Ultra-thin III–V semiconductors, which exhibit intriguing characteristics, such as two-dimensional (2D) electron gas, enhanced electron–hole interaction strength, and strongly polarized light emission, have always been anticipated in future electronics. However, their inherent strong covalent bonding in three dimensions hinders the layer-by-layer exfoliation, and even worse, impedes the 2D anisotropic growth. The synthesis of desirable ultra-thin III–V semiconductors is hence still in its infancy. Here we report the growth of a majority of ultra-thin III–V single crystals, ranging from ultra-narrow to wide bandgap semiconductors, through enhancing the interfacial interaction between the III–V crystals and the growth substrates to proceed the 2D layer-by-layer growth mode. The resultant ultra-thin single crystals exhibit fascinating properties of phonon frequency variation, bandgap shift, and giant second harmonic generation. Our strategy can provide an inspiration for synthesizing unexpected ultra-thin non-layered systems and also drive exploration of III–V semiconductor-based electronics.

Two-dimensional (2D) rare-earth oxides (REO) are a large family of materials with various intriguing applications and the precise facet control is essential for investigating new properties in the 2D limit. However, a bottleneck remains for obtaining their 2D single crystals with specific facets because of the intrinsic non-layered structure and disparate thermodynamic stability of different facets. Herein, for the first time, we achieved the synthesis of a wide variety of high-quality 2D REO single crystals with tailorable facets via designing a hard-soft-acid-base (HSAB) couple for controlling the 2D nucleation of the predetermined facets and adjusting the growth mode and direction of crystals. Also, the facet-related magnetic properties of 2D REO single crystals were revealed. Our approach provides a foundation for further exploring other facet-dependent properties and various applications of 2D REO and an inspiration for the precise growth of other non-layered 2D materials as well.

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