Control of Competing Thermodynamics and Kinetics in Vapor Phase Thin-Film Growth of Nitrides and Borides.

Isao Ohkubo,Katsumitsu Nakamura,Takao Mori,Takashi Aizawa

doi:10.3389/fchem.2021.642388

Isao Ohkubo, Katsumitsu Nakamura + Show 2 more

Open Access

https://doi.org/10.3389/fchem.2021.642388

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Abstract

Thin-film growth is a platform technique that allows the preparation of various undeveloped materials and enables the development of novel energy generation devices. Preferred phase formation, control of crystalline orientation and quality, defect concentration, and stoichiometry in thin films are important for obtaining thin films exhibiting desired physical and chemical properties. In particular, the control of crystalline phase formation by utilizing thin-film technology favors the preparation of undeveloped materials. In this study, thin-film growth of transition metal nitride and rare-earth metal boride was performed using remote plasma–assisted molecular beam epitaxy and hybrid physical–chemical vapor deposition techniques, and was successfully achieved by tuning the competition between thermodynamics and kinetics during vapor-phase thin-film growth. Growth conditions of high crystalline quality titanium nitride thin films and high phase purity ytterbium boride thin films were not thermodynamically favorable. Appropriate control of the contribution degree of thermodynamics and kinetics during vapor-phase thin-film growth is crucial for fabricating high phase purity and high crystalline quality thin films.

Highlights

Thin-film technology is actively used in various fundamental research, industries, and applications, and is instrumental in providing a possible solution for preparing high-quality samples of undeveloped materials such as groups of metal borides, nitrides, and carbides, and for preparing nanostructured materials (Nishinaga and Kuech, 2015)
Phase formation, crystalline orientation and quality, defect concentration, surface morphology, and stoichiometry in thin films are influenced by thin-film growth parameters and greatly influence their properties
In the molecular beam epitaxy of titanium nitride (TiN) on magnesium oxide (MgO) (100) substrates, the growth conditions with large thermodynamic contributions of the low growth rate and high growth temperature are located on the right-hand side of region [I] in Figure 3, where polycrystalline TiN thin films were obtained instead of phase-pure epitaxial TiN layers

Summary

INTRODUCTION

Thin-film technology is actively used in various fundamental research, industries, and applications, and is instrumental in providing a possible solution for preparing high-quality samples of undeveloped materials such as groups of metal borides, nitrides, and carbides, and for preparing nanostructured materials (Nishinaga and Kuech, 2015). In the molecular beam epitaxy of TiN on MgO (100) substrates, the growth conditions with large thermodynamic contributions of the low growth rate and high growth temperature are located on the right-hand side of region [I] in Figure 3, where polycrystalline TiN thin films were obtained instead of phase-pure epitaxial TiN layers. Appropriate control of competing thermodynamics and kinetics is necessary to obtain the crystalline phases of ytterbium borides, and this was realized by the growth conditions of a high growth rate and high growth temperature. The use of metal–organic and boron hydride sources with sufficiently high vapor pressures can achieve stable source supplies and make it possible to control the competing thermodynamics and kinetics in vapor-phase thin-film growth

CONCLUSION

Findings

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