THz Sources Based on Er-Doped GaAs Driven at Telecom-Fiber Wavelengths

This dissertation entails the investigation of ultrafast photoconductive (PC) THz sources driven by fiber and semiconductor lasers around λ= 1550-nm to utilize commercial fiber-optic telecom technology. The preferred approach is to use GaAs with a high concentration of erbium, which has performed well when driven with laser sources at both 800 nm wavelength, through intrinsic photoconductivity, and 1550 nm, through extrinsic photoconductivity. Studies in the early 1990s showed that the Er doping level has a solubility limit of ~ 7 × 1017 cm−3 at 580 °C, above which erbium is incorporated into GaAs as ErAs nanoparticles which promote resonant absorption around λ= 1550-nm. This research is focused on improving the GaAs:Er extrinsic-photoconductive device performances by engineering the material and improving the design of THz antennas. Antennas with different dimensions have been fabricated and tested, and substrates with different doping levels and epi-layer thicknesses have been studied and characterized to improve absorption of the 1550 nm radiation, increase the dark resistivity and get more THz radiation. The antennas were then fabricated with a planar-processing technique, packaged, and tested as 1550-nm driven PC THz sources. These are the first THz devices fabricated in the history of Wright State University and have already set a record in terms of power generated by THz photoconductive devices driven at 1550-nm.