Fermi hole insulator

In the case of negative bias, the Fermi level moves closer to the valence band edge. Consequently, the concentration of the majority of carriers (holes) at die insulator-semiconductor interface becomes laiger than in the bulk. This corresponds to the accumulation regime. When a positive bias is applied to die metal, the... 

At present there is a sufficiently complete picture of photoelectrochemical behavior of the most important semiconductor materials. This is not, however, the only merit of photoelectrochemistry of semiconductors. First, photoelectrochemistry of semiconductors has stimulated the study of photoprocesses on materials, which are not conventional for electrochemistry, namely on insulators (Mehl and Hale, 1967 Gerischer and Willig, 1976). The basic concepts and mathematical formalism of electrochemistry and photoelectrochemistry of semiconductors have successfully been used in this study. Second, photoelectrochemistry of semiconductors has provided possibilities, unique in certain cases, of studying thermodynamic and kinetic characteristics of photoexcited particles in the solution and electrode, and also processes of electron transfer with these particles involved. (Note that the processes of quenching of photoexcited reactants often prevent from the performing of such investigations on metal electrodes.) The study of photo-electrochemical processes under the excitation of the electron-hole ensemble of a semiconductor permits the direct experimental verification of the applicability of the Fermi quasilevel concept to the description of electron transitions at an interface. 

Semiconductors are characterized by a forbidden energy gap, Eg, (band-gap) between the valence band (VB) maximum, Evb, and the conduction band (CB) minimum, Ecb- The magnitude of the band-gap is what diiferentiates semiconductors from insulators semiconductors have smaller band-gaps (<4 eV) than do insulators. Semiconductors are termed n-type if the majority charge carriers are electrons in the conduction band and p-type if the majority carriers are holes in the valence band. The Fermi level for most pure or intrinsic semiconductors lies near the middle of the band-gap [12]. The effect of doping is to shift the Fermi level closer to Eqb for n-type semiconductors and closer to vb for p-type semiconductors. For moderate dopant levels near room temperature this can be expressed quantitatively by Fqs. 4 and 5 ... 

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