Laser terahertz emission microscopy revealing the local fluctuation of terahertz generation induced by Te inclusion

As a state-of-the-art electro-optical crystal, zinc telluride (ZnTe) is widely used in terahertz (THz) emission by optical rectification. However, the efficiency of THz generation in ZnTe is usually degraded by factors such as harmonic generation, two-photon absorption, and free-carrier absorption. In this work, we first report the effect of micro-scale Te inclusions in ZnTe on the local area THz emission. Unusual THz time-domain waveforms emitted from Te inclusions are observed to last longer than 400 ps, which is attributed to the photocurrent surge (PS) effect. This Te inclusion-associated THz radiation is proved consistent with the incident power and polarization angle dependences. Simultaneously, the Te inclusions embedded in the ZnTe matrix are visualized by laser THz emission microscopy (LTEM). According to the LTEM images, the driving force of the carrier movement is revealed, which is ascribed to the heterojunction field composed of Te and p-ZnTe. Our results not only afford a comprehensive understanding of the THz characteristics of Te inclusions but also put forward LTEM as a promising non-contact evaluation method for evaluating the bulk defects in semiconductors.