Low temperature growth of PbTe and of PbTe/ Pb1− xEuxTe multi-quantum wells by molecular beam epitaxy

Abstract

A systematic study of molecular beam epitaxy (MBE) of PbTe and Pb 1- x Eu x Te on BaF 2 (111) at substrate temperatures between 350 and 70°C is presented. Reflection high-energy electron diffraction (RHEED) intensity oscillations with more than 200 oscillation periods are observed even for substrate temperatures as low as 95°C, signifying the persistence of two-dimensional layer-by-layer growth at surprisingly low growth temperatures. In addition, for low temperature MBE growth of the ternary Pb 1- x Eu x Te, the evolution of RHEED intensity oscillations depends strongly on the beam flux composition, i.e., the Te 2 to Eu beam flux ratio, and a Te-stabilized, as well as Eu-stabilized layer-by-layer growth mode exists. A series of PbTe epitaxial layers, grown at various substrate temperatures from 350 to 120°C, was characterized by high resolution X-ray diffraction and temperature dependent Hall effect measurements. High quality epitaxial layers were obtained for substrate temperatures as low as 160°C, whereas for lower temperatures a drastic broadening of the X-ray diffraction peaks and a strong decrease of the low temperature Hall mobilities is observed. In PbTe/Pb 1- x Eu x Te multi-quantum well structures grown at various substrate temperatures, no broadening of the superlattice satellite diffraction peaks is observed when the substrate temperature is decreased down to 200°C. The high quality of the samples grown at substrate temperatures very much below the usual MBE temperatures is based on a precise control of the beam flux composition. Under such conditions, MBE of IV-VI compounds can be carried out at very low substrate temperatures, whenever technologically necessary.