Physics

The Pulling Power of Pairs

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Science  08 Jul 2011:
Vol. 333, Issue 6039, pp. 138
DOI: 10.1126/science.333.6039.138-c

The functionality and characteristics of many semiconductor devices depend crucially on the movement of electron-hole pairs in response to an applied electric field. In such ambipolar devices, it is typically the heavier holes that dominate the transport properties. As such, the packets of charged pairs move in the direction of the holes. Some experiments, however, exhibit behavior opposite to that expected motion and have been interpreted in terms of a correlation field, or friction, between the electrons and holes. Yang et al. use a transient grating spectroscopy technique to probe the electron and hole pair packets as they drift and diffuse in a single quantum-well structure. An electron-hole density grating is imprinted in the quantum well by two interfering laser beams. Monitoring the diffraction of a probe beam through the grating as it evolves and decays provides a detailed picture of the electrons' and holes' dynamics. With a model, the authors are then able to determine the degree of friction between them. The technique should provide a route to better understanding the operation of such ambipolar devices and, from the polarization dependence, the operation of spintronic devices based on the spin properties of the carriers.

Phys. Rev. Lett. 106, 247401 (2011).

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