On the increased efficiency in InGaN-based multiple quantum wells emitting at 530–590 nm with AlGaN interlayers

Abstract

InGaN/AlGaN/GaN-based multiple quantum wells (MQWs) with AlGaN interlayers (ILs) are investigated, specifically to examine the fundamental mechanisms behind their increased radiative efficiency at wavelengths of 530–590nm. The AlzGa1−zN (z~0.38) IL is ~1–2nm thick, and is grown after and at the same growth temperature as the ~3nm thick InGaN quantum well (QW). This is followed by an increase in temperature for the growth of a ~10nm thick GaN barrier layer. The insertion of the AlGaN IL within the MQW provides various benefits. First, the AlGaN IL allows for growth of the InxGa1−xN QW well below typical growth temperatures to achieve higher x (up to~0.25). Second, annealing the IL capped QW prior to the GaN barrier growth improves the AlGaN IL smoothness as determined by atomic force microscopy, improves the InGaN/AlGaN/GaN interface quality as determined from scanning transmission electron microscope images and x-ray diffraction, and increases the radiative efficiency by reducing non-radiative defects as determined by time-resolved photoluminescence measurements. Finally, the AlGaN IL increases the spontaneous and piezoelectric polarization induced electric fields acting on the InGaN QW, providing an additional red-shift to the emission wavelength as determined by Schrodinger-Poisson modeling and fitting to the experimental data. The relative impact of increased indium concentration and polarization fields on the radiative efficiency of MQWs with AlGaN ILs is explored along with implications to conventional longer wavelength emitters.