Advanced Analysis Techniques for III-Nitride Opto-Electronic Devices

The continuous optimization of gallium nitride (GaN) based LEDs lead to increasingly complex epitaxial layer structures. In addition to planar LEDs, 3-dimensional micro structures are widely investigated. The development of these devices requires fast and accurate characterization techniques to determine the elemental composition of the layers as well as their optical performance.

In this work, plasma profiling time-of-flight mass spectrometry was used for elemental depth profiling with high depth resolution at short acquisition times. Regarding the optical characterization, cathodoluminescence (CL) inside a SEM provides optical information with high spatial resolution. CL was compared to resonant and non-resonant photoluminescence on a high-efficiency blue LED utilizing time-resolved measurements.

3D-structures in the form of GaN/AlGaN core-shell microfins, serving as a model system for non-polar UV emitters with low defect density, were investigated via time-resolved CL. A rate equation based analysis allowed the separation of radiative and non-radiative lifetimes, which enabled to estimate an internal quantum efficiency (IQE) of 40 ± 6 %. This analysis is an important step for IQE determination using CL, as temperature-dependent carrier trapping processes, which can significantly affect the emission intensity, have reduced influence on the carrier lifetime of non-polar structures.