Kinetically controlled structural evolution in vapor-phase synthesis of two-dimensional GaSe microflakes

Two-dimensional (2D) GaSe is a promising candidate for nonlinear photonic applications due to its strong second-order optical response. However, precise control over its morphology and stacking order during synthesis remains a significant challenge. Herein, we report a vapor-phase growth strategy that enables the controlled synthesis of 2D GaSe with tunable crystal shapes and stacking configurations by adjusting precursor flux and temperature gradients. The growth mechanism is elucidated through a combined experimental and theoretical approach, involving density functional theory and kinetic Wulff construction analysis. We demonstrate that the competition between diffusion-limited and attachment-limited growth regimes governs the edge propagation rates, leading to the formation of triangular and nonconventional morphologies. Furthermore, we reveal that distinct stacking orders result in pronounced variations in SHG intensity and polarization dependence. These findings highlight the crucial role of stacking order in modulating the nonlinear optical properties of 2D GaSe and offer a rational pathway toward the design of layered semiconductors with tailored optical functionalities.