David Mandia1 Angel Yanguas-Gil1 Joseph Libera1 Jeffrey Elam1

1, Argonne National Laboratory, Lemont, Illinois, United States

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).