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Volumn 128, Issue 21, 2006, Pages 6854-6869

Controlling semiconductor/metal junction barriers by incomplete, nonideal molecular monolayers

Author keywords

[No Author keywords available]

Indexed keywords

ADSORPTION; CHARGE TRANSFER; ELECTRON TRANSPORT PROPERTIES; INTERFACES (MATERIALS); MONOLAYERS; SEMICONDUCTING GALLIUM ARSENIDE; SEMICONDUCTOR DOPING;

EID: 33744789190     PISSN: 00027863     EISSN: None     Source Type: Journal    
DOI: 10.1021/ja058224a     Document Type: Article
Times cited : (109)

References (111)
  • 4
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    • Hipps, K. W. Science 2001, 294, 536-537.
    • (2001) Science , vol.294 , pp. 536-537
    • Hipps, K.W.1
  • 17
    • 0345979435 scopus 로고    scopus 로고
    • Ulman, A. Chem. Rev. 1996, 96, 1533-1554.
    • (1996) Chem. Rev. , vol.96 , pp. 1533-1554
    • Ulman, A.1
  • 27
    • 33744782493 scopus 로고    scopus 로고
    • note
    • The dipole moment is a vector, oriented from the (-) to the (+) charge. We define as negative a dipole whose negative pole is closer to the semiconductor surface than its positive one. Because of its parallel orientation with the electric field at the surface of an n-type semiconductor, a negative dipole is more stable than a positive dipole because of the antiparallel alignment with respect to the field.
  • 56
    • 33744782492 scopus 로고    scopus 로고
    • note
    • We use here as the relevant dipole moment that of the molecule bound to the GaAs surface, as calculated in ref 25, rather than the free molecule's dipole moment, as we did in earlier work. We note that, as noted also in ref 25, the general trends are very similar, reflecting the changes within the series of molecules with identical binding group.
  • 66
    • 33744818369 scopus 로고    scopus 로고
    • note
    • If a metal and a semiconductor are brought in electronic contact, an electrostatic potential barrier can form between them as a result of the flow of electrons between them to equilibrate their Fermi levels (the electrochemical potentials of the electrons). The result of this is a rectifying contact, described by the so-called Schottky-Mott model. The barrier is called a Schottky barrier. The height of this barrier is the Schottky Barrier Height (SBH).
  • 69
    • 33744825894 scopus 로고    scopus 로고
    • note
    • A short summary of the basic concepts of the "dipole layer approach" and the main results are provided in section 3 of the Supporting Information, which also contains a discussion of a minor modification that needs to be made for the boundary values bordering the molecular layer.
  • 72
    • 33744824557 scopus 로고    scopus 로고
    • note
    • b2), where T is the transmission coefficient through the ith interface. Although we did refine the data to extract these two parameters, they are, not surprisingly, coupled. Such analysis showed smaller T than S variations between molecules.
  • 77
    • 33744807379 scopus 로고    scopus 로고
    • note
    • d is the doping density, and ξ is defined in the following footnote.
  • 78
    • 33744797269 scopus 로고    scopus 로고
    • note
    • ξ is a measure of the geometry of SBH variation and is determined empirically by fitting the functional form of the experimentally observed currents. Theoretically, it was found that SBHs with circular or stripe geometries that are homogeneously distributed at the interface have ξ = 2/3 or ξ = 1/2, respectively. The lower are the ξ values that are obtained by fitting the functional form of the experimentally observed currents, the higher is the SBH variation, i.e., the larger is the degree of inhomogeneity. We find ξ = 1/6, which indicates a high degree of inhomogeneity, relative to the ideal case.
  • 79
    • 33744797564 scopus 로고    scopus 로고
    • note
    • In contrast to what is the case with vacuum evaporation, with LOFO it is extremely unlikely that any diffusion of the metal will occur through the organic monolayer.
  • 80
    • 33744818079 scopus 로고    scopus 로고
    • note
    • d.
  • 81
    • 33744822094 scopus 로고    scopus 로고
    • note
    • In metal/dC-X/n-GaAs junctions, there are basically three types of SBH: (1) metal/dC-X/n-GaAs; (2) nonpinched-off metal/n-GaAs (i.e., large 2D pinholes); and (3) pinched-off metal/n-GaAs (i.e., small pinholes). However, C-V measurements cannot distinguish between pinched-off and non-pinched-off domains. This can be understood as follows. The capacitance at a given voltage is essentially determined by the depletion width at that voltage, which is determined by the average conduction band energy at the GaAs interface, the doping density in the GaAs, and the Fermi energy in the bulk of the GaAs. The detailed shape of the conduction band in the depletion region makes little difference, because there are no free carriers there anyway. This is why image force effects are not important, as pointed out in refs 46 and 61. In this case, it does not matter whether there are pinched-off points or not in the depletion region. Because that is so, the analysis of the C-V data can be used only to distinguish between large metal-GaAs pinholes and metal-molecules-GaAs domains.
  • 96
    • 33744831673 scopus 로고    scopus 로고
    • To be published
    • Haick, H. et al. and Azulay, D. et al. To be published.
    • Haick, H.1    Azulay, D.2
  • 97
    • 33744786964 scopus 로고    scopus 로고
    • note
    • Before contacting the molecularly modified surfaces, there will be some oxide in the pinholes and (at least) under the outer regions of dC-X/GaAs domains (because it should be relatively easy for O to reach there). After contacting, Pd but not Au reacts with and removes the GaAs-oxide in the pinhole areas only, leaving behind oxides below the molecularly modified domains.
  • 102
    • 33744802802 scopus 로고    scopus 로고
    • note
    • This can happen due to deposition of Pd clusters directly on the pinholes and/or diffusion of clusters from the molecular domains into the Pd-filled pinholes.
  • 106
    • 33744823983 scopus 로고    scopus 로고
    • note
    • 3 requires intentional addition of small amounts (4% v/v) of water to accomplish the adsorption properly (cf. refs 38 and 39). This need was ascribed to the high concentration of negative charge on the binding group that results from the negative dipole. This negative charge favors the formation of the radical or the carboxylate form, compared to what is the case for molecules with a positive dipole. Adding water screens the charge and decreases the activation energy barrier, thus allowing their (slow) adsorption.
  • 110
    • 33744779796 scopus 로고    scopus 로고
    • note
    • For our samples, assuming all other factors being equal, the higher dopant concentration in high-doped n-GaAs was found to give a ∼10 times higher net (negative) surface charge than the low-doped n-GaAs, both before and after dC-X adsorption.
  • 111
    • 33744831388 scopus 로고    scopus 로고
    • note
    • To increase injection efficiency with the help of an interfacial layer of molecules (excluding "conducting" ones, for which different conditions apply), the layer should be porous with maximal length of edges/area, to give highly a strongly inhomogeneous lateral electric field distribution and with a polarity to lower the barrier.


* 이 정보는 Elsevier사의 SCOPUS DB에서 KISTI가 분석하여 추출한 것입니다.