Bound hole states in direct‐gap semiconductors with screw dislocations

Abstract

The dispersion law of holes bound at a screw dislocation in cubic semiconductors is calculated on the basis of deformation potential theory taking into account the threefold degeneracy of the valence band maximum in a perfect crystal. The lowest dislocation band (the corresponding azimuthal quantum number is rn = 0) is slightly affected by the anisotropy of the effective mass. Only the change of the effective mass is observed. The states with azimuthal number rn + 0 are considerably more affected by the anisotropy of the effective mass. A mixing of longitudinal and transverse motions (with respect to the dislocation line direction) takes place and terms linear in k,, appear in the dispersion law. The optical transitions associated with these states are intense for a polarization of light transverse with respect to the dislocation line and may cause circular dichroism in the absorption. The long-wave edge of the dislocation absorption on the whole is formed by transitions from the deepest band rn = 0 and is polarized along the Burgers vector 6. B PaMKaX TeOpXEi

Polarized Light Absorption in Direct-Gap Semiconductors Related to Bound States in a Long-Range Deformation Potential of Dislocations

“…The polarization of the interband DA is most strongly pronounced for transitions of minimum energy and becomes weaker as the transition energy approaches the unpolarized fundamental absorption edge [5]. This work aims of investigating essential peculiarities of the dislocation related optical spectra within the framework of the deformation potential theory.In a cubic crystal the calculated spectra of electron and hole states bound to a single straight dislocation for the cases of an edge and a screw dislocations due to its longrange deformation potential were reported by the authors in [6,7]. In one-band approximation the spectrum of bound electron dislocation states close to the conduction band (Dc states) and the spectrum of bound hole dislocation states close to the valence band (Dv states) were treated separately.…”

“…For an edge dislocation the calculation [6] under real values of parameters shows that the dipole momentum of this transition is perpendicular to the dislocation line and parallel to the Burgers vector. For a screw dislocation the dipole momentum of the lowest energy transition is parallel to the dislocation line and to the Burgers vector [7]. Further analysis of the DA spectra is presented below.…”

“…For a screw dislocation a mixing of longitudinal and transverse motions with respect to the dislocation line direction takes place and terms linear in k k appear in the dispersion law [7]. Thus, an optical circular dichroism (i.e.…”

“…In the model considered the Dv states associated with a screw dislocation are characterized by the radial and azimuthal quantum numbers n 1, 2, F F F and m 0, AE1, F F F , and the longitudinal wave vector k k . It is natural to present the wave function Y l Y nmk k in terms of the unit vectors of polarization e a , a z, , À, e z being parallel to the dislocation line and e e x ie y a 2 p , e À e x À ie y a 2 p corresponding to the left and right circular polarizations, respectively [7],…”

“…In an effective mass approximation the components of the envelope wave function of v-states form a vector Y l [7] and the dipole momentum d kcY l is determined as…”