Generation of terahertz radiation from large aperturep-i-n diodes

This thesis presents the generation of subpicosecond electromagnetic pulses having terahertz bandwidths from large aperture p-i-n diodes under illumination with femtosecond optical pulses. Based on the transport current model, a relationship between the time dependent radiation field and the transient velocity of the photogenerated carriers is derived. By studying the radiation signals from the large aperture Si p-i-n diode under different bias voltages, the field dependence of the risetime of the transient velocity of photogenerated carriers is determined with subpicosecond time resolution. From the radiation field generated by the large aperture GaAs p-i-n diodes, evidence of velocity overshoot of the photogenerated electrons in GaAs is observed. Under high fluences of femtosecond optical excitation, large amplitude teraherts radiation field is generated. The bias field dependence and optical fluence dependence of the radiation field is explained by the field screening in the diodes due to space-charge effects under high carrier density condition. This experimental technique provides not only a new way to generate terahertz radiation but also a method to study the transient dynamics of photogenerated carriers in semiconductors.