Spatially dependent carrier dynamics in single InGaN/GaN core-shell microrod by time-resolved cathodoluminescence

Abstract

The optical properties of InGaN/GaN core-shell microrods are studied by time-resolved cathodoluminescence. Probing the carrier dynamics along the length of the rod from 4 to 300 K enables us to decompose radiative (τr) and non-radiative (τnr) lifetimes. At 300 K, τnr decreases from 500 at the bottom of the rod to 150 ps at its top. This variation results from an increased In-content in the upper part of the rod that causes a higher density of point defects. We further observe that thanks to the use of nonpolar m-plane growth, τr remains below 1.5 ns up to room temperature even with a thick active layer, which is promising for pushing the onset of the efficiency droop to higher current densities.

Efficient Carrier Recombination in InGaN Pyramidal µ-LEDs Obtained through Selective Area Growth

“…The above observations suggest that a higher indium content was incorporated into the top of the pyramid. As already mentioned before, the variations in MQW thickness and composition along the semi-polar plane were induced by a limited gas diffusion towards the pyramid base, or in other words, a higher flow of precursors near the top [25,26]. This matches well with the TEM observation shown in Figure 2.…”

Progress and Challenges of InGaN/GaN-Based Core–Shell Microrod LEDs

“…Thus, the variations in the bandgap of the different active areas of the microrods that lead to multiple EL peak also cause inhomogeneities in both color and EL intensity across the microrod LED chip. For a microscopic analysis of the microrod active region, photoluminescence (PL) mapping [44,46,48]and cathodoluminescence (CL) measurements [16,21,40,45,[49][50][51][52][53]were performed by different groups to gain insight into the various spectral contributions of the EL. Cathodoluminescence (CL) uses an electron beam scanning the sample and generating electron-hole pairs which recombine.…”

“…The IQE at low excitation is influenced by nonradiative losses, while, at high excitation conditions, the droop phenomenon occurs [ 14 ]. Spatially resolved IQE measurements show a higher IQE at the bottom than at the tip, attributed to a higher In-content and, hence, a higher defect density close to the tip [ 44 , 45 ].…”

Characterisation of Semiconductor Nanowires by Electron Beam Induced Microscopy and Cathodoluminescence

“…In the same vein, similar measurements were performed on an energy gradient in InGaN/GaN core-shell NWs, where the picosecond TR-CL helps to characterize the hopping process between localized states 104 . As a final example, by probing the carrier dynamics with a nanometer spatial and picosecond time resolution, picosecond TR-CL has been used to characterize the internal quantum efficiency of NW LEDs 105 .…”