6 research outputs found
Ultrafast Green Single Photon Emission from an InGaN Quantum Dot-in-a-GaN Nanowire at Room Temperature
In recent years, there has been a growing demand for room-temperature visible
single-photon emission from InGaN nanowire-quantum-dots (NWQDs) due to its
potential in developing quantum computing, sensing, and communication
technologies. Despite various approaches explored for growing InGaN quantum
dots on top of nanowires (NWs), achieving the emission of a single photon at
room temperature with sensible efficiency remains a challenge. This challenge
is primarily attributed to difficulties in accomplishing the radial confinement
limit and the inherent giant built-in potential of the NWQD. In this report, we
have employed a novel Plasma Assisted Molecular Beam Epitaxy (PAMBE) growth
approach to reduce the diameter of the QD to the excitonic Bohr radius of
InGaN, thereby achieving strong lateral confinement. Additionally, we have
successfully suppressed the strong built-in potential by reducing the QD
diameter. Toward the end of the report, we have demonstrated single-photon
emission ( = 561 nm) at room-temperature from the NWQD and measured
the second-order correlation function as 0.11, which is notably low
compared to other reported findings. Furthermore, the lifetime of carriers in
the QD is determined to be 775 ps, inferring a high operational speed of the
devices
Investigation of Magnesium Silicate as an Effective Gate Dielectric for AlGaN/GaN Metal Oxide High Electron Mobility Transistors (MOSHEMT)
In this study, a 6 nm layer of Magnesium Silicate (Mg-Silicate) was deposited
on AlGaN/GaN heterostructure by sputtering of multiple stacks of MgO and
SiO, followed by rapid thermal annealing in a nitrogen (N)
environment. The X-ray photoelectron spectroscopy (XPS) analysis confirmed the
stoichiometric Mg-Silicate (MgSiO) after being annealed at a temperature
of 850 C for 70 seconds. Atomic force microscopy (AFM) was employed to
measure the root mean square (RMS) roughness (2.20 nm) of the Mg-Silicate. A
significant reduction in reverse leakage current, by a factor of three orders
of magnitude, was noted for the Mg-Silicate/AlGaN/GaN metal-oxide-semiconductor
(MOS) diode in comparison to the Schottky diode. The dielectric constant of
Mg-Silicate() and the interface density of states
(D) with AlGaN were approximated at 6.6 and 2.0
10 cmeV respectively, utilizing capacitance-voltage (CV)
characteristics
Triple-photoinduced electron transfer (tri-PET) catalysis for activation of super strong bonds
Single electron redox processes allow the formation of highly reactive radicals – valuable intermediates that enable unique transformations in organic chemistry (1,2). An established concept to create radical intermediates is photoexcitation of a catalyst to a higher energy intermediate, subsequently leading to a photoinduced electron transfer (PET) with a reaction partner (3–7). The known concept of consecutive photoinduced electron transfer (con PET) leads to catalytically active species even higher in energy by the uptake of two photons (8). This process has already been used widely for catalytic reductions; however, limitations towards strong bonds and electron rich substrates remain (9,10). Generally speaking, increased photon uptake leads to a more potent reductant. Here, we introduce triple-photoinduced electron transfer catalysis, termed tri-PET, enabled by the three-photon uptake of a dye molecule leading to an excited dianionic super-reductant which is more potent than Li metal (11) – one of the strongest chemical reductants known. Irradiation of the metal-free catalyst by violet light enables the cleavage of strong carbon-fluoride bonds and reduction of other halides even in very electron-rich substrates. The resulting radicals are quenched by hydrogen atoms or engaged in carbon-carbon and carbon-phosphorus bond formations, highlighting the utility of tri-PET for organic chemistry. Thorough spectroscopic, chemical and computational investigations are presented to understand this novel mode of photoredox catalysis. The existence of the dianion which takes up a third photon when irradiated was proven by X-ray diffraction analysis