Terahertz generation with ballistic photodiodes under pulsed operation

Abstract

We investigate high field and ballistic carrier transport in a 1.55 μm photomixing device based on pin-diodes by time resolved terahertz (THz) spectroscopy. The device consists of 3 stacked In(Al)GaAs pin diodes (n-i-pn-i-p superlattice) attached to a broadband logarithmic-periodic antenna. Each pin diode is optimized for exhibiting ballistic transport and a reduced transit time roll-off. Ballistic transport signatures could be confirmed directly in these experiments. The data are compared with results from continuous-wave experiments and from simulations both supporting our theoretical expectations. It is demonstrated that n-i-pn-i-p superlattice photomixers are also efficient THz emitters under pulsed operation, showing a maximum THz field strength of ∼0.5 V cm -1 (peak to peak) at 30 mW average optical power.

International System of Units (SI) Traceable Noise-Equivalent Power and Responsivity Characterization of Continuous Wave ErAs:InGaAs Photoconductive Terahertz Detectors

“…For CW, however, non-harmonic and higher harmonic contributions average out, allowing to describe the carrier velocity by an average value. On the other hand, intrinsic samples with few scattering centers can even show a velocity overshoot [18]; but it is generally accepted that a velocity overshoot is not expected for photoconductors due to scattering with trap states and the short carrier lifetime. We therefore expect that the mean velocity of photogenerated electrons on the sub-ps time scale, relevant for THz rectification, is smaller than the average DC velocity v av relevant for DC measurements.…”

Special Issue on Terahertz Devices

“…A first group of papers deals with optical generation and antennas. Müller-Landau et al analyse the THz generation by optimized ballistic In(Al)GaAs n-i-pn-i-p superlattice photomixers attached to a broadband logarithmic-periodic antenna under CW and pulsed operation [20]. Photoconductive antennas (PCAs) are studied by Prajapati et al aiming at the derivation of analytical expressions for the radiative field considering the effect of the substrate with an improved carrier-dynamics model [21], and by Lavrukhin et al who report on an approach for shaping the spectra of THz pulse generation in PCAs by frequency-dependent modulation of antenna impedance [22].…”