Identification of the zinc-oxygen divacancy in ZnO crystals

Abstract

An electron paramagnetic resonance (EPR) spectrum in neutron-irradiated ZnO crystals is assigned to the zinc-oxygen divacancy. These divacancies are observed in the bulk of both hydrothermally grown and seeded-chemical-vapor-transport-grown crystals after irradiations with fast neutrons. Neutral nonparamagnetic complexes consisting of adjacent zinc and oxygen vacancies are formed during the irradiation. Subsequent illumination below ∼150 K with 442 nm laser light converts these (VZn2− − VO2+)0 defects to their EPR-active state (VZn− − VO2+)+ as electrons are transferred to donors. The resulting photoinduced S = 1/2 spectrum of the divacancy is holelike and has a well-resolved angular dependence from which a complete g matrix is obtained. Principal values of the g matrix are 2.00796, 2.00480, and 2.00244. The unpaired spin resides primarily on one of the three remaining oxygen ions immediately adjacent to the zinc vacancy, thus making the electronic structure of the (VZn− − VO2+)+ ground state similar to the isolated singly ionized axial zinc vacancy. The neutral (VZn2− − VO2+)0 divacancies dissociate when the ZnO crystals are heated above 250 °C. After heating above this temperature, the divacancy EPR signal cannot be regenerated at low temperature with light.

Negative-Uand polaronic behavior of the Zn-O divacancy in ZnO

“…The divacancy can nominally exist in two different configurations, axial (aligned along the [0001] direction) or azimuthal (lying in the basal plane). Holston et al 17 have assigned an EPR signal to the azimuthal configuration of the divacancy only, and our calculations indicate that this configuration is more stable, although the difference in energy is small. For this reason, we present results for the azimuthal configuration only.…”

“…Several recent experimental studies highlight the closeassociate V Zn V O pair, hereby referred to as the divacancy, as another important defect in ZnO, especially in processed samples, e.g., after irradiation, annealing or polishing [15][16][17] . In contrast to its isolated constituents, however, first-principles calculations on the divacancy are scarcely available in the literature 16,[18][19][20][21][22] , and predominantly based on semilocal functionals.…”

Role of defects and their complexes on the dependence of photoconductivity on dark resistivity of single ZnO microwires

“…Since V Zn are more mobile than V O , 32 they can migrate to the surface during the TT and reach the V O to form the divacancy. 33,34 This complex acts as a recombination center that fades out the photoresponse of the samples as its concentration increases. Then, for low q d the quantity of V O , introduced by the TT, overpasses the number of preexistent V Zn , relatively low concentration of complexes is formed, and the PC increases due to the new traps generated.…”

Multistability of isolated and hydrogenated Ga–O divacancies in β−Ga2O3

“…Divacancies are also likely be introduced by H-or He implantation. For example, Holston et al [16] observed an EPR signal in neutron-irradiated ZnO, which they assigned to the Zn-O divacancy. Moreover, both isolated and hydrogenated divacancies have been identified in H-implanted silicon [17].…”