Semiconductor nanowires: towards enhanced terahertz sources
The main objective of this work is achieving efficient electromagnetic radiation in terahertz (THz) frequency region by utilizing semiconductor nanowires due to advantages attributed to their one-dimensional structure, and also studying materials properties by adopting ultrafast THz time-domain spectroscopy (THz-TDS). In order to achieve stronger THz emission from semiconductor nanowires, we suggest a novel approach for preparing the nanowires such that we fabricate the wires from top to bottom by utilizing nanofabrication methods as opposed to growing them with bottom-up approach via conventional growth methods. Most common methods for generation and detection of THz pulses are explained along with the design of THz-TDS technique used in this research. Using THz-TDS measurement results, important materials properties can be extracted through some calculation methods which were addressed in this work. Upon analysis of these extracted properties, a material can be designated as a candidate for optoelectronic devices, photovoltaics, or even generation of THz radiation. Since it is crucial to have excellent-vertically aligned NWs with perfectly uniform distribution for enhanced THz emission, we fabricate InP and InGaAs NWs by top-down nanofabrication process that utilizes electron-beam lithography followed by reactive ion etching. Unbiased THz emission from fabricated InP and InGaAs NWs are compared, and furthermore, an interdigitated electrodes pattern is designed and fabricated along with InGaAs NWs in between the electrodes in order to investigate the enhancement of THz emission from nanowires under a DC bias field. To the best of our knowledge, this is the very first demonstration of THz emission from fabricated NWs under a bias voltage, and significant enhancement is achieved with the increasing bias voltage.