Structural origin of V-defects and correlation with localized excitonic centers in InGaN/GaN multiple quantum wells

In the growth of InGaN/GaN multiple quantum well (MQW) structures, a novel defect (called the “V-defect”) initiates at threading dislocations in one of the first quantum wells in a MQW stack. This defect is common to almost all InGaN MQW heterostructures. The nature of the V-defect was evaluated using transmission electron microscopy (TEM), scanning TEM (STEM), and low-temperature cathodoluminescence (CL) on a series of In0. 20Ga0. 80N/GaN MQW samples. The structure of the V-defect includes buried side-wall quantum wells (on the 101̄1 planes) and an open hexagonal inverted pyramid which is defined by the six 101̄1 planes. Thus, in cross section this defect appears as an open “V”. The formation of the V-defect is kinetically controlled by reduced Ga incorporation on the pyramid walls (101̄1 planes). The V-defect is correlated with the localized excitonic recombination centers that give rise to a long-wavelength shoulder in photoluminescence (PL) and CL spectra. This long-wavelength shoulder has the following characteristics: (i) its intensity is correlated with the side-wall quantum wells; (ii) the temperature independence of the full width at half maximum strongly supports a localized exciton recombination process.