  Identification of complex defect has been a long-sought-after physics problem
for controlling the defect population and engineering the useful properties in
wide bandgap oxide semiconductors. Here we report a systematic study of
(GaZn-VZn)- acceptor complex defect via zinc self-diffusion in Ga-doped ZnO
isotopic heterostructures, which were conceived and prepared with delicately
controlled growth conditions. The secondary ion mass spectrometry and
temperature-dependent Hall-effect measurements reveal that a high density of
controllable (GaZn-VZn)- is the predominant compensating defect in Ga-doped
ZnO. The binding energy of this complex defect obtained from zinc
self-diffusion experiments (~0.78 eV) well matches the electrical activation
energy derived from the temperature-dependent electrical measurements (~0.82
eV). The compensation ratios were quantitatively calculated by energetic
analysis and scattering process to further validate the compensation effect of
(GaZn-VZn)- complex in Ga-doped ZnO. Meanwhile, its energy level structure was
suggested based on the photoluminescence spectra, and the lifetime was achieved
from the time-resolved photoluminescence measurements. The electron transitions
between the (GaZn-VZn)- complex defect levels emit the light at ~650 nm with a
lifetime of 10-20 nanoseconds. These findings may greatly pave the way towards
novel complex defects-derived optical applications.
