All MoS2based 2D/0D localized unipolar heterojunctions as flexible broadband (UV-vis-NIR) photodetectors

This report demonstrates the fabrication of all MoS(2)based 2D/0D unipolar heterojunctions using a simple one pot hydrothermal process and their utilization in a flexible broadband photodetector covering the spectral range from the ultraviolet to the near infrared region. The discontinuous deposition of 0D MoS2, which has absorbance in the UV region, on 2D MoS2, having absorbance in the visible and near-infrared (NIR) regions, enables broadband detection. Further, contact engineering was performed wherein both the metal contacts were fabricated on 2D MoS2, thereby enabling the effective capture of photogenerated carriers. Also, a unipolar junction formed due to the Fermi level difference between 2D and 0D MoS(2)produces a localized electric field that helps in the efficacious separation of photogenerated electron-hole pairs. The responsivity values of the fabricated photodetector were calculated to be 7.56 mA W-1, 12.8 mA W-1, and 3.95 mA W(-1)in the UV, visible and NIR regions, respectively, indicating that the fabricated device is more sensitive towards the visible region. A detailed understanding of the photodetection mechanism of this unique heterostructure is presented using bandgap theory and trap states. The successful demonstration of such a cost-effective, scalable 2D/0D based broadband photodetector should lead to potential applications in optoelectronics, security, and wearable electronics.