Recently, Prof. Jing Lu's team makes big progress in the study on all-metallic vertical transistors based on stacked Dirac materials. The results are published onlinein Adv. Func. Mater.on 3rd Nov. [“All-metallic Vertical Transistors Based on Stacked Dirac Materials”,Adv. Funct. Mater. DOI: 10.1002/adfm.201402904 (2014)].

Since the semiconductor industry based on Si is approaching limit of performance improvement, it is a persisting pursuit to use metal as channel material in a field effect transistor (FET). All-metallic FETs could be scaled down to smaller size with less energy consume and performance at higher frequency.No metal or semimetal has shown any notable field effect until the appearance of Dirac materialgraphene. Dirac materials, such as graphene, silicene, and germanene, are one-atom thick andfeatured by a very high carrier mobility up to 105 cm2/(V∙s) and are quite attractive for application in high-performance nanoelectronics. Dirac materialsare semimetal but thecurrent is sensitive to electrical field due to their extreme thicknesses. However, the on/off current ratio is very poor due to their zero band gaps.This greatly limits the application of pure Dirac materials in electronics at room temperature. Any successful successor to the silicon metal-oxide-semiconductor FET (MOSFET) that is to be used in complementary MOS-like logic must have an on/off ratio of between 104 and 107, which requires a semiconducting channel with a band gap of over 0.4 eV. However, the existing approaches to open a band gap in Dirac materials often suffer from a too small band gap (< 0.3 ev) and thus a poor on/off current ratio (< 1000). prof. lu’s team proposes a creative approach: due to momentum mismatch, in dirac material heterostructures electron transport from one dirac material to the other near ef is forbidden without assistance of phonon. although, this heterostructure is all-metallic, a large transport gap of over 0.4 ev is observed in an ab initio quantum transport simulation of a single-gated two-probe model, accompanied by a high on/off current ratio of up to 107. such an intriguing property in dirac material heterostructures is robust against the relative rotation of the two dirac materials and can also be expanded to homogenous twisted bilayer graphene (blg). therefore, novel avenue is opened up for dirac material vertical structures in high-performance devices without opening their band gaps. the first author of this work is yangyang wang, phd student in school of physics, peking university and exchange studentat mit. the main co-workers are prof. dapeng yu, prof. junjie shi and prof. jinbo yang in school of physics, peking university and prof. ju li at mit.

Whether the Dirac cone can be preserved or not in the epitaxial silicene layer is a very hot and important topic in the 2d materials field. Prof. Lu's team has studied the electronic structure of silicene on various metal substrates, revealing the destruction of the Dirac cone without exception because of the strong band hybridization between substrate and silicene. Besides, they proposed an approach to recover the Dirac cone in epitaxial silicene -- insert the alkali atoms between silicene and the substrate. The inserted alkali atom will weaken the interaction between silicene and substrate, while the alkali atoms do not affect the Dirac cone too much. Recent work has recently been published in Scientific Reports (“Does the Dirac Cone Exist in Silicene on Metal Substrates?” Sci. Rep. 4,5476 (2014),DOI: 10.1038/srep05476). The first author of this work is RugeQuhe, PhD student in Academy for Advanced Interdisciplinary Studies and School of Physics, Peking University.

These works were supported by the National Natural Science Foundation of China, the National Basic Research Program of China, State Key Laboratory for Mesoscopic Physics and and Collaborative Innovation Center of Quantum Matter.