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

Full Article  |  PDF Article

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