Characterisation of InAs:GaAs quantum dot-based photoconductive THz antennas

The THz optoelectronics field is now beginning to mature and semiconductor-based THz signal emitter/detector devices are becoming more widely implemented as analytical tools in spectroscopy and imaging¹. The predominant area of development in this field has always been the photoconductive (PC) active material which forms the basis of the necessary ultrafast switching process. These materials traditionally are optically pumped using, for example, a Ti:Sapphire laser which can generate ultrashort pulses with photonic energy higher than the active material bandgap. This allows the generation of (photo)carrier pairs which are accelerated by the E-field of an integrated antenna electrode pair and then captured over ultrashort timescales (τ_c < 1ps) usually by defects and trapping sites throughout the active material lattice. As a defective material (such as low-temperature-grown GaAs, 'LT-GaAs') is typically used, many parameters such as carrier mobility and PC gain are greatly compromised. It has been shown previously that quantum dots (QDs) deposited within or over GaAs can enable and/or enhance the efficiency of THz signal generation². We demonstrate here the efficient generation of THz output signals using PC THz antennas based on semiconductor structures comprised of InAs quantum dots (QDs) embedded in high quality crystalline GaAs, whereby the embedded QDs act as the ultrafast capture mechanism³.