Atomic distribution in Inx Ga1-x N single quantum wells studied by extended x-ray absorption fine structure

The anisotropy of the local structure around In atoms in high quality Inx Ga1-x N (x=0.145,0.20,0.275) single quantum wells (SQWs) was investigated by fluorescence extended x-ray absorption fine structure measurements using linearly polarized x ray whose electric field was set to be both horizontal and vertical to the SQWs. The interatomic distance was isotropic for the nearest In-N, whereas for the second nearest In-Ga and In-In, the interatomic distance for out-of-plane atoms was longer than that for in-plane atoms. From the analyses of the coordination number for In-In and In-Ga, the In atom distribution in the In0.275 Ga0.725 N SQW was found to be statistically random in both directions. On the other hand, In atoms in the In0.20 Ga0.80 N SQW, corresponding to green light-emitting diodes (LEDs), were randomly distributed in the horizontal direction but aggregated in the vertical direction. Correlation was suggested between the vertical aggregation and the higher efficiency of InGaN-based blue to green LEDs.