Two-Dimensional Electron Gases Formed in Strain-Engineered Ferroelectric SrTiO₃ Thin Films

Two-dimensional electron gases (2DEGs) in quantum paraelectric SrTiO₃ (STO) exhibit high electron mobilities at low temperature, superconductivity, and efficient spin-charge interconversion owing to their Rashba spin-orbit coupling. However, such 2DEGs have almost exclusively been generated in STO single crystals, and few attempts to replace crystals by heteroepitaxial STO films have mostly resulted in low mobilities, limiting device integration and functional tuning such as strain-induced ferroelectricity. Here, we use hybrid oxide molecular beam epitaxy to grow high-quality strain-engineered STO films that are ferroelectric up to 165 K. By sputtering thin aluminum layers at room temperature, we generate a 2DEG at their surface. Raman spectroscopy and magnetotransport measurements indicate that the ferroelectric character is retained after 2DEG formation. These results suggest that our samples behave as ferroelectric 2DEGs up to temperatures well above previous results based on Ca-STO substrates (∼30 K), opening the way toward thin-film-based ferroelectric 2DEGs operating at room temperature.