Well Thickness Dependence of the Internal Quantum Efficiency and Carrier Concentration in GaN-Based Multiple Quantum Well Light-Emitting Diodes

The internal quantum efficiency (IQE) dependence characteristics of seven-well multiple quantum well (MQW) GaN-based light-emitting diodes (LEDs) on well thickness were obtained based on the rate equation without setting specific values for the coefficients. The IQE increased with increasing well thickness until the thickness reached 3.0 nm, where the IQE reached a maximum, and then decreased with further increases in well thickness. This IQE well thickness dependence is consistent with that of the measured light emission efficiency. In addition, using various values of the radiative recombination coefficient B , which contained the effects of the carrier density and polarization fields (and was thus dependent on the well thickness), we calculated the rate coefficients. The results indicate that the main factor that is limiting the well thickness dependence of the IQE is Shockley–Read–Hall (SRH) nonradiative recombination. Also, at B = 10 10 cm 3 s −1 in a 3.0 nm thick well, the optimal values in the rate equation of A , corresponding to the SRH nonradiative recombination, and C , corresponding to the carrier leakage (or Auger recombination), are 2.25 × 10 8 s −1 and 9.2 × 10 −31 cm 6 s −1 , respectively. Also, at a given current, the maximum carrier concentration and the minimum radiative recombination lifetime were achieved using a 3.0 nm well thickness. Overall, for the seven-well MQW InGaN/GaN LEDs studied, the optimal well thickness was 3.0 nm.