In Section 4.4, it was shown that when the value of P in Eq. (4.42) is small compared to koa, the behavior of electrons in the 1-D periodic lattice should resemble that of the free-electron case in which the energy band is continuous in k-space. In a semiconductor, the outer-shell valence electrons are loosely bound to the atoms, and the effect of the periodic crystal potential on the electron wave functions can be treated as a perturbing potential. In this case, the nearly- free electron (NFE) approximation can be applied to deal with these valence electrons.
In order to apply the NFE approximation to a 3-D crystal lattice, the periodic potential must be treated as a small perturbation. In doing so, one assumes that the perturbing potential is small compared to the average energy of electrons. The problem can then be solved using the quantum mechanical stationary perturbation theory. From the wave mechanics, the stationary perturbation method can be derived using the first- and second-order approximations in the time-independent Schrödinger equation. In the NFE approximation, it is assumed that the total Hamiltonian H
In Section 4.4, it was shown that when the value of P in Eq. (4.42) is small compared to koa, the behavior of electrons in the 1-D periodic lattice should resemble that of the free-electron case in which the energy band is continuous in k-space. In a semiconductor, the outer-shell valence electrons are loosely bound to the atoms, and the effect of the periodic crystal potential on the electron wave functions can be treated as a perturbing potential. In this case, the nearly- free electron (NFE) approximation can be applied to deal with these valence electrons.In order to apply the NFE approximation to a 3-D crystal lattice, the periodic potential must be treated as a small perturbation. In doing so, one assumes that the perturbing potential is small compared to the average energy of electrons. The problem can then be solved using the quantum mechanical stationary perturbation theory. From the wave mechanics, the stationary perturbation method can be derived using the first- and second-order approximations in the time-independent Schrödinger equation. In the NFE approximation, it is assumed that the total Hamiltonian H
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