γ-phase inclusions as common structural defects in alloyed β-(AlxGa1−x)2O3 and doped β-Ga2O3 films
Abstract
β-Ga2O3 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, we find the thermodynamically unstable γ-phase is a ubiquitous structural defect in both β-(AlxGa1−x)2O3 films and doped β-Ga2O3 films grown by molecular beam epitaxy. For undoped β-(AlxGa1−x)2O3 films, we observe γ-phase inclusions between nucleating islands of the β-phase at lower growth temperatures (∼500–600 °C). In doped β-Ga2O3, 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 °C. Ga interstitials are observed in the β-phase, especially near the interface with the γ-phase. By imaging the same region of the surface of a Sn-doped β-(AlxGa1−x)2O3 after ex situ heating up to 400 °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 toward 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 Ga2O3. However, more modeling and simulation of the γ-phase and the interstitials are needed to understand the energetics and kinetics, the impact on electronic properties, and how to control them.
Document Details
- Document Type
- Pub Defense Publication
- Publication Date
- May 01, 2021
- Source ID
- 10.1063/5.0038861
Entities
People
- Celesta S. Chang
- David A. Muller
- Debdeep Jena
- Huili Grace Xing
- Nicholas Tanen
- Shin Mou
- Thaddeus J. Asel
- Vladimir Protasenko
Organizations
- Air Force Office of Scientific Research
- Air Force Research Laboratory
- Cornell University
- Division of Materials Research