The role of stacking faults and their associated 0.13 eV acceptor state in doped and undoped ZnO layers and nanostructures

Abstract

Cathodoluminescence spectra recorded with high spatial and wavelength resolution on tilted ZnO epitaxial layers allow to identify a very prominent emission peak at 3.314 eV as a free electron to shallow acceptor (E A % 130 meV) transition. By correlation with TEM cross-section images recorded on the same samples we can find these acceptor states to be located on basal plane stacking faults (BSFs). Locally, high concentrations of acceptor states are found. Since this spectral feature is often reported in literature especially after attempts to obtain p-type or transition metal doping, we conclude that stacking faults are a common by-product when group V or other extrinsic atoms are incorporated in ZnO layers or nanostructures.

Low temperature near band edge recombination dynamics in ZnO nanorods

“…They concluded that lines at 3.314 eV and at 3.30 eV (at 15 K) are associated with (e,A o ) and DAP emissions, respectively, induced by BSFs. Similar to Schirra et al, 29 Thonke et al 30 also reported an acceptor binding energy of 130 meV. Although the chemical origin of the acceptor is unknown, the Zn vacancy was suggested as a possible candidate by both.…”

“…33 Also reported recently is the formation of a quantum wire at the intersection between a 3.8 nm thick (Al,Ga)N/GaN quantum well and BSFs, leading to radiative recombination of localized excitons. 34 Although the energetic position reported by Khranovskyy et al 5 is considerably higher than what has been reported by Schirra et al, 29 Thonke et al 30 and also in this work, Khranovskyy et al 5 clearly demonstrated the presence of a high density of BSFs perpendicular to the c-axis. They also studied temperature and laser power dependent PL and concluded that the line has an excitonic nature.…”

“…This assignment was based on the similarity in peak energies and temperature dependencies presented by Schirra et al, 29 Thonke et al, 30 Shan et al, 31 and previous temperature dependencies reported by this group (see Ref. 32).…”

“…It is also important to point out that these two lines have different temperature dependencies. While the (e,A o ) line is quite stable with measurement temperature, the DAP line quenches at around 40 K. [29][30][31] Also, in a previous paper from our group, very similar temperature dependencies of the two lines at almost identical energies (3.320 eV and 3.305 at 2 K) were reported for ZnO thin films grown by metal organic chemical vapor deposition (MOCVD) on GaAs substrate, although the chemical origin of the acceptor was incorrectly assigned. 32 These observed abrupt decrease in the intensity of the DAP emission with temperature is consistent with the rapid ionization of the shallow donor, leaving the (e,A o ) recombination as the dominant mechanism.…”

“…The binding energy of the acceptor involved in both transitions was determined to be $130 meV. Thonke et al 30 also studied the role of stacking faults in a doped and undoped bulk ZnO using CL with high spatial and wavelength resolution and temperature dependent PL. They concluded that lines at 3.314 eV and at 3.30 eV (at 15 K) are associated with (e,A o ) and DAP emissions, respectively, induced by BSFs.…”