Band offsets and charge storage characteristics of atomic layer deposited high-k HfO2∕TiO2 multilayers

Abstract

We have investigated the structural and band alignment properties of nanoscale titanium dioxide (TiO 2) thin films deposited on epitaxial crystallographic oriented Ge layers grown on (100), (110), and (111)A GaAs substrates by molecular beam epitaxy. The TiO 2 thin films deposited at low temperature by physical vapor deposition were found to be amorphous in nature, and high-resolution transmission electron microscopy confirmed a sharp heterointerface between the TiO 2 thin film and the epitaxially grown Ge with no traceable interfacial layer. A comprehensive assessment on the effect of substrate orientation on the band alignment at the TiO 2 /Ge heterointerface is presented by utilizing x-ray photoelectron spectroscopy and spectroscopic ellipsometry. A band-gap of 3.33 6 0.02 eV was determined for the amorphous TiO 2 thin film from the Tauc plot. Irrespective of the crystallographic orientation of the epitaxial Ge layer, a sufficient valence band-offset of greater than 2 eV was obtained at the TiO 2 /Ge heterointerface while the corresponding conduction band-offsets for the aforementioned TiO 2 /Ge system were found to be smaller than 1 eV. A comparative assessment on the effect of Ge substrate orientation revealed a valence band-offset relation of DE V (100) > DE V (111) > DE V (110) and a conduction band-offset relation of DE C (110) > DE C (111) > DE C (100). These band-offset parameters are of critical importance and will provide key insight for the design and performance analysis of TiO 2 for potential high-j dielectric integration and for future metal-insulator-semiconductor contact applications with next generation of Ge based metal-oxide field-effect transistors. V C 2014 AIP Publishing LLC.

Electronic Structure and Charge-Trapping Characteristics of the Al2O3-TiAlO-SiO2 Gate Stack for Nonvolatile Memory Applications

“…One of the reasons may be that the films were deposited by electron beam evaporation, which is likely to have lots of defects that could limit the P/E performance of the memory device. Charge-trapping memory devices fabricated by atomic layer deposition (ALD) exhibits excellent electrical performances [12, 19]. In the future, if we can use high-quality film growth method such as ALD to fabricate the dielectric stack, the electrical performance of the present TiAlO charge-trapping memory device may have a lot of space to be further improved.…”

Transmission Electron Microscopy of Multilayer Thin Films

“…In HfO 2 /TiO 2 multilayer structures the band offset is also of interest because of the potential applications of these structures in charge-trapping information storage devices. Maikap et al (129) used HREM and X-ray photoelectron spectroscopy (XPS) to analyze the interfacial abruptness in these systems and to correlate this with the charge-storage characteristics of the films. Similarly, Pennycook et al (130) used STEM-HAADF imaging to image local atomic relaxation at the interface in NiO/ZrO 2 layered films.…”

Annealing Effect of Sol-Gel TiO2 Thin Film on pH-EGFET Sensor

“…For application, anatase TiO 2 could be used in photocatalysts [6,7] and anti-reflective coating for solar cells [8,9]. In contrast, rutile TiO 2 can be applied in insulator for memory devices [10]. Furthermore, thin films TiO 2 can be formulated by using sputtering [11], molecular beam epitaxial (MBE) [12], metal-organic chemical vapor deposition (MOCVD) [13], plasmaenhanced chemical vapor deposition (PECVD) [14] and sol-gel [9,15] process, etc.…”