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Tunable subpicosecond optoelectronic transduction in superlattices of self-assembled ErAs nanoislands


In applications as diverse as fibre-optic communications and time-domain or terahertz spectroscopy, researchers are keen on ultrafast optoelectronic transducers that can be tailored to specific needs. The molecular beam epitaxy of photoconductors composed of equidistant layers of self-assembled ErAs-islands in a III–V semiconductor matrix, which act as efficient non-radiative carrier capture sites, enables this flexibility. Here, photocurrent autocorrelation techniques are applied to metal–semiconductor–metal photodetectors patterned on ErAs:GaAs superlattices. The experiments demonstrate that the electrical response speed can be conveniently tuned over at least two orders of magnitude starting from 190 fs by increasing the thickness of the GaAs spacer separating adjacent ErAs layers. The same concept is applied to the narrower bandgap InGaAs matrix. We demonstrate an electron lifetime of approximately 1 ps for this material. This brings closer the prospect of implementing terahertz technology at the important optical communication wavelengths of 1.3 and 1.55 μm.

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Figure 3: Lifetime of the photoexcited mobile electrons τe as a function of the ErAs:GaAs superlattice period L (right axis, solid symbols).
Figure 4: Current–voltage characteristics of the photoconductive switches when illuminated and in the dark.
Figure 1: Nonlinear behaviour of the photocurrent and optical set-up for temporal carrier density autocorrelation measurements.
Figure 2: Photocurrent autocorrelation measurement on a 60-nm ErAs:GaAs superlattice and the polarization-dependent transmission properties of the metal–semiconductor–metal geometry.
Figure 5: Device structure of and lifetime measurements on 40 nm period ErAs:InGaAs samples.


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The authors thank R. R. Gerhardts for help with the theoretical description of the experiments. They also acknowledge R. A. Wyss for discussions and M.-H. Stapleton for assistance during the experiments. This research has been supported by the German Science Foundation, the Jet Propulsion Laboratory and QUEST.

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Correspondence to Jurgen H. Smet.

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Griebel, M., Smet, J., Driscoll, D. et al. Tunable subpicosecond optoelectronic transduction in superlattices of self-assembled ErAs nanoislands. Nature Mater 2, 122–126 (2003).

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