Optical spectra of Zn1-xBexTe mixed crystals determined by IR-VIS-UV ellipsometry and photoluminescence measurements

• Spectroscopic ellipsometry in the photon energy range from 0.04 eV to 6.50 eV is used for investigation of the optical response of Zn1-xBxTe crystals grown by a high-pressure Bridgman method in the composition range x andlt;= 0.12. Infrared spectra display absorption bands centred between 411 cm(-1) and 420 cm(-1) associated with BeTe-type optical phonon modes. The positions of the transverse-optical and longitudinal-optical phonon modes have been found by modelling the line shape of the complex dielectric functions, (epsilon) over tilde and Im(-(epsilon) over tilde (-1)), using a classical damped Lorentzian oscillator approach. Ellipsometric measurements in the VIS-UV range allow determination of the fundamental energy-gap (E-0) and the higher threshold energies (E-1, E-1 + Delta(1), E-2) originating from the band edge and spin-orbit splitting critical points. We have found that the Be content x = 0.12 causes an increase of the fundamental energy gap about 0.15 eV at room temperature when compared to the E-0 = 2.23 eV of ZnTe crystal at the same temperature. Photoluminescence spectra were measured in the temperature range from 30 K to room temperature. Luminescence at temperature Tandgt;200 K is very weak. The peak positions of the exciton emission lines agree well with the E-0 band-gaps derived from ellipsometric data if corrected for their temperature dependence.

Nyckelord

ZnBeTe

Ellipsometry

Dielectric function

Lattice vibration

Interband transitions

Photoluminescence

TECHNOLOGY

TEKNIKVETENSKAP

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