Hole conductivity through a defect band in $\rm ZnGa_2O_4$

Abstract

Semiconductors with wide band gap (> 3.0 eV), high dielectric constant (> 10), good thermal dissipation, and capable of n and p-type doping are highly desirable for high-energy power electronic devices. Recent studies indicate that ZnGa 2 O 4 may be suitable for these applications, standing out as an alternative to Ga 2 O 3 . The simple face centered cubic spinel structure of ZnGa 2 O 4 results in isotropic electronic and optical properties, in contrast to the large anisotropic properties of the β-monoclinic Ga 2 O 3 . In addition, ZnGa 2 O 4 has shown, on average, better thermal dissipation and potential for n-and p-type conductivity. Here we use density functional theory and hybrid functional calculations to investigate the electronic, optical, and point defect properties of ZnGa 2 O 4 , focusing on the possibility for p-and n-type conductivity. We find that the cation antisite GaZn is the lowest energy donor defect that can lead to unintentional n-type conductivity. The stability of self-trapped holes (small hole polarons) and the high formation energy of acceptor defects make it difficult to achieve p-type conductivity. However, with excess of Zn, forming Zn (1+2x) Ga 2(1-x) O 4 alloys display an intermediate valence band, facilitating p-type conductivity. Due to the localized nature of this intermediate valence band, p-type conductivity by polaron hopping is expected, explaining the low mobility and low hole density observed in recent experiments.