The non-ionizing radiation and the high sensitivity to weak interactions of terahertz (THz) waves make THz technology a great applicability in the field of biosensing and medical detection. Besides, benefitted from the flexible capability of metasurface in manipulating the electromagnetic (EM) waves, the high-sensitivity THz sensors can be achieved to promote the development of THz sensing. However, the polarization dependence of hybrid-resonances-based metasurface and the single resonance cause the reduction in sensitivity, which is urgent to be settled. In this paper, we proposed a centrosymmetric metasurface to produce high-quality and polarization-insensitive resonance for improving the sensitivity of THz sensing. The designed metasurface is locally asymmetric, which can induce the high-quality Fano resonance. However, the entire structure is centrosymmetric and thus exhibits polarization-independent characterization. The designed metasurface possesses a polarization-independent resonance peak of transmittance spectrum in 0.1-2THz, which also shows high sensitivity related to ambient refractive index. The advantage of transmitted structure and polarizationindependent resonance can relief the difficulty of measurement. We believe these studies will promote the development of high-sensitivity THz biosensing.
Mg-doped AlGaN/GaN superlattice has been grown by metalorganic chemical vapor deposition (MOCVD). Rapid
thermal annealing (RTA) treament are carryied out on the samples under nitrogen as protect gas. Hall,
photoluminescence (PL), high resolution x-ray diffraction (HRXRD) and atomic-force microscopy (AFM) are used to
characterize the electrical, optical and structural properties of the as-grown and annealed samples, respectively. After
annealing, the Hall results indicate more Mg acceptors are activated, which leads to higher hole concentration and lower
p-type resistivity. The PL intensity of Mg related defect band shows a strong decrease after annealing. The annealing of
the superlattice degrade the interface quality of the AlGaN/GaN from the HRXRD results. Many nanometer-grains can
be observed on the surface of AlGaN/GaN superlattice from the AFM image. This maybe related with the decomposing
of GaN or the separating of Mg from the AlGaN/GaN superlattice.
AlInGaN Quaternary Alloys were successfully grown on sapphire substrate by radio-frequency plasma-excited
molecular beam epitaxy (RF-MBE). Different Al content AlInGaN quaternary alloys were acquired by changing the Al
cell's temperature. The streaky RHEED pattern observed during AlInGaN growth showed the layer-by-layer growth
mode. Rutherford back-scattering spectrometry (RBS), X-Ray diffraction (XRD) and Cathodoluminescence (CL) were
used to characterize the structural and optical properties of the AlInGaN alloys. The experimental results show that the
AlInGaN with appropriate Al cell's temperature, could acquire Al/In ratio near 4.7, then could acquire better crystal and
optical quality. The samllest X-ray and CL full-width at half-maximum (FWHM) of the AlInGaN are 5arcmin and 25nm,
respectivly. There are some cracks and V-defects occur in high-Al/In-ratio AlInGaN alloys. In the CL image, the cracks
and V-defect regions are the emission-enhanced regions. The emission enhancement of the cracked and V-defect regions
may be related to the In-segregation.
InGaN/GaN multiple quantum wells (MQWs) structure for ultraviolet emission has been grown on sapphire by
metalorganic chemical vapor deposition (MOCVD). The High resolution x-ray diffraction (HRXRD), atomic-force
microscopy (AFM) and photoluminescence (PL) are used to characterize the structural and optical prosperities of
MQWs, respectively. HRXRD shows multiple satellite peaks to 3rd order indicates the high quality of InGaN/GaN layer
interface. AFM measurement shows that there are some spiral growth hillocks and 3D nanostructures on the MQWs
surface. They are related with the surface kinetics or thermodynamics of InGaN growth. Temperature-dependent PL
results show that there exists a clear excition-localization effect in the InGaN/GaN MQWs. The fitted σvalue of
InGaN/GaN MQWs is around 8meV. The emission peak was almost unchanged with the increase PL excitation power.
Those results indicate there is almost none piezoelectric field-induced quantum-confined stark effect in the InGaN/GaN
MQWs due to the low In content and thin quantum well thickness.
Hydrogenated nanocrystalline silicon thin films have been deposited by helicon wave plasma chemical vapor deposition technique over the range of magnetic field strength (0-200Guass) using a mixture of silane and hydrogen gas. The effects of magnetic field on the structural and optical properties of the deposited films are characterized by Raman spectroscopy, x-ray diffraction and ultraviolet-visible transmittance spectroscopy. It has been found that the crystalline fraction and optical band gap Eg of the films change with magnetic field strength monotonically, while the deposition rate, the grain size and the B factor relating to the overall structural disorder reach a maximal value at 150 Guass. The variation of Raman scattering intensity ratio between silicon TA and TO mode indicates that the inner microstructure of the films becomes more orderly with increasing magnetic field strength until 150 Guass. The decrease trend of the optical band gap Eg and the changes of the B value with magnetic field strength from the ultraviolet-visible transmittance spectroscopy analysis are related to the increase of the grain size, the crystalline fraction and the hydrogen. The observed results have been discussed by the increase of hydrogen weak bond etching and dangling bond passivating effect with increasing magnetic field strength.
Silicon carbide thin films have been deposited by helicon wave plasma enhanced chemical vapor deposition (HW-PECVD) technique under the conditions of variant deposition temperatures from 300 to 600°C. Silane, methane and hydrogen are used as reactive gas. The structural properties of the deposited films are characterized using Fourier transform infrared (FTIR), scan electron microscopy (SEM), transmission electron microscopy (TEM) and ultraviolet-visible optical absorption techniques. Detailed analysis of the FTIR spectra indicates that the onset of growing nanocrystalline SiC films at low substrate temperature is closed related with the high plasma ionization rate of helicon wave plasma and the condition of low working gas pressure and strong hydrogen dilution in experiment. The SEM and TEM measurements confirm that the structure of the deposited films is nanocrystalline SiC grains embedded in amorphous matrix and the size of the crystalline gains increases with substrate temperature.
Access to the requested content is limited to institutions that have purchased or subscribe to SPIE eBooks.
You are receiving this notice because your organization may not have SPIE eBooks access.*
*Shibboleth/Open Athens users─please
sign in
to access your institution's subscriptions.
To obtain this item, you may purchase the complete book in print or electronic format on
SPIE.org.
INSTITUTIONAL Select your institution to access the SPIE Digital Library.
PERSONAL Sign in with your SPIE account to access your personal subscriptions or to use specific features such as save to my library, sign up for alerts, save searches, etc.