“Epitaxial Large-gap topological insulator on semiconductor for seamless device integration” by Prof. Feng LIU | Thursday, November 6, 2025, 3:30pm Room 522, 5/F, Chong Yuet Ming Physics Building, HKU

Significant advances have been made in fundamental research of topological insulators (TIs), yet their device applications remain elusive. We propose an approach towards seamless integration of two-dimensional (2D) TIs into semiconductor devices. Using first-principles calculations, we show that heteroepitaxially grown III-V semiconductor ultrathin films can self-convert into 2D TIs. Remarkably, on GaSb(111) monolayer GaAs1-xBix becomes universally a 2D TI at any alloy concentration, x, enabled by natural formation of semiconductor heterojunctions. For the GaAs-rich monolayer, having type-II (III) band alignment with GaSb, an intriguing interfacial band offset inversion emerges between surface Ga-s and substrate Sb-p bands; for the GaBi-rich monolayer, with type-I (I’) alignment, the conventional intra-surface band gap inversion arises between Ga-s and Bi-p bands. The lattice-matching epitaxy of GaAs0.25Bi0.75 alloy enables growth of thin-film 2D TIs with a gap up to ~330 meV. Our findings pave the way to engineering wafer-scale large-gap 2D TIs to potentially operate at room temperature.