Journey of Electrons in Mesoscopic and Microscopic World
Shiekh Tanveer Ahmad · IETE Technical Review · 1997
Electrons are characterized by their effective mass, energy band structure and drift velocity in semiconductors involved in the fabrication of microelectronic devices. These electronic properties are retained till the semiconductor dimensions involved are larger than the mean free path. For dimensions smaller than the mean free path, the diffusive transport of electrons changes to quasi ballistic and ballistic transport, which are devoid of usual scatterings. Beside this, the dielectric layers involved in microelectronics devices, which are generally opaque to electrons, become transparent due to tunneling probability for their thickness in the range of few nanometers. These two attributes of electrons, namely quasi ballistic/ballistic transport combined with tunneling, have been found to lead to the development of some interesting devices like resonant tunneling diode/transistor and single electron transistor. These devices, formed out of mesoscopic size (few nanometer) semiconductors, are believed to be the building blocks for future development of nanoelectronic devices and circuits having better performance than those of VLSI/ULSI of today. Basic concepts involved in this transition from microelectronic to mesoscopic transport of electrons are discussed in brief in this review with the help theoretical explanations and experimental results. Future prospects of using molecules and atoms for electronic switching are also included in the discussion for the purpose of continuity in extending the idea of quantum transport still further.