The contribution of reduction of threading dislocation densities (TDDs) to optical properties is investigated for
InGaN/GaN light-emitting diodes (LEDs) grown on sapphire substrate. The external quantum efficiency (EQE) curves
depending on the TDDs are discussed both theoretically and experimentally. At the current density of <20 A/cm2, the
EQE increases with decreasing the edge-type TDD from 5 e8/cm2 to 2 e8/cm2. The current density at the maximum EQE
shifts to lower value as the edge-type TDD decreases, whereas the EQE presents no remarkable difference in the highercurrent
density range irrespective of the TDD. According to the rate equation (ABC) model, the peak shift reflects the
Shockley-Read-Hall non-radiative process (A coefficient). Analysis of the photoluminescence (PL) decay and the
dependence of integrated PL intensity on excitation power reveals that the threading dislocations act as non-radiative
recombination centers in the multiple quantum well active region. The TDD of <2 e8/cm2 is required for highly efficient
blue LEDs operating at current density of around 15 A/cm2, whereas the TDD of <5 e8/cm2 in required for the LEDs
operating at around 50 A/cm2.
Yoshiyuki Harada, Toshiki Hikosaka, Shigeya Kimura, Maki Sugai, Hajime Nago, Koichi Tachibana, Naoharu Sugiyama, Shinya Nunoue, "Effect of dislocation density on efficiency curves in InGaN/GaN
multiple quantum well light-emitting diodes," Proc. SPIE 8278, Light-Emitting Diodes: Materials, Devices, and Applications for Solid State Lighting XVI, 82780J (6 February 2012);