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

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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 (μ10K=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.

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