Ferromagnetic behavior of native point defects and vacancy-clusters in ZnO studied by first principle calculation

Cai-Qin Luo,Chi-Hang Lam,Francis Chi-Chung Ling,Si-Cong Zhu

doi:10.1088/2053-1591/aba14a

Abstract

The origin of room temperature ferromagnetism in undoped ZnO is still a question of debate. Experimental and theoretical findings are inconclusive as to the predominant contributor for the magnetic behavior of undoped ZnO. First principle calculation pseudopotential method was used to systematically determine the relaxed atomic geometry, the formation energies and the magnetic properties of the native point defects (vacancies, interstitials and antisites), and vacancy clusters (VZnVO, VZn − 2VO and 2VZn − VO) in ZnO. The results show that ZnO cells consisting of the VZn and the Oi have non-zero magnetic moments, energetically favoring ferromagnetic states and close-to-room-temperature Curie temperatures (294 K). VZn and Oi are also characterized by their low formation energies, in particular in the case of n-type (i.e. Fermi level close to the conduction band minimum) and O-rich conditions. The energy differences between the ferromagnetic state and anti-ferromagnetic state for VZn and Oi are larger than kT at room temperature but still relatively small (∼34 meV). Although VZn and Oi would contribute for the room temperature ferromagnetism, the ferromagnetism states would not be robustly stable for thermal excitation to the anti-ferromagnetic states.

Highlights

Diluted magnetic semiconductor (DMS) has been receiving extensive attention since Munekata et al’s first fabrication of (In, Mn)As DMS [1]
Dietl et al [7] studied the Curie temperature TC for different p-type semiconductors, found that room-temperature ferromagnetism (RTFM) can be realized in p-type ZnO doped by Mn
Despite numerous experimental observations of RTFM in transition metal (TM) doped ZnO, it is still uncertain as to what are the relevant origins of the RTFM in doped ZnO, which may be originated from the introduced dopant, the interaction between dopant and intrinsic defect, or second phase, etc

Summary

Introduction

Diluted magnetic semiconductor (DMS) has been receiving extensive attention since Munekata et al’s first fabrication of (In, Mn)As DMS [1] These fundamental studies of DMS have been of interest for the development of spintronic devices [2]. Yi et al [8] proposed that RTFM observed in Li-doped ZnO may be associated with the VZn vacancy based on the results of positron annihilation spectroscopy (PAS) study. They found that doping with appropriate dopants can lower the formation energy of VZn. Besides, VO is critical in one way or another on magnetic property. Hsu et al [9] found a

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