This paper examines an eight-band k⋅p theory of strained semiconductors yielding energy bands, wave functions, and momentum matrices. Only if the symmetry of the strained crystal is accounted for in all terms of the Hamiltonian, a consistent definition and calculation of the momentum matrix becomes possible. The band structure and wave functions are nonanalytical functions of strain and crystal momentum. For strained crystals, the extrapolation from the Γ point into the Brillouin zone, such as the effective-mass approximation for the optical-matrix elements, can be misleading. For certain cases, the heavy- and light-hole isoenergetic surfaces form complex figures resembling the indicatrix of birefringent biaxial crystals. The symmetry of the hole wave functions causes dichroism for photon energies close to the gap energy, while the crystal becomes optically isotropic for larger photon energies. Numerical results are presented for the eight-band k⋅p model of biaxially strained bulklike 1.3-μm–InxGa1-xAsyP1-y on InP being an important material in optoelectronics.
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