Effective
doping techniques that precisely and locally control the conductivity
and carrier polarity, i.e., electron (n-type) or hole (p-type), play
a vital role in the remarkable success of Si-based technology and
thus are critical for developing useful devices based on two-dimensional
layered transition-metal dichalcogenides (TMDs). In contrast to the
previous approaches based on either chemical doping or phase transition
that requires complex chemicals or a high thermal budget and shows
limited tunability and reliability, we propose a simple yet effective
electron-beam irradiation (EBI) technique as an alternative for facilitating
polarity transformation and transport modulation in selected regions.
The EBI process may generate a precise amount of native chalcogen
defects in both MoS2 and MoTe2 by controlling
the EBI dosage. First-principles simulations support that the presence
of native chalcogen vacancies may substantially reduce the band gaps
of TMDs. In MoTe2, the progressive evolution of p-type
conduction, n-type conduction, to metallic-like conduction can be
observed with increasing EBI dosage. The high conductivity of metallic-like
MoTe2 induced by EBI is comparable to that in a metallic
1T′-MoTe2, demonstrating the ability to selectively
form extremely conductive regions in semiconducting TMDs. The proposed
EBI technique could be potentially applied to a wide range of layered
TMDs and facilitate the development of high-performance TMD-based
devices in the future.
This
paper reports on the fabrication of a ferroelectric field
effect transistor (FeFET) using a monolayer MoS2 film and
a perovskite GdNi0.2Fe0.8O3 (GFNO)
ferroelectric film. We demonstrate the tuning of electrical characteristics
using pulse voltage to evoke a 2H–1T′ phase transition
in the MoS2. Coupling at the MoS2–GFNO
interface is the mechanism responsible for the electronic tuning.
Locally reversing the ferroelectric polarization of the perovskite
GFNO through the application of pulse voltage makes it possible to
manipulate the carrier concentration and associated phase of the MoS2 via heterostructure interactions. Our experiment results
are supported by free energy calculations pertaining to heterostructures
under the effects of an electric field. Analysis of the nonvolatile
properties of the FeFET using the scanning probe method and scanning
photoelectron spectroscopy revealed that the transition indeed occurred
across much of the device landscape. The design established in this
study paves the way to the development of laterally two-dimensional
FeFET, which could provide nonvolatile characteristics with a less
destructive read–write process.
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