Influence of quantum-confined Stark effect on optical properties within trench defects in InGaN quantum wells with different indium content

Abstract

The trench defects in InGaN/GaN multiple quantum well structures are studied using confocal photoluminescence (PL) spectroscopy and atomic force microscopy. A strong blueshift (up to ∼280 meV) and an intensity increase (by up to a factor of 700) of the emission are demonstrated for regions enclosed by trench loops. The influence of the difference in the well width inside and outside the trench loops observed by transmission electron microscopy, the compositional pulling effect, the strain relaxation inside the loop, and corresponding reduction in the built-in field on the PL band peak position and intensity were estimated. The competition of these effects is mainly governed by the width of the quantum wells in the structure. It is shown that the PL band blueshift observed within the trench defect loops in the InGaN structures with wide quantum wells is mainly caused by the reduction in efficiency of the quantum-confined Stark effect due to strain relaxation.

Directly correlated microscopy of trench defects in InGaN quantum wells

“…its height relative to the surroundings, where a positive prominence implies the defect enclosed region protrudes up above the surrounding undefected surface) 21 . Emission from QWs in the enclosed region was usually redshifted relative to emission from the surrounding QWs, though a blueshift in emission has also been seen under certain growth conditions 22 . Increasing trench thickness firmly correlated with an increase in this relative redshift, and the intensity of the emission relative to the surroundings also increased.…”

Application of patterned sapphire substrate for III-nitride light-emitting diodes

“…Heteroepitaxial growth of III-nitrides on sapphire substrate gives rise to strained films consisting of a high density of defects due to the large mismatch in the lattice and thermal expansion coefficients between the c -plane sapphire substrate and epilayers. Several types of defects have been reported, including threading dislocation, 86 stacking fault, 87 point defect, 88 V-pit, 89,90 trench defects 91 and misfit dislocations. 92 In particular, dislocations and point defects serve as nonradiative recombination centres that introduce the defect levels into the bandgap of III-nitrides and reduce the possibility of radiative recombination by capturing carriers, finally degrading the IQE of LEDs.…”

Green InGaN/GaN based LEDs: high luminance and blue shift

“…Higher content indium spots will have a lower optical threshold voltage, hence emitting at lower bias values. It is regularly reported in literature that high content indium amalgamation with GaN is a harsh path to consider 11,12 . Another reason to this light speckle pattern may also come from a local variation of contact resistivity.…”