STM of Semiconductors

The semiconductor/electrolyte contact has been extensively investigated since the 1970s. A recent review [32] and text books [33, 34] furnish details of the theory and applications of semiconductor electrodes. Below are given only some elements necessary for the discussion. Phenomenologically the liquid junction behaves more or less like a solid-state Schottky diode, with the electrolyte playing the role of the metal layer. 

At equilibrium, when Fermi levels are equal the contact on both sides of the interfacial distribution of charges is that shown in Fig. 3 a Qsc is the space charge in the semiconductor and extends over a distance w of several hundred nanometers, since the density of electronic charges available in the solid is several orders of magnitude 

The full determination of the energy diagram is achieved by measuring the flat band potential which can be performed by various methods [35]. The bottom of the conduction-band is given by  

GaAs ( 4.1 eV [39]). This corresponds to a charge of the order of 10 elemental charges/cm for a Helmholtz capacitance of 10 pF/cm.  

In aqueous solutions shifts by -0.06V/pH unit for many materials. The generally accepted reason is specific adsorption of OH or H ligands, especially on materials forming oxide or hydride layers, which is the case for III-V compounds, Ge, Si, and oxides, for instance. Specific adsorption means that a chemical bond is formed according to a reaction of the type 

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