Ultrafast Photoexcitation and Transient Mobility of GaP for Photoconductive Terahertz Emission

The prospects for photoconductive (PC) terahertz (THz) generation are studied for wide-bandgap semiconductors exhibiting transient mobility. Such semiconductors offer practical benefits (by resisting dielectric breakdown and minimizing Joule heating) as well as improved frequency responses (by accentuating high-frequency PC THz emission). It is shown that GaP can offer these wide-bandgap and transient mobility characteristics. The ultrafast photoexcitation and subsequent transient mobility are investigated for a GaP PC THz emitter with photoexcitation fluences of 18, 36, and 72 μJ/cm². The 100 fs rise and 700 fs fall in the transient photocurrent, due to the respective photoexcitation and transient mobility responses, yields far-field THz emission that improves upon that of the well-established GaAs PC THz emitter. It is ultimately found that semiconductors with both wide-bandgap and transient mobility characteristics can offer strategic improvements for emerging high-power PC THz technologies.