Optical and dielectric properties of self-assembled germanium nanostructures and applications

Abstract

With recent advancement in the semiconductor technology, various electronic gadgets have been designed and produced to keep up with the strong demand from end customers. Compared with the electronic products of twenty years ago, the electronic gadgets are now smaller, faster and have more functionalities as the semiconductor wafer technology now reaches the nanoscale. However, as the current transistor technology node will continue to scale down, various breakdown problems will be encountered.

Alternative methods to solving the issues such as transistor breakdown in electronic devices are to integrate photonics technology with the current electronic technology and implement semiconductor nanostructures in both optical and electronic devices. With challenges on the understanding of new physics behind, nanostructures demonstrate many intriguing properties that cannot be seen from the otherwise bulk counterpart. Coupled with the advanced fabrication technology and microscopy technology, the nanostructures can be easily synthesized and characterized to understand its physics for future device applications.

To our best knowledge, Si has always been the preferred choice, because Si has less leakage current, higher threshold voltage, and is less temperature dependent compared with Ge. However, in the research point of view for photonics, Si simply loses out to Ge, as Ge has larger dielectric constant, smaller band gap, and smaller electron and hole effective masses compared with bulk Si. The size effect of Ge nanostructures is more obvious than that of Si nanostructures, so the change in the properties of Ge nanostructures is more pronounced and tunable. Thus, because of the intriguing properties and exciting potential applications in microelectronics and photonic devices, this thesis focuses on the optical and dielectric properties of Ge nanostructures (i.e. thin film and nanocrystals).