Charged Domain Walls Enhanced Photoelectric Response of KTN Crystals under UV Irradiation

Ultraviolet (UV) illumination has been applied in KTN electro-optic device development to enhance performance, revealing the material’s potential for UV photoelectric response. Here we systematically investigate the photocurrent behavior of KTN crystals under UV illumination, with a particular focus on the role of charged domain walls (CDWs) in the ferroelectric phase. Temperature-dependent photocurrent profiling reveals a peak response in the ferroelectric phase, approximately 20 °C below the Curie point ( T C ), with a magnitude nearly an order higher than that in the paraelectric phase. The enhanced photocurrent is attributed to head-to-head (H–H) and tail-to-tail (T–T) CDWs, as confirmed by microscopic characterizations. These CDWs generate internal electric fields that separate photogenerated carriers and induce local band bending, facilitating the formation of high-mobility conduction channels along domain walls. A drift–diffusion model incorporating the effects of CDWs explains the temperature-dependent photocurrent across the phase transition. Transient photocurrent response shows that CDWs sustain photocurrent growth in the ferroelectric phase, while the response decays in the paraelectric phase. These findings highlight the critical role of CDWs in modulating carrier dynamics and improving UV photoelectric performance in ferroelectric materials.