Ultrafast Spectroscopic Noninvasive Probe of Vertical Carrier Transport in Heterostructure Devices
Technical Report,01 Oct 2012,01 Sep 2015
US Army Research Laboratory Aberdeen Proving Ground United States
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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.