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(a) A tightly focused pump laser pulse injects pairs of electrons and holes in a bulk GaAs sample by interband absorption. (b) After a certain period of time, the injected carriers have diffused away from the excitation spot. The expanded carrier density profile is detected by a tightly focused probe pulse. (c) A schematic of the experimental setup.
Profiles of the differential transmission signal measured with probe delays of 0, 10, 20, and 30 ps, as labeled in each panel. The sample temperature is 10 K.
(a) The differential transmission signal as functions of the probe delay and , measured by scanning the probe spot along the -axis and the probe delay. (b) Cross section of (a) at several probe delays as labeled in the figure. (c) The squared width of the profiles of the differential transmission signal as a function of probe delay obtained by fitting the profiles with Gaussian functions [solid lines in (b)]. The solid line is a linear fit, with a diffusion coefficient of .
The ambipolar diffusion coefficient as a function of the lattice temperature (solid squares) deduced by repeating the measurement shown in Fig. 3 with different temperatures. The open circles show the ambipolar diffusion coefficient calculated from reported mobilities of electrons and holes (see text).
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