Efficient broadband terahertz generation by above band-gap excitation of the pyroelectric ZnSnN2

TL;DR

This study demonstrates that pyroelectric ZnSnN2, when excited above its band gap, can efficiently generate broadband terahertz radiation spanning from below 1 to above 30 THz, highlighting its potential as a versatile THz emitter.

Contribution

It reveals that above-band-gap excitation of ZnSnN2 induces ultrafast photocurrents via pyroelectric effects, enabling broadband THz generation with performance comparable to spintronic emitters.

Findings

THz electric field spans 1 to 30+ THz

Ultrafast pyroelectric effect drives photocurrent

Structural disorder enhances broadband operation

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, ZnSnN2, and find that 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 to above 30 THz. Our results suggest that the photocurrent is primarily driven by an ultrafast pyroelectric effect where the photo-excited carriers screen the spontaneous electric polarization of ZnSnN2. Strong structural disorder reduces the photocarrier lifetime significantly and, thus, enables broadband operation. ZnSnN2 shows similar THz-emitter performance as the best spintronic THz emitters regarding bandwidth and amplitude. Our study unveils the large potential of pyroelectric materials as efficient and broadband THz emitters with built-in bias fields.