No abstract

The g-factor tensors of electron and hole in self-assembled (In,Ga)As/GaAs quantum dots are studied by time-resolved ellipticity measurements in a three dimensional vector magnet system. Both g-factor tensors show considerable deviations from isotropy. These deviations are much more pronounced for the hole than for the electron and are described by different anisotropy factors, which can even have opposite signs.

The band-edge optical absorption in EuTe is studied in the framework of the 5d conduction band atomic model. Both relaxed antiferromagnetic order, and ferromagnetic order induced by an external magnetic field, were analyzed. For ferromagnetic arrangement, the absorption is characterized by a hugely dichroic doublet of narrow lines. In the antiferromagnetic order, the spectrum is blueshifted, becomes much broader and weaker, and dichroism is suppressed. These results are in excellent qualitative and quantitative agreement with experimental observations on EuTe and EuSe published by us previously ͓Phys. Rev. B 72, 155337 ͑2005͔͒. The possibility of inducing ferromagnetic order by illuminating the material at photon energies resonant with the band gap is also discussed.

The magnetic europium chalcogenide semiconductors EuTe and EuSe are investigated by the spectroscopy of second harmonic generation ͑SHG͒ in the vicinity of the optical band gap formed by transitions involving the 4f and 5d electronic orbitals of the magnetic Eu 2+ ions. In these materials with centrosymmetric crystal lattice the electric-dipole SHG process is symmetry forbidden so that no signal is observed in zero magnetic field. Signal appears, however, in applied magnetic field with the SHG intensity being proportional to the square of magnetization. The magnetic field and temperature dependencies of the induced SHG allow us to introduce a type of nonlinear optical susceptibility determined by the magnetic-dipole contribution in combination with a spontaneous or induced magnetization. The experimental results can be described qualitatively by a phenomenological model based on a symmetry analysis and are in good quantitative agreement with microscopic model calculations accounting for details of the electronic energy and spin structure.

Low-temperature photolLminescence of epitaxial GaSb grown by M O ~P E from TMGa and TMSb on various sdbstrates is studied an0 compared witn exist ng results for GaSb grown oy otner techniques. The enecls of growth condit o n s are cons dereo It is touno that a growtn IemperatJre of 650 .C is too h gh, ana tne layers are of v e r y poor qdality. while below t h e opt mLm temperature of 600 ' C tne growth rate slows. a thoLgh t h e optica quality appears unaftected. lnvestigations into tne range of IIIV ratios over wh ch good qLal ty mater al cou d be grown indicated that I n s factor was more critica for GaSo than for GaAs; So-rich condit.ons proddceo samples w In poor radial ve etlic ency. whale samples grown under Ga-r ch conditions were covered on excess Ga orop ets. n addition. w e found that m common witn otner growth techniqdes, the concentrat on of t h e nat ve aefect n GaSb cou d be controlled dsing the l l l V ratio. and an excel e n t corre ation was found between electrical resu ts and features in tne pnoto um nescence Spectra For layers not lahlce-matcnea 10 t h e substrate. t h e spectrum IS red-sniheo W e surm se tnat th s is d u e to dilferenlia thermal contract on of t h e e p layer and substrate A homoepitaxial sample was chosen for aeta led stday ana lrom the depenaence 01 tho spectra on temperatLre and excitation ntensity. a previoLsiy ooserved bOdnd exciton was confirmed and an acceptor of 15 meV bind,ng energy was founo 107 107b 108 109 219 220 221 222 223 299 302 321 374 395 414 475t 477t 478t 479t 5187 1nAs