High-mobility oxide heterostructures could be applied for high-frequency devices, transparent conductors, and spin-orbit logic devices. SrTiO$_3$ 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 2-dimensional electron gas (2DEG) of $\gamma$-Al$_2$O$_3$/SrTiO$_3$. The formation mechanism and origin of the high electron mobility are not yet fully understood. This investigation presents a successful growth protocol to synthesise high mobility $\gamma$-Al$_2$O$_3$/SrTiO$_3$ interfaces, and a description of the underlying growth optimisation. Furthermore, indicative features of high-mobility $\gamma$-Al$_2$O$_3$/SrTiO$_3$, including the room-temperature sheet resistance, are presented. Signs of epitaxial and crystalline growth are found in a high-mobility sample ($\mu^{ 10K} = 1.6 \times 10^4 \mathrm{ cm}^2/\mathrm{ Vs}$). Outlining the growth mechanisms and comparing 40 samples, indicates that high-fluence ($F > 3\mathrm{ J}/\mathrm{ cm}^2$) and low pressure ($P \approx 1 \times 10^{ -6} \mathrm{ mbar}$) are essential growth parameters for high-mobility $\gamma$-Al$_2$O$_3$/SrTiO$_3$ interfaces. $\gamma$-Al$_2$O$_3$ having single-element cations allows higher laser fluences during growth, compared to thin films with multi-element cations such as LaAlO$_3$, without causing stoichiometric imbalances.
Categories: cond-mat.mtrl-sci