Temporal response of the optically generated electric field in InAs/GaAs coupled quantum dots
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1208-O05-02
Temporal response of the optically generated electric field in InAs/GaAs coupled quantum dots Kushal C. Wijesundara,1 Mauricio Garrido,1 Swati Ramanathan,1 E. A. Stinaff,1 A. S. Bracker,2 and D. Gammon2 1 Department of Physics and Astronomy, and Nanoscale and Quantum Phenomena Institute, Ohio University, Athens, OH 45701-2979, USA. 2 Naval Research Laboratory, Washington, DC 20375, USA. ABSTRACT Coupled quantum dots (CQDs) can provide a sensitive probe of the electric field within a device. With non-resonant excitation above the wetting layer (WL) energy, optical generation of an electric field within the CQD structure was observed. By alternating this non-resonant excitation the temporal response of the optically generated electric field was measured. Decay of this field was measured to be on the order of 110-140 µsec. The onset of the optically generated electric field was observed to be less than the temporal resolution of our experiment (7.4 µsec). This may provide a means for fast, non-contact, electric field modulation techniques. INTRODUCTION For many experiments involving quantum dot devices, such as differential transmission, the electric field needs to be modulated which can require specialized equipment and complicated sample preparation.1,2,3 A possibly simpler solution may be to modulate the applied electric field by means of an optically created electric field. Through the use of CW laser excitation we have shown that it is possible to shift the electric field at which the interactions between energy levels take place. In this paper we further the measurement of such an optically generated field with time-resolved measurements to characterize the dynamics. With laser excitation above the WL energy, we optically generate an electric field within a device containing CQDs and observe the field strength through a shift in the CQD photoluminescence spectra. The indirect recombination from the CQD was used as a sensitive probe to quantify and monitor the strength of the optically generated field in the device. The excitation above the WL energy was seen to generate a shift of a few tenths of a Volt in the bias map of the electric field dependent photoluminescence spectra of CQDs as opposed to excitation below the WL energy where only a negligible shift was observed.4 By modulating the above WL excitation, oscillation of the optically generated electric field can be created. By monitoring the photoluminescence energy of the indirect excitonic emission at different time delays from the creation to the extinction of the optically generated electric field we were able to determine the decay rate of the optically generated electric field within the device. EXPERIMENT For the present study self-assembled InAs/GaAs CQDs were created using the spontaneous island formation in Stranski-Krastanov growth mode as described in the literature.5 CQDs were embedded in a Schottky diode structure, which allows for control of the total charge and relative energy levels of the two dots. The diode structure was grown
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