Research ArticlePHYSICS

Ultrabroadband photosensitivity from visible to terahertz at room temperature

See allHide authors and affiliations

Science Advances  03 Aug 2018:
Vol. 4, no. 8, eaao3057
DOI: 10.1126/sciadv.aao3057
  • Fig. 1 RT NC-CDW phase in 1T-TaS2 and its electronic properties.

    (A) Schematic images of layered structure. (B) Temperature dependence of the four-probe resistivity on temperature cycling. The inset depicts the lattice distortions associated with NC-CDW phase. (C) Schematic of the two-terminal device used for photoresponse characterization. (D) The I-V curve under dark for the two-terminal device measured under voltage sweep up and down modes at RT. The abrupt switching between LC and HC states can be driven by the applied bias. The inset shows the quasi-linear I-V at low fields (the blue dashed is a guideline) and a nonlinear behavior at the relative high fields.

  • Fig. 2 Absorbance spectra and electrical response under illuminations.

    (A) In-plane optical absorbance spectrum of freshly cleaved surface of 1T-TaS2 crystal samples. a.u., arbitrary units. (B) The photoresponse of dc electrical current of a device for voltage sweep up mode. The light intensity is 0.7 W cm−2. (C) The threshold voltage VT changes linearly with the incident light intensity. (D) Current switching effects for applied bias 0.71 V (left) and 0.73 V (right), as bias values are marked out as blue circles in (B). For the experiment, the illumination (0.7 W cm−2) is chopped at a frequency of 5 Hz. The illuminations were provided by a continuous-wave solid-state laser at λ = 1550 nm, with a laser spot of ~2.7 mm in diameter focusing on the device.

  • Fig. 3 The Uultrabroadband photoresponse.

    (A) The current response as the function of incident intensities was investigated at illumination of λ = 1550 nm for applied voltages below the initial threshold of dark. For relatively weak illuminations, a linear relationship for the current with incident intensity can be established. While for intense illuminations, the conduction transition of LC-HC can be achieved. (B) The ultrabroadband photoresponsivity measured at external bias 0.72 V. The illuminations were provided by continuous-wave solid-state lasers from Vis to THz at λ = 532, 635, 1064, and 1550 nm and λ = 10, 96.3, 118.8, and 163 μm, respectively (see Materials and Methods).

  • Fig. 4 Temporal photoresponse studied by pulse excitations.

    (A) Rise and fall edges showing fast and slow components. The yellow lines are guides identifying three different relaxation processes including a short retention of ~30 ns, a fast fall in another 30 ns, and a slow tail. The small superimposed oscillations are due to ringing of the circuit. (B) Close-up views of the fast components of the rise edges and short retention. The rise time shorter than 2 ns can be recognized, and the accurate rise time analysis is out of the limitation of our oscilloscope. Here, in the experiments, the pulsed femtosecond lasers are provided at wavelengths λ = 0.8 μm (~100 fs, 1.2 mJ cm−2) and λ = 2.5 μm (~150 fs, 1 mJ cm−2), with the repetition rate of 1 kHz.

Supplementary Materials

  • Supplementary material for this article is available at http://advances.sciencemag.org/cgi/content/full/4/8/eaao3057/DC1

    Materials characterization

    Photoresponse spectra as the function of applied bias and incident intensity

    Estimation of the temperature rise

    THz response characterization

    Ultrabroadband photoresponsivity operating at quasi-linear photoresponse conditions

    Noise characteristics of 1T-TaS2 devices

    Temporal response of the device after the femtosecond pulse excitations

    Fig. S1. Energy dispersive spectrum analysis of the 1T-TaS2 as-grown crystals.

    Fig. S2. In-plane IR spectra of the 1T-TaS2 measured at 300 and 78 K.

    Fig. S3. Optical images of 1T-TaS2 as-growth crystals and devices.

    Fig. S4. I-V characteristics of the device as the function of applied bias and incident intensity.

    Fig. S5. The estimated steady-state value of temperature rises for the illumination of ~1 W cm−2 at various wavelengths in our measurement range for a sample with the dimension ~ 780 μm × 23 μm × 6 μm.

    Fig. S6. THz response characterizations at λ = 118.8 μm.

    Fig. S7. Ultrabroadband photosensitivity operating at quasi-linear photoresponse conditions.

    Fig. S8. Noise current analysis for the 1T-TaS2 device at external bias 0.71 V.

    Fig. S9. Temporal response of the device after the 150-fs pulse excitations.

    Table S1. Parameters for 1T-TaS2, graphene, and topological insulator–based photodetectors.

    References (3138)

  • Supplementary Materials

    This PDF file includes:

    • Materials characterization
    • Photoresponse spectra as the function of applied bias and incident intensity
    • Estimation of the temperature rise
    • THz response characterization
    • Ultrabroadband photoresponsivity operating at quasi-linear photoresponse conditions
    • Noise characteristics of 1T-TaS2 devices
    • Temporal response of the device after the femtosecond pulse excitations
    • Fig. S1. Energy dispersive spectrum analysis of the 1T-TaS2 as-grown crystals.
    • Fig. S2. In-plane IR spectra of the 1T-TaS2 measured at 300 and 78 K.
    • Fig. S3. Optical images of 1T-TaS2 as-growth crystals and devices.
    • Fig. S4. I-V characteristics of the device as the function of applied bias and incident intensity.
    • Fig. S5. The estimated steady-state value of temperature rises for the illumination of ~1 W cm−2 at various wavelengths in our measurement range for a sample with the dimension ~ 780 μm × 23 μm × 6 μm.
    • Fig. S6. THz response characterizations at λ = 118.8 μm.
    • Fig. S7. Ultrabroadband photosensitivity operating at quasi-linear photoresponse conditions.
    • Fig. S8. Noise current analysis for the 1T-TaS2 device at external bias 0.71 V.
    • Fig. S9. Temporal response of the device after the 150-fs pulse excitations.
    • Table S1. Parameters for 1T-TaS2, graphene, and topological insulator–based photodetectors.
    • References (3138)

    Download PDF

    Files in this Data Supplement:

Navigate This Article