The search for adequate binary metal oxide dielectric nanolaminates (NLs) to prevent degradation of power semiconductor devices is ongoing and involves the atomic layer deposition (ALD)-growth of a variety of binary metal oxide combinations. In the present work, we explore the ALD growth of amorphous (x)HfO2/(y)Al2O3 NLs on Si (with native SiO2 layer) substrates and then on both GaN and Ga2O3 single crystals. A variety of samples ranging from their homogeneous mixtures to HfO2 or Al2O3-rich NLs are assessed before and after a thermal annealing by spectroscopic ellipsometry (SE), XAS techniques such as X-ray photoelectron spectroscopy (XPS) and X-ray absorption fine structure (EXAFS) measurements in order to elucidate the structural evolution of the NL at the GaN (or Ga2O3)-NL interface. By quantifying the HfO2 incorporation throughout the Al2O3 layer and using the programmable nature of ALD to alternate layers of the HfO2 and Al2O3 in an (AB)x-(CD)y fashion, the influence of HfO2 mobility within Al2O3 layer on the NL dielectric constant can be verified unequivocally. EXAFS is a powerful tool for determining the local coordination environment of the Hf at the GaN (or Ga2O3(001))-HfO2 interface and, at low super-cycle numbers (sub-nm scale), the ultimate stability of the NLs can be probed and optimized such that the bulk material properties are retained. Finally, via a modified Kraut’s method,1 Ultraviolet photoelectron spectroscopy (UPS) is used to obtain the valence band maximum (VBM) of the GaN and Ga2O3(001) substrates and combined with the high-resolution XPS data for the Hf and Ga shallow core-level photoelectrons ejected from the thin HfO2/Al2O3 overlayer in order to assess the conduction band offset (CBO) at the film-substrate heterojunction. Probing the insulator properties imparted by the high-k overlayer on the wide bandgap semiconductor surfaces of GaN and Ga2O3(001) is crucial in order to understand and prevent the degradation problem in Ga2O3/GaN-based power semiconductor devices.
1 E.A. Kraut, R.W. Grant, J.R. Waldrop, S.P. Kowalczyk, Phys. Rev. Lett. 44, 1620 (1980).