While solution-processed methods have driven much of the progress in halide perovskite research, their integration with silicon-based semiconductor platforms remains challenging due to issues of compatibility and process scalability. In contrast, vapor-phase growth offers a scalable, solvent-free approach that is inherently more compatible with semiconductor industry standards, while also providing precise control over interfacial structure, strain, and crystallographic orientation. In vapor-grown systems, the interface between the perovskite and the substrate is critical in determining phase formation, growth direction, and optical properties. In this work, we demonstrate that by carefully tuning vapor-phase growth parameters, we can control the geometry and orientation of CsPbBr₃ microwires, including the formation of angled out-of-plane wires.

By tuning substrate and growth conditions, we obtain two distinct microwire geometries: in-plane wires, which grow flat and aligned with the substrate, and out-of-plane wires, which emerge at a fixed angle relative to the surface. The in-plane wires exhibit well-faceted, rectangular prism morphologies, while the out-of-plane wires consistently grow at an angle of 57° ± 3°, as determined by angle-resolved cathodoluminescence. This angle corresponds to growth along the [100] direction with the {111} CsPbBr₃ facet at the substrate interface. Additionally, we report room-temperature lasing from the wires under nanosecond pulsed excitation. These wires show high emission efficiency and intense linear polarization, approaching 100% degree of polarization.

Additionally, we analyze and explore the role of competing Cs₄PbBr₆ phases, which act as nucleation seeds for CsPbBr₃ growth. We spatially resolve emission and lifetime properties across the interfaces using cathodoluminescence microscopy, revealing how the seed influences the emission characteristics. Our results resonate and support previous observations of similar heterostructures that were grown under very different growing conditions, indicating the generality of the observed effect and robustness of the measurement technique. 

 Together, these results offer new insights into the microscopic origins of light emission in halide perovskites and establish design rules for tailoring optical behavior through growth-controlled morphology and interface engineering.