Phase Competition and Rutile Phase Stabilization of Growing GeO2 Films by MOCVD

TL;DR

This paper presents a seed-driven stepwise crystallization method for growing phase-pure rutile GeO2 films via MOCVD, overcoming polymorphic competition and enabling phase-selective thin-film engineering.

Contribution

Introduction of SDSC, a segmented growth strategy, for stabilizing rutile GeO2 films on TiO2 substrates during vapor phase deposition.

Findings

Achieved continuous, phase-pure rutile GeO2 films with low x-ray rocking curve FWHM.

Demonstrated suppression of non-rutile phases through SDSC growth cycles.

Provided insights into phase selection mechanisms during vapor phase growth.

Abstract

Rutile germanium dioxide (r-GeO2) is an ultra-wide bandgap semiconductor with potential for ambipolar doping, making it a promising candidate for next-generation power electronics and optoelectronics. Growth of phase-pure r-GeO2 films by vapor phase techniques like metalorganic chemical vapor deposition (MOCVD) is challenging because of polymorphic competition from amorphous and quartz GeO2. Here, we introduce seed-driven stepwise crystallization (SDSC) as a segmented growth strategy for obtaining r-GeO2 films on r-TiO2 (001) substrate. SDSC divides the growth into repeated cycles of film deposition and cooling-heating ramps, which suppress the non-rutile phases. We discuss the underlying mechanisms of phase selection during SDSC growth. We demonstrate continuous, phase-pure, partially epitaxial r-GeO2 (001) films exhibiting x-ray rocking curves with a FWHM of 597 arcsec. SDSC-based growth provides a generalizable pathway for selective vapor-phase growth of metastable or unstable phases, offering new opportunities for phase-selective thin-film engineering.