Nucleation and Stochiometry Dependence of Rutile-TiO 2 (001)/GaN(0001) Thin Films Grown by Plasma-Assisted Molecular Bea

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1108-A09-32

Nucleation and Stoichiometry Dependence of rutile-TiO2(001)/GaN(0001) Thin Films Grown by Plasma-Assisted Molecular Beam Epitaxy Costel Constantin1, Kai Sun2, R. M. Feenstra3 1 Seton Hall University, 400 South Orange Ave, South Orange, NJ 07079, U.S.A. 2 University of Michigan, Ann Arbor, Michigan 48109-2143 3 Dept. Physics, Carnegie Mellon University, Pittsburgh, PA 15213 ABSTRACT

In this work we explore both the initial nucleation and the stoichiometry of rutileTiO2(001) grown on wurtzite GaN(0001) by radio-frequency O2-plasma molecular beam epitaxy. Two studies are performed; in the first, the dependence of the growth on stoichiometry (Ti-rich and O-rich) is observed using reflection high energy electron diffraction and high resolution transmission electron microscopy. In the second study we examine the effect of different initial nucleation surfaces (i.e. Ga-terminated and excess Ga-terminated) and compare the interfaces and bulk crystallinity of the TiO2(001) films grown on top of these surfaces. High-resolution transmission electron microscopy and x-ray diffraction measurements show a better interface for TiO2(001)/Ga-terminated - GaN(0001) as compared to the TiO2(001)/excess Ga-terminated GaN(0001). INTRODUCTION Considerable interest has been shown of late in transition-metal oxides. One case is the titanium dioxide system, which can have applications as a high-k dielectric gate insulator for Sibased devices1. In this work we explore the growth of rutile-TiO2(001) on wurtzite GaN(0001) by oxygen plasma-assisted molecular beam epitaxy. We study the dependence of the growth on both the stoichiometry of the TiO2(001) film. From reflection high-energy electron diffraction (RHEED) we find 2-dimensional growth for the Ti-rich growth conditions and 3-dimensional for O-rich. We also examine the influence of the GaN termination on the growth, using GaN films that are terminated with a Ga-bilayer or that have additional Ga on the surface (Ga-terminated and excess Ga-terminated, respectively). For the latter case we find in x-ray diffraction (XRD) measurements the presence of additional peaks at 2θ = 52.95836° ± 0.00693, which implies the existence of additional phases besides the rutile TiO2(001). In addition, high-resolution transmission electron microscopy (HRTEM) performed on these samples show a higher degree of disorder for the films grown on top of excess Ga-terminated, as compared to the samples grown on top of the Ga-terminated surface. EXPERIMENT The growth experiments are performed in a hybrid oxide-nitride MBE system utilizing gallium effusion cell as a Ga source, and mini-Ti ball titanium sublimation pump as a titanium source. The O2 and N2 gases were delivered through a custom designed hybrid rf-plasma source; the O2 and N2 flow rates were in the range of 1.80 – 3.17, and 1.83 sccm, respectively. Throughout the entire growth, the rf-plasma power for both gases (O2 and N2) was maintained constant at 400 W. The substrates were commercially available wurtzite Ga-polar GaN(0001) grown by hydride