Electron Device Potential of 2D Crystal Semiconductors

2D crystal semiconductors such as graphene and transition metal dichalcogenide are emerging as potentially attractive candidates for extending existing electronic device paradigms.  More importantly, in the attempt to replicate existing electronic devices, the structural and electronic properties of these materials point towards potentially novel devices [1].  In this contribution, FOUR aspects of this emerging story will be presented, combining theory and experimental demonstrations. 

FIRST, the physical properties of 2D crystal materials such as graphene, MoS₂, etc will be compared with conventional semiconductors such as Si, Ge, GaAs, GaN, etc.  Structural properties, energy bandgaps, electron/hole transport properties, etc pertinent to electronic devices will be compared, and contrasted specifically as the dimensions are scaled down to nanoscale thicknesses.

SECOND, the novel transport properties of 2D crystal semiconductors will be discussed.  In particular, the mobilities of these materials within a band are affected by the coupling to surrounding dielectrics and by the presence of d-orbital band-edge states.  The effect of out-of plane phonon vibrations and charged impurity scattering currently limits the mobilities severely in the MoS₂ family of 2D semiconductors.  Methods to boost the transport properties as predicted by the theoretical analysis will be presented.  In addition, interband tunneling transport in both graphene and gapped MoS₂-type chalcogenide semiconductors will be presented, with an eye towards novel electron device applications.

THIRD, conventional FET-type devices using these materials will be discussed and contrasted with existing state-of-the-art performance with Si and III-V semiconductor devices.  Challenges and opportunities in this arena for 2D crystal semiconductors such as advantages of electrostatic scaling advantages, and ohmic contact challenges will be discussed.  Experimental results on 2D crystal semiconductor FETs with high on/off ratios, respectable mobilities, and robust current saturation will be presented.

FOURTH, novel nanoelectronic devices that depend on tunneling transport will be presented.  Specifically device proposals that exploit the intrinsic properties of 2D crystal semiconductors, such as graphene nanoribbon tunnel-FETs (TFET), Symmetric FET (SymFET), and TFETs with transition metal dichalcogenides will be presented.  Finally, the very recent experimental demonstrations of some of these proposed devices will be discussed, and the challenges in realizing these devices, and their promise will be discussed. 

[1] D. Jena, Proceedings of the IEEE, 101, 1705 (2013).