Abstract-Thin Film Tandem Nanoplasmonic Photoconductive Antenna for High Performance Terahertz Detection

Saman Ghorbani, 

Mohammad Bashirpour, 

Jafar Poursafar, 

Mohammadreza Kolahdouz, 

Mohammad Neshat, 

Amirali Valinejad

https://www.sciencedirect.com/science/article/pii/S0749603618309352
Photoconductive antennas (PCA) have attracted lots of attention for terahertz application, due to their room temperature operation and compact design. On the other hand, their main problem is acquiring low output power. Lately, plasmonic structures of different geometries have been proposed to overcome the mentioned issue. Here, we have proposed and simulated a PCA on a silicon-on-sapphire substrate and a layout of a plasmonic nanostructure in which the effect of geometrical parameters of the nanostructure on PCA’s output was investigated and optimized. According to the results for one layer plasmonic nanostructure, two different geometries showed more than 700% improvement in the device photocurrent which are related to different types of surface plasmons. By combining these layouts and benefiting from both simultaneously, a final proposed nanostructure was constructed. After optimizing the new structure’s parameters, a significant increase of 15400% in photocurrent enhancement was achieved by comparing to the conventional THz PCAs on similar substrate.

Abstract-Terahertz Dielectric Resonator Antenna Coupled to Graphene Plasmonic Dipole

Seyed E. Hosseininejad, Mohammad Neshat, Reza Faraji-Dana, Sergi Abadal, Max C. Lemme, Peter Haring Bolívar, Eduard Alarcón, Albert Cabellos-Aparicio

https://arxiv.org/abs/1801.03834

This paper presents an efficient approach for exciting a dielectric resonator antenna (DRA) in the terahertz frequencies by means of a graphene plasmonic dipole. Design and analysis are performed in two steps. First, the propagation properties of hybrid plasmonic onedimensional and two-dimensional structures are obtained by using transfer matrix theory and the finite-element method. The coupling amount between the plasmonic graphene mode and the dielectric wave mode is explored based on different parameters. These results, together with DRA and plasmonic antenna theory, are then used to design a DRA antenna that supports the TE112y mode at 2.4 THz and achieves a gain (IEEE) of up to 7 dBi and a radiation efficiency of up 70%. This gain is 6.5 dB higher than that of the graphene dipole alone and achieved with a moderate area overhead, demonstrating the value of the proposed structure.

Abstract-Bias-free and antenna-coupled CW terahertz array emitter with anomalous Schottky barriers

Mohammad Javad Mohammad-Zamani, Morteza Fathipour, Mohammad Neshat, Fakhroddin Nazari, and Mahdi Ghaemi

https://www.osapublishing.org/josab/abstract.cfm?uri=josab-34-9-1771&origin=search

We present a new bias-free antenna-coupled CW terahertz photomixer with interdigitated electrodes. Each finger pair is made of metal/semiconductor/metal (MSM) electrodes with dissimilar Schottky barriers. The two dissimilar metals in each MSM have a barrier height of difference (Δϕ𝐵$\mathrm{\Delta }{\mathrm{\varphi }}_B$) and a finite lateral spacing (𝑠$s$). In the proposed teraheretz emitter, not only is the optical absorption and hence photogeneration enhanced by the surface resonant modes, but also the high built-in field increases the terahertz current. Furthermore, by having a large radiation resistance of the antenna integrated to the array electrodes, based on our simulations, it is possible to achieve the maximum power of 35 μW from a dipole antenna coupled to the proposed electrode array with 10 μm ×10  μm$10\mathrm{\mu m}\times 10\mathrm{\mu m}$ active area and pitch of Λ=800  nm$\mathrm{\Lambda }=800\mathrm{nm}$. This is more than 196 times larger terahertz power than the highest terahertz power radiated from the array emitters of the same area that contains the bias-free antennaless array of far-field emitters with double pitch size. We have also investigated the limits of thermal breakdown and efficiency degradation of the proposed emitter that play an important role due to the reduction of the active area. Such terahertz sources can pave the way to various biomedical applications such as endoscopic imaging without a need for hazardous external circuitry for biasing, reducing patient health risk.

