Vanadium dioxide (VO2) as a phase-change material controls the transferred heat during phase transition process between metal and insulator states. At temperature above 68°C, the rutile structure VO2 keeps the heat out and increases the IR radiation reflectivity, while at the lower temperature the monoclinic structure VO2 acts as the transparent material and increase the transmission radiation. In this paper, we first present the metal-insulator phase transition (MIT) of the VO2 in high and low temperatures. Then we simulate the meta-surface VO2 of metamaterial reflector by Ansys HFSS to show the emittance tunability (Δε) of the rutile and monoclinic phase of the VO2. In next section, we will review the recent progress in the deposition of thermochromic VO2 on glass and silicon substrate with modifying the pressure of sputtering gases and temperature of the substrate. Finally, we present the results of the in-situ sputtered VOx thin film on thick SiO2 substrate in different combination of oxygen and argon environment by V2O5 target at temperature higher than 300°C and then, analyze it with x-ray diffraction (XRD) method. The thermochromic VO2 based metamaterial structures open a new route to the passive energy-efficient optical solar reflector in the past few years.
The need for rapid, compact, and accurate biosensing capability has increased dramatically in recent times in biomedical and environmental applications. Optical biosensing is one of the most promising methods for virus and chemical substance detection. With analytes or substance binding to the ligands that are attached to the surface or nanoparticles, the optical spectra shift accordingly resulting in detection of a specific substance. Localized surface plasmon resonance (LSPR) technique can be applied to enhance the detection sensitivity, providing an improvement on optical biosensor devices. However, the literature on wide bandgap GaN-based optical biosensor utilizing LSPR is limited, even though GaN-based visible optoelectronic devices have been widely implemented in various applications. Thus, it is important to design and optimize the GaN-based biosensors for their use in optical biosensing applications. In this work, optical properties of GaN-based structure with LSPR effect are investigated using the Finite-Difference-Time-Domain (FDTD) simulation method. GaN-based structures are constructed with nanoparticles coated on GaN surface. The nanoparticles are designed taking into consideration the size and metal elements such as gold, silver, and titanium. A modified refractive index-varying layer is incorporated to mimic the substance attachment on the structure surface. Electric field spectra show that optimizing the GaN-based structures will lead to the LSPR effect, confirming its potential for biosensing applications In addition, the optical spectra of the GaN-based sensor structures show sharp shifts (~ 4 nanometers per .01 refractive index change) when the refractive index of the substance layer is tuned. Additional investigations on the GaN-based sensor with various optimized design parameters will be discussed in further detail.
Material characterizations were carried out to investigate the optical properties and surface morphology of Ga2O3:Se wafer obtained through ion implantation. Se concentration in Ga2O3 varies by adjusting the implant dosage up to 1⨉10^16 ions/cm2. The scanning electron microscopy (SEM) and atomic force microscope (AFM) were conducted to reveal the surface morphology, which shows the surface quality of the samples is likely to be improved with Se-implantation. Optical absorption measurement was also carried out to determine the effect of Se on the properties of Ga2O3. The results indicate the potential use of Ga2O3:Se in ultraviolet photodetector or electronic device applications.
Efficient p-type doping of III-nitride materials is notoriously difficult due to their large band gaps, intrinsic n-type doping, and the large ionization energy of acceptors. Dilute-anion III-nitride materials are a promising solution for addressing this issue and increasing the activation efficiency of p-type dopants. Upward movement of the valence bands reduces the ionization energy of the dopants, allowing for enhanced p-type conductivity in comparison to the conventional nitrides. Incorporation of a dilute-arsenic impurity into AlN significantly reduces the ionization energy of Mg-acceptors from 500 meV to 286 meV, allowing for a two-order magnitude increase in activation efficiency in 6.25%-As AlNAs.
First-Principles DFT calculations are carried out to investigate electronic and structural properties of (BxGa1-x)2O3 alloys in both monoclinic and orthorhombic phases. Generally, the alloying with boron results in the increasing of the bandgap energy and reduction of the lattice constants of (BxGa1-x)2O3 alloys. In addition, the formation enthalpy is calculated to predict its growth feasibility. The band alignment between Ga2O3 and B2O3 is also investigated, which shows the type-II offset in monoclinic phase and type-I offset in orthorhombic phase, respectively. Our studies provide important insight regarding the potential of (BxGa1-x)2O3 alloys for III-Oxide based electronic and optoelectronic device applications.
The authors report on the nanowires-like and nanodots-like lasing behaviors in addition to multiple-wavelength
interband transitions from InAs/InAlGaAs quantum dash (Qdash) lasers in the range of ~1550 nm. The presence of
lasing actions simultaneously from two different dash ensembles, after postgrowth intermixing for crystalline quality
improvement, indicate the absence of optical phonon emission due to the small variation in quantized interband
transition energies. This effect is reproducible and shows different lasing characteristics from its quantum dot and
quantum wire laser counterparts. Furthermore, the small energy spacing of only 25 nm (at center lasing wavelength of
~1550 nm) and the subsequent quenching of higher energy transition states at higher bias level in Qdash lasers suggest
the absence of excited-state transition in highly inhomogeneous self-assembled Qdash structures. However, the
appearance of a second lasing line in a certain range of high injection level, which is due to the presence of different
sizes of dash assembles, corresponds to the transition from smaller size of Qdash ensembles in different planar active
medium. This unique transition mechanism will affect the carrier dynamics, relaxation process in particular and further
indicates localized finite carrier lifetime in all sizes of Qdash ensembles. These phenomena will lead to important
consequences for the ground-state lasing efficiency and frequency modulation response of Qdash devices. In addition,
these imply that proper manipulation of the Qdash ensembles will potentially result in localized nanolasers from
individual ensemble and thus contributing towards enormously large envelope lasing coverage from semiconductor
devices.
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