STM and TS Study of InAs Quantum Dots Immobilized on Au and Pt Surfaces

Abstract

The first study of the electrical properties of nanometer-size InAs particles is presented. InAs quantum dots (Q-InAs) deposited as films onto Pt and Au electrodes are examined using scanning tunneling microscopy (STM), tunneling spectroscopy (TS), and macroscopic conductivity measurements. In addition, single Q-InAs particles adsorbed on Au-covered mica substrates are examined by STM. The following results are reported in this study: (1) The size distribution of Q-InAs obtained from cross sections of STM images agreed with previous XRD and TEM size measurements, and the measured size was well below the exciton diameter estimated for InAs. (2) The TS I-V curves for Q-InAs films on Au show a larger zero-current region than that obtained for sulfide-passivated, bulk single crystal p-InAs; consistent with the magnitude of strong confinement predicted for particles of this size by the effective mass model. (3) Macroscopic I-V measurements acquired under vacuum for Q-InAs films deposited onto Au interdigitated array electrodes show the absence of an effect of charge transport at either the Q-InAs/Q-InAs or the Q-InAs/Au interfaces on TS energy gap measurements. These results supported our conclusion that the zero-current region in the TS spectra of Q-InAs is reflective of a wider HOMO-LUMO gap in the quantum dots. These I-V plots also showed that the conductivity of the Q-films is only 2 orders of magnitude lower than bulk InAs.