AVS 58th Annual International Symposium and Exhibition
    Thin Film Division Monday Sessions
       Session TF-MoM

Invited Paper TF-MoM2
Flux and Surfactant-Assisted Physical Vapor Deposition: New Approaches for Improving Complex Oxide Thin Film Growth

Monday, October 31, 2011, 8:40 am, Room 107

Session: Thin Films: Growth and Characterization I
Presenter: Jon-Paul Maria, North Carolina State University
Authors: J.-P. Maria, North Carolina State University
E.A. Paisley, North Carolina State University
B.E. Gaddy, North Carolina State University
M.D. Biegalski, Oak Ridge National Laboratory
D.L. Irving, North Carolina State University
A.R. Rice, North Carolina State University
R. Collazo, North Carolina State University
Z. Sitar, North Carolina State University
Correspondent: Click to Email
Epitaxial integration of complex oxides with wide band gap polar semiconductors such as GaN (0002) presents the possibility for high-power, high-frequency, and high temperature GaN electronics by virtue of 2-D charge carriers at polar interfaces and possible access to non-linear dielectric properties. This work describes synthesis and characterization of such thin film heterostructures by MBE, with specific attention given to controlling film growth. Our previous work has shown growth of high-quality MgO (111) and CaO (111) films on GaN with measured valence band offsets > than 1 eV and conduction band offsets ~ 3.2 eV (MgO) and ~2.5 eV (CaO). However, the terminal 3D rocksalt growth surface is determined by the tendency for the high-energy (111) polar orientation to form (100)-oriented low-energy facets, and the interfacial symmetry between cubic MgO and hexagonal GaN. Therefore, realizing smooth oxide films on GaN requires the ability to overcome the rocksalt (001) faceting tendency through a surfactant growth method. In this presentation we will discuss a newly-developed surfactant approach to MBE growth of rocksalt oxides utilizing water vapor to hydroxylate CaO and MgO (111) surfaces in situ, which changes the equilibrium habit from cubic to octahedral, eliminating the (100) faceting tendency. RHEED oscillations and AFM images of these films show 2D growth, suggesting that altering the surface chemistry during growth plays a critical role in determining the surface orientation. We demonstrate through electrical property measurements the impact of smooth (111) rocksalt surfaces as leakage current densities for thin CaO films are reduced by two orders of magnitude when films of equivalent thickness are grown using a 2-D vs. a 3-D mode. Finally, we will present a set of temperature ab-initio thermodynamic calculations of CaO surface energies with and without H-containing terminations that validate the surface-chemical mechanism of facet stabilization.