Tunneling Spectroscopy and III-V Semiconductor Interfaces
The (110) cleavage plane of GaAs is of high interest for the characterization of semiconductor multilayers grown along the <001> direction. After cleaving in ultra-high vacuum (UHV), the (110) GaAs face exhibits a simple and regular, unreconstructed 1×1 surface unit cell with both Ga and As atoms showing up in the terminating surface,1 fig. 1. For the clean surface, electronic surface states are found outside the semiconductor bandgap, in the valence and conduction band.2 Hence, the electronic spectroscopy at the surface has a similarity to that of the bulk material. Such a situation is not found on the silicon surfaces, where the surface states dominate in the semiconductor bandgap.3 As the (110) plane is an orthogonal cross section to the <001> growth direction, the tunneling spectroscopy on this face might be used to study the electronic properties along the growth direction, in a similar sense that TEM reflects the structural coordination in the interfaces.4 The instrument used for the experiments described here is a usual ‘pocket size’ scanning tunneling microscope (STM), which is mounted inside a UHV electron microscope;5 in a connected UHV chamber, the GaAs samples are cleaved and the tunneling tips are prepared by sputtering and heating. Both samples and tips are transferred in UHV to the analysis chamber where the SEM is used to move the tunneling tip to the layers of interest. A description of the operation of the STM can be found in the literature.
KeywordsScanning Tunneling Microscope Scanning Tunneling Microscope Image Adsorbed Atom Tunneling Spectroscopy Local Conductivity
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