Ab-initio studies on Li doping, Li-pairs, and complexes between Li and intrinsic defects in ZnO

Abstract

First-principles density functional calculations have been performed on Li-doped ZnO using allelectron projector augmented plane wave method. Li was considered at six different interstitial sites (Li i), including anti-bonding and bond-center sites and also in substitutional sites such as at Zn-site (Li zn) and at oxygen site (Li o) in the ZnO matrix. Stability of Li Zn over Li i is shown to depend on synthetic condition, viz., Li Zn is found to be more stable than Li i under O-rich conditions. Hybrid density functional calculations performed on Li Zn indicate that it is a deep acceptor with (0/-) transition taking place at 0.74 eV above valence band maximum. The local vibrational frequencies for Li-dopants are calculated and compared with reported values. In addition, we considered the formation of Li-pair complexes and their role on electronic properties of ZnO. Present study suggests that at extreme oxygen-rich synthesis condition, a pair of acceptor type Li Zn-complex is found to be stable over the compensating Li i þ Li Zn pair. The stability of complexes formed between Li impurities and various intrinsic defects is also investigated and their role on electronic properties of ZnO has been analyzed. We have shown that a complex between Li Zn and oxygen vacancy has less formation energy and donor-type character and could compensate the holes generated by Li-doping in ZnO. V

Anisotropic polaron localization and spontaneous symmetry breaking: Comparison of cation-site acceptors in GaN and ZnO

“…11,19 The Li Zn defect in ZnO has also been studied recently with several hybrid functionals. 3,[29][30][31] The polaronic structural distortion due to hole trapping has been reproduced in these studies. These results are a significant improvement over previous calculations using local density functionals.…”

Abrupt and tunable quenching of photoluminescence in ZnO

“…They also predicted that the Li Zn defect in ZnO may have a dual nature, where, in addition to the deep localized state, a shallow acceptor state may exist at about 0.21 eV above the valence band and be revealed in certain experimental conditions [18]. DFT calculations based on hybrid functional schemes predicted a binding energy of 0.75 eV [19,20] and 0.46 eV [21] for the Li Zn acceptor in ZnO. Carvalho et al [22] concluded that, by using different pseudopotentials and functionals, the calculated binding energy of the Li Zn acceptor varies between 0.6 and 1.1 eV.…”

p-type doping of MgZnO films and their applications in optoelectronic devices

“…One of the most challenging issues of ZnO lies in the difficulty of realizing efficient p-type conduction. Although quite a few reports claimed the realization of p-type ZnO films, and some optoelectronic devices have been demonstrated [6][7][8], the performance of such devices is still far below expectation. It is accepted that heterostructures constituted by alloyed semiconductor with different compositions can ensure efficient carrier injection and confinement, and thus may help to realize high-performance optoelectronic devices.…”