  InGaN-based light emitting diodes (LEDs) are known to suffer from low
electron and hole wavefunction overlap due to high piezoelectric field.
Staggered InGaN quantum wells (QWs) have been proposed to increase the
wavefunction overlap and improve the efficiency of LEDs especially for long
wavelength emitters. In this work we evidence that the growth of staggered QWs
has also another beneficial effect as it allows to reduce the formation of
defects, responsible for nonradiative Shockley-Read-Hall recombination, at the
bottom interface of the QW. Staggered QWs comprised an InGaN layer of an
intermediate In content between the barrier and the QW. We show that insertion
of such a layer results in a significant increase of the luminescence
intensity, even if the calculated wavefunction overlap drops. We study the
dependence of the thickness of such an intermediate In content layer on
photoluminescence (PL) intensity behavior. Staggered QWs exhibit increased
cathodoluminescence (CL) homogeneity that is a fingerprint of lower density of
defects, in contrast to standard QWs for which high density of dark spots are
observed in QW emission mapping. Transmission electron microscopy of standard
QWs revealed formation of basal-plane stacking faults (BSFs) and voids that
could have resulted from vacancy aggregation. Stepwise increase of the In
content in staggered QWs prevents formation of point defects and results in an
increased luminescence efficiency. The In composition difference between the
barrier and the well is therefore a key parameter to control the formation of
point defects in the high-In content QWs, influencing the luminescence
efficiency.
