Ge(001) before and after gold evaporation and annealing
Kernel of the 4-probe microscope (left), crushed tip on Si surface (middle), two STM tips over gold structures on Ge(001) surface

Investigation of atomic stucture of III-group element rich reconstructions of AIIIBV coumpounds.

Semiconductors from group AIIIBV (AIII=Ga, In; BV=Sb, As, P) are of great interest due to their numerous applications in electronic industry. Despite the fact that probes into their properties have been carried out from decades a number of basic problems are still not resolved. One of the most important questions is determining atomic structures of their reconstructed (001) surfaces.
Reconstruction and chemical composition depends on the preparation method (see Xue et al. for review). Generally, surfaces enriched in BVelement can be prepared only as a result of MBE growth of the crystal, whereas surfaces enriched in AIII metal can be also prepared by ion beam sputtering and annealing of epi-ready wafer. The former are known better, mainly due to scanning tunneling microscopy (STM) results. The latter, however, were found to be difficult to image and analyze by STM. Surface X-ray diffraction was employed to determine some of the structures (see Kumpf), however, need for a technique for direct surface imaging other that STM is clear.
  • In our opinion dynamic force microscopy (DFM) is a method allowing for direct surface imaging and additionally supplying complementary information to STM. The experiments performed in our group were focused on:
  • preparation of reconstructed semiconductor surfaces (especially GaAs(001) and InSb(001)) be ion bombardment and annealing
  • investigation of the prepared surfaces by diffraction methods (LEED) and for chemical composition (AES)
  • imaging of the prepared surfaces by DFM
  • As a result of experiments a large amount of data was collected. The most important results are:
  • for the first time, to our knowledge, atomic resolution on reconstructed AIIIBV by DFM has been obtained
  • structure of c(8x2) reconstructed InSb(001) and GaAs(001) has been analyzed in terms of Kumpf model; in general we have found that the model is consistent with our data, however, some details, such as occupation of certain sites are different; to read more: J.J. Kolodziej et al. to be published soon ion Phys. Rev. Lett.
  • structure of (nx6)GaAs(001) has been imaged (#GaAs1x6.jpg); occupation of As dimers has been found to be 50 % (much smaller than postulated in existing models) but x6 periodicity remains visible; therefore As dimers may not be the essential part of the reconstruction; to read more check for: B. Such et al. Surf. Sci. 530 (2003) 149.
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