Photoreflectance (PR) experiments have been performed from 4.2 K to 300 K to study the temperature dependence of the internal electric fields in MBE grown n-type GaAs with various doping profiles. Franz-Keldysh oscillations (FKO) were observed in the PR spectra from thick (3μm) Si-doped samples at all temperatures. The peak separation of the FKO, and thus the internal electric field, increased with increasing temperature. In thin samples (< 1μm) with an undoped protection cap (< 0.5μm), two sets of FKO were observed. The one with large oscillation period originated from the modulation of the internal electric field in the cap region and the one with small period was due to the modulation of the internal electric field near the thin film/substrate interface. The internal electric fields were deduced from the peak separations of the FKO. The temperature dependence of the internal electric field in the space-charge regions, deduced from the FKO, agreed with the calculated results.
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