Discovery of New Polymorphs of Gallium Oxides with Particle Swarm Optimization‐Based Structure Searches
Xue Wang, Muhammad Faizan, Guangren Na, Xin He, Yuhao Fu, Lijun Zhang
Abstract
Abstract Gallium oxide (Ga 2 O 3 ) has attracted significant research interest for next‐generation high‐efficiency power devices because of its unique electronic properties such as ultra‐wide band gap, high breakdown electric field, and large Baliga’s figure of merit. Ga 2 O 3 crystallizes in a series of reported polymorphs including β‐, α‐, ε‐, κ‐, γ‐, and δ‐Ga 2 O 3 , the structures of some of which are still in serious controversy. A polymorph structure search study of Ga 2 O 3 is herein performed by combining particle swarm optimization with first‐principles energetic calculations. In addition to producing the predominant experimental known phases of β‐, α‐, and κ‐Ga 2 O 3 , two new polymorphs are found with space group P and Pmc 2 1 consisting of four‐ and five‐fold coordinated Ga. They show comparable energy with β‐ and α‐Ga 2 O 3 with the energy difference of several meV per atom, and exhibit robust phonon stability. Similarly, the new phases show quite wide band gaps and small electron effective masses by comparing it with other known phases. The Pmc 2 1 phase shows a calculated spontaneous polarization of 0.277 C m −2 , close to that of ε/κ‐Ga 2 O 3 . The systemic structure searches also establish a structural relationship between ε‐Ga 2 O 3 and κ‐Ga 2 O 3 and how the electronic properties vary with polymorphic phase change.