IUVSTA 15th International Vacuum Congress (IVC-15), AVS 48th International Symposium (AVS-48), 11th International Conference on Solid Surfaces (ICSS-11)
    Organic Films and Devices Thursday Sessions
       Session OF+EL+TF-ThA

Paper OF+EL+TF-ThA5
Organic Modified Schottky Contacts: Barrier Height Engineering and Chemical Stability

Thursday, November 1, 2001, 3:20 pm, Room 131

Session: Electronic Properties of Organic Thin Films
Presenter: D.R.T. Zahn, TU Chemnitz, Germany
Authors: D.R.T. Zahn, TU Chemnitz, Germany
T.U. Kampen, TU Chemnitz, Germany
S. Park, TU Chemnitz, Germany
A. Bushell, University of Wales Aberystwyth
M. Rus, TU Chemnitz, Germany
Correspondent: Click to Email
The electronic properties of metal-GaAs(100)-contacts have been modified using 3,4,9,10-perylene-tetracarboxylic dianhydride (PTCDA) and dimethyl-3,4,9,10-perylen-tetracarboxylicdianhydride (DiMe-PTCDI). Silver is used as a top electrode. The influence of the organic films on the electronic transport properties was investigated using in situ current-voltage (IV) and capacitance-voltage (CV) measurements. The IV curves show a strong dependence on the modification of the Schottky contacts with PTCDA. The effective barrier height varies between 0.81 ~ 0.64 eV by changing the thicknesses of the PTCDA interlayer between 0 ~ 60 nm. For layer thickness above 60 nm space-charge limited currents in the organic layer determine the carrier transport in the diodes. The CV characteristics do not vary upon introducing an organic interlayer, indicating that the overall capacitance is dominated by the depletion layer within the GaAs substrates and that the width of the depletion region is hardly affected by the PTCDA modification. Therefore, the change in the effective barrier height can be explained by an increasing image-force lowering in the presence of the organic interlayer. The decrease in barrier height as a function of the organic layer thickness is not observed after an exposure of the samples to air. Here, barrier heights are independent of the organic layer thickness and have a value similar to the one of a bare Ag/GaAs(100) Schottky contact. This sensitivity to air is attributed to a reaction of the anhydride groups of the PTCDA with oxygen and/or water leading to carrier type conversion in the organic layer. Similar experiments are currently being performed using DiMe-PTCDI. First results also reveal a comparable decrease in barrier height. In addition, the DiMe-PTCDI modified Schottky contacts are found to be less sensitive to exposure to air because the imide groups are chemically more stable compared to the anhydride groups of the PTCDA.