High photoelectric conversion efficiency and fast relaxation time of FA_(0.4)MA_(0.6)PbI_(3) applied in ultrafast modulation of terahertz waves

Active control of terahertz(THz)waves is attracting tremendous attentions in terahertz communications and active photonic devices.Perovskite,due to its excellent photoelectric conversion performance and simple manufacturing process,has emerged as a promising candidate for optoelectronic applications.However,the exploration of perovskites in optically controlled THz modulators is still limited.In this work,the photoelectric properties and carrier dynamics of FA_(0.4)MA_(0.6)PbI_(3)perovskite films were investigated by optical pumped terahertz probe(OPTP)system.The ultrafast carrier dynamics reveal that FA_(0.4)MA_(0.6)PbI_(3)thin film exhibits rapid switching and relaxation time within picosecond level,suggesting that FA_(0.4)MA_(0.6)PbI_(3)is an ideal candidate for active THz devices with ultrafast response.Furthermore,as a proof of concept,a FA_(0.4)MA_(0.6)PbI_(3)-based metadevice with integrating plasma-induced transparency(PIT)effect was fabricated to achieve ultrafast modulation of THz wave.The experimental results demonstrated that the switching time of FA_(0.4)MA_(0.6)PbI_(3)-based THz modulator is near to 3.5 ps,and the threshold of optical pump is as low as 12.7μJ cm^(-2).The simulation results attribute the mechanism of ultrafast THz modulation to photo-induced free carriers in the FA_(0.4)MA_(0.6)PbI_(3)layer,which progressively shorten the capacitive gap of PIT resonator.This study not only illuminates the potential of FA_(0.4)MA_(0.6)PbI_(3)in THz modulation,but also contributes to the field of ultrafast photonic devices.

Terahertz wave avalanche breakdown transistor for high-performance switching

There is still a lack of high-performance terahertz(THz) modulators with wide operation bandwidth and large modulation depth due to the underlying physics limitation behind existing approaches. Meanwhile, for many applications, simple compact THz modulators working straightforward in the transmission mode are also highly desired. Here, we demonstrate a THz modulator with a maximal transmission-amplitude modulation depth of 99.9%(switching ratio of 1000) based on a commonly used silica-on-silicon structure. Different from those reported graphene or metamaterials enhanced proposals, the device we proposed works within a reversible avalanche breakdown region of silicon that has not been studied yet and has the potential to modulate/switch THz waves efficiently. Further, we proved that the modulation depth exceeds 97% in the frequency range from 0.2 to 1 THz in the experiment. The simplicity and generality of this new type of near-perfect THz modulator will undoubtedly attract lots of attention of researchers in the near future due to its potential to be engineered into integrated devices.

Terahertz wave modulation properties of thermally processed BST/PZT ferroelectric photonic crystals

BST(Ba0.5Sr0.5TiO3)/PZT(Pb0.52Zr0.48TiO3)photonic crystals were fabricated by magnetron sputtering and annealed at 620℃-700℃.By controlling the crystallinity and the oxygen vacancies of the ferroelectric photonic crystals,the optically and electrically controllable terahertz wave modulations were realized.The variation in refractive index of the 680℃ anncaled sample showed the highest modulation to the optical pump and increased to 11.9 due to the highest absorption near 532 nm.In the optical pump,the electrons from Ti^3+2p3/2 ions could be stimulated and captured by Ti^4+2p3/2 ions,and the ratio of Ti^3+/Ti^4+ observed increased with the increasing annealing temperature,indicating the increasing oxygen vacancies concentration,which increased the 532 nm optical absorption and contributed to the improved optical modulation.The excess Pb migrating to the surface at higher annealing temperature might be one reason for the degradation of optical modulation.The increasing polarization and leakage current could contribute to the increasing permittivity and loss with the increasing annealing temperature.Two different results were observed on the sample annealed at 680℃ when the order of applying external optical and electric fields was changed,due to the different migration mechanisms of excited carriers.This work provides a potentially effective approach to fabricate THz sensing,imaging,and communi-cations devices with multi-function in the modulation of optical and electric multi-fields.