Kavli Affiliate: Debdeep Jena
| First 5 Authors: Martin S. Williams, Manuel Alonso-Orts, Marco Schowalter, Alexander Karg, Sushma Raghuvansy
| Summary:
The growth of $alpha$-Ga$_2$O$_3$ and $alpha$-(In$_x$Ga$_{1-x}$)$_2$O$_3$
on $m$-plane $alpha$-Al$_2$O$_3$(10$bar{1}$0) by molecular beam epitaxy (MBE)
and metal-oxide-catalyzed epitaxy (MOCATAXY) is investigated. By systematically
exploring the parameter space accessed by MBE and MOCATAXY, phase-pure
$alpha$-Ga$_2$O$_3$(10$bar{1}$0) and
$alpha$-(In$_x$Ga$_{1-x}$)$_2$O$_3$(10$bar{1}$0) thin films are realized. The
presence of In on the $alpha$-Ga$_2$O$_3$ growth surface remarkably expands
its growth window far into the metal-rich flux regime and to higher growth
temperatures. With increasing O-to-Ga flux ratio ($R_{text{O}}$), In
incorporates into $alpha$-(In$_x$Ga$_{1-x}$)$_2$O$_3$ up to $x leq 0.08$.
Upon a critical thickness, $beta$-(In$_x$Ga$_{1-x}$)$_2$O$_3$ nucleates and
subsequently heteroepitaxially grows on top of
$alpha$-(In$_x$Ga$_{1-x}$)$_2$O$_3$ facets. Metal-rich MOCATAXY growth
conditions, where $alpha$-Ga$_2$O$_3$ would not conventionally stabilize, lead
to single-crystalline $alpha$-Ga$_2$O$_3$ with negligible In incorporation and
improved surface morphology. Higher $T_{text{G}}$ further results in
single-crystalline $alpha$-Ga$_2$O$_3$ with well-defined terraces and step
edges at their surfaces. For $R_{text{O}} leq 0.53$, In acts as a surfactant
on the $alpha$-Ga$_2$O$_3$ growth surface by favoring step edges, while for
$R_{text{O}} geq 0.8$, In incorporates and leads to a-plane
$alpha$-(In$_x$Ga$_{1-x}$)$_2$O$_3$ faceting and the subsequent ($bar{2}$01)
$beta$-(In$_x$Ga$_{1-x}$)$_2$O$_3$ growth on top. Thin film analysis by STEM
reveals highly crystalline $alpha$-Ga$_2$O$_3$ layers and interfaces. We
provide a phase diagram to guide the MBE and MOCATAXY growth of
single-crystalline $alpha$-Ga$_2$O$_3$ on $alpha$-Al$_2$O$_3$(10$bar{1}$0).
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