Abstract
Al2O3 is used to form Al2O3/GaN and Al2O3/Si heterostructures for many electronic and optoelectronic devices. Yet the origins of the positive interfacial charges in the Al2O3/GaN heterostructure and negative interfacial charges in the Al2O3/Si heterostructure are often elusive. Herein, in-depth studies of the Al2O3/GaN and Al2O3/Si heterostructures are conducted, especially on how the atomic coordination structure affects the interfacial charges. It is discovered that the octahedral [AlO6](9-) coordination surpassed tetrahedral [AlO4](5-) coordination at the Al2O3/GaN interface, whereas tetrahedral [AlO4](5-) coordination dominated at the Al2O3/Si interface. Therefore, the interfacial charge polarity is correlated with the nonstoichiometry atomic coordination of Al2O3 at the two interfaces. This study reveals the atomic origin of charge polarity at high-k/semiconductor interfaces and could facilitate the development of high-performance optoelectronic and electronic devices through engineering the atomic coordination structure of the high-k materials.