Broadband infrared photodetection using a narrow bandgap conjugated polymer

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Science Advances  09 Jun 2021:
Vol. 7, no. 24, eabg2418
DOI: 10.1126/sciadv.abg2418
  • Fig. 1 Infrared absorption of the high-spin conjugated polymer.

    (A) Molecular and electronic structure of the narrow bandgap polymer. The measured magnetic properties exhibit a high-to-low spin energy gap of 9.15 × 10−3 kcal mol−1 and exchange coupling constant (J) of 1.60 cm−1 that is consistent with ferromagnetic coupling between spins. (B) Transmission spectra of a thin film spin-coated from chlorobenzene onto an NaCl substrate (blue trace), calculated exitance of a 1000 °C blackbody radiator (orange), and spectral transmissivity of the Al2O3 encapsulant (gray).

  • Fig. 2 Device structure and IR photocurrent response.

    (A) Equivalent circuit of a photoconductive detector: VD is the DC bias, RL is the load resistance, RD is the resistance of the detector element modulated by photon absorption, and CD is the detector capacitance. (B) Schematic illustration of the 60 μm × 1 mm detector active area. (C) Single-element photoconductive devices mounted in a ceramic LCC. Inset shows (a) transmission lines, (b) a dielectric substrate, (c) the detector active area, and (d) the boundary of the polymer and dielectric encapsulant. (D) Photocurrent generated under irradiation with a 1000 °C blackbody without a spectral bandpass filter, using a SWIR bandpass filter (λ = 1 to 3 μm), a MWIR filter (λ = 3 to 5 μm), and a partial LWIR filter (λ = 8 to 12 μm). The applied bias was +5 V, and the integrated SWIR, MWIR, and LWIR spectral power is 2.17, 1.55, and 0.255 nW, respectively. Photo credit: Lifeng Huang, The University of Southern Mississippi.

  • Fig. 3 Performance characteristics of the photoconductive detector at room temperature.

    (A) Responsivity as a function of applied bias over four IR spectral regions. (B) JOLI D* and BLIP D*. (C) Photoconductive polymer response (blue) and a commercial InGaAs photodiode response substituted for the polymer (red) toward a train of femtosecond laser pulses (1550 nm, 1 kHz, 150 fs). (D) (Top) Expansion of a single femtosecond detector transient and a single exponential fit (red) gives a 10 to 90% rise time of 115 μs and a decay constant of 109 μs. (Bottom) Bode plot of the photoconductive detector showing a −3 dB bandwidth of 1.6 kHz.

  • Fig. 4 Spectral D* under JOLI and BLIP conditions for this photoconductive (PC) detector compared with that of other detector technologies.

Supplementary Materials

  • Supplementary Materials

    Broadband infrared photodetection using a narrow bandgap conjugated polymer

    Jarrett H. Vella, Lifeng Huang, Naresh Eedugurala, Kevin S. Mayer, Tse Nga Ng, Jason D. Azoulay

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