High field dielectric response in κ-Ga₂O₃ films

κ-Ga₂O₃ has been predicted to be a potential ferroelectric material. In this work, undoped Ga₂O₃ films were grown by either plasma-enhanced atomic layer deposition (PEALD) or metal organic chemical vapor deposition (MOCVD) on platinized sapphire substrates. 50 nm thick PEALD films with a mixture of κ-Ga₂O₃ and β-Ga₂O₃ had a relative permittivity of ∼27, a loss tangent below 2%, and high electrical resistivity up to ∼1.5 MV/cm. 700 nm thick MOCVD films with predominantly the κ-Ga₂O₃ phase had relative permittivities of ∼18 and a loss tangent of 1% at 10 kHz. Neither film showed compelling evidence for ferroelectricity measured at fields up to 1.5 MV/cm, even after hundreds of cycles. Piezoresponse force microscopy measurements on bare κ-Ga₂O₃ showed a finite piezoelectric response that could not be reoriented for electric fields up to 1.33 MV/cm.