Schottky barrier contacts behaving

Schottky contact — Alternative denomination of metal-semiconductor contact presenting a Schottky barrier. Depending on metal - work function, semiconductor electron affinity, doping of the semiconductor, conditions of the surface of the semiconductor before contact preparation, and preparation process, Schottky contacts with high rectification can be prepared. Devices encor-porating such contacts behave like a diode and for this reason, are also denominated Schottky diodes, whose main features are the capability of high frequency operations and low forward-voltage drop. 

A continuous metal deposit layer may behave as an ohmic contact or a Schottky barrier. For a relatively thick metal film the silicon can still behave like a semiconductor before the onset of current. For example, for n-Si deposited electrochemically with 150nm An, the electrode behavior is similar to that of bare silicon electrode At positive potentials the anodic current is small whereas at cathodic potentials current from hydrogen evolution increases with increasing polarization. " In the potential region before the onset potential for the cathodic current a linear Mott-Schottky plot is obtained giving a flatband potential similar to that of bare silicon sample. In the potential region where hydrogen evolution occurs, it behaves like a metal with potential drops mostly in the Helmholtz layer. 

The previously described four-probe technique [43,44] allows a separate determination of the source and drain contact resistances. If contacts would behave as Schottky barriers, one would expect the voltage drop at source to be substantially higher than that at drain. This is what is indeed observed with bad contacts. However, good contacts show comparable drops at both electrodes. A possible origin of this behavior has been recently put forward [46]. The model assumes that the regions immediately adjacent to the electrodes are made of organic material of quality different from that of the rest of the conducting channel, with very low mobility. 

There are some further aspects which must be considered when photochemical diodes are used. When a metal (catalyst) is deposited on a semiconductor, then frequently a Schottky barrier instead of an ohmic contact is formed at the semiconductor-metal interface. In this case, the latter junction behaves as a photovoltaic system by itself, which may determine or essentially change the properties of the photochemical diode. The consequences have been discussed in detail in [14, 27]. Frequently, colloidal semiconducting particles have been used, their size being much smaller than the thickness of the space charge region expected. 

Schottky barriers occur when majority carriers are depleted when a semiconductor contacts a metal and behave very much as do diodes. They are, however, majority carrier devices with a different form of the reverse current... 

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