Stimulated emission mechanisms in perovskite semiconductors

During the last years, the family of semiconductors called perovskites or “perovskite semiconductors” (PS) have emerged as new class of materials with extraordinary perspectives for active photonics. Fabricated under low-cost and straightforward solution process technologies, PSs are usually characterized by an excellent quantum yield emission at room temperature, bandgap tunability with the composition, and slow Auger nonradiative recombination, among other outstanding properties. Their capabilities as an excellent optical gain media have been demonstrated through the near 1000 papers regarding the implementation of lasers or optical amplifiers. Indeed, the generation of Amplified Spontaneous Emission (ASE) has been obtained with many PS morphologies, including polycrystalline thin films, CsPbX3 nanoparticles, 2D nanosheets, and, more recently, with lead-free perovskites. Here, the progress on the synthesis and the design on the photonic devices resulted in the reduction of the ASE threshold down to ∼nJ/cm2 or the demonstration of lasing under continuous wave operation, among other impressive results. This chapter reviews the extraordinary progress carried out by the scientific community in the generation of ASE with PS, the strategies to reduce the thresholds of the stimulated emission, and the physical mechanisms responsible for the generation of optical gain. A rate equation model based on these mechanisms is proposed and applied in a waveguide geometry as an interesting tool to design of active photonic devices based on PS. The chapter is organized as follows. First, Section 2 summarizes the theory of optical gain in semiconductors and Section 3 the state of art of ASE with PS. Section 4 deals about the experimental results of ASE obtained in PS, mainly with polycrystalline thin films and nanocrystals, and how the parameters influencing the stimulated emission can be extracted from these experiments. These parameters are used in Section 5 to reproduce or predict the generation of optical of a given active photonic device containing PS. Finally, Section 5 includes the conclusions and perspectives within this research field.