Abstract
The V-pits and potential fluctuations in InGaN/GaN multiple quantum wells (MQWs) are key factors for understanding the performance of InGaN/GaN-based light-emitting diodes (LEDs). However, photoluminescence (PL) measurements using conventional optical microscopy only provide ensemble information due to the spatial resolution limit, known as the diffraction barrier, which hinders the analysis of dislocations and potential fluctuations. Here, in order to investigate the influence of the V-pits and potential fluctuations on local optical properties, we performed nanoscopic luminescence mapping for standard and V-pit InGaN/GaN MQWs samples with different sized V-pits using near-field scanning optical microscopy (NSOM) with illumination mode (I-mode) at various laser excitation powers. From the nanoscopic PL mapping data, we could clearly observe luminescence features associated with dislocations and potential fluctuations in the InGaN/GaN MQWs. We also employed correlation analysis to quantitatively analyze the nanoscopic PL mapping data for the different MQWs samples. Based on the results of NSOM PL with I-mode and correlation analysis, we could demonstrate that carrier transfer in the MQWs sample with large sized V-pits is suppressed by deeper potential fluctuations and higher energy barriers compared to the standard sample.
Highlights
InGaN/GaN based light-emitting diodes (LEDs) have attracted tremendous attention for a wide range of applications, including displays and general illumination[1,2,3]
Monochromatic nearfield scanning optical microscopy (NSOM) PL mapping images of the standard and V-pit samples obtained only from the main multiple quantum wells (MQWs) wavelength regime with 100 μWlaser power are shown in Fig. 3a and d, respectively
The emission spectrum of each sample consists of two peaks which come from the main MQWs and the InGaN/GaN SLs
Summary
Monochromatic NSOM PL mapping images of the standard and V-pit samples obtained only from the main MQWs wavelength regime with 100 μWlaser power are shown in Fig. 3a and d, respectively. Despite these results, it is difficult to quantitatively describe the influence of V-pits and potential fluctuations using such mappings, because they have much greater spatial information compared to a conventional PL in the same area. Characterizing the optical properties of V-pits and potential fluctuations using the I-mode NSOM PL and correlation analysis methods allowed us to explain the enhancement in LED efficiency provided by MQWs with V-pits
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