Bifunctional Design of Ferroelectric‐Order and Band‐Engineering in Cu:KTN Crystal for Extended Self‐Powered Photoelectric Response

Abstract

Photoelectric conversion in ferroelectric crystals can support many important applications in modern on‐chip technology, but suffering from two problems, low responsive current and narrow responsive range. Especially, wide‐gap ferroelectric oxides are only active at short‐wavelength ultraviolet region with weak photocurrent at nanoampere levels. Here, a bifunctional design strategy of ferroelectric‐order and electronic‐band to improve the photocurrent and extend the responsive range simultaneously, is proposed. In a Cu‐doped KTa1−xNbxO3 (KTN) perovskite crystal, a conductive channel is constructed by “head‐to‐head” ferroelectric domains, associated with the emergence of micrometer‐scale supercells. In addition, the introduction of Cu+ ion can induce defect levels, thus extending the responsive range beyond the inherent absorption of pure KTN. Through rational device optimization, a record self‐powered responsivity of 5.23 mA W−1 is realized in Cu:KTN photodetector, which is two orders of magnitude higher than undoped KTN crystal. The temperature‐dependent light diffraction and photocurrent show that the ferroelectric‐order is dominated in this photoresponse behavior. Moreover, Cu:KTN detector is active in the broadband range from 390 to 1030 nm, covering ultraviolet, visible, and near‐infrared regions. This work provides an effective method for the design of next‐generation self‐powered photodetectors with ultrahigh responsivity and ultrawide responsive range.