The Role of Barium In the Heteroepitaxial Growth of Insulator and Semiconductors On Silicon

Abstract

The epitaxial growth of an insulator, BaF2, and semiconductors of the II-VI and the IV-VI families on Si substrates were carried out. In-situ XPS analyses during the growth of the first monolayers were used to study the surface chemical reactions involved. The results point to a common ingredient in these growths: that the Ba atoms are involved in forming interfacial compounds that would facilitate the heteroepitaxies. In the case of BaF2/Si, a BaSi2 compound has been identified previously. In the case of PbTe and CdTe, the heteroepitaxies on Si are made possible with the BaSi2 buffer. As a result, the impinging semiconductor molecules are broken up, and the metallic elements are ejected from the BaSi2 surface. A new surface chemical, BaTe, is thereby formed. These surface Ba compounds appear to be the dominant factors as the crystal orientations of the BaF2, CdTe, and PbTe layers are independent of those of the Si substrates.

CrO2 (100) and TiO2 (100) film heteroepitaxy on a BaF2 (111)/Si (100) substrate

“…1 shows the relative orientations of these two hexagonal surface meshes with respect to the underlying Si (1 0 0) surface; one mesh is oriented with Si ½0 11 || BaF 2 ½1 01, and the other is oriented with Si ½0 11 || BaF 2 ½1 12. Santiago et al [19,20] have shown that a BaSi 2 compliance layer of approximately 1-2 monolayers forms at the BaF 2 (1 1 1)-Si (1 0 0) interface, and this compliance layer likely plays a role in producing the (1 1 1) rather than the (0 0 1) BaF 2 orientation for this system.…”

“…Details of the BaF 2 /Si growth process and characterization of the BaF 2 film are discussed elsewhere [19]. For this study, the BaF 2 buffer layer was 30 nm thick as determined by Rutherford backscattering measurements.…”

“…This sample processing eliminates adventitious carbon and oxygen species without affecting the BaF 2 composition and structure as determined by XPS and XRD. TiO 2 growth temperatures were varied between 300 and 600 1C; at temperatures of 650 1C and greater, BaF 2 has been shown to dissociate and react with the Si substrate to form a BaSi 2 interfacial reaction product [19]. All other deposition parameters remained fixed for the different TiO 2 film growths, including deposition rate (0.02 nm/s), ECR plasma power (200 W), oxygen ECR plasma pressure (10 À5 Torr) and TiO 2 film thickness (50 nm).…”

“…BaF 2 thin films have been shown to form well-defined layers on Si (1 0 0) [19,20] which possess excellent insulating qualities for semiconductor-on-insulator (SOI) [21] and metal-insulator-semiconductor (MIS) [22] device applications. The use of a 30 nm BaF 2 (1 1 1) buffer layer film for growth of oxide films on Si (1 0 0) has also been examined for the WO 3 system [23].…”