Surface States and Band Tails

There are two kinds of surface states entrapment and polarization. The dangling bonds or surface impurities are subject to polarization, which add impurity states within the Eq of semiconductors. Termination of the dangling bonds by H adsorption could minimize the impurity states. The other is the entrapment in the relaxed surface region, which offsets the entire band strucmre down associated with Eq enlargement and the presence of band tails. 

The difference between an assembly of nanosolids and a bulk solid in amorphous state is the distribution of defects of the same nature. In the amorphous phase, the randomly distributed CN deficiency causes the bond length and angle of the specific atom to distort in a non-predictable way, which adds traps randomly in depth inside the bulk. In an amorphous solid, the number of the undercoordinated atoms is hardly controllable as the amorphous state depends heavily on the processing conditions. For a nanosolid or nanocrystallite, CN deficiency only happens 

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