Paper EM-ThP20
Differentiating True Tunneling from Defect Dominated One, Using Current-Voltage Curve Fitting

Thursday, October 18, 2007, 5:30 pm, Room 4C

The shapes of current-voltage curves which originate from either true tunneling across the insulating film or from metallic shorts through the film (defects) are extremely similar.^1,2 While this problem is known since the 1960’s,³ there is yet no direct solution for it. An evidence for tunneling is received only by complementary observations such as characteristic vibronic features (IETS, molecules)⁴ or magneto-resistance below T_c (superconductors).² The uncertainty regarding defect transport means that the nominal junction’s geometry (namely contact area and insulator thickness) is not necessarily relevant. This motivated a search for a simplified modeling of charge transfer which avoids any prerequisite input parameters and relays solely on graphically extracted parameters. In my talk, I will show that the two popular, highly non-linear current-voltage (I-V) relations of inelastic tunneling (Simmons model⁵) and nonresonant super-exchange (Mujica-Ratner model⁶) can be reasonably approximated by simple cubic relations of two characteristic parameters: the equilibrium conductance (G₀) and the shape factor (ρ).⁷ Both G₀ and ρ depend on barrier height and width while contact area contributes only to G₀. Therefore, correlating between G₀ and ρ is highly informative in evaluating the actual junction parameters. In case of defect dominated transport, the extracted contact area would be much smaller than the nominal one, providing a direct experimental indication for the quality of the junction. This approach can be extended also to the Fowler-Nordheim relations describing field emission at high bias range. The proposed analysis would be demonstrated on various experimental and simulated I-V’s.

¹ Z.S. Zhang and D.A. Rabson, J. Appl. Phys. 95, 557-560 (2004).
² B.J. Jonsson-Akerman et al., Appl. Phys. Lett. 77, 1870-72 (2000).
³ J.L. Miles and H.O. McMahon, J. Appl. Phys. 32, 1176-1177 (1961).
⁴ J.G. Kushmerick et al., Nano Lett. 4, 639-642 (2004).
⁵ J. G. Simmons, J. Appl. Phys. 34, 1793-1803 (1963).
⁶ V. Mujica and M.A. Ratner, Chemical Physics 264, 365-370 (2001).
⁷ A. Vilan, J. Phys. Chem. C 111, 4431-4444 (2007).