Fig. 6. Time parameters and gain determination of 2D photodetectors.

a Calculated fall time does not reach a stable value which is inaccurate, where ${\tau }_f^{\prime }$ is inaccurate calculated fall time, ${\tau }_f$ is accurate calculated fall time. (The bule line represents the square signal curve, the yellow line represents the typical response curve of 2D photodetectors.) b Response time measurement of photodetector may not reach a stable value under pulse signal, which will lead to an inaccurate result. The inset shows pulse signal. The ${\tau }_r$ is inaccurate calculated rise time. c Variation of photocurrent and responsivity of photoconductive photodetectors with the incident optical power density¹⁴. d Rise and fall response time of photodetector should be calculated from a complete periodic signal. e Typical −3 dB bandwidth response curve of photodetector, where $R_0$ represents stable responsivity value, $f_c$ represents the −3 dB cutoff frequency. f Gain-bandwidth product of various photodetectors, where photo-FET is photo-field-effect transistor, PVFET is photovoltage field-effect transistor¹⁴.