Comparison of electrical and interfacial characteristics between atomic-layer-deposited AlN and AlGaN on a GaN substrate

The electrical and interfacial characteristics of AlN/GaN and AlGaN/GaN heterostructures prepared by thermal atomic layer deposition (ALD) were investigated in this work. According to the parallel conductance method, the AlGaN/GaN sample showed two border traps with energies of ~ 0.38 and ~ 0.46 eV, which were not observed for the AlN/GaN sample. The AlN/GaN sample also showed a lower interface trap density and a lower reverse leakage current. X-ray photoelectron spectroscopy analysis indicated that during the initial ALD deposition process, most of the Al and N atoms tended to combine with oxygen atoms as opposed to Ga atoms. As a result, AlGaN layer formation was delayed, resulting in the creation of a defective interfacial layer at the AlGaN/GaN interface. Thus, our results indicate that the initial ALD process should focus on removing the defective interfacial layer during AlGaN deposition for device optimization.