Nanoscopic structural and emission properties of red InGaN hybrid single quantum wells

Using atomic force microscopy (AFM) and scanning near-field optical microscopy (SNOM)-photoluminescence (PL) spectroscopy (SNOM-PL), we study the nanoscopic structural and emission properties of a red InGaN hybrid single quantum well (SQW), consisting of a blue and a red InGaN SQW. AFM images reveal the presence of threading-dislocation (TD)-related V-pits and shallow trench defects. The trench defects are classified into three categories on the basis of their height relative to a flat QW: lowered-, level-, and raised-center trench defects. SNOM-PL images demonstrate that TDs and all types of shallow trench defects exhibit a low emission intensity, indicating that they act as non-radiative recombination centers. Unlike previous studies on low-In content samples, all the trench defects exhibit a low emission intensity in our high-In content sample because of In segregation. Given the correlation of dark emission positions between the blue and red emissions, as well as the lower screw-type TD density at the surface than at the n-GaN layer, screw-type TDs should be one of the triggers in the formation of shallow trench defects. Therefore, to enhance the external quantum efficiency of hybrid InGaN red LEDs, it is crucial to suppress In segregation within shallow trench defects and decrease screw-type TD density.