Effect of PbPc on electron structure and carrier dynamics of black phosphorus

Abstract

Using lead phthalocyanine (PbPc) as surface doping material on black phosphorous (BP) we observe enhanced photo-excited carriers in the PbPc/BP heterostructure. The interfacial energy level alignment is investigated with ultra violet photoemission spectroscopy (UPS) and x-ray photoemission spectroscopy (XPS). The heterojunction is type I with gap of BP nested in that of PbPc, facilitating confinement of electrons and holes in BP. Ultrafast time-resolved two-photon photoemission (TR-2PPE) spectroscopy is used to study the influence of PbPc on the photo excited unoccupied electronic states and the dynamics of the relaxation processes. Monolayer PbPc can greatly increase the pump excited hot electrons and the 2 photon emission of BP. The enhanced population in the intermediate states is attributed to the straddling of the band alignment which benefits the photo excited electrons in PbPc transferring to BP. Density functional theory calculations supported the interface dipole and charge redistribution. Our results provide a fundamental understanding of the excellent opto-electrical response of PbPc/BP interface of promising application in the high efficient photo detectors.