Electron transport and detection of terahertz radiation in a GaN/AlGaN submicrometer field-effect transistor
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Electron Transport and Detection of Terahertz Radiation in a GaN/AlGaN Submicrometer Field-Effect Transistor V. I. Gavrilenkoa^, E. V. Demidova, K. V. Marem’yanina, S. V. Morozova, W. Knapb, and J. Lusakowskib aInstitute
for Physics of Microstructures, Russian Academy of Sciences, Nizhni Novgorod, 603950 Russia ^e-mail: [email protected] bGroupe d’Etude de Semiconducteur, CNRS—Université Montpelier 2 Place E. Bataillon 34950 Montpelier, France Submitted June 27, 2006; accepted for publication July 4, 2006
Abstract—Electron transport and photoresponse in the terahertz range in a GaN/AlGaN field-effect transistor with the submicrometer gate (0.25 µm) and two-dimensional electron gas in the channel (the electron concentration ns ≈ 5 × 1012 cm–2) were studied at 4.2 K. The charge-carrier mobility in the transistor’s channel µ ≈ 3500 cm2/(V s) was determined from the dependence of the conductance on magnetic field. It is found that the dependence of photovoltage at the radiation frequency f = 574 GHz on the gate voltage (i.e., on the concentration of two-dimensional electrons) features a characteristic maximum, which is related to a resonance response of the subgate plasma in the transistor channel. PACS numbers: 61.82.Fk, 68.65.Fg, 71.10.Ca DOI: 10.1134/S1063782607020224
1. INTRODUCTION The terahertz frequency range (0.3–10 THz) encompasses the frequencies of a number of excitations in condensed media; these excitations include phonons, transitions with the involvement of shallow-level impurities, cyclotron and spin resonances, and rotational and vibrational excitations in liquids, gases, and biological objects. The use of terahertz methods for nondestructive control and visualization is of great interest for applications in medicine, environmental monitoring, the food industry, and fighting terrorism [1]. At present, broadband radiation detectors are mostly used for detection of terahertz radiation. At the same time, the use of selective and tunable detectors in spectral analysis makes it possible to do away with diffraction gratings and mechanically tunable interferometers. A fieldeffect transistor that contains a two-dimensional (2D) electron gas in the channel and is tuned by the gate voltage can serve as the above detector. The resonance and nonresonance detection in field-effect transistors with a 2D electron gas was observed in [2–5]. In the conventional mode, the highest attainable frequency of a fieldeffect transistor is limited by the reciprocal transit time. The use of plasma-related effects makes it possible to extend the operational frequency of submicrometer field-effect transistors to the terahertz frequency range [6, 7] since the characteristic velocity of the plasma waves can be as high as 108 cm/s, which is much higher than the drift velocity of electrons in the transistor’s channel. Resonance detection of terahertz radiation has already been attained for two types of field-effect transistors: a commercial GaAs/AlGaAs field-effect tran-
sistor [2, 3, 8, 9] and a field-
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