Research ArticleAPPLIED PHYSICS

Extraordinary linear dynamic range in laser-defined functionalized graphene photodetectors

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Science Advances  26 May 2017:
Vol. 3, no. 5, e1602617
DOI: 10.1126/sciadv.1602617
  • Fig. 1 Raman spectroscopy study of structural changes in laser-irradiated FeCl3-FLG.

    (A) G bands in FeCl3-FLG before (top) and after (bottom) exposure to a 30-mW laser for 3 s (λ = 532 nm). Experimental data (black dots) is shown alongside a superposition of Lorentzian fits to the G0, G1, and G2 peaks (red line). (B) Optical micrograph of the FeCl3-FLG flake (red dotted lines) with the laser-irradiated region highlighted (green). Raman spectra are acquired along r before (left) and after (right) FeCl3 displacement. (C) G1 (bottom) and G2 (top) peak positions representing stages 1 and 2 intercalated states, respectively. Data points are Lorentzian fits of the spectral peaks in (B).

  • Fig. 2 Scanning photocurrent microscopy of p-p′ junctions in FeCl3-FLG.

    (A) Total charge carrier concentration before and after laser-assisted displacement of FeCl3, estimated from G peak positions in Fig. 1C. (B) Short-circuit configuration (top) for scanning photocurrent measurements of a p-p′-p junction (p-p′ region in green). Schematic band structure (bottom) of each region shows photogenerated carriers drifting under a chemical potential gradient. (C) Optical micrograph (top) of an FeCl3-FLG flake (red dashed lines) with Au contacts (yellow lines). Scanning photocurrent maps (bottom) before and after selective laser-assisted displacement of FeCl3 (white dashed lines). The photoresponse is measured for excitation wavelengths of 375, 473, and 561 nm.

  • Fig. 3 Characterization of photocurrent at p-p′ junctions in FeCl3-FLG.

    (A) Photocurrent produced by λ = 473 nm excitation as a function of incident power density measured at a laser-defined p-p′ junction and for pristine monolayer graphene (black). Power-law exponents (IphPα) are detailed for each data set with fits shown as solid lines. Powers within the range at which photocurrent in pristine graphene that has been reported to saturate are highlighted in green (see table S1). Yellow-shaded area represents the extended range of FeCl3-FLG. (B) Photocurrent measured at the p-p′ junction A in Fig. 2B using various excitation wavelengths. Solid lines are linear fits (see main text). (C) Spectral responsivity of a p-p′ junction in FeCl3-FLG shown with (filled circles) and without (open circles) correction for reflections from the Si/SiO2 substrate (section S6) are extrapolated from (B). The dashed line is a guide to the eye. Inset: Schematic of the model used to correct ℜ(λ) for substrate reflections. Power density and responsivity values are calculated considering the area illuminated by the laser spot (see Materials and Methods).

  • Fig. 4 High-resolution photoactive junctions in FeCl3-FLG defined using near-field scanning microscopy.

    (A) Spatial map of photocurrent in a uniformly doped graphene flake before laser-assisted deintercalation. (B) AFM topography and (C) scanning photocurrent maps of the FeCl3-FLG flake after laser-assisted deintercalation by a λ = 632 nm laser scanned over a 500-nm long region (white dashed lines). Insets: Illustrations of the chemical structure in p- and p′-doped regions. Schematic of the excitation wavelength focused on a metallized AFM tip in each measurement are included in (A) to (C); outlines of the flake are superimposed (black dashed lines). Scale bars, 500 nm. Magnified concurrent AFM topography and scanning photocurrent maps are shown before (D) and after (E) laser writing. (F) Line scans of photocurrent measured across laser-defined p-p′-p junctions [(D) and (E), red and black dashed lines] before (top) and after (middle) displacement of molecules. First-derivative plots of the photocurrent signal after displacement (bottom) show a peak-to-peak distance of 250 nm between adjacent p-p′ junctions (red arrows). All photocurrent measurements were taken in short-circuit configuration.

Supplementary Materials

  • Supplementary material for this article is available at http://advances.sciencemag.org/cgi/content/full/3/5/e1602617/DC1

    section S1. Supplementary data on laser irradiation

    section S2. Supplementary photocurrent measurements

    section S3. Power dependence of the photothermoelectric and photovoltaic effects

    section S4. Estimation of chemical potential and conductivity for decoupled graphene layers

    section S5. Physical explanation for a purely photovoltaic response

    section S6. Correction of responsivity spectra for substrate reflections

    fig. S1. Inferred stacking order of four-layer FeCl3-FLG.

    fig. S2. Calibration of laser-induced displacement of FeCl3.

    fig. S3. Bandwidth of a laser-written FeCl3-FLG junction device.

    fig. S4. NEP of laser-written FeCl3-FLG junction device.

    fig. S5. Characterization of supported pristine graphene devices.

    fig. S6. Additional measurements of photocurrent in supported pristine graphene devices.

    fig. S7. Photoresponse at p-p′ junction in FLG.

    fig. S8. Calculation of the carrier concentration and chemical potential at p-p′ interfaces of FeCl3-FLG.

    fig. S9. Direction of photocurrent at p-p′ junctions of FeCl3-FLG.

    fig. S10. Correction of spectral responsivity for substrate reflections.

    table S1. LDR of graphene and functionalized graphene devices.

    table S2. Summary of power-law exponents possible for photocurrent originating from the photothermoelectric effect.

    table S3. Corrections to responsivity for the laser wavelengths used in this work.

    References (3847)

  • Supplementary Materials

    This PDF file includes:

    • section S1. Supplementary data on laser irradiation
    • section S2. Supplementary photocurrent measurements
    • section S3. Power dependence of the photothermoelectric and photovoltaic effects
    • section S4. Estimation of chemical potential and conductivity for decoupled graphene layers
    • section S5. Physical explanation for a purely photovoltaic response
    • section S6. Correction of responsivity spectra for substrate reflections
    • fig. S1. Inferred stacking order of four-layer FeCl3-FLG.
    • fig. S2. Calibration of laser-induced displacement of FeCl3.
    • fig. S3. Bandwidth of a laser-written FeCl3-FLG junction device.
    • fig. S4. NEP of laser-written FeCl3-FLG junction device.
    • fig. S5. Characterization of supported pristine graphene devices.
    • fig. S6. Additional measurements of photocurrent in supported pristine graphene devices.
    • fig. S7. Photoresponse at p-p′ junction in FLG.
    • fig. S8. Calculation of the carrier concentration and chemical potential at p-p′ interfaces of FeCl3-FLG.
    • fig. S9. Direction of photocurrent at p-p′ junctions of FeCl3-FLG.
    • fig. S10. Correction of spectral responsivity for substrate reflections.
    • table S1. LDR of graphene and functionalized graphene devices.
    • table S2. Summary of power-law exponents possible for photocurrent originating from the photothermoelectric effect.
    • table S3. Corrections to responsivity for the laser wavelengths used in this work.
    • References (38–47)

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