Fig. 4: Infrared Photoresponse of the 2D heterojunction by interlayer optical excitation.

a I-V_ds curves of ReS₂/Au/WSe₂ at different excitation wavelengths of 550, 600, 700, 1150, 1200, and 1250 nm. b Zoom-in part of I-V_ds curves in (a), where the open circuit voltage of about 0.3 V is marked by the vertical black dash line. c Spectral photocurrents of the device from visible to NIR range. When the incident wavelength is less than ~880 nm (marked by the vertical black dashed line), the response is from intralayer transition. On the contrary, it is from interlayer transition. d Comparison of spectral responsivities of ReS₂/Au/WSe₂ and ReS₂/WSe₂, where obvious photoresponse enhancement is observed in the interlayer transition region. e Time dependence of photoresponse under 1250 nm illumination, corresponding to the interlayer transition pathway with power intensities from 2 to 40 W/cm². Inset: Power dependence of photocurrents under 1250-nm illumination. The values are fitted by the power law I_ph ~ P^α, where the exponent α = 1.00. f One circle on-off switching of photoresponse identifies the response time of this device, demonstrating the fast rise and fall times of ~20 and 15 ms, respectively. g Calibrated spectral photoresponse modulated by different V_bg experimentally. With the increase of negative V_bg from −17 V to −29 V, the cut-off wavelength varies from ~1150 to ~1470 nm, corresponding to the range between 1.07 and 0.84 eV, which also determines the operational spectral range of this spectrometer. The colorbar represents the varied V_bg. h Bandgaps E_g for the experimental (Exp.) and calculational (Calc.) ML WSe₂-ML ReS₂ transistors against the gate voltage.