Fig. 3

MoS₂ pn junction defined by locally patterned ferroelectric polarization and its characteristics. a Formation principle of MoS₂ pn junction by locally patterned upward (P↑) and downward (P↓) ferroelectric polarization using a scanning AFM tip. b Piezoelectric force microscope (PFM) phase image of the formed FE polarization pattern on device 2 (Dev-2). The bright and dark-colored region correspond, respectively, to the polarization states of P↑ and P↓ in FE copolymer, which cause, respectively, p- and n-type doping to MoS₂. c I–V characteristic of the pn-doped MoS₂ channel compared to complete p and n doping. d I–V characteristic of the MoS₂ pn junction under 532 nm laser illumination of different intensities, from dark to 14.5, 26, and 49 mW cm⁻², showing photovoltaic-like behavior. e Transient photoresponse of the self-powered pn junction compared to the pristine MoS₂ device in photoconductor configuration. f Spatial photocurrent map of Dev-3 in short circuit compared to its optical microscope image. Self-driven photocurrent is confirmed to generate from the pn junction defined in the middle of channel rather than from contact effects