AVS 53rd International Symposium
    Electronic Materials and Processing Thursday Sessions
       Session EM1-ThA

Invited Paper EM1-ThA1
Interfacial Transport Properties in Metal-Molecule-Semiconductor Diodes

Thursday, November 16, 2006, 2:00 pm, Room 2001

Session: Contacts to Organic and Molecular Devices
Presenter: J.W.P. Hsu, Sandia National Laboratories
Authors: J.W.P. Hsu, Sandia National Laboratories
W.J. Li, Simon Fraser University
Y. Jun, University of Minnesota
C. Highstrete, Sandia National Laboratories
C.M. Matzke, Sandia National Laboratories
K.L. Kavanagh, Simon Fraser University
X.-Y. Zhu, University of Minnesota
A.A. Talin, Sandia National Laboratories
S.V. Faleev, Sandia National Laboratories
F. Leonard, Sandia National Laboratories
M.D. Halls, Indiana University
R. Krishnan, Indiana University
Correspondent: Click to Email
Integrating molecular functions with conventional semiconductors opens up new possibilities for future electronic devices. However, the formation of molecular monolayers on semiconductors is much less mature than their counter parts on metals, and the study of buried molecular junctions is hampered by the dearth of experimental tools. In this talk, I will discuss the formation of alkanethiol or alkanedithiol monolayers on (001) GaAs and electronic transport across these molecular layers by ballistic electron emission microscopy (BEEM). Using X-ray photoemission spectroscopy and ellipsometry, we found that the monolayer thicknesses of hexadecanethiols (C16MT) and of octanedithiols (C8DT) are about the same even though C16MT is almost twice as long as C8DT. Using BEEM, we examined transport properties of Au-molecule-GaAs and Au-molecule-metal-GaAs diodes where molecule = C16MT or C8DT. BEEM is one of the very few experimental techniques that are capable of measuring the local electronic transport through such buried interfaces. The barrier heights determined from BEEM are compared with Schottky barrier heights determined from temperature dependent current-voltage (I-V-T) measurements. A major difference between the two measurements is that the local barrier height determined from BEEM is without applying a bias across the molecular layer while a large field could exist across the molecules. We found that the presence of the molecule dramatically increases the BEEM threshold voltage compared to reference Au/GaAs diodes while the I-V barrier heights are about the same. Comparing the experimental results to a 1D model with two tunneling barriers, we concluded that ballistic electron transmission through the molecular layer occurs through the lowest unoccupied level. The BEEM threshold is in a reasonable agreement with the position of lowest unoccupied level from quantum chemical calculations.