Collaborative Research: Urbach-Tail Dynamics and Implications for Photonic Devices

University Of New Mexico, Albuquerque NM

Investigators

Abstract

Technical Description: Scientists in the University of New Mexico (UNM) and the Johns Hopkins University (JHU) are engaged in a multi-investigator research project to study the physics of energy states located at and below the optical band-gap energy of semiconductors. While the presence of these states has been known since the earliest days of semiconductors, there has been an ongoing disconnect between experimental and theoretical research. This project aims to close that gap. The band-tail states, also called Urbach tail, are studied by measuring and modeling the dynamics of absorption, luminescence, and heat transfer to the lattice using established and new methods of time-resolved optical and terahertz spectroscopy. The temporal response of the band-tail states holds a wealth of interesting and important physics. The project sheds new light on energy band-tail states in semiconductors by studying their temporal response to optical perturbation. New and improved methods of time-resolved spectroscopy leading to extremely high sensitivity are being developed at UNM. JHU is producing a new theory of band-tail state dynamics that is crucial to the interpretation of the experiments. This theory is sufficiently general to accommodate states that are extended, local, or a mixture. Non-technical Description: The research project aims at gaining a fundamental understanding of light absorption by semiconductors at the long-wavelength absorption tail and the subsequent photoluminescence (emission) from these materials. A success of the project can have implications for future development of optoelectronic devices and semiconductor laser refrigeration. The project also serves as a vehicle to educate and train graduate students who are in the early stages of their careers. It is particularly valuable because of its multidisciplinary nature in the broad fields of physics, materials science, and optics. An important educational component is an exchange program between UNM and the Southwestern Indian Polytechnic Institute, co-located in Albuquerque. Supported UNM students are responsible for setting up optics labs and mentoring at both facilities.