Extrinsic photoconductivity in an ErAs:GaAs photoconductive (PC) switch is studied as a function of wavelength from 1535 nm to 1793 nm and 2516 nm to 3293 nm; which corresponds to photon energies of 0.69 to 0.81 eV (0.48 to 0.57 UG) and 0.37 to 0.49 eV (0.26 to 0.35 UG). A gradual decline is seen in photoconductive response vs wavelength in the higher energy range, and practically no response in the lower energy range. Also, a series of local peaks is seen in the higher range, suggesting that the absorption is associated with quantum-dot-to-band electron transitions. This is an important step in understanding the new method of creating THz sources from ultrafast extrinsic photoconductivity.
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