ABSTRACT
TWO-DIMENSIONAL LOW-RESISTANCE CONTACTS FOR HIGH PERFORMANCE WSe2 and MoS2, TRANSISTORS
by
Hsun-jen Chuang
May 2016
Advisor: Dr. Zhixian Zhou
Major: Physics
Degree: Doctor of Philosophy
Two-dimensional layered materials beyond graphene such as transition metal dichalcogenides (TMDs) have attracted a lot of interests due to their superior property in many aspects. In this work, I am focusing on two TMD materials: WSe2 and MoS2. The main objective this work is to develop novel approaches to fabricating low-resistance ohmic contacts to TMDs for low power, high performance electronic applications. First, we used graphene as electrical contacts for WSe2 field-effect transistor with superior performance, including a high ON/OFF ratio of \u3e107 at 170 K, large electron mobility of ~330 cm2V-1s-1 and he hole mobility of ~270 cm2V-1s-1 at 77 K, and low contact resistance of ~ 2kΩ µm. Second, we developed a novel 2D to 2D contacts strategy2 for a variety of TMDs by van der Waals assembly of substitutionally doped TMDs as drain/source contacts and TMDs with no intentional doping as channel materials. The high intrinsic behavior of the device is revealed, where it exhibits low contact resistances of ~0.3 kΩ µm, on/off ratios up to \u3e 109 as well as two-terminal field-effect hole mobility μFE ≈ 2×102 cm2 V-1 s-1 at 300K, which increases to \u3e 6×103 cm2 V-1 s-1 down to 10K. The 2D/2D low-resistance ohmic contacts presented here represent a new device paradigm that overcomes a significant bottleneck in the performance of TMDs and other 2D materials as the channel materials in post-silicon electronic
