We describe the saturation properties and power scaling of large-aperture planar photoconducting antennas. These antennas have been used to emit and detect electromagnetic pulses with terahertz bandwidth. At high optical fluences, the amplitude of the radiated electric field saturates, at a value comparable to the bias field in agreement with a simple model of the radiation. We also discuss the saturation properties of the large-aperture photoconducting antennas with different semiconductor materials.

Saturation properties of large-aperture photoconducting antennas

A compact planar antenna sources with on-chip fabrication and high directivity in order to achieve large depth-of-field for better image resolution is the prospective demand for THz imaging application. Therefore, the small-gap photoconductive dipole antennas have been explored to fulfil such applications demand. However, there are certain modalities for improving the photoconductive dipole antenna performance which need to identify to accomplish high THz average radiated power and improved total efficiency. The unit-cell small-gap photoconductive dipole antenna radiation power enhancement methods need to optimize the design parameters with photoconductive material selection from theoretical simulation. Further, the potential improvement of coupling efficiency of THz wave with air as well as femto-second laser incident efficiency is also important parameters to enhance the radiation power of small-gap photoconductive dipole antenna. In this paper, we have presented an analytical procedure employing explicit mathematical expression leading to the physical behaviour of small-gap photoconductive dipole antenna. The effects of biased lines on the antenna performance parameters are discussed with the help of proposed equivalent circuit model. We have explored the effect of gap-size on the THz radiated power and on total radiation efficiency from the proposed photoconductive dipole antennas.

Analytical framework of small-gap photoconductive dipole antenna using equivalent circuit model

This paper presents the antenna design parameter dependency on the impedance and radiation characteristics of a terahertz coplanar stripline dipole antenna. The antenna response is numerically investigated by applying a semi-inflnite substrate and by generating a constant voltage source to drive a signal on the antenna. In this way, we can analyze the antenna characteristics without the photoconductive material response and the substrate lens geometrical efiects. Further, we explain the mechanism underlying the preferable uses of several millimeter length DC bias striplines in a typical THz coplanar stripline dipole antenna design. The antenna, consisting of a center dipole connected to long bias striplines, has a traveling wave characteristic supporting an attenuated current, rather than a resonant characteristic supporting a standing wave of current. The traveling wave behavior produces stable antenna input impedances and minimal changes in the antenna radiation patterns. We also found that the length of the center dipole has a prominent efiect on the antenna gain response.

/pdf/effects-of-antenna-design-parameters-on-the-characteristics-1nv9id8f00.pdf

Effects of Antenna Design Parameters on the Characteristics of a Terahertz Coplanar Stripline Dipole Antenna

Many terahertz applications such as sensing, imaging, and spectroscopy require coherent terahertz (THz) sources. A basic Ti-Au dipole antenna on GaAs substrate is designed initially and it is enhanced into a photoconductive antenna for terahertz emission. A spectral width of 120 GHz is obtained from the emission spectrum. In order to compare the spectral characteristics, a graphene dipole antenna is designed on the same substrate. It is observed that graphene dipole yields a narrower spectral width of 70 GHz, due to its high Q factor. Spectral width of the graphene dipole antenna is further made narrow to 25 GHz, by incorporating a λ/4 stub on the stripline to produce a filtering operation. The antenna provides a directivity of 6.14 dBi with stub which shows an improvement of 0.3 dB when compared with an antenna without stub.

A Narrow Spectrum Terahertz Emitter Based on Graphene Photoconductive Antenna

Ferroelectric materials with remnant polarization can effectively modulate the built‐in electric field of semiconductor devices and hold great promise for the development of high‐performance self‐powered optoelectronic devices. However, the low depolarization and low separation efficiency of photo‐generated carriers limit the performance of existing ferroelectric/semiconductor‐based self‐powered photodetectors. In this study, a n‐GaN/Pb(Zr0.2Ti0.8)O3 (PZT)/ITO self‐powered ultraviolet (UV) photodetector with an inverted structure and GaN as the optical absorption material is fabricated. By coupling the strong depolarization field (Edp) of PZT with the enhanced built‐in electric field (EPZT/GaN) of GaN/PZT heterojunction, this device exhibits outstanding performances with an ultra‐high light‐to‐dark current (Ilight/Idark) ratio of 3.07 × 107, a high responsivity of 176 mA W−1, a high detectivity of 2.36 × 1013 Jones, and a fast response time of 0.52/0.58 ms. Its comprehensive detection performance surpasses most reported advanced ferroelectric/semiconductor‐based UV photodetectors. The proposed strategy provides a simple and feasible approach for the design of high‐performance GaN‐based self‐powered UV photodetectors.

Inverted‐Structural Self‐Powered Gan/PZT/ITO UV Photodetector Enhanced by Ferroelectric Modulation

High-Performance Self-Driven Single GaN-Based p–i–n Homojunction One-Dimensional Microwire Ultraviolet Photodetectors

We study the rectangular tips of the dipole photoconduc- tive antenna, which has been widely used for terahertz radiation and detection, with difierent blend radii efiect on the emission performance of terahertz (THz) radiation. For the amplitude of THz radiation pulse is proportional to the local electric fleld in the gap, the increased max- imum bias electric fleld by blending tips is able to achieve higher THz radiation power. Both considering the in∞uence to the maximum bias electric fleld and the emission e-ciency, the blend radius of the rect- angular tips is suggest to be larger than 5"m and the radiation power is largely enhanced. Comparing to the previous work, our method has better THz radiation performance.

/pdf/enhancing-terahertz-radiation-from-dipole-photoconductive-1yuwd834wp.pdf

Enhancing terahertz radiation from dipole photoconductive antenna by blending tips

High-Performance Self-Driven Single Gan-Based P-I-N Homojunction One-Dimensional Microwire Ultraviolet Photodetector

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High-Performance Self-Driven Single GaN-Based p–i–n Homojunction One-Dimensional Microwire Ultraviolet Photodetectors

Enhancing terahertz radiation from dipole photoconductive antenna by blending tips

High-Performance Self-Driven Single Gan-Based P-I-N Homojunction One-Dimensional Microwire Ultraviolet Photodetector