Skip to main page content
U.S. flag

An official website of the United States government

Dot gov

The .gov means it’s official.
Federal government websites often end in .gov or .mil. Before sharing sensitive information, make sure you’re on a federal government site.

Https

The site is secure.
The https:// ensures that you are connecting to the official website and that any information you provide is encrypted and transmitted securely.

Access keys NCBI Homepage MyNCBI Homepage Main Content Main Navigation
. 2017 Jan 20:8:14184.
doi: 10.1038/ncomms14184.

Imperfect two-dimensional topological insulator field-effect transistors

William G Vandenberghe  1 , Massimo V Fischetti  1
Affiliations

Imperfect two-dimensional topological insulator field-effect transistors

William G Vandenberghe et al. Nat Commun. .

Abstract

To overcome the challenge of using two-dimensional materials for nanoelectronic devices, we propose two-dimensional topological insulator field-effect transistors that switch based on the modulation of scattering. We model transistors made of two-dimensional topological insulator ribbons accounting for scattering with phonons and imperfections. In the on-state, the Fermi level lies in the bulk bandgap and the electrons travel ballistically through the topologically protected edge states even in the presence of imperfections. In the off-state the Fermi level moves into the bandgap and electrons suffer from severe back-scattering. An off-current more than two-orders below the on-current is demonstrated and a high on-current is maintained even in the presence of imperfections. At low drain-source bias, the output characteristics are like those of conventional field-effect transistors, at large drain-source bias negative differential resistance is revealed. Complementary n- and p-type devices can be made enabling high-performance and low-power electronic circuits using imperfect two-dimensional topological insulators.

PubMed Disclaimer

Figures

Figure 1
Figure 1. Topological insulator band structure and wavefunctions in bulk and ribbon.
(a) Bulk topological insulator band structure, (b) 15 nm topological insulator ribbon band structure and (c) the magnitude of the four wavefunction components of the valence band edge states for k=0.05 Å−1 (solid) and k=0.2 Å−1 (dashed). The states traversing the bulk bandgap in the ribbon band structure (indicated in red in b) are the topologically protected spin-polarized edge states. The states for k=0.05 Å−1 lie in the bulk bandgap, are localized on the left and right edge and decay exponentially between both edges. The states k=0.2 Å−1 (dashed line in c) do not decay exponentially and have a significant overlap.
Figure 2
Figure 2. Schematic of a TI FET in the on-state and off-state.
In the on-state, current is carried by edge states and back-scattering is almost negligible in wide ribbons. In the off-state the states are no longer localized on the edge and scattering between states is dramatically increased. Only the spin-up component is illustrated. For spin-down, forward and backward transport will take place on the opposite edge.
Figure 3
Figure 3. Boltzmann distributions.
Boltzmann distribution for the first conduction band in a TI FET with Vgs=0.1 V (a) and Vgs=0.5 V (b), for Vds=0.1 V. The gate bias makes the charge density larger in the gate region (10–30 nm) compared with the source and drain regions. The strong asymmetry with respect to momentum of the distribution in a indicates a much larger current flow compared with the distribution in b, which is almost symmetric.
Figure 4
Figure 4. TI FET transfer characteristics.
(a) Transfer characteristics (Ids−Vgs) of a TI FET obtained by solving the Boltzmann equation for Vds=0.1 V for different strengths of the scattering with imperfections U=0…16 eV nm. Scattering is strong for Vgs≈−0.4 V and Vgs≈0.4 V (off-state) and weak for Vgs≈0 V (on-state). For a TI with many imperfections, scattering reduces the off-current by more than two orders of magnitude while the on-current remains high. (b) Current for Vds=0.2 V with U=16 eV nm on a linear scale with adjusted workfunctions. The nTI FET workfunction is decreased by 0.3 V while the pTI FET workfunction is increased by 0.43 V compared with the workfunction of the 2D TI. The current at Vgs=0 V is Ioff,n=23 nA for the nTI FET and Ioff,p=16 nA for the pTI FET.
Figure 5
Figure 5. TI FET output characteristics.
(a) Output characteristics (Ids−Vds) of a TI FET for two different TIs, the first with Eg0=0.5 eV resulting in a bandgap of 0.33 eV and the second with Eg0=1.0 eV resulting in a bandgap of 0.5 eV. Accounting for the difference in the position of the valence maximum between both TIs, a gate bias of Vgs=−0.1 V is applied to the first and Vgs=0.V to the second. The imperfection scattering parameter is set to U=16 eV nm. At large drain bias in the on-state, negative differential resistance appears since scattering becomes inevitable. The peak at which the negative differential resistance occurs is proportional to the bandgap of the TI. (b) Similar to Fig. 4b for the larger bandgap 2D TI: Ids for Vds=0.3 V with U=16 eV nm on a linear scale with adjusted workfunctions. The nTI FET workfunction is decreased by 0.3 V and has Ioff,n=16 nA while the pTI FET workfunction is increased by 0.6 V and has Ioff,p=94 nA.
Figure 6
Figure 6. Benchmarking the TI FET versus other devices.
Switching delay versus energy for a 32-bit ALU determined using the methodology presented in ref. . The results for the smaller gap 2D TI FET with the 0.2 V supply voltage are indicated as TIFET LV and those for the 0.3 V supply voltage are indicated as TIFET HP.
Figure 7
Figure 7. Bulk topological insulator band structure calculated from first principles.
. Band structure without spin–orbit coupling (a) and with spin–orbit coupling (b).
See this image and copyright information in PMC

Similar articles

See all similar articles

Cited by

References

    1. Fischetti M. V., Fu B. & Vandenberghe W. G. Theoretical study of the gate leakage current in sub-10-nm field-effect transistors. IEEE Trans. Electron. Devices 60, 3862–3869 (2013).
    1. Liu H. et al.. Phosphorene: an unexplored 2d semiconductor with a high hole mobility. ACS nano 8, 4033–4041 (2014). - PubMed
    1. Wang Q. H., Kalantar-Zadeh K., Kis A., Coleman J. N. & Strano M. S. Electronics and optoelectronics of two-dimensional transition metal dichalcogenides. Nat. Nanotechnol. 7, 699–712 (2012). - PubMed
    1. Ionescu A. M. & Riel H. Tunnel field-effect transistors as energy-efficient electronic switches. Nature 479, 329–337 (2011). - PubMed
    1. Vandenberghe W. G. et al.. Figure of merit for and identification of sub-60 mv/decade devices. Appl. Phys. Lett. 102, 013510 (2013).

Publication types