Propriedades Magneto-Ópticas do Pb(x)Eu(1-X)Te COM 0 ≤ x ≤ 0.2 / MAGNETO-OPTICAL PROPERTIES OF Pb(x)Eu(1-X)Te WITH 0 ≤ x ≤ 0.2

AUTOR(ES)
DATA DE PUBLICAÇÃO

2007

RESUMO

The optical properties of epitaxial samples of PbxEu1-xTe with 0 ≤ x ≤ 0.2 have been investigated by photoluminescence measurements at various temperatures and magnetic fields and through transmittance and reflectance measurements at room temperature. The samples were grown by molecular beam epitaxy in a Riber 32p MBE system at LAS-INPE on freshly cleaved BaF2 (111) substrates. The good crystalline quality of the samples was confirmed by rocking curve measurements carried out using a high resolution X-ray diffractometer and by the existence of narrow photoluminescence lines, related to magnetic polarons, on most of the EuTe samples. For Pb contents higher than 1 %, an additional broad emission band at ~ 1.8 eV is observed in PbEuTe alloy. This band, that we have called Alloy Band (AB), has not been observed previously. The AB has a FWHM of ~ 200 meV and a Stokes shift of ~ 400 meV. With increasing Pb content, the AB shift to lower energies and its FWHM increases. In addition, the AB intensity has a maximum at ~ 10 % of Pb content. At 2 K, the AB shifts to lower energies with increasing magnetic field. For low fields, the shift is non linear, and becomes linear for higher fields up to the saturation field ~8.5 T. Furthermore, with increasing field the FWHM of the AB decreases monotonically, and its intensity briefly increases and then decreases. For fields above saturation, the AB position and FWHM remain constant. With increasing temperatures, the AB initially shifts to higher energies, and then to lower ones. Besides, the AB intensity initially increases till ~10 K, and then decreases till the AB extinction at temperatures between 150 K and 200 K, depending on the sample Pb content. The absorption coefficient spectra extracted from the reflectance and transmittance measurements at room temperature, strongly increases from ~ 2.2 eV (energy gap) in all samples. However, for PbxEu1-xTe samples a weak absorption at lower energies is also observed. This absorption increases in value and deepens inside the gap with the increase of Pb content. The AB is presumably related to deep levels slightly above the 4f levels, whose origin depends on Pb content in the alloy. At low temperatures there are magnetic polarons bound to holes in these levels and the radiative recombination of carriers forming these magnetic polarons would originate the AB. The below gap absorption, on the other hand, is originated by transitions from deep Pb related levels to levels in the band tail that emerges inside the gap as expected in mixed crystals.

ASSUNTO(S)

teluteros de chumbo európio material physics optcal properties propriedades ópticas fotoluminescência lead tellurides pitaxia por feixes moleculares europium material magnético photoluminescence magnetic material molecular beam epitaxy fÍsica de materiais

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