Abstract
We propose and investigate the intrinsically thinnest transistor concept: a monolayer ballistic heterojunction bipolar transistor based on a lateral heterostructure of transition metal dichalcogenides. The device is intrinsically thinner than a Field Effect Transistor because it does not need a top or bottom gate, since transport is controlled by the electrochemical potential of the base electrode. As typical of bipolar transistors, the collector current undergoes a tenfold increase for each 60 mV increase of the base voltage over several orders of magnitude at room temperature, without sophisticated optimization of the electrostatics. We present a detailed investigation based on self-consistent simulations of electrostatics and quantum transport for both electron and holes of a pnp device using MoS$_2$ for the 10-nm base and WSe$_2$ for emitter and collector. Our three-terminal device simulations confirm the working principle and a large current modulation I$_\text{ON}$/I$_\text{OFF}\sim 10^8$ for $\Delta V_{\rm EB}=0.5$ V. Assuming ballistic transport, we are able to achieve a current gain $\beta\sim$ 10$^4$ over several orders of magnitude of collector current and a cutoff frequency up to the THz range. Exploration of the rich world of bipolar nanoscale device concepts in 2D materials is promising for their potential applications in electronics and optoelectronics.
Highlights
The bipolar junction transistor (BJT) has been the first semiconductor transistor manufactured in volume [1] and for 30 years the workhorse of semiconductor electronics, before being taken over by the metal-oxide-semiconductor field-effect transistor (MOSFET)
We propose the concept of a ballistic lateral heterojunction bipolar transistor based on transition metal dichalcogenides (TMDCs), and assess its potential in electronics applications with self-consistent quantum transport and electrostatics simulations using the nonequilibrium
In order to assess the potential of 2D BJTs, we need to assume that technological challenges in the doping of 2D materials on a large scale can be solved, as has been demonstrated in laboratory conditions [5,6]
Summary
The bipolar junction transistor (BJT) has been the first semiconductor transistor manufactured in volume [1] and for 30 years the workhorse of semiconductor electronics, before being taken over by the metal-oxide-semiconductor field-effect transistor (MOSFET). Device physicists and engineers are much more familiar with MOSFETs than BJTs, and the recent explosion of interest for electron devices based on two-dimensional (2D) materials has been mainly focused on MOSFETs [3,4], for the possibility of enabling an extension, or even an acceleration, of the so-called Moore’s law, i.e., the exponential increase of the number of transistors in an integrated circuit as a function. This possibility is predicated on the fact that 2D materials can provide an extremely thin layer with a relatively high mobility, thereby enabling scaling of the channel width and length while preserving a good electrostatic behavior and low delay times
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