HfO2 Research Papers - Academia.edu (original) (raw)

Vertical hot electron transistors incorporating atomically-thin 2D materials, such as graphene or MoS 2 , in the base region have been proposed and demonstrated in the development of electronic and optoelectronic applications. To the best... more

Vertical hot electron transistors incorporating atomically-thin 2D materials, such as graphene or MoS 2 , in the base region have been proposed and demonstrated in the development of electronic and optoelectronic applications. To the best of our knowledge, all previous 2D material-base hot electron transistors only considered applying a positive collector-base potential (V CB > 0) as is necessary for the typical unipolar hot-electron transistor behavior. Here we demonstrate a novel functionality, specifically a dual-mode operation, in our 2D material-base hot electron transistors (e.g. with either graphene or MoS 2 in the base region) with the application of a negative collector-base potential (V CB < 0). That is, our 2D material-base hot electron transistors can operate in either a hot-electron or a reverse-current dominating mode depending upon the particular polarity of V CB. Furthermore, these devices operate at room temperature and their current gains can be dynamically tuned by varying V CB. We anticipate our multi-functional dual-mode transistors will pave the way towards the realization of novel flexible 2D material-based high-density and low-energy hot-carrier electronic applications. Since 1960, ballistic hot electron transistors (HETs) have been vigorously researched and implemented in diverse material systems (e.g. cold cathode transistor exploiting a thin metal base 1,2 , planar doped barrier transistor incorporating III-V compound semiconductors 3 , two-dimensional electron gas (2DEG)-based HETs 4–6 , etc.) for their potential in high-speed applications. Analogous in design to a bipolar transistor, HETs are comprised of an emitter, base, and collector. However, various properties of the injected ballistic hot electrons, such as their initial velocity, higher kinetic energy, and quasi-mono-energetic distribution upon injection via quantum tunneling, differ from the diffusive transport in bipolar transistors 2,7. In HETs, the ballistic hot electrons are injected through a thin tunnel barrier separating the emitter from the base, and a portion of these hot electrons are collected upon traversing a filter barrier at the base-collector junction (e.g. contribute towards the on-state collector current). Furthermore, the cutoff frequency of HETs is primarily governed by the base thickness and the resistances and capacitances of the emitter and collector regions. To this end, various bulk semiconductor heterostructures, such as InGaAs/InP and AlGaAs/GaAs, have been precisely engineered with undoped and narrow (< 100 nm) base regions since the 1970 s with the introduction of advanced epitaxial technologies, such as molecular beam epitaxy (MBE) and metal-organic chemical vapor deposition (MOCVD) 7. However, several issues including inelastic electron scattering in the finite-width base region, finite base transit time, and quantum-mechanical reflections (e.g. impedance-mismatching) at the collector-base junction typically resulted in subpar current gains at or below room temperature 2,4,5. In addition, these epitaxial techniques add to the complexity in the time and cost of fabricating such structures.