Quantum engineering of nanoelectronic devices: the role of quantum confinement on mobility degradation

Transport properties in semiconductor nanostructures, spanning nanometer dimensions comparable to the de Broglie wavelength of charge carriers, are shown to depend upon the geometry of confinement as quantum waves are encountered. Approximate wave functions are obtained for prototype AlxGa1-xAs/GaAs/AlxGa1-xAs quantum wells (QWs) with finite boundaries that depend on the alloy composition x and those in MOSFET that depend on the applied gate electric field. The leakage of the wave function in classically forbidden regions is accounted for by an enhanced effective width in an equivalent model with infinite boundaries. By relative comparison of the transport parameters obtained in rectangular quantum well (RQW) and triangular quantum well (TQW), we convincingly show that the mobility degradation is a direct result of quantum confinement, in direct contrast to a model that predicts it as being degraded due to electrons becoming hot. The gate capacitance as well as transport in the quasi-free direction is affected by the quantum confinement as wave function peaks at a distance removed from the interface while vanishing at the interface. (C) 2001 Elsevier Science Ltd. All rights reserved.