A photoconductive antenna (PCA) for terahertz (THz) waves consists of a highly resistive direct semiconductor thin film with two electric contact pads. The film is usually made of III-V compound semiconductors like GaAs. This material is epitaxially grown on a semi-insulating GaAs substrate (SI-GaAs), which is also a highly resistive material.The important difference between the SI-GaAs substrate and the film is the relaxation time for the excited carriers. In a SI-substrate the carrier lifetime is about 20ps, but in the film shorter than 1ps. Many attempts have been made over the past years to enhance PCAs performance using new material systems. Many of these explorations directed toward developing antennas for telecom wavelength excitation (1550 nm). The First realization of these antennas was in 2005 using ion-implanted InGaAs. Later on Be-doped (GaIn)As/(AlIn)As quantum wells on InP substrate were introduced. The main issue with these material systems found to be the reduced carrier mobility due to scattering effects. Currently Commercial antennas operating at 1550 nm wavelength are offered by several companies including TeTechS Inc. Researchers are trying to enhance the properties of these material systems by e.g.separating antennas photoconductive regions from regions with high defect densities. In this scenarios, (GaIn)As wells play the role of photoconductive regions with low defect densities.
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