| The field effect characteristic of a DNA molecular device is investigated in a tight binding model with binary disorder and side site correlation. The DNA molecule in our device is deposited on the insulating substrate and is subjected to a uniform electric field which is perpendicular to the surface of the substrate (gate voltage). It is found that the system has isolate extended state that is irrespective of the DNA sequence and can be modulated by the gate voltage. When the gate voltage reaches some proper value, the isolated extended state appears at the Fermi level of the system and the long range charge transport is greatly enhanced. It is also found that if the coupling strength between the DNA and the surface is in a certain region, the Fermi level of the system turns to be an isolate extended state twice as the gate voltage varies monotonically. We attribute this phenomenon to the combination of the external field, the surface interaction, and the intrinsic disorder of DNA. Based on this mechanism, we propose that the single molecular field effect transistor can be fabricated with long mixed DNA sequence, such as ?-DNA, attached to some substrate surface. In addition, we emphasize that the mechanism of the isolate extended state can also be valid for the nanowire of binary alloy or conductive dimer that interact with the substrate surface. In this paper, the transfer matrix (TM) method is used to calculate the transmittivity and the Lyapunov Exponent (LE). The current is computed with the Landauer-Biittiker formula. This paper is organized with four sections:Section 1 gives the general introduction to the topic, including the history and background of the study about DNA transport. Section 2 investigates the main physics models of DNA wire and its important properties of transport. Section 3 is mainly about the results and discussion of our calculation. Finally, the conclusions are summarized in section 4 and an outlook is also provided. |
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