Density defect state

Hydrogenation has been found to reduce defect state densities and potential barriers associated with grain boundaries in Si (Johnson et al.,... 

Fig. 11. (a) Capacitance transient spectra from Co-60 - irradiated, n-type Si samples, one of which had been pretreated in an H plasma. Note the reduced defect state density in this sample, (b) Concentration profile of the O-V centers induced in these samples. There is a reduced defect concentration only in the region in which atomic hydrogen was incorporated. 

Figure 1.20 Defect state densities ND of the passive films on grains a (xxxO) and b (0001) as a function of formation potential derived from the Schottky-Mott plots [6],...

Figure 1.47 Defect state density ND and Debye length LD as a function of Ta20s film thickness (source Refs. [11, 13]).

Multijunction solar cells divide the solar spectrum into segments of increasing energy. Each junction absorbs a lower portion of this spectrum. These devices have higher efficiencies if each junction performs well but are more sensitive to defect state density. 

The tetrahedrally bonded materials, such as Si and Ge, possess only positional disorder however, materials of this type exhibit high density of defect states (DOS). It is only with the addition of elements such as hydrogen and/or a halogen, typically fluorine, that the DOS is reduced to a point such that electronic device appHcations emerge. These materials contain up to - 10 atomic % hydrogen, commonly called hydrogenated amorphous siHcon (i -Si H). 

Figure4.ll Bottom optimized ions HSE03 total density of states and integrated number of defect states (An) for Ovac. The integrated charge density corresponding to the defect states is shown in the top panel from two different perspectives for the same isocontour value (green 10 6eA 3). O red, Ti cyan (unpublished work).

For H at T in Si, Katayama-Yoshida and Shindo (1983, 1985) used a Green s function method to carry out spin-density-functional calculations. They found a reduction of the spin density by a factor 0.41. However, their results are subject to some uncertainty because they obtained an erroneous result for the position of the defect state in the band gap, probably due to an insufficiently converged LCAO basis set. 

Lester Guttman, Relation between the Atomic and the Electronic Structures A. Chenevas-Paule, Experiment Determination of Structure 5. Minomura, Pressure Effects on the Local Atomic Structure David Adler, Defects and Density of Localized States... 

The excess free carriers (and excitons) do not represent stable excited states of the solids. A fraction of them recombine directly after thermahzation either radiatively or by multiphonon emission. In most materials, nonradiative transitions to defect states in the gap are the dominant mode of decay. The lifetime of free carriers T = 1/avS is determined by the density a of recombination centers, their thermal velocity v, and the capture cross section S, and may span 10-10 s. Electrons, captured by states above the demarcation level, and holes, captured by states below the hole demarcation level, may get trapped. The condition for trapping is given when the occupied electron trap has a very small cross section for recombining with a free hole. The trapping process has, until recently, not been well understood. 

The recombination of electrons and holes is a rather complicated process. We have to distinguish between (a) the direct recombination of electrons and holes, occurring in particular at high concentrations of charge carriers (b) recombination via defect states which depends, among other factors, on the densities and capture cross-sections of the defects (recombination centers) located in the bulk of the solid or on its surface. 

S. Minomura, Pressure Effects on the Local Atomic Structure David Adler, Defects and Density of Localized States... 

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