AVS 61st International Symposium & Exhibition
    Surface Science Tuesday Sessions
       Session SS-TuP

Paper SS-TuP19
Electron Percolation via In-Gap States in Semiconductor Quantum Dot Arrays

Tuesday, November 11, 2014, 6:30 pm, Room Hall D

Session: Surface Science Poster Session
Presenter: Yingjie Zhang, University of California, Berkeley and Lawrence Berkeley National Laboratory (LBNL)
Authors: Y. Zhang, University of California, Berkeley and Lawrence Berkeley National Laboratory (LBNL)
D. Zherebetskyy, LBNL
S. Barja, LBNL
L. Lichtenstein, LBNL
N.D. Bronstein, University of California, Berkeley
P. Alivisatos, University of California, Berkeley and LBNL
L.-W. Wang, LBNL
M.B. Salmeron, University of California, Berkeley and LBNL
Correspondent: Click to Email
Charge hopping and percolation in disordered semiconductors has been widely studied, but the microscopic nature of the percolation process is not understood and has never been determined. Here we directly image the charge percolation pathways in 2-D PbS quantum dot (QD) arrays using Kelvin probe force microscopy. We showed that the electrons percolate via in-gap states (IGS) instead of the conduction band, while holes percolate via valence band states. This exotic transport behavior is explained by the electronic structure and energy level alignment of the individual QDs, which was measured by scanning tunneling spectroscopy. Density functional theory and spectroscopic analysis show that the IGS are induced by oxygen molecules adsorbed on the QDs’ surface. These states are partially hybridized with the valence band states, enabling inter-IGS coupling and electron transport via IGS. Surface chemical treatments open the way of defect engineering, achieving tunable electronic structure and transport properties by controlling the IGS.