High performance flexible phototransistors based on transferrable silicon nanomembranes

MOSFET type photodetectors, also known as phototransistors, have the advantages of not only high photo sensitivity and responsivity, but also integrability into conventional CMOS chips. In this work, flexible phototransistors with a back gate configuration based on transferrable single crystalline Si nanomembrane (Si NM) have been demonstrated [1–3]. The schematic illustration of the device fabrication process flow is shown in Figs. 1(a)-(e). Having the Si NM as the top layer enables full exposure of the active region (Fig. 1(f)) to an incident light and thus allows for effective light sensing. As shown in Fig. 1(g), flexible phototransistors are performed in two operation modes: (1) the high light detection mode which exhibits a photo-to-dark current ratio of 10
⁵
at voltage bias of V
GS
< 0.5 V, and V
DS
= 50mV and (2) the high responsivity mode which shows a maximum responsivity of 52A/W 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 [3], the device exhibited stable responsivity with less than 5% of variation under bending at small radii of curvatures (up to 15mm) as shown in Fig. 1(h). 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 multi-functional applications.