Low Threshold Vertical Cavity Surface Emitting Lasers Based on CsPbI3 Thin Films.

Metal halide perovskites are attractive gain media for compact coherent light sources. Although the all-inorganic CsPbI3 is a particularly promising representative, low-threshold laser operation remains challenging in CsPbI3 thin films due to phase instability and difficulties in preparing high-quality thin films within low-loss optical resonators. Here, we demonstrate the first vertical-cavity surface-emitting lasers (VCSELs) based on CsPbI3 thin films. The devices are fabricated via planar hot pressing using CsPbI3 thin films prepared through poly(vinylpyrrolidone)-assisted phase stabilization, which enables simultaneous fabrication of smooth gain layers and well-defined vertical cavities consisting of two distributed Bragg reflectors. Variable stripe length measurements on the CsPbI3 thin films are used for optical gain spectroscopy to guide the design of the VCSEL cavity mode by a rigorous coupled-wave analysis. The optimized VCSELs afford optically pumped lasing at 720.4 nm coinciding with the maximum of the optical gain spectrum at a record-low threshold energy density of only 2.8 µJ cm-2. Moreover, the VCSELs provide an outstandingly stable operation even under ambient conditions, which is attributed to the encapsulation inherently provided by the VCSEL structure. These results establish a pathway toward practical, low-threshold perovskite VCSELs and highlight the potential of this platform for next-generation laser devices.