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The NW photodetector. (a) Device geometry and working principle. Optical micrograph image shows a contacted NW forming the QD photodetector. Inset: circuit schematics. (b) Illuminated (, top line; , middle line; 1.5 eV) and dark noise (bottom line) current-voltage characteristic of the photodetector. (c) Incident photon rate dependence of the photocurrent for excitation with an energy of 2.33 eV (squares) and 1.5 eV (triangles). Gray lines indicate linear intensity dependence (, ). (d) Time resolved PL measurement under pulsed optical excitation for (squares) and 2 V (circles). Data obtained using a streak-camera. Lines represent exponential fits to the decay (excitation focused to a spot size of , photon , , collection energy range of 1.37–1.49 eV, integration time 600 s).
Nonresonantly excited PL and photocurrent (laser spot focused to QD position). (a) PL spectra of the QD as a function of laser excitation intensity. The box indicates PL conditions for (b) whereas the dashed line indicates QD -shell resonance (excitation , , ). (b) Comparison of the integrated PL intensity to the photocurrent as a function of applied source-drain bias (excitation , photon , , integration ). Top, band-structures of the NW photodetector QD indicating radiative recombination and tunneling processes.
The QD photodetector. (a) Contour plot of the photocurrent as a function of laser position under resonant excitation of the QD -shell [see Fig. 2(a), dashed line, for resonance energy]. Contacts and nanowire (dashed lines) correspond to geometry presented in Fig. 1(a) (laser , incident photon , , ). (b) Polarization dependence of the photocurrent under resonant excitation of the QD (laser , photon , , ). Each square represents the average current over . The data fits to , which is represented by the solid line. At the incident light is polarized along the NW axis.
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