Hydrogen terminated $4H\text{−}\mathrm{Si}\mathrm{C}\left(1\overline{1}00\right)$ and $\left(11\overline{2}0\right)$ surfaces studied by synchrotron x-ray photoelectron spectroscopy

Using x-ray photoelectron spectroscopy (XPS), synchrotron x-ray photoelectron spectroscopy (SXPS), low-energy electron diffraction (LEED), and Fourier- transform infrared absorption spectroscopy (FTIR) we have investigated structure and composition of hydrogen saturated $4H\text{−}\mathrm{Si}\mathrm{C}\left(1\overline{1}00\right)$ and $\left(11\overline{2}0\right)$ surfaces. The hydrogen saturated surfaces are clean and unreconstructed. On both surface orientations a hydrogen induced surface core level shift is observed in the C $1s$ spectra, which is consistent with carbon monohydrides. The identification of a corresponding component in the Si $2p$ spectra is discussed. On $4H\text{−}\mathrm{Si}\mathrm{C}\left(1\overline{1}00\right)$ a sharp absorption line due to the $\mathrm{Si}-\mathrm{H}$ stretch mode indicates the presence of silicon monohydrides. Structural models for hydrogen saturated $4H\text{−}\mathrm{Si}\mathrm{C}\left(1\overline{1}00\right)$ and $\left(11\overline{2}0\right)$ surfaces are proposed which are consistent with our spectroscopic results. Annealing in ultrahigh vacuum leads to considerable changes in the core level spectra although the surface periodicity remains unchanged at $(1\times 1)$. The thermally induced line shape variations are more prominent in the C $1s$ spectra than in the Si $2p$ spectra.

Figure 1

XPS survey scans of H-terminated $6H\text{−}\mathrm{Si}\mathrm{C}\left(0001\right)$, $6H\text{−}\mathrm{Si}\mathrm{C}\left(000\overline{1}\right)$, $4H\text{−}\mathrm{Si}\mathrm{C}\left(1\overline{1}00\right)$, and $4H\text{−}\mathrm{Si}\mathrm{C}\left(11\overline{2}0\right)$.

Figure 2

(Color online) LEED patterns of H-terminated $4H\text{−}\mathrm{Si}\mathrm{C}\left(1\overline{1}00\right)$ taken at different electron energies. The rectangle inside the diffraction image indicates the $(1\times 1)$ unit mesh of the reciprocal lattice. Also shown is a top view of the unreconstructed $4H\text{−}\mathrm{Si}\mathrm{C}\left(1\overline{1}00\right)$ surface indicating the $(1\times 1)$ unit cell. Dark filled circles and dark lines indicate atoms and bonds of the top surface layer, respectively, while lighter shading is used for the second layer.

Figure 3

(Color online) LEED patterns of H- terminated $4H\text{−}\mathrm{Si}\mathrm{C}\left(11\overline{2}0\right)$ taken at different electron energies. The rectangle inside the diffraction image indicates the $(1\times 1)$ unit mesh of the reciprocal lattice. Also shown is a top view of the unreconstructed $4H\text{−}\mathrm{Si}\mathrm{C}\left(11\overline{2}0\right)$ surface indicating the $(1\times 1)$ unit cell. Dark filled circles and dark lines indicate atoms and bonds of the top surface layer, respectively, while lighter shading is used for the second layer. The vertical line indicates the position of a glide-plane.

Figure 4

(Color online) Comparison of C $1s$ core level spectra of H-terminated SiC surfaces taken at $350\mathrm{eV}$. The binding energy is given with respect to the bulk component.

Figure 5

(Color online) C $1s$ core level spectra of (a) $4H\text{−}\mathrm{Si}\mathrm{C}\left(11\overline{2}0\right)$ and (b) $4H\text{−}\mathrm{Si}\mathrm{C}\left(1\overline{1}00\right)$ taken at two different photon energies. The graphs also show the results of a deconvolution of the spectra into different components. The binding energy is given with respect to the bulk component.

Figure 6

(Color online) Comparison of Si $2p$ core level spectra of H-terminated SiC surfaces taken at $350\mathrm{eV}$. The binding energy is given with respect to the bulk component of the corresponding C $1s$ core level spectra.

Figure 7

(Color online) Si $2p$ core level spectra of (a) $4H\text{−}\mathrm{Si}\mathrm{C}\left(11\overline{2}0\right)$ and (b) $4H\text{−}\mathrm{Si}\mathrm{C}\left(1\overline{1}00\right)$ taken at two different photon energies. The graphs also show the results of a deconvolution of the spectra into two spin-orbit split doublets. The binding energy is given with respect to the bulk component.

