as defect states they may provide doping and (co-) determine the position of the chemical potential. spatial fluctuation of the defect density may then give rise to corresponding fluctuations in the position of the chemical potential. If the bands are relatively flat, then small fluctuations of the chemical potential may give rise to quite some distortions of the resulting Fermi surfaces and hence potentially transport properties (depending on the level of [self] doping we are talking about).

Dear Dr. Suresh Sharma 

Have a nice time and good day

Dangling bonds are defect states, they play an important role in AC-electrical conductivity. The model of AC- conduction which has this property is the correlated barrier hopping model CBH. This model is applied in case of all chalcogenide materials, where it is assumed that in general the charged centers that give rise to the Coulombic potentials, and which, when they overlap, lead to a lowering of the activation energy barrier to hopping are the structural (dangling bond) defects D+, D- (in nomenclature of Mott); or equivalently c+3, c-1 (in the notation of Kastner et al).

Kastner M., Adler D., Fritzche H. (197G) phys. Rev. Lett., j7. 1s04

Shimizu T.,Kumeda M.,  Ishikawa M. (1979): J. Non-cryst.solids, 33,1

Yours,

Ahmed S. Hassanien

Dear colleague Suresh Sharma,

Have a nice time and good day.

This can be partially explained using the density of states model in amorphous solids

proposed by Mott and Davis [N.F. Mott, E.A. Davis, Electronic Processes in Non-

Crystalline Materials, Clarendon Press, Oxford, 1979,p. 210, and M. Dongol, M. Abou Zied,G.A. Gamal, A. EI-Denglawey, Physica B 353 (2004) 169–175].. According to this model, the width of the localized states nearthe mobility edge depends on the degree of disorder and on the defects present in the amorphous structure. In particular, it is known that unsaturated bonds are responsible for the formation of some defects in amorphous solids. Such defects produce localized states in the band structure. The presence of a high concentration of localized states is responsible for relatively low values of the optical gap in the case of as-deposited amorphous films. In the process of heat treatment, the unsaturated defects are gradually annealed, producing a large number of structure bonds. The reduction of the number of unsaturated defects reduces the density of localized states in the band structure and consequently increases the optical gap.

Also the density of this dangling bonds of localized states play an important role to classify any material to amorphous, poly crystalline or crystalline material, this depends on the presence ratio of such this dangling bonds of localized states which can be easily detected by X-ray diffraction (XRD), Scanning electron microscope(SEM) and   Transmission electron microscope (TEM). You can distinguish between the amorphous, poly crystalline and the crystalline materials through the aforementioned three techniques:1- XRD the produced curve of  amorphous materials has a broad hump and no any sharp diffraction peaks, the presence of sharp diffraction peaks is an indication of crystalline material. 2-  SEM of of amorphous material don't release any features and no particles can be distinguished  otherwise crystalline material. 3- TEM of  amorphous material contains a hallow (white) and no diffraction rings otherwise crystalline material. 4- The presence of spotlight is an indication of single crystals.

Notice that the high concentration of dangling bonds or localized is found in amorphous materials and decreases in poly crystalline materials then mat tends to zero in single crystal. Please see the attached file I wish this issue is useful .

Ohhh...wov....

Thanks Dr. A. Eldenglawey for such a nice explanation. ....

It's really very helpful for the underlying concept of dangling bonds.

have Good time...

Yours,

Suresh K. Sharma

Hello Dr. A. S. Hassanain,

How are you?

Thanks for explaining the problem, it's really very informative.

Have a good day Sir....

Yours,

Suresh K.Sharma

Hello Dr. Kai Fauth,

Very deep physics involved in your explanation, still a question arises in my mind do you want to say that these dangling bonds are responsible for chemical potential?

If yes, then could you please elaborate a bit more and how doping is linked with......

Have a good day ahead......!!!

Yours,

Suresh K. Sharma

In an undoped semiconductor, the chemical potential at zero temperature [= Fermi level] is in midgap positon by definition (nicely discussed in Ashcroft & Mermin's classical text on solid state physics).

As a semiconductor is doped, the CP is shifted (and, in general, temperature dependent, but this dependence is not a peculiarity of semiconductors). With n-doping, the CP moves towards the conduction band, with p-doping towards the valence band.

So, if dangling bond sites contribute to (surface) self doping, surface band bending and/or a contribution to the position of the CP shall result and depend on the density of these sites.

In my first post I referred to Fermi surfaces, when taken seriously, this means that the CP has moved into either the valence or conduction band (-> degenerate semiconductor). I did overlook, however, that you were referring to amorphous materials, which honestly is outside my expertise for talking about (changes to) Fermi surfaces.

Thanks Dr. Fauth,

Though its all about semiconductors, but its really informative. ....

Yours,

Suresh K. Sharma

I am quite agree with A. El-Denglawey