The Study Of Rare Earth Doped GaN And Its Defect Complexes By The First Principle Mathod

Diluted magnetic semiconductors(DMS)are promising to design more excellent spintronic devices.By using the first-principles method based on the density functional theory,we studied the crystal structure,electronic structure,formation energy and magnetic moment of GaN doped with Gd,Eu and Tm and defect complexes.We calculated the formation energy and electronic structure of defect complexes,formed by substitional Gd and the point defects such as Ga vacancy,N vacancy,N interstitial or O interstitial atom in GaN doped with Gd.We found that the lattice constants expanded after doping Gd in GaN,and the direct band gap semiconductor GaN turned into indirect band gap semiconductor.Ga vacancies can introduce the impurity levels in the forbidden band and cause a magnetic moment,but its formation energy is high.By contrast,N vacancy has the lower formation energy,but its contribution to the magnetic moments of GaN:Gd is smaller.An octahedral interstitial N can introduce the magnetic moment of 2.5?_B to GaN:Gd system.Therefore,Ga vacancy and octahedral interstitial N may be the source of the large magnetic moments in GaN:Gd found in experiment.In addition,for GaN:Gd without defects,the total energy of ferromagnetic configuration of Gd is a bit lower than antiferromagnetic configuration,but the energy difference is very small,which suggests that the interaction between Gd is unable to lead to long-range ferromagnetism in GaN:Gd.In addition,we also investigated the magnetic properties of Eu(Tm)doped GaN and the defect complexes with Ga vacancy,N vacancy,N interstitial atom and O interstitial atom.The results show that the lattice constants also increase after Eu,Tm doping GaN due to the larger radius of Eu(Tm)than Ga.Similarly,Ga vacancies complexes can lead to the local magnetic moments,whose magnitude depends strongly on their position as well as the concentration of Ga vacancies.By contrast,N vacancies have less effect on the magnetic moment of the doping system.The calculated results for interstitial N and O show that an octahedral O can introduce the local magnetic moments of 1.6?_B in GaN:Tm.According to the formation energy,it is found that the defects in GaN doped with Eu(Tm)are very difficult to form,while the implanation of Eu(Tm)to GaN in the presence of defects is relatively easy.The dopant Eu(Tm)and defects can attract to each other,which indicate the existence of defects is favorable for the formation of rare earth Eu and Tm.