Figure 8

(Color online) FTIR-ATR spectra of the $\mathrm{Si}-\mathrm{H}$ stretch mode region taken from H-terminated $4H\text{−}\mathrm{Si}\mathrm{C}\left(1\overline{1}00\right)$. The sketch above the spectrum shows the measurement geometry used for this experiment.

Figure 9

(Color online) Side view projection of the H-terminated $4H\text{−}\mathrm{Si}\mathrm{C}\left(11\overline{2}0\right)$ surface. The vertical dashed lines indicate the dimension of the $(1\times 1)$ unit cell in the direction of the $c$ axis.

Figure 10

(Color online) Side view projection of the four different possible structures of H-terminated $4H\text{−}\mathrm{Si}\mathrm{C}\left(1\overline{1}00\right)$ with $(1\times 1)$ periodicity. The vertical dashed lines indicate the dimension of the $(1\times 1)$ unit cell in $c$ axis direction.

Figure 11

(Color online) (a) Si $2p$ spectra taken at $\hslash \omega =170\mathrm{eV}$ of $4H\text{−}\mathrm{Si}\mathrm{C}\left(11\overline{2}0\right)\text{−}(1\times 1)\text{−}8\mathrm{H}$ after successive annealing steps in UHV. (b) Si $2p$ spectra taken at two different photon energies after annealing at $990°\mathrm{C}$ together with the result of a peak fit. (c) Relative intensities of the different components in the Si $2p$ core level spectra of $4H\text{−}\mathrm{Si}\mathrm{C}\left(11\overline{2}0\right)\text{−}(1\times 1)\text{−}8\mathrm{H}$ taken at $\hslash \omega =170\mathrm{eV}$ as a function of annealing temperature. The relative error in the intensities is estimated to be $\pm 10\%$.

Figure 12

(Color online) (a) C $1s$ spectra taken at $\hslash \omega =350\mathrm{eV}$ of $4H\text{−}\mathrm{Si}\mathrm{C}\left(11\overline{2}0\right)\text{−}(1\times 1)\text{−}8\mathrm{H}$ after successive annealing steps in UHV. (b) C $1s$ spectra taken at two different photon energies after annealing at $990°\mathrm{C}$ together with the result of a peak fit. (c) Relative intensities of the different components in the C $1s$ core level spectra of $4H\text{−}\mathrm{Si}\mathrm{C}\left(11\overline{2}0\right)\text{−}(1\times 1)\text{−}8\mathrm{H}$ taken at $\hslash \omega =350\mathrm{eV}$ as a function of annealing temperature. The relative error in the intensities is estimated to be $\pm 10\%$.

Figure 13

(Color online) (a) Si $2p$ spectra taken at $\hslash \omega =170\mathrm{eV}$ of $4H\text{−}\mathrm{Si}\mathrm{C}\left(1\overline{1}00\right)\text{−}(1\times 1)\text{−}(1\times 1)\text{−}4\mathrm{H}$ after successive annealing steps in UHV. (b) Si $2p$ spectra taken at two different photon energies after annealing at $990°\mathrm{C}$ together with the result of a peak fit. (c) Relative intensities of the different components in the Si $2p$ core level spectra of $4H\text{−}\mathrm{Si}\mathrm{C}\left(1\overline{1}00\right)\text{−}(1\times 1)\text{−}(1\times 1)\text{−}4\mathrm{H}$ taken at $\hslash \omega =170\mathrm{eV}$ as a function of annealing temperature. The relative error in the intensities is estimated to be $\pm 10\%$.

Figure 14

(Color online) (a) C $1s$ spectra taken at $\hslash \omega =350\mathrm{eV}$ of $4H\text{−}\mathrm{Si}\mathrm{C}\left(1\overline{1}00\right)\text{−}(1\times 1)\text{−}4\mathrm{H}$ after successive annealing steps in UHV. (b) C $1s$ spectra taken at two different photon energies after annealing at $990°\mathrm{C}$ together with the result of a peak fit. (c) Relative intensities of the different components in the C $1s$ core level spectra of $4H\text{−}\mathrm{Si}\mathrm{C}\left(1\overline{1}00\right)\text{−}(1\times 1)\text{−}4\mathrm{H}$ taken at $\hslash \omega =350\mathrm{eV}$ as a function of annealing temperature. The relative error in the intensities is estimated to be $\pm 10\%$.