Principle of SBSC Operation

The quantity c()g which represents the energy required by an electron situated at the metal Fermi level to become part of the electron distribution within the semiconductor conduction band is termed the Schottky barrier height. 

In Fig 3 downward band bending at the p-type silicon surface is produced by the choice of a metal whose work function is much less than that of the semiconductor In this case a depletion region and also a strong electric field of opposite sense to that of Fig 2 are produced below the semiconductor surface. The quantity ( )gp which represents the energy required by a hole situated at the metal Fermi level to become part of the hole distribution in the semiconductor is also termed the Schottky barrier height. The subscripts n and p are used to distinguish between the semiconductor material type . 

It is well knownii-itf that the barrier heights existing between metals and semiconductors are extremely sensitive to the surface properties (surface states, surface charge etc) of the semiconductor and often bear little relation to the difference in work functions between the two. For this reason barrier heights are best determined experimentally for the particular metal and semiconductor surface properties. 

Considering an incident photon of energy hv it can be seen that if hv E an electron hole pair will be produced within the silicon substrate on a unity quantum efficiency basis. Those electrons and holes which are produced within or near the depletion region are immediately separated by the electric field whilst those produced deeper within the substrate diffuse slowly towards the junction. Whether or not these reach the junction before they recombine depends upon the minority carrier lifetime within the substrate. 

For both n and p-type SBSCs the net result of this action is an accumulation of opposite charge on either side of the junction causing it to become forward biassed. For n-type SBSCs the metal becomes positively charged with respect to the semiconductor and for p-type SBSCs the metal becomes negatively charged. In both cases the emf may be used to dissipate power in an external electrical load. This effect is known as the photoelectric effect. 

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