In this paper, we present a terahertz (THz) band-stop filter realized by fabricating a metallic T-shaped resonator pattern on the high-resistivity silicon wafer. The filter exhibits two typical band-stop response characteristics depending on the incident direction of electric field with respect to the T-shaped resonator. When the long and the short arms of the T-shaped resonator were electrically polarized by changing the incident THz wave transmission directions, the corresponding central frequencies of the band-stop filter were found to be 0.436 THz at 42dB and 0.610 THz at 28 dB, respectively. Using three-dimensional (3D) finite-integral time-domain simulations, the band-stop filter was designed, which can operate in the wavelength between 0.2 and 0.8 THz. Experimental verification was also performed using a free space THz time-domain spectroscopy system. The band-stop response characteristics are in good agreement with the simulation results. The interesting THz band-stop filtering properties suggest a promising application in the modern THz communication systems, THz time-domain spectroscopic imaging and THz continuous wave imaging.
The electronic band structures, densities of states （DOSs）, and projected densities of states （PDOSs） of the wurtzite In1-xGaxN with x=0, 0.0625, 0.125 are studied using the generalized-gradient approximation （GGA） and GGA＋U in density functional theory. Our calculations suggest that in the case of wurtzite InN it is important to apply an on-site Hubbard correction to both the d states of indium and the p states of nitrogen in order to recover the correct energy level symmetry and obtain a reliable description of the InN band structure. The method is used to study the electronic properties of the wurtzite In1-xGaxN. The conduction band minimum （CBM） energy increases, while the valence band maximum （VBM） energy decreases with the increase of the gallium concentration. The effect leads to broadening the band gap （BG） and the valence band width （VBW）. Furthermore, the compressive strain in the crystal can cause the BG and the VBW to increase with the increase of gallium concentrations.
