13 research outputs found
Wavelength-Controlled Photocurrent Polarity Switching in BP-MoS Heterostructure
Layered two-dimensional van der Waals (vdW) semiconductors and their
heterostructures have been shown to exhibit positive photoconductance (PPC) in
many studies. A few recent reports have demonstrated negative photoconductance
(NPC) as well that can enable broadband photodetection besides multi-level
optoelectronic logic and memory. Controllable and reversible switching between
PPC and NPC is a key requirement for these applications. This report
demonstrates visible-to-near infrared wavelength-driven NPC and PPC, along with
reversible switching between the two, in an air stable, high mobility,
broadband black phosphorus (BP) field effect transistor (FET) covered with a
few layer MoS flake. The crossover switching wavelength can be tuned by
varying the MoS bandgap through its flake thickness and the NPC and PPC
photoresponsivities can be modulated using electrostatic gating as well as
laser power. Recombination-driven NPC and PPC allows for reversible switching
at reasonable time scales of a few seconds. Further, gate voltage-dependent
negative persistent photoconductance enables synaptic behavior that is
well-suited for optosynaptic applications.Comment: Main Manuscript and Supporting Informatio
Electrically Controlled Reversible Strain Modulation in MoS Field-effect Transistors via an Electro-mechanically Coupled Piezoelectric Thin Film
Strain can efficiently modulate the bandgap and carrier mobilities in
two-dimensional (2D) materials. Conventional mechanical strain-application
methodologies that rely on flexible, patterned or nano-indented substrates are
severely limited by low thermal tolerance, lack of tunability and/or poor
scalability. Here, we leverage the converse piezoelectric effect to
electrically generate and control strain transfer from a piezoelectric thin
film to electro-mechanically coupled ultra-thin 2D MoS. Electrical bias
polarity change across the piezoelectric film tunes the nature of strain
transferred to MoS from compressive 0.23% to tensile 0.14% as
verified through peak shifts in Raman and photoluminescence spectroscopies and
substantiated by density functional theory calculations. The device
architecture, built on a silicon substrate, uniquely integrates an MoS
field-effect transistor on top of a metal-piezoelectric-metal stack enabling
strain modulation of transistor drain current 130, on/off current ratio
150, and mobility 1.19 with high precision, reversibility and
resolution. Large, tunable tensile (1056) and compressive (-1498) strain gauge
factors, easy electrical strain modulation, high thermal tolerance and
substrate compatibility make this technique promising for integration with
silicon-based CMOS and micro-electro-mechanical systems.Comment: Manuscript and Supplementary Informatio
Near-direct bandgap / type-II pn heterojunction for enhanced ultrafast photodetection and high-performance photovoltaics
PN heterojunctions comprising layered van der Waals (vdW) semiconductors have
been used to demonstrate current rectifiers, photodetectors, and photovoltaic
devices. However, a direct or near-direct bandgap at the heterointerface that
can significantly enhance optical generation, for high light absorbing
few/multi-layer vdW materials, has not yet been shown. In this work, for the
first time, few-layer group-6 transition metal dichalcogenide (TMD) is
shown to form a sizeable (0.7 eV) near-direct bandgap with type-II band
alignment at its interface with the group-7 TMD through density
functional theory calculations. Further, the type-II alignment and
photogeneration across the interlayer bandgap have been experimentally
confirmed through micro-photoluminescence and IR photodetection measurements,
respectively. High optical absorption in few-layer flakes, large conduction and
valence band offsets for efficient electron-hole separation and stacking of
light facing, direct bandgap on top of gate tunable are shown
to result in excellent and tunable photodetection as well as photovoltaic
performance through flake thickness dependent optoelectronic measurements.
Few-layer flakes demonstrate ultrafast response time (5 s) at high
responsivity (3 A/W) and large photocurrent generation and responsivity
enhancement at the heterostructure overlap region (10-100X) for 532 nm laser
illumination. Large open-circuit voltage of 0.64 V and short-circuit current of
2.6 A enables high output electrical power. Finally, long term
air-stability and a facile single contact metal fabrication process makes the
multi-functional few-layer / heterostructure diode
technologically promising for next-generation optoelectronic applications.Comment: Manuscript- 27 pages, 8 figures. Supporting Information- 17 pages, 17
figure
An electroplating-based plasmonic platform for giant emission enhancement in monolayer semiconductors
Two dimensional semiconductors have attracted considerable attention owing to
their exceptional electronic and optical characteristics. However, their
practical application has been hindered by the limited light absorption
resulting from their atomically thin thickness and low quantum yield. A highly
effective approach to manipulate optical properties and address these
limitations is integrating subwavelength plasmonic nanostructures with these
monolayers. In this study, we employed electron beam lithography and
electroplating technique to fabricate a gold nanodisc (AuND) array capable of
enhancing the photoluminescence (PL) of monolayer MoS giantly. Monolayer
MoS placed on the top of the AuND array yields up to 150-fold PL
enhancement compared to that on a gold film. We explain our experimental
findings based on electromagnetic simulations
Recurrent endobronchial actinomycosis following an interventional procedure
Actinomycosis is an indolent, slowly progressive infection caused by anaerobic or microaerophilic bacteria, primarily from the genus Actinomyces. Thoracic involvement is observed in approximately 15% of cases of infection with actinomycosis. Here, we present a case of a 61-year-old male who presented with recurrent endobronchial actinomycosis. The case is being presented because of its rarity on three counts – endobronchial involvement, which is uncommon, recurrence in different sites in the bronchial tree, which is even rarer and development of the disease following an endobronchial procedure
Enhanced responsivity and detectivity of fast WSe2 phototransistor using electrostatically tunable in-plane lateral p-n homojunction
In photodetectors based on 2D materials, a trade-off often exists between responsivity and speed. Here, the authors attenuate this issue via integration of a lateral, in-plane, electrostatically tunable p-n homojunction with a conventional WSe2 phototransistor
Near-Infrared and Visible-range Optoelectronics in 2D Hybrid Perovskite/Transition Metal Dichalcogenide Heterostructures
The application of ultrathin two-dimensional (2D) perovskites in
near-infrared and visible-range optoelectronics has been limited owing to their
inherent wide bandgaps, large excitonic binding energies and low optical
absorption at higher wavelengths. Here, we show that by tailoring interfacial
band alignments via conjugation with low-dimensional materials like monolayer
transition metal dichalcogenides (TMD), the functionalities of 2D perovskites
can be extended to diverse, visible-range photophysical applications. Based on
the choice of individual constituents in the 2D perovskite/TMD
heterostructures, our first principles calculations demonstrate widely tunable
type-II band gaps, carrier effective masses and band offsets to enable an
effective separation of photogenerated excitons for enhanced photodetection and
photovoltaic applications. In addition, we show the possibilities of achieving
a type-I band alignment for recombination based light emitters as well as a
type-III configuration for tunnelling devices. Further, we evaluate the effect
of strain on the electronic properties of the heterostructures to show a
significant strain tolerance, making them prospective candidates in flexible
photosensors.Comment: 38 pages, main manuscript and supporting informatio