Photoluminescence measurements from the two polar faces of ZnO

Abstract

The crystal structure of ZnO is wurtzite and the stacking sequence of atomic layers along the ''c'' axis is not symmetric. As a result, a ZnO crystal surface that is normal to the c axis exposes one of two distinct polar faces, with ͑0001͒ being considered the O face and ͑0001͒ the Zn face. Photoluminescence ͑PL͒ measurements on the two faces reveal a striking difference. Two transitions are observed in PL that are dominant from the O face and barely observed in PL from the Zn face. These lines are identified as phonon replicas of a particular D 0 ,X transition using energy separations, excitation dependence, and time-resolved PL measurements. In addition, PL emission from free excitons is found to be more intense from the O face than from the Zn face.

Electrical properties of ZnO nanorods studied by conductive atomic force microscopy

“…Furthermore, in contrast to the ð0001Þ plane there are few data available on ð1010Þ side planes. 33 However, from the variation in photoluminescence results of different crystal facets, 34,35 it is reasonable to expect that electrical properties also differ. In addition, secondary ion mass spectroscopy investigation has demonstrated higher incorporation of impurities in O-terminated compared to Znterminated ZnO epitaxial films.…”

Photoluminescence and damage recovery studies in Fe-implanted ZnO single crystals

“…Similar emission lines were previously reported. 1,8,9 The transitions are currently assigned to D 0 X ͑and A 0 X) complexes, TES, and DAP recombinations. 1,8,9 After implantation and annealing procedures, the NBE PL is mainly dominated by the 3.36 eV emission, with minor lines at 3.309 and 3.239 eV also observed for the sample annealed in air.…”

“…7 Typically, with intrinsic excitation, the low-temperature photoluminescence ͑PL͒ spectra of undoped ZnO single crystals are characterized by complex near-band-edge ͑NBE͒ spectra dominated by the recombination of free excitons ͑FXA͒, rotor states (EϾ3.37 eV), and neutral donor/ acceptor bound-exciton complexes (D 0 X,A 0 X) near 3.36 eV followed by 72.8-meV LO phonon replicas. 1,8,9 At lower energies, 29.9 meV below the exciton complexes, two-electron satellite ͑TES͒ recombination is observed. 1,8,9 Donoracceptor pair ͑DAP͒ recombination at 3.22 eV followed by LO phonon replicas is usually present.…”

“…1,8,9 At lower energies, 29.9 meV below the exciton complexes, two-electron satellite ͑TES͒ recombination is observed. 1,8,9 Donoracceptor pair ͑DAP͒ recombination at 3.22 eV followed by LO phonon replicas is usually present. 1,8,9 Besides these structured NBE emissions, deep-level structureless emissions are commonly observed in undoped ZnO single crystals, 10,11 powder samples, 12,13 thin films, 14,15 and nanocrystalline particles.…”

“…1,8,9 Donoracceptor pair ͑DAP͒ recombination at 3.22 eV followed by LO phonon replicas is usually present. 1,8,9 Besides these structured NBE emissions, deep-level structureless emissions are commonly observed in undoped ZnO single crystals, 10,11 powder samples, 12,13 thin films, 14,15 and nanocrystalline particles. 16 The centers responsible for the unstructured emission bands in the green, yellow, and red spectral regions are usually assumed to be due to different native defects in ZnO, such as oxygen vacancy (V O ), zinc vacancy (V Zn ), interstitial zinc, interstitial oxygen, and antisite defect (O Zn ).…”