Graphene and 2-Dimensional Materials for Nanoelectronics Applications

Graphene science and technology has evolved substantially over the past 10 years. It is now entering a phase, where researchers and industry start to collaborate more closely on applications and to address issues of scalability and manufacturability. In addition to the semimetal graphene, recent years have seen the emergence of a number of related two-dimensional materials. These include insulators such as hexagonal boron nitride, semiconducting transition metal dichalcogenides (TMDs) like molybdenum disulfide (MoS₂) or tungsten diselenide (WSe₂) or silicene and germanene, similar in structure but less stable than graphene.

The talk will focus on graphene-based hot electron transistors (Graphene Base Transistors, GBTs) for analog radio frequency applications [1], [2]. The operating principle of GBTs is based on vertical current flow by quantum mechanical tunneling through an insulating barrier (Figure 1). The current (red arrow) can be controlled over several orders of magnitude by a base electrode made of graphene (Figure 2). The advantage of graphene over a metal base electrode is its ultimate thinness while maintaining good conductivity. If the barrier materials are optimized, GBTs have the potential to reach cut off frequencies (f_T) on the order of 1 THz [3].

In the second part of the talk, options for optoelectronic devices based on 2D materials will be discussed. These include photodetectors / phototransistors made from graphene [4], where the photoresponse can be tuned by the voltage applied to a gate. In addition, photodiodes based on MoS₂/silicon heterojunctions will be discussed.

[1]        W. Mehr, J. C. Scheytt, J. Dabrowski, G. Lippert, Y.-H. Xie, M. C. Lemme, M. Ostling, and G. Lupina, “Vertical Transistor with a Graphene Base,” IEEE Electron Device Lett., vol. 33, pp. 691–693, 2012.

[2]        S. Vaziri, G. Lupina, C. Henkel, A. D. Smith, M. Östling, J. Dabrowski, G. Lippert, W. Mehr, and M. C. Lemme, “A Graphene-based Hot Electron Transistor,” Nano Lett., vol. 13, p. 1435−1439, 2013.

[3]        F. Driussi, P. Palestri, and L. Selmi, “Modeling, simulation and design of the vertical Graphene Base Transistor,” Microelectron. Eng., vol. 109, pp. 338–341, Sep. 2013.

[4]        M. C. Lemme, F. H. L. Koppens, A. L. Falk, M. S. Rudner, H. Park, L. S. Levitov, and C. M. Marcus, “Gate-Activated Photoresponse in a Graphene pn Junction,” Nano Lett., vol. 11, pp. 4134–4137, 2011.