The effect of metal work function on current conduction in metal-insulator-semiconductor tunnel junctions

Camporese, D.S.; Pulfrey, D.L.

doi:10.1063/1.334761

Cited by 8 publications

(11 citation statements)

References 4 publications

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“…This result is consistent with the results presented by Engelkes et al, where variations in the metal work function for MIM junctions of alkyl thiols or dithiols had a pronounced effect on the net current, but not on the length decay (β). 70 In addition, Nesher et al, considering transport through alkyls on GaAs, 63 61,67,71 we find that the contact conductances are (4.7 ( 1.3) × 10 -7 G 0 (with G 0 ≡ (2q 2 )/(h) ) 77.4 µS) for alkyl and (13 ( 8) × 10 -7 G 0 for alkenyl monolayers. As noted earlier for alkyl chain (and other molecular) junctions, the experimental G C values are much lower than G 0 48 and are sensitive to interface chemistry.…”

Section: Resultssupporting

confidence: 57%

Hg/Molecular Monolayer−Si Junctions: Electrical Interplay between Monolayer Properties and Semiconductor Doping Density

et al. 2010

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Metal-organic molecule-semiconductor junctions are controlled not only by the molecular properties, as in metal-organic molecule-metal junctions, but also by effects of the molecular dipole, the dipolar molecule-semiconductor link, and molecule-semiconductor charge transfer, and by the effects of all these on the semiconductor depletion layer (i.e., on the internal semiconductor barrier to charge transport). Here, we report on and compare the electrical properties (current-voltage, capacitance-voltage, and work function) of large area Hg/organic monolayer-Si junctions with alkyl and alkenyl monolayers on moderately and highly doped n-Si, and combine the experimental data with simulations of charge transport and electronic structure calculations. We show that, for moderately doped Si, the internal semiconductor barrier completely controls transport and the attached molecules influence the transport of such junctions only in that they drive the Si into inversion. The resulting minority carrier-controlled junction is not sensitive to molecular changes in the organic monolayer at reverse and low forward bias and is controlled by series resistance at higher forward bias. However, in the case of highly doped Si, the internal barrier is smaller, and as a result, the charge transport properties of the junction are affected by changing from an alkyl to an alkenyl monolayer. We propose that the double bond near the surface primarily increases the coupling between the organic monolayer and the Si, which increases the current density at a given bias by increasing the contact conductance.

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Section: Resultssupporting

confidence: 57%

Hg/Molecular Monolayer−Si Junctions: Electrical Interplay between Monolayer Properties and Semiconductor Doping Density

et al. 2010

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“…If an n-semiconductor is in deep inversion, further increasing the work-function of the top metal contact will not affect the current at reverse and low forward bias. 23 To test if the n-Si is indeed in deep inversion, we used Au contacts, as the work function of Au is 0.2-0.5 eV higher than that of Hg. 24 "Ready made" Au pads were used as contacts, adapting the method described in refs 25 and 26 to measure the J-V characteristics.…”

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confidence: 99%

“…The reason is that with the semiconductor in deep inversion, the minority-carrier current is limited by processes in the Si (recombination or diffusion), independent of the band bending or the presence of an interfacial insulator. [17][18][19]23 So far we focused on the semiconductor-limited J-V region, where neither the metal work function nor the insulator thickness affects the current. However, metal work function and insulator thickness are expected to dictate the bias, above which transport becomes limited by tunneling across the (molecular) insulator.…”

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confidence: 99%

Molecular Electronics at Metal/Semiconductor Junctions. Si Inversion by Sub-Nanometer Molecular Films

et al. 2009

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Electronic transport across n-Si-alkyl monolayer/Hg junctions is, at reverse and low forward bias, independent of alkyl chain-length from 18 down to 1 or 2 carbons! This and further recent results indicate that electron transport is minority, rather than majority carrier-dominated, occurs via generation and recombination, rather than (the earlier assumed) thermionic emission and, as such is rather insensitive to interface properties. The (m)ethyl results show that binding organic molecules directly to semiconductors provides semiconductor/metal interface control options, not accessible otherwise.

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“…Therefore, we regard Figure as additional confirmation for the applicability of MIS theory ,, to MOMS. Moreover, Figure suggests that the excellent reproducibility observed in MOMS at low and high forward bias might originate in their transport physics and does not imply perfect monolayers because there are variations in the monolayer, but these can be expressed only in the transition window.…”

Section: Resultsmentioning

confidence: 78%

“…With MoPALO contacts we can, in principle, study the effect of metal work function on MIS transport. The J − V curves of inorganic MIS junctions were predicted and found to be independent of metal work function as long as the semiconductor is inverted; that is, varying the metal’s work function in the direction of stronger inversion is not expressed directly in the magnitude of the semiconductor-limited current. , The exact forward bias of the transition from semiconductor- to tunneling-limited current (i.e., the inflection point) increases (for n-type) with increasing work function . Au has a 0.2 to 0.6 eV higher work function than Hg (depending on how clean the Au is), , so that we would expect its inflection point to appear at higher positive bias than for Hg.…”

Section: Resultsmentioning

confidence: 99%

Nondestructive Contact Deposition for Molecular Electronics: Si-Alkyl//Au Junctions

et al. 2010

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One of the major problems in molecular electronics is how to make electronically conducting contact to the "soft" organic and biomolecules without altering the molecules. As a result, only a small number of metals can be applied, mostly by special deposition methods with severe limitations. Transferring a predefined thin metal leaf onto a molecular layer provides a nondestructive, noninvasive contacting method that is, in principle, applicable to many types of metal and a variety of metal/molecules combinations. Here we report a modification of our earlier lift-off, float-on (LOFO) method, using as a basis its offspring, the polymer-assisted lift-off (PALO) method, where a backing polymer enables simultaneous deposition of multiple contacts as well as reduces wrinkles in the thin metal leaf. The modified PALO (MoPALO) method, reported here, adds lithography steps to obviate the need to punch through the polymer, as is done to complete PALO contacts. Morphological characterization of the electrodes indicates highly uniform, wrinkle-free contacts of negligible roughness. The good electrical performance of the MoPALO contacts was proven with metal/organic-monolayer/ semiconductor (MOMS) junctions, which are known to be very sensitive to molecular degradation and metal penetration. We also show how MoPALO contacts enabled us to compare the effect of varying the metal work function and contact area on the current-voltage characteristics of MOMS devices.

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The effect of metal work function on current conduction in metal-insulator-semiconductor tunnel junctions

Cited by 8 publications

References 4 publications

Hg/Molecular Monolayer−Si Junctions: Electrical Interplay between Monolayer Properties and Semiconductor Doping Density

Hg/Molecular Monolayer−Si Junctions: Electrical Interplay between Monolayer Properties and Semiconductor Doping Density

Molecular Electronics at Metal/Semiconductor Junctions. Si Inversion by Sub-Nanometer Molecular Films

Nondestructive Contact Deposition for Molecular Electronics: Si-Alkyl//Au Junctions

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