Interfacial band alignment and structural properties of nanoscale TiO2 thin films for integration with epitaxial crystallographic oriented germanium

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.

Germanium Based Field-Effect Transistors: Challenges and Opportunities

“…Crystallographic-orientation agnostic TiO 2 -based MIS contacts may be particularly useful in the next generation of Ge FinFETs, where different Ge orientations can be exploited to facilitate mobility enhancement for n - and p -channel devices [148]. …”

“…This is the primary mechanism behind the metal-insulator-semiconductor (MIS) contact to Ge [ 145 ]. The insertion of thin potential barriers, such as that provided by thin layers of Al 2 O 3 [ 146 ], SiN 3 [ 147 ], TiO 2 [ 145 , 148 ], ZnO [ 24 ], Ge 3 N 4 [ 149 ], GeO x [ 150 , 151 ], MgO [ 152 , 153 ], and Y 2 O 3 [ 154 ] have been shown to reduce the Schottky barrier height as well as facilitate the unpinning of Fermi-level in n-type Ge.…”

“…It has been recently reported that the lower CBOs obtained for the crystallographic oriented TiO 2 /Ge system, irrespective of the Ge crystallographic orientation, presents a potential for employing a TiO 2 insulating layer for MIS contact applications. Crystallographic-orientation agnostic TiO 2 -based MIS contacts may be particularly useful in the next generation of Ge FinFETs, where different Ge orientations can be exploited to facilitate mobility enhancement for n - and p -channel devices [ 148 ].…”

TiO2/Bi2S3 core–shell nanowire arrays for photoelectrochemical hydrogen generation

“…[8][9][10][11][12][13][14] Despite these advantages, the photoconversion efficiencies of TiO 2 NWA photoanodes are extremely depressed due to the large energy band gap (3.0 eV for rutile TiO 2 ). 15,16 This large energy band gap restricts their solar energy utilization only in the ultraviolet region. Therefore, considerable efforts have been made to enhance their visible light harvesting ability.…”

Effects of Carbon Incorporation on Electrical Characteristics and Thermal Stability of Ti/TiO2/n-Ge MIS Contact

“…As an ultrathin insulator is inserted between metal and semiconductor as an interfacial layer, the penetration of the electron wave function from a metal into a semiconductor could be reduced; this suppresses the FLP effect [10,11]. Among several high-k dielectrics, titanium dioxide (TiO2) is a promising candidate as an interfacial layer of MIS contact because of negligible conduction band offset (CBO) on an n-Ge (100) substrate and its relatively high conductivity, which contributes to the low tunneling resistance of MIS contacts [12][13][14]. However, considering that the high thermal budget process after the formation of S/D contact such as conventional back-end-of-line (BEOL) processes, the thermal stability of MIS contacts in the n-Ge device must be guaranteed above 400 ℃ to achieve the low S/D contact resistance.…”