Preparation And Characterization Of Cesium Lead Bromide Nanocrystal Vertical-Cavity Surface-Emitting Laser

All-inorganic perovskite nanocrystals（NCs）have excellent optical and electrical properties such as high quantum yield,narrow full width at half maximum,tunable emission wavelength,good stability,high carrier mobility and large defect tolerance.Therefore,inorganic perovskite NCs have received extensive attention in the fields of photoelectric detection,solar cells,light-emitting devices and lasers,especially as optical gain materials.By combining inorganic perovskite NCs with the distributed Bragg reflector（DBR）cavity to fabricate a vertical-cavity surface-emitting laser（VCSEL）,it is very beneficial to achieve a high-performance highly directional single-mode laser,which also lays the foundation for the application of perovskite micro-nano lasers in optoelectronic integrated circuits.Currently,most of the studies based on perovskite NC VCSELs are multi-mode lasers,which have a poor color purity and time stability.In addition,the transient lasing characteristics of perovskite NC VCSELs are rarely studied,and the understanding of their photophysical mechanism is still in its infancy.In this paper,CsPbBr₃ NCs were synthesized by the antisolvent recrystallisation method,and the NC VCSEL was fabricated based on the DBR cavity.The steady-state lasing characteristics and lasing pulse characteristics of the CsPbBr₃ NC VCSEL were investigated by photoluminescence and time-resolved photoluminescence tests,and the carrier dynamics within the NC laser was thoroughly investigated.The main contents are as follows:（1）CsPbBr₃ NCs with a uniform size distribution were synthesized by the antisolvent recrystallisation method.The crystal structure characterized by XRD and TEM showed that the crystal size was about 12 nm and the crystalline phase was tetragonal.The photoluminescence peak was confirmed to be located at 522 nm,corresponding to a band gap of 2.38 eV,which is consistent with the result of the absorption spectrum.The absorption peak was located at about 505 nm.（2）A CsPbBr₃ NC VCSEL was fabricated based on a resonant cavity composed of two DBRs.Under femtosecond optical pumping,a single-mode CsPbBr₃ NC VCSEL with a stable emission wavelength of 527 nm,a lasing threshold of 22μJ/cm2,a quality factor of 1076 and a degree of polarization of 36%was realised.The optical field distribution in the CsPbBr₃ NC VCSEL was simulated.It was found that the active layer had a strong coupling with the optical field,resulting in the low lasing threshold observed in the experiment.（4）The carrier decay dynamics and pulse characteristics of theVCSEL were investigated using the streak camera system.The ultrafast lasing decay time of～10 ps was obtained.The gain-switching phenomenon and linear down chirp of theVCSEL were observed,and an ultrashort pulse of no more than 20 ps was obtained.By calculating the carrier density at the lasing threshold,it is suggested that the lasing is generated by the electron-hole plasma（EHP）mechanism.