Optical orientation of holes in strained nanostructures

A theory describing the optical orientation and Hanle effect for holes in quantum wells or quantum dots based on cubic semiconductors is developed. It is demonstrated that the presence of internal or external strain in quantum-confinement heterostructures leads to the dependence of the Hanle effect on the orientation of the magnetic field with respect to the heterostructure growth axis.     

Specific features of optical orientation and relaxation of electron spins in quantum wells with a large spin splitting

The processes of optical spin orientation and spin relaxation of electrons are treated theoretically for semiconductor quantum wells, in which the spin splitting of the energy spectrum is comparable with the characteristic energy of charge carriers. The density matrix of photoexcited electrons at the instant of optical excitation is obtained in explicit form. A system of kinetic equations describing the behavior of the spin density matrix at an arbitrary relation between the average energy of charge carriers and the spin splitting is derived. It is demonstrated that, upon photoexcitation, a noticeable degree of orientation can be attained only in the pulse mode of operation, when the photoexcitation pulse duration is comparable with the period of spin precession in the field of spin splitting. It is shown that the total spin of the ensemble of electrons exhibits oscillations damping with time; the shape and damping time of the oscillations are sensitive to the parameters of photoexcitation and the spin splitting.     

Photoluminescence of CuGaTeAs and CuGaSnGa complexes in n-GaAs under resonance polarized excitation

Photoluminescence (PL) of n-type GaAs:Te:Cu and GaAs:Sn:Cu with an electron density of about 10¹⁸ cm^?3 was studied at 77 K. A broad band with a peak at the photon energy near 1.30 eV (GaAs:Te:Cu) or 1.27 eV (GaAs:Sn:Cu) was dominant in the PL spectrum under interband excitation. This band arose from the recombination of electrons with holes trapped by Cu_GaTe_As or Cu_GaSn_Ga complexes. It has been found that the low-energy edge of the excitation spectrum of this PL band at photon energies below ～1.4 eV is controlled by the optical ejection of electrons from a complex into the conduction band or to a shallow excited state. The PL polarization factors upon excitation by polarized light from this spectral range suggest that the complexes have no additional distortions caused by an interaction of a hole bound at the center in the light-emitting state with local phonons of low symmetry. This feature makes Cu_GaTe_As and Cu_GaSn_Ga complexes different from those with the Ga vacancy (V _Ga) instead of Cu_Ga. The dissimilarity arises from the difference in the intensity of interaction of a hole localized at the orbital of an isolated deep-level acceptor in the state corresponding to its preemission state in the complex (Cu _Ga ^? and V _Ga ^2? ) with low-symmetry vibrations of atoms. The perturbation of the hole orbital induced by the donor in the complex practically does not affect this interaction.