The Photonic Atom Probe as a Tool for the Analysis of the Effect of Defects on the Luminescence of Nitride Quantum Structures.

By collecting simultaneously optical and chemical/morphological data from nanoscale volumes, the Photonic Atom Probe (PAP) can be applied not only to the study of the relationship between optical and structural properties of quantum emitter but also to evaluate the influence of other factors, such as the presence of point defects, on the photoluminescence. Through the analysis of multiple layers of InGaN/GaN quantum dots (QDs), grown so that the density of structural defects is higher with increasing distance from the substrate, we establish that the light emission is higher in the regions exhibiting a higher presence of structural defects. While the presence of intrinsic point defects with non-radiative recombination properties remains elusive, our result is consistent with the fact that QD layers closer to the substrate behave as traps for non-radiative point defects. This result demonstrates the potential of the PAP as a technique for the study of the optical properties of defects in semiconductors.

Understanding the degradation mechanisms of InGaN/GaN multiple quantum well UV photodetectors submitted to different current stresses.

The degradation characteristics of InGaN/GaN multiple quantum well (MQW) photodetectors (PDs) stressed at 100 and 200 mA over 480 h are investigated. We have observed that the luminescence intensity, short circuit current density, and open circuit voltage decrease strongly, whereas the leakage current increases intensely due to the constant current stress. The strong activity of the Mg dopant and trap-assisted tunneling under the direct current stress are critical factors in the degradation of InGaN/GaN MQW PDs. Further, the photocurrent spectroscopy results reveal that for 100 mA stress current, the peak value of relative external quantum efficiency (EQE) slightly increases due to the widening of the space-charge region while, for the 200 mA of stress current, the peak value of EQE decreases (∼15.4%) due to some permanent damages in the active region and/or the metal/semiconductor interface, and the associated resistive effects.

Super-resolution Optical Spectroscopy of Nanoscale Emitters within a Photonic Atom Probe.

Atom Probe Tomography (APT) is a microscopy technique allowing for the 3D reconstruction of the chemical composition of a nanoscale needle-shaped sample with a precision close to the atomic scale. The photonic atom probe (PAP) is an evolution of APT featuring in situ and operando detection of the photoluminescence signal. The optical signatures of the light-emitting centers can be correlated with the structural and chemical information obtained by the analysis of the evaporated ions. It becomes thus possible to discriminate and interpret the spectral signatures of different light emitters as close as 20 nm, well beyond the resolution limit set by the exciting laser wavelength. This technique opens up new perspectives for the study of the physics of low dimensional systems, defects and optoelectronic devices.