Influence of dislocation decoration with mobile donors on exciton luminescence in ZnO crystals

Abstract

In ZnO single crystals, the influence of grown-in and introduced by mechanical damage dislocations on room temperature exciton luminescence was investigated. It was found that the higher dislocation density the weaker the luminescence and the lower the intensity of its short-wavelength side with respect to that of long-wavelength one. After introduction of dislocations, gradual quenching of exciton luminescence and the suppression of its short-wavelength side took place. Observed effects were accounted for by the formation of optical absorption "tail" due to decoration of dislocations with mobile shallow donors, which resulted in the increase of reabsorption of emitted light in the crystal.1 Introduction It is known that dislocations can strongly influence not only electrical, but also optical properties of semiconductors. The changes of optical absorption and luminescence caused by introduction of dislocations were observed in many semiconductors [1−8]. In last years, zinc oxide attracts much attention as a promising material for UV-blue light emitters. Lasing effect was obtained in ZnO single crystals, polycrystalline layers, epitaxial films and nanostructures over the temperature range 77−300 K, laser emission taking place at the wavelength of free exciton or its phonon replicas. The dependence of ZnO exciton luminescence on dislocation density is, therefore, an actual question, which is intensively studied [9−14]. In ZnO crystals, films and ceramics, such dislocation-induced effects as the quenching of initially present luminescence [9, 11−14] as well as the appearance of new luminescence bands [10,13] were observed. In the present paper, the influence of dislocations on ZnO room temperature exciton luminescence intensity and spectrum shape has been found. This effect has been shown to result from accumulation of mobile shallow donors on dislocations.

Dislocation-mediated electronic conductivity in rutile

“…Furthermore, it will certainly be of great interest how dislocations modify photoelectric properties. It could already be shown for ZnO to modify light absorption significantly (43). Therefore, new pathways for the use of TiO2 in photoelectric applications could be developed.…”

Edge dislocation effect on optical properties in wurtzite ZnO

“…By applying a direct electric field, the movement of GL from anode to cathode indicates that GL is due to complex defects involving zinc interstitials [39]. These point defects can be localized at dislocations due to the strain field, causing the negatively charged dislocations and introducing electronic states within the band gap [20,21,23,34]. Lin et al [20] proposes that doubly charged Zn vacancies accumulated around dislocations contribute to conduction band bending, consistent with Read's model [25].…”

“…The BE peak intensity has been shown to decrease as dislocation density increases [22,27,[31][32][33][34]. The most commonly reported DL emission is a green luminescence (GL) band ranging from 2.3 to 2.5 eV [27,32,35,36].…”