Confocal microphotoluminescence of InGaN-based light-emitting diodes

Abstract

Spatially resolved photoluminescence (PL) of $\mathrm{In}\mathrm{Ga}\mathrm{N}∕\mathrm{Ga}\mathrm{N}∕\mathrm{Al}\mathrm{Ga}\mathrm{N}$ -based quantum-well-structured light-emitting diodes (LEDs) with a yellow-green light $\left(530\mathrm{nm}\right)$ and an amber light $\left(600\mathrm{nm}\right)$ was measured by using confocal microscopy. Submicron-scale spatial inhomogeneities of both PL intensities and spectra were found in confocal micro-PL images. We also found clear correlations between PL intensities and peak wavelength for both LEDs. Such correlations for yellow-green and amber LEDs were different from the reported correlations for blue or green LEDs. This discrepancy should be due to different diffusion, localization, and recombination dynamics of electron-hole pairs generated in InGaN active layers, and should be a very important property for influencing the optical properties of LEDs. In order to explain the results, we proposed a possible carrier dynamics model based on the carrier localization and partial reduction of the quantum confinement Stark effect depending on an indium composition in InGaN active layers. By using this model, we also considered the origin of the reduction of the emission efficiencies with a longer emission wavelength of InGaN LEDs with high indium composition.