Structural, Electronic and Optical Properties of Bixbyite In ₂ O ₃ Compound: A Complex Study by Way of Density Functional Theory Investigations and Five Tandem Accurate Spectroscopic Techniques

Abstract

ABSTRACT Metal oxides have been widely studied in recent years due to their promising applications in catalysis and optoelectronic devices. Among these metal oxides, Indium Oxide (In 2 O 3 ), attracts a special attention exhibiting excellent electrical, optical and catalytic properties. Therefore, the investigation of the chemical composition, electronic structure, and optical properties of this compound is very important to define the defects that can affect its practical application in peculiar areas. Consequently, the properties of the compound can be developed to obtain optimal results. In this context, here we carry out a complex study of physicochemical surface properties of In 2 O 3 using a new approximation for exchange correlation potential denoted nKTB‐mBJ and a tandem consisting of five very powerful experimental techniques. The spectroscopic measurements used in present work involve such ultrahigh vacuum (UHV) precise methods as X‐ray photoelectron spectroscopy (XPES), Auger electron spectroscopy (AES), reflective electron energy loss spectroscopy (REELS), Ultraviolet photoelectron spectroscopy (UPS) and temperature dependent/independent photoluminescence spectroscopy (PLS) possessing high sensitivity while characterising the material surface and interfaces properties. These techniques were used to investigate the surface stoichiometry and valence band structure of In 2 O 3 when being subjected to ion cleaning in UHV conditions. A robust combination between experiments via UPS and theory employing density functional theory DFT lead us to corroborate three well distinguish sub‐peaks located at (4.4, 11.0 and 13.8 eV) and attribute each one to the appropriate orbitals of In and O. Furthermore, photoluminescence spectroscopy (PLS) was also used to carry out room temperature (RT) measurements, as well as those at variable temperatures and high vacuum conditions achieved by using a cryostat coupled with a multistage axial‐flow turbo molecular EdwardnEXT240D pump, to investigate the impact of temperature on the bandgap states of In 2 O 3 . The results present good stability of In 2 O 3 under the ion sputtering process. The PLS spectra reveal the thermal sensitivity of the intrinsic point defect energy levels in the optical band gap of bulk In 2 O 3 and a high emission around 580 nm at RT conditions, indicating that the compound under study is very useful for optoelectronic applications. The chromaticity CIE 1931 diagram shows the temperature effect at the structural defect states and hence the emission of bulk In 2 O 3 . Furthermore, we have employed a number of theoretical approaches to study in detail the structural and electronic configuration of In 2 O 3 . In particular, our data indicate that the calculated energy band gap of 3.30 eV, the intense visible emission at 2.1 eV assigned to oxygen vacancies and the electron effective mass of 0.31 m 0 collectively confirm the n ‐type character of In 2 O 3 that are of high importance for the practical application of this compound.