Intrinsic Defects in ZnO Films Grown by Molecular Beam Epitaxy

Abstract

We have investigated the intrinsic defects in ZnO films grown by molecular beam epitaxy by annealing them in O2 and N2 atmosphere. We found that there is a good correlation between the annealing condition and photoluminescence characteristics. The results of annealing experiments suggest that the photoluminescence at 3.358 eV is caused by the excitons bound to oxygen vacancies. The green-yellow emission at around 2.3 eV is also observed in as-grown ZnO epitaxitial films. This emission becomes weak and the electron concentration increases when ZnO films are annealed in O2 atmosphere at 1000°C or in N2 atmosphere at 700°C. Since the donor in undoped ZnO is related to the oxygen vacancy, the observed green-yellow emission at around 2.3 eV is probably caused by defects other than oxygen vacancies. Our experimental results imply that it is related to interstitial Zn.

Photoluminescence and photoconductive characteristics of hydrothermally synthesized ZnO nanoparticles

“…There− fore, the shallow donor level of the Z ni is suggested to locate at~0.34 eV below the conduction band in this study because the violet photoluminescence appears at~2.987 eV. A blue emission centered at~2.56 eV (481 nm) is due to a radiative transition of an electron from the shallow donor level of Z ni to an acceptor level of neutral V Zn [26]. In this study, it can be estimated that the acceptor level of V Zn locates at 0.42 eV above the valence band.…”

Growth of ZnO Nanostructures Produced by MOCVD: A Study of the Effect of the Substrate

“…Therefore, the visible emission band observed in our samples has to be associated with the intrinsic defects of ZnO generated during the growth. In fact, various intrinsic defects, such as Zn and oxygen interstitials, [41,42] Zn and oxygen vacancies, [43][44][45][46] antisite oxygen, [47] and hydroxyl groups, [45,48,49] have been reported as responsible for the visible emission. Actually, hydroxyl groups are considered responsible for the yellow emission at about 2.15 eV [45,49] but the most intense visible emission observed in the present samples, i.e., the green band at 2.45 eV, is likely to be attributed to Zn vacancy as previously reported.…”

Band gap tailoring and enhanced visible emission by two-step annealing in Zn0.94Cu0.04Cr0.02O nanocrystals

“…The blue emission centered at 478 nm is due to a radiative transition of an electron from the deep donar level of Zn i to an acceptor level of neutral V Zn [58]. The green emission at 527 nm is attributed to radiative transition of an electron from the deep donor level of Zn i to an acceptor level caused by singly ionized charged state of the defect V Zn -in ZnO [59].…”