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Surfactant enhanced solid phase epitaxy of Ge/CaF2/Si(111): Synchrotron x-ray characterization of structure and morphology
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Image of FIG. 1.
FIG. 1.

(Color online) XRR analysis of (a) CaF2/Si(111) and (b) Ge/CaF2/Si(111). Dots denote the experimental data, while the solid lines show fitting curves to the data following the Parratt algorithm with modeling of the interface via Nevot-Crocet ansatz.

Image of FIG. 2.
FIG. 2.

(Color online) XRD characterization of (a) CaF2/Si(111) and (b) Ge/CaF2/Si(111). The (111) Bragg peak of the Si substrate is at l = 1. Dashed lines show the positions of bulk Ge and bulk CaF2, respectively. The well-developed fringes point to very homogeneous films.

Image of FIG. 3.
FIG. 3.

(Color online) In-plane scans for Ge/CaF2/Si(111) with fixed vertical scattering vector . The broad but intense peak for l = 0.96 is caused by the relaxed Ge film.

Image of FIG. 4.
FIG. 4.

(Color online) Schematical drawing of the reciprocal space assuming bulk lattice constants of Si, CaF2, and Ge as well as both A orientation and B orientation of the epitaxial CaF2 film and Ge film, respectively.

Image of FIG. 5.
FIG. 5.

(Color online) In-plane scans with GIXRD geometry for CaF2/Si(111): () CTR (top) and () CTR (bottom). The splitting of the CaF2 Bragg peak into two peaks points to coexisting relaxed and pseudomorphic CaF2 phases. The solid lines denote Lorentzian-like contributions due to relaxed CaF2(left) and pseudomorphic CaF2(right). The dashed line shows additional intensity attributed to diffuse scattering at the rough CaF2-Si interface. All fitting curves are shifted for clarity.

Image of FIG. 6.
FIG. 6.

(Color online) CTR analysis of the () CTR, () CTR, and () CTR (from top to bottom) for CaF2/Si(111). Open dots are experimental results, while the solid lines show the diffraction analysis following kinematic diffraction theory to obtain structural data. The CaF2 Bragg peaks show that the CaF2 is B oriented to an overwhelming extent. The CaF2 film is very homogeneous, as concluded from well-developed fringes.

Image of FIG. 7.
FIG. 7.

(Color online) In-plane scans of the CTR. The three immediately visible diffraction peaks are due to relaxed Ge film, the relaxed CaF2 film, and the Si(111) substrate (from left to right). In addition, a peak due to pseudomorphic CaF2 has to be assumed to describe the scans completely. Solid lines (shifted for clarity) show the contributions of the different films to the diffraction pattern at L = 0.03.

Image of FIG. 8.
FIG. 8.

(Color online) In-plane scans of the CTR. The three peaks are due to relaxed Ge, relaxed CaF2, and pseudomorphic CaF2(from left to right). Solid lines represent fits of the different contributions to modified Lorentzians for L = 0.29.

Image of FIG. 9.
FIG. 9.

(Color online) Analysis of the intensities of the different peaks of the in-plane scans of both CTR and CTR (cf. Fig. 8). The oscillations of the intensities of the peaks due to CaF2 demonstrate the extreme homogeneity of the film thickness. The peaks due to Ge do not show oscillations, since the film thickness is inhomogeneous.

Image of FIG. 10.
FIG. 10.

(Color online) CTR analysis of the () CTR (top) and () CTR (bottom) for Ge/CaF2/Si(111) for relaxed Ge ( = 0.96) and the interfering CaF2 and Si(111) ( = 1.00). The CTRs for  = 1.00 show that the CaF2 film is B oriented and very homogeneous. The CTRs for  = 0.96 demonstrate that the Ge film is relaxed and exhibits both A-oriented as well as B-oriented parts. Open dots show experimental results. The solid lines for  = 1.00 are calculated from kinematic diffraction theory. The solid lines for the Ge CTRs for are fit to Lorentzians because of the rough and inhomogeneous Ge film.


Generic image for table
Table I.

Bulk and surface notation for the Bragg conditions of Si substrate and completely relaxed CaF2 and Ge films (cf. Fig. 4). The surface indices are scaled with respect to the reciprocal space of the underlying Si substrate.


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752b84549af89a08dbdd7fdb8b9568b5 journal.articlezxybnytfddd
Scitation: Surfactant enhanced solid phase epitaxy of Ge/CaF2/Si(111): Synchrotron x-ray characterization of structure and morphology