RUI: Dimensionality Dependence of Semiconductor Ultrafast Optical Response

Williams College, Williamstown MA

Investigators

Abstract

The ability to make well-controlled structures on the nanometer scale represents one of the most important scientific advances of recent decades. Such nanostructures are already in use in a variety of optoelectronic devices, and promise to be of increasing importance as communication speeds increase. The fundamental physics of these structures lies in the quantum confinement of electrons. However, the influence of such confinement on the ultrafast electronic interactions which determine both nonlinear optical response and relaxation rates is unclear. This project will use ultrafast spectroscopy to determine how confinement influences interactions on the femtosecond time scale. It begins with the development of a very pure set of semiconductor heterostructures with varying width. These samples will then be studied via several ultrafast optical techniques to fully characterize the influence of confinement on ultrafast dynamics. This project will take place at Williams College, an entirely undergraduate institution in which young students take active, central roles in research. The research training provided by this project will allow ten undergraduates to become familiar with research, and specifically with cutting edge optical and electronic techniques, at the earliest point in their careers. The drive for increasing speed in communications and computers is pushing technology toward ever smaller semiconductor devices. A fundamental question as these devices are developed is the following: is smaller always faster, or is miniaturization not the best way to increase speed? This project begins to answer the question by exploring the ways in which electron interactions change as semiconductors become extremely small. It will proceed by using an ultra-fast laser to inject energy into nanoscale semiconductor structures, and then to measure how those structures respond. The results will demonstrate the ways size alters the fastest electronic interactions, which take place in less than a trillionth of a second. This work is of both fundamental and technological importance, since these interactions ultimately allow electrons to relax after excitation, and thus set the speed limit for electronic and optical device performance. This project will take place at Williams College, an entirely undergraduate institution in which young students step up to take active, central roles in research. The research training provided by this project will allow ten undergraduates to become familiar with research, and specifically with cutting edge optical and electronic techniques, at the earliest point in their careers.