Effects of ion irradiation induced phase transformations and oxygen vacancies on the leakage current characteristics of HfO₂ thin films deposited on GaAs

Abstract We report on ion-induced phase transformations, defect dynamics related to oxygen vacancies and the resulting leakage current characteristics of RF sputtered HfO 2 thin films grown on GaAs. A systematic growth of HfO 2 grains and ion prompted phase transformations of HfO 2 to crystalline phases such as monoclinic and tetragonal/orthorhombic (mixed phase) in otherwise amorphous HfO 2 thin films have been observed after irradiation. At lower fluences, ion induced enhancement in the dielectric properties of HfO 2 thin films resulted in a reduction in the leakage current, whereas ion prompted defect formation at higher fluences caused a systematic increase in the leakage current density. Further, the effects of Poole-Frenkel tunneling and Fowler-Nordheim tunneling on the leakage current have also been investigated. These mechanisms showed the existence of impurities in the as-grown films. Photoluminescence study suggests that the variation in the defect configuration related to O-vacancies and the slight shift in the peak positions due to swift heavy ion irradiation are responsible for the observed changes in electrical characteristics. This study offers worthwhile information for considering the effects of electronic excitation prompted defect annealing and defect creation on the performance of HfO 2 /GaAs based photonic and optoelectronic devices, particularly, when such devices are operated in a radiation harsh environment.