Fig. 2

a ω-2θ scan curves of these three GaN-based LEDs measured by the high resolution X-ray diffraction; b Indium concentrations measured by SIMS for the MQWs of these three LEDs; c, d Bright field TEM images and Indium concentrations measured by SIMS for the three pairs of quantum wells/barriers near the p-GaN of LED II and LED III: LED I is In_0.13Ga_0.87N/GaN–based LED, LED II is In_0.14Ga_0.86N/In_0.03Ga_0.97N–based LED and LED III is In_0.13Ga_0.87N/In_0.07Ga_0.93N-based LED