Kavli Affiliate: Grace Xing
| First 5 Authors: Len van Deurzen, Mikel Gómez Ruiz, Kevin Lee, Henryk Turski, Shyam Bharadwaj
| Summary:
This report classifies emission inhomogeneities that manifest in InGaN
quantum well blue light-emitting diodes grown by plasma-assisted molecular beam
epitaxy on free-standing GaN substrates. By a combination of spatially resolved
electroluminescence and cathodoluminescence measurements, atomic force
microscopy, scanning electron microscopy and hot wet KOH etching, the
identified inhomogeneities are found to fall in four categories. Labeled here
as type I through IV, they are distinguishable by their size, density, energy,
intensity, radiative and electronic characteristics and chemical etch pits
which correlates them with dislocations. Type I exhibits a blueshift of about
120 meV for the InGaN quantum well emission attributed to a perturbation of the
active region, which is related to indium droplets that form on the surface in
the metal-rich InGaN growth condition. Specifically, we attribute the blueshift
to a decreased growth rate of and indium incorporation in the InGaN quantum
wells underneath the droplet which is postulated to be the result of reduced
incorporated N species due to increased N$_{2}$ formation. The location of
droplets are correlated with mixed type dislocations for type I defects. Types
II through IV are due to screw dislocations, edge dislocations, and dislocation
bunching, respectively, and form dark spots due to leakage current and
nonradiative recombination.
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