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THz Radiation Source Trough Periodically Modulated Structures

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Interim rept. no. 9, Dec 97-Feb 98

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We have shown that the quenching of the miniband states is independent of the direction of the applied bias for a 5 period super lattice. Experiments on a 10 period super lattice show that the transmission becomes asymmetric enhanced for positive bias a and reduced for negative bias. This effect becomes more and more pronounced with increasing length of the SL. From a comparison of the calculated transfer ratio under the presence of interface roughness scattering we are able to estimate the typical island sizes to be of the order of 10 nm. Bow tie structures are developed and optimized for the purpose of a broad band antenna in the range of THz frequencies. The optimized antennas are presently combined with small mesa structures for emission measurements. At present we have difficulties to couple the large antennas to the small 2 microns x 2 microns mesas. A population inversion in non-equilibrium plasmas can be achieved by driving a constant current through the plasma. Based on these ideas we have grown a set of structures where the plasma instability may be realized. The basic concept requires the realization of a large population inversion. The IV curves of the grown structures agree with the calculated IV curves. However from the IV curves it is not directly evident that a plasma instability is present. Therefore emission measurements, using a grid structure for coupling out of the light are under way to prove the existence of these instabilities which are expected to lead to strong THz emission.

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  • Solid State Physics

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