© 2017 Optical Society of America

Abstract-Unbiased continuous wave terahertz photomixer emitters with dis-similar Schottky barriers

Mohammad Javad Mohammad-Zamani, Mohammad Kazem Moravvej-Farshi, and Mohammad Neshat
https://www.osapublishing.org/oe/abstract.cfm?uri=oe-23-15-19129

We are introducing a new bias free CW terahertz photomixer emitter array. Each emitter consists of an asymmetric metal-semiconductor-metal (MSM) that is made of two side by side dis-similar Schottky contacts, on a thin layer of low temperature grown (LTG) GaAs, with barrier heights of difference (ΔΦB) and a finite lateral spacing (s). Simulations show that when an appropriately designed structure is irradiated by two coherent optical beams of different center wavelengths, whose frequency difference (∆f) falls in a desired THz band, the built-in field between the two dis-similar potential barriers can accelerate the photogenerated carriers that are modulated by ∆ω, making each pitch in the array to act as a CW THz emitter, effectively. We also show the permissible values of s and ΔΦB pairs, for which the strengths of the built-in electric field maxima fall below that of the critical of 50 V/μm— i.e., the breakdown limit for the LTG-GaAs layer. Moreover, we calculate the THz radiation power per emitter in an array. Among many potential applications for these bias free THz emitters their use in endoscopic imaging without a need for hazardous external biasing circuitry that reduces the patient health risk, could be the most important one. A hybrid numerical simulation method is used to design an optimum emitter pitch, radiating at 0.5 THz.

© 2015 Optical Society of America

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Abstract-Unbiased continuous wave terahertz photomixer emitters with dis-similar Schottky barriers

Mohammad Javad Mohammad-Zamani, Mohammad Kazem Moravvej-Farshi, and Mohammad Neshat
https://www.osapublishing.org/oe/abstract.cfm?uri=oe-23-15-19129

We are introducing a new bias free CW terahertz photomixer emitter array. Each emitter consists of an asymmetric metal-semiconductor-metal (MSM) that is made of two side by side dis-similar Schottky contacts, on a thin layer of low temperature grown (LTG) GaAs, with barrier heights of difference (ΔΦB) and a finite lateral spacing (s). Simulations show that when an appropriately designed structure is irradiated by two coherent optical beams of different center wavelengths, whose frequency difference (∆f) falls in a desired THz band, the built-in field between the two dis-similar potential barriers can accelerate the photogenerated carriers that are modulated by ∆ω, making each pitch in the array to act as a CW THz emitter, effectively. We also show the permissible values of s and ΔΦB pairs, for which the strengths of the built-in electric field maxima fall below that of the critical of 50 V/μm— i.e., the breakdown limit for the LTG-GaAs layer. Moreover, we calculate the THz radiation power per emitter in an array. Among many potential applications for these bias free THz emitters their use in endoscopic imaging without a need for hazardous external biasing circuitry that reduces the patient health risk, could be the most important one. A hybrid numerical simulation method is used to design an optimum emitter pitch, radiating at 0.5 THz.

© 2015 Optical Society of America

Full Article  |  PDF Article

Abstract-A hybrid analysis method for plasmonic enhanced terahertz photomixer sources

Saman Jafarlou, Mohammad Neshat, and Safieddin Safavi-Naeini »View Author Affiliations
http://www.opticsinfobase.org/oe/abstract.cfm?uri=oe-21-9-11115
A hybrid analysis of a continuous-wave terahertz photomixer source structure with plasmonic nano-grating electrodes is presented. Using the hybrid analysis, the enhancement of the optical power absorption due to the presence of the one-dimensional metallic nano-grating is investigated by defining an absorption enhancement factor. We show that the proposed absorption enhancement factor can be used as a design tool, whose maximization provides the optimum geometrical parameters of the nano-grating. Based on drift-diffusion model, the photocurrent enhancement due to the nano-grating electrodes is studied under three different bias configurations. Moreover, the dependence of the photocurrent on the physical parameters of the photomixer is analyzed.
© 2013 OSA