Influence of the atomic layer deposition temperature on the structural and electrical properties of Al/Al2O3/p-Ge MOS structures

Abstract

The influence of deposition temperature on the structural, chemical, and electrical properties of atomic layer deposition (ALD)-Al2O3 thin films is investigated. ALD-Al2O3 films were deposited on p-type Ge substrates at 80, 150, 200, 250, and 300 °C. The atomic force microscopy analysis reveals smooth and cohesive films with extremely low roughness (0.2–0.6) nm at 150, 200, 250, and 300 °C. On the contrary, Al2O3 films deposited at the lowest available deposition temperature (80 °C) exhibit holes and aggregates implying a nonhomogeneous deposition. The x-ray photoelectron spectroscopy (XPS) analysis indicates the presence of stoichiometric Al2O3 films at all deposition temperatures. The calculated thickness from the analysis of XPS spectra seems to be in good agreement with the ALD nominal thickness for the films deposited at all deposition temperatures except the one of 80 °C. Transmission electron microscopy (TEM) analysis reveals a flat interface between Al2O3 and p-Ge in an atomic level. In addition, TEM and XPS analyses indicate the absence of any oxidized interlayer between p-Ge and Al2O3 films. Furthermore, C-V, G-V, C-f, G-f, and J-V measurements were performed in order to study the electrical properties and evaluate the density of interfacial traps (Dit) of the structures prior and following forming gas annealing procedure. Forming gas annealing clearly improves the electrical response of all tested structures, as expected, by reducing significantly the “streching out” effect and the frequency dispersion at the depletion regime. Leakage currents and Dit in the order of 10−4 A/cm2 (for applied voltage 1 V) and 1011 eV−1 cm−2, respectively, were measured-calculated for all tested structures.