Observation of THz Oscillations and Efficient THz Emission from Contacted Low Temperature Grown GaAs Structures.

摘要

We have performed femtosecond differential transmission experiments in low temperature grown GaAs (LT-GaAs) layers under high electric fields. The fields were induced by voltages up to 60 V applied to interdigitated contacts with a few micrometer period. Up to about 10 oscillations of the field-induced transmission changes with a period of T = 2.2 Ps were detected in a structure where the high-frequency effective length of the contacts was kept short. The large amplitude of the AC component of the differential transmission signal indicated that the amplitude of the light pulse induced oscillating electric field has to be of the same order of magnitude as the applied DC field. Thus the same has to be true also for the AC voltage between the fingers. In order to test this interpretation we have performed photomixing experiments. They yield a maximum emitted rf power of about 60 nW at a beat frequency of V = 1/T = 0.44 THz, at only 10 mW of incident optical laser power. Computer simulations yield the same frequency for the contact structure considered as a microstrip patch antenna.