A Comparison of Photoconductive Semiconductors with Long and Short Charge Carrier Lifetimes for Pulsed and CW Terahertz Generation and Detection

Parameters of nonequilibrium charge carriers in a semiconductor are important for the operation of devices for terahertz generation and detection. Generally it is believed that for photoconductive dipole antenna (PDA) a short charge carrier lifetime is required. The development of methods and technologies for the modification of semiconductor materials in order to change the nonequilibrium charge carrier lifetime is important. For this, appropriate technologies for modifying the properties of semiconductors (doping from melt, diffusion doping, ion implantation and irradiation, temperature treatments) can be used [1,2]. In the present study PDAs on SI-GaAs:Cr and LT-GaAs were fabricated and studied. The created devices were tested as pulsed terahertz sources and detectors under excitation by femtosecond laser pulses. Also the PDAs were tested as terahertz photomixers at excitation by laser diodes. It is important to note that charge carrier lifetime in LT-GaAs can be as low as 100-500 fs, while in SI-GaAs:Cr it can be of the order of 1-20 ns in the bulk. To modify properties of GaAs:Cr, the surfaces of the wafers were chemically and mechanically treated. The geometrical configurations of the PDAs tested are presented in Fig. 1.