EAGER: Collaborative Research: Epitaxial Stabilization of Polar Epsilon-phase Gallium Oxide Thin Films

Washington University, Saint Louis MO

Investigators

Abstract

Non-technical description: Semiconductors and ferroelectrics are ubiquitous electronic materials. In semiconductors, the conductivity can be tuned using doping and the velocity of charge carriers in typical semiconductors used for device applications is large. Ferroelectric materials exhibit inherent electric polarization that can be reversed using an external electric field; however charge carriers in ferroelectrics typically have lower electron velocity. This research aims at combining both the properties in a single material by stabilizing a new ferroelectric semiconductor based on the metastable, epsilon phase of gallium oxide. This project is an early effort on developing a fundamental understanding of how the structure and synthesis conditions of epsilon-phase gallium oxide affects its material properties. Theoretical studies and predictions guide the experimental efforts. By combining the properties of semiconductors and ferroelectrics in epsilon-phase gallium oxide, this project aims to unlock its potential, prospects and limitation for devices with multiple functionalities, such as power, high frequency, and memory, all in a single materials platform. The project provides training to undergraduate and graduate students and a post-doctoral scholar to synergistically combine theory and modeling, advanced material synthesis, and materials characterization to develop fundamental structure-property correlations in this new class of materials. Technical description: The metastable, epsilon phase of gallium oxide has been predicted to be a rare, ferroelectric semiconductor with an ultra-wide band gap. This project seeks to stabilize epsilon-phase gallium oxide using epitaxy and demonstrate electric-field switching of polar domains. The research employs a combination of first-principles density-functional theory calculations and metal-organic vapor phase epitaxy to grow epsilon gallium oxide thin films on various predicted substrates and control their quality. It uses a variety of characterization techniques, including aberration-corrected scanning transmission electron microscopy, to characterize the structure, electrical, optical and polar properties of the deposited thin-films and develop structure-property-processing correlations. The realization of high-quality ferroelectric semiconductor based on epsilon-phase gallium oxide is expected to open up pathways to design novel devices for power and high-frequency electronics, information storage and processing applications. Education and outreach aspects include training of undergraduate and graduate students and the organization of a summer program for high-school students and teachers from Utah-region schools to the Utah Nanofab and epitaxy facility to provide exposure to nanotechnology. This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.