Threading dislocations (TDs) in (Al,In,Ga)N semiconductors are known to affect the
luminescence efficiency of near-band-edge (NBE) emissions in bulk films and quantum structures.
However, the principal role of point defects such as vacancies on the luminescent properties has not
been fully understood. In this article, impacts of point defects on the luminescence quantum
efficiency of NBE emissions and on the intensity of deep emission bands will be described, based on
the results of steady-state and time-resolved photoluminescence (TRPL) and positron annihilation
measurements. The room temperature nonradiative lifetime (τNR) of the NBE excitonic
photoluminescence (PL) peak in polar (0001) and (000-1) , nonpolar (11-20) and (10-10), and
zincblende (001) GaN layers prepared by various growth techniques was shown to increase with the
decrease in concentration or size of Ga vacancies (VGa) and with the decrease in gross concentration
of point defects including complexes, leading to an increase in the NBE PL intensity. As the edge TD
density decreased, the concentration or size of VGa tended to decrease and τNR tended to increase.
However, there existed remarkable exceptions. The results indicate that the nonradiative
recombination process is governed not by single point defects, but by certain defects introduced with
the incorporation of VGa, such as VGa-defect complexes. Similar relations were found in AlxGa1-xN
alloy films grown by metalorganic vapor phase epitaxy: i. e. τNR at room temperature increased with
the decrease in the concentration of cation vacancies (VIII) and with the decrease in gross
concentration of point defects. In addition to nonradiative processes, the VIII concentration was found
to correlate with the intensity ratio of characteristic deep emission band to the NBE emission
(Ideep/INBE). For example, Ideep/INBE at low temperature for the deep emission bands at 4.6, 3.8, and 3.1
eV of AlN epilayers grown by NH3-source molecular beam epitaxy had a linear correlation with the
concentration or size of Al vacancies (VAl). Since the relative intensities of 3.1 eV and 3.8 eV bands
increased remarkably with lowering the supply ratio of NH3 to Al (V/III ratio) and growth
temperature (Tg), they were assigned to originate from VAl-O as well as VAl-shallow donor complexes.
The VAl concentration could be decreased by adjusting the V/III ratio and Tg. In the case of AlxGa1-xN
alloys, the concentration or size of VIII and Ideep/INBE at 300 K increased simultaneously with the
increase in x up to approximately 0.7. Similar to the case for GaN and AlN, the deep emission band
was assigned as being due to the emission involving VIII-O complexes.
Radiative Lifetime of Excitons in GaInN/GaN Quantum Wells
