Figure 2: Experimental signatures of photo-thermionic emission. | Nature Communications

Figure 2: Experimental signatures of photo-thermionic emission.

From: Photo-thermionic effect in vertical graphene heterostructures

Figure 2

(a) Photocurrent (PC) spectrum measured at room temperature in the G/WSe2/G region with laser power P=90 μW, VB=0.6 V and VG=0 V (same conditions for b,c). The insets illustrate the absorption process taking place in the different photoresponse regimes: absorption in WSe2 for Ephoton>Eg and absorption in graphene for Ephoton<Eg. The transition between these two regimes is represented by the background colour gradient, where red (blue) corresponds to the graphene (WSe2) absorption regimes. The vertical orange dashed line corresponds to the energy of the bulk WSe2 bandgap. (b) Power dependence of the photocurrent for various values of photon energy Ephoton. The dots represent experimental data and the solid lines are power law fits (PCPα) obtained with a fit range P=70–120 μW. (c) Fitted power law index α versus photon energy, showing the transition from linear to superlinear power dependence. This transition occurs around Ephoton=Eg, the indirect bandgap of WSe2. The error bars correspond to the s.d. obtained from the linear fit. (d) Time-resolved photocurrent change ΔPCt)=PC(Δt)−PCt→∞), measured using the setup and technique described in ref. 24 with an average laser power of 260 μW (wavelength 800 nm), at low temperature (30 K) and bias (VB=0.04 V) in order to suppress the contribution of the photocurrent originating from WSe2 absorption. Experimental data are represented by orange dots and the solid black line is a decaying exponential fit with time constant τcool=1.3 ps. Inset: same data and fit in logarithmic scale.

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