Interfacial Characterization and Transport Conduction Mechanisms in Al|HfO2|p-Ge Structures: Energy Band Diagram

Abstract Ge-based metal-oxide semiconductor structures exhibiting thin ALD-grown high-k dielectric HfO2 films were fabricated and characterized chemically, structurally, and electrically. X-ray photoelectron (XP) spectroscopy confirms the good stoichiometry of the ALD-grown HfO2 films. Furthermore, through the analysis of the XP spectra, the conduction and valence band offsets of HfO2|p-Ge were calculated to be equal to 1.8 ± 0.2 eV and 2.8 ± 0.2 eV, respectively. C(V) and G(V) analysis reveals structures with a well-defined MOS behavior with Dit values in the range of 1011 eV–1 cm–2 and a dielectric constant of HfO2 films of 20. The dominant carrier transport conduction mechanisms were studied through J(V) analysis, performed at both substrate and gate electron injection. Specifically, in the low voltage region (V < 0.2 V), the prevailing conduction mechanism is Ohmic, with an activation energy of 0.28 eV for both substrate and gate electron injection. In the voltage range 0.4–1.5 V, the dominant conduction mechanism is Frenkel–Poole, through which the trap energy level into HfO2 films (φt) is calculated to be φt = 0.36 eV. Schottky conduction mechanism is the prevailing one, for high applied bias voltages (V > 3.0 V) and high temperatures (>450 K). Applying Schottky’s emission model the energy barrier heights of HfO2|p-Ge and Al|HfO2 interfaces were evaluated equal to 1.7 ± 0.2 eV and 1.3 ± 0.2 eV, respectively. Combining the XPS and J(V) analysis results, the energy band diagram of Al|HfO2|p-Ge structures is constructed. The calculated values of conduction and valence band offsets via XPS and J(V) measurements are in very good agreement.