Microrod carrier dynamics map out potential ability to offset LED efficiency losses at high current
Microrod carrier dynamics map out potential ability to offset LED efficiency losses at high current lead image
Embedding certain nano- and microstructure into the active region of LEDs will mitigate a problematic efficiency drop they suffer at high current densities. Above 10 amps per square centimeter, the high carrier densities suffer from Auger recombination. Core-shell InGaN/GaN microrods can potentially alter the carrier dynamics to prevent this Auger annoyance.
Using a time-resolved cathodoluminescence (CL) method, authors report in Applied Physics Letters nanoscale, spatially resolved, radiative and nonradiative lifetimes of core-shell InGaN/GaN microrods. The carrier dynamics insight offered with this level of precision is a valuable asset in optimizing the efficiency of LEDs.
These microrods each feature a single quantum well (QW) at the sidewall of the rod, the result of a growth technique called selective areas metalorganic vapor phase epitaxy (MOVPE). The authors probed the rods using time-resolved CL, taking measurements over a 4 to 300 Kelvin range in temperature to discern the radiative and nonradiative lifetimes.
“Our study demonstrates that the core-shell microrod has short radiative lifetimes (< 1.5 nanoseconds),” said co-author Wei Liu, “which means the injected carriers would transfer to photons efficiently, rather than building up high carrier density in the active [LED] region.” The short radiative lifetimes exist, notably, even at room temperatures and with thick active layers. These promising carrier dynamics could increase the current density threshold of LEDs’ efficiency droop.
The time-resolved CL technique is a powerful tool for characterizing a variety of nanostructures for optoelectronics devices, which Liu looks to continue using. “I am interested in studying the carrier dynamics in the nanostructures, such as dislocation and alloy disorder in III-nitride materials, quantum dots for single photon sources, 2-D materials, etc.,” he said.
Source: “Spatially dependent carrier dynamics in single InGaN/GaN core-shell microrod by time-resolved cathodoluminescence,” by W. Liu, C. Mounir, G. Rossbach, T. Schimpke, A. Avramescu, H.-J. Lugauer, M. Strassburg, U. Schwarz, B. Deveaud, and G. Jacopin, Applied Physics Letters (2018). The article can be accessed at https://doi.org/10.1063/1.5009728 .
