Molybdenum Disulfide Thin Film Transistors with Graphene Contact and Al2O3 Capping Layer
Date Issued
2014
Date
2014
Author(s)
Yang, Shih-Chi
Abstract
In the thesis, we mechanically exfoliated MoS2 nanosheet, checking their thickness by optical microscopy and atomic force microscopy. After choosing the nanosheet with an appropriate thickness, we fabricate MoS2 TFT with it. However, the MoS2-to-metal interface is strongly impacted by Fermi level pinning close to the conduction band of the MoS2, resulting in a large contact resistance. In view of this, we insert graphene between the metal and MoS2 to prevent Fermi-level pinning and to modulate the work function, resulting in a smaller Schottky barrier height. TFTs with graphene/metal hetero-contact performs better than those with only metal contact, achieving the best on/off current ratio of 5 order of magnitude and the mobility of 12 cm2/V-sec.
. In addition, we tune the growth temperature of ALD-Al2O3 to achieve a uniform coverage on MoS2. Since physical adsorption is the dominant adsorption method at the MoS2 surface, growth at lower temperature helps attain a better coverage. When the temperature was down to 190°C and 170°C, we observed a uniform Al2O3 layer formed on MoS2 surface and no evident pinpoles were observed. Finally, we capped the Al2O3 layer grown at 190°C on our devices, the mobility can be enhanced to about 32 cm2/V-sec. The electrical properties of passivated MoS2 TFTs are stable despite the devices were exposed to atmosphere for 20 days.
Subjects
二硫化鉬
薄膜電晶體
石墨烯
原子層沉積技術
氧化鋁
Type
thesis
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