Quantum confinement in amorphous TiO₂films studied via atomic layer deposition

Abstract

Despite the significant recent increase in quantum-based optoelectronics device research, few deposition techniques can reliably create the required functional nanoscale systems. Atomic layer deposition (ALD) was used here to study the quantum effects attainable through the use of this ångström-level controlled growth process. Size-dependent quantum confinement has been demonstrated using TiO(2) layers of nanoscale thickness applied to the surfaces of silicon wafers. TiO(2) films were deposited at 100 °C using TiCl(4) and H(2)O(2) in a viscous flow ALD reactor, at a rate of 0.61 Å/cycle. The low-temperature process was utilized to guarantee the amorphous deposition of TiO(2) layers and post-deposition thermal annealing was employed to promote crystallite-size modification. Hydrogen peroxide significantly reduced the residual chlorine that remained from a typical TiCl(4)-H(2)O ALD process at this temperature, down to 1.6%. Spectroscopic ellipsometry was used to quantify the optical properties both below and above the bandgap energy. A central composite design was employed to map the surface response of the film thickness-dependent bandgap shift for the as-deposited case and up to a thermal annealing temperature of 550 °C. The Brus model was used to develop a correlation between the amorphous TiO(2) film thickness and the quantum length to promote equivalent bandgap shifts.

Titania/alumina bilayer gate insulators for InGaAs metal-oxide-semiconductor devices

“…The extracted band gap values are 3.6 6 0.2 eV for TiO 2 and 6.7 6 0.2 eV for Al 2 O 3 , which are in good agreement with literature for amorphous phase Al 2 O 3 and TiO 2 . 17 Based on these findings, we can plot the band alignment diagram of the TiO 2 /Al 2 O 3 /InGaAs system (Fig. 4(c)), where the conduction band offset was calculated by the equation…”

Kinetic Monte Carlo simulations and cross-sectional scanning tunneling microscopy as tools to investigate the heteroepitaxial capping of self-assembled quantum dots

“…At the moment, only a few techniques, e.g. reflection high energy electron diffraction (RHEED) 19 , in-situ accumulated stress measurements 20 , and spectroscopic ellipsometry 21 , can give real time information during the growth and thereby help monitoring the growth. But if such techniques provide valuable information about the growth surface, the averaging nature of the techniques make them of little use when study atomic-scale processes such as intermixing or segregation.…”

Deposition temperature dependence of titanium oxide thin films grown by remote‐plasma atomic layer deposition

“…Therefore, if pure anatase TiO 2 phase with high thermal stability were synthesized, many more applications using anatase TiO 2 would be realized. TiO 2 thin films have been fabricated by many different physical and chemical deposition methods [14,15] [16,17]. The metal-organic precursors, which are used extensively in the thermal ALD process (ozone-or water-based), often produce the critical problems of high impurity content and low film density due to insufficient reactivity with reactants.…”