Tunnel junction, current-voltage characteristic

Amman M, Wilkins R, Ben-Jacob E et al (1991) Analytic solution for the current-voltage characteristic of two mesoscopic tunnel junctions coupled in series. Phys Rev B 43 1146-1149... 

Tunneling junctions are most often produced in a crossed stripe geometry so that 4-terminal measurements of their current-voltage characteristics can be made. Electrical contacts are made to the films ( often with miniature brass "C" clamps ), the samples are mounted in a Dewar insert, and cooled to liquid helium temperatures ( 4.2 ° K or below ). 

Fig. 6.3. Semiconductor representation for (a) NIN, (b) NIS, and (c) SIS tunnel junctions showing the DOS vs. energy. The expected current/voltage characteristic for each type of junction is included on the right hand side. In each case the Fermi level of metal 1 is raised by e F with respect to metal 2. The dashed lines indicate the characteristics at T>0, and the solid lines indicate the current for T — 0.

Theoretical work fnnction on electrical transport (tunneling) in metal-mole-cule-metal jnnctions indicates that junction impedance is significantly affected by the properties of the metal-molecule contacts. Specifically, the presence of barriers to electron (or hole) injection leads to drops in electrostatic potential at the metal-molecule interface, resulting in contact impedances. Various methods are currently available for probing the electrical conductance of discrete molecules or clusters of molecules bridged between metal or semiconductor electrodes to understand how the structure and electroiuc properties of molecules and their associated contacts affect the current-voltage (I V) characteristics observed for the junction [133,136,146-161]. 

Figure 2. (a) The dependence of the time-averaged current I on U (the I U) characteristic) for a single tunnel junction. Coulomb blockade appears at voltages below ejC. (b) Time development of the junction charge imposed by a constant current source. 

As the second step, the STM tip was locked over the desired particle, feedback was temporally switched off, and voltage-current (V-I) characteristics were measured. The typical trend of the V-I characteristics is shown in Figure 29. Current steps are clearly observable in the presented curve, indicating that the single-electron junction was formed. It is worth mentioning that the characteristics observed in areas without particles demonstrate a normal tunneling behavior (see Fig. 30). 

Figure 4. Tunneling characteristics of an Al-AlOx-4-pyridine-COOH-Ag junction run at 1.4 K with a 1 mV modulation voltage, (a) Modulation voltage Vu across the junction for a constant modulation current Iu. This signal is proportional to the dynamic resistance of the sample, (b) Second harmonic signal, proportional to d2V/dI2. (c) Numerically obtained normalized second derivative signal G , dG/ dfeVJ, which is more closely related to the molecular vibrational density of states, (d) Normalized G0 dG/d(eVJ with the smooth elastic background subtracted out...

The ZT- bias curves are almost symmetric and linear at low bias voltages (Fig. 23A). The estimated tunneling resistance of the Au-tip/BPn/Au(lll)-(1x1) junction follows the same trend as discussed in the analysis of the distance tunneling characteristics. The current increases exponentially at higher bias voltages. The experimental data can be qualitatively represented by the Simmons tunneling model [187] in - 0.500 V < Fbias < 0.500 V. 

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