Download Point Defects in Semiconductors I: Theoretical Aspects by Dr. Michel Lannoo, Dr. Jacques Bourgoin (auth.) PDF

By Dr. Michel Lannoo, Dr. Jacques Bourgoin (auth.)

From its early starting earlier than the struggle, the sphere of semiconductors has developped as a classical instance the place the traditional approximations of 'band concept' might be adequately used to check its attention-grabbing digital homes. therefore in those covalent crystals, the digital constitution is simply weakly coupled with the atomic vibrations; one-electron Bloch features can be utilized and their power bands might be effectively computed in the community of the strength hole among the valence and conduction bands; nand p doping should be received through introducing substitutional impurities which in basic terms introduce shallow donors and acceptors and will be studied by way of an effective-mass weak-scattering description. but, even first and foremost, it used to be recognized from luminescence experiences that those basic recommendations did not describe many of the 'deep degrees' brought close to the center of the power hole through robust localized imperfections. those imperfections not just comprise a few interstitial and lots of substitutional atoms, but additionally 'broken bonds' linked to surfaces and interfaces, dis­ place cores and 'vacancies', i.e., vacant iattice websites within the crystal. In some of these instances, the digital constitution should be strongly correlated with the main points of the atomic constitution and the atomic movement. simply because those 'deep degrees' are strongly localised, electron-electron correlations may also playa major position, and any susceptible perturbation remedy from the suitable crystal constitution evidently fails. therefore, approximate 'strong coupling' concepts needs to frequently be used, in line' with a extra chemical de­ scription of bonding.

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Extra resources for Point Defects in Semiconductors I: Theoretical Aspects

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0) (0) new representation, which is the direct product r 1 x r J . This representation can be decomposed into irreducible components r(k). In the following, 26 we shall label their basis functions fr(k) ,m . 37) of V in the stress tensor components we obtain < ~ r (i) ,m IVI~ r (i) ,R. J ,Cl Gr(j),Cl < ~ r (i) ,m IVr (j) ,Cl I~ r (i) ,R. 47) ... each matrix element is a linear combination of r ,n terms like (1. 48) with [f r (k) ,n IVr (j) ,Cl ] = J fr (k) ,n Vr (j) ,Cld, (1. 50) This allows the reduction of all matrix elements in terms of a minimal number of parameters, the [fIV]r(k).

However, instead of working directly with the ~nk' we shall again take their Fourier transforms as we have done previously for the ~nk. We thus define modified Wannier functions vn(r - ~i) as vn(r - ~i) = ;, YI~ L exp(-i~. 39) - The set of vn(r-~i) defined in this way is also orthonormal since the quantities (llYN) exp(-~~i) are the coefficients of a unitary transformation. These modified Wannier functions have also a localized character since they are Fourier transforms of delocalized functions.

18 for a T2 state of the group Td . defect orientational stre .. orientation splitting spliHing 'I'~ ,'I'.. //;,"" _ - - - '1'. -:: '" '" ====:1(",,- --~-------- 't. '1'•. '1'. , 'fL 0> ~-------- 'I'~ '1',. p~ (00') ......... ~ ______- '1'. 18. 81) where D is the dipole moment of the system. For one-electron states ~i and ~j' the intensity is simply the product ~ • r, where ~ is the unit vector of the direction of polarization and r the position vector of the electron. In this case, the calculation of this intensity requires knowledge of the matrix elements of x,y,z, the components of r which belong to the representation T2 , between the basis functions of the levels ~i and ~j' The procedure for calculating these elements is completely analogous to the calculation of the matrix elements of the perturbation produced by a stress aT2 ,i' 35 Consider the case of the Td group developed in the preceeding section.

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