Nanopillar Emitters: Photonic Crystals, Heterostructures, and Waveguides
Compound semiconductors, which consist mostly of column III and column V elements, are widely used in opto-electronic devices such as light-emitting diodes, lasers, and solar cells. Thin-film, one-dimensional III-V devices are a mature technology used in industrial and commercial applications. Because of this, there is little left to explore in one-dimensional structures to improve device performance significantly, with advances usually attributed to improvements in fabrication and production volume.
In order to further explore the possibilities of compound semiconductors, research has to led to the development of nanowires and nanopillars. These nanostructures, with diameters ranging from 10 - 100 nm and lengths of several micrometers, are synthesized in a bottom-up approach, rather than being etched with standard nanofabrication techniques. This approach allows researchers to develop unique three-dimensional structures with differing III-V compositions in order to make transformational, rather than incremental improvements in device performance. The ability to control III-V synthesis in three-dimensions has led to numerous demonstrations of opto-electronic devices with broad applications in solid-state lighting, medical sensing, spectroscopy, and telecommunications.
In this dissertation, nanopillar-based emitters, particularly in the near-infrared, are explored. The fundamental motivation behind this work is the ability to directly grow GaAs and InGaAs nanopillars on Si (111) substrates without dislocation defects, making them promising for applications such as low-power lasers for optical interconnects. We begin with an analysis for the needs of a laser design to reach power levels necessary for chip-scale optical interconnects. This sets the direction for research on nanopillar-based emitters. First, the photonics of nanopillar arrays are explored, which led to the demonstration of photonic crystal cavities and photonic crystal lasers. Then, the fabrication of electrically-driven nanopillar emitters is demonstrated and used to develop advanced heterostructures for current injection and carrier confinement. Finally, we show the monolithic waveguide integration of nanopillar devices and effective coupling between a single-mode optical fiber and nanopillar device, paving the way for future development of nanopillar lasers for optical interconnects.