Interest in bringing p- and n-type monolayer semiconducting transition metal dichalcogenides (TMD) into contact to form rectifying pn diode has thrived since it is crucial to control the electrical properties in two-dimensional (2D) electronic and optoelectronic devices. Usually this involves vertically stacking different TMDs with pn heterojunction or, laterally manipulating carrier density by gate biasing. Here, by utilizing a locally reversed ferroelectric polarization, we laterally manipulate the carrier density and created a WSe2 pn homojunction on the supporting ferroelectric BiFeO3 substrate. This non-volatile WSe2 pn homojunction is demonstrated with optical and scanning probe methods and scanning photoelectron micro-spectroscopy. A homo-interface is a direct manifestation of our WSe2 pn diode, which can be quantitatively understood as a clear rectifying behavior. The non-volatile confinement of carriers and associated gate-free pn homojunction can be an addition to the 2D electron–photon toolbox and pave the way to develop laterally 2D electronics and photonics.
The
role of additives in facilitating the growth of conventional
semiconducting thin films is well-established. Apparently, their presence
is also decisive in the growth of two-dimensional transition metal
dichalcogenides (TMDs), yet their role remains ambiguous. In this
work, we show that the use of sodium bromide enables synthesis of
TMD monolayers via a surfactant-mediated growth mechanism,
without introducing liquefaction of metal oxide precursors. We discovered
that sodium ions provided by sodium bromide chemically passivate edges
of growing molybdenum disulfide crystals, relaxing in-plane strains
to suppress 3D islanding and promote monolayer growth. To exploit
this growth model, molybdenum disulfide monolayers were directly grown
into desired patterns using predeposited sodium bromide as a removable
template. The surfactant-mediated growth not only extends the families
of metal oxide precursors but also offers a way for lithography-free
patterning of TMD monolayers on various surfaces to facilitate fabrication
of atomically thin electronic devices.
The magneto-structural coupling of BiFeO3 (BFO)–CoFe2O4 (CFO)/LaAlO3 (LAO) heteroepitaxy with various lateral sizes of CFO pillars embedded in a BFO matrix was investigated.
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