Nanomorphological characteristics of the single-crystal Si(100) surface subjected to microwave plasma processing at weak adsorption

The influence of the conditions and composition of the highly ionized plasma of an electron cyclotron resonance low-pressure microwave gas discharge on the nanomorphology of the single-crystal Si(100) surface is studied. Model mechanisms of the processes controlling the main nanomorphological parameters of silicon crystals subjected to low-energy microwave plasma processing in chemically active and inactive gaseous media under the conditions of weak adsorption are considered.     

Influence of sublayer atoms on Si(100) surface reconstructions

Influence of sublayer atoms on Si(100) surface reconstruction has been examined with density functional theory and molecular dynamic simulation. We found that the displacements of sublayer atoms under the buckled dimer affect the motions of their neighboring atoms and thus play an important role in determining the surface reconstructions. The present results reveal the relationship between the surface dimer reconstruction and the motion of the sublayer atoms and provide an account for experimental observations of Si(100) surface reconstructions at very low temperatures.     

Twisting of dimers on the Si(100) surface

We investigate the twisting of asymmetric dimers on the Si(100) surface, as predicted by the LEED results of Yang, Jona and Marcus. Minimisation of the MINDO/3 cluster energy yields no twisting for clusters containing a single dimer or a pair of parallel dimers. The long range electrostatic interaction of the dipoles associated with the charge transfer in the asymmetric dimer does indeed produce a twisting torque, but it is too small to account for the elastic distortion required by the LEED model.     

Theoretical study of the properties of adsorbed oxygen complexes on a Si(100) surface

The results from quantum-chemical calculations of the properties of adsorbed oxygen complexes on a Si(100) surface are presented. Semi-empirical MNDO quantum-chemical modeling, implemented in the MOPAC software package, is used to model the physicochemical properties and estimate the energy parameters. The dependences of the total energy of the silicon cluster-oxygen system are calculated in dependence on the location of oxygen in the Si(100) surface layer, and the geometrical and electron characteristics of the equilibrium states of a cluster with adsorbed oxygen.     

Image-potential-induced surface state at Si(100)

We have identified a surface state on Si(100) (2×1) at a binding energy of 0.69±0.05 eV with respect to the vacuum level. Band-structure calculations within the GW method reveal that almost 80% of the probability density of the resonance is located in front of the surface. We therefore assign the surface resonance to an image-potential state. It has a lifetime of about 10 fs and contributes significantly to two-photon photoemission from Si(100). PACS 73.20.At; 79.60.Bm; 79.60.Dp; 79.60.Ht     

Structural phase transitions of the Si(100) surface

A Monte Carlo study of the structural phase transitions on the Si(100) surface for both the “(2×1)” and “c(2×2)” reconstruction families is carried out using the asymmetric dimer model. A second order phase transition is observed at about 250 K from a p(2×2) (layered antiferromagnetic) to a disordered (paramagnetic) state in the “2×1” family. A similar transition is observed about 800 K from a c(2×2) (ferromagnetic) to a disordered state in the “c(2×2)” family. These results are in agreement with real-space renormalization group results. The variation of the specific heat, susceptability and the absolute value of the order parameter as a function of temperature is obtained in the range 200 to 300 K for the “2×1” family and 750 to 850 K for the “c(2×2)” family. Also, the order parameter correlation function is computed for ten different temperatures in the above ranges.     

DC-electric-field-modified second-harmonic generation at the Si(100) surface

1 resonances for clean and H covered surfaces shift as a function of the dc field in agreement with experiment. This suggests the presence of built-in electric fields whose strength depends on the H coverage, and which are strongly localized in the subsurface region. Received: 20 September 1998     

Thermal desorption of surface phosphorus on Si(100) surfaces

Thermal desorption of phosphorus on Si(100) surfaces has been investigated by varying the phosphorus coverage from zero to one monolayer (ML). The reaction path of phosphorus desorption is complicated and strongly dependent upon the phosphorus coverage. In the thermal desorption spectra, there are three apparent desorption peaks at 750, 850 and 1000°C. The entire phosphorus atoms on the surface desorb as P₂ through recombinative reactions irrespective of the desorption temperature and the coverage. In the lower coverages below 0.2 ML, the thermal desorption spectra are characterized by a single peak at 900°C which is considered to be the desorption from Si---P heterodimers. At higher coverages exceeding 0.2 ML, it is considered that three desorption schemes from P---P, Si---P dimers and defects coexist in the reaction stage.     

Control of the degree of surface graphitization on 3C-SiC(100)/Si(100)

The current method of growing graphene by thermal decomposition of 3C-SiC(100) on silicon substrates is technologically attractive. Here, we investigate the evolution of the surface graphitization as a function of the synthesis temperature. We establish that the carbon enrichment of the surface is characterized by a clear modulation of the surface potential and structuration. The structural properties analysis of the graphene layers by low energy electron diffraction and micro-Raman spectroscopy demonstrate a graphitization of the surface.     

Dimer elongation on the monohydride-covered Ge/Si(100) surface

Using transmission ion channeling, we have made the first measurement of the Ge dimer geometry for the monohydride-covered Ge/Si(100)-2×1 surface. Comparison of calculated angular scans with experimental angular scans near the 100 and 110 directions has resulted in a measured Ge dimer bond length of 2.8 Å, which is 8% longer than the corresponding dimer bond length reported for Ge on Si(100) in the absence of H. This elongation is similar to that reported for Si dimers on the Si(100) surface. Also, relative to the (100) surface plane, the dimers change from tilted without H to untilted with H.     

Effect of self-assembled Ge nanostructures on Si surface electronic properties

Incorporating self-assembled Ge islands on Si surfaces into electronic devices has been suggested as a means of forming small features without fine-scale litho- graphy. For use in electronic devices, the electrical properties of the deposited Ge and their relation to the underlying Si substrate must be known. This report presents the results of a surface photovoltage investigation of the surface energy barrier as increasing amounts of Ge are added to a Si surface by chemical vapor deposition. The results are interpreted in terms of band discontinuities and surface states. The surface barrier increases as a wetting layer is deposited and continues to increase as defect-free islands form. It saturates as the islands grow. As the amount of Ge continues increasing, defects form, and the surface barrier decreases because of the resulting allowed states at the Ge/Si interface. Qualitatively similar behavior is found for Si(001) and Si(111). Covering the Ge with Si reduces the surface-state density and possibly modifies the wetting layer, decreasing the barrier to one more characteristic of Si. Initial hydrogen termination of the surface decreases the active surface-state density. As the H desorbs, the surface barrier increases until it stabilizes as the surface oxidizes. The behavior is briefly correlated with scanning-tunneling spectroscopy data. Received: 13 November 2000 / Accepted: 14 November 2000 / Published online: 23 May 2001