Ferromagnetism in lightly Gd doped GaN: The role of defects
- PDF / 564,697 Bytes
- 10 Pages / 612 x 792 pts (letter) Page_size
- 41 Downloads / 164 Views
Ferromagnetism in lightly Gd doped GaN: The role of defects J. K. Mishra1, S. Dhar1,*, M. A. Khaderabad2 and O. Brandt3 1
Physics Department, Indian Institute of Technology Bombay, Powai Mumbai - 400076, India. 2 Electrical Engineering Department, Indian Institute of Technology Bombay, Powai Mumbai-400076, India 3 Paul-Drude-Institut für Festkörperelektronik, Hausvogteiplatz 5–7, 10117 Berlin, Germany. ABSTRACT Gd:GaN layers grown with different Gd concentrations by molecular beam epitaxy (MBE) are studied using photoconductivity and photo-thermoelectric power spectroscopy. Our study reveals that the incorporation of Gd produces a large concentration of acceptor-like defects in the GaN lattice. The defect band is found to be located ~450meV above the valence band. Moreover, the concentration of defects is found to increase with the Gd concentration. The effect of annealing on the structural and the magnetic properties of GaN implanted with Gd is also investigated. A clear correlation between the saturation magnetization and the defect density is observed in implanted samples. The colossal magnetic moment per Gd ion and the ferromagnetism observed in this material is explained in terms of the formation of giant defect cluster around each Gd ion. INTRODUCTION An interesting magnetic behavior has been observed in lightly Gd-doped GaN layers, in which Gd is doped either in situ or implanted on epitaxial GaN layers [1,2,3]. The material exhibits ferromagnetism above room temperature even with a Gd concentration as low as 7×1015 cm-3 [1]. Room-temperature ferromagnetism has been reported in Eu-doped GaN and Tm-doped (Al,Ga)N layers as well [4,5]. Moreover, the effective magnetic moment per Gd ion is found to be as high as 4000 Bohr-magneton (μB) in Gd-doped GaN layers [1]. However, the microscopic mechanism that gives rise to this interesting magnetic property in these materials is not yet understood. Dhar et al. has found that the value of the effective magnetic moment per Gd ion is more in implanted samples as compared to that of a GaN:Gd layer doped in situ [2]. Since, the defect density in the implanted samples is expected to be higher than that in epitaxially grown GaN:Gd layers, this finding clearly suggest that native point defects play an important role in governing the magnetic properties of this material. So far, however, there has been no direct evidence for the presence of these defects in GaN:Gd layers doped in situ. Here, we show by a variety of experimental techniques that a large concentration of acceptor-like defects is formed in GaN during Gd incorporation in reactive molecular beam epitaxy. The defect concentration is found to be vastly exceeding the concentration of Gd in these layers and
also found to increase with the Gd concentration. The effect of annealing on the structural and the magnetic properties of GaN implanted with Gd ions are also investigated. A clear correlation between the saturation magnetization and the defect density is observed in implanted samples suggesting that defects must b
Data Loading...
