Paper SA-MoA1
Operando Soft X-ray Spectromicroscopy on Electronic States of Graphene Transistors

Monday, October 19, 2015, 2:20 pm, Room 112

Graphene, the tiny monolayer honeycomb, is promising for high-speed communication owing to excellent electronic properties, such as carrier mobility and saturation velocity, arising from a linear band dispersion, and vanishment of short-channel effects owing to ultrathinness of graphene. The ultrathinness, on the other hand, deteoriates device performances because the ultrathinness easily induces interface modulation of electronic properties of the graphene channel in the graphene transistor. This produces a gap between material properties of graphene layers and device performances of graphene transistor.

To bridge the gap, we have developed operando observation, i.e. observation under operation (gate-bias application in this work), of electronic states using soft x-ray spectromicroscopies with spatial resolutions of 20-100 nm, such as photoemission electron microscopy (PEEM) [1] and three-dimensional scanning photoelectron microscopy (3D nano-ESCA) [2]. This operando PEEM reveals gate-bias-dependent modulation of electronic states of the lateral interface between the graphene channel and contact metal. This interface modulation is brought about by the charge transfer between the graphene channel and the metal contact in the lateral direction. The charge transfer region is relatively large owing to a limited density of states near the Dirac point of graphene. In addition, the operando 3D nano-ESCA directly evidences the linear band dispersion of the graphene transistor in operation by doing a pinpoint C 1s core-level spectromicroscopy at the center of graphene channel, followed by analyzing the shift of the graphene peak by the gate bias.

In conclusion, these operando spectroscopies provides valuable information on graphene transistors. Further operando spectromicroscopy study is in progress to clarify the reason for degradation of high-frequency performances of the graphene transistor [3].

Profs. Oshima, Horiba and Kotsugi and Dr. Nagamura and staff members of BL17SU and BL07LSU of SPrinb-8 are gratefully appreciated for the operando spectromicroscopy. This work has been done partly as the projects of BL07LSU and BL17SU at SPring-8 and also as the academic-industry alliance NEDO project.

[1] H. Fukidome et al., Sci. Rep. 4 (2014) 3713.

[2] H. Fukidome et al., Appl. Phys. Exp. 7 (2014) 065101

[3] M.-H. Jung, H. Fukidome et al., Proc. IEEE 101 (2013) 1603.