Detector for terahertz applications based on a serpentine array of integrated GaAs/InGaAs/AlGaAs-field-effect transistors D.M. Yermolaev 1,2 , I. Khmyrova 3 E. A. Polushkin 1 , A. V. Kovalchuk 1 , V.I. Gavrilenko 4 , K.V. Maremyanin 4 , N.A. Maleev 5 , V.M. Ustinov 5 , V.E. Zemlyakov 6 , V.A. Bespalov 6 , V.I. Egorkin 6 , V.V. Popov 7 , and S.Yu.Shapoval 1 1 Institute of Microelectronic Technology and High-Purity Materials, 14243 Chernogolovka, Russia 2 JSC Russian Space System, Moscow, 111250, Russia 3 University of Aizu, Aizu-Wakamatsu, Fukushima, 965-8580, Japan 4 Institute for Physics of Microstructures, 603950 Nizhny Novgorod, Russia 5 Ioffe Physical Technical Institute, 194021 St. Petersburg, Russia 6 National Research University of Electronic Technology, 124498 Zelenograd, Russia 7 Kotelnikov Institute of Radio Engineering and Electronics (Saratov Branch), 410019 Saratov, Russia Abstract— Performance of a detector based on AlGaAs/InGaAs/GaAs-material system was studied. The detector was comprised of large serpentine array of high-electron mobility transistors (HEMTs) connected in series. The floating drain contact of each transistor (except the last one) served as a source for the next one. Detection of terahertz (THz) radiation was based on the excitation of electron plasma oscillations in the HEMT’s channel. The peculiarities of THz response of the detector in question including an enhanced noise-equivalent power were demonstrated. * Keywords - FET array, terahertz radiation, plasma waves, floating electrode I. I NTRODUCTION Detection and generation of terahertz (THz) ra- diation based on excitation of plasma wave oscil- lations in the two-dimensional electron gas (2DEG) channel of field-effect transistor (FET)-like structures were theoretically predicted by M. Dyakonov and M. Shur [1]. In recent years the achieved responsiv- ity and noise equivalent power (NEP) of such de- tectors have approached the values meeting the de- mands of practical applications [2-7]. Main designs of plasma wave THz detectors include single transis- tors with the antenna [3,4,7], single transistors with grating/interdigitated gate [2,8,9] and several transis- tors connected by external wires or integrated on a chip [5,6]. Lateral dimensions of most highly sensitive detectors are much smaller than the half-wavelength of THz radiation [5,6] and in an experiment one usually deals with a single detector surrounded by wiring. Indeed, the performance of such detectors arranged in the focal plane array (FPA) as well as the effect of external wiring are of great interest. In a regular quasi-optical systems radiation beam can be focused on a spot with a diameter of half- wavelength covering several detectors in the FPA. Therefore, the radiated power will be distributed * ISBN 978-80-261-0641-8, c University of West Bohemia, 2017 among neighboring detectors so that the power per one detector in the FPA will be proportional to the ratio of the detector area to the area of the irradiated spot which will affect the responsivity as well. We should also keep in mind the contribution of irradiated wiring which is different in the case of a single detector and FPA. In the study of a FPA with 3 × 5 pixels [7] each pixel consisted of a transistor with patch antenna and integrated amplifier and had dimensions 200 × 150 μm 2 . At room temperature the detectors have demon- strated following performance: responsivity of about 70 kV/W with 43 dB voltage amplifier at 650 GHz, NEP =300 pW/ √ Hz at 30 kHz. A single detector with a log-periodic aerial antenna with diameter of 1.5 mm has been investigated in the frequency range 200-600 GHz at liquid helium temperature [10]. This detector has demonstrated a responsivity of 2.5 kV/W at excitation frequency of 240 GHz, its calculated NEP 100 pW/ √ Hz at 750 Hz. Other configura- tions of transistors on a single chip have been also studied [2,5,6]. However, FPAs or single detectors with a size corresponding to radiation half-wavelength were not reported so far although the performance of detectors in the FPA as well as single detector of radiation half-wavelength dimensions are of great interest and worth to be investigated. In this paper we present experimental results on THz response of a detector comprising of connected in series individual transistors which can be treated as FPA or as a single detector with dimensions of radiation half-wavelength. II. DETECTOR FABRICATION THz detectors with GaAs/InGaAs/AlGaAs het- erostructures on semi insulating GaAs substrate were fabricated. At room temperature electron mobility and concentration in the channel were 5900 cm 2 /V×s and 3 × 10 12 cm -2 , respectively. The cap layer was n- doped with Si up to 6 × 10 18 cm -3 . Ohmic contacts