Abstract-Fast and sensitive bolometric terahertz detection at room temperature through thermomechanical transduction

Journal of Applied Physics

 Ya Zhang, Suguru Hosono, Naomi Nagai, Sang-Hun Song,  Kazuhiko Hirakawa

(a) Wafer structure used to fabricate the doubly clamped GaAs beam resonator. (b) Schematic illustration of the GaAs beam resonator fabricated by selective etching. (c) Microscope image of a fabricated GaAs MEMS beam resonator (100 × 30 × 1.2 μm3). The 2DEG layer and the top gates on both ends of the beam form two piezoelectric capacitors, C1 and C2. A 15-nm-thick NiCr THz absorbing layer was deposited on the beam. This metal film was also used as a heater to calibrate the thermal responsivity of the resonator. (d) The resonance spectra measured by sweeping the driving frequency at various input heating powers, Pin, from 0 μW to ∼1100 μW. The red curve is the resonance spectrum at Pin = 0. (e) Normalized frequency shift as a function of Pin.

https://aip.scitation.org/doi/abs/10.1063/1.5045256

Terahertz (THz) electromagnetic spectrum draws wide attention for nondestructive and/or biocompatible sensing. In order to be widely applicable to the THz sensing, it is of prime importance to develop THz sensors that can be operated at room temperature and have high sensitivity and fast operation speed. However, conventional room-temperature THz thermal sensors fall short of expectations in these characteristics required in various applications of THz sensing, including THz cameras. Utilizing a thermomechanical transduction scheme, we have developed an uncooled, sensitive, and fast THz bolometer by using a doubly clamped GaAs microelectromechanical system (MEMS) beam resonator as a sensitive thermistor. Owing to its ultrahigh temperature sensitivity (the noise equivalent temperature difference of ∼1 μK/√Hz), the present bolometer achieves not only high sensitivity but also an operation bandwidth of several kHz, which is more than 100 times faster than other uncooled THz thermal sensors. The obtained electrical noise equivalent power is as low as ∼90 pW/√Hz, which is close to the limit set by the thermal fluctuation noise. The MEMS bolometers are fabricated by the standard semiconductor fabrication processes and are well suited for making detector arrays for realizing THz cameras.

Abstract-Terahertz Intersublevel Transitions in Single Self-Assembled InAs Quantum Dots with Variable Electron Numbers

Ya Zhang *†, Kenji Shibata †‡, Naomi Nagai †, Camille Ndebeka-Bandou †§, Gerald Bastard †§, and Kazuhiko Hirakawa *†‡

†Center for Photonics Electronics Convergence, Institute of Industrial Science and ‡Institute for Nano Quantum Information Electronics, University of Tokyo, 4-6-1 Komaba, Meguro-ku, Tokyo 153-8505, Japan

§ Laboratoire Pierre Aigrain, Ecole Normale Superieure, 24 rue Lhomond F75005, Paris, France

Nano Lett., Article ASAP

DOI: 10.1021/nl5042319

Publication Date (Web): January 12, 2015

Copyright © 2015 American Chemical Society

http://pubs.acs.org/doi/abs/10.1021/nl5042319

We propose a method for performing terahertz spectroscopy on nanometer (nm)-scale systems by using metal nanogap electrodes. Intersublevel transition spectra of single self-assembled InAs quantum dots (QDs) have been measured with high signal/noise ratios by using a single electron transistor geometry that consists of a QD and nanogap metal electrodes as a terahertz detector. Photocurrent distribution with respect to the Coulomb diamonds indicates that there are two mechanisms for the photocurrent generation. When the p shell was fully occupied, we observed rather simple photocurrent spectra induced by the p → d transitions. However, when the p shell was half-filled, the photocurrent spectra exhibited a markedly different behavior, which we attribute to the fluctuation in electron configuration when the empty p state is filled back from the electrodes.

Keywords: 

Terahertz spectroscopy; nanostructures; intersublevel transitions; quantum dots; nanometer-scale spectroscopy

Abstract-Terahertz intersublevel transitions in single self-assembled InAs quantum dots with variable electron numbers

Ya Zhang , Kenji Shibata , Naomi Nagai , Camille Ndebeka-Bandou , Gerald Bastard , and Kazuhiko Hirakawa

Nano Lett., Just Accepted Manuscript

DOI: 10.1021/nl5042319

Publication Date (Web): January 12, 2015

Copyright © 2015 American Chemical Society

http://pubs.acs.org/doi/abs/10.1021/nl5042319?journalCode=nalefd

We propose a method for performing terahertz spectroscopy on nanometer (nm)-scale systems by using metal nanogap electrodes. Intersublevel transition spectra of single self-assembled InAs quantum dots (QDs) have been measured with high signal/noise ratios by using a single electron transistor geometry that consists of a QD and nanogap metal electrodes as a terahertz detector. Photocurrent distribution with respect to the Coulomb diamonds indicates that there are two mechanisms for the photocurrent generation. When the p shell was fully occupied, we observed rather simple photocurrent spectra induced by the p→d transitions. However, when the p shell was half-filled, the photocurrent spectra exhibited a markedly different behavior, which we attribute to the fluctuation in electron configuration when the empty p state is filled back from the electrodes.