Leveraging high fluence and low pressure for pulsed laser deposition of high-mobility $\gamma$-Al$_2$O$_3$/SrTiO$_3$ heterostructure growth

TL;DR

This paper demonstrates a growth protocol for high-mobility $ ext{γ}$-Al$_2$O$_3$/SrTiO$_3$ heterostructures using high laser fluence and low pressure, advancing oxide interface applications.

Contribution

It introduces a novel growth optimization method for high-mobility oxide heterostructures, highlighting the importance of high fluence and low pressure during pulsed laser deposition.

Findings

High mobility achieved with $ ext{μ}^{10K} = 1.6 imes 10^4$ cm$^2$/Vs.

High-fluence ($>3$ J/cm$^2$) and low-pressure ($ ext{~}10^{-6}$ mbar) are key for high mobility.

Epitaxial and crystalline growth signs correlate with high mobility samples.

Abstract

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.