ECE Seminar Series

ECE Department

Title: Understanding and Controlling the Impact of Defects on Electronic and Magnetic Phase Transitions in Materials
Speaker: Darshana Wickramaratne
Affiliation: US Naval Research Laboratory
Day: Monday, March 30, 2020
Time: 11:00 am - 12:00 pm
Location: Video Conference

Abstract: Materials discovery and device design requires a thorough knowledge of the structural, optical, and electronic properties of materials and the interaction between them. Point defects in materials are inevitable, and they can strongly impact the performance of devices. They may act as recombination centers, charge traps, and enable or suppress phase transitions in materials. I will discuss the theoretical advances that are enabling us to calculate the properties of defects in materials with unprecedented accuracy and illustrate these points with two case studies. V2O3 is a widely studied transition metal oxide, that hosts a range of phase transitions, including a metal-insulator transition (MIT). One outstanding experimental puzzle is the insensitivity of the MIT in V2O3 to point defects. I will show how the MIT in V2O3 also leads to a concomitant structural and magnetic phase transition, which is crucial to understand the insensitivity of the MIT in V2O3 to defects. These insights impact the search for materials that exhibit a metal-insulator transition, which is being pursued for applications ranging from neuromorphic computing to sensing. Defect-assisted nonradiative recombination can severely affect the efficiency of electronic and optoelectronic devices. The rule of thumb for assessing whether a defect will lead to strong nonradiative recombination has been based on whether the defect level is close to mid-gap. However, I will demonstrate how strong nonradiative recombination can occur for defects that fail to meet this criterion. These insights impact the search for novel materials that are used as platforms for light emitters, photovoltaics and single photon emission for quantum information science.

Bio: Darshana Wickramaratne received his Ph.D from the University of California, Riverside, and then was a postdoctoral associate at the University of California, Santa Barbara. He is now a National Research Council research associate in the Center for Computational Materials Science at the US Naval Research Laboratory. He uses computational techniques based on density functional theory to predict the electronic, optical and magnetic properties of materials, with a focus on applications in optoelectronics, power-electronics and quantum information science.