Origin and consequences of a high stacking fault density in epitaxial ZnO layers

Transmission electron microscopy was applied to study ZnO grown by metalorganic vapor phase epitaxy on ${\mathrm{Al}}_2{\mathrm{O}}_3\text{(0001)}$ substrates. The defect structure of the material is dominated by an extraordinary high density of small stacking faults with extensions between 5 and 25 nm which induce a bright small-scale speckle contrast under weak-beam imaging conditions. The stacking faults are terminated by Frank partial dislocations with Burgers vectors of the type 1/6 $\text{〈22̄03〉.}$ The precipitation of interstitial atoms is the most likely process for the generation of the stacking faults, which are characterized by an additional (0002) plane. The high stacking fault density can be considered as an indicator for high point defect concentrations, which are expected to aggravate the control of the electrical conductivity.