Broadband electroluminescence from reverse breakdown in individual suspended carbon nanotube pn-junctions
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Broadband electroluminescence from reverse breakdown in individual suspended carbon nanotube pn-junctions Bo Wang1, Sisi Yang1, Yu Wang3, Younghee Kim4, Ragib Ahsan2, Rehan Kapadia2, Stephen K. Doorn4, Han Htoon4, and Stephen B. Cronin1,2 () 1
Department of Physics and Astronomy, University of Southern California, Los Angeles, CA 90089, USA Ming Hsieh Department of Electrical Engineering, University of Southern California, Los Angeles, CA 90089, USA 3 Mork Family Department of Chemical Engineering and Materials Science, University of Southern California, Los Angeles, CA 90089, USA 4 Center for Integrated Nanotechnologies, Materials Physics and Applications Division, Los Alamos National Laboratory, Los Alamos, NM 87545, USA 2
© Tsinghua University Press and Springer-Verlag GmbH Germany, part of Springer Nature 2020 Received: 14 November 2019 / Revised: 6 June 2020 / Accepted: 19 June 2020
ABSTRACT There are various mechanisms of light emission in carbon nanotubes (CNTs), which give rise to a wide range of spectral emission characteristics that provide important information regarding the underlying physical processes that lead to photon emission. Here, we report spectra obtained from individual suspended CNT dual-gate field effect transistor (FET) devices under different gate and bias conditions. By applying opposite voltages to the gate electrodes (i.e., Vg1 = –Vg2), we are able to create a pn-junction within the suspended region of the CNT. Under forward bias conditions, the spectra exhibit a peak corresponding to E11 exciton emission via thermal (i.e., blackbody) emission occurring at electrical powers around 8 µW, which corresponds to a power density of approximately 0.5 MW/cm2. On the other hand, the spectra observed under reverse bias correspond to impact ionization and avalanche emission, which occurs at electrical powers of ~ 10 nW and exhibits a featureless flat spectrum extending from 1,600 nm to shorter wavelengths up to 600 nm. Here, the hot electrons generated by the high electric fields (~ 0.5 MV/cm) are able to produce high energy photons far above the E11 (ground state) energy. It is somewhat surprising that these devices do not exhibit light emission by the annihilation of electrons and holes under forward bias, as in a light emitting diode (LED). Possible reasons for this are discussed, including Auger recombination.
KEYWORDS ballistic, avalanche, high-field, band-to-band, photoemission
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Introduction
Our ability to control, produce, and enhance light emission from carbon nanotubes (CNTs) is based largely on photoluminescence measurements in which an intense laser is used to photoexcite the nanotubes. Over the past ten years, several research groups have reported that oxygen doping of CNTs using ozonolysis produces localized exciton states, which exhibit long photoluminescence lifetimes (> 1 ns), enhanced photoluminescence intensities (~ 20×), and promising g(2)-factors up to room temperature [1–11]. Kato’s group recently reported single photon emission at room temperature from air-suspended
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