In this paper, the physical mechanisms responsible for optical gain in ${\mathrm{CH}}_3{\mathrm{NH}}_3{\mathrm{Pb}\mathrm{I}}_3$ (MAPI) polycrystalline thin films are investigated experimentally and theoretically. Waveguide structures composed by a MAPI film embedded in between PMMA and silica layers are used as an efficient geometry to confine emitted light in MAPI films and minimize the energy threshold for amplified spontaneous emission (ASE). We show that photogenerated exciton density at the ASE threshold is as low as $(2.4-12)\times {10}^{16}{\mathrm{cm}}^{-3}$, which is below the Mott transition density reported for this material and the threshold transparency condition deduced with the free-carrier model. Such a low threshold indicates that the formation of excitons plays an important role in the generation of optical gain in MAPI films. The rate-equation model including gain is incorporated into a beam-propagation algorithm to describe waveguided spontaneous emission and ASE in MAPI films, while using the optical parameters experimentally determined in this work. This model is a useful tool to design active photonic devices based on MAPI and other metal-halide semiconductors.

中文翻译：

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集成在光波导中的CH3NH3PbI3钙钛矿薄膜中自发和放大自发发射的机理

在本文中，负责光增益的物理机制 ${\mathrm{CH}}_3{\mathrm{NH}}_3{\mathrm{铅含量}\mathrm{一世}}_3$（MAPI）多晶薄膜的实验和理论研究。由嵌入在PMMA和二氧化硅层之间的MAPI膜组成的波导结构被用作有效的几何形状，以将发射的光限制在MAPI膜中，并使放大的自发辐射（ASE）的能量阈值最小。我们显示出在ASE阈值处的光生激子密度低至$（2.4-12）\times {10}^{16}{\mathrm{厘米}}^{-3}$，低于此材料报告的Mott跃迁密度和自由载流子模型推导的阈值透明性条件。如此低的阈值表明，激子的形成在MAPI膜的光学增益的产生中起着重要作用。包含增益的速率方程模型被合并到光束传播算法中，以描述MAPI薄膜中的波导自发辐射和ASE，同时使用这项工作中实验确定的光学参数。该模型是设计基于MAPI和其他金属卤化物半导体的有源光子器件的有用工具。