Challenges in band alignment between semiconducting materials: A case of rutile and anatase TiO2

This topical review focuses on the recently active debate on the band alignment between two polymorphs of TiO2, rutile and anatase. A summary is given to the popular methods for measurement and calculation of band alignment between materials. We point out, through examination of recently experimental and theoretical reports, that the outstanding discrepancy in the band alignment between two TiO2 phases is attributed to factors that influence band alignment rather than needs a definite answer of which band alignment is right. According to an important factor, the presence of an interface, a new classification of band alignment is proposed as the coupled and intrinsic band alignments. This classification indeed reveals that the rutile/anatase interface can qualitatively change the type of their band alignment. However, further systematic information of the interface and other factors that influence band alignment will be needed to better understand changes in energy bands of materials. The results obtained from discussion of the band alignment between rutile and anatase may also work for the band alignment between other semiconductors. This topical review focuses on the recently active debate on the band alignment between rutile and anatase TiO2, and points out that factors such as the rutile/anatase interface influence their band alignment. [Display omitted] •The discrepancy in the band alignment between the rutile and anatase TiO2 is attributed to factors that influence band alignment.•An interface is one of the most important factors that influence the band alignment.•There is a need of a systematic study for the effect of these factors mentioned in this topical review on the band alignment.