Microscopic origins of decoherence in Er³⁺:TiO₂/III–V semiconductor hybrid structures

Rare-earth ions in oxides exhibit coherent optical transitions, thus being of growing interest for hybrid platforms based on III-V semiconductors. Realizing such hybrid systems requires interfacing the oxides with III-V semiconductors to enable efficient optical coupling and device functionality. However, the heterointerface between the oxide and the semiconductor introduces strain, noise, and structural disorder that limit the optical coherence. Here, we investigate the microscopic origins of decoherence in Er³⁺ ions incorporated into epitaxial TiO₂ films grown on GaAs and GaSb (III-V) substrates. Using photoluminescence excitation spectroscopy combined with ab initio crystal-field calculations and noise modeling, we analyze the contributions of strain, noise, and interfacial disorder to transition energies and linewidths for both bulk-doped and pseudo-δ-doped configurations. The results reveal distinct coherence-limiting mechanisms across spatial regimes that depend on dopant proximity to the interface and are further influenced by thermal processing conditions. This work provides quantitative insight into interfacial noise in oxide/III-V hybrids and establishes design principles for scalable, coherent rare-earth–based quantum platforms.