Abstract
Controlling and modulating terahertz signals is of fundamental importance to allow systems level applications. We demonstrate an innovative approach for controlling the propagation properties of terahertz (THz) radiation, through use of both the excitation optical wavelength (colour) and intensity. We accomplish this using two-dimensional (2D) layered hybrid trihalide perovskites that are deposited onto silicon substrates. The absorption properties of these materials in the visible range can be tuned by changing the number of inorganic atomic layers in between the organic cation layers. Optical absorption in 2D perovskites occurs over a broad spectral range above the bandgap, resulting in free carrier generation, as well as over a narrow spectral range near the bandedge due to exciton formation. We find that only the latter contribution gives rise to photo-induced THz absorption. By patterning multiple 2D perovskites with different optical absorption properties onto a single device, we demonstrate both colour selective modulation and focusing of THz radiation. These findings open new directions for creating active THz devices.
Highlights
Controlling and modulating terahertz signals is of fundamental importance to allow systems level applications
The appeal arises from a combination of compelling properties that set these materials apart from conventional inorganic semiconductors: (i) a number of solution and vapor-phase deposition techniques can be used to fabricate thin films on a wide range of substrates[22,23,24], (ii) changes in the chemical structure of the materials allow for tuning of the bandgap over a wide spectral range in the visible[25] and (iii) recent work using methyl-ammonium based perovskites have demonstrated power conversion efficiencies exceeding 20%26–28
We exploit the properties of 2D hybrid lead-trihalide perovskites –(C6H5C2H4NH3)2PbI4(PEPI) – and its Ruddlesden–Popper (R–P) mixtures with CH3NH3PbI334, to enable colour selective THz modulation using plasmonic structures fabricated on a semiconductor substrate
Summary
Controlling and modulating terahertz signals is of fundamental importance to allow systems level applications. We demonstrate an innovative approach for controlling the propagation properties of terahertz (THz) radiation, through use of both the excitation optical wavelength (colour) and intensity We accomplish this using two-dimensional (2D) layered hybrid trihalide perovskites that are deposited onto silicon substrates. Compared to electrically controlled devices, where the need for ohmic contact adds complexity, contact-free optical modulators can be designed more In such devices, modulation of THz radiation can be realized when the incident optical control beam has a photon energy above the bandgap, where the generation of charge carriers leads to increased absorption of the incident THz radiation. Modulation of THz radiation can be realized when the incident optical control beam has a photon energy above the bandgap, where the generation of charge carriers leads to increased absorption of the incident THz radiation While this approach has been proven successful, there are limitations. This only occurs when the incident radiation corresponds to the wavelength range associated with exciton absorption
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