Leveraging high fluence and low pressure for pulsed laser deposition of high-mobility γ-Al₂O₃/SrTiO₃ heterostructure growth

High-mobility oxide heterostructures could be applied for high-frequency devices, transparent conductors, and spin-orbit logic devices. SrTiO₃ is one of the most studied oxide substrate materials for heterostructures. To date, the highest SrTiO₃-based charge carrier mobility at 2 K was measured in the interfacial two-dimensional electron gas (2DEG) of γ-Al₂O₃/SrTiO₃. The formation mechanism and the origin of the high electron mobility are not yet fully understood. This investigation presents a successful growth protocol to synthesize high-mobility γ-Al₂O₃/SrTiO₃ interfaces, and a description of the underlying growth optimization. Furthermore, indicative features of high-mobility γ-Al₂O₃/SrTiO₃, including the room-temperature sheet resistance, are presented. Signs of epitaxial and crystalline growth are found in a high-mobility sample ( μ^10K = 1.6 × 10⁴ cm²/V s). Outlining the growth mechanisms and comparing 40 samples, indicates that low pressure ( P ≈ 1 × 10⁻⁶ mbar) is essential for high-mobility γ-Al₂O₃/SrTiO₃ interfaces. γ-Al₂O₃ having single-element cations allows higher laser fluences during growth, compared to thin films with multi-element cations such as LaAlO₃, without causing stoichiometric imbalances.