chapter  16

Atomistic Simulation of Disordered Nano-electronics

WithYouqi Ke

The progress in modern semiconductor technology has been driven by the miniaturization of electronic devices. The most remarkable example is the continued reduction in the size of transistor by the application of nano-fabrication and nano-materials, pushing the field into the nano-electronics. Today, a modern computer processor can integrate billion-plus nano-transistors, and each nano-transistor has barely tens of atoms long. Nowadays, the term “nano-electronics” has been developed to cover vast application areas including information processing and storage, optoelectronic devices, displays, solar energy transformation, and so on. However, since device features are already pushed down to the nanometer scale, the traditional semiconductor industry faces important technological and fundamental challenges for continuing the miniaturization, such as the increasingly difficult heat dissipation, random dopant fluctuation, and gate leakage. As devices approach nanoscale, many important effects emerge to influence or even determine the functionality of the devices. For example, (i) at the small scale, the quantum confinement effect can become prominent to significantly modulate the material’s electronic and optical properties. As an example, energy spectrum at nanoscale becomes discrete, measured as quanta, while spectra of bulk material are continuous. As a result, the quantized conductance can be observed if the typical length is small enough; (ii) the quantum tunneling effect becomes important at nanoscale, giving rise to the serious gate-leakage problem that affects the reliability of nano-transistor; (iii) at nanoscale, coupling of the device properties to the structural and chemical details becomes important. As a result, randomly distributed defects/dopants can significantly influence the device property, presenting a large variance of device characteristics. The large device-to-device variability presents a great challenge for large-scale device integration. However, due to the lack of effective theoretical method, the effects of disorders on electron transport remain largely unexplored or poorly understood; (iv) as the device becomes smaller and smaller, interfaces and surfaces become more and more important, and can even dominate the device properties. Therefore, for the emergent behaviors of nanoelectronics, the understanding of electron transport on the atomic scale is desirable and important for the science and engineering.