DFT investigation of geometrical, vibrational, elastic, electronic, optical, and thermoelectric properties of aluminum pnictogens compounds

The aim of this study is to investigate the geometrical, vibrational, elastic, electronic, optical, and thermoelectric characteristics of aluminum pnictides in monolayer square lattice and bilayer hexagonal phases (s- and h-AlX; X = N, P, As) using first principles. The s- and h-AlX materials are mechanically, energetically, and dynamically stable, through phonon dispersion and elastic properties investigations. It was observed that s-AlX materials exhibited both direct and indirect bandgaps, whereas h-AlX materials exhibited indirect bandgap behavior. The energy bandgap values for s- and h-AlX materials measured between 0.79 eV and 3.49 eV for the PBE functional, and between 1.49 eV and 4.74 eV for the HSE06 functional. The effective mass, mobility and relaxation time of electron carriers as well as hole carriers from the band structure of s- and h-AlX are examined to gain a better perception into these materials. The AlP monolayer square lattice phase has the highest mobility and relaxation time of 266129.60 cm2V-1s-1 and 740369.83 fs among entire s- and h-AlX materials. The optical characteristics of s- and h-AlX materials are examined in the existence of field polarizations. The thermoelectric properties of the AlX materials are assessed for temperature dependent. Our investigated results expose that AlP/AlP and AlAs/AlAs are the proficient thermoelectric materials at room temperature in the considered sequence. The present investigation shows that the s- and h-AlX materials are mostly active in the UV region of electromagnetic spectrum, and may find applications in UV-photodetectors and UV-protectant materials.

Properties of spoof plasmon in thin structures

Spoof surface plasmon polariton (SSPP) is an exotic electromagnetic state that confines light at a subwavelength scale at a design-specific frequency. It has been known for a while that spoof plasmon mode can exist in planar, thin structures with dispersion properties similar to that of its wide three-dimensional structure counterpart. We, however, have shown that spoof plasmons in thin structures possess some unique properties that remain unexplored. Our analysis reveals that the field interior to SSPP waveguide can achieve an exceptional hyperbolic spatial dependence, which can explain why spoof plasma resonance incurs red-shift with the reduction of the waveguide thickness, whereas common wisdom suggests frequency blue-shift of a resonant structure with its size reduction. In addition, we show that strong confinement can be achieved over a wide band in thin spoof plasmon structure, ranging from the spoof plasma frequency up to a lower frequency considerably away from the resonant point. The nature of lateral confinement in thin SSPP structures may enable interesting applications involving fast modulation rate due to enhanced sensitivity of optical modes without compromising modal confinement.