High-index GaAs as a template for lithography-free nanostructures: mechanisms, orientations, and photonic integration pathways

Abstract High-index (H-I) GaAs surfaces enable lithography-free self-assembly of ordered nanostructures by exploiting step anisotropy, surface reconstructions, and directional adatom kinetics. We emphasize representative orientations-(311)A, (553)B, (775)B, and (631)A-where intrinsic anisotropy promotes periodic faceting and nanoscale corrugation. This review synthesizes the mechanisms behind periodic faceting and nanoscale corrugation-elastic relaxation, Marchenko-type period selection, and kinetic instabilities-and compiles qualitative trends reported for how orientation, temperature, and V/III ratio influence morphology, highlighting key open questions. We sum- marize device-relevant phenomena demonstrated to date —most notably polarization-engineered emission and Vertical-Cavity Surface Emitting Lasers (VCSELs) on H–I GaAs—and discuss opportunities where the native anisotropy can facilitate distributed-feedback and Bragg elements, as well as metasurface-like functionalities, with minimal patterning. We also compare integra- tion pathways toward silicon photonics (monolithic heteroepitaxy, thin-film bonding, micro-transfer printing), outlining benefits and limitations set by defects, uniformity, and reliability. We close with an outlook on real-time growth control and data-driven optimization, coupling in situ diagnostics with predictive faceting models to design morphology on demand. By unifying mechanisms, processing considerations, and integration pathways, this review positions H–I GaAs surfaces as a practical, scalable route to bottom-up photonic and quantum architectures.