Critical thickness predicted for crack formation in Ga₂O₃ and Al₂O₃ alloys

Ga₂O₃ and (Al_xGa_1-x)₂O₃alloys are used in the fabrication of transistors for high-power electronics, enabling solid state devices with high efficiency and large energy savings. (Al_xGa_1-x)₂O₃alloy films are grown on top of a layer of Ga₂O₃, which can result in tensile strain and the formation of cracks in the alloy film. While most authors are highly focused on the functional properties of Ga₂O₃ - and its alloys, this paper highlights that the mechanical properties are another critical consideration. Mu et al. studied the formation of cracks along different orientations using quantum-mechanical first-principles calculations.

“We wanted to understand the mechanisms by which these cracks form, with the goal of providing insights that could help improve the quality,” said author Chris Van de Walle.

The study led to predictions of the crystallographic direction of crack formation for different orientations of the growth surface, and the researchers were able to determine the energy cost of forming a crack.

“We were able to predict the maximum film thickness that can be grown before cracks appear. Such information about the so-called critical thickness is very important to guide experiments,” said Van de Walle.

Additionally, they learned that certain crystallographic directions allowed for a higher critical thickness.

The process of growing the alloys involves adding gallium, aluminum and oxygen atoms to the surface. The authors then identify how these atoms adsorb on the surface and the energies of their arrangements.

“This allows us to predict how aluminum atoms will incorporate in the growing film, and whether there are limitations on how much aluminum can be incorporated,” said Van de Walle.

The authors are working on expanding these surface studies to better understand the growth process.

Source: “First-principles surface energies for monoclinic Ga₂O₃ and Al₂O₃ and consequences for cracking of (Al_xGa_1-x)₂O₃,” by Sai Mu, Mengen Wang, Hartwin Peelaers, and Chris G. Van de Walle, APL Materials (2020). The article can be accessed at https://doi.org/10.1063/5.0019915 .