Revisiting the “In-clustering” question in InGaN through the use of aberration-corrected electron microscopy below the knock-on threshold

Abstract

The high intensity of light emitted in In[subscript x]Ga[subscript 1−x]N/GaN heterostructures has been generally attributed to the formation of indium-rich clusters in In[subscript x]Ga[subscript 1−x]N quantum wells (QWs). However, there is significant disagreement about the existence of such clusters in as-grown In[subscript x]Ga[subscript 1−x]N QWs. We employ atomically resolved CS-corrected scanning transmission electron microscopy and electron energy loss spectroscopy at 120 kV—which we demonstrate to be below the knock-on displacement threshold—and show that indium clustering is not present in as-grown In[subscript 0.22]Ga[subscript 0.78]N QWs. This artifact-free, atomically resolved method can be employed for investigating compositional variations in other In[subscript x]Ga[subscript 1−x]N/GaN heterostructures.