Nature of the surface space charge layer on undoped SrTiO 3 (001)

• Published in: Journal of materials chemistry. C, Materials for optical and electronic devices Vol. 9; no. 38; pp. 13094 - 13102
• Main Authors: Lim, Hojoon, Song, Chanyang, Seo, Minsik, Kim, Dongwoo, Jung, Moonjung, Kang, Habin, Kim, Seunghwan, Lee, Kyung-Jae, Yu, Youngseok, Kim, Geonhwa, Kim, Ki-Jeong, Mun, Bongjin Simon
• Format: Journal Article
• Language: English
• Published: 07.10.2021
• ISSN: 2050-7526; 2050-7534
• DOI: 10.1039/D1TC03436G

SrTiO 3 , an ABO 3 -type perovskite structure, has been a popular choice of substrate for many important heterostructures, e.g. , ferroelectric thin films and superlattices. As numerous exotic physical phenomena are closely related to delicate electron/ion exchanges at the interfacial layer between the substrate and overlayer, precise characterization of surface/interfacial properties has become the center of many research studies. In most cases of SrTiO 3 research, Nb-doping is applied on the SrTiO 3 surface in order to characterize electrical properties with a negligible effect of contact potential between SrTiO 3 and overlayer. On the other hand, the presence of doping can possibly interfere with a correct interpretation of the surface defect states, which become critical to apprehend the electrical properties of heterostructures. In this report, the undoped SrTiO 3 (001) surface is investigated utilizing ambient-pressure XPS (AP-XPS) and low energy electron diffraction (LEED). We identified the complete chemical/structural/electronic states of O and Sr vacancies on the undoped SrTiO 3 surface from ultra-high vacuum (UHV, <10 −9 mbar) to O 2 gas pressure of 0.1 mbar conditions. Under oxygen pressure conditions, chemically stable SrO 1+ x surface oxide with a c(6 × 2) superstructure is formed, generating electron depletion and band bending, i.e. , the formation of a space charge layer underneath the surface. On the other hand, under UHV, the surface oxide comes from the O vacancy, which has different electronic properties from those of Sr vacancy-related oxides.