Atomic-Level Understanding of Interfaces in the Synthesis of Crystalline Oxides on Semiconductors: Sr- and Ba/Si(100)(2 × 3) Reconstructions

Abstract

The synthesis of novel functional crystalline films on semiconductor substrates calls for atomic-level knowledge and controlling of the initial stages of interface or junction formation. Technologically relevant epitaxial oxide films can be grown on Si(100) surfaces modified by submonolayer alkaline earth adsorbates, e.g., barium (Ba) and strontium (Sr). Nevertheless, the fundamental properties of such surfaces, that is, Ba/ Si(100) and Sr/Si(100) reconstructions are still controversial, which hinders a deeper insight into the synthesis of crystalline oxide films on silicon. In this study, scanning tunneling microscopy (STM), low-energy electron diffraction, synchrotron-radiation photoemission, and ab initio calculations have been utilized to examine Sr-and Ba-induced Si(100)(2 × 3) reconstructions that form the first mediating step in the growth of various functional oxide films on Si(100). The presented results elucidate the atomic and electronic structures of the Si(100)(2 × 3)-Sr and -Ba interfaces, giving support to the so-called (2 × 3) dimer vacancy structure. In particular, using STM, we demonstrate an evidence for the Si dimer, one of the main structural elements of metal-induced reconstructions on semiconductor (100) surfaces. It is also shown that in contrast to the dimer vacancy geometry, the other models, proposed for the Sr-and Ba/Si(100)(2 × 3) earlier, cannot be adopted.

STM and DFT study on formation and characterization of Ba-incorporated phases on a Ge(001) surface

“…It was shown for the Sr/Si(001) system that 2 × 3 and 2 × 6 structures are much more stable than other models at low coverages [32]. As the energetics of the Sr/Si(001) and Ba/Si(001) systems are very similar [31] we will adopt for the Ba/Ge(001) system the structural model proposed for the Sr/Si(001) system [26,32]. We will further verify the validity of the adopted model and associate the atomic configurations to the defects identified in the Bainduced surface reconstructions.…”

“…There has been a long debate regarding the structural models that could account for the 2 × 3 reconstruction of the incorporated phase observed on Si(001) [17,19,[25][26][27]31]. The formation of 2 × 3 is supported by the observations that the presence of the Sr adatoms on Si(001) reduces the activation energy barrier for the Si dimers to diffuse on the surface from 1.29 to 0.63 eV (for 0.5 ML Sr coverage) [26].…”

“…It is anticipated, therefore, that at elevated temperatures there may be enough energy to relocate some of the Si (Ge) surface dimers on the substrate and incorporate the adatoms to form the 2 × 3 adsorption phase. This structural model initially proposed for the Sr/Si(001) system has successfully been adopted for Ba/Si(001) [31].…”

Atomic structure of Sr/Si(0 0 1)(1 × 2) surfaces prepared by Pulsed laser deposition

“…The low repetition rate was chosen to allow a clear observation of the RHEED pattern transformations during the Sr deposition. A 1/2 ML of Sr was deposited onto the Si (0 0 1)(2 × 1) surface at 970 K. The amount of deposited Sr needed to complete the 1/2 ML coverage was determined by the appearance of the (2 × 3) surface reconstruction corresponding to the 1/6 ML Sr coverage [9,24].…”

Crucial role of vibrational entropy in the Si(111)-7$\times$7 surface structure stability

“…First-principles electronic structure methods, most notably density functional theory (DFT), have been widely used as a powerful tool to solve surface structures and to study their electronic properties. Due to its technological importance, semiconductor silicon has been a benchmark for studying surface physics, with several surface structures being extensively investigated [1][2][3][4][5][6][7][8][9][10]. When Si surface structures are composed of different building blocks as, for example, 2 × 1, 2 × 2 and 7 × 7 reconstructions on Si(111), their surface energy differences are usually significant (above 1 meV/ Å2 ), facilitating a reliable identification of the lowest energy atomistic configuration [11,12].…”