Carrier Multiplication in PbS Quantum Dots Anchored on a Au Tip using Conductive Atomic Force Microscopy

Advanced Materials
Sung-Tae KimYoung Hee Lee

Abstract

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 SiO2 /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 th...Continue Reading

References

May 12, 2005·Nano Letters·Randy J EllingsonAlexander L Efros
May 29, 2010·Nano Letters·Shujing WangTodd D Krauss
Oct 12, 2010·Science·Justin B SamburB A Parkinson
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Dec 30, 2015·The Journal of Physical Chemistry Letters·Artem A BakulinEleonora Vella
Dec 4, 2019·Nature Communications·Ji-Hee KimYoung Hee Lee

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Citations

Feb 17, 2021·Nano Letters·Jun Suk KimYoung Hee Lee

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