Efficient Broadband Terahertz Generation by Above‐Band‐Gap Excitation of the Pyroelectric ZnSnN ₂

Abstract Terahertz (THz) radiation is a powerful probe of low‐energy excitations in all phases of matter. However, it remains a challenge to find materials that efficiently generate THz radiation in a broad range of frequencies following optical excitation. Here, we investigate a pyroelectric material, ZnSnN ₂ , and find that its above‐band‐gap excitation results in the efficient formation of an ultrafast photocurrent generating THz radiation. The resulting THz electric field spans a frequency range from below 1 THz to above 30 THz. The results suggest that the photocurrent is primarily driven by an ultrafast pyroelectric effect where the photo‐excited carriers screen the spontaneous electric polarization of ZnSnN ₂ . Strong structural disorder reduces the photocarrier lifetime significantly and, thus, enables broadband operation. ZnSnN ₂ shows a similar THz‐emitter performance as the best spintronic THz emitters regarding bandwidth and amplitude. The study unveils the large potential of pyroelectric materials as efficient and broadband THz emitters with built‐in bias fields.