Supplementary Information
The two timescales in the charge trapping mechanism for the hysteresis behavior in graphene field effect transistors.
Da-cheng Mao,1 Shao-qing wang,1 Song-ang Peng,1 Da-yong Zhang,1 Jing-yuan Shi,1 Xin-nan Huang,1 Muhammad Asif1, Zhi Jin,1,*
Department of Microwave Devices and Integrated Circuits, Institute of Microelectronics, Chinese Academy of Sciences Beijing, 100029[1], China.
Fig.S1 (a-b) Optical image and the corresponding Raman spectrum of the transferred graphene via the CVD grown method.
To specify the quality of graphene, which was grown via the CVD method mentioned in this work. The Raman spectroscopy was performed, which shows the distinct G band and 2D band. The ratio of 2D band and G band indicates the monolayer property of the graphene sample, while the negligible D band intensity also shows the high quality of graphene without any distinct defects.[1]
Fig. S2 (a) Drain current vs drain voltage under different gate bias (from -40 V to 40 V) in the completed devices. (L/W= 2μm/3 μm); (b) The on-off ratio in the transfer characteristic curve; (c) The total resistance versus gate voltage along with fitting result.
To fully characterize the performance of the fabricated device, the output characteristic curves under different gate bias were carried out, which were shown in Fig.S2 (a). The curves showed a linear relation between the drain current and the drain voltage, which indicates the contact between metal and graphene is ohmic. As the gate voltage increases, the total resistance of the device increases first but then decreases around the Dirac point voltage, which exhibits the ambipolar conductivity of graphene. Besides, the on-off ratio and the mobility of the device have also been investigated, which were shown in Fig. S2 (b)-(c). Due to the lack of bandgap in graphene, the on-off ratio of the device in the transfer curve only reaches a value of around ~11, much smaller than the conventional silicon MOSFET devices. However, by employing the method from Kim[2], the carrier mobility of graphene was extracted around 3113 cm2/Vs, which showed the high potential of graphene as a radio frequency (RF) devices.
Fig.S3 Drain current vs time (Id-t) response under zero back gate voltage as initial state before new sweep starting from different direction.
In order to preclude the influence from the previous sweep, each new sweep begins from the same initial state testified by time dependent measurement under zero gate bias. The unvaried drain current curves show slight difference indicating the same initial state.
Fig. S4 (a) Drain current vs time (Id-t) response under 45V after applying different time pulse of 60V: 10ms (red circle), 50ms (green upTriangle), 100ms (blue downTriangle), 200ms (cyan diamond), 500ms (magenta leftTriangle). The initial values are listed in the figure. (b) Typical transfer characteristic curve from the same device sweeping within the range of 0V to 60V. The drain current value at the gate bias of 45V in a backward sweep was shown in the figure.
By applying the different time for the pulse of 60V, it forms different degree of screening effect due to the different density of the trapped charge carriers (i.e. electrons). The screening effect results in different initial values in the drain current when the gate voltage jumps from 60V to 45V. While matching the drain current value at 45V (8.24μA) in a typical transfer characteristic curve with these initial values, it was found the 100 ms pulse of 60V (8.13μA) is able to trapped an approximately same amount of charge density compared to the one in a backward sweeping process.
Reference:
1. L. M. Malard, M. A. Pimenta, G. Dresselhaus and M. S. Dresselhaus, Physics Reports 2009, vol. 473, pp. 51-87.
2. Seyoung Kim, Junghyo Nah, Insun Jo, Davood Shahrjerdi, Luigi Colombo, Zhen Yao, Emanuel Tutuc and Sanjay K. Banerjee, Applied Physics Letters 2009, vol. 94, p. 062107.
[1]* Corresponding author: Fax: 86-10-62021601. E-mail address: (Z. Jin).