Abstract
Photoconductive (PC) terahertz (THz) emitters are often limited by ohmic loss and Joule heating—as these effects can lead to thermal runaway and premature device breakdown. To address this, the proposed work introduces PC THz emitters based on textured InP materials. The enhanced surface recombination and decreased charge-carrier lifetimes of the textured InP materials reduce residual photocurrents, following the picosecond THz waveform generation, and this diminishes Joule heating in the emitters. A non-textured InP material is used as a baseline for studies of fine- and coarse-textured InP materials. Ultrafast pump-probe and THz setups are used to measure the charge-carrier lifetimes and THz response/photocurrent consumption of the respective materials and emitters. It is found that similar temporal and spectral characteristics can be achieved with the THz emitters, but the level of photocurrent consumption (yielding Joule heating) is greatly reduced in the textured materials.
Highlights
Photoconductive (PC) terahertz (THz) emitters are often limited by ohmic loss and Joule heating—as these effects can lead to thermal runaway and premature device breakdown
Photoconductive THz emitters are of particular interest as the strength of the emitted THz electric field can be scaled to large levels with increasingly high bias voltage amplitudes and pump optical fluences[20]
The small area of such PC THz emitters dictates that the Joule heating of the PC THz emitters must be minimized, as the threshold voltage for thermal runaway is inversely related to emitter area[22]
Summary
Photoconductive (PC) terahertz (THz) emitters are often limited by ohmic loss and Joule heating—as these effects can lead to thermal runaway and premature device breakdown. Terahertz technologies have provided advancements for applied science applications, such as tomography[10], semiconductor characterization[11,12], security[13], and biomedical applications, including medical imaging[14], diagnostics[15], and DNA analyses[16] These applications have developed over the past years along with THz generation and detection advancements. Photoconductive THz emitters radiate a THz electric field pulse by way of accelerating charge-carriers within the first few picoseconds of photoexcitation These charge-carriers often have lifetimes that are much longer than the THz pulse durations, creating residual photocurrents which lead to unnecessarily large ohmic loss and Joule heating. In response to the above challenges, researchers have investigated large-area PC THz emitters, to scale up the emitted THz electric field by increasing the optically-active area of the PC THz emitter[24] These systems can suffer from considerable Joule heating. The solutions include intricate electrode designs[26,27], patterning of the active area[28], heat sink integration[29], low-temperature substrate growth[22], www.nature.com/scientificreports/
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