MBE-GROWN HEAVILY SM-DOPED ZNTE STUDIED BY OPTICAL SPECTROSCOPY

Sm-doped ZnTe films with thicknesses of several hundred nm were grown by molecular beam epitaxy (MBE) on GaAs substrates at temperatures bet ween 300 and 400 degrees C. Total Sm concentrations between 10(18) and about 10(21) cm(-3) as determined by X-ray microprobe analysis and se condary ion mass spectrometry (SIMS) were incorporated by varying the temperature of the Sm source between 400 and 650 degrees C. Studies of optical transmission spectra between 0.6 and 2.3 eV, and photolumines cence spectra in the excitonic range, are reported. The transmission s pectra were measured after removing the substrates by etching, and fix ing the films on glass platelets. These spectra were used to evaluate absorption spectra by correcting for Fabry-Perot interferences. Two pr ominent absorption bands peaking at about 1.45 and 2.1 eV are seen, an d these are attributed, by comparison with SmTe data, to Sm2+ 4f(6)--> 4f(5) id transitions. We argue that the Sm2+ is incorporated on sites surrounded by an octahedron of Te atoms, which are formed from zincble nde interstitial sites during MBE growth. The coalescence of these cen ters occurring above approximately 10(20) cm(-3) is thought to be the reason for the observation of rocksalt-type reflections in the reflect ion high-energy electron diffraction (RHEED) patterns in this concentr ation range. (C) 1997 Elsevier Science S.A.