Sensitive RHEED signature of Ti-excess enabling enhanced cationic composition control during the molecular beam epitaxy of SrTiO₃ based solid solutions

Abstract

Monitoring the appearance of half-order streaks along the [210] RHEED azimuths instead of along the [100] azimuths during the MBE growth of SrTiO3 thin layers provides an improved accuracy of ±6.7% on the control of the cationic composition.

Strain generated by the stacking faults in epitaxial SrO(SrTiO3) N Ruddlesden–Popper structures

“…The growths were performed on as-received STO(001) substrates annealed at 700 C for 45 min under a molecular oxygen (O 2 ) partial pressure of 10 À7 Torr. After annealing, for each of the two samples, TiO 2 was deposited under reflection high-energy electron diffraction (RHEED) monitoring, until the brightness of the half-order streak along the [100] RHEED azimuth was maximized, which corresponds to a TiO 2 -terminated STO surface (Castell, 2002;Kajdos & Stemmer, 2014;Razaghi Pey Ghaleh et al, 2021).…”

“…For the first (calibration) sample, STO was grown by codepositing Sr and Ti at 700 C under a partial O 2 pressure of 10 À7 Torr, and by tuning the Sr and Ti cell temperatures to suppress/minimize the half-order streaks on the RHEED patterns along the [100], [210] and [110] azimuths (Fig. S1 in the supporting information), which correspond to stoichiometric growth conditions for STO (Sr concentration = Ti concentration) within a 6-7% uncertainty (Razaghi Pey Ghaleh et al, 2021). X-ray reflectivity and X-ray diffraction (XRD) measurements were then performed on the calibration sample (Fig.…”

Impact of Cationic Stoichiometry on Physical, Optical and Electrical Properties of SrTiO3 Thin Films Grown on (001)-Oriented Si Substrates

“…For both cases, the process window for formation of a stoichiometric material remains rather narrow; indeed, the process lacks a self-regulating mechanism due to the sticking coefficient of both cations being close to unity, and therefore, any excess or deficiency of Ti or Sr adatoms on the surface will be immediately incorporated into the epitaxial layer. The in situ and real-time reflection high-energy electron diffraction (RHEED) characterization technique is able to probe slight deviations in cation stoichiometry (up to 5%) by the appearance of specific surface reconstructions such as ×2 along [100] STO or ×2 along [110] STO , for Sr-rich or Ti-rich SrTiO 3 layers, respectively [16,17]. Larger deviations from cation stoichiometry could lead to streak extinctions along the [210] direction of STO in the case of a Ti-rich layer or additional diffraction spots in the case of Sr-rich layers, as shown in Figure 1c and [18], but are in general more difficult to interpret and evaluate.…”

“…The in situ and real-time reflection high-energy electron diffraction (RHEED) ch terization technique is able to probe slight deviations in cation stoichiometry (up to by the appearance of specific surface reconstructions such as ×2 along [100]STO or ×2 [110]STO, for Sr-rich or Ti-rich SrTiO3 layers, respectively [16,17]. Larger deviations cation stoichiometry could lead to streak extinctions along the [210] direction of ST the case of a Ti-rich layer or additional diffraction spots in the case of Sr-rich laye shown in Figure 1c and [18], but are in general more difficult to interpret and evalua (a) (b) (c) For Ti-rich STO layers, as Ti is incorporated in the form of an amorphous ma [19][20][21], it would lead to an increase in the background signal level (compare Figure but here again, it is difficult to accurately estimate the deviation from the ideal stoich etry only based on background signal.…”