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Carrier Multiplication in PbS Quantum Dots Anchored on a Au Tip using Conductive Atomic Force Microscopy
Author(s) -
Kim SungTae,
Kim JiHee,
Lee Young Hee
Publication year - 2020
Publication title -
advanced materials
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 10.707
H-Index - 527
eISSN - 1521-4095
pISSN - 0935-9648
DOI - 10.1002/adma.201908461
Subject(s) - photocurrent , materials science , quantum dot , optoelectronics , nanowire , band gap , photoconductivity , quantum efficiency , graphene , conductive atomic force microscopy , semiconductor , nanotechnology , atomic force microscopy
Carrier multiplication (CM) is the amplification of the excited carrier density by two times or more when the incident photon energy is larger than twice the bandgap of semiconductors. A practical approach to demonstrate the CM involves the direct measurement of photocurrent in the device. Specifically, photocurrent measurement in quantum dots (QDs) is typically limited by high contact resistance and long carrier‐transfer length, which yields a low CM conversion efficiency and high CM threshold energy. Here, the local photocurrent is measured to evaluate the CM quantum efficiency from a QD‐attached Au tip of a conductive atomic force microscope (CAFM) system. The photocurrent is efficiently measured between the PbS QDs anchored on a Au tip and a graphene layer on a SiO 2 /Si substrate as a counter electrode, yielding an extremely short channel length that reduces the contact resistance. The quantum efficiency extracted from the local photocurrent data with an incident photon energy exhibits a step‐like behavior. More importantly, the CM threshold energy is as low as twice the bandgap, which is the lowest threshold energy of optically observed QDs to date. This enables the CAFM‐based photocurrent technique to directly evaluate the CM conversion efficiency in low‐dimensional materials.