Understanding droop effect by analysis on carrier density dependence in InGaN/GaN multiple-quantum-well light-emitting diodes

• The rate equations are used to determine the carrier density n in LEDs.
• For the same injection current I, the carrier density n may be different.
• The efficiency-I droop curve is different from the efficiency-n one.
• The efficiency-n relationship may better reflect the physical mechanism of droop.

The droop behaviors of two InGaN/GaN multiple-quantum-well blue-green light-emitting diodes grown on c-plane sapphires with different In content are investigated. The higher-In-content sample exhibits a lower efficiency, followed by a more significant droop as current increases in comparison with the lower-In-content diode. However, it is found that for both samples their efficiency reduction trend with increasing carrier density is nearly the same. Combining with the recombination rate equations, an analysis reveals that at the same injection current level, the carrier density in the higher-In-content quantum wells which have stronger polarization effect is larger due to the smaller bimolecular recombination coefficient, resulting in a more significant droop with current. Therefore, a study on the dependence of efficiency on carrier density can provide a clear elucidation to the physical mechanism of the efficiency droop behavior.