$γ$-phase Inclusions as Common Defects in Alloyed $β$-(Al$_x$Ga$_{1\text{-}x}$)$_2$O$_3$ and Doped $β$-Ga$_2$O$_3$ Films

Celesta S. Chang; Nicholas Tanen; Vladimir Protasenko; Thaddeus J. Asel; Shin Mou; Huili Grace Xing; Debdeep Jena; David A. Muller

doi:10.1063/5.0038861

paper

$γ$ -phase Inclusions as Common Defects in Alloyed $β$ -(Al $_{x}$ Ga $_{1 - x}$ ) $_{2}$ O $_{3}$ and Doped $β$ -Ga $_{2}$ O $_{3}$ Films

arXiv:2012.00263 · doi:10.1063/5.0038861

Abstract

$β$ -Ga $_{2}$ O $_{3}$ is a promising ultra-wide bandgap semiconductor whose properties can be further enhanced by alloying with Al. Here, using atomic-resolution scanning transmission electron microscopy (STEM), we find the thermodynamically-unstable $γ$ -phase is a ubiquitous defect in both $β$ -(Al $_{x}$ Ga $_{1 - x}$ ) $_{2}$ O $_{3}$ films and doped $β$ -Ga $_{2}$ O $_{3}$ films grown by molecular beam epitaxy. For undoped $β$ -(Al $_{x}$ Ga $_{1 - x}$ ) $_{2}$ O $_{3}$ films we observe $γ$ -phase inclusions between nucleating islands of the $β$ -phase at lower growth temperatures (~400-600 $^{\circ}$ C). In doped $β$ -Ga $_{2}$ O $_{3}$ , a thin layer of the $γ$ -phase is observed on the surfaces of films grown with a wide range of n-type dopants and dopant concentrations. The thickness of the $γ$ -phase layer was most strongly correlated with the growth temperature, peaking at about 600 $^{\circ}$ C. Ga interstitials are observed in $β$ -phase, especially near the interface with the $γ$ -phase. By imaging the same region of the surface of a Sn-doped $β$ -(Al $_{x}$ Ga $_{1 - x}$ ) $_{2}$ O $_{3}$ after ex-situ heating up to 400 $^{\circ}$ C, a $γ$ -phase region is observed to grow above the initial surface, accompanied by a decrease in Ga interstitials in the $β$ -phase. This suggests that the diffusion of Ga interstitials towards the surface is likely the mechanism for growth of the surface $γ$ -phase, and more generally that the more-open $γ$ -phase may offer diffusion pathways to be a kinetically-favored and early-forming phase in the growth of Ga $_{2}$ O $_{3}$ .

$γ$ -phase Inclusions as Common Defects in Alloyed $β$ -(Al $_{x}$ Ga $_{1 - x}$ ) $_{2}$ O $_{3}$ and Doped $β$ -Ga $_{2}$ O $_{3}$ Films

Abstract

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γ-phase Inclusions as Common Defects in Alloyed β-(Alx​Ga1-x​)2​O3​ and Doped β-Ga2​O3​ Films

Abstract

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$γ$ -phase Inclusions as Common Defects in Alloyed $β$ -(Al $_{x}$ Ga $_{1 - x}$ ) $_{2}$ O $_{3}$ and Doped $β$ -Ga $_{2}$ O $_{3}$ Films