IBM Thomas J. Watson Research Center, Yorktown Heights, New York 10598, USA.
Nat Nanotechnol. 2011 Mar;6(3):179-84. doi: 10.1038/nnano.2011.6. Epub 2011 Feb 6.
A high-quality junction between graphene and metallic contacts is crucial in the creation of high-performance graphene transistors. In an ideal metal-graphene junction, the contact resistance is determined solely by the number of conduction modes in graphene. However, as yet, measurements of contact resistance have been inconsistent, and the factors that determine the contact resistance remain unclear. Here, we report that the contact resistance in a palladium-graphene junction exhibits an anomalous temperature dependence, dropping significantly as temperature decreases to a value of just 110 ± 20 Ω µm at 6 K, which is two to three times the minimum achievable resistance. Using a combination of experiment and theory we show that this behaviour results from carrier transport in graphene under the palladium contact. At low temperature, the carrier mean free path exceeds the palladium-graphene coupling length, leading to nearly ballistic transport with a transfer efficiency of ~75%. As the temperature increases, this carrier transport becomes less ballistic, resulting in a considerable reduction in efficiency.
在高性能石墨烯晶体管的制造中，高质量的石墨烯与金属接触之间的连接至关重要。在理想的金属-石墨烯结中，接触电阻仅由石墨烯中的传导模式数量决定。然而，迄今为止，对接触电阻的测量结果并不一致，并且决定接触电阻的因素仍不清楚。在这里，我们报告称，钯-石墨烯结中的接触电阻表现出异常的温度依赖性，当温度降低到 6 K 时，接触电阻显著下降到仅 110 ± 20 Ω µm，这是最小可实现电阻的两到三倍。通过实验和理论的结合，我们表明这种行为是由钯接触下石墨烯中的载流子输运引起的。在低温下，载流子平均自由程超过钯-石墨烯耦合长度，导致几乎弹道传输，转移效率约为 75%。随着温度的升高，这种载流子传输变得不那么弹道，导致效率显著降低。
