Atomic-scale investigation of $γ$-Ga$_2$O$_3$ deposited on MgAl$_2$O$_4$ and its relationship with $β$-Ga$_2$O$_3$

J. Tang; K. Jiang; C. Xu; M. J. Cabral; K. Xiao; L. M. Porter; R. F. Davis

paper

Atomic-scale investigation of $γ$ -Ga $_{2}$ O $_{3}$ deposited on MgAl $_{2}$ O $_{4}$ and its relationship with $β$ -Ga $_{2}$ O $_{3}$

arXiv:2310.12493

Abstract

Nominally phase-pure $γ$ - $G a_{2} O_{3}$ was deposited on (100) $M g A l_{2} O_{4}$ within a narrow temperature window centered at $\sim$ 470 $^{\circ}$ C using metal-organic chemical vapor deposition (MOCVD). The film deposited at 440 $^{\circ}$ C exhibited either poor crystallization or an amorphous structure; the film grown at 500 $^{\circ}$ C contained both $β$ - $G a_{2} O_{3}$ and $γ$ - $G a_{2} O_{3}$ . A nominally phase-pure $β$ - $G a_{2} O_{3}$ film was obtained at 530 $^{\circ}$ C. Atomic-resolution scanning transmission electron microscopy (STEM) investigations of the $γ$ - $G a_{2} O_{3}$ film grown at 470 $^{\circ}$ C revealed a high density of antiphase boundaries. A planar defect model developed for $γ$ - $A l_{2} O_{3}$ was extended to explain the stacking sequences of the Ga sublattice observed in the STEM images of $γ$ - $G a_{2} O_{3}$ . The presence of the 180 $^{\circ}$ rotational domains and 90 $^{\circ}$ rotational domains of $β$ - $G a_{2} O_{3}$ inclusions within the $γ$ - $G a_{2} O_{3}$ matrix is discussed within the context of a comprehensive investigation of the epitaxial relationship between those two phases in the as-grown film at 470 $^{\circ}$ C and the same film annealed at 600 $^{\circ}$ C. The results led to the hypotheses that (i) incorporation of certain dopants including Si, Ge, Sn, Mg, Al, and Sc, into $β$ - $G a_{2} O_{3}$ , locally stabilizes the " $γ$ -phase" and (ii) the site preference(s) for these dopants promotes the formation of the " $γ$ -phase" and/or $γ$ - $G a_{2} O_{3}$ solid solutions. However, in the absence of such dopants, pure $γ$ - $G a_{2} O_{3}$ remains the least stable $G a_{2} O_{3}$ polymorph, as indicated by its very narrow growth window, lower growth temperatures relative to other $G a_{2} O_{3}$ polymorphs, and the largest calculated difference in Helmholtz free energy per formula unit between $γ$ - $G a_{2} O_{3}$ and $β$ - $G a_{2} O_{3}$ than all other polymorphs.

The following article has been submitted to APL Materials

Atomic-scale investigation of γ-Ga2​O3​ deposited on MgAl2​O4​ and its relationship with β-Ga2​O3​

Abstract

Atomic-scale investigation of $γ$ -Ga $_{2}$ O $_{3}$ deposited on MgAl $_{2}$ O $_{4}$ and its relationship with $β$ -Ga $_{2}$ O $_{3}$