Optical properties of dislocations in wurtzite ZnO single crystals introduced at elevated temperatures

Abstract

Optical properties of wurtzite ZnO bulk single crystals in which an arbitrary number (typically 109–1010 cm−2) of fresh dislocations were introduced intentionally by the plastic deformation at elevated temperatures (923–1073 K) were examined. Deformed specimens showed excitonic light emission with photon energies of 3.100 and 3.345 eV, as well as their LO phonon replicas at 11 K. The light intensities increased with increasing dislocation density. The activation energy for a thermal quenching of the 3.100 or 3.345 eV emission band, which corresponds to the depth of the localized energy level associated with the emission band, was estimated to be 0.3±0.1 or 0.05±0.01 eV, respectively. The origin of the energy levels was proposed as point defect complexes involving dislocations. The introduction of the dislocations at the elevated temperatures above 923 K did not influence the intensities of the emission bands except the dislocation-related emission bands.

Edge dislocation effect on optical properties in wurtzite ZnO

“…The luminescence spectrum of ZnO consists of a strong bandedge emission (BE) at 3.37 eV [27][28][29] and a wide range of deep level emissions (DL) between 1.5 and 3.2 eV [30]. The BE peak intensity has been shown to decrease as dislocation density increases [22,27,[31][32][33][34].…”

In-Situ Analysis of Optoelectronic Properties of Semiconductor Nanostructures and Defects in Transmission Electron Microscopes

“…From the analysis of the thermal quenching processes, the depth of the defect level ΔE associated with the 3.100 eV emission and that with the 3.345 eV one are estimated to be 0.3 eV and 0.05 eV, respectively. Since the PL intensities increase with increasing dislocation density, the emission bands are associated with the dislocations introduced at elevated temperatures (Ohno et al, 2008b). Fig.…”

“…Since those dislocations are similar in type, the atomistic structure of a dislocation would be modified at elevated temperatures, presumably due to an interaction of the dislocation with point defects. Indeed, a dislocation involving point defects is the candidate for the 3.1 eV emission band (Ohno et al, 2008b). Also, the intensity of the green (2.43 eV) and yellow (2.18 eV) emissions, associated with Oand Zn-vacancies (Zhao et al, 2005), varies when dislocations modify their structure via their glide (Figs.…”

“…The inset in (a) shows a TEM image of dislocations in the deformed specimen. (Ohno et al, 2008b) In-situ TEM observation with 80 keV electrons reveals that (Ohno et al, 2009b), screw and edge dislocations glide forming mixed dislocation segments when electrons are irradiated at temperature of 120 K, as well as at room temperature (Fig. 3).…”

“…The emission band peaking at 3.1 eV, due to a defect level of 0.3 eV depth associated with dislocations (Ohno et al, 2008b), is determined by CL spectroscopy (Ohno et al, 2009b). Since a CL light emitted from a dislocation is rather weak, CL lights are obtained from an area in which a number of dislocations exist (the total length of the dislocation lines of about 2x10 3 nm).…”