Heteroepitaxial B12As2 on silicon substrates

Abstract

The morphology and crystal structure of rhombohedral B 12 As 2 thin films prepared by chemical vapor deposition on Si (100), Si (110) and Si (111) substrates were examined.For short depositions, 30 seconds at 1300 °C, the B 12 As 2 nucleated in patterns that were unique to each substrate orientation, probably due to variations in the surface atomic structure and surface activation energy of the substrates. Small square domains, one dimensional straight lines, and irregular lines were the representative morphologies on Si (100), Si (111) and Si (110), respectively. For long deposition, 30 minutes at 1300 °C, continuous thin films of B 12 As 2 formed with distinct morphologies also dependent on the orientation of the substrates. "Cross", "wire" and "chain" morphologies were formed on the Si (100), Si (111) and Si (110) substrates, respectively. X-ray diffraction showed that the B 12 As 2 films had the following predominant oriented textures: B 12 As 2 (110) on Si(100), B 12 As 2 (101) on Si(111), and B 12 As 2 (001) on Si(110). The in-plane orientations of the B 12 As 2 films as determined by XRD pole figures, is also reported.2

The coefficients of thermal expansion of boron arsenide (B12As2) between 25°C and 850°C

“…Knowing the coefficients of thermal expansion (CTE) for B 12 As 2 is important for understanding its properties when produced by both the solution growth method [5] and as thin films deposited by chemical vapor deposition (CVD) [6][7]. The B 12 As 2 can be strained on cooling from its synthesis temperature.…”

Growth mechanisms and defect structures of B12As2 epilayers grown on 4H-SiC substrates

“…High resolution cross-sectional TEM observation along the [11][12][13][14][15][16][17][18][19][20] zone axis ( Fig. 2(a)) reveals a transition layer located between the film and the substrate.…”

“…The cross-sectional TEM samples were prepared parallel to (11)(12)(13)(14)(15)(16)(17)(18)(19)(20) 4 H-SiC , which is parallel to (11)(12)(13)(14)(15)(16)(17)(18)(19)(20) B12As2 , since this orientation clearly reveals the B 12 As 2 twin boundaries and by wedge polishing technique. Atomic structure of the film/substrate interface and the epilayer was examined by HRTEM using a JEOL 2100 system with an electron voltage of 200 keV and STEM using a Hitachi HD 2700 C system at Brookhaven National Laboratory.…”

“…However, growth of a lower symmetry epilayer on a higher symmetry substrate always produces structural variants (rotational and translational) in the film that are related to each other by a symmetry operation that is present in the substrate but absent in the epilayer, which has been referred to the phenomenon as degenerate epitaxy [17,18]. Therefore, high densities of twin boundaries were observed in B 12 As 2 epilayers grown on the substrates attempted so far [14,15]. However, twinning in B 12 As 2 is expected to have a detrimental effect on device performance, which has severely hindered development of this material to date.…”

“…Hexagonal phases of SiC (a¼ 3.08Å), such as 6 H-SiC, have been the substrates of choice since they have approximately half of the basal plane lattice constant of B 12 As 2 (a¼6.14Å) [14][15][16]. However, growth of a lower symmetry epilayer on a higher symmetry substrate always produces structural variants (rotational and translational) in the film that are related to each other by a symmetry operation that is present in the substrate but absent in the epilayer, which has been referred to the phenomenon as degenerate epitaxy [17,18].…”