Epitaxial relations and electrical properties of low-temperature-grown CaF2 on Si(111)

Abstract

The temperature dependences of crystalline quality, epitaxial relations, and interface properties of CaF2 on Si(111) are studied by x-ray diffraction and electrical measurements. While the CaF2 films grown at temperatures above 400 °C exhibit B-type epitaxy, the films grown at temperatures below 400 °C show A-type epitaxy. Using low substrate temperatures, we also obtained A-type CaF2 on SiGe(111) and off-orientated Si(111). In addition to the change in epitaxial relations, the interface state density is significantly reduced when the growth temperature of the CaF2 films decreases. Although flat capacitance–voltage (C–V) curves are observed from capacitors made of CaF2 films grown at 600–800 °C, suggesting a pinned interface, unpinned C–V characteristics are observed from capacitors made of either A- or B-type epitaxial CaF2/Si(111) grown at 200–500 °C, and polycrystalline-CaF2/Si(111) grown at 25–100 °C. The C–V characteristics are also dependent on the post-annealing temperature. Our results indicate that the interface state density of CaF2/Si(111) is dominated by thermal history, rather than crystalline quality or orientation, of the CaF2 film.

Calcium fluoride as high-k dielectric for 2D electronics

“…26,27 The growth of CaF 2 on Si (111) at temperatures below 400 C leads to CaF 2 films with the same crystallographic orientation as the underlying Si (111) substrate, while the use of temperatures between 600 and 800 C results in CaF 2 films with a crystallographic orientation that is rotated by 180 relative to the surface normal (111) axis of the substrate. [28][29][30] Figure 2(a) shows the crystallographic orientation of the CaF 2 film which is the same as that of Si 30 The mismatch of 180 between the CaF 2 (111) grown by MBE at high temperatures (600-760 C) and the underlying Si (111) substrate was also observed in the high-resolution cross-sectional TEM images 31 [shown in Fig. 2(b)], which also reported the presence of pinholes 32 [shown in Fig.…”

Formation routes and structural details of the CaF1 layer on Si(111) from high-resolution noncontact atomic force microscopy data

“…1), CaF 2 has been observed to physisorb on the Si(111)-(7 × 7) reconstructed surface in a rather disordered fashion after direct deposition [25]; core level spectroscopy does not give evidence for CaF 2 dissociation [26] and the (7 × 7) reconstruction is not removed [27]. Although the interface is rather disordered at low substrate temperatures T Si during deposition, addition of further CaF 2 at substrate temperatures T Si up to about 400 • C leads to multilayer films grown in type-A epitaxy [27][28][29][30]. In this epitaxial mode, the orientation of the CaF 2 film is identical to the underlying Si(111) surface lattice; especially, the equivalent 112 Si directions of the silicon surface lattice are identical to the equivalent 112 CaF 2 directions of the adsorbed CaF 2 film.…”

Metal silicide patterning: a new approach to silicon nanoelectronics

“…CaF 2 is an epitaxial insulator (ε r = 6.8ε 0 ) which can be grown on silicon with very small lattice mismatch (0.6% at room temperature). Experimental FETs have been fabricated [39] on p-Si(100), and capacitors employing epitaxial CaF 2 films grown at 200-400 • C on Si(111) have recently demonstrated near-ideal unpinned C-V characteristics [40]. A wide range of effective interface charge, Q i ∼ 10 10 -10 12 cm −3 , was inferred in these latter experiments, however, depending upon thermal history.…”