Santos, T. Schumann, M. H. Oliveira Jr., J. M. J. Lopes, and H. Riechert