Perovskite micro-nano lasers and on-chip integration

With the rapid development of photonic technologies and micro-nano fabrication technologies, optoelectronic devices tend to be miniaturized and integrated. Photonic integrated circuits (PICs) can adress the bottleneck problems of electronic chips, such as high-power consumption and slow computing speed. Micro-nano lasers are an important part in PICs, and they are the key device to generate optical signals. Perovskites are direct band gap semiconductor materials with high exciton binding energy and low defect densities. Therefore, they have high photoluminescence quantum yield and can be used as gain materials for micro-nano lasers. In addition, perovskite materials also have advantages of low non-radiation recombination rate, low manufacturing cost, tunable bandgap width, solution treatment, and so on. Because of these advantages, perovskite materials have been widely used in micro-nano lasers and other fields. At present, researchers have developed a variety of micro-nano fabrication methods to fabricate perovskite micro-nano structures. A variety of perovskite micro-nano lasers have been obtained by using perovskite micro-nano structures under the pump of pulses or continuous lasers. In PICs, it is necessary to use optical waveguides to couple laser sources to other photonic devices to form a complete photonic circuit. This paper first summarizes the synthesis methods of perovskite materials, including spin coating methods, cooling crystallization methods, inversion crystallization methods, antisolvent crystallization methods, space limited methods, and gas phase epitaxial growth methods. Among these synthesis methods, spin coating methods are simple, but only polycrystalline perovskite materials can be prepared. Single crystal perovskites can be prepared by cooling crystallization methods, inversion crystallization methods, antisolvent crystallization methods, space limited methods, and gas phase epitaxial growth methods. Next, fabrication methods of perovskite micro-nano structures are introduced, including space limited synthetic growth methods, nano imprinting methods, focused ion beam etching methods, and electron beam exposure methods. Space limited synthetic growth methods and nano imprinting methods have no damage to perovskite materials. Electron beam exposure methods have small damage to perovskite materials, and focused ion beam etching methods cause great damage to perovskite materials. Then, perovskite micro-nano lasers, including out-plane emission lasers and in-plane emission lasers, are introduced. Out-plane emission lasers emit the laser towards the free space, and they are not favorite for on-chip integration. In-plane emission lasers emit the laser towards the in-plane space, and they are easy to be integrated with the waveguide. In addition, the combination of perovskites and metal structures is expected to reduce the size of the laser to subwavelength scales based on plasmonic effects. We also introduce the on-chip integration of perovskite micro-nano lasers, including tip manipulation methods, overlay alignment methods, and transfer printing methods. Tip manipulation and overlay alignment methods can damage perovskite materials. Transfer printing methods do not cause damage to perovskite materials. Finally, the development trends of perovskite materials and micro-nano lasers are discussed. Although perovskite micro-nano lasers have made great progress, there are still some problems to be addressed. For example, lead in perovskite materials is toxic, so it is necessary to develop lead-free perovskite materials. Perovskite materials have poor stability, and their stability should be improved. Moreover, the realization of electrically pumped micro-nano lasers and on-chip integration is also a great challenge.