Measuring charge trap occupation and energy level in CdSe/ZnS quantum dots using a scanning tunneling microscope
Author(s)Bulovic, Vladimir; Anikeeva, Polina Olegovna; Panzer, Matthew J.; Wood, Vanessa Claire; Hummon, M. R.; Stollenwerk, A. J.; Narayanamurti, V.; ... Show more Show less
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We use a scanning tunneling microscope to probe single-electron charging phenomena in individual CdSe/ZnS (core/shell) quantum dots (QDs) at room temperature. The QDs are deposited on top of a bare Au thin film and form a double-barrier tunnel junction (DBTJ) between the tip, QD, and substrate. Analysis of room-temperature hysteresis in the current-voltage (IV) tunneling spectra, is consistent with trapped charge(s) presenting an additional potential barrier to tunneling, a measure of the Coulomb blockade. The paper describes the first direct electrical measurement of the trap-state energy on individual QDs. Manipulation of the charge occupation of the QD, verified by measuring the charging energy, (61.4±2.4) meV, and analysis of the DBTJ, show trap states ∼1.09 eV below the QD conduction-band edge. In addition, the detrapping time, a measure of the tunneling barrier thickness, is determined to have an upper time limit of 250 ms. We hypothesize that the charge is trapped in a quantum-dot surface state.
DepartmentMassachusetts Institute of Technology. Department of Electrical Engineering and Computer Science; Massachusetts Institute of Technology. Research Laboratory of Electronics; Massachusetts Institute of Technology. Research Laboratory of Electronics
Physical Review B
American Physical Society
Hummon, M. R. et al. “Measuring charge trap occupation and energy level in CdSe/ZnS quantum dots using a scanning tunneling microscope.” Physical Review B 81.11 (2010): 115439. © 2010 The American Physical Society.
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