Defects modelling

Compare the theoretical and experimental densities to see which point defect model best fits the data. 

These point defect models need to be regarded as a first approximation. Calculations for stoichiometric GaAs suggest that balanced populations of vacancies on both gallium and arsenic sites, VGa and VAs, exist, as well as defect complexes. Calculation for nonstoichiometric materials would undoubtedly throw further light on the most probable defect populations present. 

Various defect models have been proposed to explain the defect structure of the doped LaMn03 oxides particularly in the oxygen-excess region. At high oxygen... 

In point defect models, vacancies and interstitial ions may be responsible for point defects. These defects may be independent of both the composition and external conditions. 

We shall now discuss this matrix element in more detail. Several approximations—namely the quantum defect model (e.g., Bebb, 1969), the use of a S function (Lucovsky, 1965), or of a Coulomb potential for the impurity— have long been well known and have been reviewed earlier (e.g., Milnes, 1973 Stoneham, 1975). Here we emphasize various recent developments. First, we present some work that analyzes the cross section in terms of the contributing matrix elements and of their symmetry. Results from this are important, since they show certain aspects to be relatively independent of the details of the deep state. Subsequently we give other recent papers, some of which consider various modifications to the impurity wave functions, others to the band wave functions. 

Let us consider the simple defect model for Cu2 O, proposed by Peterson and Wiley, based on the assumption that the concentration of defects is low and therefore the interaction among defects is negligible. Because it has been discovered, as mentioned above, that the dominant lattice defects are metal... 

Fig. 2.30 Structure image of Nbi2O29 [3 x 4]., (a) (note a defect in the centre of the image see text) and corresponding structure model (b), which has two extra metals ( ) and two extra oxygens (O), and the perfect crystal (c), which is derived from the defect model (b) by removing two oxygens and transferring two metals to regular positions.

Point Defect Models of Diffusion in Silicon. Under conditions of thermal equilibrium, a Si crystal contains a certain equilibrium concentration of vacancies, C v°, and a certain equilibrium concentration of Si self-interstitials, Cz°. For diffusion models based on the vacancy, Cv° Cf and the coefficients of dopant diffusion and self-diffusion can be described by equation 27 (15)... 

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