Physical properties and band structure of reactive molecular beam epitaxy grown oxygen engineered HfO$_{2\pm x}$

TL;DR

This study investigates how oxygen vacancies in HfO₂ thin films grown by reactive MBE affect their structure, band gap, conductivity, and magnetic properties, revealing tunable electronic features without ferromagnetism.

Contribution

It provides detailed insights into the structural and electronic modifications of HfO₂ due to oxygen engineering during MBE growth, highlighting the formation of defect bands and tunable resistivity.

Findings

Band gap decreases by over 1 eV with more oxygen vacancies.

High vacancy concentrations lead to defect bands and p-type conductivity.

Oxygen vacancies do not induce ferromagnetic behavior.

Abstract

We have conducted a detailed thin film growth structure of oxygen engineered monoclinic HfO$_{2\pm x}$ grown by reactive molecular beam epitaxy (MBE). The oxidation conditions induce a switching between ($\bar{1}11$) and (002) texture of hafnium oxide. The band gap of oxygen deficient hafnia decreases with increasing amount of oxygen vacancies by more than 1 eV. For high oxygen vacancy concentrations, defect bands form inside the band gap that induce optical transitions and $p$-type conductivity. The resistivity changes by several orders of magnitude as a function of oxidation conditions. Oxygen vacancies do not give rise to ferromagnetic behavior.