ISSN:
1089-7550
Source:
AIP Digital Archive
Topics:
Physics
Notes:
A photoinduced "transient thermoelectric effect" (TTE) has been measured for a p-GaAs crystal using a tunable pulsed laser, over the laser energy range 0.93–1.80 eV, laser intensity 0.2–130 mJ/cm2, time range 1 ns–1 ms, and temperature range 4.2–50 K, with special attention to native defects of EL2 centers, whose ground state (EL20) and excited state (EL2ex) are located, respectively, at 0.76 and 1.80 eV above the top of the valence band (their energy difference σex=1.04 eV). After laser irradiation at one end of the sample, a TTE voltage is induced within a rising time τr (1.0–1.5 μs) due to hole diffusion, followed by exponential decay with multiple decay times τ1–τ5 that depend on the laser energy, its intensity, and the temperature. The decay time τ1 is assigned to relate to photoexcited electron diffusion in the conduction band and others τ2–τ5 with electron recombinations with photogenerated holes in the valence band via EL2 centers in p-GaAs, for which a rough evaluation of the capture cross section is made. Based on the experimental data, we have discussed the photoinduced carrier generation/recombination processes in three laser energy ranges with the two boundaries σex and the band-gap energy Eg (=1.50 eV); regions I (E〈σex), II (σex≤E〈Eg), and III (E≥Eg). For these three energy regions, we have carried out computer simulations for the photoinduced TTE voltage profiles by solving one-dimensional transport equations for photogenerated electrons and holes, in qualitative agreement with the observations. © 1997 American Institute of Physics.
Type of Medium:
Electronic Resource
URL:
http://dx.doi.org/10.1063/1.365192
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