Semiconductor reconstruction model

Figures 5.2-7-5.2-17 give the accepted reconstruction models for a selection of covalent and polar semiconductors, together with STM (scanning tunneling microscopy) images of some of the surfaces. Tables 5.2-6, 5.2-7, and 5.2-8 give the positions of the atoms in reconstructed Si(lll) 2x1 and Si (111)7x7 surfaces and the parameters of the rotation/relaxation model of polar semiconductors.

Surface states can arise simply because the atomic bonding at a semiconductor surface is necessarily different from that in the bulk. For example, in a Si lattice, the bonds at the Si surface are not ftilly coordinatively saturated. To relieve this unsaturation, either a surface reconstruction can occur and/or bonds to the metallic material can be formed. This distinct type of surface bonding results in a localized electronic structure for the surface which is different from that in the bulk. The energies of these localized surface orbitals are not restricted to reside in the bands of the bulk material, and can often be located at energies that are inside the band gap of the semiconductor. Orbitals that reside in this forbidden gap region are particularly important, because they will require modifications of our ideal model of charge equilibration at semiconductor/metal interfaces. ... 

The lnP(001)(2 X 4) Reconstruction The In-rich InP(001)(2 x 4) reconstruction is the most widely investigated and best understood (001) surface of the phosphorus-containing III-V compound semiconductors. A number of publications concerning structural, electronic, optical, and other properties have been reported. As a result Schmidt et al. could propose an atomic structure model for this surface, the so-called mixed-dimer structure [41]. This model also represents the energetically most favorable InP(OOl) structure for In-rich surface conditions [41, 42, 73]. Since then, this model has been substantiated by both experimental [41, 74-76] and theoretical results [41, 77]. 

All these results obtained for InP(001)(2 x 4) are very similar to the results obtained on the (2 x4) reconstructions of GaP(OOl) and InQ45GaQ52P(001) [69, 78, 80, 81]. In the case of these two surfaces, it was also shown that the atomic surface structure is explained within the mixed-dimer model. Thus the (2 x 4) reconstruction of the (001) plane for all three P-containing semiconductors InP, GaP, and InQ4gGaQ 52P(001) are explained by the mixed-dimer model. Hence, this structural motif has a rather general character for the surface formation of III-V(OOl) surfaces [42]. 

Compared to GaN, much less is known about other compound semiconductor surfaces of the group of the III nitrides. On InN(0001)(>/3 x >/3)R30° and (2 X 2), surface reconstructions were observed [106, 107], which are depicted in Figure 13.36. These ball-and-stick models are similar to the atomic structure models discussed for GaN and dominated by adatom stabilization. 

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