Ultrafast Spectroscopic Noninvasive Probe of Vertical Carrier Transport in Heterostructure Devices

Report No. ARL-TR-7618
Authors: Blair C Connelly; Grace D Metcalfe; Stefan Svensson
Date/Pages: March 2016; 38 pages
Abstract: A major issue limiting the performance of many optoelectronic (OE) devices is poor carrier transport in the vertical direction across heterointerfaces. To address this problem, we have developed unique ultrafast spectroscopic techniques to measure directly vertical carrier transport properties in heterostructure devices over a widely tunable spectral range from the visible through long-wavelength infrared. Our approach merges 2 powerful ultrafast spectroscopy techniques, pump-probe spectroscopy and time-domain terahertz (THz) spectroscopy, into a double-pump-probe THz technique. The time-resolved detection of THz radiation induced by a second pump pulse tuned to the absorption edge of a device layer of interest provides information on nonequilibrium transients of the carrier dynamics and internal electric fields as a function of delay after the injection of carriers from an initial pump pulse. For measurements in infrared materials and devices, time-of-flight techniques using pump-probe spectroscopy and optically gated upconversion were developed. These ultrafast spectroscopy techniques are used to study transport in Army-relevant OE heterostructure devices.
Distribution: Approved for public release
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Last Update / Reviewed: March 1, 2016