Flexible Phototransistors Based on Single‐Crystalline Silicon Nanomembranes

In this work, flexible phototransistors with a back gate configuration based on transferrable single‐crystalline Si nanomembrane (Si NM) have been demonstrated. Having the Si NM as the top layer enables full exposure of the active region to an incident light and thus allows for effective light sensing. Flexible phototransistors are performed in two operation modes: 1) the high light detection mode that exhibits a photo‐to‐dark current ratio of 10⁵ at voltage bias of V_GS < 0.5 V, and V_DS = 50 mV and 2) the high responsivity mode that shows a maximum responsivity of 52 A W⁻¹ under blue illumination at voltage bias of V_GS = 1 V, and V_DS = 3 V. Due to the good mechanical flexibility of Si NMs with the assistance of a polymer layer to enhance light absorption, the device exhibits stable responsivity with less than 5% of variation under bending at small radii of curvatures (up to 15 mm). Overall, such flexible phototransistors with the capabilities of high sensitivity light detection and stable performance under the bending conditions offer great promises for high‐performance flexible optical sensor applications, with easy integration for multifunctional applications.