2D-3D integration of high-κ dielectric with 2D heterostructures for opto-electronic applications

Graphene-based devices are edging closer to industrialization, at first instance related to sensors and optoelectronics applications. In particular, graphene-based photodetectors
¹
and modulators have already shown competitive performances and proof-on-concept integration with Si-CMOS technologies has been demonstrated
²
. For example, graphene modulators are reaching, and even surpassing
³
, state-of-the-art commercial modulators. In order to fulfil all industrial requirements, new dielectric combinations providing flat encapsulation for graphene that allow high levels of doping control and hysteresis-free operation are needed.In this work, we present a newly developed dielectric combination based on two-dimensional (2D) materials and a three-dimensional (3D) high-κ dielectric. This 2D-3D integration of graphene, hexagonal Boron Nitride (hBN) and hafnium oxide (HfO
₂
) allows us to combine the high-quality of hBN-encapsulated graphene, while achieving high values of relative permittivity (ε
_r
) and high breakdown voltages (V
_BD
). To confirm the benefits of such a 2D-3D compound, we fabricated a double-layer (DL) graphene electroabsorption (EA) modulator employing this novel hBN/HfO
₂
/hBN dielectric. The graphene-based modulator shows nearly hysteresis-free operation with strong doping tunability to allow for a large extinction ratio
³
. In this work, we discuss the fabrication procedures to integrate these 2D and 3D materials and highlight the importance of the dielectric layer for the quality of graphene by comparing several dielectric combinations by means of Raman spectroscopy and opto-electronic measurements.