Explanation of low efficiency droop in semipolar (202¯1¯) InGaN/GaN LEDs through evaluation of carrier recombination coefficients
We report the carrier dynamics and recombination coefficients in single-quantum-well semipolar (202̅1̅) InGaN/GaN light-emitting diodes emitting at 440 nm with 93 differential carrier lifetime is analyzed for various injection current densities from 5 A/cm^2 to 10 kA/cm^2, and the corresponding carrier densities are obtained. The coupling of internal quantum efficiency and differential carrier lifetime vs injected carrier density (n) enables the separation of the radiative and nonradiative
... bination lifetimes and the extraction of the Shockley-Read-Hall (SRH) nonradiative (A), radiative (B), and Auger (C) recombination coefficients and their n-dependency considering the saturation of the SRH recombination rate and phase-space filling. The results indicate a three to four-fold higher A and a nearly two-fold higher B_0 for this semipolar orientation compared to that of c-plane reported using a similar approach [A. David and M. J. Grundmann, Appl. Phys. Lett. 96, 103504 (2010)]. In addition, the carrier density in semipolar (202̅1̅) is found to be lower than the carrier density in c-plane for a given current density, which is important for suppressing efficiency droop. The semipolar LED also shows a two-fold lower C_0 compared to c-plane, which is consistent with the lower relative efficiency droop for the semipolar LED (57 vs. 69 (Auger) coefficient are directly responsible for the high efficiency and low efficiency droop reported in semipolar (202̅1̅) LEDs.