(Invited) Vertically Stacked Junction Devices Fabricated Using Single-Crystal Graphene on SiC Substrate

Abstract

Graphene is a potential post-silicon nanomaterial because of its tremendous properties. Single-crystal graphene epitaxially grown on a SiC substrate is the most promising candidate for future electron devices. Single-crystal graphene with a 100 mm2 size has been successfully fabricated using a high-temperature rapid thermal annealing system [1]. In this study, two types of stacked graphene devices using graphene on SiC are demonstrated. The first device is a bi-crystal system consisting of two graphene samples as shown in Fig. 1 (a). These samples are directly bonded in a face-to-face manner. Contact pins are attached to the graphene surface for ohmic contact. The electrical characteristics of the stacked graphene junction were ohmic at a low bias voltage below 20 V. The linear characteristic at a low bias voltage is attributed to the linear dispersion relation in the band structure of graphene, Dirac cone. At a high bias voltage, the conductance of the graphene junction drastically increased. This nonlinear behavior originates from a semi-metallic property far from the Dirac point. Thermal imaging results indicated that electrical power was directly converted to infrared radiation. The radiation efficiency was estimated to be approximately 10%, which was high compared to that of a previously reported graphene blackbody emitter. The infrared emission spectrum measured using FT-IR was blackbody-like [2]. The peak wavelength of the measured spectrum was almost constant at 10.2 µm with changing applied power. The estimated junction voltage was approximately 5 V at a bias voltage of 80 V. Hot electrons were injected to the graphene layer. The results suggested that infrared emissions from the graphene–graphene stacked junction could be attributed to a nonthermal emission mechanism, such as phonon–plasmon coupling. The other vertically stacked graphene junction is a tunneling diode as shown in Fig. 1 (b). An insulative layer is sandwiched between two graphene samples. A structured water layer [3] formed by deionized water treatment on the epitaxial graphene sample acts as a tunneling barrier. Nonlinear I–V characteristics were observed. The dynamic range of the current change reached the sixth order of magnitude. The estimated thickness of the structured water layer was approximately 0.5 nm. As the tunneling barrier was sufficiently thin, a direct tunneling phenomenon could be observed in a low bias regime. In a high bias regime, the Fowler–Nordheim tunneling phenomenon was observed. A sandwich structure of a vertically stacked graphene junction with a sub-nm-thick structured water layer was constructed through simple water treatment and a direct bonding technique [4]. [1] T. Aritsuki, et al., Jpn. J. Appl. Phys. 55 (2016) 06GF03. [2] N. Murakami, et al., Jpn. J. Appl. Phys. 60 (2021) SCCD01. [3] M. Kitaoka, et al., Jpn. J. Appl. Phys. 56 (2017) 085102. [4] J. Du, et al., Jpn. J. Appl. Phys. 58 (2019) SDDE01. Figure 1