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Terahertz surface plasmon polaritons on a semiconductor surface structured with periodic V-grooves

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Abstract

We demonstrate propagation of terahertz waves confined to a semiconductor surface that is periodically corrugated with V-shaped grooves. A one-dimensional array of V-grooves is fabricated on a highly-doped silicon surface, using anisotropic wet-etching of crystalline silicon, thereby forming a plasmonic waveguide. Terahertz time domain spectroscopy is used to characterize the propagation of waves near the corrugated surface. We observe that the grating structure creates resonant modes that are confined near the surface. The degree of confinement and frequency of the resonant mode is found to be related to the pitch and depth of the V-grooves. The surface modes are confirmed through both numerical simulations and experimental measurements. Not only does the V-groove geometry represent a new and largely unexplored structure for supporting surface waves, but it also enables the practical fabrication of terahertz waveguides directly on semiconductor surfaces, without relying on reactive-ion etching or electroplating of sub-millimeter metallic surfaces.

© 2013 Optical Society of America

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Supplementary Material (4)

Media 1: AVI (3709 KB)     
Media 2: AVI (2887 KB)     
Media 3: AVI (3634 KB)     
Media 4: AVI (3686 KB)     

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Figures (6)

Fig. 1
Fig. 1 (a) Geometry of semiconductor plasmonic V-groove waveguide fabricated on a silicon substrate. The width and height are related by w / h = 2 tan ( θ / 2 ) = 2. (b) Numerically computed dispersion relations of the fundamental surface mode for three different line widths (w).
Fig. 2
Fig. 2 (a) The SEM image of a portion of the fabricated structure (side view). (b) Schematic of the experimental setup. The ZnTe crystal is used to generate terahertz via photo-rectification. The detection is done via electro-optic sampling using 1 mm thick (110) ZnTe crystal.
Fig. 3
Fig. 3 Experimentally measured frequency domain transmission spectra: (a) THz input signal used in the experiments, measured in back-to-back configuration. (b) Simulated (blue) and measured (black) transmission spectrum for plasmonic V-groove waveguide with w = 100 μm. (c) Simulated (red) and measured (black) transmission spectrum for plasmonic V-groove waveguide with w = 200 μm.
Fig. 4
Fig. 4 Electric fields calculated for w = 200 μm at four different frequencies below and above the resonant frequency: (a) 0.2 THz, below resonance ( Media 1), (b) 0.46 THz, on resonance ( Media 2), (c), 0.8 THz, above resonance ( Media 3), and (d) 1.2 THz, second-order resonance ( Media 4). The static frames shown here were captured at the peak of each cycle.
Fig. 5
Fig. 5 (a) Numerically calculated dispersion relation for the surface modes supported by a conductive grating structure with p = 250 μm, w = 150μm, and θ = 90°, 60°, 40°, 20°. (b) The associated group velocity dispersion for the three structures considered in (a), showing the progressively slower wave velocities attained by increasing the depth of the grooves.
Fig. 6
Fig. 6 Variation of confinement factor and group velocity of the fundamental surface mode with the terahertz frequency for two different depths i.e. h = 50 μm and h = 75 μm of V-grooves. The solid line corresponds to confinement while the dotted curves corresponds to the group velocity of the surface mode.

Equations (2)

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k x = k 0 [ 1 + 2 ( h p tan ( k 0 h 2 ) sinc 1 ( k 0 h 2 ) ) 2 ] 1 / 2
α = ( k x 2 k 0 2 ) 1 / 2
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