PbEuTe/PbTe Multi-Quantum Wells: Structural and Optical Properties
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OPTICAL PROPERTIES E. ABRAMOF*, P.H.O. RAPPL*, A.Y. UETA*, P. MOTISUKE*, S.O. FERREIRA** *Instituto Nacional de Pesquisas Espaciais INPE-LAS CP: 515 CEP: 12201-970 Sao Jos6 dos Campos, BRAZIL. E-mail: [email protected] "**Depto de Fisica, Universidade Federal de Vigosa, Vigosa-MG, BRAZIL
Abstract A series of PblxEuxTe/PbTe multi-quantum well (MQW) samples were grown on (111) cleaved BaF 2 substrates by molecular beam epitaxy. The Eu content was maintained at x-0.06 and the PbTe well width was varied from 50 to 200 A. The co/20 scans of the (222) Bragg reflection showed very well resolved satellite peaks for all samples indicating that sharp interfaces were obtained. The strain inside the MQW structure was obtained as a function of the PbTe well width by fitting the o)/20 scans to the ones calculated by dynamical theory of x-ray diffraction. The transition energies between the confined states in the conduction and valence bands of the PbTe well were determined through the infrared transmission measurement analysis.
Introduction Multi-Quantum Wells (MQW's) of PbEuTe/PbTe are of great interest for the fabrication of diode lasers in the mid-infrared range' 2. Both PbTe and EuTe crystallize in the rock salt structure and the lattice mismatch between these materials is relatively small (-2%). Since the EuTe energy gap (2 eV) is much higher than that of PbTe (310 meV at 295K), only a small Eu content in the ternary Pbl.-EuxTe is sufficient to produce large barriers for PbTe in the heterostructure. These material properties make the PbTe-EuTe system suitable for the fabrication of MQW structures In this work we focus our attention on the growth and characterization of a series of Pbi.xEuxTe /PbTe MQW samples where the Eu content is maintained at x-0.06 and the PbTe well width is varied. Pb1 . Eu•Te with x=0.06 (Eg=530 meV at 295K) yields a barrier of 110 meV in the Pbl.xEuxTe/PbTe heterostructure, considering a band offset of 50%3. Detailed structural characterization was made by high-resolution x-ray diffraction using a triple axis configuration. From the (222) o)/20 scans, the period of the MQW structure and the thickness of the individual layers were obtained. These spectra were calculated by dynamical theory of x-ray diffraction using Takagi-Taupin equations and compared to the measured ones. From this fitting process, the strain in the MQW structure was determined for samples with different PbTe well width. The transmission spectrum of the MQW's was measured from 500 to 4500 cm" at room temperature. The transition energies between the confined states in the PbTe well were determined by fitting the transmission spectra
339 Mat. Res. Soc. Symp. Proc. Vol. 607 © 2000 Materials Research Society
Sample growth The PblxEu×Te/PbTe MQW's were grown by molecular beam epitaxy in a RIBER 32P MBE system equipped with PbTe, Eu and Te effusion cells 4. Freshly cleaved (111) BaF2 , which were pre-heated at 500'C for 10 min before growth, was used as substrates. A Pbl-.xEuxTe buffer layer (with the same x value as of the barrie
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