THz Radiation of Photoconductive Antennas based on {LT-GaAa/GaAa:Si} Superlattice Structures
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IR, AND TERAHERTZ OPTICS
THz Radiation of Photoconductive Antennas Based on {LT-GaAa/GaAa:Si} Superlattice Structures A. N. Klochkova,*, E. A. Klimova, P. M. Solyankinb, M. R. Konnikovab, I. S. Vasil’evskiid, A. N. Vinichenkod, A. P. Shkurinovb, c, and G. B. Galieva a Mokerov
b
Institute of Microwave Semiconductor Electronics, Russian Academy of Sciences, Moscow, 117105 Russia Institute on Laser and Information Technologies, Russian Academy of Sciences—Branch of Federal Scientific Research Centre “Crystallography and Photonics,” Russian Academy of Sciences, Shatura, Moscow oblast, 140700 Russia c Moscow State University, Moscow, 119992 Russia d National Research Nuclear University MEPhI (Moscow Engineering Physics Institute), Moscow, 115409 Russia *e-mail: [email protected] Received December 16, 2019; revised January 13, 2020; accepted February 28, 2020
Abstract—A material in the form of a multilayer structure based on low-temperature LT-GaAs grown on (111)A-oriented substrates is proposed for fabrication of THz photoconductive antennas. These structures contain active LT-GaAs layers and doping acceptor GaAs:Si-based layers. At the optical pump power of 19 mW and the bias voltage of 30 V, a photoconductive antenna based on the optimized {LT-GaAs/GaAs:Si} (111)A structure emits THz pulses with the average power of 2.3 μW at the pulse repetition frequency of 80 MHz; the conversion efficiency is 1.2 × 10–4. It is shown that the dependence of the integral power of THz pulses of the antenna based on the {LT-GaAs/GaAs:Si} (111)A structure on the applied voltage is superlinear; the dependence of this parameter on the optical pump power is plotted as a curve with saturation. It is shown that the designed antennas have a practical application in THz spectroscopy of biological solutions. Keywords: pulsed THz spectroscopy, photoconductive antenna, low-temperature GaAs DOI: 10.1134/S0030400X20070097
INTRODUCTION Recently, the problem of increasing the power of pulsed broadband THz radiation sources excited by femtosecond optical pulses have become of great importance [1]. Photoconductive antennas (PCAs) are the most widespread sources and detectors of pulsed THz radiation [2]. When a PCA is irradiated by femtosecond laser pulses, nonequilibrium carriers are generated in the photoconductive material. Ac current is formed under the electric field applied to the PCA; because of the short lifetime of nonequilibrium carriers, this current (while damping) excites electromagnetic field oscillations in the microwave and THz frequency ranges. The energy and spectrum of THz pulses are determined by the characteristics of optical pump pulses, parameters of the photoconductive material, and geometry of PCA metallization. The efficiency of optic–THz energy conversion in PCA sources and the dynamic range of PCA detectors have recently been significantly increased using metal nanostructures, such as optical nanoantennas [3, 4] and plasmonic nanoelectrodes [5]. The unprecedentedly high conversion efficiency (7.5%) was obtained for pl
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