Steps on (001) silicon surfaces

Abstract

We investigate a topological method of eliminating antiphase domains in zinc-blende semiconductors heteroepitaxially grown on (00 1) Si substrates. Antiphase domains cannot occur if only one of the two atomic species of the polar overlayer bonds directly to the substrate at the heteroepitaxial interface (As, in the case of GaAs on Si) and if atoms from only one of the two inequivalent sublattices of the substrate form the termination boundary [only biatomic (a0l2) steps present]. We show that thermal equilibrium is a necessary and sufficient condition to realize this condition for (001) Si, a result of a 1T-bonded step reconstruction that lowers the relative enthalpy of reconstructed [110] biatomic steps by 0.04 eV per step atom for one type ofbiatomic step, and of correlation, which freezes out the step configuration entropy thereby suppressing the formation of all other types of steps. Our model explains selection rules and dimer orientations observed in infrared absorption, low-energy electron diffraction, and reflection high-energy electron diffraction measurements of vicinal (001) Si surfaces tilted toward (110). For general vicinal surfaces, competition from the non-1T-bonded sides of the atomically flat terraces weakens the thermodynamic driving force. For surfaces tilted toward (100) it vanishes completely, indicating that antiphase-free polar material cannot be grown on these surfaces, in agreement with experiment. If a minimum threshold energy is needed per terrace to form a primitive (00 1 ) surface, then the boundaries between antiphase-free and antiphase-dominated regions for spherically figured surfaces should be parabolic. The minimum energy estimated from the results of Akiyama et aJ. on spherically figured surfaces suggests that terrace-terrace correlations are also important factors in forming the primitive surface.

Many-Body and Correlation Effects in Surface and Interface Spectra of Optically Absorbing Materials

“…1, 2, and other measurements where derivative components are observed. The result differs from a previous interpretation [19] of derivative lineshapes in RD spectra in that it is general and not specifically restricted to E 1 transitions. Obviously, the overlap of DY n H r with the surface potential will also influence its lifetime.…”

“…Since Bloch waves are infinite in extent, without any mechanism for localizing the final state, properties such as critical point energies and broadening parameters cannot be influenced by effects in a finite surface or interface region. While spatial dispersion can cause measured values of E g to differ from their true bulk values [19], spatial dispersion is not expected to affect excited-state lifetimes and therefore cannot modify G. Thus the presence of derivative components are direct evidence of localization [8]. Using first-order time-dependent perturbation theory and retaining final-state correlations, we have shown that localization follows naturally from the finite penetration depth of photons in spectral regions where materials are optically absorbing [12].…”

Reflectance difference spectroscopy RDS/RAS combined with spectroscopic ellipsometry for a quantitative analysis of optically anisotropic materials

“…Optical anisotropy measurements were performed using an RDS spectrometer that operates at nearnormal incidence from 1.5 to 5.5 eV [21][22][23]. The anisotropy of the complex reflectance r is given by 2( ) ( ) r r r r r r α β α β D / = -/ + , where r α and r β are the complex reflectances of light linearly polarized along the α and β directions, respectively.…”

In situ ellipsometry growth characterization of dual ion beam deposited boron nitride thin films

“…A method to overcome this problem is the virtual interface ͑VI͒ approach. 31 In this approximation, the optical response of the sample at an appropriate time is converted into that of a virtual substrate material, assuming an ideal surface with no overlayer. Therefore, we did not explicitly consider the formation of the a-BN layer in the initial stage of film growth, and ellipsometric spectra at tϳ2.5 min were used to calculate the optical properties of a VI.…”