"Interactions of heat, light and electricity in high-speed semiconductor devices"

Dr. Bjorn Vermeersch, Postdoctoral Research Associate in the Birck Nanotechnology Center at Purdue University

March 29th (Friday), 11:00am
Engineering Science Building (ESB), Rm 2001

The ever continuing miniaturisation of electronic devices has induced thermal gradients inside the semiconductor that stretch over increasingly short distances and change at a faster and faster rate. Classical Fourier diffusion theory is no longer sufficient to describe the thermal transport at such small length and time scales. A good understanding of microscopic energy transport is equally important for ongoing efforts to optimise the efficiency of thermoelectric materials.
Our development of CCD-based transient thermoreflectance imaging has enabled to capture 2-D temperature maps of semiconductor devices with nanosecond temporal and submicron spatial resolutions. Pulsed laser experiments can probe electrothermal transients even further into the picosecond range, providing insight into some more fundamental aspects of energy transport at short length and time scales.

I will first present a brief overview of my research activities in this exciting field. Discussed topics include femtosecond laser thermal conductivity measurements, ballistic heat transport in thin films, and thermoreflectance imaging of submicrosecond Peltier-Joule interactions in high-speed thermoelectric SiGe microcoolers.

The rest of the talk will focus on femtosecond laser characterisation of photoconductive switches. These optoelectronic devices have been widely used as generator of ultrashort electric pulses. For our purposes, they also offer an excellent opportunity to study ultrafast thermal and electric transport inside the switch itself. I will discuss observations of picosecond Joule heating and anomalously fast diffusion inside the signal electrode. From the experiments we can also extract the carrier lifetime of the ErAs:GaAs photoconductive medium, and characterise the propagation and attenuation of the electrical pulses along the coplanar waveguide structure.

About Dr. Bjorn Vermeersch:

Bjorn Vermeersch is a Postdoctoral Research Associate in the Birck Nanotechnology Center at Purdue University under supervision of Prof. Ali Shakouri. He received his M.S. and Ph.D. in Electronic Engineering from Ghent University, Belgium, in 2005 and 2009 respectively. His main research interests lie in theoretical modeling and experimental characterisation of high-speed energy transport in semiconductor devices and materials. Dr. Vermeersch is a three-time winner of the graduate student competition of the IMAPS Workshop on Thermal Management and recipient of the Sidmar Prize for his M.S. thesis. He has published 20 articles in peer reviewed journals and made 30 contributions to international conferences.

Hosted by: Professor John Bowers, Electrical and Computer Engineering