Interrelation Between the Internal Quantum Efficiency and Forward Voltage of Blue LEDs

In InGaN/GaN multiple-quantum-well (MQW) light-emitting diodes (LEDs), carrier accumulation in MQWs due to the saturation of the radiative recombination rate affects the internal-quantum-efficiency (IQE) and forward-voltage (<inline-formula> <tex-math notation="LaTeX">${V} _{\text {F}}$ </tex-math></inline-formula>) characteristics simultaneously. In this letter, we investigate the interrelation between the IQE and <inline-formula> <tex-math notation="LaTeX">${V} _{\text {F}}$ </tex-math></inline-formula> at an operating current density, using 31 blue LEDs with MQW active layers grown under slightly different conditions. The general trend observed demonstrates that <inline-formula> <tex-math notation="LaTeX">${V} _{\text {F}}$ </tex-math></inline-formula> decreases as the IQE increases. We analyze this interrelation between the IQE and <inline-formula> <tex-math notation="LaTeX">${V} _{\text {F}}$ </tex-math></inline-formula> through separation of radiative and nonradiative current densities, and propose to use the active efficiency (AE) to quantify the performance of the active layer more precisely. We examine the two cases where only the radiative (nonradiative) current density changes and establish that the increase of the radiative current density is more desirable than the decrease of the nonradiative current density in improving the AE of the device.