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.