GaAs reconstruction

The surface unit cell of a reconstructed surface is usually, but not necessarily, larger than the corresponding bulk-tenuiuated two-dimensional unit cell would be. The LEED pattern is therefore usually the first indication that a recoustnictiou exists. However, certain surfaces, such as GaAs(l 10), have a recoustnictiou with a surface unit cell that is still (1 x i). At the GaAs(l 10) surface, Ga atoms are moved inward perpendicular to the surface, while As atoms are moved outward. 

ZnSe(llO) Zincblende structure reconstructed as GaAs(l 10) Qualitatively as above DLEED model calc. 118) 99d, 106b... 

Fig. 6.5. Perspective view, looking along surface of clean reconstructed GaAs(l 10) at left and GaAs(l 10) -h (1 X l)As at right. Open and shaded circles represent Ga and As atoms, respectively...

For growth on GaAs (001) and 3C-SiC (001) surfaces, 2x2 surface reconstruction structure has been reported by several groups since 1991 [5,8]. Then, the transition between 2x2 and c(2x2) structures was reported using GaAs (001) surfaces in 1995 for the first time [52], This study attributed the transition to the surface coverage of Ga. The surface reconstruction transition behaviour was also... 

Surface reconstruction observation has also revealed that the surface structure is different in GaN epilayers on GaAs and 3C-SiC substrates, i.e. the former show 2x2 and c(2x2) structures, and the latter show 4x1 and lxl structures. It has been clarified that 2x2 and c(2x2) structures on GaAs substrates are due to the adsorption of As on the surface [58], Besides this modification of reconstruction structure, As ambient pressure during the growth has been shown to have several surfactant effects, such as the stabilisation of the flat surface and preferential growth of the cubic phase [28,59-61], Attempts to improve the quality of cubic GaN epilayers by these As surfactant effects have been reported [60,61],... 

In the present study, we focus on adsorption of a range of fullerenes on the c(4 x 4) reconstructed GaAs(OOl) surface. For adsorption on the Si(001)-(2x 1) surface, only C60 was considered. Both surfaces were modeled as slabs. 

Figure 15-1. (a) Top and side view of reconstructed GaAs(001)-c(4 x 4) surface The white middle size balls represent As atoms, the dark balls represent Ga atoms die bottom micro white balls denote the H atoms and the top layer of As-As dimers are highlighted by larger white balls (b) Top and side view of reconstructed Si(001)-(2 x 1) surface. The dark balls represent the Si atoms and the top layer Si dimers are highlighted with large white balls, the bottom micro white balls represent the H atoms... 

Conslruci an energy-level diagram for ihc GaA.s surface, in analogy with iluu in Fig. 10-9 for silicon, indicating the cnergie.s of dangling hybrids before and after full reconstruction. 

An ideal tool for the investigation of the electronic structure of metal clusters is offered by scanning probe methods which have been used in three pioneering studies of nanometer-size clusters of Au on GaAs(llO) [229], Fe clusters on the same surface [230], and of size-selected Siio clusters on a reconstructed Au(OOl) surface [231], which all have been published already in 1989. In the first investigation [229], a characteristic spectrum of band-gap states was observed for the Au particles grown on GaAs. Both donor and acceptor states... 

Since a GaAs surface is covered with native oxide, atomic arrangement is not observed in air. When an electrode was immersed in electrolyte solution and a cathodic potential was applied, the oxide layer seemed to be reduced electrochemically as atomic arrangement was observed at the p-GaAs electrode, as shown in Fig. 2 [20]. The top view (Fig. 2(a)) and the Fourier spectrum (Fig. 2(b)) show that the atomic stnicture is of nearly four-fold symmetry with a nearest neighbor distance of about 0.42 0.04 nm. This result shows that the surface has a GaAs(100)-(lxl) structure [21]. This is in contrast with the fact that a GaAs(lOO) surface forms a reconstructed structure such as... 

---